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Fair Oaks Dairy - Digester 2

Location Fair Oaks, Indiana
Project Type Farm Scale
Animal Type Dairy
Population Feeding Digester 9,000
Baseline System Storage Tank or Pond or Pit
Digester Type Mixed Plug Flow
System Designer DVO, Inc. (formerly GHD, Inc.)
Biogas Generation 1,200,000 ft3/day
Biogas Use Cogeneration; CNG
Generating Capacity 1,050 kW
Receiving Utility Jasper County REMC

Fair Oaks Dairy is located in Fair Oaks, Indiana, and has two anaerobic digesters onsite: a large mixed-plug flow and a smaller vertical-plug flow. The dairy has approximately 12,000 lactating cows producing manure that feed the anaerobic digesters. Currently, no codigestion is conducted, but in the past ethanol syrups collected from regional ethanol plants were codigested and typically amounted to 5 percent of the feedstock.

Biogas produced from the anaerobic digesters is used to generate electricity and is also being used to produce compressed natural gas (CNG) for use as a transportation fuel.

The larger digester (mixed-plug flow) began operating in 2008 and receives manure from approximately 9,000 dairy cows each day. The larger digester produces approximately 133 ft3 of biogas per head per day (based on 9,000 head, the biogas production is 1,200,000 ft3/day). End uses for biogas from this digester include on-farm electricity generation, use of waste heat to heat the digester, and CNG for use as transportation fuel in vehicles. The larger digester is equipped with a 1,059 kW genset, which is used to produce electricity for on-farm use, and the waste heat recovered from the genset is used to heat the larger digester. Any excess electricity after the on-farm electricity needs are met is sold to the local utility. The larger digester is also equipped with a gas cleaning system that cleans and scrubs contaminants from the biogas to meet purity levels for use as a renewable transportation fuel. The farm operator expects to use the majority of the biogas for the purpose of producing CNG.

The smaller (vertical-plug flow) digester began operating in 2003 and receives manure from approximately 3,000 dairy cows each day. The digester produces an estimated 60 to 70 ft3 of biogas per head per day (based on 3,000 head, the biogas production is 180,000 to 210,000 ft3/day). The smaller digester is equipped with two 350 kW gensets that are used to produce electricity for on-farm use, and any excess electricity produced is used at the dairy visitor center. Waste heat from the genset is recovered and used to heat the digester.

The total turnkey cost (or capital cost) for the larger digester is $12 million, and the equipment is estimated to have a project lifetime of 20 years. The farm financed approximately 99 percent of the up-front capital cost of the anaerobic digester using industrial revenue bonds. For this farm, the loan period was 15 to 20 years.

Annual operating and maintenance (O&M) costs for the large digester are estimated to be approximately 5 percent of the total capital cost (or approximately $600,000 per year). On-farm use of the generated electricity allows the farm to purchase less electricity for its operating needs. There are cost savings associated with the avoided electricity purchased for the farm and dairy visitor center. In addition, the recovery of waste heat from the engine/genset to heat the digester allows the farm to avoid purchase of heating fuel for the digester. There are cost savings associated with the avoided fuel purchase for digester heating.

As mentioned earlier, the farm operator expects the majority of the biogas produced from the digester to be employed in the production of renewable CNG. The renewable CNG is used to power CNG tractor trailers that deliver milk to processing plants in three Midwestern states (these CNG-fueled vehicles replaced diesel fuel-powered vehicles). The farm received a grant under a separate program for the extra CNG tanks to extend the range of these trucks powered by CNG. The farm has reduced its use of diesel fuel by 1.5 million gallons per year. There is a cost savings associated with the avoided costs of diesel fuel for dairy trucks. The surplus clean biogas not used for on-farm purposes will be piped and sold to a CNG fueling station (although the sale price of the CNG is unknown). It is estimated that after installation of the gas cleaning system in 2011 and the beginning of CNG sales to the fueling station, the simple payback period for the gas cleaning system project will be approximately 3 years. (See Biocycle article for details.)

The smaller digester is older, and the total costs for the unit are not known. The annual O&M costs for the smaller digester are estimated to be $100,000 per year.

Beyond the end-uses of biogas for electricity, waste heat, and CNG production, the digester has no other revenue streams.

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