Posted by Zach Bouchard on February 22, 2009 at 17:22:03 from (64.136.27.226):
In Reply to: Biogas digester posted by Farmall_51 on February 21, 2009 at 20:51:27:
I don't know how cost effective it is but here's the story I found on a local dairy farm.
Vander Haak Dairy The Vander Haak Dairy is a family run farm operating in Lynden, Washington since 1968. It became the first dairy in Washington State to install a commercial anaerobic digester. The system utilizes a patented plug flow digester, designed by GHD Incorporated of Wisconsin, that handles manure from three dairies and up to 1500 dairy cows (as currently configured). In general, plug-flow digesters have few moving parts and work well with dairies, like Vander Haak, that collect cow manure by scraping instead of flushing the manure with water. The unprocessed manure is collected in a receiving pit and pumped directly into the anaerobic digester vessel where it undergoes a two-stage digestion process. In the first stage, raw manure is mixed and heated to 1000F, using the reclaimed waste heat from the engine/generator set. This facilitates the growth of acid forming bacteria that breaks down the raw manure into simpler volatile fatty acids and acetic acid. The slurry then gravity feeds into the second stage of the digester where methanogenic bacteria convert the volatile fatty acids into biogas. The second stage of the digester process takes about 20 days, after which the remaining materials flow into an effluent collection pit where they are further processed. The dairy is currently assessing the impact of other available feedstocks on the system processes. The biogas generated in the digester is collected and burned in a natural gas fueled reciprocating engine set modified to burn biogas. Waste heat from the engine set is 5 recovered and used to heat the digesters (30 to 60 percent is used), and could potentially be used in the future to provide for other thermal needs at the dairy. The engine genset produces about 285 net kW of electricity (parasitic load is 15 kW) which is sold to the power grid. This is enough electricity to serve approximately 180 average homes. The remaining digester effluent is separated into a solid and liquid stream for further processing. The separated solids are currently processed into bedding materials for the dairy or sold to other dairies for bedding. Additional work is underway to develop this material into a compost or soil amendment suitable for sale to commercial nurseries as a replacement to peat moss. The liquid stream from the digester is used as a high-value fertilizer, rich in phosphorous and useable nitrogen.
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Today's Featured Article - Talk of the Town: The Saga of Grandpa's Tractor - by The following saga is from the Tractor Talk Discussion Forum. Someone. The saga starts with the following message: Hey guys I have a decision to make. I know what you all will probably suggest and it will probably agree with me way down inside, but here it is. I have a picture blown up and framed in my "tractor room" of a Farmall M. It was my Grandpa's tractor, of which whom I never got to meet. He froze to death getting this tractor out of the barn to pull a truck out of the ditch before I was born. Anyway my dad and aunt had to sell it at the auction,
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