How a Biogas System works

how much biogas can be produced from human waste and food waste and how are biogas produced and how are biogas plants classified
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Published Date:13-07-2017
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United Nations Economic and Social Commission for Asia and the Pacific (ESCAP) is the re- gional development arm of the United Nations and serves as the main economic and social development centre for the United Nations in Asia and the Pacific. Its mandate is to foster cooperation between its 53 member countries and 9 associate members. ESCAP provides the strategic link between global and country-level programmes and issues. It supports the Governments of the region in consolidating regional positions and advocates regional ap- proaches to meeting the region’s unique socio-economic challenges in a globalizing world. The ESCAP headquarters is located in Bangkok, Thailand. Please visit the website at www. unescap.org for further information. The shaded areas of the the map are ESCAP members and associate members APCAEM is a regional institution of ESCAP, located in Beijing, China. Its mission is to assist member countries in achieving their Millennium Development Goals (MDGs) through capac- ity building/training, agricultural policy analysis, agro-technology transfer and facilitation, and information networking. The Centre focuses on three thematic cluster programmes of work: agricultural engineering and machinery, food chain management, and agro-enterprise development. For more information, please visit our website at www.unapcaem.org. Disclaimer The designations used and the presentation of the material in this publication do not imply the express opinion on the part of the ESCAP Secretariat concerning the delimitation of its frontiers or boundaries.The views expressed in this publication are those of its authors and do not necessarily reflect the views of ESCAP and APCAEM. Any mention of firm names and commercial products do not imply the endorsement of ESCAP/ APCAEM. This publication has been issued without formal editing.United Nations Asian and Pacific Centre for Agricultural Engineering and Machinery RECENT DEVELOPMENTS IN BIOGAS TECHNOLOGY FOR POVERTY REDUCTION AND SUSTAINABLE DEVELOPMENT Beijing, 2007Preface The Kyoto Protocol specifies binding commitments by most industrialized countries to reduce greenhouse gas (GHG) emissions. The Clean Development Mechanism (CDM) is one of the three flexible mechanisms established under the Kyoto Protocol. The CDM provides new oppor- tunities for the promotion of biogas in order to reduce the greenhouse effect, through the reduc- tion of methane emission into the atmosphere. Biogas has proven its viability as an energy tech- nology in rural areas of Asia, in particular, India, Nepal, Bangladesh, and China. Over the past 25 years, different types of biogas digesters have been developed and their installation has been commercialized. Technical assistance agencies, bilateral donors and multilateral financing insti- tutions have supported the promotion of biogas technology and assisted the private sector with manufacturing and dissemination of the proper technology. In 2005, the World Bank signed a Memorandum of Understanding that facilitates the trade in emission rights from biogas technology. Biogas projects in Brazil and Chile already apply CDM. Nepal recently signed the Kyoto Protocol in 2005 and biogas programmes are in place which will benefit from the sale of Certified Emission Reductions (CERs) by Nepal. Under a proper policy regime, the income from the sale of CERs can be used to reduce investment costs in biogas equipment. This will accelerate the purchase of biogas digesters by private households and investments in large biogas plants by commercial enterprises, which will further reduce pollution and provide alternative source of affordable energy. There is a potential in Asian and Pacific countries for similar CDM applications. APCAEM conducted a study on the potential applications of CDM from large-scale industrial biogas plants to small household-type digesters. The study contains a summary on the technical, political, and institutional issues involved in the application of CDM for the Asian and Pacific region. APCAEM sincerely wishes that this study report will contribute to a wider use of the biogas technology for rural poverty reduction and sustainable development. iTable of Contents EXECUTIVE SUMMARY .............................................................................................. 1 1. INTRODUCTION ...................................................................................................... 3 1.1 BIOGAS BASICS......................................................................................................... 3 1.2 TYPES OF BIOGAS PLANTS ..................................................................................... 