Air quality influences of post-combustion carbon capture

Climate change mitigation is a dynamic area that, as it is addressed, brings new challenges to other environmental aspects. Carbon capture and storage (CCS) plants are the latest development in a series of environmental controls and have some distinctive features that could potentially lead to other wider environmental problems. Whilst CCS represents a significant step towards cutting greenhouse gas emissions, consideration needs to be given to the potential wider environmental consequences especially in terms of pollutant emissions and local air quality impacts. Challenges remain for existing plants which will need to consider the most cost-effective strategies for installation of CCS plant balanced against managing air quality impacts as dispersion characteristics change. In the case of post-combustion carbon dioxide (CO2) capture technology, which is the focus of this paper, removal of CO2 from the main flue gas stream requires diversion of the flue gas through the CCS process, before it arrives at the exhaust stack. This flue gas stream may be all or part of the total plant flow or for multi-unit plants may be diverted from specific power generation units into the CCS plant before exhausting to atmosphere, either through returning back to the existing stack or through a new dedicated stack. This diversion and subsequent emission in itself poses an engineering challenge. In particular, the integration of the CCS process with the existing plant must also ensure that the diverted flue gas still achieves adequate dispersion as it contains residual levels of pollutants such as nitrogen oxides (NOx) and sulphur dioxide (SO2), despite the fact that the CCS process itself may reduce some of these pollutant levels further as a process by-product. Power plants which incorporate CCS will still be required to adhere to the appropriate pollutant emission limits and ensure effective dispersion to minimise the risk of breaching local air quality standards. This paper draws on experience gained through post-combustion CCS projects and addresses the potential effects of CCS on air quality, in the case of carbon capture retrofits. The findings of this paper are relevant to project developers, power generators and policymakers globally who have an interest in the potential for CCS to provide an emissions abatement option for existing thermal assets in the short and long term.