The farm produces 50,000 gpd of manure and other materials for treatment.
It is scraped to a pit, from which it gravity flows to the digester. They separate out their digested solids from using an Ag Environmental Solutions (AES) designed separator. The digested solids are used for bedding, and occasionally sold to neighboring farms.
|Farm Name:||Tinedale Farm|
|Herd Size:||2,400 (1,800 milking)|
|Collection Method:||scrape to pit then gravity flow|
|Bedding Type:||digested solids|
|Digester Type:||complete-mix (see notes)|
|Digester Notes:||designed as TPAD in plug-flow shape, converted to complete-mix due to problems with thermophilic phase, fixed cover|
|Date Operational||July 2003 (as meso only)|
|Design HRT:||20 days|
|Current HRT:||19-20 days|
|Design solids %:||9-10%|
|Current solids %:||~8%|
|Biogas Use:||electricity, heat (375 kW)|
|Solids Separation:||yes, post digestion, AES separator|
|Solids Use:||bedding, sales|
|Farm Owns:||digester, energy generation|
|Digester Designer:||Ag Environmental Solutions, LLC, and STS Consultants, LTD|
|Performance Data:||200,000 cfd biogas|
|Measuring Period:||6 months|
Tinesdale Farm installed a temperature phased anaerobic digester (TPAD) in 2000 and 2001.Their digester designed by AES and STS Consultants, is the first application of a TPAD system to a dairy operation in the United States. The TPAD system, to which the Iowa State University Research Foundation, Inc. owns the patent, was adapted from a partially built plug-flow type digester, and so bears the same horseshoe shape as those systems. Following numerous technical difficulties with the thermophilic phase of the system (see the History section of this profile for more details on these), the owners have switched to operating the system as a complete-mix digester in the mesophilic (~100°F range only. The digester volume is approximately 900,000 gallons, has three chambers, and measures 70'W x 135'L x 16'D. The digester is fixed and they do not use biota recycling. The manure is mixed using draft tube mixers.
Outputs and Uses
The digester has operated in steady state for the past six months. During that time it has averaged about 200,000 cfd of biogas production at about 65 percent methane content. Tinesdale now uses both an iron sponge scrubber to remove H2S and a coalescing filter to remove moisture prior to combustion. Biogas is used to fire a 375 kW Waukesha engine-generator set consistently near its rated capcity. They are recovering heat from the engine which is used to heat the digester. They have excess heat, but currently have no plans to use it in any other way.
Moisture in combination with trace amounts of H2S in the biogas has been a big problem for Tinedale's engines. The and H2S solution kept getting onto the cylinders and taking the oil off the liners causing excessive wear. They have had to fully tear down the engines twice for repair. Other routine maintenance needs for the digester and engine-generator set were not available.
AES and STS Consultants, designed and built a TPAD system at Tinedale Farm in 2001. In June 2001, they started running the digester at mesophilic temperatures. After the system stabilized, they increased the temperature in the first phase to thermophilic levels (~131°F), but found that the heat exchanger was too small to cool the manure back down to mesophilic temperatures at the end of the phase. This resulted in the first digester shutdown. During the second startup in February 2002, they seeded the digester with biosolids fro the Appleton wastewater treatment plant. Subsequent restarts in 2002 and 2003 were plagued by technical problems including engine breakdowns, and failure of the thermophilic cultures to develop as predicted. Due to these issues, operation of the digester as a TPAD was abandoned in July 2003. They decided to continue operating the system as a mesophilic complete-mix digester. As part of a university study, they are currently adding magnetite to the influent stream to see if it inhibits the formation of H2S by removing sulfur before it is converted to H2S. To boost biogas production, they are investigating the possibility of adding sweet water from a local candy plant.
Cost information was not available.
Revenues and Other Benefits
They estimate that they save $75,000 per year by using biosolids compared to cost of wood shavings. The owner really likes using the digested solids coming off the digester. When using these solids for bedding they have typically had somatic cell counts in the range of $250,000. Values for revenues from electricity sales were not available. We Energies purchases the entire electrical output and its renewable attributes at a premium. We Energies also pays an ancillary service fee to wheel the electricity to their service territory.
Lessons and Comments
Researchers studying the digester have concluded that use of a TPAD in this setting will require a better understanding of potential factors limiting its effectiveness (Katers J and Schultz J, 2003). Known barriers include ongoing equipment issues (primarily engines-related), and apparent toxicity of high volatile fatty acid concentrations and other farm additives to the thermophilic biota.
- Carl Theunis -- Tinedale Farm
- John F. Katers -- "Temperature Phased Anaerobic Digestion System Monitoring Project at Tinedale Farm: Final Report," August 31, 2003