Materials issues in black liquor gasification systems

Combined cycle black liquor gasification offers a potential for increased energy recovery with reduced gaseous emissions compared to conventional black liquor recovery boilers. However, serious issues complicate the selection of the materials for use in construction of the two preferred gasifiers types. For the low-temperature gasification system, these issues involve a number of components including the material being used for the heater tubes in the fluidized bed and the inner shield tubes at the entrance to the heater tubes. Materials selection for these components will be of greatest concern when black liquor from kraft or sulfite mills is being processed, due to the higher sulfur content of these liquors. Laboratory studies are being used to provide guidance on the selection of appropriate materials for these applications. For the high-temperature gasification system, the refractory lining has been a major concern, as have been any metallic components that have to be exposed to the gasifier environment. Laboratory studies along with in-plant exposures are showing that certain materials and/or treatments of current materials demonstrate improved performance in these environments.