BIOGAS AS AN ALTERNATIVE SOURCE FOR ELECTRICITY PRODUCTION

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1 BIOGAS AS AN ALTERNATIVE SOURCE FOR ELECTRICITY PRODUCTION C.G. Economopoulos 1, O.A. Bereketidou 1,, M.A. Goula 1, * 1 Technological Educational Institute of Western Mecedonia, Pollution Control Technologies Department, 51, Kila, Kozani, Greece Laboratory of Environmental Fuels, Measurements and Air Pollution Control University of Western Macedonia, Department of Engineering and Management of Energy Resousces, 51, Kozani, Greece E mail: mgoula@kozani.teikoz.gr, ilatsi@tee.gr ABSTRACT Renewable sources of energy are being sought as alternatives to replace fossil fuels. Biomass could be of particular interest as energy source, as it does not contribute to CO emissions. There are basically two methods for waste treatment; aerobic treatment and anaerobic digestion, from which the second one leads to methane as a final product and therefore energy could be produced. Specifically, biogas is the main product of anaerobic process and it consists of about 6% methane, 38% carbon dioxide and % other unions. In this study an approach for calculating the capital cost and the operating cost of an anaerobic digester unit will be presented. Three types of animals with satisfying production in daily manure were used to calculate the total cost and the profit in micro turbines and fuel cells. 1

2 1. INTRODUCTION Waste treatment is an inevitable procedure which is currently very much encourenged by European Union. Among various techniques, aerobic process was concidered as an appropriate one till now. According to this, organic wastes such as wastes from municipal, livestock farms, food factory etc, are transferred into a tank and mixed with cointantaneously flowing of air. This system is certified as ideal only when the quantities of wastes are high enough; however the demands for reactor tank size are extremely large. Characteristics of aerobic treatment are referred below [1, ]: - Advantages: Relatively low construction cost Smaller size of facilities - Disadvantages: Process requires energy Process has high operating cost Capital cost can t be easily payback The above drawbacks make waste owners resort to other more efficient ways for waste treatment and utilization. An ideal solution could be anaerobic digestion, as this process in contrary to aerobic treatment does not need any quantity of air, and the final product which is mainly methane could produce energy. Characteristics of anaerobic treatment are summarized below [1, ]: - Advantages: Process produces methane Process doesn t need any external power Capital cost easily payback Waste management has economic profit - Disadvantages: Huge facilities High capital cost The typical composition of the produced biogas is 6% methane, 38% carbon dioxide and % other compounds. Sometimes biogas contains hydrogen sulfide up to 1%, which must be removed though a desulphurization process. In this study a software was developed, that can be used to calculate the capital cost and the operating cost of an anaerobic digester unit. With these parameters konown, it would be easy to calculate the appropriate number of years needed to pay off the capital cost; the best value for this factor would be about five (5) years. Furthermore, in this study the total energy containing in animal wastes in Greece was calculated and the different possible ways for biogas usage, too.[1,, 3].. METHOD The main characteristic of an anaerobic digester is biogas (methane) production which includes energy and there is no need for any external energy input. Calculating construction cost, operating cost and the profits from possible ways of biogas usage with our software, we were able to have the possible size of the viable units. First step was the development of the software which would be able to calculate capital cost, operating cost and profit from sales or use of products [1,, 3, 4]. The capital cost program can estimate the cost of: - Digester (cement, bulldozer, isolation) - Mixer (motors, bases) - Cover of digester - Storage tank - Heat for digester - Fire protection - Purification unit for biogas

