High-temperature, chlorine-based corrosion is a minor consideration for most US coals as few such coals contain chlorine.  Many biomass fuels, however, contain chlorine, and some contain very high amounts.  Cofiring biomass with coal can introduce high-temperature corrosion problems if fuels and operating conditions are not properly selected.  The links at left summarize and illustrate the issues associated with corrosion, some experimental highlights from laboratory investigations, and conclusions regarding corrosion prevention.  The general guideline for corrosion is:

Fuel chlorine and alkali concentrations should be limited to less than one fifth of the total fuel sulfur on a molar basis to avoid corrosion problems. This limit should be applied to the fuel composition as fired through any single burner except in the rare case of rapid and complete mixing of in the furnace.