The implications of chlorine-associated corrosion on the operation of biomass-fired boilers

The design of new biomass-fired power plants with increased steam temperatu re raises concerns of high-temperature corrosion. The high potassium and ch lorine contents in many biomasses are potentially harmful elements with reg ard to corrosion. This paper condenses the current knowledge of chlorine-in duced, high-temperature corrosion and describes the potential corrosion pro blems associated with burning biomass fuels either alone or in blends with coal, for electricity production. Chlorine may cause accelerated corrosion resulting in increased oxidation, metal wastage, internal attack, void formations, and loose non-adherent sca les. The partial pressure of HCl in a biomass-derived hue gas, is not high enough to cause severe gasphase corrosion attacks, but may provide scale fa ilure and increased sulfidation of water walls in areas where locally reduc ing conditions occur due to poor combustion and flame impingement. The most severe corrosion problems in biomass-fired systems are expected to occur d ue to Cl-rich deposits formed on superheater tubes, The presence of alkali chloride salts in deposits may cause accelerated cor rosion well below the melting point of the salt. The corrosion can be sever e in air but may be further enhanced by SO2 which may cause intra-deposit s ulfation of the alkali chlorides liberating HCl or Cl-2 gas close to the me tal surface. In case the metal surface temperature becomes high enough for molten phases to form in the deposit, the corrosion may be even further enh anced. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.