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Combined heating & power - Reciprocating engine - 50 kW - Biogas / Canada
Case study assignment
As a supplier of farm biogas cogeneration technology, you need to quickly produce system performance and cost estimates for a farm with a herd of 140 dairy cows. Your technology consists of an anaerobic digester, with cow manure as the feedstock, which produces biogas that is fed to a reciprocating engine-powered generator.
Site information
The farm is located in the Ottawa valley near Pembroke, Ontario, Canada. The biogas will be combusted in a spark-ignition compression engine and used to produce heat and power. The heat will be used for regulating the digester temperature to 40°C, with excess heat used for farmhouse space heating and hot water. Assume a typical farmhouse with 300 m2 floor area, currently heated with propane and moderately well insulated. The average farm electrical load is 30 kW (all months). Electricity can be used to offset the farm's electrical load or traded with the utility according to a net metering agreement. The figure shows the energy flows involved. For this study, select a 50 kW engine to allow for system expansion and set the heat recovery efficiency of the engine to 50% to cover digester heating
Case study assignment
As a supplier of farm biogas cogeneration technology, you need to quickly produce system performance and cost estimates for a farm with a herd of 140 dairy cows. Your technology consists of an anaerobic digester, with cow manure as the feedstock, which produces biogas that is fed to a reciprocating engine-powered generator.
Site information
The farm is located in the Ottawa valley near Pembroke, Ontario, Canada. The biogas will be combusted in a spark-ignition compression engine and used to produce heat and power. The heat will be used for regulating the digester temperature to 40°C, with excess heat used for farmhouse space heating and hot water. Assume a typical farmhouse with 300 m2 floor area, currently heated with propane and moderately well insulated. The average farm electrical load is 30 kW (all months). Electricity can be used to offset the farm's electrical load or traded with the utility according to a net metering agreement. The figure shows the energy flows involved. For this study, select a 50 kW engine to allow for system expansion and set the heat recovery efficiency of the engine to 50% to cover digester heating
Financial information
Assume that electricity rate is $0.11/kWh and that propane fuel cost is $0.50/L. Initially assume no credits from GHG emission reductions or green power. Development costs are $10K for a feasibility study, $20K for engineering, $150K installed for the digester and associated works, and $1,500/kW for the reciprocating engine and generator. O&M costs about $5K/year (mainly for engine maintenance and refurbishments), and construction will take 6 months.
Assume financial conditions of 0% inflation and fuel cost escalation; 20-year project life with 6% discount rate; 100% agricultural loan available for 15 years at 6% interest. The income tax rate is 36% with 15% depreciation in year 1, with 30% per year thereafter.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
Real project
Results
A farm located in Cobden, Ontario, Canada, has a co-generation facility that been in operation since May 2003. The facility consists of a complete mix mesophilic anaerobic digester and a 50 kW reciprocating engine-generator.
System description
The current feedstock to the digester is manure from the farm's herd of 140 dairy cows. From this, the digester produces some 400 m3 of biogas per day with an average methane content of 55%.
The types of engine most commonly considered for biogas cogeneration are spark ignition reciprocating engines (biogas only) and compression ignition reciprocating engines (using a mix of biogas and 10% diesel fuel for combustion stability). Micro-turbines can also be used.
This facility uses a dual-fuel compression ignition engine, which drives an alternator that produces some 700 kWh of electricity per day. This can either service farm electrical loads or be exported to the grid where it is traded in accordance with a Net Metering agreement (which means that the farmer is not paid for any net export of power over the year). An incentives scheme for selling of electricity is also available, but would require the farmer to lock into a 20-year rate with only partial index-linking.
The heat from the combustion process is used for heating of the digester and the farmhouse. The digester temperature is regulated to 40 °C, which is the optimum temperature for biogas production. During winter, the heat produced is just sufficient to meet these loads. Significant excess heat is available in summer, and ways to best utilize this heat, such as crop drying, are currently under investigation.
Lessons learned
The main operation and maintenance costs centre on the reciprocating engine. Due to the relatively high sulphur content in the biogas, engine oil must regularly be changed, with a major engine overhaul every three years.
There are multiple other potential benefits of this technology:
An important area of future consideration is importing off-farm organic waste to the digester to increase biogas production and provide a safer disposal facility.
The big picture
Modern biogas technology has become well established on European farms over the past 10 years, particularly in the central European countries of Germany, Switzerland and Austria. Recent years have seen the emergence of several farm biogas co-generation systems in Canada for electricity production and heating. One reason for the current emergence of this technology in Canada is the introduction of incentives for distributed generation using renewable energy. In addition, for the farmer, it represents another source of income, without the need to purchase expensive milk or other quotas.
Despite their obvious advantages, there remain some technical and regulatory challenges. Some climates, including Canadian, are more extreme, resulting in significant waste heat in summer, hence thermal storage and grain drying are being explored as options for the excess gas. In the winter, significant amounts of the biogas have to be used to maintain digester temperatures. Off-farm waste offers the potential for significantly increased output, but brings with it a range waste-disposal rules.
Photos
Farm - Cogeneration - Biogas, Ontario, Canada
Farm - Cogeneration - Reciprocating engine - Biogas, Ontario, Canada
References
Assume that electricity rate is $0.11/kWh and that propane fuel cost is $0.50/L. Initially assume no credits from GHG emission reductions or green power. Development costs are $10K for a feasibility study, $20K for engineering, $150K installed for the digester and associated works, and $1,500/kW for the reciprocating engine and generator. O&M costs about $5K/year (mainly for engine maintenance and refurbishments), and construction will take 6 months.
