Sulfur removal at high temperature during coal combustion in furnaces: a review

Abstract

This paper focuses on sulfur removal technologies in industrial grate furnaces (IGF) and pulverized coal fired boilers (PCFB) with high flame temperature of 1200–1600 °C. The SO 2 reduction without sorbents during coal combustion, thermal stabilities of sulfation products, kinetics of sulfur retention reactions of sorbents, desulfurization processes, and sulfur removal under unconventional atmospheres at high temperature are reviewed. It is proposed that some powdered minerals or industrial wastes with effective metal components may be used as sorbents for sulfur removal to promote cost effectiveness. Because the main reason that results in low desulfurization efficiencies in IGF and PCFB is the thermal decomposition of the conventional sulfation product CaSO 4 above 1200 °C, it is key to explore new sulfation products that are thermally stable at high temperatures. It is also necessary to study the kinetic catalysis of alkali and transitional metal compounds on sulfation reactions under the combustion conditions of IGF and PCFB. The two-stage desulfurization process, in which SO 2 is captured by sorbents both in the coal bed and the combustion gas, is promising for IGF, especially with the humidification of flue gas in a water-film dust catcher. The staged desulfurization process combined with air-staged combustion, in which sorbents are injected into the primary air field and upper furnace to capture SO 2 under reducing and oxidizing atmospheres, is promising for PCFB. Flue gas recirculation is also an effective desulfurization process under O 2/CO 2 conditions and can give a high desulfurization efficiency of about 80% in furnaces.