Realizing low life cycle energy use and GHG emissions in coal based polygeneration with CO2 capture

Cogeneration of synthetic natural gas (SNG) and power from coal can realize both high energy conversion efficiency and low energy penalty for CO2 capture (CC). Life cycle energy use and GHG emission assessments are applied to coal based SNG and power cogeneration with CO2 capture. Four typical pathways are considered based on the main applications of SNG in China. Results show that when SNG is produced in a single product plant with CO2 capture and SNG is used for power generation, its life cycle energy use is averagely around 5% lower than that of supercritical coal power with CC and even can be comparable with ultra supercritical (USC) with CC pathway. Such low energy use is mainly due to much lower energy penalty for CO2 capture in a SNG production plant than in a post-combustion coal fired power plant. The life cycle energy use of cogeneration plant with CC is 10–19% lower than that of USC with CC due to system integration, the obvious higher CO2 concentration before separation and the consequent much lower energy penalties for CO2 capture. The life cycle GHG emissions of cogeneration with CC range from 135 to 150 gCO2 eq./MJ, which are obviously lower than those of all coal power pathways including USC units (10–17% lower than USC with CC). For steam and power cogeneration and pure vehicle operation pathways, the cogeneration technology with CO2 capture also shows obvious life cycle energy use and GHG emission advantages over its competitive pathways.