Superheater Tube Corrosion In Wood Gasifier Ash Deposits

The upper operating temperature of tubes in heat exchangers/steam generators is strongly influenced by the degradation that can occur because of the reaction of the exchanger/generator tubing with the deposits that accumulate on the surface of the tubes.  In fact, severe corrosion has been observed in some biomass fired systems, particularly with elevated potassium and chlorine concentrations in the deposits.  Wood gasifiers have recently been and are currently being constructed in several sites in North America.  In these systems, the syngas is burned to produce steam and the performance of the heat exchanger tubes under ash deposits is of great concern.  As temperatures within the gasifiers are increased in an effort to increase their operating efficiency, the performance of the tubes is of particular interest.  The corrosion behavior of alloy steel tubes as a function of temperature has been investigated by exposing samples of selected alloys to ash similar in composition to that collected from the steam generator fired by syngas produced in wood gasifiers.  Results of the corrosion studies as well as information about the corrosion mechanisms will be presented.

Key Words:  superheater, biomass, wood gasification