TECHNO-ECONOMIC ANALYSIS OF A MODEL BIOGAS PLANT FOR AGRICULTURAL APPLICATIONS; A CASE STUDY OF THE CONCORDIA FARMS LIMITED, NONWA, TAI, RIVERS STATE

Non-renewable energy sources

Primary and secondary energy sources

Energy sources can be categorized into primary and secondary forms Primary sources encompass both renewable and non-renewable resources that occur naturally In contrast, secondary resources, such as electricity and heat, are generated from primary sources through appropriate conversion technologies.

Available non-renewable energy sources

Nigeria spans over 0.9 million square kilometers and is home to a diverse population of approximately 140 million people The country is rich in a variety of primary energy resources, including petroleum, natural gas, coal, lignite, tar sands, shale oil, and uranium, as detailed in Table 1.1.

Table1.1 SUMMARY OF ESTIMATED NON-RENEWABLE ENERGY

Energy Reserves Units Estimated Reserves

Tar-sand 10 6 tonnes of oil equivalent.

The Earth spans over 100 million square kilometers and is home to approximately 6 billion people (Gustavsson, 2000) It is rich in diverse non-renewable energy resources, such as crude oil, natural gas, coal, lignite, tar sands, uranium, and thorium.

Table 1.2 shows the availability of non-renewable energy sources in the world.

Table1.2: SUMMARY OF ESTIMATED NON-RENEWABLE ENERGY

Crude oil 33 billion bbl 1, 067.2 billion bbl (2002)

Natural gas 159 Trillion scf 6, 280 trillion scf (2002)

Coal and lignite 2.7 billion tones 1,106 billion tonnes +

Tar-sands 31 billion bbl oil equivalent

Keys: bbl = barrel source: Iloeje, (2004) scf = Standard cubic feet

Forty years from now, oil reserves will be totally utilized in Nigeria with the present reserve But more research is going on for more oil reserves over the country.

Non-renewable energy and their advantages

Fossil fuel accounts for 91% of electricity generation in Australia In the

UK, EC, and US, percentage of fossil fuel used in electricity generation is 74.96%, 71.61%, and 55.88% respectively, Eastop and McKonkey (1999)

In the world, electricity generation from fossil fuel is 63% What a highly dependable source of energy! Other advantages include:

 They are relatively light for the amount of energy contained in them.

 They can be transported easily.

 Fossil fuels retain their properties even after long storage periods.

 They possess high energy content per unit mass

Non-renewable energy and their liabilities

Currently, approximately 80% of global energy demand is satisfied by fossil fuels However, reliable estimates indicate that fossil fuel production is on the verge of decline Hubbert (1985) projected that global petroleum production would peak between 1990 and 2000, leading to a subsequent decrease Evidence suggests that world fuel production likely peaked around 2010, marking the beginning of a downward trend.

 Fossil fuels are depleting fast without replenishment.

Air pollution, a significant environmental issue, primarily arises from the combustion of fossil fuels for transportation, electricity generation, and heating This pollution contributes to a rise in respiratory diseases and a decrease in life expectancy, as highlighted in The Energy Story (2007).

Acid rains are also produced by burning of fossil fuels – killing aquatic lives, etc.

Huge volumes of CO2 and other related gases are produced - leading to global warming and green house effects, The energy story (2007)

Fossil fuels are not distributed evenly among the countries or regions of the world – causing International problems/conflicts between suppliers and consuming nations.

Fossil fuels are not renewable

They are environmentally degrading - unfriendly

Fossil fuels, particularly coal, release radioactive materials such as Uranium and Thorium into the atmosphere during combustion In 2000, the global burning of coal emitted approximately 12,000 metric tons of thorium and 5,000 metric tons of uranium Notably, in 1982, coal burning in the US produced 155 times more radioactivity than the Three Mile Island incident Additionally, coal combustion generates fly ash and bottom ash, contributing to environmental concerns.

The extraction and distribution of fossil fuels, such as coal and oil, pose significant environmental challenges Methods like mountaintop removal and strip mining for coal, along with offshore oil drilling, threaten both terrestrial and aquatic ecosystems, leading to hazardous conditions for various organisms.

In the US, more than 90% of greenhouse gas emissions come from burning fossil fuels The energy story (2007)

Renewable energy resources

Solar energy

The Earth receives energy directly from the sun, which is the primary source of all our energy Solar energy is a silent, inexhaustible, and non-polluting resource Although solar energy collection systems, known as collectors, are twice as expensive as conventional electricity generation, they efficiently track the sun’s movement to maximize energy capture Nigeria, located in a high sunshine belt, enjoys a well-distributed solar radiation, with annual averages ranging from 12.6 MJ/m²-day in coastal areas to 25.2 MJ/m²-day in the northern regions This results in an impressive average annual solar energy intensity of 1934.5 KWh/m²-year, amounting to approximately 6,372,613 PJ/year (or 1,770 TWh/year) of solar energy falling across Nigeria, which is about 120,000 times the total annual electricity generated by the Energy Commission of Nigeria.

Solar energy has been harnessed for various applications, one of the most notable being solar water heating This technology gained popularity in the 1890s, with a significant adoption rate in the United States; by 1897, 30% of homes in Pasadena utilized solar water heaters The trend continued into the early 20th century, as evidenced by installations in Pomona Valley, California, in 1911 By 1920, the sales of solar water heaters had reached tens of thousands, showcasing the early embrace of renewable energy solutions.

Solar energy plays a significant role in various applications, particularly in the UK, where approximately 50% of building water heating is powered by solar water heaters, as noted by Eastop and McConkey (1999) These solar water heaters, often installed on rooftops, also serve to heat swimming pools Additionally, Tiwari (2006) highlights the potential of solar air heaters, which are not only effective for space heating but also for drying purposes in buildings In the agricultural sector, solar crop drying is increasingly utilized in food processing and storage, leveraging solar energy to remove moisture from crops for improved preservation Furthermore, solar distillation offers an efficient method to convert brackish or saline water into fresh drinking water, utilizing direct solar energy Lastly, solar thermal electricity generation is being explored, with experimental solar power stations established in Almeria, Spain, showcasing the versatility and potential of solar energy across multiple domains.

In California, solar thermal power plants harness solar energy to generate electricity for over 350,000 homes Additionally, the central tower power plant known as "Solar II" produces enough electricity to supply around 10,000 homes.

Solar cells, also known as photovoltaic (PV) energy, convert sunlight directly into electricity This electricity can be utilized in homes to power lights and appliances Additionally, some experimental vehicles harness PV cells to transform sunlight into energy for their electric motors.

Other applications of solar energy include:

- Collection – cum – storage water heater

- Heating of swimming pool by solar energy.

- Heating of Biogas plant by solar energy.

Wind energy

Wind technology dates back many centuries The kinetic energy of wind can be changed into other forms of energy, either mechanical energy or electrical energy.

Windmills have long been utilized to power mill mechanisms, harnessing wind energy, which is a clean, safe, and renewable resource The increasing demand for alternative energy sources has revived interest in wind power, resulting in the establishment of numerous wind-driven power stations across various scales In Nigeria, wind speeds vary significantly, ranging from 1.4 to 3.0 m/s in the southern regions and reaching 4.0 to 5.12 m/s in the northern areas Preliminary studies indicate that the total exploitable wind energy reserves at a height of 10 meters can range from 8 MWh/yr in Yola to 51 MWh/yr in the mountainous Jos Plateau, with Sokoto boasting the highest potential at 97 MWh/yr, according to the Renewable Energy Master Plan.

2005) Hence, Nigeria falls into the poor/moderate wind regime.

The history of wind power dates back to 1888 when the first wind-powered electricity plant was established in Ohio, generating 12 kW of direct current In the 1930s, the United States saw the construction of its first large-scale alternating current wind turbine By 1982, Germany introduced the Growian turbine near Marne, which boasted a significant output of 3 MW Additionally, Denmark commissioned two 630 kW wind power plants near Nibe, highlighting the advancements in wind energy technology throughout the years.

1979 and 1980 In UK, a 20M diameter wind turbine generator (250KW) on Orkney at Burgar Hill, and a 3MW unit with a 60 Inch diameter blade Still in

UK, other companies built machines of 20KW and 60Kw In 1992, there were

49 projects under way on wind-power generation with a total of 82MW. California alone has wind farms running with a capacity of 1400MW

As of 1999, California was home to 11,368 wind turbines, contributing to approximately 11% of the global wind-generated electricity output Farmers in the state harness wind energy through windmills to efficiently pump water from wells, showcasing the practical applications of this renewable energy source.

For centuries, windmills in Holland have played a crucial role in managing water levels by pumping water from low-lying areas, while also harnessing wind energy to power large grinding stones for milling wheat and corn.

Geothermal energy

Geothermal energy has been around for as long as the earth has existed “Geo” means the earth and “thermal” means heat.

Deep beneath the Earth's surface, around 10,000 feet down, water can approach hot rocks and transform into boiling water or steam, reaching temperatures exceeding 300°F (148°C) This extreme heat is higher than the boiling point of water (212°F/100°C), yet the water remains in liquid form due to lack of air contact When this superheated water escapes through cracks in the Earth, it is known as a hot spring.

Geothermal energy is harnessed by converting the heat from natural steam into electricity, with temperature increasing by 3°C for every 100 meters underground Notable examples of geothermal exploitation include Italy's Larderello, the USA's The Geysers, New Zealand's Wairakei, Mexico's Cerro Prieto, Japan, and the Philippines In 2004, a 10MW geothermal plant was established in Hawaii, showcasing the growing use of this renewable energy source Additionally, geothermal heat buildings utilize ground source heat pumps for efficient heating and cooling.

Geothermal fluids (less than 100 o C) are used in plant cultivation and animal husbandry, soil heating in the Soviet Union, Hungary and Iceland As at

1982, 45,000 apartments in France were heated by natural hot waters.

Hydropower

Hydroelectric power harnesses the kinetic energy of flowing water to generate electricity By constructing dams across rivers, water is directed through a hydroelectric power plant, where its flow pushes against turbine blades This movement causes the turbines to rotate, which in turn spins a generator to produce electricity.

In 1998, hydropower accounted for 8.9% of India’s electricity (EIA

Hydropower is a significant source of electricity in the United States, accounting for approximately 10% of California's energy and 15% nationwide Washington State is the leader in hydroelectric production, generating about 87% of its electricity from hydropower Additionally, a 20.4 MW hydroelectric power plant was established in Hawaii in 2004, contributing to the growing reliance on renewable energy sources.

Ocean energy

The ocean serves as a vital energy source, supplying power for farms, homes, and businesses Despite its potential, there are currently limited ocean power plants in operation, most of which are small-scale Energy can be harnessed from the ocean through three primary methods: utilizing ocean waves, exploiting the differences between high and low tides, and leveraging temperature variations at different water depths.

Wave energy

Kinetic energy from ocean waves can be harnessed to power turbines As waves rise, they push air out of a chamber, causing the air to spin a turbine connected to a generator When the waves recede, air flows back into the chamber through normally closed doors, allowing the process to repeat and generate sustainable energy.

Wave energy technology harnesses the up and down motion of ocean waves to drive a piston within a cylinder, which in turn activates a generator Most wave energy facilities operate on a small scale.

Tidal energy has been harnessed for over 900 years, with its documented use in the UK dating back to 1806 This renewable energy source captures tidal waves as they approach the shore, storing them in reservoirs created by dams When the tide recedes, the stored water is released, generating electricity similarly to traditional hydroelectric power plants.

Tidal energy has been used since about 11 th century Presently, modern tidal power plant exists There are two; one in Rance estuary in France (544 x

10 6 KWh/annum from twenty four 10MW units) and at Kislaya near Murmansk, Russia (400KW) The energy story (2007) The potential power is very high but so is the capital investment.

1.2.6.2 OCEAN THERMAL ENERGY CONVERSION (OTEC)

Using the temperature of water to make energy actually dates back to

1881 – with a French engineer Jacques D’Arsonval, who pioneered this technology.

Ocean Thermal Energy Conversion (OTEC) utilizes the temperature difference between warmer surface water and colder deep ocean water to generate electricity, requiring a minimum temperature difference of 23°C This innovative energy source is currently being demonstrated in Hawaii.

Hydrogen energy

Hydrogen, a colorless and odorless gas, constitutes 75% of the universe's total mass (Eastop and McConkey, 1999) On Earth, it exists solely in combination with other elements, including oxygen, carbon, and nitrogen.

Hydrogen must be separated from other elements for use, playing a crucial role in NASA's space program as fuel for space shuttles and in fuel cells that supply heat, electricity, and drinking water for astronauts Fuel cells are innovative devices that convert hydrogen directly into electricity.

In the future, hydrogen is poised to revolutionize transportation and energy by fueling vehicles, aircraft, and powering homes and offices Known for its high energy content, hydrogen burns cleanly, resulting in nearly zero pollution NASA has utilized liquid hydrogen since the 1970s for rocket propulsion, including the space shuttle, where hydrogen fuel cells not only power the shuttle’s electrical systems but also generate pure water as a clean byproduct for the crew to consume.

Fuel cells represent a promising technology for generating heat and electricity in buildings and powering vehicles Automotive manufacturers are actively developing fuel cell cars and trucks In these vehicles, an electrochemical device converts onboard hydrogen and oxygen from the air into electricity, which drives the electric motor and powers the vehicle.

In the future, hydrogen could also join electricity as an important energy carrier An energy carrier stores, moves and delivers energy in a usable form to consumers.

Biomass energy

Biomass, often perceived as waste, encompasses a variety of organic materials such as dead trees, yard clippings, leftover crops, wood chips, bark, sawdust from lumber mills, and livestock and poultry manure Additionally, it includes household waste like trash and paper products This diverse range of biomass can be effectively utilized for energy and other applications.

Recycling biomass for fuel and other uses cut down on the need for

Landfills are commonly used to manage waste, which can be transformed into valuable resources such as electricity, heat, compost, and fuels In California, over 60 million bone dry tons of biomass are produced annually In Nigeria, Lagos State generates more than 8,000 tons of waste each year, as reported by the Solar Energy Society of Nigeria in 2003 Additionally, Rivers State produces over 5,500 tons of waste annually from food processing and plastics, while Kano contributes at least 1,700 tons of waste primarily from farming industries Kaduna also plays a role, generating over 3,400 tons of industrial waste each year.

Utilizing the 60,800,600 tons of biomass waste in California and Nigeria could generate approximately 2,500MW of electricity, sufficient to power around two million homes The biomass process involves collecting waste materials such as wood and tree branches, which are then placed in large hoppers and burned in a furnace The heat produced is used to boil water in boilers, creating steam that drives turbines and generators to produce electricity.

Source: Source: ECN and UNDP, (2005), Renewable Energy Resources,

Technologies and Markets, REMP, Final Report 2005, P78

Biomass energy can be harnessed from landfills by capturing methane gas released during the decomposition of waste This methane, known as landfill gas, can be collected and utilized in power plants to generate electricity A comparable process can also be implemented at animal feedlots to produce biomass energy.

In livestock farms, animals such as cattle, pigs, goats, and poultry produce significant amounts of manure, with daily production rates for cattle reported to range between 10kg and 60kg per animal (Renewable Energy Master Plan-ECN 2005).

