California Energy Commission

Energy Innovations Small Grant (EISG) Programs

Microwave-Induced Reaction of NOx and H2S in Dairy Digester Reciprocating Engines

In June 2008 CHA Corporation received an EISG Grant (Grant #07-08) from the California Energy Commission to determine the feasibility of a carbon based, microwave treatment system to remove hydrogen sulfide (H2S) from dairy digester biogas and NOx from engine exhaust to economically meet the California Air Resources Board 2007 emission standards. First a number of microwave-induced reactions were investigated and then adsorption and microwave reactivation tests were conducted using granular activated carbon (GAC). H2S destruction efficiency above 95% was achieved through reaction with either NOx or oxygen.

NOx mixed with sulfur dioxide was reacted with carbon while applying microwave energy. The GAC had a NOx adsorption capacity of 10% by weight and was quickly regenerated with microwaves. H2S adsorption on regular GAC was found to be impractical due to rapid breakthrough.