The Kinetics and Influence Factors on Chlorine-Induced Fireside Corrosion in Biomass Combustion System Part II: Interactions Between Gas and Deposits and Their Influences on Corrosion Rate

摘要

Kinetics of chlorine-induced corrosion regarding real metal loss, and influences of gas and ash deposit on corrosion rate are discussed comprehensively in case of ferrite, martensite and austenite boiler steels. This study is divided into three parts: Part I: Corrosion kinetics regarding the rate of real metal loss and its correlation with specimen weight change Part II: Interactions of gas and ash deposit and their influence on corrosion rate Part III: Corrosion morphology of chlorine-induced corrosion In Part II, the change of ash chemistry in reducing, oxidizing and oxidizing/sulfating and the influence on metal loss are discussed. Experiments were carried out in three gas atmospheres, five ashes at 550°C and 650°C for 100 hours. The test results indicate that Cl_2 gas is the direct attack medium of metal, which is released during oxidation alkali chlorides in ash. In reducing atmosphere, the oxidants come from decomposition of sulfates ash deposits, whereas in oxidizing oxidizing/sulfating atmosphere, O_2 or SO_2 come from gas atmosphere. SO_2 has especially a great potential to activate alkali chlorides, thus oxidizing/sulfating atmosphere is more corrosive when alkali chlorides already exit in ash deposits.