Fig.1.2 Nigeria’s Production of Major Crops (in million tones)

Source: Source: ECN and UNDP, (2005), Renewable Energy Resources,

Nigeria's cattle population, estimated at 21 million in 2001, is projected to produce between 210 million kg and 1,260 million kg of manure daily, resulting in an annual output of 76.7 to 450 million tons This significant manure production contributes to an aggregate livestock manure potential of 285.1 million tons, capable of generating over 3 billion cubic meters of biogas annually, equivalent to more than 1.25 million tons of fuel oil In 1996, Nigeria's major crops yielded approximately 93.3 million tons, while the discarded crop biomass—roots, leaves, and stalks—far exceeded this amount, highlighting the vast annual agricultural biomass produced in the country When fermented in digesters, this manure releases methane gas, which can be utilized for energy on farms This technology is successfully implemented in countries like India, China, Nepal, and Brazil, with China reporting the construction of 7 million family-sized biogas digesters in the early 1980s, and India launching its biogas program in the 1960s through the Khadi and Village Industries Commission (KVIC).

India is home to approximately 2.5 million biogas plants, serving both households and communities, according to Jo Lawbuary (2007) Biogas currently fulfills 57% of the country's natural energy demand (Tata, 1998, as cited in Lawbuary, 2007) The potential for biogas in India is immense, estimated at 17,000 MW, primarily sourced from agricultural residues and dung produced by the nation's 300 million cattle.

Utilizing clean, particulate-free energy sources significantly lowers the risk of chronic diseases linked to indoor biomass fuel combustion, including respiratory infections, lung ailments, and cardiovascular diseases Implementing biogas systems derived from waste in agricultural communities can enhance productivity while promoting environmentally friendly biomass energy solutions.

Biomass, including human excreta, animal manure, sewage sludge, and vegetable crop residues, can be converted into methane for various applications This renewable energy source is beneficial for households, farms, and industrial facilities, providing fuel for cooking, heating, and lighting Additionally, larger institutions can utilize methane for power generation, promoting sustainable energy practices.

Fig.1.3: Nigeria’s Estimated Wood Requirements

Source: ECN and UNDP, (2005), Renewable Energy Resources,

AVAILABLE RENEWABLE ENERGY SOURCES Table1.3 Availability of primary energy resources in the world and Nigeria.

Hydropower (large scale) 10,000MW 14.4 trillion KWh/yr ++ (1999)

Hydro power (small scale) 734MW N.A

Fuel Wood 13.1million ha forest wood land

Animal Waste 61*million tons/yr N A

Crop Residue 83* million tons/yr N.A

Tidal Energy N.A 45 billion – 15trillion KWh/yr.

Keys:++ = technically exploitable capacity of

NA = Not available * = Estimated production

Nigeria produces an estimated 61 million tons of animal waste and 83 million tons of crop residue annually, presenting a significant opportunity for biogas generation in rural areas to meet agricultural and domestic energy needs Currently, there are no biogas-powered plants among the country's electricity generation facilities, highlighting the urgent need for Nigeria to adopt biogas technology on a large scale By integrating biogas production into the national electricity grid, Nigeria can enhance its overall power output and address energy demands effectively.

Sapele Gas & steam turbine (NG)

IPP = Independent Power Plant Source: O.C Iloeje (2004).

Bio-fuels

Biomass derived fuels are derived from agricultural sources, as distinct from petrochemical sources, is referred to as biofuels.

A Biofuel is any renewable source of combustible material whose energy content can be beneficially utilized The emphasis here is on

Renewable This means all biofuels stem from agricultural sources and the carbon (iv) oxide produced during their combustion can be recycled as

Table1.4 INSTALLED ELECTRICITY GENERATION PLANTS IN

NIGERIA AND AVAILABLE CAPACITIES renewed biofuel Fossil fuel such as coal, oil and natural gas are not renewable They are finite sources and once consumed, they are lost forever.

Thus, for both environmental reasons and the need to consider future energy requirements, the transition to biofuel-based society is practically inevitable.

1.2.9.1 CURRENT BIOFUELS USED AS ENERGY SOURCES

Bio-ethanol is primarily produced through the fermentation of sugars, such as those found in molasses The process of saccharification allows for the conversion of starch, broadening the range of feedstocks to include corn, barley, sorghum, and triticale Traditional methods, like beer brewing and the production of sake and vodka, exemplify this process, but the use of these more affordable starch sources paves the way for the commercial production of bio-ethanol as a transport fuel Additionally, bio-ethanol can be produced through the enzymatic conversion of cellulose and semi-cellulose, highlighting the diverse chemical reactions involved in its production.

Thus, in terms of molecular weight conversion, 180kg of glucose can theoretically produce 92kg of ethanol and 88kg of carbon (iv) oxide.

The conversion of starch into bio-ethanol involves multiple steps, beginning with the creation of a "beer" from milled grain This mixture is then distilled to extract alcohol, after which the residual solids are recovered, and water is recycled for further use.

Fig.1.4: STARCH - BIO-ETHANOL CONVERSION PROCESS

To ensure efficient conversion in the biological process, it is crucial to carefully manage each step, as stray reactions can lead to yield loss, and different grains have unique processing requirements Key considerations throughout the process sequence include maintaining optimal conditions and closely monitoring reactions.

Bio-ethanol is a clear colorless liquid, which boils at a temperature of

80 o C, well within the distillation range of gasoline It has a similar density and fully miscible with gasoline It is used mostly as transportation fuel.

Biodiesel is a renewable fuel made from the transesterification of animal fats and vegetable oils, resulting in a mixture of methyl esters derived from long-chain fatty acids such as lauric, palmitic, stearic, and oleic acids Common feedstocks for biodiesel production include vegetable oils like canola, soybean, sunflower, and palm oil, as well as animal fats from beef, sheep, and poultry, along with used cooking oil Regardless of the source, the underlying chemistry of biodiesel remains consistent, making it a versatile and eco-friendly alternative to traditional fossil fuels.

The production of biodiesel requires the thorough mixing of methanol with oil or fat, facilitated by a suitable catalyst, followed by the gravitational separation of the lighter methyl ester from the heavier glycerol The efficiency of this process is influenced by the equilibrium achieved and the presence of competing reactions.

1 oil or fat + 3 methanol 3 methyl esters + 1 Glycerin

R1, R2 and R3 are symbolic representations of the fatty chains, which can vary in molecular chain length from typically C8 to C22, and also their degree of unsaturation

Bio-diesel is used as transport fuel, and heating fuel Its price is not very sensitive to capital cost making it more economic fuel source.

Biogas

Environmental requirements for anaerobic digestion

3 rd Stage: Methane producing bacteria – [14 days 25 o C]

Convert the substance produced in 1 st and 2 nd stage CH4 and CO2

Anaerobic digestion is a complex process governed by multiple parameters, each influencing the system either directly or through interactions with other factors Understanding these parameters is crucial for optimizing the anaerobic digestion process.

PARAMETER REQUIREMENTS a) Temperature (inside digester) 25-40 o C(optimum 37 o C, mesophilic)

50-60 o C[thermophilic] b) PH 6.6-7.6 (optimum 7.0-7.2) c) Alkalinity (mg CaCo3 /L) 2,500-5,000 d) Loading rate

In (kgVS/m 3 -day) 1-4 (dispersed growth digesters)

Feed solid content (%) 5-10 e) Hydraulic Retention Time (days) 10-60 (d.g.d)

1-10 (a.g.d.) 0.5-6 (up-flow sludge blanked digester) f) C/N ratio 25 - 30 g) Mixing:

Mixing of slurry is important to provide better contact between the anaerobic bacteria and the incoming organic wastes, so that biogas production is enhanced. h) Presence of toxic compounds:

The presence of some elements and compounds e.g K, Ca, Na,

Cu, Cr, Ni, Fe, S, NH4, volatile acids in inhibiting concentration must be checked regularly Diluting the content of digester could do this.

The biodegradability of organic substrates is a crucial factor influencing reactor performance, with biodegradable materials typically making up 30-50% of total waste Enhancing biodegradability can be achieved through physical, chemical, and biological pretreatment methods; however, due to high costs, only physical and biological techniques are commonly employed Physical methods, such as cutting, grinding, or shredding, aim to increase the surface area available for hydrolytic enzyme action Meanwhile, the biological pretreatment method involves pre-composting agricultural residues prior to digestion, further optimizing the process.

Biogas plants in integrated farms

Biogas Application in integrated farms

Biogas is a versatile energy source for integrated farms, providing essential applications such as cooking fuel for farmers, lighting solutions, and heating for birds and animals through biogas lamps Additionally, it can be utilized to power internal combustion engines commonly found in farm settings, enhancing operational efficiency.

Biogas slurry is a high-quality organic manure that outperforms farmyard manure due to its higher nutrient content It can be utilized as dried sludge to feed farm animals and serves as a superior input for fishponds compared to raw cow dung When applied as fertilizer, slurry significantly enhances plant disease tolerance, acting as a biochemical pesticide against issues like potato wilt and late blight Additionally, soaking early season rice seeds in digested slurry improves their cold-resistance properties, while also increasing crop resistance to various diseases and enhancing yield quality.

The use of biogas in integrated farms is rapidly expanding across countries such as Nepal, India, China, Tanzania, and Kenya This renewable energy source powers various farm operations, including refrigerators and incubators in poultry farms, and is also effective for boiling water.

Biogas plants can be categorized into two main types: continuous and batch Continuous biogas plants operate with daily feeding, allowing digested slurry to overflow in proportion to the amount of feed In contrast, batch biogas plants involve feeding at intervals and require complete emptying once the digestion process is finished.

Furthermore, digesters are divided into:

- Floating gas holder digester (Indian)

- Plug-flow digesters (Horizontal displacement digesters)

- Anaerobic filter (Young and McCarty, 1969)

- Up-flow anaerobic sludge blanket [UASB] reactor.

Normally, biogas plant in integrated farms is a continuous plant with automatic discharge at the overflow The digester content or the substrate flowing out of the plant is called ‘slurry’.

 A light solid fraction, mainly straw or fibrous particles, which float to the top forming the scum [total solid 15 - 50%];

 A very liquid watery fraction remaining in the middle layer of the digester [total solid is 1-2%];

 A viscous fraction below which is the real slurry or sludge [total solid is 6 -7%];

 The heavy solids [soil sand particles], which rest at the bottom.

There are three main types of biogas plants suitable for integrated farms – the fixed dome plant, the floating drum plant and the plastic covered ditch.

The fixed – dome plants are more durable and cheaper than the floating drum plants.

Fig 1.7: FLOATING DRUM [GAS HOLDER] DIGESTER

The floating drum digester, while more costly, necessitates less excavation compared to other systems In areas where temperatures drop below 25°C, biogas plants can be effectively heated to 37°C through either passive or active heating methods.

 Use of water heater/solar stills over dome.

 Constructing the digester with insulating materials to reduce the bottom and side losses.

Over 90% of rural populations are involved in agriculture, making any technology that impacts agricultural practices crucial for both biogas users and the farming community as a whole.

Agricultural by-products, particularly animal waste and crop residues, serve as essential inputs for biogas plants, which produce methane for various farm uses such as lighting, cooking, and heating The digested slurry, a valuable output of these plants, can be reintroduced into the agricultural system as an organic fertilizer, significantly enhancing crop production due to its rich nutrient content, growth hormones, and enzymes Additionally, dried slurry can partially substitute for animal and fish feed concentrates, while its treatment improves the feed value of low-protein fodder Incorporating digested slurry into the food chain of crops and livestock promotes sustainable increases in farm income.

This close relationship between biogas and agriculture can be taken as an indicator of “environmental friendly” nature of the technology as shown in figure1.8.

Fig 1.8 Relationship between Biogas Plant and Agriculture in a Farming

Family Source: (FAO/TCP/NEP/4415-T, 1996)

Biogas plants in integrated farms are commonly found in countries such as

India Others are China with more than 7 million installed units, Tanzania and

Egypt Vietnam, Thailand and Indonesia also install biogas plants in farms.

Nepal has since the early 1970s, put effort to diffuse the technology

Livestock and poultry BY – PRODUCTS

1.5 SOLAR HEATING OF BIOGAS PLANTS

Fig 1.9 CROSS SECTIONAL VIEW OF AN ACTIVE FIXED-DOME BIOGAS PLANT

In cold regions where temperatures drop below 25°C, it is essential to heat biogas digesters on farms to maintain an optimal fermentation temperature of 37°C This ensures efficient biogas production while minimizing the retention period Utilizing active heating methods can effectively achieve the desired temperature for enhanced fermentation.

The biogas plant features a solar collector panel connected to a heat exchanger within the digester, as illustrated in figure 1.9 This system allows heated water from the collector to transfer heat to the slurry through conduction and convection, effectively raising its temperature However, it's crucial to heat the slurry gradually to prevent excessive temperature increases that could harm anaerobic bacteria, ensuring their survival for optimal microbiological processes.

In an active biogas plant, increased fermentation leads to higher methane gas production Additionally, the ideal temperature for optimal biogas production is reached quickly during the retention period.

The environmentally friendly use of biogas involves the reduction and recycling of organic waste, which conserves essential nutrients like nitrogen, phosphorus, and potassium for agricultural use (Agunwamba, 2001) The nutrient-rich slurry produced during biogas production acts as an organic fertilizer, enhancing soil conservation This process also optimizes the carbon-nitrogen ratio, mineralizing organic nutrients into forms such as ammonium and nitrate that are readily available for plant uptake Additionally, biogas serves as a clean energy source, significantly decreasing the risk of chronic diseases linked to indoor combustion of biomass fuels, including respiratory infections and various lung ailments (BanerJee, 1996, as cited in Jo Lawbuary, 2007).

Utilizing biogas leads to a substantial decrease in emissions from biofuels, significantly lowering pollutants such as sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), total suspended particles (TSPs), poly-aromatic hydrocarbons (PAHs), and carbon dioxide (CO2) This reduction plays a crucial role in mitigating global warming and acid rain, contributing to a cleaner environment and sustainable energy solutions.

It reduces the concentration of pathogens (typhoid, paratyphoid, cholera, and dysentery bacteria) considerably, thereby breaking the cycle of re-infection and leading to improved public health (Gustavsson, 2000)

The environmental benefits of biogas application are significant, particularly in combating deforestation By reducing reliance on fuel wood, biogas helps to mitigate the pressures that lead to tree loss Additionally, unlike fossil fuels, biogas is a clean energy source that does not contribute to air pollution, making it a sustainable alternative for protecting our environment.

This project utilized a triangulation method that included a literature review, background research, case studies, and direct interviews to explore biogas production and its applications The literature review provided essential insights into biogas, detailing its production processes and existing technologies Background research and case studies offered comparative data relevant to the proposed biogas project at Concordia Farms, focusing on optimal plant size, capacity, and type Direct interviews were conducted with local farm workers, including farmers, managers, and equipment operators, to gather firsthand information about organic waste management These interviews were ethically approved by Concordia Farms' Office of Research Ethics, ensuring that participants were selected based on their proximity to the farm and the volume of waste generated, particularly from agricultural operations.

A series of inquiries were made regarding the current disposal of waste, energy sources, energy costs, and the energy requirements of farms, alongside their willingness to donate organic waste for a proposed biogas plant Data collected was analyzed to assess the additional organic waste needed for the plant and to evaluate its economic feasibility Following this analysis, discussions were held, leading to recommendations and alternatives for the project's viability This triangulation method employs innovative technologies to reduce potential operational challenges, highlighting the positive impact a biogas operation could have on the local community and Concordia Farms Limited.

Update of Biogas technology in some Countries

Environmental impact

Biogas production is an environmentally friendly process that reduces and recycles organic waste, conserving essential nutrients like nitrogen, phosphorus, and potassium for agricultural use (Agunwamba, 2001) The resulting slurry acts as an organic fertilizer, enhancing soil health and nutrient content This process not only narrows the carbon-nitrogen ratio but also mineralizes organic nutrients into forms like ammonium and nitrate, which are readily available for plant uptake Additionally, utilizing biogas as a clean energy source minimizes the health risks associated with indoor combustion of biomass fuels, reducing the incidence of respiratory infections, lung diseases, and other serious health conditions (BanerJee, 1996; Jo Lawbuary, 2007).

