Energy analysis of underground coal gasification with CO2 capture and auxiliary power production

Underground coal gasification is a method of converting in situ coal into synthesis gas through the same chemical reactions that occur in surface gasifiers. If underground coal gasification systems are combined with carbon capture and storage methods, CO2 emissions can be greatly reduced. Carbon capture and storage methods require considerable amount of energy to separate CO2 and prepare it for transport and storage, which is typically considered a parasitic loss. This study investigates utilizing waste heat rejected during processing of syngas from underground coal gasification using an auxiliary power plant, to supply the required energy associated with amine-based CO2 capture and compression processes necessary for transport and sequestration. The system investigated is the Newman Spinney underground coal gasification test plant coupled with a basic Rankine cycle. It is shown that the energy requirement for CO2 processing can be met through the use of an auxiliary plant. The basic model illustrates that the power produced by the auxiliary plant is 2.1 times greater than that required by CO2 compression, while supplying the required heat for amine-based CO2 capture. Parametric analyses are performed to investigate the impact of air injection rate, syngas cooling and CO2 capture and compression requirements on system performance.

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