Volume 7 geothermal energy 7 05 – direct heat utilization of geothermal energy

Volume 7 geothermal energy 7 05 – direct heat utilization of geothermal energy Volume 7 geothermal energy 7 05 – direct heat utilization of geothermal energy Volume 7 geothermal energy 7 05 – direct heat utilization of geothermal energy Volume 7 geothermal energy 7 05 – direct heat utilization of geothermal energy Volume 7 geothermal energy 7 05 – direct heat utilization of geothermal energy Volume 7 geothermal energy 7 05 – direct heat utilization of geothermal energy Volume 7 geothermal energy 7 05 – direct heat utilization of geothermal energy

7.05 Direct Heat Utilization of Geothermal Energy JW Lund, Geo-Heat Center, Oregon Institute of Technology, Klamath Falls, OR, USA © 2012 Elsevier Ltd All rights reserved 7.05.1 7.05.2 7.05.3 7.05.4 7.05.4.1 7.05.4.2 7.05.4.3 7.05.4.4 7.05.4.5 7.05.5 7.05.5.1 7.05.5.2 7.05.5.3 7.05.6 7.05.7 7.05.7.1 7.05.7.2 7.05.7.3 7.05.7.4 7.05.7.5 7.05.7.6 7.05.7.7 7.05.7.8 References Further Reading Introduction Current Utilization Global Distribution of Geothermal Heat Utilization Development of Direct Heat Utilization Projects Spas and Pools Space and District Heating Greenhouses Aquaculture Industrial and Agricultural Drying Selecting the Equipment Downhole Pumps Piping Heat Exchangers Environmental Considerations Case Histories Tomato Drying in Greece District Heating in Reykjavik, Iceland Greenhouse Heating in Hungary Timber Drying in New Zealand Onion Dehydration in the United States Combined Heat and Power in Austria Individual Building Heating in the United States Aquaculture Pond Heating in the United States 171 171 171 171 172 173 176 176 176 177 178 179 180 181 182 182 182 183 183 184 184 186 186 187 188 7.05.1 Introduction The direct heat utilizations of geothermal energy are traditional and well established worldwide The people of Japan have lived in harmony with the earth’s heat for centuries, utilizing it mainly for bathing and cooking food In the Americas, the indigenous people have been awed by geothermal phenomena considering them sacred sites and a place of refuge Nowadays there are many large-scale uses of geothermal energy Well-known examples are district heating in Iceland, greenhouse heating in Hungary, process heat with steam in New Zealand, mineral extraction in Italy, and individual residential space heating in the United States Direct heat applications of geothermal energy are also called nonelectric uses to distinguish them from electric power generation The technology of direct uses is generally well established The various applications include: (1) space heating, including district heating systems; (2) greenhouse and covered ground heating; (3) aquaculture pond and raceway heating; (4) agricultural drying; (5) industrial applications; (6) bathing, swimming pools, and spa heating; and (7) snow melting and space cooling Many of these earlier applications have been documented for over 25 countries in Stories from a Heated Earth – Our Geothermal Heritage [1] More recent applications have been described in countries’ reports for the World Geothermal Congress 2010 [2] The Lindal diagram [3, 4], named after Baldur Lindal, the Icelandic engineer who first proposed it, indicates the temperature range suitable for various direct-use activities (Figure 1) His diagram indicates the specific temperature most suitable for the application This diagram has recently been updated by the Geothermal Education Office to reflect the temperature range suitable for various applications rather than a single temperature (Figure 2) Typically, the greenhouse and aquaculture uses require the lowest temperatures, with geothermal fluid values from 25 to 90 °C Space heating requires resource temperatures in the range of 50–100 °C Industrial applications and refrigeration normally require temperatures over 100 °C Swimming and spa pools require temperatures in the range of 30–50 °C, which often involves direct heat utilizations of geothermal energy 7.05.2 Current Utilization Today, 78 countries have reported some form of direct utilization of geothermal energy with a total installed capacity of 15 358 MWt and an annual energy use of 223 667 TJ (62 135 GWh; excluding geothermal heat pumps) [2] The growth over the past 15 years is Comprehensive Renewable Energy, Volume doi:10.1016/B978-0-08-087872-0.00707-1 171 Direct Heat Utilization of Geothermal Energy �C 200 �F 180 350 Refrigeration by ammonia absorbtion Conventional electric generation Digestion in paper pulp Saturated steam 172 160 Drying of fish meal 300 140 Alumina via Bayer’s process Canning of food Evaporation in sugar refining 120 250 Evaporation Binary fluid electric generation Drying and curing of cement block 100 200 Drying of agricultural products Drying of stock fish 80 Space heating (building and greenhouses) Hot water 150 60 Cold storage Air conditioning Animal husbandry 40 100 Soil warming Swimming pools, de-icing 20 50 Space heating with heat pumps Fish farming Figure The Lindal diagram shown in Figure Installed capacity has increased during this period by 2.26 times or 5.57% annually, and the annual energy