Utilizing biogas leads to a substantial decrease in harmful emissions linked to biofuel combustion, including sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), total suspended particles (TSPs), polycyclic aromatic hydrocarbons (PAHs), and carbon dioxide (CO2) This reduction plays a crucial role in mitigating global warming and acid rain, contributing to a cleaner environment.

It reduces the concentration of pathogens (typhoid, paratyphoid, cholera, and dysentery bacteria) considerably, thereby breaking the cycle of re-infection and leading to improved public health (Gustavsson, 2000)

The environmental benefits of biogas application are significant, particularly in combating deforestation by reducing reliance on fuel wood Unlike fossil fuels, biogas is a clean energy source that does not contribute to air pollution, making it a sustainable alternative that supports both ecological health and energy needs.

Methodology

This project utilized a triangulation method, incorporating a literature review, background research, case studies, and direct interviews to explore biogas The literature review provided a foundational understanding of biogas, detailing its production processes and potential applications, while also summarizing existing studies and current projects utilizing biogas technology Background research and case studies were analyzed to compare with the proposed Concordia Farms project, offering insights into the optimal size, capacity, and type of biogas plant suitable for Concordia Farms Limited Additionally, interviews were conducted with local farm workers, including farmers, farm managers, equipment operators, and marketers, to gather information on organic waste management These interviews received approval from the Concordia Farms Office of Research Ethics, ensuring compliance with ethical standards Participants were selected based on their proximity to the farm and the volume of waste they could generate, maximizing the potential for effective waste collection compared to other sources.

A series of questions were posed to assess the current waste disposal practices, energy sources, and costs associated with energy on farms, as well as their willingness to contribute organic waste for a proposed biogas plant The collected data was analyzed to identify the additional organic waste required for the biogas facility, and an economic feasibility study was conducted based on this information The findings were followed by discussions, recommendations, and alternative strategies to enhance the project's viability This triangulation approach aims to leverage cutting-edge technologies to reduce potential operational challenges while highlighting the positive impacts of a biogas operation on the local community and Concordia Farms Limited.

Update of Biogas technology in some Countries

Since the 1950s, countries like China, India, Germany, and Nepal have effectively utilized biogas for energy production, waste management, and as a liquid fertilizer for soil enhancement By 2005, more than 25 million small-scale biogas systems were operational globally, with over a million new installations each year, alongside over 100,000 large centralized biogas plants converting biogas into valuable energy (Agama Energy, 2007) In rural South Africa alone, over 300,000 households are viable candidates for on-site energy production through biogas technology, which can fulfill their cooking needs (Agama Energy, 2007).

This section provides an overview of biogas technology and research developments in various countries, particularly in sub-Saharan Africa It highlights the strengths and weaknesses in biogas development capacities across different nations According to Table 1.5, a summary of countries with biogas production units as of 2007 is presented, along with the sizes of the largest plants built globally While large-scale anaerobic digestion technology has advanced significantly in Europe and Asia, its development in Africa remains in the early stages, despite the continent's considerable potential.

Table 1.5 Countries with biogas producing units

Source: (Anthony 1 & Wilson 2 2009; GTZ & ISAT 2007)

Country Number of small/medium

CHAPTER TWO 2.0 DESCRIPTION OF THE FARM

2.1 Description of the case study farms

Concordia Farms, fully operational since 2000, spans over 809,371.2 m² in Nonwa village, Tai Local Government Area, Rivers State The farm features a poultry section with over 3,000 birds, a piggery housing around 400 pigs, and an animal husbandry section that raises approximately 300 cattle and 200 sheep Additionally, it boasts 25 innovative fish ponds that utilize the farm's natural environment for fish farming The farm also cultivates a diverse plantation of fruits, including pineapple, garden egg, maize, pumpkin, and okra, across an area ranging from 404,685.5 to 809,371.2 m².

The office accommodation at the farm is set to expand, housing key personnel such as the Farm Manager, Accountant, Sales Clerk, MD, and CEO, along with a general office space Additionally, the farm features essential facilities including stores, poultry houses, piggery housing, animal husbandry structures, and a security post It also provides accommodation for a sizable workforce, comprising farm managers, permanent staff, and temporary casual workers.

2.1.2 GROWTH LEVEL OF THE FARM

Concordia Farms has experienced steady growth, primarily focusing on commercial production of poultry, meat, pigs, fish, crops, organic manure, and eggs, catering to local markets The farm aims to enhance its export capabilities and expand its livestock section, although it currently operates at only 25% of its potential due to bureaucratic challenges related to importation and financing for farm equipment To align with its exportation goals, Concordia Farms is increasing production levels, with the poultry section expanding from 2,000 to 3,500 layers and the piggery section also growing, allowing for the supply of pigs for pork and sausage production Looking ahead, the farm plans to enter food processing within the next five years to reduce waste from surplus produce.

The farm has invested in advanced mechanized farming equipment, including a tractor sourced from Germany, along with various implements such as harrows, ploughs, and ridgers A detailed overview of these facilities can be found in Table 1.5.

Table2.1: Major facilities in the farm

Pick-up van Goods only + driver and 2 persons

Toyota bus Goods only + driver and 2 persons

The farm operates solely on a 250KVA generating set, as the grid power supply is non-functional This generator consumes approximately 322.58 liters of diesel daily Additionally, the farm has two vehicles, a Toyota pick-up and a Toyota bus, that rely on petrol for their daily operations Cooking for the 25 permanent workers is done using kerosene stoves, which require kerosene Furthermore, the farm utilizes fuel wood and charcoal to prepare blood meals, which serve as feed for fish, poultry, and other animals.

During cultivation periods, tractors and equipment utilize diesel for land preparation, while a generating set provides electrical power for lighting and essential farm operations, including incubators, hatchers, ceiling fans, water pumps, and slaughtering machines The monthly fuel consumption and associated costs are detailed in Table 2.2.

Table 2.2: Monthly fuel consumption of the farm

Table 2.3: Types and number of livestock reared on the farm

3.0 TECHNICAL ANALYSIS OF THE BIOGAS PLANT

3.1 ANALYSIS OF THE ENERGY REQUIREMENTS FOR THE

The various forms of energy consumption and cost distribution account will be analyzed in this sub-section.

Table 3.1 Heating values of some fuels

Fuels Heating values (KJ/Kg) Heating values (MJ/Kg)

ENERGY AUDIT OF THE FARM

This article presents a model designed to assess the energy consumption and flow within farms It emphasizes tracking the monthly energy output from various fuels, calculating the total energy usage, and analyzing the monthly energy costs along with the unit cost of energy.

Mathematical Formulation Cost (C) = mass/quantity of fuel used (Q) * price per unit (P)………3.0a For jth types of fuels,

Cj = Qj * Pj……… 3.0b Energy (E) = mass/quantity of fuel used (Q) * heating value of fuel (H)… 3.0c For j th types of fuels

Ej = Qj * Hj……….3.0dUnit cost (U) = cost (C)/energy (E)………3.0eFor jth types of fuels,

Uj = Cj/Ej………3.0f (Where j =kerosene, fuelwood, charcoal, diesel, petrol, denoted by k, f, c, d, p) Below are the main equation equations that represent energy consumed, it cost and unit cost respectively;

Cost/month ; Cf= Qyf*Pf 3.1

Cp= Qyp*Pp 3.5 energy/month;Ef = Qyf *Hf 3.6

Ep = Qyp *Hp 3.10 unit cost;Ucf = Cf / Ef 3.11

ETotal = (Ef + Ek + Ec + Ed+ Ep) 3.16

CTotal = (Cf+ Ck + Cc + Cd +Cp ) 3.17

Table 3.2 ENERGY AUDIT TABLE OF THE FARM

Fuelwood 20,000 12.00 6.40 Cf= Qyf*Pf Ef = Qyf *Hf Ucf = Cf / Ef

Kerosene 4,725 46.25 70.00 Ck =Qyk*Pk Ek = Qyk *Hk Uck = Ck /

Charcoal 3,500 9.00 2.50 Cc = Qyc*Pc Ec = Qyc *Hc Ucc = Cc /

Diesel 8,350 46.00 65.00 Cd =Qyd*Pd Ed = Qyd *Hd Ucd = Cd /

P.M.S 7,350 46.80 70.00 Cp= Qyp*Pp Ep = Qyp *Hp Ucp = Cp /

3.1.2 ANALYSIS OF ORGANIC WASTE GENERATION OF THE FARM

Here, we wish to calculate the total organic waste generated per day on the farm The farms have the following number of animals;

Table3.3 show discharge per day, total solid value of fresh discharge and water to be added to make favorable TS condition

Table 3.3 Discharge per day, total solid value of fresh discharge & water to be added to make favourable TS condition

TS value of fresh discharge (% by wt)

Water to be added with fresh discharge to make the TS value 8% (Kg)

Source: Bio-gas project, LGED (2006)

Total discharge per day for the various animals;

For cows: Cdtc (kg/day) = Cdc * Nc 3.18

In livestock management, the daily discharge rates for various animals can be calculated using specific formulas For pigs, the daily discharge (Cdtp) is determined by multiplying the discharge coefficient (Cdp) by the number of pigs (Np) Similarly, for birds, the daily discharge (Cdtb) is calculated by multiplying the discharge coefficient (Cdb) by the number of birds (Nb) For sheep, the daily discharge (Cdts) is found by multiplying the discharge coefficient (Cds) by the number of sheep (Ns) The total discharge (CDTotal) is then obtained by summing the individual discharges of all animal types, represented by the formula: CDTotal (kg) = [(Cdc * Nc) + (Cdp * Np) + (Cdb * Nb) + (Cds * Ns)].

3.1.3 DESIGN OF THE PROPOSED BIOGAS PLANT

DESCRIPTION OF THE PROPOSED ACTIVE SOLAR HEATED BIOGAS PLANT

Fig 3.1 A cross-section view of a fixed – dome biogas plant

The structure consists of a cylindrical well dug into the ground, typically featuring walls made of bricks, though alternatives like chicken wire or reinforced concrete are also utilized The cover is generally crafted from mild steel or various materials, including Ferro cement, bamboo cement, plastics, and fiberglass Additionally, the dome may be constructed using a network of iron rods reinforced with concrete For the slurry inlet and outlet, two PVC pipes of a specified internal diameter are employed.

The floor consists of a reinforced concrete foundation with a minimum thickness of 25cm, featuring a wire-mesh design Additionally, inlet and outlet pits are excavated and linked to the main digester via inclined channels designed for the installation of PVC pipes for slurry inlet and outlet.

In order to make digester internally air-tight, plastering and sealing are carried out on the inside walls – as follows:

The initial plastering of the digester involves a 5mm thick mixture of cement and sand in a 1:2 ratio, followed by cement mortar application and curing for several days A layer of melted paraffin wax is then applied to the digester's surface, particularly on the gasholder Inside the digester, two vertically positioned iron rods create partitions to improve slurry mixing The slurry enters through an inlet and exits via an outlet after gas production To maintain optimal slurry temperature for maximum biogas production, additional thermal energy is supplied through a heat exchanger connected to solar collectors The working fluid, which may vary based on climate, is heated by solar energy and circulated by a pump to transfer heat to the slurry The collector panel can be easily detached from the heat exchanger for maintenance Unglazed collectors, such as plastic panels or strip collectors, are cost-effective options for heating Gas outlet pipes are integrated into the dome, with gas production monitored via a manometer, while paraffin wax seals the manhole cover to prevent leakage.

Fermentation pre-ditches (2) i) Material: Reinforced concrete. ii) Maximum capacity: 20 m 3 each. iii) Placement: Adjacent to the digesters and in serial.

Description of the case study farms

Accommodation/Offices

The farm features essential office accommodations for key personnel, including the Farm Manager, Accountant, Sales Clerk, MD, and CEO, along with a general office Additionally, it includes various facilities such as stores, poultry houses, piggery housing, animal husbandry structures, and a security post To support its sizable workforce, the farm provides accommodation for farm managers, permanent employees, and temporary casual workers.

2.1.2 GROWTH LEVEL OF THE FARM

Concordia Farms is experiencing steady growth, primarily focusing on commercial production of poultry, meat, pigs, fish, crops, organic manure, and eggs for local markets The farm aims to enhance its export capabilities and expand its livestock section, despite currently operating at only 25% of its potential due to bureaucratic challenges and financing issues at the ports To align with its export plans, Concordia Farms is increasing production levels, with the poultry section expanding from 2,000 to 3,500 layers and the piggery section also growing, enabling the supply of pigs for pork and sausage production Looking ahead, the farm plans to venture into food processing within the next five years to reduce waste by preserving surplus produce.

The farm has invested in advanced mechanized farming equipment, including a German-made tractor, along with essential tools such as harrows, ploughs, and ridgers A detailed overview of these facilities can be found in Table 1.5.

The farm operates solely on a 250KVA generator, as grid power is unavailable, consuming approximately 322.58 liters of diesel daily Additionally, the farm has two vehicles—a Toyota pick-up and a Toyota bus—that rely on petrol for daily operations Cooking for the 25 permanent workers is done using kerosene stoves, which require kerosene For preparing blood meals used as feed for fish, poultry, and other animals, the farm utilizes fuel wood and charcoal.

During cultivation periods, tractors and equipment utilize diesel for land preparation, while a generator supplies power for all electrical lighting on the farm, operating continuously This generator also powers essential equipment such as incubators, hatchers, ceiling fans, water pumps, and slaughtering machines The monthly fuel consumption and associated costs for the farm are detailed in Table 2.2.

This article presents a model designed to assess the energy consumption and flow within farms It emphasizes the monthly energy contributions from various fuels, calculates the total energy usage, and analyzes the monthly energy costs along with the unit cost of energy.

To calculate the daily discharge of various livestock, the following formulas are used: for pigs, the daily discharge (Cdtp) in kilograms per day is determined by multiplying the discharge coefficient (Cdp) by the number of pigs (Np) For birds, the daily discharge (Cdtb) is calculated by multiplying the discharge coefficient (Cdb) by the number of birds (Nb) For sheep, the daily discharge (Cdts) is obtained by multiplying the discharge coefficient (Cds) by the number of sheep (Ns) The total discharge (CDTotal) in kilograms is the sum of the individual discharges from each type of livestock, represented by the formula: CDTotal = [(Cdc * Nc) + (Cdp * Np) + (Cdb * Nb) + (Cds * Ns)].

A cylindrical well is typically excavated into the ground, with walls commonly constructed from bricks, although reinforced concrete using chicken or bunding wire mesh can also be utilized The well cover is generally made from mild steel or alternative materials such as ferro cement, bamboo cement, various plastics, and fiberglass Additionally, the dome may consist of a network of iron rods reinforced with concrete, while two PVC pipes of a specified internal diameter serve as the slurry inlet and outlet.

The floor consists of a wire-mesh reinforced concrete foundation with a minimum thickness of 25 cm Additionally, inlet and outlet pits are excavated and linked to the main digester via inclined channels designed for the installation of slurry inlet and outlet PVC pipes.

The initial plastering of the digester involves a 5mm thick mixture of cement and sand in a 1:2 ratio, followed by the application of cement mortar and curing for several days A layer of melted paraffin wax is then applied to the digester's surface, particularly on the gasholder Inside the digester, two vertically positioned iron rods act as partitions to facilitate effective slurry mixing The slurry is introduced through an inlet and, after gas production, exits through an outlet To optimize the slurry's temperature for maximum biogas production, thermal energy is supplied via a heat exchanger connected to solar collector panels The working fluid, which may vary depending on climatic conditions, is heated by solar energy and circulated through the heat exchanger by a pump, transferring heat to the slurry The collector panel can be easily detached from the heat exchanger using a gate valve Unglazed collectors, such as plastic panels or strip collectors, are a cost-effective option for heating Additionally, gas outlet pipes are integrated into the dome, with gas production monitored by a manometer, while leakage from the manhole cover is mitigated by sealing it with paraffin wax.