6 1.3 BIOGAS APPLIANCES ............................................................................................... 8 1.4 ORGANIC FERTILIZER FROM BIOGAS PLANTS................................................... 15 1.5 CLIMATIC CONDITIONS FOR BIOGAS DISSEMINATION ...................................... 16 2. CURRENT SITUATION AND RECENT DEVELOPMENTS ...................................21 2.1 DEVELOPMENTS IN LEADING ASIAN COUNTRIES .............................................. 21 2.2 HOUSEHOLD BIOGAS DEVELOPMENT PROGRAMMES ..................................... 23 2.3 COMMERCIAL LARGE-SIZE BIOGAS SYSTEMS ................................................... 26 2.3.1 On-farm biogas systems ................................................................................ 26 2.3.2 Community biogas installations ..................................................................... 29 2.4 BIOGAS FOR INDUSTRIAL WASTE AND WASTE WATER MANAGEMENT ................... 32 2.5 ANAEROBIC DIGESTION AS PART OF ECOLOGICAL SANITATION .................... 34 3. THE APPLICATION OF CDM TO BIOGAS TECHNOLOGY .................................37 3.1 POTENTIALS AND CONSTRAINTS OF INTEGRATED BIOGAS SYSTEMS .................. 37 3.2 THE COMMUNITY DEVELOPMENT CARBON FUND ............................................. 39 4. LESSONS LEARNED AND BEST PRACTICES ....................................................43 4.1 BARRIERS IN DEVELOPING CDM PROJECTS ..................................................... 43 4.2 MAIN ISSUES FOR LARGE SCALE BIOGAS PROJECTS ..................................... 46 4.3 MAIN ISSUES FOR MEDIUM AND SMALL SCALE BIOGAS PROJECT .................... 47 4.4 LIMITATIONS OF CDM AS FINANCING INSTRUMENTS ........................................ 52 5. STRATEGIES FOR BIOGAS DEVELOPMENT .....................................................55 5.1 INVOLVEMENT OF THE PRIVATE SECTOR ........................................................... 55 5.2 INVOLVEMENT OF THE GOVERNMENTAL SECTOR ............................................ 59 5.3 SNV BIOGAS PROGRAMMES IN ASIA ................................................................... 60 6. CONCLUSIONS AND RECOMMENDATIONS .......................................................65 6.1 EXPERIENCES FROM LEADING COUNTRIES ...................................................... 65 6.2 SOCIO-CULTURAL ASPECTS OF BIOGAS PROJECTS ........................................ 68 6.3 POLITICAL AND ADMINISTRATIVE CONSIDERATIONS ........................................ 70 ENDNOTES .................................................................................................................73 iiiList of Figures FIGURE 1: A TYPICAL BIOGAS CONFIGURATION .................................................................. 5 FIGURE 2: SIMPLE BIOGAS PLANTS. ...................................................................................... 7 FIGURE 3: INDUSTRIAL BIOGAS PLANT WITH UTILIZATION OF DOMESTIC ORGANIC WASTE ......................................................................... 8 FIGURE 4: LIGHTWEIGHT AND STABLE TWO-FLAME GAS BURNERS ...................................... 9 FIGURE 5: BIOGAS STOVE IN CHINA ...................................................................................... 9 FIGURE 6: BIOGAS LAMP IN THAILAND ................................................................................ 10 FIGURE 7: SCHEMATIC STRUCTURE OF A BIOGAS LAMP ................................................. 11 FIGURE 8: BIOGAS LAMPS IN CHINA .................................................................................... 11 FIGURE 9: GLOBAL 15 C ISOTHERMS FOR JANUARY AND JULY ...................................... 17 FIGURE 10: SCHEMATIC DIAGRAM OF THE BIOGAS COURTYARD MODEL IN NORTHERN CHINA ......................................................................................... 24 FIGURE 11: TRADITIONAL ENERGY SUPPLY SYSTEM IN PURA ......................................... 29 FIGURE 12: PURA'S ALTERNATIVE (MODERN) ENERGY SUPPLY SYSTEM OF THE PURA VILLGE ..........................................................................................30 FIGURE 13: CDM PROJECT CYCLE COMPARED WITH CONVENTIONAL PROJECT DEVELOPMENT ................................................................................. 45 FIGURE 14: FLOWCHART FOR TESTING ADDITIONALITY OF LARGE SCALE CDM PROJECTS ..................................................................................... 48 List of Tables TABLE 1: POTENTIAL GAS PRODUCTION OF SWINE ....................................................... 26 TABLE 2: MANURE PRODUCTION FROM INDIVIDUAL HOGS ........................................... 26 TABLE 3: MANURE AND GAS PRODUCED BY ONE ANIMAL ............................................. 27 TABLE 4: CAPITAL COST ESTIMATION (US) OF TREATMENT UNITS (US) ........................ 27 TABLE 5: TOTAL COST ESTIMATION OF BIOGAS SYSTEMS, US (HAWAII, USA) .............................................................................................. 