use has increased 2.29 times or 5.67% annually The various applications of direct use for the period 1995–2010 are presented in Tables and for installed capacity, annual energy use, and capacity factor The capacity factor reflects the equivalent full-load operating hours in a year (annual energy use/ (installed capacity � 8760 h yr−1)) The higher the number, the more efficient the use of the geothermal resource (Table 3) 7.05.3 Global Distribution of Geothermal Heat Utilization The leading users of geothermal energy for direct utilization of the heat are given in Tables and In terms of the contribution of geothermal direct heat utilization to the national energy budget, two countries stand out: Iceland and Turkey In Iceland, geothermal meets 89% of the country’s space heating needs, which is important since heating is required almost all year-round and saves about US$100 million in imported oil [5] Turkey has increased its installed capacity over the past years from 1495 to 2084 MWt, most for district heating systems [6] A summary of some of the significant geothermal direct-use contributions to various countries is given in Table 7.05.4 Development of Direct Heat Utilization Projects Before proceeding with a direct heat utilization project, several questions need to be investigated and answered by the potential developer: (1) What are the estimated (or known) temperature and flow rate of the resource? (2) What is the chemistry of the resource? (3) What potential markets they have for the energy, and what would be the expected income? (4) Do they have the experience, or are you willing to hire experienced people to run the project? (5) Do they have financing and is the estimated net income enough to justify the investment? (6) Do they own or can you lease the property and the resource, and are there limitations on its use? Figures and can help answering some of these questions – at least to establish the potential uses depending upon the temperature of the resource The following sections describe in more detail some of the potential uses based on temperature and possible limitations 7.05.4.1 Spas and Pools People have used geothermal and mineral water for bathing and their health for many thousands of years Balneology, the practice of using natural mineral water for the treatment and cure of disease, also has a long history A spa originates at a location mainly due to the Direct Heat Utilization of Geothermal Energy 173 700°F Geothermal energy uses 400°F 204°C 350°F Flash & Dry Steam Geothermal Power Plants Hydrogen Production* & Minerals Recovery Typical uses of geothermal energy at different temperatures 177°C Ethanol, Biofuels Production 300°F 149°C Cement & Aggregate Drying 250°F Binary geothermal Power Plants Hydrogen Production* 121°C 200°F Onion & Garlic Drying 95°C 150°F 66°C 100°F Soft Drink Carbon­ ation 38°C 50°F 40°F/4°C Geothermal Heat Pumps Concrete Block Curing Food Processing Snow Melting & De-icing 70°F 60°F Lumber Drying Pulp & Paper Processing Fruit & Vegetable Drying Mushroom Culture Refriger­ ation & Icemaking Aqua­ culture** Fabric Dyeing Beet Sugar Evaporation & Pulp Drying Building Heating & Cooling & Water Heating Greenhousing & Soil Sterilization Blanching, Cooking & Pasteur­ ization Biogas Process Bathing Soil Warming *Geothermal electricity can be used to produce renewable hydrogen **Cool water is added to make the temperature just right for the fish Figure The Geothermal Education Office diagram water from a spring or well The water, with certain mineral constituents and often warm, gives the spa certain unique characteristics that will attract customers Associated with most spas is the use of muds (peoloids), which either are found at the site or are imported from special locations The use of geothermal and mineral water for drinking and bathing, and the use of muds are thought to give certain health benefits to the user Spas and pools for swimming, bathing, and soaking can use some of the lower temperature resources (generally 300 MWt) Table Country Installed capacity (MWt) Major use(s) China Japan Turkey Iceland Italy Hungary USA New Zealand Brazil Russia 3688 2086 2046 1822 636 615 612 386 360 307 Bathing, district heating Bathing District heating, bathing District heating Space heating, bathing Bathing, greenhouses Space heating, aquaculture Industrial Bathing Greenhouses, space heating Table Leading countries in terms of annual energy use (>3000 TJ yr−1) Country Annual energy (TJ yr−1) Major use(s) China Turkey Japan Iceland New Zealand Hungary USA Italy Brazil Mexico Slovakia Argentina 46 313 36 349 25 630 24 341 513 249 152 980 622 023 054 048 Bathing, district heating Bathing, district heating Bathing, space heating District heating Industrial Bathing, greenhouses Bathing, space heating Space heating, aquaculture Bathing Bathing Bathing, space heating Bathing heating usually involves one geothermal well per structure District heating system has one or more wells serving a number of buildings through a central control station and an extensive piping network An important consideration in district heating projects is the thermal load density, or