Comprehensive Greenhouse Gas Evaluation of Underground Coal Thermal Treatment for Production of Syngas and Liquid Fuels

摘要

Although methane recovery from coal seams is common, it produces less than 1% of the energy content of the coal bed. This work focuses on the evaluation of a novel technology, underground thermal treatment (UCTT) to provide energy and potentially reduce greenhouse gas (GHG) emissions. UCTT transforms coal in the ground to a synthetic gas stream containing hydrogen, low molecular-weight hydrocarbons and potentially to liquid fuels by slowly heating it. The product flows to a power plant and/or to a processing facility. This process has the potential to leave large portions of the carbon from the coal in the ground. For power generation, GHG gas emissions can further be controlled by capture of CO_2 and reinjecting it into the coal seam during and after product recovery or for use in enhanced oil recovery. Injection of CO_2 may also enhance gas production if injected during treatment. Although UCTT requires additional energy input compared to coal bed methane (CBM), the added resource utilization and carbon management may be make this process worthwhile and motivates its evaluation. The ultimate goal of is work focuses is to perform a life-cycle energy and GHG evaluation of UCTT, but a preliminary analysis indicated the importance of determining the energy requirement and product yields associated with the coal. Consequently, this manuscript focuses on an energy balance and yields for the process of heating the coal formation based on laboratory-scale data (from a high-temperature, high-pressure 3/4" fixed-bed reactor) and larger scale data (from a 6" high-pressure, high-temperature rubbleized-bed reactor).