Technology Review: Post-Combustion Carbon Capture for Natural Gas Fired Power Plants

Coal power plants have so far been the focus of regulations to curb greenhouse gas emissions; however, natural gas power plants are also large point source emitters of CO2. CO2 regulations currently considered for coal power plants are expected to ultimately expand to apply to NGCC power plants. Conventional wisdom has suggested that a post-combustion carbon capture (PCC) process that effectively removes CO2 from coal flue gas should, with relatively modest design adjustments, also perform well on natural gas flue gas.

This report elucidates the major differences and similarities between CO2 capture on coal and natural gas flue gases and examines opportunities to optimize PCC processes for NGCC units. Chemical absorption, physical and chemical adsorption, selective membranes, and cryogenic processes are considered.  To understand technology developer insights and activities to optimize PCC processes economically for natural gas flue gas, telephone interviews were conducted with a selection of technology developers and are summarized in this report—with a focus on technologies that have advanced beyond early-stage development. Fundamental calculations are made of the minimum work required for the separation of CO2 from power plant flue gases, with an emphasis on NGCC flue gas properties. NGCC-related CO2 capture R&D needs are also reviewed.

Most companies and research institutions have examined the ability of their capture agents and systems to perform on simulated or actual natural gas flue gas. Individual developers generally know their specific additional R&D needs to validate or improve existing processes for NGCC applications but may not have investigated alternative chemistries or process configurations.

Changes in the power industry are challenging the economics of applying CO2 capture to NGCC plants. With the growth of intermittent renewable resources on the electric grid, fossil power plants—and especially natural gas power plants—are being called on for greater load-following and cyclic duty, which tends to reduce their capacity factors. For CO2 capture processes with high capital costs, high capacity factors are needed to achieve reasonable levelized $/tonne-CO2 captured or $/MWh costs.

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