the heat demand divided by the ground area of the district A high heat density, generally >1.2 GJ h−1 ha−1, or a favorability ratio of >2.5 GJ ha−1 yr−1 is recommended Often fossil fuel peaking is used to meet the coldest period, rather than drilling additional wells or pumping more fluids, as geothermal can usually meet 50% of the Direct Heat Utilization of Geothermal Energy 175 Table Summary of the various applications for direct use worldwide for the period 1995–2010 2010 2005 2000 1995 366 404 616 157 484 401 371 86 12 885 263 246 605 74 474 957 114 137 870 579 085 097 67 544 085 115 238 810 Capacity (MWt) Space heating Greenhouse heating Aquaculture pond heating Agricultural drying Industrial uses Bathing and swimming Cooling/snow melting Others Total 394 544 653 125 533 701 368 42 15 360 Space heating Greenhouse heating Aquaculture pond heating Agricultural drying Industrial uses Bathing and swimming Cooling/snow melting Others Total Utilization(TJ yr−1) 63 025 55 256 23 264 20 661 11 521 10 976 635 013 11 746 10 868 109 410 83 018 126 032 955 045 223 682 185 869 42 926 17 864 11 733 038 10 220 79 546 063 034 167 424 38 230 15 742 13 493 124 10 120 15 742 124 249 97 824 Space heating Greenhouse heating Aquaculture pond heating Agricultural drying Industrial uses Bathing and swimming Cooling/snow melting Others Average Capacity factor 0.37 0.48 0.56 0.41 0.70 0.52 0.18 0.72 0.46 0.42 0.45 0.61 0.44 0.68 0.64 0.30 0.70 0.54 0.47 0.46 0.39 0.53 0.59 0.46 0.31 0.30 0.46 0.40 0.47 0.57 0.41 0.71 0.49 0.18 0.39 0.46 District heating is approximately 85% of the space heating values Table Iceland Turkey Tunisia Japan France Hungary China National geothermal direct-use contribution Provides 89% of the country’s space heating needs through 30 urban district heating systems and 200 rural systems Space heating has increased by 40% in the past years, supplying 201 000 equivalent residences, and 30% of the country will be heated with geothermal energy in the future Greenhouse heating has increased from 100 to 194 over the past years Over 2000 hot spring resorts (onsens), over 5000 public bath houses, and over 15 000 hotels, visited by 15 million guests per year Geothermal district heating supplies heat to 150 000 dwellings, mainly in the Paris and Aquitaine basins Geothermal energy is used for a variety of applications, including heating greenhouses and animal farms, heating of spas and sports centers, for secondary oil recovery, and for district heating Almost equal amount of geothermal energy is utilized for fish farming, heating greenhouses, agricultural crop drying, industrial process heat, district heating, and bathing and swimming The country is the largest user of geothermal energy in the world, accounting for 20% of the annual energy used load 80–90% of the time, thus improving the efficiency and economics of the system [8] as shown in Figure Geothermal district heating systems are capital intensive: the principal liabilities are initial investment costs for production and injection wells, downhole and circulation pumps, heat exchangers, pipelines and distribution network, flow meters, valves and control equipment, and building retrofit The distribution network may be the largest single capital expense, at approximately 35–75% of the entire project cost Operating expenses, however, are in comparison lower and consist of pumping power, system maintenance, control, and management The typical savings to consumers range from approximately 30% to 50% per year of the cost of natural gas [9] 176 Direct Heat Utilization of Geothermal Energy (�C) 100 −20 −15 Fossil fuel Percentage of peak demand 75 −10 −5 Peaking boiler (6%) Geothermal 50 Geothermal heat pump (31%) 25 10 Geothermal (63%) Domestic hot water 15 0 2000 4000 6000 8000 Hours per year Meeting peak demand with fossil fuel Figure Peaking a geothermal system with fossil fuel 7.05.4.3 Greenhouses A variety of commercial crops can be raised in greenhouses, making geothermal resources in cold climates particularly attractive Crops include vegetables, flowers (potted and cut), houseplants, and tree seedlings Greenhouse heating can be accomplished by several methods: finned pipe, unit heater and fan coil units delivering heat through plastic tubes in the ceiling or under benches, radiant floor systems, bare tubing, or a combination of these methods The use of geothermal energy for heating can reduce operating costs and allow operation in colder climates where commercial greenhouses would not normally be economical It is also important, for certain crops as shown in Figure 5, to keep temperatures constant to optimize growth – a task ideally suited for geothermal energy Economics of a geothermal greenhouse operation depends on many variables, such as type of crop, climate, resource temperature, type of structure, and market Peak heating requirements in a temperate climate zone are around 1.0 MJ m−2, and a 2.0 facility would require 20 GJ yr−1 (5.5 MWt) of installed capacity With a load factor of 0.50, the annual energy consumption would be around 90 TJ yr−1 (25 million kWh yr−1) 7.05.4.4 Aquaculture Aquaculture involves the raising of