28 TABLE 6: ROLE OF IBS IN MEETING THE MDGS BY STRENGTHENING THE FIVE CAPITALS ............................................................................................. 38 TABLE 7: NUMBER OF CDM PROJECT CERS GENERATED.............................................. 45 TABLE 8: LARGE-SCALE AGRICULTURAL CDM PROJECTS ............................................. 47 TABLE 9: MEDIUM AND SMALL SCALE AGRICULTURE CDM PROJECTS .......................... 49 TABLE 10: TRANSACTION COSTS FOR NORMAL AND SMALL SCALE CDM PROJECTS (US DOLLARS) ......................................................................... 50 TABLE 11: SMALL SCALE CDM BIOGAS PROJECTS ............................................................ 52 ivList of Abbreviations AEPC Alternative Energy Promotion Centre BDT Bangladesh Taka BgM Biogas Manure BMW Bio-organic Municipal Wastes BORDA Bremen Overseas Research and Development Association BOT Build, Operate and Transfer BSP Biogas Support Programme CDCF Community Development Carbon Fund CDM Clean Development Mechanisms CERs Certified Emission Reductions CNY Chinese Yuan CO2 Carbon Dioxide DNA Designated National Authority ERPA Emission Reduction Purchase Agreement FAO Food and Agriculture Organization GATE German Appropriate Technology Exchange GDP Gross Domestic Product GTZ German Agency for Technical Assistance IBS Integrated Biogas Systems INR Indian Rupees IRR Internal Rate of Return MDGs Millennium Development Goals MFI Micro Finance Institute MNES Ministry of Non-Conventional Energy Sources MSW Municipal Solid Wastes MW Megawatt NGO Non-Governmental Organizations vNPV Net Present Value PDD Project Design Document UNFCCC United Nations Framework Convention on Climate Change USD US Dollars viEXECUTIVE SUMMARY EXECUTIVE SUMMARY iogas is a proven and widely-used source of energy in Asia. There has been a renewed interest in biogas owing to rising concerns over the greenhouse effect, high price of Bfossil fuels, and other environmental and health concerns. The Clean Development Mecha- nism (CDM) opens up new opportunities for the promotion of biogas. As a regional centre, APCAEM is involved in institutional- and policy-related work on agricultural engineering and agro-industry. This publication will be useful for policy- and decision-makers in governments, the donor community, and the privater sector dealing with biogas programmes. The introduction chapter of the publication provides basic information on the different aspects of _ biogas technology utilization, types and configurations of biogas digesters, end-use appliances and technologies for biogas, generation of fertilisers as well as additional benefits of biogas generation, and the climatic and environmental considerations for biogas development and applications. Chapter 2 reviews the current situation and recent developments in biogas in the Asia-Pacific region, focusing on the activities, projects and programmes implemented in the three countries _ that have led the way in biogas development, applications and commercialization China, India and Nepal. Chapter 3 introduces CDM as a possible mechanism for financing biogas projects and discusses the potential of biogas development and application as CDM projects. In particular, the require- ments of the Community Development Carbon Fund, a prototype CDM funding mechanism, are presented. Chapter 4 draws much of its discussion from one of the papers presented at an International _ Biogas Conference analyzing the specific barriers for utilizing CDM for financing biogas projects and assessing risk-mitigation strategies that may be implemented to make biogas attractive for CDM financing. Chapter 5 discusses the current approaches and strategies being undertaken by the countries in the regions that are paving the way for the dissemination and commercialization of biogas technology. The role of the private sector in Nepal and China is presented. The thrusts of the _ _ biogas programmes for the other three Asian countries Bangladesh, Cambodia and Vietnam are also presented. These approaches, strategies and programmes are aimed at addressing the barriers to commercialization of biogas, including possible sources of CDM for financing biogas investments. 1EXECUTIVE SUMMARY Chapter 6 highlights lessons learned from the experiences of the leading countries and discusses, in particular, the social and economic considerations in formulating and implementing biogas projects. These discussions identify concerns that need to be addressed in order for the potential biogas energy projects to contribute to the socio-economic development of the targeted communities, particularly by improving rural livelihoods of the region. 