The digesters are constructed from reinforced concrete and feature a non-permeable interior lined with resins They have a cylindrical geometry with inner surface areas of 120.48 m² for the top dome, 166.19 m² for the cylindrical wall, and 108.58 m² for the bottom, providing an available digestion volume of 681.25 m³ each Insulation is achieved through well-projected polyurethane coated with volcanic sand Manure is introduced via gravity from pre-ditches through 0.25 m² ports located at the base of the structure Heating is facilitated by integrated solar panels connected to a heat exchanger, while intermittent timed gas recirculation at 0.4 kg/cm² ensures effective stirring.

Table 3.4 presents the types, quantities, and costs of construction materials required for the biogas digester, reflecting current market prices A comprehensive market survey was conducted to determine the costs of various items essential for the construction process.

Building multiple smaller plants instead of one large facility may simplify maintenance due to their size and cost However, this approach could lead to higher initial capital and maintenance expenses, operational challenges with the digesters, and a greater need for land for construction.

5 Trips of sharp sand 14 Trip 750 10,500.00

6 Trips of chippings of maximum of 12mm aggregate 28 Trip 54,000 1,512,000.0

7 2400mm x 1200mm x 12mm plywood for form work 140 Nr 3000 420,000.00

19 Heat exchangers (230 lengths of ẵ’’ pipe & 8 lengths of 3”/4 pipe)

B) Total solid (TS) contents calculations of organic materials

The total solids (TS) in a specific quantity of materials serve as a key metric for determining the biogas production potential of those materials, with an optimal TS value of 8% being most desirable for efficient biogas generation.

Liquid part: - This is the percentage of water content contained in a certain amount of materials It is usually more than 8%.

C) Favorable temperature, pH value and C/N ratio for good fermentation:

Table3.4: Materials, Quantity, and Cost of construction the Biogas plant

D) Table3.5: shows discharge per day, TS value of fresh discharge and water to be added to make favorable TS condition.

Water to be added with fresh discharge to make the TS value 8% (kg)

For mesophilic digestion where temperature varies from 20 o C – 35 o C and HRT is greater than 20 days.

Fig.3.2 RELATIONSHIP BETWEEN TEMPERATURE, HRT AND TS VALUE

Figure 3.2 illustrates the correlation between temperature, hydraulic retention time (HRT), and the total solid (TS) value in discharged animal waste, highlighting how TS values fluctuate significantly with changes in both temperature and HRT.

Fig3.3: Cross – Section of a Digester

Farm implements and facilities

The farm has invested in mechanized farming equipment, including a German tractor, harrows, ploughs, and ridgers, enhancing its operational efficiency Key facilities are detailed in Table 1.5.

Farm power

The farm relies entirely on a 250KVA generating set for power, as grid installations are non-functional This generator consumes approximately 322.58 liters of diesel daily Additionally, the farm operates two vehicles—a Toyota pick-up van and a Toyota bus—that utilize petrol Cooking for the 25 permanent workers is done using kerosene stoves, which require kerosene For preparing blood meals to feed fish, poultry, and livestock, the farm utilizes fuel wood and charcoal.

During cultivation periods, tractors and equipment utilize diesel for land preparation, while a generating set provides electrical power for farm operations, including lighting, incubators, hatchers, ceiling fans, and water pumps Additionally, it powers slaughtering machines and other essential equipment The monthly fuel consumption and associated costs are detailed in Table 2.2.

A comprehensive model has been developed to assess the energy consumption and flow on farms This model analyzes the monthly energy usage from various fuel sources, calculates the total energy expenditure, and determines the monthly unit cost of energy, providing valuable insights for efficient energy management in agricultural operations.

To calculate the daily discharge for various livestock, the following formulas are used: for pigs, the daily discharge (Cdtp) is determined by multiplying the daily discharge coefficient (Cdp) by the number of pigs (Np) For birds, the daily discharge (Cdtb) is calculated by multiplying the daily discharge coefficient (Cdb) by the number of birds (Nb) In the case of sheep, the daily discharge (Cdts) is found by multiplying the daily discharge coefficient (Cds) by the number of sheep (Ns) The total discharge (CDTotal) is then obtained by summing the individual discharges from all livestock, represented by the equation: CDTotal (kg) = [(Cdc * Nc) + (Cdp * Np) + (Cdb * Nb) + (Cds * Ns)].

The structure consists of a cylindrical well dug into the ground, typically featuring walls made of bricks, but alternatives like chicken wire or reinforced concrete are also utilized The cover is generally crafted from mild steel, with options including ferro cement, bamboo cement, various plastics, and fiberglass Additionally, the dome may be constructed using a network of iron rods and reinforced concrete Two PVC pipes of a specified internal diameter serve as the inlet and outlet for slurry.

The floor consists of a reinforced concrete foundation, featuring a minimum thickness of 25 cm, supported by a wire mesh Additionally, inlet and outlet pits are excavated and linked to the main digester via inclined channels designed for the installation of PVC pipes for slurry inlets and outlets.

The initial plastering of the digester involves a 5mm thick layer of a cement-sand mixture with a 1:2 ratio, followed by the application of cement mortar and a curing period of a few days To enhance the surface, melted paraffin wax is applied, particularly on the gasholder Inside the digester, two vertically positioned iron rods create partitions for improved slurry mixing The slurry enters through an inlet, and after gas production, it exits through an outlet To maintain an optimal temperature for maximum biogas production, thermal energy is supplied via a heat exchanger connected to solar collectors, with the working fluid varying based on climate conditions The solar-heated fluid circulates through the heat exchanger, transferring heat to the slurry The collector panel can be easily detached for maintenance Unglazed collectors, such as plastic or strip collectors, are cost-effective for this purpose Gas production is monitored via a manometer, and paraffin wax seals the manhole cover to prevent leaks.

The digesters are constructed from reinforced concrete and feature a non-permeable interior lined with resins Their cylindrical geometry includes an inner surface area of 120.48 m² for the top dome, 166.19 m² for the cylindrical wall, and 108.58 m² for the bottom, providing an available digestion volume of 681.25 m³ each Insulation is achieved through a well-projected layer of polyurethane coated with volcanic sand Manure is introduced via gravity flow from pre-ditches through ports measuring 0.25 m² at the base of the structure Heating is facilitated by integrated solar panels connected to a heat exchanger, while intermittent stirring is managed through timed gas recirculation at a pressure of 0.4 kg/cm².

Table 3.4 presents the types, quantities, and costs of construction materials required for the biogas digester, reflecting current market prices A comprehensive market survey was conducted to gather the costs of the various items essential for the construction process.

Building multiple smaller plants instead of a single large facility may simplify maintenance, but this approach can lead to higher initial capital and ongoing maintenance costs Additionally, it can create operational challenges for the digesters and necessitate a larger land area for construction.

The total solids (TS) present in a specific quantity of materials serve as a key metric for determining the biogas production rate An optimal TS value for maximizing biogas yield is approximately 8%.

Figure 3.2 illustrates the correlation between temperature, hydraulic retention time (HRT), and the total solid (TS) content in discharged animal waste, highlighting how TS values fluctuate significantly with changes in both temperature and HRT.

Figure 3.3 illustrates a longitudinal section of the biogas digester, clearly labeling its various sections or chambers for simplified calculations The designated volumes include the gas collecting chamber (Vc), gas storage chamber (Vgs), fermentation chamber (Vf), hydraulic chamber (VH), and sludge layer (Vs).

Total volume of digester V = Vc + Vgs + Vf + Vs

D = Net internal span of the digester body [diameter]

F1 = Net vector rise of the top dome

F2 = Net vector rise of the bottom

R1 = Curvature radius of the top dome

R2 = Curvature radius of the inverted dome bottom

Fig.3.4 Geometric dimensions of the cylindrical shaped fixed-dome biogas digester

The diagram illustrates the geometry of the biogas digester, with various chambers and dimensions clearly labeled Each geometrical measurement is meticulously calculated to ensure precise dimensions for optimal functionality.

The assumptions below was extracted from the literature; Bio-gas project, Local Government Engineering Department (LGED), ‘Design of biogas pant’

Where K = Gas production R2 = 1.0625 D rate per m 3 digester volume f1 = D/5 per day K = 0.4 m 3 / m 3 d f2 = D/8

3.1.4 Volume calculation of digester and hydraulic chamber:

A) Volume calculation of digester chamber: i) For N c cows of body weight W b (kg) each,Temp =Ti C

For volume For geometrical dimensions

Let HRT = n days (for temp = Ti C)

Total discharge, Cdtc (kg/day) = Cdc * Nc 3.23

TSc(kg) of fresh discharge,= Cdtc * TSvcd 3.24a

TSc(kg) = Cdc * Nc * TSvcd 3.24b

In 8 % concentration of TS(To make favourable condition)

TSc (kg)solid = (X2 * Cdc * Nc * TSvcd)/ X1 3.25a Influent required qc = (X2* Cdc * Nc * TSvcd)/ X1 (kg) 3.25b

Ldc (kg) = [(X2 * Cdc * Nc * TSvcd/ X1)-( Cdc * Nc)] 3.26a

Ldc(kg) = Cdc * Nc *[( X2* TSvcd /X1)-(1)] 3.26b ii) for N p pigs of body weight W b (kg) each,Temp = Ti C

Total discharge,Cdtp(kg/day) = Cdp*Np 3.27

TSp(kg) of fresh discharge = Cdtp *TSvpd 3.28a

TSp(kg) = Cdp*Np * TSvpd 3.28b

In 8% concentration of TS(To make favourable)

TSp(kg) solid = (X2 * Cdp*Np * TSvpd)/ X1 3.29a Influent required qp = (X2 * Cdp*Np * TSvpd )/ X1 (kg) 3.29b

Ldp(kg) = [(X2 * Cdp*Np * TSvpd / X1)-( Cdp*Np)] 3.30a

Ldp (kg) = Cdp*Np *[( X2 * TSvpd / X1)-(1)] 3.30b iii) For N b birds of body weight W b each,Temp = Ti C

Total discharge, Cdtb(kg/day) = Cdb*Nb 3.31

TSb(kg) of fresh discharge = Cdtb *TSvbd 3.32a

TSb(kg) = Cdb*Nb * TSvbd 3.32b

TSb (kg) solid = (X2 * Cdb*Nb * TSvbd )/ X1 3.33a Influent required q = (X2 * Cdb*Nb * TSvbd)/ X1 (kg) 3.33b

Ldb(kg) = [(X2 * Cdb*Nb * TSvbd / X1)-( Cb*Nb)] 3.34a

Ldb (kg) = Cdb*Nb *(X2 * TSvbd / X1)-(1)] 3.34b iv) For N s sheep of body weight W b each, Temp = Ti C

Total discharge,Cdts(kg) = Cds*Ns 3.35

TSs(kg) of fresh discharge = Cdts *TSvsd 3.36a

TSs(kg)= Cds*Ns * TSvsd 3.36b

In 8% concentration of TS(To make favourable condition)

TSs (kg)solid = (X2 * Cds*Ns * TSvsd)/ X1 3.37a Influent required q = (X2 * Cds*Ns * TSvsd)/ X1 (kg) 3.37b

Lds(kg) = [(X2 * Cds*Ns * TSvsd / X1)-( Cds*Ns)] 3.38a

Lds(kg) = Cds*Ns [X2 (* TSvsd / X1)-(1)] 3.38b Total influent qT(kg)= (X2 / X1)[ (Cdc * Nc * TSvcd )+(Cdp*Np * TSvpd )+

(Cdb*Nb * TSvbd )+ (Cds*Ns * TSvsd )] 3.39

Ldt = {[ Cdc * Nc *( X2 * TSvcd / X1 )-(1)]+[ Cdp*Np *[( X2 * TSvpd / X1)-(1)]+[ Cdb*Nb

*[( X2 * TSvbd / X1)-(1)]+ [Cds*Ns (X2 * TSvsd / X1)-(1)]} 3.40 Working volume of digester = Vgs + VF ………3.41

Now we find from assumptions, as we know the value of “D” & “H”

B) Volume calculation of hydraulic chamber

Fig 3.5: The Hydraulic chamber of the digester

VGS = 0.50 x (VGS + VF + VS) x k………3.53a (Where k = Gas production rate per m 3 digester vol /day)

VGS = 50% of daily gas yield……….3.53b

VGS = (0.5 x TS x gas producing rate per kg Ts)……… 3.53c

VGS(m^3) = [0.5*[(TSc*Mgsc)+(TSp*Mgsp)+(TSb*Mgsb)+(TSs*Mgss)] 3.53d

We fixed h = 8000mm water volume (1mm = 10N/M 2 ) hn = h3 + F1 + H1 ………3.56Again we know that VGS = VH or, VGS = 3.4 x (D4) 2 x h3/4 ……… 3.57aAgain, Vb 0.2225*(PTS) 2.7717 ……….3.57b

FTotal = Total surface Area of digester,

Note: FT = surface Area of top dome

FC = surface Area of the cylindrical wall, FB = surface Area of the bottom.

The ideal temperature for maximizing biogas production from slurry is approximately 37°C However, achieving this temperature naturally can be challenging in colder regions, such as Rivers State, during winter months To maintain the optimal temperature for effective biogas production, external energy is necessary This study utilizes active heating methods, including hot charging and the integration of collectors with the digester via a heat exchanger, to heat the slurry efficiently.

Technical Analysis of the Biogas plant

Analysis of organic waste generation of the farm

To calculate the daily discharge for different livestock, use the following formulas: for pigs, the daily discharge (Cdtp) in kilograms is determined by multiplying the discharge coefficient (Cdp) by the number of pigs (Np) For birds, the daily discharge (Cdtb) is calculated by multiplying the discharge coefficient (Cdb) by the number of birds (Nb) For sheep, the daily discharge (Cdts) is found by multiplying the discharge coefficient (Cds) by the number of sheep (Ns) The total discharge (CDTotal) in kilograms is the sum of the individual discharges for each type of livestock, represented by the equation: CDTotal = [(Cdc * Nc) + (Cdp * Np) + (Cdb * Nb) + (Cds * Ns)].

Design of the proposed biogas plant

The structure consists of a cylindrical well dug into the ground, typically featuring walls made of bricks, though reinforced concrete with chicken or bunding wire mesh is also utilized The cover is generally crafted from mild steel, with alternatives including ferro cement, bamboo cement, various plastics, and fiberglass Additionally, the dome may be constructed using a network of iron rods reinforced with concrete For the slurry inlet and outlet, two PVC pipes of a specified internal diameter are employed.

The floor consists of a wire-mesh reinforced concrete foundation with a minimum thickness of 25 cm In addition, inlet and outlet pits are excavated and linked to the main digester via inclined channels designed for the installation of PVC pipes for slurry inlet and outlet.

The initial plastering of the digester involves a 5mm thickness mixture of cement and sand in a 1:2 ratio, followed by applying cement mortar and curing for several days A layer of melted paraffin wax is then applied, particularly on the gasholder's surface Inside the digester, two vertically standing iron rods create partitions to facilitate proper slurry mixing Slurry enters through an inlet and gas exits via an outlet To optimize the slurry temperature for enhanced biogas production, thermal energy is introduced through a heat exchanger connected to solar collectors, with the working fluid varying based on climatic conditions Solar energy heats the fluid, which is circulated by a pump to transfer heat to the slurry The collector panel can be easily detached from the heat exchanger using a gate valve Unglazed collectors, such as plastic panels or strip collectors, are cost-effective alternatives for heating applications Gas production is monitored using a manometer, and leakage from the manhole cover is mitigated by sealing it with paraffin wax.