freshwater or marine organisms in a controlled environment to enhance production rates The principal species raised are aquatic animals such as catfish, bass, tilapia, sturgeon, shrimp, tropical fish, and even alligators The application temperature in fish farming depends on the species involved, ranging from 13 to 30 °C, and the geothermal water can be used in raceways, ponds, and tanks The benefit of a controlled rearing temperature in aquaculture operations can increase growth rates by 50–100%, and thus increase the number of harvest per year (Figure 6) A typical outdoor pond in a temperature climate zone would require 2.5 MJ h−1 m−2, and a 2.0 facility would require an installed capacity of 50 GJ yr−1 (14 MWt) peak With a load factor of 0.60, the annual heating requirement would be 260 TJ yr−1 (73 million kWh yr−1) Water quality and disease control are important in fish farming and, thus, need to be considered when using geothermal fluids directly in the ponds 7.05.4.5 Industrial and Agricultural Drying Industrial and agricultural drying applications mostly need higher temperature as compared to space heating, greenhouses, and aquaculture projects, which is generally >100 °C Examples of industrial operations that use geothermal energy are heap leaching operations to extract precious metals in the United States (110 °C), dehydration of vegetables in the United States (104 °C), Direct Heat Utilization of Geothermal Energy 177 Temperature (°F) 32 125 50 68 Percent of possible growth Lettuce 86 104 Tomato 100 75 50 25 Cucumber 0 10 15 20 25 30 35 40 Temperature (°C) Figure Temperature–growth relationship for various greenhouse vegetables Temperature (°F) 32 50 68 Cows 86 104 Chickens Percent of optimum growth 100 80 Trout 60 Catfish Shrimp 40 20 0 10 20 30 40 Temperature (°C) Figure Temperature–growth relationship for various aquaculture species diatomaceous earth drying in Iceland (180 °C), and pulp and paper processing in New Zealand (205 °C) Drying and dehydration may be the two most important process uses of geothermal energy A variety of vegetable and fruit products can be considered for dehydration at geothermal temperatures, such as onions, garlic, carrots, pears, apples, and dates Industrial processes also make more efficient use of the geothermal resources as they tend to have high load factors in the range of 0.4–0.7 High load factors reduce the cost per unit of energy used as indicated in Figure (Rafferty, 2003) 7.05.5 Selecting the Equipment It is often necessary to isolate the geothermal fluid from the user side to prevent corrosion and scaling Care must be taken to prevent oxygen from entering the system (geothermal water is normally oxygen free), and dissolved gases and minerals such as boron, arsenic, and hydrogen sulfide must be removed or isolated as they are harmful to plants and animals Hydrogen sulfide will also attack copper 178 Direct Heat Utilization of Geothermal Energy Cost of energy US$ GJ−1 Cost of energy 10 0.1 0.15 0.2 0.25 0.3 0.35 0.4 System load factor Figure Load factor vs cost of energy (Rafferty, 2003) 130 °F (55 °C) Plate heat exchanger Energy User system 170 °F (75 °C) 180 °F (80 °C) Geothermal Production wellhead equipment 140 °F (60 °C) Injection wellhead equipment Peaking/ backup unit Figure Typical direct-use geothermal heating system configuration and solder, in addition to being deadly to humans On the other hand, carbon dioxide, which often occurs in geothermal water, can be extracted and used for carbonated beverages or to enhance growth in greenhouses The typical equipment for a direct-use system is illustrated in Figure 8, which includes downhole and circulation pumps, heat exchangers (normally the plate type), transmission and distribution lines (normally insulated pipes), heat extraction equipment, peaking or backup plants (usually fossil fuel fired) to reduce the use of geothermal fluids and to reduce the number of wells required, and fluid disposal systems (injection wells) [10] 7.05.5.1 Downhole Pumps Pumping is often necessary to bring geothermal fluids to the surface, if the well is not artesian For direct heat applications, there are two main types of downhole pumps used in producing geothermal fluids: (1) the lineshaft turbine pump and (2) the submersible pump The difference between the two is the location of the driver In a lineshaft pump, the driver, usually a vertical shaft electric motor, is mounted above the wellhead and drives the pump, which may be located as much as 600 m below the ground surface, by means of a lineshaft In pumping geothermal waters, the lineshaft usually has to be enclosed and an oil drip system used to lubricate the bearings, as hot and cold water not lubricate the bearings In a submersible pump, the driver, a long, small-diameter electric motor, is located in the well below the surface of the fluid being pumped and below the pump itself and drives the pump through a relatively short shaft with a seal section to protect the motor from the well fluid [11] Lineshaft pumps have three limitations: (1) they must be installed in relatively straight wells; (2) they are economically limited to settings of