Preventing the chlorine-induced high temperature corrosion in power boilers without loss of electrical efficiency in steam cycles

Abstract

The installation of combustion plants for waste and biomass with a connected boiler and steam cycle brought forth the problem of high temperature corrosion in the steam generators. This phenomenon originates from the composition of these fuels and in particular from the molar ratio of sulphur to chlorine, which is in the range of 2 and lower. Therefore, it is necessary to observe several demands on the construction and design of steam generators in order to prevent this sort of corrosion. All of these requirements arise from the limitation of the heating surface wall temperature as a function of the corresponding flue gas temperature and the gas velocity at the heat exchanger tube. It is, therefore, paramount to place the heating surfaces in the appropriate boiler areas to meet the temperature limits. The demands on steam generators to prevent high temperature chlorine corrosion are presented in this present work. Furthermore, one possible process design is presented, which in turn offers the possibility to operate a steam cycle at high pressure levels without the risk of high temperature corrosion or exceeding the limit for the final wetness at the steam turbine exit. This comparison points out that the new steam cycle gains the highest electrical efficiency when compared with two conventional cycles that meet the same goals.