The digesters are constructed from reinforced concrete and feature a non-permeable interior lined with resins Their cylindrical geometry includes inner dimensions with a top dome surface area of 120.48 m², a cylindrical wall of 166.19 m², and a bottom area of 108.58 m², providing an available digestion volume of 681.25 m³ each Insulation is achieved using well-projected polyurethane coated with volcanic sand Manure is introduced via gravity fall from pre-ditches through 0.25 m² ports at the base of the structure Heating is facilitated by integrated solar panels connected through a heat exchanger, while intermittent timed gas recirculation at 0.4 kg/cm² ensures proper stirring.

Table 3.4 outlines the types, quantities, and costs of construction materials required for the biogas digester, reflecting current market prices A comprehensive market survey was conducted to gather the pricing information for the various items essential for the construction process.

Building multiple smaller plants instead of a single large facility may simplify maintenance, but this approach will lead to higher initial capital and ongoing maintenance costs, create operational challenges for the digesters, and necessitate a larger land area for construction.

The total solids (TS) present in a given quantity of materials serve as a key indicator for assessing the biogas production potential of those materials An optimal TS value for maximizing biogas yield is typically around 8%.

Figure 3.2 illustrates the correlation between temperature, hydraulic retention time (HRT), and the total solid (TS) value in discharged animal waste, highlighting how variations in temperature and HRT significantly affect the TS value.

Figure 3.3 illustrates a longitudinal section of the biogas digester, highlighting its various chambers for clarity in calculations The gas collecting chamber volume is denoted as Vc, while the gas storage chamber volume is represented as Vgs Additionally, the fermentation chamber volume is labeled Vf, the hydraulic chamber volume as VH, and the sludge layer volume as Vs.

Total volume of digester V = Vc + Vgs + Vf + Vs

D = Net internal span of the digester body [diameter]

F1 = Net vector rise of the top dome

F2 = Net vector rise of the bottom

R1 = Curvature radius of the top dome

R2 = Curvature radius of the inverted dome bottom

Fig.3.4 Geometric dimensions of the cylindrical shaped fixed-dome biogas digester

The diagram illustrates the geometry of a biogas digester, featuring various chambers and dimensions that are crucial for its design Each labeled section is calculated to ensure precise measurements, optimizing the digester's efficiency and functionality.

The assumptions below was extracted from the literature; Bio-gas project, Local Government Engineering Department (LGED), ‘Design of biogas pant’

Where K = Gas production R2 = 1.0625 D rate per m 3 digester volume f1 = D/5 per day K = 0.4 m 3 / m 3 d f2 = D/8

3.1.4 Volume calculation of digester and hydraulic chamber:

A) Volume calculation of digester chamber: i) For N c cows of body weight W b (kg) each,Temp =Ti C

For volume For geometrical dimensions

Total discharge, Cdtc (kg/day) = Cdc * Nc 3.23

TSc(kg) of fresh discharge,= Cdtc * TSvcd 3.24a

TSc(kg) = Cdc * Nc * TSvcd 3.24b

In 8 % concentration of TS(To make favourable condition)

TSc (kg)solid = (X2 * Cdc * Nc * TSvcd)/ X1 3.25a Influent required qc = (X2* Cdc * Nc * TSvcd)/ X1 (kg) 3.25b

Ldc (kg) = [(X2 * Cdc * Nc * TSvcd/ X1)-( Cdc * Nc)] 3.26a

Ldc(kg) = Cdc * Nc *[( X2* TSvcd /X1)-(1)] 3.26b ii) for N p pigs of body weight W b (kg) each,Temp = Ti C

Total discharge,Cdtp(kg/day) = Cdp*Np 3.27

TSp(kg) of fresh discharge = Cdtp *TSvpd 3.28a

TSp(kg) = Cdp*Np * TSvpd 3.28b

TSp(kg) solid = (X2 * Cdp*Np * TSvpd)/ X1 3.29a Influent required qp = (X2 * Cdp*Np * TSvpd )/ X1 (kg) 3.29b

Ldp(kg) = [(X2 * Cdp*Np * TSvpd / X1)-( Cdp*Np)] 3.30a

Ldp (kg) = Cdp*Np *[( X2 * TSvpd / X1)-(1)] 3.30b iii) For N b birds of body weight W b each,Temp = Ti C

Total discharge, Cdtb(kg/day) = Cdb*Nb 3.31

TSb(kg) of fresh discharge = Cdtb *TSvbd 3.32a

TSb(kg) = Cdb*Nb * TSvbd 3.32b

TSb (kg) solid = (X2 * Cdb*Nb * TSvbd )/ X1 3.33a Influent required q = (X2 * Cdb*Nb * TSvbd)/ X1 (kg) 3.33b

Ldb(kg) = [(X2 * Cdb*Nb * TSvbd / X1)-( Cb*Nb)] 3.34a

Ldb (kg) = Cdb*Nb *(X2 * TSvbd / X1)-(1)] 3.34b iv) For N s sheep of body weight W b each, Temp = Ti C

Total discharge,Cdts(kg) = Cds*Ns 3.35

TSs(kg) of fresh discharge = Cdts *TSvsd 3.36a

TSs(kg)= Cds*Ns * TSvsd 3.36b

In 8% concentration of TS(To make favourable condition)

TSs (kg)solid = (X2 * Cds*Ns * TSvsd)/ X1 3.37a Influent required q = (X2 * Cds*Ns * TSvsd)/ X1 (kg) 3.37b

Lds(kg) = [(X2 * Cds*Ns * TSvsd / X1)-( Cds*Ns)] 3.38a

Lds(kg) = Cds*Ns [X2 (* TSvsd / X1)-(1)] 3.38b Total influent qT(kg)= (X2 / X1)[ (Cdc * Nc * TSvcd )+(Cdp*Np * TSvpd )+

(Cdb*Nb * TSvbd )+ (Cds*Ns * TSvsd )] 3.39

Ldt = {[ Cdc * Nc *( X2 * TSvcd / X1 )-(1)]+[ Cdp*Np *[( X2 * TSvpd / X1)-(1)]+[ Cdb*Nb

*[( X2 * TSvbd / X1)-(1)]+ [Cds*Ns (X2 * TSvsd / X1)-(1)]} 3.40 Working volume of digester = Vgs + VF ………3.41

Now we find from assumptions, as we know the value of “D” & “H”

B) Volume calculation of hydraulic chamber

Fig 3.5: The Hydraulic chamber of the digester

VGS = 0.50 x (VGS + VF + VS) x k………3.53a (Where k = Gas production rate per m 3 digester vol /day)

VGS = 50% of daily gas yield……….3.53b

VGS = (0.5 x TS x gas producing rate per kg Ts)……… 3.53c

VGS(m^3) = [0.5*[(TSc*Mgsc)+(TSp*Mgsp)+(TSb*Mgsb)+(TSs*Mgss)] 3.53d

We fixed h = 8000mm water volume (1mm = 10N/M 2 ) hn = h3 + F1 + H1 ………3.56Again we know that VGS = VH or, VGS = 3.4 x (D4) 2 x h3/4 ……… 3.57aAgain, Vb 0.2225*(PTS) 2.7717 ……….3.57b

FTotal = Total surface Area of digester,

Note: FT = surface Area of top dome

FC = surface Area of the cylindrical wall, FB = surface Area of the bottom.

To maximize biogas production, the optimum slurry temperature is approximately 37°C However, achieving this temperature naturally during colder months in regions like Rivers State is challenging Therefore, external energy is essential to maintain the ideal temperature for effective biogas production This study employs active heating methods, including hot charging and the integration of collectors with the digester via a heat exchanger, to ensure the slurry reaches the required temperature.

This article presents a derived analytical expression for the thermal efficiency of an active, fixed-dome biogas plant, focusing on the designed parameters of the heat exchanger, collector panel, and digester It analytically explores the impact of each parameter on the design of an active system aimed at effectively heating the slurry.

To achieve optimal slurry temperature for enhanced biogas production, additional thermal energy is introduced into the digester via a heat exchanger linked to a collector panel The working fluid in this system may vary based on climatic conditions, with solar energy heating the fluid in the collector, which is then circulated through the heat exchanger by a pump This process transfers heat from the hot fluid to the slurry, raising it to the desired temperature For cost-effectiveness and convenience, unglazed collectors, such as plastic panels or strip collectors, are recommended, similar to those used for swimming pool heating.

In writing the energy –balance equations for the gas and the slurry, the following assumptions are made;

(i) Each component of the system is perfectly insulated

(ii) Each component of the system is isothermal

In the integrated system of the digester and collector panel, the slurry and working fluid exhibit no temperature gradient in the radial direction The energy balance equations governing both the digester/slurry and the gas are essential for understanding the system's performance.

Qu=Ms*Cs*(dTs/dt)+h1*Ah*(Ts-Tg)+hb*(A 1 t)*(Ts-Ta) 3.63

And h1*Ah*(Ts - Tg)=Uo*(A 1 to)*(Tg-Ta)……… … ….3.64 Where,

Qu=h*L*(Tf-Ts)=F (t)*{[(α*τ)*I(t)/U L ]-(Ts-Ta)} ………… 3.65

Tf=Ts+ {[(mf*Cf)/h*L]*(Tf0-Ts)*[1 -exp(-B)]}………… ….3.66

Tfo={[α*τ*I(t)]/U L +Ta}+{Tfi-Ta-[α*τ*I(t)]/U L }*exp(-K)……… 3.67

Tfi =Ts+(Tfo-Ts)*exp(-B)……… ……… 3.68 F(t)=mf*Cf*{[1-exp(-B)]*[1-exp(-K)]/[1-exp(-K-B)] … … …3.69

K=(N*Ac*UL*F 1 )/(mf*Cf) ……… ………….3.70 B=h*L/ (mf*Cf) ……… …………3.71 (At)1=At + Ato ……… ……… ……….3.72 (The preceding equations are combined to give)

(dTs/dt)+a*Ts=f(t)…… ………3.73 Where: a={F(t)+[(1/(Uo*Ato))+(1/(h1*Ah))] -1 +hb*A 1 t}/(ms*Cs) 3.74 And f(t)=(1/ms*Cs)*{[F(t)*α*τ*I(t)/U L ]+[F(t)+h1*Ah*Uo*Ato/(Uo*Ato+h1*Ah)

The solution to Eq (3.73) is

Ts={[f(t)/a]*[1-exp(-a*t)]+Tso*exp(-a*t)…… ……….3.76 (Which gives the slurry temperature as a function of time The instantaneous efficiency of the biogas system is); ŋt=ms*Cs*(Ts-Tso)/[I (t)*N*Ac*t]

={[1-exp(-a*t)]/(a*t*N*Ac)}*{[(F(t)*α*τ/UL]-a*ms*Cs*(Tso-Ta)/I(t)}.…………3.77

The preceding equations determine the thermal efficiency of an active biogas plant and can be used for the design of a biogas system with a given heat capacity (ms Cs).

The thermal efficiency of an active biogas system given by equation (3.77) will now be considered for two cases.

Case (i) if a < 1 then, ( 1 – exp (- at) / (at) 1

To achieve maximum thermal efficiency in a biogas plant, it is essential to optimize the design parameters for a specific capacity Minimizing the numerator of “a” in equation (3.74) is crucial for enhancing plant performance, as the second and third terms represent various losses to the environment and ground These losses must be minimized through effective insulation of the digester By focusing on reducing the second and third terms of equation (3.74), the thermal capacity of the biogas plant can be significantly increased for a given value of F(t).

Thermal analysis

To maximize biogas production, the optimal slurry temperature is approximately 37°C However, achieving this temperature naturally can be challenging in colder regions, such as Rivers State, during winter months Therefore, external energy is essential for maintaining the ideal temperature in the digester This study employs active heating methods, including hot charging and the integration of heat collectors with the digester via a heat exchanger, to effectively heat the slurry.

This article presents an analytical expression for the thermal efficiency of an active, fixed-dome biogas plant, focusing on the design parameters of the heat exchanger, collector panel, and digester It provides a detailed analysis of how each parameter influences the system's performance in heating the slurry, offering valuable insights for optimizing design in active biogas systems.

To achieve optimal slurry temperatures for enhanced biogas production, additional thermal energy is introduced into the digester via a heat exchanger linked to a collector panel Depending on climatic conditions, the working fluid in this system may vary from water Solar energy heats the fluid in the collector, which is then circulated through the heat exchanger by a pump, allowing heat transfer to the slurry For convenience and cost-effectiveness, unglazed collectors such as plastic panels, strip collectors, or plastic-pipe collectors are recommended, similar to those used for swimming pool heating.

In writing the energy –balance equations for the gas and the slurry, the following assumptions are made;

(i) Each component of the system is perfectly insulated

(ii) Each component of the system is isothermal

In the system, there is a uniform temperature throughout the slurry and the working fluid within both the collector and the heat exchanger, indicating no radial temperature gradient The energy balance equations governing the digester/slurry integrated with the collector panel and the gas are essential for understanding the system's performance.

Qu=Ms*Cs*(dTs/dt)+h1*Ah*(Ts-Tg)+hb*(A 1 t)*(Ts-Ta) 3.63

And h1*Ah*(Ts - Tg)=Uo*(A 1 to)*(Tg-Ta)……… … ….3.64 Where,

Qu=h*L*(Tf-Ts)=F (t)*{[(α*τ)*I(t)/U L ]-(Ts-Ta)} ………… 3.65

Tf=Ts+ {[(mf*Cf)/h*L]*(Tf0-Ts)*[1 -exp(-B)]}………… ….3.66

Tfo={[α*τ*I(t)]/U L +Ta}+{Tfi-Ta-[α*τ*I(t)]/U L }*exp(-K)……… 3.67

Tfi =Ts+(Tfo-Ts)*exp(-B)……… ……… 3.68 F(t)=mf*Cf*{[1-exp(-B)]*[1-exp(-K)]/[1-exp(-K-B)] … … …3.69

K=(N*Ac*UL*F 1 )/(mf*Cf) ……… ………….3.70 B=h*L/ (mf*Cf) ……… …………3.71 (At)1=At + Ato ……… ……… ……….3.72 (The preceding equations are combined to give)

(dTs/dt)+a*Ts=f(t)…… ………3.73 Where: a={F(t)+[(1/(Uo*Ato))+(1/(h1*Ah))] -1 +hb*A 1 t}/(ms*Cs) 3.74 And f(t)=(1/ms*Cs)*{[F(t)*α*τ*I(t)/U L ]+[F(t)+h1*Ah*Uo*Ato/(Uo*Ato+h1*Ah)

The solution to Eq (3.73) is

Ts={[f(t)/a]*[1-exp(-a*t)]+Tso*exp(-a*t)…… ……….3.76 (Which gives the slurry temperature as a function of time The instantaneous efficiency of the biogas system is); ŋt=ms*Cs*(Ts-Tso)/[I (t)*N*Ac*t]

={[1-exp(-a*t)]/(a*t*N*Ac)}*{[(F(t)*α*τ/UL]-a*ms*Cs*(Tso-Ta)/I(t)}.…………3.77

The preceding equations determine the thermal efficiency of an active biogas plant and can be used for the design of a biogas system with a given heat capacity (ms Cs).

The thermal efficiency of an active biogas system given by equation (3.77) will now be considered for two cases.

