Spray drying absorption for desulphurization: a review of recent developments

Sulphur dioxide (SO₂) abatement technologies, i.e. flue gas desulphurization (FGD), have proven effective in curtailing the harmful SO₂ emissions resulting from coal combustion for electrical power generation. New regulations on these emissions now require some power utilities to retrofit new FGD units to existing coal-fired power plants to meet required emission standards. Wet FGD limestone scrubbing has been predominantly used over other competing technologies. However, the simplicity of the spray-drying absorption (SDA) technology has made it an attractive alternative to the wet scrubbing process. SDA offers huge savings on energy, water, operating cost and maintenance. Despite high cost of the sorbent (hydrated lime) used, recent advances in SDA process offer considerable economic and technical advantages ranging from improved sorbent utilization, better atomization and enhanced performance. Alternative sorbents and additives are continuously being explored for simultaneous removal of pollutant gases from flue gas. The performance improvement areas in a lime spray drying system include the use of inorganic salt additives, recycling of the dried product and the use of siliceous materials. This study is intended to review FGD systems applicable to coal-fired power plants, through a technical comparison between competing technologies. Additionally, a review of the spray-drying absorption process and operating parameters affecting their efficiency was carried out, together with a critical assessment of the literature published to date.