THE KINETICS AND MECHANISM OF ALKALI REMOVAL FROM FLUE-GASES BY SOLID SORBENTS

Kaolinite, bauxite and emathlite have been found suitable for alkali removal from hot flue gases in coal conversion systems. The effect of temperature on the kinetics and mechanism of alkali adsorption/reaction on these sorbents was studied under a simulated flue gas atmosphere. Kaolinite and emathlite reacted irreversibly with the alkali; however for bauxite, 10% of the total weight gained was due to physisorption. Kaolinite was found to have the highest capacity and the largest activation energy for alkali removal. The overall sorption process is not just physical and non-selective, but rather a combination of physical and chemical processes, which are dependent on the temperature and sorbent chemistry. The reaction product of alkali with emathlite has a melting point of approximately 1270 K, while kaolinite and bauxite form compounds with a melting point of about 1870 K. Consequently, kaolinite and bauxite are more suitable for in situ removal of alkali, while all three can be used for downstream alkali removal. © 1990.