Coupling dairy manure anaerobic digesters with commercial greenhouses – an assessment of technical and economic feasibility
•
2 likes•1,043 views
The full proceedings paper is at: www.extension.org/72775 U.S. Secretary of Agriculture Tom Vilsack declared a goal in 2011 of bringing one new manure-based anaerobic digestion (AD) system on-line per week; however, there are some real challenges that need to be overcome to make this goal a reality. To help achieve this goal, the economics of farm-based AD systems need to be improved. Making better use of AD surplus heat (mostly released to the ambient atmosphere), improving generator efficiency, and electricity use are real opportunity that needs to be flushed out. Greenhouses in the Northeast and similar climates are energy-intensive and therefore an excellent candidate to partner with AD systems to utilize their engine waste heat and electrical energy.
Recommended
More Related Content
What's hot
What's hot (20)
Viewers also liked
Viewers also liked (20)
Similar to Coupling dairy manure anaerobic digesters with commercial greenhouses – an assessment of technical and economic feasibility
Similar to Coupling dairy manure anaerobic digesters with commercial greenhouses – an assessment of technical and economic feasibility (20)
More from LPE Learning Center
More from LPE Learning Center (20)
Recently uploaded
Recently uploaded (20)
Coupling dairy manure anaerobic digesters with commercial greenhouses – an assessment of technical and economic feasibility
- 1. Coupling Dairy Manure Anaerobic Digesters with Commercial Greenhouses: An Assessment of Technical and Economic Feasibility Tim Shelford, Ph.D. and Curt Gooch, P.E. Biological and Environmental Engineering Cornell PRO-DAIRY 2015 Waste to Worth Conference
- 2. Project Sponsors USDA-Hatch (research) and Smith Lever (extension) Federal Formula Funds Cornell PRO-DAIRY Program Some equipment used in monitoring supplied by New York State Energy Research and Development Authority (NYSERDA)
- 3. Thanks to: Dairies Synergy Dairy (Covington, NY) Stonyvale Farm (Exeter, ME) Sunnyside Dairy (Venice, NY) Willet Dairy (Locke, NY) Commercial Greenhouses Challenge Industries (Ithaca, NY) Durham Foods (Port Perry, ON)
- 4. Presentation Summary Project is looking at the technical and economic possibility of a synergistic relationship between dairy manure based anaerobic digesters and commercial greenhouses. Project consists of field monitoring of existing systems, development of a three computer simulation models, and extension/outreach material development/delivery. October 2012 to September 2015 Preliminary results are showing considerable promise
- 5. Farm Manure Management Needs/Wants/Goals Odor Control Pathogen Reduction Energy Greenhouse Gas Reduction Fertilizer for Field Crops Low Cost Manure Application Nutrient Concentration/Exportation Revenue Anaerobic Digestion
- 6. 120 117 1,680 150 25 4 390 18 94 37 66 9891 310 105 88 311 49 31 1,265 134 208 480 301 114 145 260 15 247 84 33 19 147 85 20 63 118 590 680 36153 17 80 9 13 23 1.4 20 AK- 1.3 U.S. Dairy Farm Demographics Thousands of Cows per State About 60,000 Dairy Farms in the US and just 85 intensively managed anaerobic digestion systems.
- 8. AD: Electricity Production in New York State Most independent power producers (dairy farms) are controlled by “Net Metering” regulations Limits the capacity of the generating system to 1 MW Farms are credited when they put surplus power onto the grid Farms are debited when they draw power from the grid Accounts are settled once per year if surplus is credited to the grid and paid the avoided cost.
- 10. AD: Heat Production Heat is recovered from the engine-generators through engine-oil heat exchangers and coolant loops Recovered heat is used to maintain temperature in the digester, which is typically 100F
- 11. AD: Heat Production As much as 75% of the produced heat is wasted Excess heat is typically dumped to the ambient using large radiators Some (few) farms use recovered heat in a beneficial manner… Waste heat usage represents a valuable opportunity for farms
- 12. Project Goals: Collect energy production and use data from operating digesters and greenhouses Work with the AD partners to measure how much waste heat/power they have, and options for better using it Work with the greenhouse partners to explore technical feasibility of locating a greenhouse adjacent to an AD project Use the data to validate a digester and greenhouse energy production and use model
- 13. Project Goals: Develop user friendly computer programs to: Predict the surplus heat and electricity available from digesters of user specified size, design and operational characteristics. Predict the required heat and electricity for a greenhouse of user specified size, design and operational characteristics. Use the output from the AD computer program, and determine the size of greenhouse that could be supported by the specified digester, or the portion of the energy usage of a specified greenhouse that could be digester supported.
