Cold-side desulfurization by humidification of fly ash in CFB boilers

It is expected that sulfur emission regulations for fluidized bed boilers will continue to become more stringent. By capturing sulfur in-situ with furnace limestone injection, circulating fluidized bed (CFB) boilers have been quite successful in achieving capture efficiencies of up to 93%. However, CFB operating experience has shown that extending sulfur capture beyond this level results in a diminishing return relationship and requires a substantial increase in limestone consumption, especially for fuels with a relatively low (< 1.0%) sulfur content. Such an increase in limestone consumption can have numerous effects upon boiler design and performance, including: increased ash handling system requirements; higher operating cost of increased limestone consumption; increased NO{sub x} emissions; a detrimental effect upon SNCR performance, higher pH of ash leachate; and lower boiler efficiency. For future power generation projects, which are predicted to require increasingly higher sulfur capture efficiencies, the combination of the above listed conditions could result in a CFB boiler being cost-prohibitive in comparison to a pulverized coal boiler for a given coal. Clearly, CFB boilers will require a refined operating strategy, together with a consideration of auxiliary desulfurization technology, in order to remain competitive in the future energy equipment market.