2Introduction 1. Introduction iogas is a proven and widely used source of energy in Asia. There is now yet another wave of renewed interest in biogas due to the increasing concerns of climate change, Bindoor air pollution and increasing oil prices. Such concerns, particularly for climate change, open opportunities for the use of the Clean Development Mechanism (CDM) in the pro- motion of biogas. As a regional centre, the United Nations Asian and Pacific Centre for Agricultural Engineering and Machinery (APCAEM) is involved in institutional- and policy-related programme of agricultural engineering and agro-industry. One of the activities of APCAEM is promoting the application of CDM to agriculture in the Asian and Pacific region. An International Seminar on Biogas Technology for Poverty Reduction and Sustainable Develop- ment was organized by APCAEM in cooperation with the Ministry of Agriculture of China, from 17 to 20 October 2005 in Beijing, China. One of the objectives of this Seminar was to identify innova- tive developments in biogas technology and the areas of application of CDM. During the round- table discussion, the follow-up activities were identified: Review the materials submitted and presented on biogas technology for poverty reduction and sustainable development. Based on the outline of the publication, to publicize the recent development in biogas technology. APCAEM has prepared this publication to provide information and technology useful to the policy makers in Governments, the donor community, and other key stakeholders in biogas develop- ment and commercialization. 1 1.1 Biogas Basics What is Biogas? Biogas originates from bacteria during the process of bio-degradation of organic materials under anaerobic (without air) conditions. The natural generation of biogas is an important part of the biogeochemical carbon cycle. Methanogens (methane-producing bacteria) are the last link in the chain of micro-organisms that degrade organic materials and return the decomposed products to the environment. It is in this step of the biogeothermal carbon cycle that biogas, a source of renewable energy, is generated. Biogas and the Global Carbon Cycle Each year, some 590-880 million tons of methane are released worldwide into the atmosphere through microbial activity. About 90 percent of the emitted methane derives from biogenic sources, 3Introduction i.e., from the decomposition of biomass. The remainder is of fossil origin (e.g., petrochemical processes). In the northern hemisphere, the present tropospheric methane concentration amounts to about 1.65 ppm. Biology of Methanogenesis Knowledge of the fundamental processes involved in methane fermentation is necessary for planning, building and operating biogas plants. Anaerobic fermentation involves the activities of three different bacterial communities. Biogas production also depends on certain specific conditions. For example, changes in ambient temperature can have a negative effect on bacterial activity. Substrate and Material Balance of Biogas Production In general, all organic materials can ferment or be digested. However, only homogenous and liquid substrates can be considered for simple biogas plants: faeces and urine from cattle, pigs and possibly poultry, as well as wastewater from toilets. When the plant is at capacity, the excre- ment is diluted with an equal quantity of liquid, such as urine if available. Waste and wastewater from food-processing industries are only suitable for simple plants if they are homogenous and in liquid forms. The maximum gas-production from a given amount of raw material depends on the type of substrate. Composition and Properties of Biogas Biogas is a mixture of gases mainly composed of: Methane (CH ): 40-70 % by volume 4 Carbon dioxide (CO ): 30-60 % by volume 2 Other gases: 1-5 % by volume, including: _ Hydrogen (H ): 0-1 % by volume 2 _ Hydrogen sulfide (H S): 0-3 % by volume 2 Similar to any pure gas, the properties of biogas are pressure- and temperature-dependent. They are also affected by the moisture content and other major factors such as: Change in volume as a function of temperature and pressure Change in calorific value as a function of temperature, pressure and water-vapor content Change in water-vapor content as a function of temperature and pressure 3 The calorific power of biogas is about 6 kWh/m - this corresponds to about half a litre of diesel oil. The net calorific value depends on the efficiency of the burners or appliances. Methane is the most valuable component if the biogas is to be used as a fuel. Utilization The historical evidence of biogas utilization shows independent developments in various devel- oping and industrialized countries. Normally, the biogas produced by a digester can be used as is, the same way as any other combustible gas. It is possible that further treatment or conditioning is necessary, for example, to reduce the hydrogen-sulfide content in the gas. When biogas is mixed with air at a ratio of 1:20 a highly explosive gas forms; therefore, leaking gas pipes in enclosed spaces poses a hazard. 