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___________________________________ ___________________________________ ___________________________________ What Kinds of Digesters Fit into What Kinds of Farms and How Do They Work? ___________________________________ ___________________________________ Kurt F. Roos AgSTAR Program U.S. Environmental Protection Agency ___________________________________ ___________________________________ ___________________________________ Presentation Overview • • • • • • • ___________________________________ What are anaerobic digesters? What makes them work? What kinds of systems are there? Where do they make sense? What benefits do they offer? What do they cost? What is the status of US livestock digester? ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Introduction: Farm Processes BUILDING PRETREATMENT TREATMENT/ STABILIZATION STORAGE ___________________________________ LAND APPLICATION Above/below ground storage ponds, tanks, basins, pits Separation Liquid Slurry Semisolid Gravity Mechanical Chemical ___________________________________ Combined Treatment & Storage Lagoon Open Treatment Lagoon Storage Pond Anaerobic Digesters Storage Pond Aeration Storage Pond ___________________________________ ___________________________________ Surface or Injection ___________________________________ ___________________________________ Evaporation Pond Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 23 ___________________________________ What are Anaerobic Digesters? ___________________________________ Biological treatment/stabilization systems applicable to liquid, slurry, and semi-solid waste that collect and combust off-gases. ___________________________________ Digesters separate manure treatment from storage functions which can result in lower initial installation costs for new or expanding farms ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Typical Digester Configuration ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ What Makes Digesters work? ___________________________________ BIODEGRADABLE FRACTION Anaerobic digestion is a biological process. It occurs in an oxygen free environment. ___________________________________ Protein Carbohydrate Hemicellulose ___________________________________ Acitogenic Phase Acid Forming Bacteria Acitogens VOLATILE ACIDS Proprionic Acetic (Intermediate Odor Producing (Compounds) Methanogens ___________________________________ ___________________________________ Methanogenic Phase Methane Forming Bacteria Methanogens ___________________________________ BIOGAS 70% CH4 30% CO2 Trace H 2S Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 24 ___________________________________ Industry Interest in Anaerobic Digestion Technologies ___________________________________ ___________________________________ 1) Offer Air Quality benefits -Control odors from storage and field application -Reduces Greenhouse gases (methane) -Controls other emissions (H2S) ___________________________________ 2) Offer Water Quality benefits ___________________________________ -Stabilize manure organics (BOD) -Significantly reduce pathogens -Provide nutrient management predictability and flexibility ___________________________________ 3) Offer return on Investment -Energy revenues -Carbon Markets -Greenhouse Production -Peat market (dairy only) -Bedding offsets (dairy only) ___________________________________ ___________________________________ Example Retrofit Project ___________________________________ Retrofit Plan ___________________________________ ___________________________________ ___________________________________ After Before ___________________________________ ___________________________________ ___________________________________ Anaerobic Digester Types Characteristics Digestion Vessel Level of Technology Supplemental Heat Total Solids Solids Characteristics HRT (days) Farm Type Optimum Climate for Energy Production Covered Complete Mix Lagoon Digester Deep Lagoon Round/Square In/Above Ground Tank Low Medium No Yes 0.5 - 3% 3 - 10% Fine Coarse 40-80 Dairy, Hog Temperate and Warm Climates 15+ Dairy, Hog All Climates Plug Flow Digester Rectangular/Horse Shoe In-Ground Tank Low Yes 11 - 13% Coarse 15+ Dairy Only All Climates ___________________________________ Attached Film ___________________________________ Tank Medium No <1% Very Fine 2+ Dairy, Hog Temperate and Warm Climates ___________________________________ ___________________________________ ___________________________________ ___________________________________ Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 25 ___________________________________ Selecting a Digester - Hog and Dairy industry constitute >90% of market potential ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Attached Film Covered Anaerobic Lagoons USDA Practice Standard 365, Ambient Temperature Flush Manure handling ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Solids Separation (Dairy Only) ___________________________________ ___________________________________ ___________________________________ ___________________________________ Lagoon Considerations ___________________________________ • Sized to maintain bacterial populations to ensure year round manure treatment and gas production ___________________________________ – Loading Rate and Hydraulic Retention Time are key – Dairy requires separation ___________________________________ ___________________________________ ___________________________________ Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 26 ___________________________________ Cover Considerations ___________________________________ • Functions to continuously move gas to a gas take-off point ___________________________________ • Three considerations: ___________________________________ – Fabrication: Cover assembly and