3 - Biogas processing (compression, dry, counter) In the section of operating cost program it can be estimated: - The maintenance of biogas use system - The purification system - Workers and special studies - Type of biogas use - The fire protection system - Workers In the section of profit from biogas usage program it can be estimated: - type of biogas use (burn, electricity generation, hydrogen production) - sell or gain of products The second step was the identification of viable units for different livestock farms. Three types of animals were used; diary cows, beefs and pigs with the assumption that in these viable units biogas was only used for power and heat generation. The third step was a case study for the Greek area, the energy capacity from livestock farms and the possibility of anaerobic digestion units construction for electric power generation and heat generation [1,, 3, 4, 5]. There are three different types of anaerobic digester; in this study the selected type was a plug flow reactor with flexible top. Sell prices for products are referred below: - Electricity,69 /kwh,8 /kwh - Heat /kwh,33 /kwh - Manure /5kg 3 /5kg The above prices include the minimum and maximum sell prices in Greek area [5]. The generation of electricity was calculated for a micro turbine having total efficiency of 3% and for fuel cells 4%, while recovered heat in both cases was 45% [6, 7, 8, 9, 1,11]. 3. RESULTS AND DISCUSSION 3.1 Viable units with different types of generator Different animals have different production of manure. For this reason in this study three types of animals were selected, which have manure that could be easily collected in stable or not stable livestock farms. The three types of animals were diary cows, beefs and pigs and the results are presented in the following tables. TABLE 1. Minimum required population for a viable unit with diary cows. Animal Sell prices Electricity Heat Manure Payback Profit Payback Profit Population Cost ( /kwh) ( /kwh) ( /5kg) (years) ( /year) (years) ( /year) ( ) Cost ( ) 1791,69 5, , ,69,33 5, , ,69 3 5, , ,69,33 3 5, , ,8 5, , ,8,33 5, , ,8 3 5, , ,8,33 3 5, , *35% of produced energy consumed for digester requirement, micro turbine electricity efficiency 3%, fuel cell electricity efficiency 4%, 6% methane containing in biogas 3

4 TABLE. Minimum required population for a viable unit with beefs. Animal Sell prices Population Electricity ( /kwh) Heat ( /kwh) Manure ( /5kg) Payback (years) Profit ( /year) Cost ( ) Payback (years) Profit ( /year),69 5, , Cost ( ) 566,69,33 5, , ,69 3 5, , ,69,33 3 5, , ,8 5, , ,8,33 5, , ,8 3 5, , ,8,33 3 5, , *35% of produced energy consumed for digester requirement, micro turbine electricity efficiency 3%, fuel cell electricity efficiency 4%, 6% methane containing in biogas TABLE 3. Minimum required population for a viable unit with pigs. Animal Sell prices Population Electricity Heat Manure Payback Profit Payback Profit ( /kwh) ( /kwh) ( /5kg) (years) ( /year) Cost ( ) (years) ( /year) Cost ( ) 164,69 5, , ,69,33 5, , ,69 3 5, , ,69,33 3 5, , ,8 5, , ,8,33 5, , ,8 3 5, , ,8,33 3 5, , *35% of produced energy consumed for digester requirement, micro turbine electricity efficiency 3%, fuel cell electricity efficiency 4%, 6% methane containing in biogas From the above presented results it can be concluded that only units with a large number of animals could be viable with the assumption that the incomes comes only from electricity selling. On the other hand units for which their owners could sell heat or manure or both of them, could be viable having smaller required number of animals and lower capital cost. The fuel cell system increases the electricity efficiency, but also increases the capital cost with direct effect on the number of payback years. For this reason, we considered the first case with viable units (selling only electricity) from each animal and studied incomes and number of years needed for payback as a function of selling products. 4

5 Figure1. Profit of anaerobic unit with diary cows with different product price and different method of electricity production. Figure 3. Profit of anaerobic unit with.4 beefs with different product price and different method of electricity production. Profit (Euro/year) Diary Cows (1791 Heads Unit) Payback (years) Beefs (4 Heads Unit) 1,69//3,69/,33/3,8//,8/,33/,8//3,8/,33/3 Sell prices of product (electricity/heat/manure),69//3,69/,33/3,8//,8/,33/,8//3,8/,33/3 Sell prices of products (energy/heat/manyre) Figure. Payback years on anaerobic unit with different sell product price and different methods on electricity production. Figure 4. Payback years on anaerobic unit with different sell product price and different method on electricity production. 1 Diary cows (1791 Heads Unit) 45 Beefs (4 Heads Unit) Payback (Years) Profit (euro/year) ,69//3,69/,33/3,8//,8/,33/,8//3,8/,33/3 Sell price of products (electricity/heat/manure),69//3,69/,33/3,8//,8/,33/,8//3,8/,33/3 Sell prices of products (Electricity/heat/manure) 5

