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Converting Dairy Manure into Energy.An introduction to anaerobic digestion of farm waste
Stefan GrimbergAssociate Professor
Dept. Civil Environ. EngClarkson University
Thank you to Floyd Schanbacher
Anaerobic Digester Potential Benefits
Odor Control Reduced liability
Manure stabilization Help with nutrient management Soil stability
Energy generation Offset farm electricity requirements from grid Sale of extra energy Heat generation to reduce fuel required
Reuse of bedding solids Offset bedding cost
Plug Flow Digesters
Little mixing Few mechanical parts Simple
Mixed Digesters
Mechanical mixing in tankMore gas productionSlightly higher capital cost
Behringen co-fermentation plant in Germany
Community Digester
Digester Feed
Large-scale Digester Performance
Capital Cost of Manure Management Technology
Source: AgStar Publication:
Digester economics
Dr. Fick’s estimated fixed of $660 per cow is a little low for the farms we are looking at.
Tinesdale farm (in Minnesota), with1800 cows, invested about $1,000 per head.
Good estimate $1,000 per cow? At this capital assumption AD system become
economical based on sold energy alone at power sale price of $0.09/kWh.
(Mehta, 2002)
Case Study
•Gordondale Farms, Nelsonville, WI•750 head dairy•Sell biogas to utility that generates electricity on site, utility owns and operates generator•Sell at 0.015 $/kWh generated
Martin, J.H., 2005. An evaluation of a mesophilic, modified plug flow anaerobic digester for dairy cattle manure. Final report for EPA contract GS10F-0036K
Summary
Martin, 2005
Martin, 2005
Martin, 2005
Martin, 2005
Martin, 2005
Martin, 2005
Martin, 2005
Martin, 2005
Economic Evaluation
Capital costs with co/gen: $748,000 Annual sale of power: $18,396 Avoided annual bedding cost: $60,000 Sale of extra solids: $8,600 Total benefits: $86,996 Payback period: Approx 6 years.
Digester Systems Model
Digester Solids Sep.
Cogen
ManureOther Input
Biogas
Electricity offsetSurplus electricitySurplus heat
Spread liquid fraction
Solids for beddingSale of solidsSolids field application
Heat
Example
500 cow dairy Free stall barn Scraped manure Include flush from milking parlor Northern NY
Model Estimate: 500 cow dairyItem Cost/Benefit
Capital Cost Digester/Cogen system $656,180
Total Annual Cap. Cost over 10 yrs $68,774
Annual Operating Costs Maintenance, Repair $23,553
Potential Annual Benefits Fiber sales $9,133
Electric Sales (surplus) $17,707
Thermal Sales (surplus) $12,368
Methane Credit $7,646
Renewable Energy Tax Credit $4,203
Farm savings-Electric (internal) $25,171
Farm savings-Thermal (internal) $8,495
Tax Offset $16,739
Onsite Fiber value $10,000
Total Annual Benefits $111,463
Annual Net Benefit per Cow $38.27
Annual Net Benefit per Cow if excess heat cannot be sold $13.54
Annual Net Benefit per Cow without excess heat and methane credits -$1.8
Run Digester Model
Demonstrate: Effect of size Power cost Bedding off set
Any scenarios of interest?
Conclusions
Anaerobic digestion of manure has significant potential to decrease fossil fuel use in rural areas.
Community digesters may be very cost effective due to larger scale and mixed feed composition