Comparative environmental benefits of power generation from underground and surface coal gasification with carbon capture and storage

Underground gasification combined cycle (UGCC), when combined with carbon capture and storage (CCS), is widely judged to be a promising approach for clean coal utilization especially in the context of carbon neutral energy pathways. Nevertheless, the overall operation processes may consume a multiple of energy and inevitably trigger environmental concerns. Hence, a careful evaluation of the potential environmental impacts associated with UGCC is needed. In this study, we assessed environmental impacts of UGCC with and without CCS by the life cycle assessment method, and compared the results with those of surface integrated gasification combined cycle (IGCC) to gain better insight into tradeoffs of two coal gasification technologies and lighten the environmental burden by design optimizations. The results demonstrated that most mid-point impact values of UGCC power plants, which reflect pollution emissions and corresponding damage degree, were lower. Inversely, the global warming potential was 16.9% higher than those of IGCC power plants. Furthermore, UGCC power plants have superior end-point environmental benefits, which represent the damage of ecosystem quality, human health and resources. As demonstrated by the fact that the value of above three impact types were 23%, 15% and 4%, lower than those of IGCC power plants, respectively. In addition, the implement of CCS in two types of power plants decreased human health damage due to reduced greenhouse gas emissions, but notable environmental trade-offs are the increase in ecosystem quality damage and resource damage. The aggregated results show that UGCC with or without CCS has a more outstanding environmental performance with exception of global warming potential than IGCC with or without CCS. Enhancing UCG process control, improving syngas heating value and decreasing the energy in gasification agent preparation are effective methods to further reduce the GHG emissions. Approached in an improved way, UGCC-CCS stands to provide a low-carbon and self-contained solution for power production and energy provision.