Better fuel utilization is achieved in the SCFBC, which achieves a carbon burnout of 97.1% versus 95.0% for the AFBC. The SCFBC advantage is due to the staging of combustion in two beds. The thermal efficiency of the SCFBC is higher than that of the AFBC (85.4% versus 81.65%) due to two factors. First, the better fuel efficiency mentioned above contributes to this advantage. Second, the spent solids leaving the lowest combustion stage of the SCFBC are cooled by the incoming air, reducing heat loss with the spent solids. The SCFBC accomplishes the specified SO/sub 2/ removal with a significantly reduced amount of limestone adsorbent. The SCFBC achieved a sulfur capture efficiency of 81.6% with a calcium to sulfur ratio of 2.05, while the AFBC capture efficiency was 90% with a calcium to sulfur ratio of 3.5. The SCFBC has several other technical advantages over the AFBC. Stages of combustion air in the SCFBC can reduce NOx emissions to one-half to one-third of that achievable with the AFBC. The SCFBC achieves a higher volumetric heat release than the conventional AFBC by a factor of three to one. The SCFBC can achieve higher turndown ratios than the AFBC by changing fluidized bed depths to tailor heat transfer rates to the turned down condition. Turndown ratios of 7 to 1 are possible with the SCFBC compared with a ratio of 3 to 1 achievable in a single bed conventional AFBC. The capitol cost of the SCFBC is 24.0% lower than that of the AFBC and the annual operating cost is 7.4% lower.