Variables affecting mixed oxidant corrosion of stainless steel in gasifiers

摘要

This paper is the final installment of EPRI's project on corrosion in syngas coolers of integrated coal gasification combined cycle plant. In previous papers we explored the effect of chloride species on mixed oxidant corrosion of stainless steels (CORROSION 97, Paper 134) and iron aluminides (CORROSION 98, Paper 185). It was found that the amount of chloride species in the gas and in deposits largely determined the rate of corrosion. Armed with this understanding the effect of a few common process variables is explored in this paper. It was found that corrosion rates decline at higher temperatures, when chloride-enhanced mixed oxidant corrosion occurs at lower temperatures, but corrosion rates increase with temperature for pure sulfidation/oxidation, as may be expected. System pressure was generally of secondary importance, but again higher corrosion rates were generally experienced at elevated pressure, when chloride-enhanced corrosion was predominant, especially at lower temperatures. A simulated temperature excursion below the syngas dewpoint had similar effects, and also caused chloride-enhanced corrosion in 310 stainless steel, which usually does not show this type of corrosion, except when exposed to aqueous corrosion during downtime. A pleasant surprise was the almost complete lack of corrosion when H{sub}2S and HCl levels were reduced to those expected downstream from gasifiers using in-bed desulfurization. It would appear that 12Cr steels may be adequate here. This is being explored further.