installation critical • Quality, non-leaking seams are key (air intrusion) – Materials: Need to resist sun, temperature extremes • Tearing, blistering, and de-lamination – Design: Stress caused by wind rain and other natural occurring events • Rainfall accumulation can interrupt gas flow • Stress can tear or sink covers causing catastrophic failure ___________________________________ ___________________________________ ___________________________________ ___________________________________ Cover Types • Bank-to-Bank: Field fabricated cover completely spans lagoon surface and edges secured in perimeter trenches – All off-gases are captured – All precipitation is excluded from lagoon – Requires proper floatation • Modular: Uses smaller multiple cover sections over 50-90% of lagoon surface area, secured w/ tether ropes, cable, or perimeter trenches – Modules fabricated off-site and assembled on-site – Can be installed in stages reducing one-time capital outlay – Rainfall is not excluded – Requires proper floatation ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Cover Types: Illustrated Bank-to-Bank ___________________________________ ___________________________________ ___________________________________ Modular Cover ___________________________________ ___________________________________ ___________________________________ Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 27 ___________________________________ Material and Design Failures ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Plug Flow Digester USDA Practice Standard 366, Controlled Temp. ___________________________________ ___________________________________ Scrape Dairy Manure Only ___________________________________ ___________________________________ OR ___________________________________ ___________________________________ ___________________________________ Complete Mix Digester USDA Practice Standard 366, Controlled Temp. Scrape Manure Handling OR Process Water Added + ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 28 ___________________________________ Attached Film ___________________________________ Flush Manure Handling ___________________________________ Separation (All livestock) ___________________________________ ___________________________________ + ___________________________________ ___________________________________ ___________________________________ Gas Use: Flares ___________________________________ Odor Control and Greenhouse Gas Mitigation ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Gas Use: Heat Boilers ___________________________________ Forced Air ___________________________________ ___________________________________ ___________________________________ Hot Water Storage Hot Water Use ___________________________________ ___________________________________ Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 29 ___________________________________ Gas Use: Electrical Generation Gas Handling Recip. Engines 40-250kW ___________________________________ ___________________________________ ___________________________________ C O M P ___________________________________ O N E Engine Controller N T Electric Metering ___________________________________ S ___________________________________ ___________________________________ Gas Use: Electric More Engines ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Gas Use: Gas Purification Emerging process ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 30 ___________________________________ US Background ___________________________________ Digester Distribution 2005 ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ @100 operational @90 in planning ___________________________________ Project Types • ___________________________________ On-Farm or Farm Scale: System is owned and operated by farm owner/manager ___________________________________ – Currently the predominant project type in the U.S. • Regional or Centralized Digesters: Off farm management and operation with a third party – Ideally located at a large energy (electric or heat) consuming source or interconnection point (feed mills or utility substation) ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ General Costs: Livestock Basis Digester Type Attached Media Complete Mix Covered Lagoon Plug Flow Cost per Cow (1,400 lbs.) ___________________________________ ___________________________________ $500-800 $400-700 ___________________________________ $300-1,000 $400-700 ___________________________________ Swine equivalents: 4 sows = cow;10 feeder pigs = cow Most important factor affecting Covered Lagoon cost is process water Higher HRT = larger lagoon = more surface area to cover = higher cost ___________________________________ ___________________________________ Note: Cost assumes all manure is collected and include engine gensets and separators (dairy systems) Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 31 ___________________________________ Cost Ranges Can Be Larger ___________________________________ ___________________________________ Financial Performance Breakeven Price (kWh) Costs of 35 Commercial Digester Projects ___________________________________ $0.30 $0.25 $0.20 ___________________________________ $0.15 $0.10 ___________________________________ $0.05 $0.00 $- $5,000 $10,000 $15,000 $20,000 $25,000 Cost per kW Installed ___________________________________ ___________________________________ ___________________________________ ___________________________________ AgSTAR Resources ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Thank You ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ AgSTAR National Conference, Sacramento, Nov. 27-28 ___________________________________ See the AgSTAR Website at www.EPA.GOV/AGSTAR Proceedings of the 6th Annual Arizona Dairy Production Conference Ô October 11, 2007Ô Phoenix, AZ - 32
