The Anaerobic Process to Make Biogas In the absence of oxygen naturally occurring bacteria will break down manure The break down and conversion to methane occurs in four basic steps. –Hydrolysis –Acidogenesis –Acetogenesis –Methanogenesis The final stage methanogensis is the actual break down of the immediate compounds to methane Biogas is usually composed of 55-75 percent methane. Carbon Dioxide and Hydrogen Sulfide make up the bulk of the remainder.
Three Main Types of Digester Design Options 1.Complete Mix (CSTR) – fully homogeneous contents 2.Plug Flow – mimics a series of laterally mixed units 3.Lagoon – energy recovery from treatment oriented design
Other Digester Types 1.Batch- fed reactor, such as the anaerobic sequential batch reactor (ASBR) 2.Temperature- phased anaerobic digester (TPAD) 3.Suspended particle reactor 4.Anaerobic filter reactor 5.Upflow solids reactor 6.Continuously stirred tank reactor with solids recycle 7.Upflow anaerobic sludge blanket reactor 8.Anaerobic pump digester 9.Fluidized- and expanded- bed reactors 10.Fixed film anaerobic digester AgSTAR August 2002 Haubenschild Farms Anaerobic Digester Final Report
Complete Mix Digester Contents kept mixed or periodically mixed Batch or semi-batch operation Mixing accomplished using mixer or pump High rate and extent of biogas production Complex solids handling Comparatively expensive Common with smaller systems Lower L/S ratios (more water [+ & -]) High level of mechanical wear Barn. ManureSlurry Flash Mix Water Solids Separator Water CSTR Digestor Biogas
Plug Transport Plug Flow Digester Mixing tankPF Digestor Biogas Not 100% Necessary (Slurry in Digester) PROS Low maintenance Batch or semi-batch operation Rapid recovery time/ low retention time needed Can be used effectively in multiple climates CONS Comparatively expensive Smaller reactor volume Labor intensive material handling issues Barn. Manure Water Solids Separator
Covered Lagoon Barn. Manure Water Solids Separator Biogas PROS Least Expensive Low Maintenance Material handling Can handle low solids manure CONS Land availability Efficient only in high temp climates High retention time needed b/c of low low efficiency and liquid amounts
Barn Screen Digestor Biogas Milking Parlor or other market. Heaters Biogas Storage Gas Compressor IC Engine Electricity Generation Heat Recovery Liquid Solids Separator Digestor Heating (winter) Compost Potential Protein Recovery Liquid Fertilizer Cultured Growth Plant Bedding Liquids Storage Tank/ Lagoon To Grid
General Benefits of a Digester System Odor Control Cash savings Reduced risk of being subject to legal action Renewable Energy Production –Heat –Electricity Pathogen Reduction Greenhouse gas reduction Reduction in TOD (Total Oxygen Demand)
Two Sites in Mississippi The Land Water Timber Resource Board has funded Mississippi Alterative Energy Enterprise (MAEE) to construct two Methane gas capture systems. Swine system located in Montpelier, MS Dairy system located in Forest, MS
Dairy System Dairy manure characteristics matches well with a plug flow manure. –Due to the high solid content dairy manure can easily be scraped versus flushed –A scraping system adds no or very little water into the system. Thus a plug flow system is common. However, this system at Forest is a hybrid system. It utilizes a high pressure low volume flushing system. The manure will enter the digester at about 3- 6% solids.
Dairy Methane Gas Capture System Location: Mills Dairy in Forest, MS Farmer: Quentin Mills Total Project Cost ~$750,000-$800,000 Digester system cost: ~$282,000 Gas Use: Heating and Electricity –Heating – direct use –Electricity- through methane capable genset Estimated Annual Power Savings –Farmer: $25,000 Construction is due to be completed by April 22, 2004. (Earth Day) A tour will be scheduled in the afternoon.
Why Here? Why Now? Mills Dairy (a 400 head dairy) –Within the range of successful digester farms –Accurate representation of an average to high number Mississippi Farm. Farm Bureau pointed us toward the Mills Dairy because they were transitioning from pasture to a confined operation This transition time was a perfect penetration point due to capital expenditures, construction economies of scale and need for manure management changes. (lagoon would not be large enough)
Dairy System Schematic Spray irrigation Genset methane Existing Lagoon Solids Separator Compost Equalization Basin Anaerobic Digestion Barns Electricity to operate system, excess to Grid Clear Water Offset purchased Propane Recirculation for barn flushing
Swine Methane Gas Capture System Review Location: M&N Nursery in Montpelier, MS Farmer: Mike Shinn LWTRB Grant: $114,000 Prestage has donated $20,000 Gas Use: Heating and Electricity –Heating – direct use –Electricity- through methane capable genset Estimated Annual Savings –Farmer: $11,587 –Prestage:$3,755 (see next slide) 8 barns = ~ 6,500 hogs at an average weight of 38 pounds per hog. (grown from 12-50lbs) M&N is paying ~ 7.5 cents per kwh for power and consuming ~ 88,685 kwh per year. In 2000 M&N paid $6,659 Because M&N is a Prestage grower they have a capped cost of 45 cent per gallon of propane. However the total propane cost in 2000 was $16,614
Swine System Savings ($.85/ gal $.07 retail $.02 sell back) retail actual =.075 per kwh (Total Savings $15,343)
IC Engine Liquid Fertilizer Cultured Growth Biogas for direct burn Covered lagoon Existing lagoon Liquids pumped from lagoon Genset To the grid Used on farm barn biogas M&N Swine System
Swine System Technology- This system utilizes a covered lagoon approach Markets for Biogas- The biogas will fill all heating needs and will then flow over to a generator to supplement or replace power needs. Construction- Construction should be complete by April 22,2004 Paybacks was based on Propane cost offset and on gas production. However, assuming average production and $1.00 per gallon of propane cost the system should be able to pay itself back within 5-6 years simple payback
Swine Activities to Date Many necessary “back office” issues have been completed. These activities pave the way for construction activities Meeting with DEQ to determine possible permitting Construction contracts in draft form Feasibility study performed earlier by Phil Badger Detailed financial models produced Investment secured from Prestage Farms. (09-12-03)
Swine Activities to Date cont… Soil samples have been taken for digester site to determine necessity for clay lining and amount of clay needed Educated participating farmer on the system Complete working agreement and contracts Identify planning assumption Engineering blueprints Finalize equipment/ contractors agreements Procure all equipment and materials Site Preparation
Key Closing Thoughts Economics or regulatory demands will drive the proliferation of these systems in the Southeast. Types of manure match well with certain technologies at this point; however, the lines are being blurred by new technologies. A predetermined market for power or biogas product is key to the economic viability Relationship with the Local Power Provider is key