A Compararitive Review of Next-generation Carbon Capture Technologies for Coal-fired Power Plant

Abstract

Despite the demonstration of large-scale carbon capture and storage (CCS) at a small number of coal power plants in North America, development of the technology remains slow in Europe, where several large projects have been cancelled in the last five years. Established CO2 capture technologies such as amine scrubbing consume significant amounts of energy, reducing power plant efficiency by around 10%pts and contributing to increases in the cost of electricity production by up to 80%. Within these economic constraints, CCS demonstrations have been limited to regions where CO2 has a value for enhanced oil recovery, a low cost coal supply is available, and effective CO2 emissions caps or pricing are in place. For CCS to be competitive as a low carbon energy source in a broader context, there is clearly a need for new technologies which can achieve dramatic reductions in the cost of capture, primarily through a reduction in the process energy consumption.Concerted research efforts worldwide are therefore developing a wide range of innovative solutions to the fundamental gas separation step at the heart of nearly all forms of carbon capture, whether post-combustion, pre-combustion or oxyfuel combustion. Dedicated research programmes in the US and Europe in particular have set ambitious targets for new technologies to achieve a CO2 capture cost approaching $20/t. Novel solvents aim to achieve lower regeneration energy requirements than conventional amines, with phase change systems, ionic liquids and other non-aqueous solvents, and enzyme-activation all representing promising approaches. Alternatively, techniques used in other commercial gas separations, including solid sorbents, membranes, and cryogenic separation, have also been widely investigated. Whilst challenging for post-combustion capture applications, these techniques may be of particular benefit to pre-combustion capture systems where much higher partial pressures of CO2 are available, and integration of the CO2 capture step and water gas shift reaction can be achieved using sorbents or membranes. In oxyfuel combustion, pressurised systems have demonstrated the most potential for efficiency improvements, with novel power cycles such as the supercritical CO2 cycle well-suited to exploiting the unique combustion conditions. Developments in ceramic membranes for oxygen production may also provide a lower cost alternative to cryogenic air separation. Finally, chemical looping combustion is a unique approach to carbon capture which can achieve dramatic energy savings through its inherent avoidance of any gas separation step. This technology has recently begun to see significant scale up by a number of companies and research institutes, with a focus on low-cost oxygen carriers.This paper will review these developments in novel capture technologies and compare them on the basis of efficiency penalty, cost of electricity, cost of CO2 capture, and their current developmental status. Processes which inherently incorporate CO2 capture with the power generation process, such as chemical looping combustion or the oxyfuel-based Allam Cycle appear to offer the greatest potential to meet the economic targets. For retrofit applications, high performances are associated with capture plant which is able to compensate for energetic losses by acting as an additional source of power, with calcium looping and fuel-cell based processes as notable examples.