Case (i) if a < 1 then, ( 1 – exp (- at) / (at) 1

Achieving maximum thermal efficiency is crucial for optimizing the design parameters of a biogas plant with a specific capacity To ensure optimal performance, it is essential to minimize the numerator of “a” in equation (3.74), as the second and third terms represent various losses to the environment and ground Reducing these losses is vital, and effective insulation of the digester on all sides is key to achieving this optimization For a biogas plant with significant thermal capacity, minimizing the second and third terms of equation (3.74) is necessary while maintaining a consistent value of F(t).

To optimize biogas production, it is essential to maximize the mass flow rate (Mf) of the working fluid while maintaining a specific number of collectors, as indicated by equations (3.69) to (3.71) Additionally, the area (A) must also be considered to achieve the best results.

B should be minima Also, the length of the heat exchanger (L) and its heat – transfer coefficient (h) should be maximum.

Case (ii) if at >> 1 then, [1 – exp(-at)] / at 0This case is not useful since it refers simply to no heating of the slurry.

Analysis of biogas generation prospects of the Farm with its energy requirements

THE FARM WITH ITS ENERGY REQUIREMENTS

The potential for biogas generation largely relies on the availability of common raw materials known as organic waste materials These materials include human excreta, animal manure, sewage sludge, and crop residues, which play a crucial role in the biogas production process.

Exploring affordable energy sources and implementing innovative conversion technologies are essential for transforming the vast amounts of organic waste produced by Concordia farms into valuable biogas energy.

The daily production volume of biogas (Y in m³) generated from organic waste, such as cattle dung, sheep dung, pig droppings, and poultry droppings, is directly related to the total discharge of organic waste (CDTotal in Kg/day).

Ytb = Yb*Cdtb, 3.81 The total yield is then given by;

YT = (Ytc+ Yts + Ytp + Ytb) 3.82 Hence, energy, Eb is given by;

And volume of biogas generated is given by;

Vb=0.2225(PTS)^2.7717 (Igoni , et al, 2008)……… 3.84

The analysis reveals the biogas generation potential of Concordia Farms, allowing for the optimization of its energy requirements The energy produced can be effectively utilized for various purposes, including cooking, lighting, heating, and warming on the farm.

Economic Feasibility

Introduction

At Concordia Farms, biogas is primarily utilized as a technology to fulfill the farm's energy needs, highlighting its importance in agricultural operations This focused application of biogas technology holds considerable potential, as numerous farms can reap significant benefits from its implementation.

This section focuses on the economic aspects of technology, specifically examining the production of biogas and slurry at the commercial farm level.

Financial analysis

Financial analysis serves as a crucial tool for determining the financial viability of installing a biogas plant on a farm The core premise of this analysis is that a farm will only invest in new technology if it anticipates a positive effect on its financial performance.

In this analysis, all costs and benefits are valued from the point of view of the farms for which this is being done.

Before deciding to install the plants, it is crucial to accurately estimate all associated costs and benefits as they will directly impact the user, or farm, utilizing the plant installation.

The benefits and costs associated with a biogas plant can fluctuate based on the inputs and outputs utilized by farms For instance, if there are extra expenses related to sourcing inputs, like purchasing cattle dung or hiring additional labor for plant operation, these costs—though not accounted for in this analysis—should be factored into the overall financial assessment.

The financial analysis evaluates the timing and distribution of costs and benefits throughout the project's lifespan, providing a detailed yearly breakdown It specifically focuses on costs and benefits directly influenced by the adoption of the technology, excluding any unrelated financial changes This approach ensures a clear assessment of the biogas plant's financial viability.

The major parameters that need to be considered for the financial viability of this biogas plant are discussed below;

Project life

A fixed dome type biogas plant can have a lifespan exceeding 40 years, contingent upon construction quality and materials However, for economic evaluations, its operational life is typically considered to be 20 years, as any costs or benefits beyond this period hold minimal present value Consequently, this analysis assumes that a 681.3 m³ biogas plant will cease to function by the end of its 20th year post-commissioning.

Benefits and cost

Unpriced benefits of a biogas plant are challenging to quantify and cannot be easily compared to market prices of similar products or services For instance, assigning a monetary value to the advantages of a cleaner homestead or the reduction in harmful pathogens present in the slurry is complex Key unpriced benefits include improved environmental health and enhanced sanitation.

Farmers can significantly reduce production costs by utilizing slurry as a feed supplement, which can account for up to 30% of the feed for raising pigs or fish This innovative approach not only enhances profitability but also promotes sustainable farming practices.

Biogas technology enhances the management of biological fertilizers, as research indicates that effluent serves as an effective soil conditioner and fertilizer, according to Jo Lawbuary (2007).

The primary health benefit of enhancing the indoor environment is significant, especially in rural Nigeria, where air pollution from fuel wood usage poses serious health risks The harmful pollutants present in the smoke are linked to four major categories of health issues, highlighting the urgent need for improved air quality solutions.

• Acute respiratory infections (ARI) in children.

• Adverse pregnancy outcomes for women exposed during pregnancy, Jo Lawbuary (2007)

• Chronic lung diseases and associated heart diseases in adults.

This will reduce spending on health care on the national level, and lead improved health and lower susceptibility to disease on individual level.

The fermentation process effectively reduces harmful pathogens and parasites in slurry, leading to a significant decrease in fly populations around dung heaps As a result, organic compounds become stabilized, contributing to a cleaner environment free from waste accumulation.

 TOURISM: - New opportunities are created

 DEVELOPMENT – RELATED BENEFITS:- Improve situation on the farm. Provide employment for masons and extension workers A replacement for fossil fuels.

Indirect valuation of biogas plants highlights their economic benefits by quantifying savings in fuel costs, such as petrol (PMS), charcoal, and diesel (A.G.O) These savings are calculated based on local market prices, demonstrating how farms can significantly reduce expenses by avoiding the purchase of fuel wood, kerosene, and other traditional energy sources.

Biogas offers significant benefits for lighting in addition to its use for cooking, as it can replace kerosene, charcoal, fuel wood, diesel, and PMS, leading to substantial cost savings Biogas lamps deliver more reliable and superior lighting compared to traditional sources like electricity, kerosene, PMS, and diesel Although the convenience of biogas lighting is challenging to quantify, it represents a valuable aspect of the overall benefits, despite its minor contribution to the total value stream not being included in the analysis.

The salvage value of a biogas plant is excluded from the financial analysis benefit stream, as the plant and its components will not be resalable after 20 years of operation.

Biogas provides significant value for farms by serving as a cooking fuel, replacing traditional sources like fuel wood, kerosene, and charcoal The adoption of biogas leads to substantial savings in the quantity and cost of these fuels, highlighting the economic benefits of biogas plants Additionally, the use of biogas eliminates the challenges related to the collection, storage, and usage of conventional fuels such as fuel wood, kerosene, diesel, and PMS, thereby enhancing operational efficiency on farms.

The valuation of time saved in agricultural work varies significantly, with farmers either spending just 15 minutes or gaining up to 4.5 hours daily, largely influenced by their access to forest resources and water A study involving 100 biogas households across 16 districts indicated an average net labor saving of 3.10 hours per day (FAO/TCP/NEP/4415-T, 1996).

In all these studies, the availability of firewood and water were the critical factors to determine the extent of labour saved (East Consult, 1994)

The time saved through labor can be allocated to leisure or other economic pursuits Valuing this leisure time involves complex economic principles; however, a simpler approach is to consider that the saved labor could be redirected to alternative economic activities or sold in the local labor market To accurately assess this value, it's essential to base assumptions on current employment rates and the market wage for unskilled labor For instance, if 3.09 hours are saved from the installation of a biogas plant, this time can be translated into economic benefits.

3.09 = gross saving in time for fuel wood Collection, cooking and cleaning of utensils

8 = working hour per day of labour

P = current market wage rate for labour (N300/day)

The money valuations of the above calculation come to be N42, 294.375 i.e.

For effective financial analysis, it is essential to consider that the average employment in agricultural activities for both men and women is approximately 200 days per year, translating to a value of N23,175.00 for those 200 days.

The valuation of slurry from biogas plants highlights its superior benefits for soil health and productivity when compared to fresh or composted dung This enhancement is attributed to the production of enzymes and vitamins during the anaerobic digestion process, which contribute positively to soil quality.

Also, bio-chemical composition of some of the nutrient such as nitrogen is changed and becomes more readily available for plant Because of the

8hr cumulative effects of these elements in biogas slurry, its value as feed and manure is enhanced.

The financial value of slurry benefits is contingent on its actual usage by the farm, such as feeding livestock or enhancing crop yields If slurry is not utilized for these purposes, its potential benefits should not be considered in the financial analysis Therefore, the manure value of slurry can only be included if there is a tangible increase in crop yield resulting from its application.

A literature review highlights various methods for assigning monetary value to slurry, as noted by Guatam (1988) A prevalent approach involves calculating the value based on the increased levels of nitrogen (N), phosphorus (P), and potassium (K) in slurry compared to traditional dung, using market prices of these nutrients in chemical fertilizers as a reference Additionally, the enhanced protein content in slurry can be valued when utilized as a component of cattle feed, although this comes with a degree of uncertainty regarding the anticipated benefits (Rubab and Kandpal, 1996).

Cash flow Analysis

The cash flow analysis for the gas plant involves recording all projected annual income over the project's estimated lifespan as inflows, while yearly expenditures are documented as outflows By subtracting total expenditures from total income, the resulting figure represents the net cash flow or net benefit of the project.

Generally, in the initial year(s) of the project, the net cash flow or benefit tend to be negative, because of the expenditures incurred to meet establishment costs (Gittinger 1982).

Time Value of Money and Discount Rate

The real value of money changes over time The reasons for such changes are;

- Money can be invested to earn a return in the future; and

- People or investors have time preferences, i.e they prefer now to future.

For example if N100, 000 is invested today at an interest rate of 20% per annum, this will be work N120, 000 a year’s time, N144, 000 after two yeas etc.

Net present value (N P V)

To effectively compare the costs and benefits of a project over its useful life, it is essential to express them in a common denominator This involves deriving the annual cash flow and discounting it to allow for comparison against a single year's value The resulting discounted net cash flow serves as a key measure of the project's profitability By discounting all future values to their present equivalents, we express them as Net Present Worth (NPW) or Net Present Value (NPV).

The NPV techniques evaluate the viability of the biogas project by converting annual cash flows into a single present value A positive NPV signifies that the project's benefits exceed its costs throughout its lifespan This relationship between future amounts and present value is achieved through a process called discounting, which can be represented by a specific equation.

P = present worth of cost (money)

A = End of year payments or savings i = Rate of interest

When selecting a discount rate, it is essential to consider the interest rate charged by banks on loans and the opportunity cost of capital when private investments are made Currently, the discount rate applied to biogas investments stands at 20 percent.

Therefore, the NPV and benefit cost ratio (BCR) calculated in this work is at the rate of 20%.

Internal Rate of Returns (I R R)

The Internal Rate of Return (IRR) is a key metric for assessing project profitability, representing the percentage rate at which the Net Present Value (NPV) of a project equals zero Essentially, IRR indicates the discount rate that balances the present value of a project's benefits with its costs Furthermore, it can be interpreted as the effective interest rate earned on the investment Calculating IRR typically involves trial and error techniques.

To determine the Internal Rate of Return (IRR), the Net Present Value (NPV) must be calculated using various discount rates until the NPV reaches zero An approximate value of IRR can be derived using an interpolation equation.

The IRR is the i*% at which

RK = net receipt for k-year

DK = net disbursement for k-year and

Benefit-Cost ratio

The benefit-cost ratio (BCR) is a valuable metric for evaluating a project's profitability A BCR greater than 1.0 indicates that the project is worth pursuing, and since the B/C ratio in this analysis exceeds 1.0, the project is considered viable.

PRr = Rr{[(1+i) N -1]/[i(1+i) N ]}, Present value of savings 3.89

PI = Present value of investment 3.90

PDd = Dd{[(1+i) N -(1)]/[i(1+i) N ]},Present value of disbursment 3.91 Total expenses PT = (PI + PDd) 3.92 Net present value NPV = [(PRr)-( PI + PDd)] 3.93

(ii) IRR – INTERNAL RATE OF RETURNS

- PI +[Rr-Dd]*[(1+i) N -(1)]/[i(1+i) N ] = 0 3.94a -P+[Rr-Dd]*(P/A,i*%,N th ) = 0………3.94b (P/A,i*%,N th ) = [Rr-Dd]/P……… 3.94c

Net revenue = PRr 3.95Net Expenses = (PI + PDd) 3.96B/C ratio = PRr /( PI + PDd) 3.97

Generalized cost distribution of a Biogas plant

5year guaranty pipe & fittings cement accessories transport unskilled labour sand & gravel overhead

Fig.3.6 A Generalized Cost Distribution Of A Biogas Plant

The calculations for material composition in construction are expressed as percentages of the total weight For cement, the formula is θcement = (Pcement*100)/Ptotal Similarly, the proportion of sand and chipings is calculated using θsand/chipings = (Psand/chipings*100)/Ptotal The percentage for rod, wire, and wood is determined by θrod/wire/woods = (Prod/wire/woods*100)/Ptotal Accessories are represented as θaccessories = (Paccessories*100)/Ptotal, while the transmission materials are calculated with θtrans = (Ptrans*100)/Ptotal The formula for pipes, fittings, and nails is θpipes/fittings/nails = (Ppipes/fittings/nails*100)/Ptotal, and finally, labor is quantified as θlabour = (Plabour*100)/Ptotal.

Ptotal,θ overhead = (Poverhead*100)/ Ptotal, 3.98h θsolar panel = (Psolar panel*100)/ Ptotal, ……….3.98i

Fig3.7 Factors influencing the financial viability of a biogas plant

Energy demand Availability of F.S S.P Gas yield Dilution factor Type of T.S Degree of digestion Temperature Material cost Labour cost Geographical condition Fuel wood

Kerosene Diesel P.M.S Charcoal End use Utilizing pattern Materials Services Brick masonry Stone masonry Concrete

Construction cost of the biogas plant

Economic Analysis

Economic valuation of firewood

The reliance on firewood for cooking on farms adversely impacts local forest density, subsequently disrupting the area's microclimate and affecting the surrounding community Consequently, the economic cost of firewood should be elevated for society compared to individual users, leading to greater economic returns on investment.

There is currently no universally accepted value for fuel wood that accurately represents its social costs or benefits Some experts classify firewood as a non-traded good, assigning it a value below its financial price, while others estimate its worth to be slightly higher Additionally, certain authorities consider the economic price of firewood to be approximately 20 percent above the financial price.

Economic valuation of Kerosene, PMS, and Diesel

The economic value of kerosene, PMS, and diesel in Nigeria is easier to determine due to their marketability and the calculable subsidy value Nigeria refines some petroleum products locally while importing others, with payments for imports made in US dollars If the official exchange rate accurately represents the true economic value of these goods, the border price for imported products serves as their economic price, while the cost of production applies to locally refined products Additionally, a 10 percent increase is added to account for transportation and handling costs of kerosene, diesel, and PMS within the country.

Economic valuation of labor

Utilizing biogas significantly reduces the time required for unskilled labor, allowing for more efficient farming practices To align labor costs with large-scale agricultural operations, a reduction factor is applied to the wage rate for unskilled labor According to Gautam (1988), a factor of 0.65 was used to calculate a more economical wage rate for unskilled workers.

Valuation of slurry

Slurry is highly regarded for its rich nutrient content, especially nitrogen (N), phosphorus (P), and potassium (K) In Nigeria, where all chemical fertilizers are imported, the economic significance of these nutrients is determined based on the international market prices of N, P, and K fertilizers.

Investment cost

When calculating the total investment in biogas construction, any guarantee fees and service charges from builders should be subtracted, as they represent mere transfer payments Conversely, any subsidies received should be added to the investment cost Additionally, to accurately reflect the true economic cost of materials and labor, the total construction expenditure should be adjusted using a weighted average construction factor, such as the 0.76 factor applied in Gautam's case study.

