Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations

Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations Bioenergy systems for the future 2 technological aspects of nonfood agricultural lignocellulose transformations

Technological aspects of nonfood agricultural lignocellulose transformations H Honkanen, J Kataja JAMK University of Applied Sciences, Tarvaala, Finland Abbreviations BFB BIGCC CFB CHP DC dmt/a GHG HEC SRWC 2.1 bubbling fluidized bed biomass integrated gasification combined cycle circulating fluidized bed combined heat and power dust combustion dry matter tons per year greenhouse gas herbaceous energy crops short-rotation woody crops Introduction Biomass stands for the biodegradable fraction of products, waste, and residues of biological origin from agriculture (including vegetable and animal-based matter), forestry, and related industries, including fisheries and aquaculture, as well as the biodegradable fraction of industrial and municipal waste Research and development activities have been focused on identifying suitable type of biomass fractions from agriculture and rural areas, which can provide high-energy efficiency, to replace fossil fuel energy sources The type of biomass fractions required is largely determined by the energy conversion process and the form in which the energy is required 2.2 2.2.1 Material flows of biomasses from agriculture Classification of biomass Researchers characterize the various types of biomass in different ways, but one simple method is to define four main types, woody plants, herbaceous plants, aquatic plants, and manures Within this categorization, herbaceous plants can be further subdivided into those with high- and low-moisture contents Apart from specific Bioenergy Systems for the Future http://dx.doi.org/10.1016/B978-0-08-101031-0.00002-8 © 2017 Elsevier Ltd All rights reserved 44 Bioenergy Systems for the Future applications or needs, most commercial activity has been directed toward the lowermoisture-content types, woody plants, and herbaceous species, and these will be the types of biomass described in this chapter Aquatic plants and manures are intrinsically high-moisture materials and, as such, are more suited to “wet” processing techniques (McKendry, 2002) Based primarily on the biomass moisture content, the type of biomass selected subsequently dictates the most likely form of energy conversion process On the basis of the moisture content, herbaceous biomasses can be divided into two groups—green biomass and yellow biomass, as shown in Fig 2.1 Green biomasses are highmoisture-content raw materials, such as the herbaceous plants (grasses by growing season harvesting) or sugarcane and clovers, which lend themselves to a wet/aqueous conversion process, involving biologically mediated reactions, such as fermentation Yellow biomasses are dry raw materials such as straw, corn stover, or reed canary grass (spring harvesting) that are more economically suited to gasification, pyrolysis, or combustion (Table 2.1) Both woody and herbaceous plant species have specific growing conditions, based on the soil type, soil moisture, nutrient balances, and sunlight, which will determine their suitability and productive growth rates for specific, geographic locations Many types of perennial grasses, such as sugarcane and cereals like wheat and maize, have widely different yields, depending on the growing conditions: Thus, wheat can be grown in both hot and temperate climates with a wide range of rainfall, whereas sugarcane can be grown successfully only in warm, moist climatic conditions (McKendry, 2002) Required characteristics of cultivated biomass crops will also depend on local climate and soil conditions, as you can see Fig 2.2 Precipitation and effective temperature sum of the growing season are major constraints in many areas of the world Other important characteristics are drought resistance, pest resistance, and fertilizer requirements of the biomass crops All the cultivation of biomass (green biomass, yellow biomass, and woody biomass) should have moderate requirements concerning soil and fertilization and still Press juice Green biomass Press cake Cellulose Grain Yellow biomass Straw / stover dedicated energy crops Woody biomass Wood based residues / dedicated energy crops Nonfood agricultural lignocellulose biomass Hemicellulose Lignin Pulpwood/ timber Fig 2.1 The feedstocks of nonfood agricultural lignocellulose biomass Table 2.1 The classification of biomass Green biomass Yellow biomass Woody biomass Other biomass Sugarcane Grasses (summer harvesting) Clovers (summer harvesting) Sugar beets/bagasse/tops Cereal straw Maize stover Willow (SRWC) Poplar (SRWC) Soybean Rapeseed Miscanthus (HEC) Branches and logging residues Wood processing residues Eucalyptus Sunflower Switchgrass (HEC) Hemp Giant reed (HEC) Reed canary grass (HEC) Ethiopian mustard Flax Kenaf HEC, herbaceous energy crops; SRWC, short-rotation woody crops Fig 2.2 Climate zones and recommended biomass crops for each one Modified from Alexopoulo, E., Kretschmer, B Mapping biomass crop options for EU27 Biomass Futures Policy Briefings http://www.biomassfutures.eu/work_packages/WP6% 20Policy/Biomass%20Futures%20D6.4_4Fcrops%20policy%20briefing.pdf (referred to 26 June 2016); Metzger, M.J., Bunce, R.G.H., Jongman, R.H.G., Mucher, C.A., Watkins, J.W., 2005 A climatic stratification of the environment of Europe Global Ecol Biogeogr 14, 549–563 46 Bioenergy Systems for the Future produce high biomass yield with a minimum need of weeding; high tolerance for pests, diseases, frost, drought; or excess of water that enables cultivation in areas not suited for more demanding food crops Energy consumption is dependent on various parameters, including transportation of the raw material and nitrogen fertilizer used A maximal benefit of the land area could be obtained when the crop would be primarily used for production of food and secondarily as a source of biomass residue for biofuels However, also in the future, the main aim will be to produce the maximum amount of biofuels with the minimum environmental consumption (McKendry, 2002; Mikkola and Ahokas, 2009; B€ orjesson, 1996) 2.2.2 Biomass properties Numerous crops have been proposed or are being tested for commercial energy farming Potential energy crops include woody crops (poplar and willow) and grasses/herbaceous plants (all perennial crops), starch and sugar crops, and oilseeds In general, the characteristics of the ideal energy crop are - high yield (maximum production of dry matter per hectare), low energy input to produce, low cost, composition with the least contaminants, low nutrient requirements However, there are other factors that must be taken into consideration in determining the election of the conversion process, apart from simply moisture content, especially in relation to those forms of biomass that lie midway between the two extremes of “wet” and “dry.” Examples of such factors are the ash, alkali, and trace component contents, which impact adversely on thermal conversion processes, and the cellulose content, which influences biochemical fermentation processes (Table 2.2) Biomass contains varying amounts of cellulose, hemicellulose, lignin, and small amount of other extractives, as you can see Fig 2.3 Woody plant species are typically characterized by slow growth and are composed of lightly bound fibers, giving a hard external surface, while herbaceous plants are usually perennial, with more loosely bound fibers, indicating a lower proportion of lignin, which binds together the cellulosic fibers: both materials are examples of polysaccharides and long-chain natural polymers The relative proportion of cellulose and lignin is one of the determining factors in identifying the suitability of plant species for subsequent processing as energy crops It is the inherent properties of the biomass source that determines both the choice of conversion process and any subsequent processing difficulties that may arise Equally, the choice of biomass source is influenced by the form in which the energy is required, and it is the interplay between these two aspects that enables flexibility to be introduced into the use of biomass as an energy source As indicated above, the categories of biomass considered in this study are woody and herbaceous species; the two types are examined by most biomass researchers and technology providers For dry biomass conversion processes, the first five properties are of interest, while for wet biomass conversion processes, the first and last properties are of prime Technological aspects of nonfood agricultural lignocellulose 47 Table 2.2 Agronomic characteristic of selected nonfood agricultural lignocellulose biomass Sugarcane bagasse Maize stover Wheat straw HEC SRWC Field dmt/a Photosynthesis mechanism Annual/ perennial plant Harvesting 9–22 C4 6–30 C4 3–7 C3 5–30 C3/C4 7–40 C3 Annual Annual Annual Perennial Perennial Annual Annual Annual Annual Harvesting equipment Nutrient requirements Special Normal agri high Normal agri High Normal agri Low Rotation of 3–7 years Special high Low HEC, herbaceous energy crops; SRWC, Short-rotation woody crops; dmt/a, dry matter tons per year Modified from Davis, S., Hay, W., Pierce, J., 2014 Biomass in the energy industry: an introduction Energy Biosciences Institute http://www.bp.com/energysustainabilitychallenge; Faaij, A., 2008 Bioenergy and global food security, WBGU Hauptgutachten 2008, Welt im Wandel: Zukunftsf€ahige Bioenergie und nachhaltige Landnutzung, Berlin http://www.wbgu.de/fileadmin/templates/dateien/veroeffentlichungen/hauptgutachten/jg2008/wbgu_jg2008_ ex03.pdf (referred to 26 June 2016); Pakarinen, A., Maijala, P., Stoddard, F., Santanen, A., Kym€al€ainen, M., Tuomainen, P., Viikari, L., 2011 Evaluation of annual bioenergy crops in the boreal zone for biogas and ethanol production Biomass Bioenergy 35, 3071–3078 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 20% 20% 16% 16% 15% 10% 5% 10% 16% 22% 15% 23% 30% 36% 25% 53% 38% 50% 45% Corn stover Straw SRWC HEC 35% Sugarcane bagasse Cellulose Hemisellulose Lignin Others Fig 2.3 The averaging composition of selected nonfood agricultural lignocellulose biomass feedstocks HEC, herbacenous energy crops; SRWC, short ration woody crops Data from McKendry, P., 2002 Energy production from biomass (part 1): overview of biomass Bioresour Technol 83, 37–46; Hamelick, C., Hooijdonk, G., Faaij, A., 2005 Ethanol from lignocellulosic biomass: techno-economic performance in shot-, middle- and long-term Biomass Bioenergy 28, 348–410 48 Bioenergy Systems for the Future concern The quantification of these material properties for the various categories of biomass is discussed in the following section (McKendry, 2002) Looking from the perspective of nonfood agricultural lignocellulose, biomass engineering is particularly interested in the partitioning among cellulose, hemicellulose, and lignin The importance of understanding the chemical composition and structure of crops used as raw materials for bioenergy production cannot be overestimated To achieve the best possible conversion efficiency of different crops from field to fuel, knowledge on the effects of preservation, pretreatments, and used parameters in enzymatic hydrolysis, for example, is essential The selection of suitable crops in the existing climate conditions and how to convert the raw materials into the most convenient energy carriers are nationally and internationally important issues (McKendry, 2002; Pakarinen, 2012; Mikkola and Ahokas, 2009; B€ orjesson, 1996) 2.3 2.3.1 Energy use pathways of biomasses from agriculture Biomass to bioenergy Bioenergy production is regarded as renewable energy The use of biomass, many times from local origin, as energy source, supports energy self-sufficiency and helps tackling with greenhouse gas (GHG) emission load and with other negative environmental effects to air and water quality Bioenergy currently accounts for two-thirds of renewable energy in Europe Bioenergy is the only renewable energy source able to provide green fuel for all the following energy applications: heating and cooling, power generation, and transport applications (European Biomass Association, 2016) The global potential from agriculture is still largely underexploited, and this sector is expected to grow The global potential of agricultural and forestry residues and organic waste in bioenergy production is essential during forthcoming decades (International Energy Agency, 2012) Increasing the production of liquid biofuels supports the growth of low-carbon societies along with solar power use in smart energy systems, new energy storage technologies, and distributed energy generation Also the importance of biogas production and the use of waste-derived fuels will continue to grow in the future meanwhile cutting down the use of fossil fuels Bioenergy stands for energy produced from biomass, so it excludes, for example, wind, solar, or hydroenergetic power Biomass energy products are generated from agricultural crops and residues, herbaceous and woody materials, and biodegradable wastes These feedstock materials can be either directly combusted for energy production or processed into energy products or carriers such as biodiesel, bioethanol, and biogas, which are then used as transportation fuels or for the production of steam, heat, and electricity Bioenergy production is strongly promoted by different drivers and sustainability including legislation, economic, and environmental perspective (Fig 2.4) In addition to environmental incentives, energy supply system has to meet expectations such as undisturbed availability and competitive price Costs of biomass-derived energy are expected to decrease over time, due to both technology development and economies of Technological aspects of nonfood agricultural lignocellulose 49 Drivers: legislation, economy, environment Dedicated crops, by-products and residues from agriculture • Quality • Volumes • Properties Refining processes Bioenergy production Fuels Direct use Other solid, liquid and gaseous products Human factor: awareness Fig 2.4 The use of biomasses from agriculture to energy with drivers and incentives scale in larger commercial plants Social and cultural aspect of sustainability so-called human factor refers to consumers’ voice and acceptance, local decision-making, labor, and well-being Human factor aspect plays