6 Figure 5. Profit of anaerobic unit with 16.4 pigs with different product price and different method of electricity production. Figure 6. Payback years on anaerobic unit with different sell product price and different method on electricity production. Profit (Euro/year) Pigs (164 Heads Unit) Fuel cell Payback (Years) Pigs (164 Heads Unit),69//3,69/,33/3,8//,8/,33/ Sell prices of products (electricity/heat/manure),8//3,8/,33/3,69//3,69/,33/3,8//,8/,33/ Sell prices of product (electricity/heat/manure),8//3,8/,33/3 From the above figures carefull observation it can be concluded that most units could be viable, when there is a possibility of selling two or more products, even units which use fuel cells. Using micro turbine in these units, there are some advantages as low capital cost, well known performance and easy operating handling. Furthermore, there are many companies all over the world which produce and sell micro turbines. The use of micro turbines has the main disadvantage of very low electricity efficiency, only up to 3%. On the other hand, fuel cells have at least 37% efficiency reffering to these days commercializing systems, while their higher efficiency could reach values at about 47%. The main drawback with FCs is their high cost, estimated about 3 /kwh, comparing with those of micro turbines which is about 6 /kwh. In the foreseeable future many companies will aim to develop fuel cell units with electricity efficiency up to 5% and cost only 33 /kwh. If this target will be accomplished soon, we will be evidenced the whole market of electricity generation to be overturned. Having in mind all the above data describing well a viable unit and the amount of electricity profit from each unit, it would be easy to calculate the profit of constracting an anaerobic digestion unit in the Greek area [7, 8, 9, 1,11]. 3. Case study Anaerobic digestion units (A.D.U.) may help electricity production with direct benefits in environment protection, because the feedstock in electricity generation system is biogas which contains carbon from atmosphere (close carbon circle). Statistic data for Greek involves 5 different animals: beefs, ships, goat, pigs and horses. Data for these animals and the containing energy are presented in table 4. 6

7 The conclusion from this table is that a significant quantity of energy is contained in manure and can be utilized for cogeneration. Economic profit from these units is extremely high, namely about 44M /year can be received from a full process utilization of manure, only for electricity and by using micro turbines. Fuel cell system can achieve 6M /year with total profit (heat and manure sell) up to 19M /year [1, 13, 14, 15]. Biogas m 3 /day TABLE 4. Energy containing in Greek manure Electricity (kwh/day) Energy containing Advance Hydrogen Heat (kwh) Manure Beefs Sheep & Goat Pigs Horses Profit ( /day) (price kwh,69) Profit (kg lignite/day) Profit (kg CO /day) Profit (euro/year) Profit (tn lignite/year) Profit (tn CO /year) Profit (electricity+heat+manure) (euro/year) *Sheep and goats have same production in manure and biogas. Ships and goats have half production from pigs. Horses have the same production in manure and biogas with beefs. **Micro turbine electricity efficiency 3%, electricity efficiency 4% and advance FC 5%. Heat recover 45%. 3% of produced energy consumed in digester. *** Lignite energy 13kcal/kg, CO 1kg/GJ produced energy 4. CONCLUSIONS Biogas is an alternative source which can be used into three different energy converters. According to the classic method, biogas could be burned into a micro turbine, which has the drawback of low electricity efficiency. A promising method for electricity generation could be using fuel cells with a typical efficiency about 4% and with cogeneration up to 87%. The main problem for using fuel cells would be the extremely high cost with an average value of about 3 /kwh, but this situation is expected to change in the future, with cost for kwh about 33. The third alternative option could be hydrogen production into a steam reformer, while in small quantities hydrogen cost is too high and the unit is unviable. Data from Greek area for manure production are very impressive. There are high quantities of biomass which can result in a significant amount of biogas production, a new source for electricity production. Fuel cells lead to the best results in energy conversion, heat recovery and lower CO emissions by minimizing the amount of lignite. The main drawback of using fuel cells is the high capital cost, which is expected to become minimum in the next two years with the development of advanced fuel cells. 7

8 6. REFERENCES 1. Ludwig Sasse, Biogas Plants (GTZ, 1988). Uil Werner/Ulrich Stohr/Nicolai Hees, Biogas plants in animal husbandry (GTZ, 1989) Albanis J.A., Economopoulos G.K., Goula M.A. *, Economical viability of a unit for animal waste treatment for electricity and energy production, nd Environmental Congress of Macedonia, 8-1 October, 5, Thessaloniki, Greece Klaus von Mitzlaff, Engines for biogas (GTZ, 1988) 7. Lee F. Brown, A comparative study of fuels for on-board hydrogen production for fuel-cellpowered automobiles, International Journal of Hydrogen Energy, Vol. 6, 1, pp AEA Technology, The Feasibility, Costs and Markets for Hydrogen Production, September 13. NREL, Survey of the economics of hydrogen technologies, Technical Report,September Waichi Iwasaki, A consideration of economic efficiency of hydrogen production from biomass, International Journal of Hydrogen Energy, Vol. 8, (3), pp