Materials issues in bubbling PFBC systems

Abstract

In recent years, considerable experience and insight regarding the behavior of materials and components in the bubbling pressurized fluidized-bed combustion (PFBC) of coal has been developed, largely as a result of the operation of a fleet of 80-MW(e) PFBC-based power plants installed by ABB Carbon. The first plant went into operation over 10 years ago and it appeared timely to review this practical experience and to document areas where improvements have been made, or can be suggested.In keeping with general bubbling-bed experience, the in-bed heat exchanger and water-wall tubes experienced metal loss. Other plant areas that experienced difficulties were the hot-gas cyclone system, the gas-turbine expander, and some balance-of-plant items including solids-handling equipment, valving, and expansion joints. The captured dust removal lines from the cyclones sometimes plugged sending high dust loadings over to the turbine expander. Consequently the turbine blades experienced material deposition and significant erosion damage. Concerns about turbine longevity in this application have led to attempts to develop high-temperature filter systems that protect the turbine by removing all the dust from the flue gas prior to expansion. These filters have themselves suffered from a range of materials problems, which is not unexpected for a relatively new technology. The current experience of these and other materials issues is reviewed.