an important role in the bioenergy field and business in accordance with realization of implementation of new technology and processes Local production of raw materials, fuels, and bioenergy offers income for agricultural industry However, if traditional thinking of bioenergy is linked closely to countryside, new refinery processes and transformations have expanded operating range and integrated processes with forest and chemical industry and business Whereas long-distance transportation reduces economic and environmental attractiveness of biomass, conversion into higher energy density product, for example, bio-oil, could facilitate also international trade As presented above, lignocellulosic biomasses contain cellulose, hemicellulose, and lignin, which can be used in different ways in refining processes Plant species differ in the relative amounts and in the chemical structures of these main polymers, depending strongly on its origin As being raw material for higher value bio-based products such as fuels, chemicals, polymers, or materials, hemicellulose and lignin are also suitable for lower value use for combined heat and power (CHP) applications Also residues of cellulose for sugar processes can be used in energy production 2.3.2 Integration of energy use, new biobased products and nutrient recovery There are numerous ways to process and utilize agricultural lignocellulose-based biomass Processes result in energy, products, by-products, and residues These products include solid, liquid, and gaseous materials to be used as fuels, chemicals, and other materials for industry, agriculture, and municipalities Ash and treated sludge 50 Bioenergy Systems for the Future Bioenergy and nutrients recovery from agricultural lignocellulose based biomass Origin: agriculture and rural areas Peat Dedicated energy Wood based wood crops residues Field and Biodegradable grass crops waste Sludges from Sludge from waste By-products agriculture water treatment from industry Raw material flows Pyrolysis/thermal Combustion Torrefaction gasification Fermentation Hydrolysis Anaerobic digestion Thermal drying Chemical treatment Composting Processing / utilization Product / by-product Ash (many types) Syngas Biochar Methanol (motor fuel, fuel cells) Ethanol Biogas Methane (motor fuel) + reject (combustion, (hygienic) motor fuel) Treated sludge (hygienic) Compost Biofuels for renuwable energy production Sources of nutrients - fertilizing fields and forests Fig 2.5 Bioenergy and nutrient recovery routes for agricultural lignocellulose-based biomass from wastewater treatment and from anaerobic digestion process contain nutrients to be used for fertilizing in suitable target of application in cultivation and forestry There are also other thermal, biological, and chemical processing technologies to stabilize and disinfect material streams for further use Nutrient recovery option may bring operators and process owner’s possibilities to offer new products and to enhance feasibility Fig 2.5 shows processing and bioenergy pathways of agricultural lignocellulosebased biomass The main raw material flows are dedicated energy wood crops, wood-based residues mainly from farming and rural area industries, field and grass crops, biodegradable waste, and sludges like manure from agriculture Biodegradable waste stands in great parts for agricultural residues, which constitute the part of the crop that is discarded after the useful products have been extracted from the harvest Also yard and municipal waste can also be considered as source for energy production Further, sludge from wastewater management refers to sludge originated either from sparsely populated areas treated locally or from centralized wastewater management plants By-products from industry refer mainly to forest industry or other large-scale industry using lignocellulose-based biomass, with own circulation and utilization routes for their, for example, stem-wood-based by-products These by-products and peat and sludges are acknowledged as possible bio-based material flows for combinations depending on, for example, the volume requirements or quality restrictions Woody and herbaceous biomass from agriculture and rural areas is processed via several routes to produce energy In this case, biomass has optional exploitation paths Technological aspects of nonfood agricultural lignocellulose 51 to be processed or utilized in combustion, gasification, pyrolysis, fermentation, hydrolysis, or anaerobic digestion to produce biofuels of energy Some of the optional routes are in parallel and some in series, for example, when biomass is firstly processed into biofuel and then utilized in energy production plant Feedstocks may be combined if preferable; also processing technologies may be integrated and centralized, for example, in