The economic costs associated with the installation of biogas plants are lower than those considered in financial analyses Additionally, the benefits derived from biogas usage are valued more favorably in economic assessments compared to financial evaluations Consequently, any biogas plant deemed financially viable for an individual user is likely to demonstrate even greater viability when viewed from an economic or social perspective, highlighting its potential for higher returns.

CHAPTER FOUR 4.0 RESULTS, DISCUSSIONS AND CONLUSION 4.1 PARAMETERS AND VALUES USED IN ANALYSIS

Table 4.1: PARAMETERS AND VALUES USED IN ANALYSIS

Parameter Description Units Value ατ Product of Absorptivity &

Transmissivity - 0.8 a Standard volume of water Kg 1000

Ah Horizontal Area of digester M 2 165.7

At Total Area of digester M 2 384.5

Ato Curved area of top dome M 2 108.8

Cdb Discharge from bird Kg 0.10

Cdc Discharge from cow Kg 10

Cdp Discharge from pig Kg 6

Cds Discharge from sheep Kg 1.5

Cf Specific heat of fluid J/Kg-C 4190

Cs Specific heat of the slurry J/Kg-C 4180

F 1 Collector efficiency factor 0.81 h Heat transfer coefficient of heat exchanger

H1 Heat transfer coefficient from slurry to gas W/m-C 19.23

Hb Heating value of biogas MJ 26 hb Heat transfer coefficient from slurry to the ground W/m-C 3.194

Hc Heating value of Charcoal MJ/Kg 30

Hd Heating value of diesel MJ/Kg 46.00

Hf Heating value of fuelwood MJ/Kg 18.4

Hk Heating value of kerosene MJ/Kg 46.25

Hp Heating value of petrol MJ/Kg 46.80

HRT Hydraulic Retention Time days 40 i Interest rate % 0.2

L Length of the heat exchange M 19.83 mf Mass flow rate through Kg/sec 4.0 the exchanger

Mgsb Gas producing rate per

Mgsc Gas producing rate per

Mgsp Gas producing rate per

Kg TS of pig M 3 /KgTS 0.561

Mgss Gas producing rate per

Ms Mass of the slurry Kg 13625

Ns Number of sheep 200 p Pai 3.14 paccessories Price accessories N 7000.00

Pc Unit price of charcoal N 2.50

Pd Unit price of diesel N 65.00

Pf Unit price of fuelwood N 6.40

PI Present value of investment

Pk Unit price of kerosene N 70.00

Pp Unit price of petrol N 70.00

Ppipes/fitting/nails Price of pipes/fittings/nails N 112,000.00

Prod/wire/wood Price of rod/wire/wood N 2.573E+06

Psand/chippings Price of sand/chippings N 1.523E+06

Psolarpanel Price of solar penel N 451,400.00

PTotal Total price of materials N 6.254E+06

Qyc Quantity of charcoal Kg 3500

Qyd Quantity of diesel Kg 8350

Qyf Quantity of firewood (Kg) 20000

Qyk Quantity of kerosene Kg 4725

Qyp Quantity of petrol Kg 7350

Rr Revenue N 18,314,175 t Heating time Seconds 17,337

Tso Temperature of outlet effluent C 29

TSvbd TS value of fresh discharge for bird

TSvcd TS value of fresh discharge for cow

TSvpd TS value of fresh discharge for pig (% by wt) 0.20

TSvsd TS value of fresh discharge for sheep (% by wt) 0.20

UL Over all heat transfer coefficient for the flat plate collectors

Uo Over all heat transfer coefficient from the gas to the ambient

W/m- 0 C 17.08 y Gross saving in time for fuel wood Collection, cooking and cleaning of utensils

Yb Gas yield/day for bird droppings M 3 0.0112

Yc Gas yield/day for cow dung

Yp Gas yield/day for pig droppings

Ys Gas yield/day for sheep dung M 3 0.10

4.2 Energy Audit of the farm

According to the energy audit results, Concordia Farm consumes 1,218,111.25 MJ of energy monthly, incurring a significant cost of N1,524,250 The analysis highlights the monthly energy values, costs, and unit costs for each energy source, noting that the farm does not utilize electricity due to the lack of power supply The audit indicates a pressing need for more economical, cost-effective, and environmentally friendly energy alternatives, such as Biogas, as the current energy expenditures are excessively high.

Table 4.2: Results of energy audit of the farm

Ec Energy from charcoal MJ 31,500.00

Ed Energy from diesel MJ 384,100.00

Ef Energy from fuelwood MJ 240,000.00

Ek Energy from kerosene MJ 218,531.00

Ep Energy from petrol MJ 343,980.00

ETotal Total Energy of fuels MJ 1,218,111.25

Ucc Unit cost of charcoal N 0.2778

Ucd Unit cost of diesel N 1.413

Ucf Unit cost of fuelwood N 0.5333

Uck Unit cost of kerosene N 1.514

Ucp Unit cost of petrol N 1.496

4.3 Volume calculations of digester and hydraulic chamber

A digester volume (V) of 681.3 m 3 capacities has been estimated for Concordia farms This is based on the total influent (q) value of 13,625Kg for a hydraulic retention period HRT of 40 days.

The hydraulic chamber is so design to contain the effluent The height and diameter have also been calculated H1 is 2.722m, h3 is 2.981m and Dh is 12.62m.

4.3.3 Area and dimension of digester

The total area of the digester, comprising the top dome (Ft), horizontal body (Fc), and bottom dome (Fb), is calculated to be 384.4 m², with detailed results presented in Table 4.3.

Table 4.3: Areas and Dimensions of digester

Cdtb Total discharge from birds Kg 350

Cdtc Total discharge from cows Kg 3000

Cdtp Total discharge from pigs Kg 2400

Cdts Total discharge from sheep Kg 300

Dh Diameter of hydraulic chambers M 12.62

F1 Net vector rise of the top dome M 2.296

F2 Net vector rise of the bottom dome M 1.435

Fb Surface Area of the bottom M 2 110

Fc Surface Area of the cylindrical wall M 2 165.7

Ft Surface Area of top dome M 2 108.8

FTotal Total surface Area of digester M 2 384.4

Hn Height of hydraulic column M 8

Ldb Added water to make bird discharge

Ldc Added water to make cow discharge 8% concentration of TS Kg 3000

Ldp Added water to make pig discharge 8% concentration of TS

Lds Added water to make sheep discharge

The total volume of water added is 7,575 kg, while the influent contributions from various animals include 875 kg from birds, 6,000 kg from cows, 6,000 kg from pigs, and 750 kg from sheep In total, the influent amounts to 13,625 kg.

R1 Curvature radius of the top dome M 8.325

R2 Curvature radius of the inverted dome M 12.2

TSb Total Solid of fresh discharge from birds Kg 70

TSc Total Solid of fresh discharge from cows Kg 480

TSp Total Solid of fresh discharge from pigs Kg 480

TSs Total Solid of fresh discharge from sheep Kg 60

Vc Volume of gas collecting chamber M 3 34.06

Vgs Volume of gas storage chamber M 3 372.9

Now the dimensions of digester chamber is known and drawn (not to scale) in fig.4.1

Fig.4.1: Calculated Dimensions of the cylindrical shaped biogas digester

Now we know the dimensions of hydraulic chamber Moreover keeping h00mm,we can choose or re-arrange the dimension considering availability of site and construction suitability.

4.3.4 Variation of volume of biogas generated with percentage total solids concentration

The volume of biogas produced is significantly influenced by the concentration of total solids in organic waste Higher total solid concentrations lead to increased material digestion, resulting in greater biogas production during anaerobic fermentation in a digester This relationship between percentage total solids (PTS) and biogas volume (Vb) is illustrated in Figure 4.2 and detailed in Table 4.4.

Table 4.4 Relationship between PTS and V b

Figure 4.2 Graph of percentage total solid vs volume of biogas generated

The analysis presented in Figure 4.2 demonstrates that the volume of biogas produced rises with an increase in the percentage of total solids (PTS) By applying the formula Vb=0.2225*(PTS)².7717 from section 3.1.6, various biogas volumes were calculated based on different PTS values, and the findings are illustrated in Figure 4.2 These results align with the earlier findings reported by Igoni et al.

(2008) Also, using equation (3.82) in section 3.1.6, the total volume of biogas generated per day stand at 1713.92 M 3 A marginal increase in PTS results in a geometrical increase in the volume of biogas produced.

4.3.5 Variation of digester volume with substrate at hydraulic retention time of

The volume of a biogas digester is directly influenced by the amount of substrate available for input, which is why biodigesters are typically located in areas with ample waste or dung A greater availability of dung necessitates a larger digester size By applying equation (3.43b) from section 3.1.4, various digester volumes were calculated based on different quantities of slurry, maintaining a fixed hydraulic retention time (HRT) of 40 days The results are clearly illustrated in Table 4.5 and Figure 4.3.

Table 4.5 Variation of digester volume V d with substrate Q at HRT of 40 days

The volume of a biogas digester increases with the amount of substrate available, making substrate availability a crucial factor in selecting and positioning a digester This finding aligns with experimental results.

4.3.6 Variation of volume of digester with hydraulic retention time

The calculated influent value is 13,625 Kg, determined using equation (3.39) from section 3.1.4 This value was then applied in equation (3.43b) to analyze the relationship between digester volume (Vd in m³) and varying hydraulic retention time (HRT in days), with results presented in table 4.6 and figure 4.4 The analysis revealed that an increase in HRT corresponds to an increase in digester volume, indicating that smaller digesters operate with shorter HRTs, while larger digesters require longer HRT periods, as supported by Mattocks (1984).

Table 4.6 Variation of Vd with HRT at substrate value of 13,625 Kg

Excessively long Hydraulic Retention Time (HRT) in biogas digesters is undesirable due to the need for larger, more capital-intensive construction, which is not ideal for household biogas systems Conversely, a shorter HRT poses the risk of washout, where active bacteria are expelled from the digester prematurely, leading to an unstable bacterial population and reduced efficiency in biogas production.

Figure 4.4 Graph of V d vs HRT

4.4 Comparism of biogas generation prospects of the farm with its energy requirements

The potential for biogas generation is largely influenced by the organic waste materials utilized, such as human excreta, animal manure, sewage sludge, and vegetable crop residues For instance, processing 6,050 kg of organic waste can produce approximately 1,713.92 m³ of biogas daily This translates to a substantial monthly output of around 51,417.6 m³ of biogas from farms, highlighting the significant role of organic waste in sustainable energy production.

Table 4.7: Biogas yield of the farm

Eb Energy value of biogas produced MJ 1.337E+06

YT Total volume of biogas yield per day M 3 1,714

Ytb Volume of biogas yield from birds M 3 3.92

Ytc Volume of biogas yield from cow M 3 1,080

Ytp Volume of biogas yield from pigs M 3 600

Yts Volume of biogas yield from sheep M 3 30

Since 1m 3 of biogas is equivalent to 0.4Kg of diesel, 0.6Kg of petrol, 1.3Kg of fuel wood, and 0.8Kg of charcoal and 0.5Kg of kerosene (FAO/TCP/NEP/4415-T, 1996)

One can say generating 51,420 m 3 of biogas in a month is equivalent to buying the fuel quantities in column three at the prices in column seven of table4.8

Table 4.8: Equivalent Value of Biogas Consumption Per Month

Concordia Farms' energy analysis reveals significant monthly expenditures on various fuel types, including petrol at 30,852 kg costing 1,443,873, fuelwood at 66,846 kg for 1,229,966, charcoal at 41,136 kg totaling 1,234,080, and kerosene at 25,710 kg amounting to 1,189,344 The total costs for these fuels highlight a substantial investment in energy resources, far exceeding the quantities and expenses typically incurred.

Concordia Farms will have access to 1,336,920 MJ of energy each month, surpassing the estimated monthly energy consumption of 1,218,111.25 MJ as indicated in the farm's energy audit This surplus in biogas generation demonstrates the farm's potential to fully meet its energy requirements, which can be effectively utilized for cooking, lighting, heating, and warming activities on-site.

Details of gas yield from the various sources are as shown in table 4.7

4.5 Thermal analysis of the biogas plant

The calculations indicate a thermal efficiency of only 25%, highlighting the inefficiency of the plant's heating system due to significant heat losses to the environment and ground Additionally, the unglazing effect of collectors, which reduces solar flux at the absorber plate through convection, further diminishes thermal efficiency To optimize performance, it is essential to ensure perfect insulation of the digester on all sides Moreover, maximizing the mass flow rate of the working fluid, as well as the length of the heat exchanger and its heat transfer coefficient, will contribute to improved efficiency.

4.6 Financial Analysis of the Biogas plant

Energy Audit of the Farm

According to the energy audit results, Concordia farm consumes a total of 1,218,111.25 MJ of energy monthly, incurring a significant cost of N1,524,250 The data highlights the monthly energy values, costs, and unit costs for each energy source utilized, noting that electricity is not available at the farm The audit underscores the necessity for the farm to adopt more economical, cost-effective, and environmentally friendly energy sources, such as biogas.

Volume calculation of digester and hydraulic chambers

Volume of digester

A digester volume (V) of 681.3 m 3 capacities has been estimated forConcordia farms This is based on the total influent (q) value of 13,625Kg for a hydraulic retention period HRT of 40 days.

Hydraulic chamber

The hydraulic chamber is so design to contain the effluent The height and diameter have also been calculated H1 is 2.722m, h3 is 2.981m and Dh is12.62m.

Area and Dimension of digester

The areas of the top dome (Ft), horizontal body (Fc), and bottom dome (Fb) of the digester were calculated, yielding a total area (F) of 384.4 m² Detailed results can be found in Table 4.3.

Table 4.3: Areas and Dimensions of digester

Cdtb Total discharge from birds Kg 350

Cdtc Total discharge from cows Kg 3000

Cdtp Total discharge from pigs Kg 2400

Cdts Total discharge from sheep Kg 300

Dh Diameter of hydraulic chambers M 12.62

F1 Net vector rise of the top dome M 2.296

F2 Net vector rise of the bottom dome M 1.435

Fb Surface Area of the bottom M 2 110

Fc Surface Area of the cylindrical wall M 2 165.7

Ft Surface Area of top dome M 2 108.8

FTotal Total surface Area of digester M 2 384.4

Hn Height of hydraulic column M 8

Ldb Added water to make bird discharge

Ldc Added water to make cow discharge 8% concentration of TS Kg 3000

Ldp Added water to make pig discharge 8% concentration of TS

Lds Added water to make sheep discharge

The total volume of water added is 7,575 kg, with influents from various sources contributing to the overall total The influent from birds amounts to 875 kg, while cows contribute 6,000 kg, pigs also add 6,000 kg, and sheep contribute 750 kg In total, the influent from all sources reaches 13,625 kg.

R1 Curvature radius of the top dome M 8.325

R2 Curvature radius of the inverted dome M 12.2

TSb Total Solid of fresh discharge from birds Kg 70

TSc Total Solid of fresh discharge from cows Kg 480

TSp Total Solid of fresh discharge from pigs Kg 480

TSs Total Solid of fresh discharge from sheep Kg 60

Vc Volume of gas collecting chamber M 3 34.06

Vgs Volume of gas storage chamber M 3 372.9

Now the dimensions of digester chamber is known and drawn (not to scale) in fig.4.1

Fig.4.1: Calculated Dimensions of the cylindrical shaped biogas digester

Now we know the dimensions of hydraulic chamber Moreover keeping h00mm,we can choose or re-arrange the dimension considering availability of site and construction suitability.

