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.  GAC impregnated with copper oxide (CuO) was tested and found to have much better adsorption performance. The saturated impregnated GAC was reactivated with air by microwaves through conversion of copper sulfide to CuO.

An integrated microwave system was designed consisting of two GAC fixed beds for NOx removal and two CuO-impregnated GAC beds for H2S removal. Microwaves reactivate saturated media and desorbed NOx and SO2 are destroyed in a carbon bed with microwave energy. Total annualized treatment cost for 299-hp engine running on biogas at the Tollenaar Holsteins Dairy Farm was estimated at $0.021per kWh. When H2S was combusted in the engine, total annualized cost was reduced to $0.018 per kWh. The integrated microwave treatment system will meet the stated project goal.

Microwave System for Hydrogen Production From Dairy Digester Biogas

In October 2011 CHA Corporation received another EISG Grant (Grant #10-05) from the California Energy Commission. The two project goals were to determine whether a microwave hydrogen production system using dairy biogas could be used for the pre-combustion control of NOx from engine exhaust and if biogas could be converted to hydrogen for use in fuel cells.

Microwave steam-methane reforming reactions with nickel catalyst were investigated experimentally with and without oxygen. Water gas shift reaction tests were conducted using copper oxide and zinc oxide catalysts. Finally, the microwave-reforming reactor was integrated with the water gas shift and hydrogen sulfide removal reactors. This integrated microwave system ran for 11 hours with methane containing 2,350-ppm hydrogen sulfide to simulate dairy biogas.

Over 75 percent of the methane was converted into hydrogen. The ratio of hydrogen produced per mole of methane was 3.8, which substantially surpassed the project target of 3.0. The addition of oxygen to the reformer increased the methane conversion but did not increase total hydrogen production. A redesigned microwave reactor with inlet gas pre-heating also increased methane conversion significantly, eliminating the benefit of oxygen addition. We found the copper and zinc oxide catalyst was very effective for microwave-induced water gas shift reaction and provided over 90 percent carbon monoxide conversion at very low microwave power. This catalyst also effectively scrubbed hydrogen sulfide from the feed gas to avoid nickel catalyst sulfur poisoning.

The total annualized treatment cost for 500-kW internal combustion biogas engine was estimated at $0.01 per kWh. NOx removal costs were estimated at $10,200/ton and $22,960/ton for the exhaust gas NOx concentration of 100 and 50-ppm, respectively.

Cracking Raw Fuels for hydrogen Stations Without Greenhouse Gas Emission

In August 2013 CHA Corporation received an EISG Grant (Grant #57649A/13-01G )  to determine the feasibility of producing on-site hydrogen (H2) for H2 fueling stations without emission of CO2 and other air pollutants using a single microwave reactor combining desulfurization and hydrocarbon cracking.  The carbon in the natural gas (NG) feed is recovered as carbon black that can be used industrially or sequestered.  This technology will expand the on-site production of H2 for fueling stations to supply fuel cell electric vehicles (FCEVs) efficiently and cost effectively without greenhouse gas emissions.  By 2016, California should have at least 68 H2 fueling stations to serve the growing number of FCEVs. California’s FCEV launch is part of the State’s plan to reduce air pollution and fight global warming. Governor Brown signed an executive order and developed the Zero Emission Vehicles (ZEV) Action Plan that will put a significant number of ZEVs on California roads. Not only does the process directly reduce CO2 from vehicle emissions, the produced carbon black can offset the use of carbon black from thermal processes that also emit large quantities of CO2.

The majority of bulk H2 is produced at large industrial plants and transported as a compressed gas.  Production and transportation costs of H2 are high and result in criteria air pollutants and CO2 emissions.  The delivered cost of compressed H2 was estimated to range from $11.00-$17.50/kgH2 depending on quantity and delivery distance.  This is cost prohibitive, especially for small fueling stations. An onsite method to generate H2 would reduce the transportation cost.

About 95% of H2 produced today is made via steam reforming, a process in which high-temperature steam is used to produce H2 from natural gas (NG). The process is highly endothermic, requiring about 35 kWh per kg H2.  The on-site H2 production cost by thermal steam reforming of NG was estimated at $9.29/kgH2 ($5.92 for production and $3.37 for compression and storage).  H2 can also be produced by electrolysis of water, but with a very high-energy conversion penalty that is too costly for H2 stations (53.44 kWh/kgH2).

CHA Corporation is currently conducting laboratory investigation for the microwave conversion of NG to H2 and carbon black under this EISG grant. This project examines combining desulfurization and cracking in a single reactor and increasing the efficiency of the process to make it commercially viable. Our target is to obtain the CH4 conversion efficiency greater than 80% in the presence of sulfur impurities such as H2S and odorants in natural gas.