biorefineries Some of the mentioned processes are discussed further later on in this chapter and in some later chapters of this book Thermal drying, chemical treatment, and composting are presented as alternative processing, aiming to further use and utilization of their nutrient content Combustion processes for producing steam and power produce ash as sidestream containing mainly inorganic material as result of fuel oxidation With poor combustion efficiency, ash contains also unburnt fuel Ash output from combustion could be used in fertilizing purposes depending on the chemical composition and composition of feedstock, combustion technology, possible use of chemicals in the process, and ash collection technology Torrefaction is a thermal process to enhance the energy density and durability of biomass Produced biochar or traditionally charcoal can be used as energy carrier with versatile use Charcoal is considered as the most important processed biomass fuel (Rosillo-Calle et al., 2007) Also, other applications are introduced for biochar, for example, used as soil conditioner or as fertilizer (Alakangas et al., 2016) Biogas, a mixture of methane and carbon monoxide, is the most important gaseous biomass-based fuel Biogas is produced in a digester by anaerobic process using mainly sludges and wet biodegradable waste as feedstock Anaerobic processing combines waste disposal with energy and fertilizer production, in small and large centralized scale, in both developed and developing countries The use of reject of the process as material for fertilizer depends on the contents of the original feedstock For example, wastewater treatment may restrict fertilizing use of the reject Presented solid, liquid, and gaseous fuels can be used in suitable energy production, for example, boilers or motors Also, other hydrocarbons and hydrogen can be products from the different processing routes 2.3.3 Energy production technologies and fuel characteristics For energy recovery, solid biomass is processed with combustion, gasification, or pyrolysis With combustion, biomass can be converted into steam for industry purposes, heating energy, or electricity with turbine and generator Gasification produces syngas, mainly mixture of carbon oxide and hydrogen, to be used in heat and power generation and in other processes, for example, production of methanol or dimethyl ether Via pyrolysis, biomass can be converted into bio-oil, which can be used for heating or producing biodiesel Wet biomass originated in agriculture is processed with anaerobic digestion for producing biogas Biogas is used widely for heat and power production It can also be used as vehicle fuel in many kinds of applications 52 2.3.3.1 Bioenergy Systems for the Future General about refining bio fuels A wide range of new conversion technologies are under continuous development to produce bioenergy carriers for energy production both small- and large-scale applications Converting biomass feedstock into secondary fuels aims to better adaptation to long-distance transport and application in modern energy converting systems (van Swaaij and Kersten, 2015) Particularly the solid biomass resources that are dispersed, available on seasonal basis, have low physical and energy density and high-moisture content and require processing for efficient further use Many of the conversion technologies are close to commercial maturity but are awaiting further technical breakthroughs to increase the process efficiency, followed by large-scale demonstrations to help reduce the risks and cut down the costs Biochemical technologies are expected to be used to convert the cellulose to sugars that in turn can be converted to bioethanol, biodiesel, dimethyl ester, hydrogen, and chemical intermediates in biorefineries In addition, biochemical and thermochemical synthesis processes could be integrated in a biorefinery such that the biomass carbohydrate fraction is converted to ethanol and the lignin-rich residue gasified and used to produce heat, electricity, or fuels In general, biorefinery may contain combination of physical, chemical, and biological conversion steps, producing variety of products such as food and feed, materials, chemicals, fuels, fertilizers, heat, and power (van Swaaij and Kersten, 2015) In anaerobic treatment process, the feedstock is partially digested to form a methane-rich biogas Biogas is generally produced from organic waste materials such as sewage sludge, agricultural wastes, industrial wastes, and municipal solid wastes Agricultural residues consist of either crop residues or processing residues Crop residues refer mainly to disposed parts of crops after harvest Processing wastes are leftovers from the processing of the harvested portions of agricultural crops for uses such as food, fiber, and feed Leftover