Research progress and future study of carbon emission reduction for UCG

The integration of underground coal gasification (UCG) and carbon emission reduction is expected to become an excellent green energy technology during the transitional stage from the current to the arrival of carbon neutrality, and even play an important role in the longer history of carbon neutrality in the future. Looking back at the research history and current situation, the systematic strategy for UCG emission reduction has been basically formed, which can be summarized into five specific approaches. Among them, the targeted underground in-situ regulation can reduce the CO2 release and promote the quality and yield increase of UCG synthesis gas, and the relevant strategies and approaches can be summarized as the Carbon Regulation and Reduction (CRR). There are many research achievements on the supercritical gas storage of UCG-CO2 in underground space, mainly focusing on storage media, storage space, storage capacity, etc., with some discussions for storage mechanisms. The mineralization and storage of UCG-CO2 in underground space are not constrained by the harsh conditions of geological stability and sealing, and there is a potential dual effect of both carbon sequestration and gas conversion, but there are not many research results yet. The previous exploration of UCG-CO2 reinjection, utilization and storage focuses on two aspects, such as enhancing coalbed methane production and improving the production of UCG synthesis gas, and a series of explorations have been initiated for the emission reduction and utilization of CO2 from the tail gas of UCG hydrogen production in recent years. The CRR, as an active emission reduction strategy, targetedly reduces the CO2 concentration in the UCG synthesis gas by adjusting the gasifying agent and its injection method, and there are many theoretical achievements and preliminary on-site verification, which are expected to become a practical clean coal technology that integrates clean energy production and carbon reduction. Reviewing the progress and analyzing the shortcomings, the scientific and technological research for UCG carbon emission reduction has made many substantial achievements, but also still faces some challenges of sustainable development, and the future study should focus on four aspects. One is to prioritize the development of UCG-CO2 underground conversion and utilization technology with a focus on the UCG-CRR based on feasibility. The second is to focus on the shortcomings and to strive for the breakthrough of the collaborative mechanism and key technological bottlenecks of both UCG emission reduction and synthesis gas quality improvement. The third is to make solid progess and promote the prior implementation of UCG-CRR pilot tests and engineering demonstrations for the achievement of practical results step by step. The fourth is to ensure the implementation and establishment of the “trinity” policy support system for the UCG emission reduction consisting of carbon neutrality and management strategy, special science and technology action plans, and professional talent training.