Sodium-based flue gas desulphurisation for the South African coal-fired power industry a review

A comprehensive review of sodium-based flue gas desulphurisation is presented in this article. The paper provides a comparison of various sodium-based technologies with regards to sulphur removal efficiency, sorbent cost, by-product valorisation and overall process economics. More emphasis was placed on dry sorbent injection (furnace sorbent injection, economizer sorbent injection, duct sorbent injection) and semi-dry flue gas desulphurisation. Particular effort was devoted in identifying state-of-the-art technologies and potential research gaps in a summarized way. In water-scarce countries, where sodium-based technologies are more economically feasible, and duct sorbent injection processes are favourable, it is recommended to use sodium-based absorbents since they will have higher sorbent utilization and improved electrical resistivity (compared to their calciumbased and/or magnesium-based sorbent equivalents). However, the check-and-balance of the associated advantages and disadvantages are a pivotal determinant of the sorbent choice. Apart from sulphur dioxide abatement, the additional advantages of sodium-based absorbents include its high sulphur trioxide removal efficiency as well as its hydrogen fluoride and hydrogen chloride removal capability. A scarcity in literature, especially as it relates to application in the South African coal-fired power generation industry, necessitates the need for further research with particular focus on local sodium-based absorbent markets, the physiochemical properties and sulphur dioxide reduction potential of locally acquired sodium-based absorbents, modelling of sulphation reaction kinetics in semi-dry and dry application, as well as the techno-economic feasibility of sorbent based technologies for the South African power industry.