4Introduction Figure 1: Typical biogas configuration Source: GTZ Biogas Basics. Benefits of Biogas Technology Well-functioning biogas systems can yield a range of benefits for users, the society and the envi- ronment in general: Production of energy (heat, light, electricity); Transformation of organic wastes into high-quality fertiliser; Improvement of hygienic conditions through reduction of pathogens, worm eggs and flies; Reduction of workload, mainly for women, in firewood collection and cooking; Positive environmental externalities through protection of soil, water, air and woody vegetation; Economic benefits through energy and fertiliser substitution, additional income sources and increasing yields of animal husbandry and agriculture; Other economic and eco-benefit through decentralized energy generation, import substitution and environmental protection. Biogas technology can substantially contribute to conservation and development, if the concrete conditions are favourable. However, the required high level of investment in capital and other limitations of biogas technology should also be thoroughly considered. Affordability of Biogas Technology An obvious obstacle to the large-scale introduction of biogas technology is the fact that the poorer strata of rural populations often cannot afford the initial investment cost for a biogas plant. This barrier remains despite the fact that biogas systems have proven to be economically sound in- vestments in many cases. Efforts must be made not only to reduce construction costs, but also to develop credit and other financing mechanisms for biogas technology. A larger number of biogas operators ensure that, apart from the private user, the society as a whole can benefit from the use of biogas. Financial support from the government can be seen as an investment to curb future costs incurred through the importation of petrol products and inorganic fertilisers, increasing costs for health and hygiene, as well as natural resource degradation. 5Introduction Fuel and Fertiliser In developing countries, there is a direct link between the problem of fertilization and progressive deforestation due to a high demand for firewood. In many rural areas, most inhabitants are de- pendent on dung and organic residue as fuel for cooking and heating. Such is the case, for example, in the treeless regions of India (Ganges plains, central highlands), Nepal and other countries of Asia, as well as in the Andes mountains of South America and wide expanses of the African Continent. According to the data published by the FAO, some 78 million tonnes of cow dung and 39 million tonnes of phytogenic waste were burned in India alone in 1970. That amounts to approximately 35 percent of India’s total non-commercial/non-conventional en- ergy consumption. The burning of dung and plant residue is a considerable waste of plant nutrients. Farmers in developing countries are in dire need of fertiliser for maintaining cropland productivity. Nonetheless, many small farmers continue to burn potentially valuable natural fertilisers, despite being unable to afford chemical fertilisers. The amount of technically available nitrogen, potassium and phos- phorous in the form of organic materials is around eight times as high as the quantity of chemical fertilisers actually consumed in developing countries. Biogas technology is a suitable tool, espe- cially for small farmers, for maximizing the use of scarce resources. After extraction of the energy content of dung and other organic waste material, the resulting sludge is still a good fertiliser, supporting soil quality as well as higher crop yields. 2 1.2 Types of Biogas Plants The three main types of simple biogas plants are shown in Figure 2: Balloon plants Fixed-dome plants Floating-drum plants Balloon Plants The balloon plant consists of a digester bag (e.g., PVC) in the upper part in which the gas is stored. The inlet and outlet are attached directly to the plastic skin of the balloon. The gas pres- sure is achieved through the elasticity of the balloon and by added weights placed on the balloon. The advantages of this system are its low cost, ease of transportation, low construction sophistication, high digester temperatures, and its rather simple cleaning, emptying and maintenance. The disadvantages can be the relatively short life span, high susceptibility to damage, little cre- ation of local employment and, therefore, limited self-help potential. A variation of the balloon plant is the channel-type digester, which is usually covered with plastic sheeting and a sunshade (see Figure 2E). Balloon plants can be recommended wherever the balloon skin is not likely to be damaged and where temperatures are not too high. 6Introduction Figure 2: Simple biogas plants Note:Floating-drum plant (A), fixed-dome plant (B), fixed-dome plant with separate gas holder (C), balloon plant (D), channel-type digester with plastic sheeting and sunshade (E). Source: Biogas Plants, L. Sasse, GATE, 1988, p.14. Fixed-Dome Plants The fixed-dome plant consists of a digester with a fixed, non-movable gas holder, which sits on top of the digester. When the production of gas starts, the slurry is displaced into the compensa- tion tank. The gas pressure increases with the volume of gas stored and the height difference