Assume financial conditions of 0% inflation and fuel cost escalation; 20-year project life with 6% discount rate; 100% agricultural loan available for 15 years at 6% interest. The income tax rate is 36% with 15% depreciation in year 1, with 30% per year thereafter.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
- For the heating load, typical values would be 70 W/m2 with a base case heating system seasonal efficiency of 65% and an additional 10% for hot water.
- The engine availability depends on the volume of biogas available - 155 m3 per day or 56,400 m3 per year. The Energy Model worksheet calculates how much biogas is consumed by the engine (see Energy Model worksheet, Proposed case system summary). For a 50 kW engine with a typical electrical energy efficiency of 30%, this will provide an availability of 2,853 hours for the year.
- The "Biogas Tool" user-defined facility can be used with the following data to give an annual biogas production: 140 dairy cattle; 545 kg average weight.
- Since electricity is net metered, the minimum engine-generator size has no effect on the overall economics except for the initial and maintenance costs. When choosing the size of the engine-generator, selecting an availability of around 50% allows for future increased biogas yields and for taking advantage of time-of-day electricity pricing. Short-term stopping of the engine for a few hours is possible without excessive build-up of methane pressure or cooling of the digester.
- GHG emission reduction is achieved for two reasons. First from the combustion of naturally occurring methane to carbon dioxide. Methane is 21 times more active than carbon dioxide and is produced naturally from the decomposition of the manure. Second, from the displacement of other fuels used for heating and electricity production.
- In Canada, the Tax Class 43.1 rule allows for 15% depreciation in year 1, with 30% thereafter. The user needs to toggle "Yes" on the line "Half year rule - year 1" of the Financial Analysis worksheet.
- The RETScreen solution shows the system to have limited financial viability. This is a reasonable reflection of the current situation. Many of the existing facilities have benefited from grants and other support. Currently there is significant activity to improve project economics through product standardization, utilizing off-farm organic wastes, electricity rate incentives and other measures. The following sensitivities are suggested: Electricity rate increased to 0.15/kWh; 15% reduction of initial costs; GHG credits at $10/tonne of CO2 over 20 years; 15% reduction in O&M costs; debt over 10 or 20 years.
Real project
Results
A farm located in Cobden, Ontario, Canada, has a co-generation facility that been in operation since May 2003. The facility consists of a complete mix mesophilic anaerobic digester and a 50 kW reciprocating engine-generator.
System description
The current feedstock to the digester is manure from the farm's herd of 140 dairy cows. From this, the digester produces some 400 m3 of biogas per day with an average methane content of 55%.
The types of engine most commonly considered for biogas cogeneration are spark ignition reciprocating engines (biogas only) and compression ignition reciprocating engines (using a mix of biogas and 10% diesel fuel for combustion stability). Micro-turbines can also be used.
This facility uses a dual-fuel compression ignition engine, which drives an alternator that produces some 700 kWh of electricity per day. This can either service farm electrical loads or be exported to the grid where it is traded in accordance with a Net Metering agreement (which means that the farmer is not paid for any net export of power over the year). An incentives scheme for selling of electricity is also available, but would require the farmer to lock into a 20-year rate with only partial index-linking.
The heat from the combustion process is used for heating of the digester and the farmhouse. The digester temperature is regulated to 40 °C, which is the optimum temperature for biogas production. During winter, the heat produced is just sufficient to meet these loads. Significant excess heat is available in summer, and ways to best utilize this heat, such as crop drying, are currently under investigation.
Lessons learned
The main operation and maintenance costs centre on the reciprocating engine. Due to the relatively high sulphur content in the biogas, engine oil must regularly be changed, with a major engine overhaul every three years.
There are multiple other potential benefits of this technology:
- Reduction of greenhouse gases through both the combustion of naturally occurring methane (which is some 21 times more active that carbon dioxide), and the displacement of other sources of energy. Greenhouse gas credits may also accrue to the farmer;
- Significant reduction of pathogens in the digester;
- Odour removal;
- Production of a high grade, low-pathogen, odourless, fast-acting fertilizer; and
- Reduced water pollution from farm slurry.
An important area of future consideration is importing off-farm organic waste to the digester to increase biogas production and provide a safer disposal facility.
The big picture
Modern biogas technology has become well established on European farms over the past 10 years, particularly in the central European countries of Germany, Switzerland and Austria. Recent years have seen the emergence of several farm biogas co-generation systems in Canada for electricity production and heating. One reason for the current emergence of this technology in Canada is the introduction of incentives for distributed generation using renewable energy. In addition, for the farmer, it represents another source of income, without the need to purchase expensive milk or other quotas.
Despite their obvious advantages, there remain some technical and regulatory challenges. Some climates, including Canadian, are more extreme, resulting in significant waste heat in summer, hence thermal storage and grain drying are being explored as options for the excess gas. In the winter, significant amounts of the biogas have to be used to maintain digester temperatures. Off-farm waste offers the potential for significantly increased output, but brings with it a range waste-disposal rules.
Photos
Farm - Cogeneration - Biogas, Ontario, Canada
Farm - Cogeneration - Reciprocating engine - Biogas, Ontario, Canada
References
- Foss, Aidan, "Personal Communication," ANF Energy Solutions Inc., 2007.
- Klaesi, Paul, "Personal Communication," Fepro Farms, 2007.
- Strehler, Benjamin, "Personal Communication," Genesys Biogas Inc., 2007.
