Behaviour of Boiler Steel Exposed to Combustion Gases Containing Bromide and Chloride Additives

Abstract

Mercury emissions from coal-fired power plants need to be reduced. In a coal-fired power plant, mercury enters the system primarily with the coal, and exits the system as bound particle compounds, soluble mercury or vapor-phase mercury. Oxidized mercury is effectively removed in wet flue gas desulfurization scrubbers – WFGD.one of the options for enhancing the process of mercury absorption is adding oxidizing agents such as bromide/bromine or chloride/chlorine. The present work describes simulation tests performed in order to evaluate the effect of bromide/chloride additions on the behavior of various steels under a combustion environment in a diesel fed steam boiler. The tested samples A209-T1A, A213-T11, A213-T22 and AISI 1020 were exposed at two locations in the boiler system: inside the flame chamber near the wall and in the middle of the stack at a temperature of 250- 300° C for 3 months. XRD and SEM techniques were used to analyze and to inspect the crystallographic structure. The results clearly show that high temperature interaction between the metal surface and the fire combustion products lead to the deposition of a protective layer composed mainly of CaSO4, FeSO4 and Fe3O4. Negligible weight loss was detected in all the tested cases. No harmful effect was detected in the presence of bromide, added as CaBr2, or chloride, added as CaCl2, to diesel fuel, up to a level of 1000 ppm.