Biogas project advances in California

The National Renewable Energy Laboratory (NREL) has given a `thumbs up` rating to the high solids anaerobic digester project which is designed to produce biogas. The Sacramento Municipal Utility District (SMUD), the local utility, is considering the use of biogas to run a fuel cell pilot project. The designs for the three digesters are state-of-the-art, with each containing a horizontal trough measuring 120 feet long, 32 feet wide and 22 feet tall. NREL was asked by the PIA to review the mixing method in the digesters and analyze the overall potential success of the operation. The design employs a redundant system for foam removal from the digester gas, and has provisions to remove moisture from the biogas. However, there are no systems specified to reduce hydrogen sulfide levels. Since hydrogen sulfide is known to be corrosive, it may be destructive to the ultimate use as biogas in fuel cells. A suggested remedy from NREL is to add redundant iron sponge systems to remove hydrogen sulfide gases. A redundant system would allow regenerating one while the other is in service. In general, the lab found the design offers low construction costs, relative ease of operation, and a reasonably high level ofmore » anticipated success in operation. Therefore, NREL recommends proceeding with the current digester design plans, once the modifications as indicated are made.« less