grasses such as those grown in buffer zones protecting water systems are suitable feedstocks to anaerobic digestion process However, process has to have sufficient retention time for grass-type biomass Biodiesel is produced from vegetable oils and animal fats and used as an alternative fuel of petroleum diesel for vehicles Biological and chemical biomass refining processes are further discussed in forthcoming chapters of this book 2.3.3.2 Mechanically and thermally treated solid biofuels Biomasses like small-diameter wood from forest management, energy willow, straw, and agricultural waste such as low-quality grain and sorting waste can be utilized as energy by combustion or gasification to produce heat, electricity, syngas, or other products Agricultural biomass waste can be mixed and processed with other biomass to suit better its use Usually, solid biofuel is produced with pretreating the biomass mechanically, for example, drying, chipping, crushing, chopping, baling, shredding, pelletizing, or briquetting Usually, pellets are made from by-products of the Technological aspects of nonfood agricultural lignocellulose 53 mechanical forest industry, but suitable materials are also fresh biomass, bark, and wood chips, in which case the raw material needs to be crushed and dried before pressing (Alakangas et al., 2016) Biomass can also be torrefied with thermochemical process, in which the biomass is heated up to 200°C–300°C to affect its qualities as fuel Torrefication is conducted with restricted amount of oxygen and normal air pressure Biomass loses its moisture and part of its volatile material resulting to the increase of energy density Torrefied biomass repels moisture and is poor substrate for fungal or microbe growth Pelletizing increases mechanical durability of torrefied biomass and presents 25%–30% higher energy density than conventional wood pellets Other treatment processes for biomasses are hydrothermal carbonization for production of biochar and steam explosion for pretreatment in ethanol production or steam-exploded pellets Hydrothermal carbonization is a thermochemical process typically used to treat wet biomasses, such as many types of industrial sludges but also agricultural sludge, digestion waste from biogas plants, algae, or food waste Hydrothermal carbonization takes place in water at a temperature range of 180°C–250°C and at pressure of 2–5 MPa Steam explosion technique for woody or agricultural biomass involves pressurized reactor heated up to a saturation point using steam Energy density of steam-exploded pellets is of the same magnitude as that of torrefied pellets (Alakangas et al., 2016) 2.3.3.3 Direct use of solid biomass in energy production Lignocellulose biomass is widely used as a fuel in direct combustion applications with production of steam, heat, and electricity The main routes for energy conversion of solid biomass from agriculture are presented in Fig 2.6 Either the biomass can be from wastes and residues that are traditionally discarded and have no value as raw material or they may be dedicated energy crops grown specifically for the production of bioenergy Sometimes, pricing can steer biomass for energy conversion processes Energy conversion routes of solid biomass from agriculture Biomass feedstock: -Wood (dedicated crops) (residues) Combustion Gasification -Field crops -Biodegradable waste and residues Steam heat electricity + other products Pyrolysis Fig 2.6 Thermochemical energy conversion technologies of solid biomass from agriculture 54 Bioenergy Systems for the Future according to certain quality requirements for the fuel Globally, important agricultural wastes for bioenergy production are corn stover, rice and wheat straw, bagasse, and grapevine pruning ( Jameel et al., 2010) The thermochemical conversion of chosen low-moisture biomass to energy can be carried out using many types of processes, depending on the end-user requirements and the nature and quality of the raw material However, combustion technologies produce about 90% of the energy from biomass, converting fuels into energy, for example, in the form of hot air, hot water, steam, and electricity (Rosillo-Calle, 2007) The scale of direct biomass combustion can vary from small-batch-type fireplaces or stoves, to continuously operating heating systems and boiler plants, to large industrial-scale CHP plants Most of biomass-to-energy applications locates in developed countries It is also stated that lower quality fuels are mostly used in large-scale combustion systems while high-quality fuels are more frequently used in small application systems (Rosillo-Calle, 2007) Large-scale (>50 MW) biomass power plants are important in reducing GHG emissions in electricity generation at high efficiencies and relatively low costs Even though smaller-scale (