- 14. Monitoring Surplus Heat Of Digesters
- 15. Monthly CHP-Digester Heat Flows
- 16. Monthly Heat Requirements for Digester Function
- 17. Anaerobic Digester Surplus Heat
- 18. Greenhouse Heating and Cooling: Greenhouses typically heated to: 65 to 75F Typical systems burn CH4 in a boiler and distribute heat through hot water pipes and radiators 23
- 19. Greenhouse Purchased Heat In General, it can cost 10 - $20 per sq. ft. per year to heat an Upstate New York greenhouse.
- 20. Out of Sync Heat Production and Consumption (3,200 Cows) (1,000 heads of lettuce daily)
- 21. New York Freestall Barn Dairy Monthly Electricity Use Source: Adapted from Peterson, Northeast Agriculture Technology Corporation 2014
- 22. NY Greenhouse Yearly Electricity Usage
- 24. Anaerobic Digesters and Greenhouses: Mutual Benefits Anaerobic Digesters Can sell their electricity for a much better price than what they currently receive Can find a use for the considerable waste heat they produce Greenhouses Can greatly offset their production costs (~30%) through reduced heat and electricity purchases
- 25. Recommendations for Greenhouse and Digester Synergies Size greenhouses according to market demands: Utilities (heat and electricity) represent 1/3 of production cost in NY Labor and packaging make up the bulk of the remaining cost of production Locate system where backup source of heat and power exists Digester engine-generators require regular maintenance and while digesters can tolerate periods with no heat production, greenhouses cannot
- 26. Recommendations for Greenhouse and Digester Synergies (con’t) CO2 utilization in greenhouses requires extensive and expensive gas conditioning/cleanup May not be able to use CO2 from digesters (though other sources may still be economic) Greenhouse should be independently operated Dairy farmers are focused on making their dairy farms profitable
- 27. Digester Simulation Computer Program
- 28. Greenhouse Simulation Computer Program
Editor's Notes
- The decisions about AD project boil down to economics. One major consideration in NY is getting more value from the energy produced by the digester
- Unfortunately there is not a good market or incentive to produce extra electricity in New York State New York independent power producers are controlled by “Net Metering” regulations Farms are credited when they put surplus power onto the grid and debited when they draw power from the grid These laws limit the capacity of the generating system to 1 MW Accounts are settled once per year with a check issued for any surplus remaining, or a bill if there is a deficit
- New York farms are only paid the “avoided cost of production”. Typically only $0.03 to $0.05 per kWhr Whereas industrial consumers in NY pay on average about 11 cents per kWhr Other forms of renewable energy receive subsidies in the form of a “feed-in tariff” which means they are paid a premium, or extra money for producing renewable power. In New York, wind and solar energy receive benefits, but biomass renewable energy does not. Other locations encourage renewable energy production through very generous “feed-in tariff” rates, Germany pays 31 cents per kWhr for manure derived electricity, and Ontario in Canada pays 72 cents per kWhr for agricultural roof mounted solar energy. This is even though Biomass derived electricity is consistent and predictable, unlike wind and solar
- New York farms are only paid the “avoided cost of production”. Typically only $0.03 to $0.05 per kWhr Whereas industrial consumers in NY pay on average about 11 cents per kWhr Other forms of renewable energy receive subsidies in the form of a “feed-in tariff” which means they are paid a premium, or extra money for producing renewable power. In New York, wind and solar energy receive benefits, but biomass renewable energy does not. Other locations encourage renewable energy production through very generous “feed-in tariff” rates, Germany pays 31 cents per kWhr for manure derived electricity, and Ontario in Canada pays 72 cents per kWhr for agricultural roof mounted solar energy. This is even though Biomass derived electricity is consistent and predictable, unlike wind and solar
- For this reason farms do not always operate their generators at full capacity. As we can see in this chart the time on line for these 7 farm generators is less than 100%. This may be due to engines going down for maintenance, or regular oil changes, or other more serious problems. The capacity factor is defined as the actual amount of energy produced, divided by the amount of energy that could have been produced. This means that though the generator was running, less biogas was fed to it than was required to operate at peak output. Generally farms produce electricity to offset their expensive power purchases. There is little incentive to produce more power than that.
- Another potentially valuable byproduct of digestion is surplus heat Heat is recovered from the engine-generators through engine-oil heat exchangers and coolant loops As the generators only operate at 18 to 35% efficiency, there is a large amount of heat produced. The primary use of this heat is to maintain the temperature of the digester.
- As much as 75% of the produced heat is wasted, typically through large radiators Though some farms use recovered heat in dairy milking operations to provide hot water for cleaning. Waste heat usage represents a valuable opportunity for farms Waste heat and surplus power from digesters could provide the energy input for greenhouses
- so that we can characterize exactly how much waste heat and surplus power might be available from an AD project, and the demand for heat and electricity from typical commercial greenhouses in the Northeast.
