Two Illinois He,rdn No. 6 coals and one Illinois showspromisefor the direct combustionof coalfor SpringfieldNo. 5 coal were separately combusted power generationin a cost-effective, reliable, and in a laboratory-scale (15-cm dia) pressurized environmentally acceptablemanner. Severaldemofluidized-bedcombustor(PFBC) combined with an nstrationand commercial plants are already being alkali sorber. These coals were combusted in a operated {1"aI.In PFBC/GTCCS, the high-temperafluidized bed of Tymochtee dolomite at ture, high-pressure(HTHP) flue gas exitingfromthe temperatures ranging from 910 to 950°C and a PFBC combu._,lor is expandedthrougha gas turbine system pressure of 9.2 atm absolute. Alkali-vapor to recoverthermal energyfor improvedoverallcycle emission (Na and K) in the PFBC flue gas was efficiency. To protect the gas turbine from erosion determined by the analytical activated-bauxite and hot corrosion, the entrained ash particulates sorber bed technique developed at Argonne and alkalis (such as chlorides and sulfates of National Laboratory.The test results showed that sodium and potassium)in the PFBC flue gas must sodium isthe major alkali-vapor speciespresentin be reducedto acceptable levels. the PFBC flue gas, and that the level of sodiumvapor emissioninc,'easeslinearlywith both Na and Alkaliexistsin bothcoal and 'the sorbent.In PFBC, CI contents in the coals. This suggests that the alkali can be transported to the gas turbine as sodium-vapor emission results from direct particulates and vapors. Several HTHP particulate vaporization of N_LCIpresent in the coals. The cleanup devices (such as SiC candle, ceramic measuredalkali-vaporconcentration(Na + K), 67 to membranecross-flow,and granular-bedfilters)have 90 ppbW, is more than 2.5 times greater than the been demonstrated to achieve acceptable allowable alkali limitof 24 ppb for an industrial gas particulate reduction for gas turbine systems. turbine. Combusting these coals in a PFBC for However, alkalivapor is still a concern because of power generationmay requiredevelopinga method its potential penetrability through the particulate to controlalkali vapors, cleanup devices. Alkali-vapor emission from coal can be functionsof coal and sorbentmineralogyand
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