Enhancement of Substituted Natural Gas Production - Sorption-Enhanced Steam Hydrogasification Process with In Situ Carbon Dioxide Capture

The California Energy Commission has identified renewable natural gas as an important alternative fuel that can contribute to achieving California’s goals related to replacing conventional fuel and reducing emissions in the transportation sector.
The University of California, Riverside recently developed a new process to remove carbon dioxide (CO2) and increase the energetic gas (hydrogen and methane) yield from renewable natural gas, called sorption enhanced steam hydrogasification. Results from a laboratory-scale bench reactor showed that adding a sorbent (a material used to adsorb liquids or gases) such as calcium oxide could remove CO2 in steam hydrogasification and increase hydrogen and methane production from different kinds of feedstock. The amount of hydrogen, in particular, increased dramatically, by as much as 60 percent compared to production without the addition of sorbent. The hydrogen content in the gas produced by the process was enough to maintain a self-sustained supply back to the steam hydrogasification when the ratio of calcium oxide to carbon was larger than 0.29.
Researchers developed a bench-scale circulating fluidized bed reactor through the mockup test. The results showed a 76 percent carbon-to-gas conversion. Process simulation software used the bench-scale demonstration results to perform a technoeconomic analysis that included a detailed heat and mass balance for renewable natural gas production. Compared to other production processes, the sorption enhanced steam hydrogasification process had the lowest CO2 footprint (43.6 kilograms per million British Thermal Units) and lowest production costs ($14.8 per million British Thermal Units) among other processes.
The project team completed a preliminary design for a pilot plant that could produce approximately 20,000 diesel gallon equivalents per year of fuel grade renewable natural gas using 0.8 dry metric tons per day feed throughput from commingled green waste and biosolids.