Negative Net CO2 Emissions from Oxy-Decarbonization of Biogas to H2

Abstract

Current biomass-to-energy technologies usually are not economically competitive compared with fossil fuel-based technologies. Therefore, further developments in bioenergy are still needed and new concepts such as “negative net CO2 emissions” that can improve the economics of biomass utilization are of great interest. Accordingly, an ODB-H2-WGS process integrated with CO2 capture, a fuel cell and an oxygen generator is proposed. The ODB-H2-WGS process can decarbonize biogas and simultaneously generate high-purity hydrogen. The ODB-H2-WGS process is illustrated by means of the case study in which three reactors are simulated, i.e. the oxyforming reactor, the HT-WGS reactor and the LT-WGS reactor. The results show that the ODB-H2-WGS process can produce a CO2-H2 mixture from which H2 is separated and the remaining CO2 is ready for compression and sequestration. The oxyforming reactor enables complete conversion of methane. CO is shifted in the HT-WGS and further in the LT-WGS reactors to its equilibrium concentration. The results reveal that the properly designed LT-WGS reactor is crucial for WGS reaction completion due to likely departure from the equilibrium conversion. Consequently, by using the ODB-H2-WGS process pure hydrogen is produced from renewable biogas with the maximal yield of 3.3176 H2:CH4 on molar basis.