Mixed oxidant high temperature corrosion in gasifiers and power plants

Abstract

Data from long term exposure tests in several gasification plants are now available and will be critically reviewed. Exposure times ranged from 2000 to 20,000 hours. All exposures were in syngas coolers of entrained slagging gasifiers, where the gas composition is not in equilibrium. Due to rapid cooling of the syngas, the high temperature (>1,000°C) equilibrium is frozen in. Exposure temperatures ranged from 250–550°C. Most samples were exposed in water or steam-cooled loops. Corrosion rates observed were variable, quite high for low alloy steels, but generally moderate to low for stainless steels. Scale spallation, possibly caused by aqueous corrosion during downtime was found to accelerate the corrosion of stainless steels significantly, but not that of low alloy steels. Introduction of low NO_x burner systems, using overfire air, has resulted in accelerated corrosion in many supercritical boilers in the USA. The accelerated corrosion is most likely to be due to an increase in the CO and H₂S content of the fluegas near the waterwall and the presence of FeS deposits.

Keywords:

• sulfidation
• gasification
• low NO_x burners