between the slurry level in the digester and the slurry level in the compensation tank. The advantages of this system are the relatively low construction costs and the absence of mov- ing parts and rusting steel parts. If well-constructed, fixed-dome plants have a long life span. The underground construction saves space and protects the digester from temperature changes. The construction provides opportunities for skilled local employment. The disadvantages are mainly the frequent problems with the gas-tightness of the brickwork gas holder, where even a small crack in the upper brickwork can cause a heavy loss of biogas. Therefore, fixed-dome plants are recommended only where construction can be supervised by experienced biogas technicians. The gas pressure fluctuates substantially depending on the volume of the stored gas. Even though the underground construction buffers temperature extremes, digester temperatures are low. 7Introduction Floating-Drum Plants Floating-drum plants consist of an underground digester and a moving gasholder. The gasholder floats either directly on the fermentation slurry or in a water jacket of its own. The gas is collected in the gas drum, which rises or moves down, according to the amount of gas stored. The gas drum is prevented from tilting by a guiding frame. If the drum floats in a water jacket, it cannot get stuck, even in substrate with a high solid content. The main advantage of this system is its simple, easy operation, as the volume of stored gas is directly visible to the user. The gas pressure is constant and determined by the weight of the gas holder. The construction is relatively easy and mistakes do not lead to major problems in opera- tion or gas yield. The disadvantages are high material costs of the steel drum and the susceptibility of steel parts due to corrosion. Because of this, floating-drum plants have a shorter life span than fixed-dome plants and regular maintenance costs for the painting of the drum. To contrast these simple biogas plants, Figure 3 gives an impression about dimensions of indus- trial plants that have been built in Europe. Figure 3: Industrial biogas plant with utilization of domestic organic waste Source: GTZ. 3 1.3 Biogas Appliances Biogas is a lean gas that can, in principle, be used like other fuel gases for households and industrial purposes: Gas cookers/stoves Lamps Radiant heaters Incubators 8Introduction Refrigerators Engines Gas Cookers/Stoves Biogas cookers and stoves must meet various basic requirements: Simple and easy operation Versatility, e.g., for pots of various size, for cooking and broiling Easy to clean, acceptable cost and easy repair Good burning properties, i.e., stable flame, high efficiency Agreeable appearance Two-flame burners A cooker is more than just a burner. It must satisfy certain aesthetic and utility requirements, which can vary widely from region to region. There is no such thing as a standard biogas burner. Most households prefer two-flame burners. The burners should be set initially and then fixed so that efficiency remains at a high practical level. Single-flame burners and lightweight cook-stoves tend to be regarded as stop-gap solutions until more suitable alternatives can be found. Figure 4: Lightweight and stable two-flame gas burners Source: GTZ. Biogas cookers require careful installation with adequate protection from the wind. Before any cooker is used, the burner must be carefully adjusted. For a compact, bluish flame the pot should be cupped by the outer cone of the flame without being touched by the inner cone; The flame should be self-stabilizing, i.e., flameless zones must re-ignite automatically within 2 to 3 seconds. Test measurements should be performed to optimize the burner setting and minimize consumption. Figure 5: Biogas Stove in China Source: Grosch, GTZ/GATE. 9Introduction Gas demand The gas demand can be defined on the basis of energy consumed previously. For example, 1 kg firewood then corresponds to 200 litres biogas, 1 kg dried cow dung corresponds to 100 litres biogas and 1 kg charcoal corresponds to 500 litres biogas. The gas demand can also be defined using the daily cooking times. The gas consumption per person and meal lies between 150 and 300 litres biogas. For one litre of water to be boiled, 30-40 litre of biogas are required, for 1/2 kg rice 120-140 litres, and for 1/2 kg legumes 160-190 litres. Lamps Efficiency of biogas lamps In villages without electricity, lighting is not only a basic need, but also a status symbol. However, biogas lamps currently provide little relief as they are not very energy-efficient and they tend to get very hot. The bright light of a biogas lamp is the result of incandescence, i.e., the intense heat- induced luminosity of special metals, so-called “rare earth” metals like thorium, cerium, lanthanum, etc., at temperatures of 1,000-2,000 C. If they hang directly below the roof, they pose a potential fire hazard. Also, the mantles do not last long. It is important that