4.3.4 Variation of volume of biogas generated with percentage total solids concentration

The volume of biogas produced is significantly influenced by the concentration of total solids in organic waste Higher total solid concentrations lead to increased digestion of materials, resulting in greater biogas generation during anaerobic fermentation This relationship between percentage total solids (PTS) and the volume of biogas generated (Vb) is illustrated in Figure 4.2 and Table 4.4.

Table 4.4 Relationship between PTS and V b

Figure 4.2 Graph of percentage total solid vs volume of biogas generated

The analysis presented in Figure 4.2 demonstrates a direct correlation between the increase in total solids percentage (PTS) and the volume of biogas generated Utilizing the equation Vb = 0.2225 * (PTS)².7717 from section 3.1.6, various biogas volumes were calculated by adjusting PTS values, with the findings illustrated in Figure 4.2 These results are consistent with previous research conducted by Igoni et al.

(2008) Also, using equation (3.82) in section 3.1.6, the total volume of biogas generated per day stand at 1713.92 M 3 A marginal increase in PTS results in a geometrical increase in the volume of biogas produced.

4.3.5 Variation of digester volume with substrate at hydraulic retention time of

The volume of a biogas digester is directly influenced by the amount of available substrate, such as waste or dung, which is why biodigesters are typically located in areas rich in these materials A greater availability of dung necessitates a larger digester size Utilizing equation (3.43b) from section 3.1.4, various digester volumes were calculated based on different slurry quantities while maintaining a fixed hydraulic retention time (HRT) of 40 days The findings are clearly presented in Table 4.5 and illustrated in Figure 4.3.

Table 4.5 Variation of digester volume V d with substrate Q at HRT of 40 days

The increase in digester volume is directly correlated with the amount of substrate available, as illustrated in figure 4.3 Therefore, the availability of substrate is a crucial factor when selecting and positioning a biogas digester, a finding that aligns with experimental results.

4.3.6 Variation of volume of digester with hydraulic retention time

The calculated influent value is 13,625 Kg, determined using equation (3.39) from section 3.1.4 This value was further analyzed with equation (3.43b) to study the relationship between digester volume (Vd in m³) and varying hydraulic retention time (HRT in days), with results presented in table 4.6 and figure 4.4 The findings indicate that as HRT increases, the digester volume also increases, highlighting that smaller digesters have shorter HRTs compared to larger capacity digesters, as corroborated by Mattocks (1984).

Table 4.6 Variation of Vd with HRT at substrate value of 13,625 Kg

Excessively long hydraulic retention times (HRT) in biogas digesters are undesirable due to the need for larger digesters and increased capital investment, which negatively impacts household biogas production Conversely, shorter HRT can lead to washout, where active bacteria are expelled from the digester prematurely, resulting in an unstable microbial population and reduced efficiency in biogas generation.

Figure 4.4 Graph of V d vs HRT

4.4 Comparism of biogas generation prospects of the farm with its energy requirements

The potential for biogas generation is largely influenced by the types of organic waste materials utilized, including human excreta, animal manure, sewage sludge, and vegetable crop residues For instance, processing 6,050 kg of organic waste can produce approximately 1,713.92 m³ of biogas daily This translates to a monthly output of about 51,417.6 m³ of biogas from the farms, highlighting the significant energy potential of organic waste.

Table 4.7: Biogas yield of the farm

Eb Energy value of biogas produced MJ 1.337E+06

YT Total volume of biogas yield per day M 3 1,714

Ytb Volume of biogas yield from birds M 3 3.92

Ytc Volume of biogas yield from cow M 3 1,080

Ytp Volume of biogas yield from pigs M 3 600

Yts Volume of biogas yield from sheep M 3 30

Since 1m 3 of biogas is equivalent to 0.4Kg of diesel, 0.6Kg of petrol, 1.3Kg of fuel wood, and 0.8Kg of charcoal and 0.5Kg of kerosene (FAO/TCP/NEP/4415-T, 1996)

One can say generating 51,420 m 3 of biogas in a month is equivalent to buying the fuel quantities in column three at the prices in column seven of table4.8

Table 4.8: Equivalent Value of Biogas Consumption Per Month

Concordia Farms' energy analysis reveals significant monthly expenditures on various fuel sources, with petrol costing 30,852 kg at 70.00, totaling 2,159,640.00 Fuelwood amounts to 66,846 kg at 6.40, resulting in 427,814.00, while charcoal is consumed at 41,136 kg for 2.50, leading to a cost of 102,840.00 Kerosene usage stands at 25,710 kg, priced at 70.00, culminating in an expense of 1,799,700.00 Overall, these figures indicate that the total quantities and costs of fuel consumed far exceed the monthly purchases and payouts by Concordia Farms.

The farm will generate a total of 1,336,920 MJ of energy each month, surpassing the estimated monthly consumption of 1,218,111.25 MJ as indicated by the energy audit This significant surplus in biogas production demonstrates the farm's potential to meet its energy needs effectively The generated energy can be utilized for various purposes, including cooking, lighting, heating, and warming, thereby enhancing the overall sustainability of Concordia Farms.

Details of gas yield from the various sources are as shown in table 4.7

4.5 Thermal analysis of the biogas plant

The calculations indicate a thermal efficiency of only 25%, highlighting the poor performance of the plant's heating system This inefficiency is primarily attributed to significant heat losses to the environment and the ground, as well as the unglazing effect of collectors, which reduces solar flux at the collector plate due to convection To minimize these losses, optimization strategies should include perfect insulation of the digester from all sides Additionally, maximizing the mass flow rate of the working fluid, as well as the length of the heat exchanger and its heat transfer coefficient, is essential for improving overall efficiency.

4.6 Financial Analysis of the Biogas plant

The financial analysis evaluates the capital and maintenance costs, system lifespan, and savings from reduced purchases of wood, kerosene, PMS, diesel, and labor The total cost avoided, or savings (Rr), amounts to N18,314,175, while the investment cost (PI) is N5,954,100, alongside the maintenance cost (Dd).

The project, with an initial investment of N100,000, incurs total expenses of N6,441,060 and yields a net present value (NPV) of N82,741,646.58, alongside a total present worth of savings amounting to N89,128,706.58 With an interest rate set at 20% and a project lifespan of 20 years, there is no salvage value considered The economic life of the plant is determined to be 20 years, as any costs incurred beyond this period become negligible when discounted to their present worth.

Savings from owning a biogas plant represent the monetary costs avoided, such as the annual expenses on traditional fuels For example, a farmer who previously spent N10,000 yearly on kerosene for cooking can now save that amount by utilizing biogas instead This shift not only eliminates the need for kerosene but also highlights the financial benefits of adopting biogas technology Table 4.9 illustrates the annual fuel consumption costs at Concordia Farms Limited, emphasizing the savings achieved through biogas ownership.

Table 4.9: Annual Cost of Fuel Consumption of the Farm

Fuel Type Quantity/Month Cost/Month

Therefore, by owning a biogas plant, the farm will save or avoid the cost of N3,969,000.00 on buying Kerosene (see table 4.9) each year throughout the

Thermal Analysis

The calculated thermal efficiency of the heating system is only 25%, indicating significant inefficiencies primarily due to heat losses to the environment and ground Additionally, the unglazing effect of collectors, which reduces solar flux at the absorber plate due to convection, further diminishes thermal efficiency To optimize performance, it is crucial to ensure perfect insulation of the digester and maximize the mass flow rate of the working fluid relative to the collector's area and number Furthermore, increasing the length of the heat exchanger and enhancing its heat transfer coefficient are essential for improved efficiency.

Financial Analysis

The financial analysis evaluates the capital and maintenance costs, system lifespan, and savings from avoiding expenses on wood, kerosene, PMS, diesel, and labor The total savings amount to N18,314,175, while the investment cost is N5,954,100, and the maintenance cost is represented by Dd.

The project, with a total investment of N100,000, incurs expenses amounting to N6,441,060, resulting in a net present value (NPV) of N82,741,646.58 and a total present worth of savings of N89,128,706.58 Assuming an interest rate of 20% and a project lifespan of 20 years, it is important to note that the economic life of the plant is capped at 20 years, as any costs incurred beyond this period become negligible when discounted to their present value.

Savings from owning a biogas plant represent the monetary costs avoided, such as the annual expenditure on kerosene For example, a farmer who previously spent N10,000 on kerosene for cooking can now redirect that amount into savings by utilizing biogas instead This transition not only eliminates the need for kerosene but also highlights the financial benefits of biogas adoption Table 4.9 illustrates the annual fuel consumption costs incurred by Concordia Farms Limited, showcasing the savings achieved through biogas usage.

Table 4.9: Annual Cost of Fuel Consumption of the Farm

Fuel Type Quantity/Month Cost/Month

Therefore, by owning a biogas plant, the farm will save or avoid the cost of N3,969,000.00 on buying Kerosene (see table 4.9) each year throughout the

The biogas plant has a lifespan of 20 years, with annual savings represented in Table 4.10 from years one to twenty Due to space constraints, the table truncates in column six, indicating that the annual savings continue from the fifth to the twentieth year, denoted as 5 20 Throughout the project’s life, these annuities, in the form of savings or revenue, remain consistent Additionally, inflation plays a crucial role when discounting the net savings or benefits to their present value, as calculated using equation (3.93) in section 3.2.9.

IRR = above 50 percent BCR = more than 13

4.7 COST DISTRIBUTION OF THE BIOGAS PLANT

The cost distribution percentages for the active bio-digester plant have been analyzed and presented as a fraction of the plant's total expenses, as detailed in Table 4.11 and illustrated in Figure 4.5.

Table 4.11: cost distribution of the biogas plant

The cost distribution for various construction parameters is as follows: accessories account for 0.01119%, cement constitutes 11.13%, and labor represents 11.06% Overhead costs are at 1.599%, while pipes, fittings, and nails make up 1.791% Rods, wires, and wood are significant at 41.14%, and sand and chippings contribute 24.34% Solar panels have a cost percentage of 7.218%, with transportation also at 1.599%.

The construction costs of the digester plant are primarily driven by iron rod, iron wire, and wood, which together account for 41.14% of the total expenses Other significant costs include sand and chippings, cement, and labor, while digester accessories represent the lowest portion of the overall costs.

COST DISTRIBUTION OF THE BIOGAS PLANT

41% accessories cement labour overhead pipe/fittings/nails sand/chipings solarpanel transport rod/wire/wood

Figure 4.5: Cost Distribution of 681.3 m 3 Biogas Plant

When considering the establishment of a biogas plant, two key factors must be evaluated: the availability of adequate organic waste to serve as raw material and the energy requirements of the surrounding area Additionally, the size of the biogas plant should be determined by both the volume of waste produced locally and the energy consumption needs of the community.

To secure a sustainable energy future, it is essential to develop innovative energy technologies, conserve energy, and enhance its efficiency The detrimental effects of non-renewable energy sources on the environment, coupled with their limited availability, have heightened concerns about climate change, air and water pollution, and energy security As a result, there is a growing interest and investment in renewable energy sources, including solar, wind, wave, geothermal, hydrogen, hydropower, and biomass energy.

While fossil fuels and nuclear energy will remain essential in the short term, it is crucial to advance renewable technologies for long-term sustainability This necessity has prompted a Technical and Economic Feasibility study for a proposed biogas plant at Concordia Farms Limited.

The technical feasibility study assessed the farm's energy needs, identified organic waste as the primary raw material source, evaluated the potential waste generation, and designed a suitable biogas plant Additionally, it included a thermal analysis of the solar-heated biogas system.

The case study farm generates several thousand kilograms of waste daily and consumes millions of megajoules of energy annually, significantly impacting the design of the biogas digester volume for these farms.

The economic analysis reveals that a 681.25m³ solar-heated biogas plant can achieve positive net cash flow in its first year without subsidies, making it a viable investment for commercial or large-scale farmers However, subsidies are still necessary to further promote this technology Additionally, the economic feasibility is enhanced by the significant savings in petrol, diesel, and kerosene, indicating that the profitability of the biogas plant hinges on reinvesting these savings into the farming business for increased income generation.

Further, the profitability of investment in biogas will increase with the increase in the price of firewood, kerosene, diesel, etc in the future

Our analysis of organic waste generation on the case study farms, along with their energy requirements, has highlighted the potential for biogas production Additionally, the economic assessments demonstrate the project's overall viability.

Biogas is a potential renewable energy source for rural Nigeria Taking biogas generation as a farm base activity, the energy requirements of these farms can be meet

From these analyses, it is concluded that the designed biogas plant will be suitable for this farm.

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Here is a copy of the verbal questionnaire that was used to extract relevant information about Concordia farms limited for the purpose of this research work.

(1) Please could you tell me a brief history of your farm?

(2) How is the organizational pattern of Concordia farms?

(3) How would you assess the growth level of the farm since its inception?

(4) What is the size of your farm (in terms of land area)?

(5) What types(s) of farming is being practice by Concordia farms?

(6) Please give me a detail of the type and number of live stock/bird/fish reared on your farm?

(7) What types of crop does your farm cultivate?

(8) What does your farm uses the huge organic waste generated for?

(9) Which is/are your source(s) of energy to the farm?

(10) What quantity of fuels does your farm consume per mouth?

(11) How much (cost in Naira or Dollar), does your farm spent on each types of fuel, say, in one month?

(12) What farming operations do your farm uses these fuels for?

(13) Please mention the farm equipments/implements and facilities available on your farm, stating their capacities, quantities and ratings?

(14) What are the sources of farm power available to Concordia

(15) Does Concordia farms uses electricity supplied from external source?

(16) Does your farm buy chemical fertilizers for manure?

(17) Have your farm built/own a biogas plant (past or present)?

TABLE-B 1: THE TOTAL SOLID CONTENT OF COMMON FERMENTATION

MATERIALS IN RURAL AREAS (APROXIMATELY)

Materials Dry matter content (%) Water content (%)

TABLE-B2: BIOGAS-PRODUCING RATES OF SOME COMMON FERMENTATION

MATERIALS AT DIFFERENT TEMPERATURES (M 3 /Kg TS)

Materials Medium temperature (35 o C) Water content (8 o  25 o C)

Experimental conditions: - The fermentation period of the excrement materials lasts 60 days and that of the stalk type lasts 90 days The fermentation material concentration (total solid content) is 6%.

TABLE –B 3: BIOGAS PRODUCING RATES OF SOME FERMENTATION

MATERIALS AND THEIR MAIN CHEMICAL COMPONENTS.

Materials and their main components

TABLE -B 4: BIOGAS – PRODUCING RATES OF SEVERAL

Amount of biogas produced in a period of time (as a % of the total yield)

The fermentation process occurs at a temperature of 30°C and utilizes batch-fed fermentation methods YpCMDV indicates the average biogas yield per cubic meter of digester volume throughout the normal fermentation period, measured in m³/kg TS.

TABLE – B 5: THE SPEED OF BIOGAS PRODUCTION WITH COMMON

Speed Amount of biogas produced in a period of time (expressed as a percentage of the total yield of biogas)

* Biogas producing is at the highest speed.

** Amount of biogas produced to more than 90% of the total yield of a fermentation period.

Tiêu đề	Techno-Economic Analysis Of A Model Biogas Plant For Agricultural Applications; A Case Study Of The Concordia Farms Limited, Nonwa, Tai, Rivers State
Tác giả	Torbira Mtamabari Simeon
Người hướng dẫn	Engr. Professor S.O. Enibe (Supervisor), Engr. Professor S.O. Onyegegbu (Head of Department)
Trường học	University of Nigeria, Nsukka
Chuyên ngành	Mechanical Engineering
Thể loại	Project Report
Năm xuất bản	2009
Thành phố	Nsukka

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Số trang	130
Dung lượng	2,81 MB