- The goal is that these user friendly computer programs will expand the project’s utility beyond the farms we are directly monitoring. In addition, the programs will allow the users to identify how operational decisions such as importing food waste could affect the heat and power output of their systems. Greenhouse users can investigate different strategies for supplemental lighting, temperature set points, and other factors that impact their energy usage.
- For the data monitoring component of the project We have collected (and continue to collect) data from four dairy AD projects, and two commercial greenhouses. To measure the surplus heat produced by an anaerobic digester we used a Btu meter that measures heat flow through the radiator using two type of measurement. Thermocouples are installed on the supply (hot) and return (cold) lines to measure the temperature drop of the fluid in the heat pipe. A flow meter measures the rate of fluid flow Using the delta T, the flow rate and the specific heat of the fluid the meter automatically calculates and stores the amount of heat lost or gained
- As we can see in this chart, digesters require the most heat to operate when the weather is coldest Though heat is lost through the digester to the environment, the largest use of heat is in heating up the incoming manure to the digester operating temperature. A few digesters use heat exchangers to recover the heat from the effluent to warm the influent, however that can add system complexity and cost through increased maintenance, and most digesters have more than enough heat anyways.
- As we can see in this chart, digesters require the most heat to operate when the weather is coldest Though heat is lost through the digester to the environment, the largest use of heat is in heating up the incoming manure to the digester operating temperature. A few digesters use heat exchangers to recover the heat from the effluent to warm the influent, however that can add system complexity and cost through increased maintenance, and most digesters have more than enough heat anyways. The major difference between Stonyvale and the other two farms is that Stonyvale digester serves only 870 cows vs 3200 and 3500 for Sunnyside and Willet. However Stonyvale supplements their manure with significant co-digestion, and all three digesters produce enough biogas to fuel 1 MW generators.
- From one farm we can see the results of the monitoring. As expected the amount of surplus heat falls off during the winter, and then picks up again in the spring.
- From one farm we can see the results of the monitoring. As expected the amount of surplus heat falls off during the winter starting in November, and then picks up again in the spring.
- Unfortunately digesters require the most heat to operate in the winter time when ambient temperatures are cold. This is the same time that greenhouses use the most heat too. However, typically digesters produce so much waste heat that they usually still have a large surplus even in winter. In this figure the surplus heat of a 3200 cow digester is plotted along with the heat required by a medium sized commercial greenhouse capable of producing 1000 heads of lettuce per day. Even in the coldest part of winter there is more than enough surplus heat to provide for the greenhouse.
- Electricity use on dairy farms is relatively constant year round with the exception of ventilation requirements Large fans are typically needed to provide cooling for the cows in the late spring and summer months For this reason, electricity usage peaks in the summer
- Greenhouse energy use in vegetable production is heavily influenced by supplemental lighting. For consistent year round production, significant energy is required to provide artificial lighting through the darker winter months.
- Fortunately Electricity use by farms and digesters is complementary One aspect of the electricity synergy is that due to net metering laws, digesters can “store” any surplus power they produce on the grid. So even if the demands of the greenhouse and digester were in sync (as for heat requirement) it would not matter as long as the digester produced enough electricity for both operations over the course of the year. However, there is a significant demand charge for providing power to the farm, and reducing peak usage can greatly decrease the cost of power.
- The final recommendation on the previous slide was that greenhouses should be independently operated. One alternative to having many small independent greenhouses is to have a food hub operations model In such a system seedlings are grow in a single centralized operation where an expert grower can supervise them closely during this critical stage. When they are ready to transplant, the seedlings are then trucked to finish their growth at smaller distributed operations, located to take advantage of inexpensive heat and power.
- On the return trip, the truck brings with it the full sized plants, on specialized racks, back to the centralized operation. At the centralized operation, the racked plants can be harvested, packaged and stored for later shipping to market. This greatly reduced the cost when compared to operating many small single greenhouses, though removing the need to duplicate expensive production steps at each small location. In addition it reduces the need for expert growers, and shares management, marketing and other clerical duties that would have to be performed by a single person at each small greenhouse. This operations model is the most likely to succeed with paired greenhouse/digesters as most digesters are not nearly large enough to provide enough heat to power an economically viable single operation.
- This is a screen capture of the Anaerobic digester simulation program. It allows a user to input the characteristics of the farm and digester and how it’s managed/operated. The program then predicts how much surplus heat and electricity the digester produces, and when it’s available.
- This is a screen capture of the greenhouse model, which is quite similar to the digester model. It allows a user to define a greenhouse based on it’s characteristics of construction and operation, and then predict the magnitude and timing of energy usage. Both of these programs allow the user to use estimated (suggested) values for many of the input parameters, if a farm doesn’t have that information readily available. These programs also allow a user to save and load projects so that a user can quickly see the effect of varying different operational and construction parameters on energy flows.