TABLE OF CONTENTS Fluidized-bed coal combustors have been called the "commercial success story of the last decade in the power generation business" and are perhaps the most significant advance in coal-fired boiler technology in half a century. Originally, development of the technology was focused on manufacturing a compact, package boiler that could be pre-assembled at the factory and shipped to a plant site, thereby providing a lower cost alternative to onsite assembly of conventional boilers. By the mid-1960s, however, it became apparent that the fluidized-bed boiler not only represented a potentially lower cost, more efficient manner to burn coal, but also generated less emissions than conventional boilers. Because the technology can control sulfur dioxide and nitrogen oxides at lower cost than conventional boilers, FBC technology has been developed from the "package boiler" concept to the utility boiler concept. This section discusses pollutant formation and control with an emphasis on sulfur and nitrogen oxides.
Sulfur in the fuel is oxidized to SO 2 during the combustion process. In an FBC boiler, the SO 2 is captured in situ by adding a sorbent material, which most commonly is limestone but sometimes can be dolomite. Sulfur retention can be greater than 95% in an FBC boiler, but sorbent utilization levels are relatively low (e.g., typically only about 40% of the calcium is utilized in the capture of sulfur). A discussion of the effect of operating parameters and sorbent characteristics on sulfur...
