Governor Brown signed an executive order and developed the Zero Emission Vehicles (ZEV) Action Plan that set goals of reaching 1 million ZEVs by 2020 and 1.5 million ZEVs by 2025. By 2016, California should have 68 public hydrogen (H2) fueling stations throughout the state to serve the growing number of Fuel Cell Electric Vehicles (FCEVs). California’s FCEV launch is part of the state’s plan to reduce air pollution and fight global warming. Consequently, there is a great need for a new H2 production system as current systems use great amounts of energy and produce greenhouse gases and other air pollutants.
CHA found that the unique characteristics of microwave energy could be utilized to significantly enhance chemical reactions. CHA developed two process concepts that utilize these unique microwave characteristics for on-site hydrogen production.
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).
Microwave Steam Reforming
Microwave energy enhances steam-reforming reactions by reducing the activation energy and reaction temperatures. Under California Energy Commission EISG Grant # 56938A/10-05, CHA studied the feasibility of a microwave system for H2 production from dairy biogas. Thereforming reactions were investigated with a nickel catalyst with and without oxygen. Microwave enhanced water-gas shift and sulfur removal systems were also tested. During testing about 80% of the methane containing 2,350 ppm H2S was converted into H2. A copper oxide and zinc oxide catalyst was very effective for the microwave water gas shift reaction and provided over 90% carbon monoxide conversion with very low microwave power. This catalyst combined with low microwave power, also eliminated H2S completely and prevented sulfur from poisoning the nickel reforming catalyst.
The estimated hydrogen production cost for microwave steam reforming is $2.40/kgH2, which is much lower than the cost of conventional steam-CH4 reforming, $5.92/kgH2. Microwave steam reforming produced 6kg CO2 per kg H2, which is much lower than conventional steam reforming (11.89kg CO2/kg H2).
Microwave steam reforming is economically and environmentally better than conventional steam reforming for onsite hydrogen production. The technology is ready to build a commercial demonstration unit. CHA has 3 U.S. patens of microwave steam reforming (US Patent No. 8,431,083, US Paten No. 6,783,632 and US patent No. 6,592,723).
The microwave cracking process produces H2 and solid carbon black from NG. The carbon black is stable, resulting in carbon sequestration, and could also be used industrially. The process uses a single microwave reactor combining desulfurization and hydrocarbon cracking. Ignoring the potential revenue from carbon black sales, the H2 production cost excluding compression and storage was estimated at $3.68/kgH2.If carbon black is sold at $0.50/kgC, the H2 production cost is reduced to $2.39/kgH2, which is comparable to microwave steam reforming. The microwave cracker will be integrated into an existing or new system for on-site production of H2 at fueling stations using NG as the primary fuel. This technology allows hydrogen-fueling stations to utilize existing natural gas infrastructure to produce hydrogen on-site for servicing FCEVs and fuel cell powered material handling trucks.
The microwave unit could also be integrated into stationary fuel cells to supply H2 internally. The near term market of the microwave unit will be 1-10 kW stationary fuel cells. The following is a list of advantages of microwave cracking process.
- The microwave cracking system is much simpler and cheaper than steam-methane reforming systems and thermal carbon black processes.
- The energy required for the microwave cracking is much lower than water electrolysis, conventional steam reforming and thermal black processes.
- Desulfurization and reforming steps are combined in a single reactor.
- Carbon black can be sold or used as a soil amendment to increase soil fertility and agricultural productivity.
- Recovering carbon black provides cost effective carbon sequestration to eliminate or significantly reduce CO2 emissions from hydrogen stations.
Under the EISG Grant #57649A/13-01G from the California Energy Commission, CHA is currently conducting the feasibility of microwave cracking for onsite H2 from NG for H2 fueling stations. CHA has 4 U.S. patents for microwave cracking process (US Patent No. 8,431,083, US Patent No. 6,419,799, US Patent No. 6,207,023, and US Patent No. 6,187,988).