Corrosion during gasification of biomass and waste

Abstract
The gasification of biomass and waste results in severe atmospheric corrosion conditions. The problems arise because of the low oxygen content which prevents the metal forming stable and protective oxide surface layer. Consequently it is possible for the aggressive sulphur and chlorine present in the gas to attack the metal. In the Studsvik CFB gasification pilot plant, which uses RDF (Refuse Derived Fuel), the performance of 20 metallic and ceramic materials has been studied. Materials tested are Fe-based alloys, Fe/Ni-based alloys, Ni-based alloys, refractory and engineering ceramics. This paper reports the results for the alloys, while the refractories and ceramics are reported in reference [1]. They were regularly removed, examined and then put back into the gasifier. The metal degradation varies from 0.01 to 0.1 mm after three gasification campaigns. The gas composition was about 14% CO₂, 12% CO, 11% H₂O, 10% H₂, 4% CH₄, 2% C₂H₄, 300 ppm H₂S, 300 ppm HCl, bal. N₂. The corrosivity of the gas has been evaluated, concerning the potentials of oxygen, sulphur and chlorine. This gas characterisation has been made by calculating the potentials from the gas composition, and by examining the corrosion products on pure metals. Long time tests are running in a full scale power plant. Metallic and ceramic materials are being exposed for varying times in a biomass gasification atmosphere. Further, the environment in the gasifier is being characterized using pure metals.