System optimization and performance evaluation of shale gas chemical looping reforming process for efficient and clean production of methanol and hydrogen

In order to explore the efficient and clean technology for methanol production from shale gas, this work firstly presents shale gas chemical looping reforming processes for methanol and hydrogen co-production using three types of fuels (purge gas, shale gas and purge gas, and hydrogen and purge gas), which are directly combusted by air for heating the reforming reactors. In these processes, the important parameters of oxygen carrier flow, steam flow, air flow, and recycle ratio of unreacted syngas have been optimized to maximize methanol and hydrogen production and energy saving. The novel processes with hydrogen and purge gas as fuel have low exergy efficiencies between 74.6% and 75.1%. The process with shale gas as fuel has high exergy efficiency of 76.7% with productions of methanol-2158 kmol/h and hydrogen-937 kmol/h, while it possesses the highest CO2 emissions of 580 kmol/h. This work further integrates chemical looping reforming and combustion to reduce the CO2 emissions. The chemical looping combustion technology makes its direct CO2 emissions as low as about 39 kmol/h, significantly lower than the first three processes. The exergy efficiencies of the last process without and with considering the CO2 exergy as product exergy can be reached at as high as 76.8% and 77.5%, respectively. Obviously, the integration between chemical looping reforming and combustion has obvious competitive advantages and application prospect for efficient and green production of methanol and hydrogen.