the gas and air in a biogas lamp are thoroughly mixed before they reach the gas mantle, and that the air space around the mantle is adequately warm. Light output The light output (luminous flux) is measured in lumen (lm). At 400-500 lm, the maximum light-flux values that can be achieved with biogas lamps are comparable to those of a normal 25-75 W light bulb. Their luminous efficiency ranges from 1.2 to 2 lm/W. By comparison, the overall efficiency of a light bulb comes to 3-5 lm/W, and that of a fluorescent lamp ranges from 10 to 15 lm/W. One lamp consumes about 120-150 litres of biogas per day. Optimal tuning Figure 6: Biogas lamp in Thailand The performance of a biogas lamp is de- pendent on optimal tuning of the incan- descent body (gas mantle) and the shape of the flame at the nozzle, i.e., the incan- descent body must be surrounded by the inner (and hottest) core of the flame at the minimum gas consumption rate. If the incandescent body is too large, it will show dark spots; if the flame is too large, gas consumption will be too high for the light- flux yield. The lampshade reflects the light downward, and the glass prevents the loss of heat. Source: Kossman, GTZ/GATE. 10Introduction Shortcomings of commercial-type biogas lamps Practical experience shows that commercial-type gas lamps are not optimally designed for the specific conditions of biogas combustion (fluctuating or low pressure, variable gas composition). The most frequently observed shortcomings are: Excessively large nozzle diameters; Excessively large gas mantles; No possibility of changing the injector; Poor or lacking means of combustion-air control. Such drawbacks result in unnecessarily high gas consumption and poor lighting. While the ex- pert/extension officer has practically no influence on how a given lamp is designed, s/he can at least give due consideration to the mentioned aspects when it comes to selecting a particular model. 1 Figure 7: Schematic structure of a biogas lamp Figure 8: Biogas lamps in China Source: Grosch, GTZ/GATE. 1 Photo: Production and Utilization of Biogas in Rural Areas of Industrialized and Developing Countries, Schriftenreihe der gtz No. 97, p.186. 11Introduction Radiant Heaters Infrared heaters are used in agriculture for achieving the temperatures required for raising young stock, e.g., piglets and chicken, in a limited amount of space. The nursery temperature for piglets begins at 30-35 C for the first week and then gradually drops off to an ambient temperature of 18- th th 23 C in the 4 /5 week. Temperature control consists of raising or lowering the temperature. Good ventilation is important in the stable nursery in order to avoid excessive concentrations of CO or CO . Consequently, the animals must be kept under regular supervision, and the temperature 2 must be checked at regular intervals. Heaters for pig or chicken rearing require some 200-300 l/ h in general. Thermal radiation of heaters Radiant heaters develop their infrared thermal radiation via a ceramic body that is heated to 600- 800 C (red-hot) by the biogas flame. The heating capacity of the radiant heater is defined by multiplying the gas flow by its net calorific value, since 95 percent of the biogas energy content is converted to heat. Small-heater outputs range from 1.5 to 10 kW thermal power. Gas pressure Commercial-type heaters are designed for operating on butane, propane and natural gas at a supply pressure of between 30 and 80 mbar. Since the primary air supply is factory-set, convert- ing a heater for biogas-use normally consists of replacing the injectors. However, experience shows that biogas heaters rarely work satisfactorily because the biogas has a low net calorific value and the gas supply pressure is below 20 mbar. The ceramic panel, therefore, is not ad- equately heated, i.e., the flame does not reach the entire surface, and the heater is very suscep- tible to drafts. Safety pilot and air filter Biogas-fuelled radiant heaters should always be equipped with a safety pilot, which turns off the gas supply if the temperatures go too low, i.e., the biogas does not burn any longer. An air filter is required for sustained operation in dusty barns. Incubators Incubators are supposed to imitate and maintain optimal hatching temperatures for eggs. They are used to increase brooding efficiency. Warm-water-heated planar-type incubators Indirectly warm water-heated planar-type incubators, in which a burner heats water in a heating element for circulation through the incubating chamber, are suitable for operating on biogas. The temperature is controlled by ether cell-regulated vents. Biogas-Fuelled Engines Gas demand If the output of a biogas system is to be used for fueling engines, the plant must produce at least 3 3 10 m /day of biogas. For example, to generate 1 kWh of electricity with a generator, about 1.0 m biogas is required. Small-scale systems are therefore not suitable as energy suppliers for engines. 12

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