Alkali-vapor emission from PFBC of Illinois coals

Two Illinois Herrin No. 6 coals and one Illinois Springfield No. 5 coal were combusted in a laboratory-scale PFBC/alkali sorber facility with a bed of Tymochtee dolomite at temperatures ranging from 910 to 950 degree C and a system pressure of 9.2 atm absolute. Alkali vapor emission (Na and K) from combustion was determined by analytical activated-bauxite sorber bed technique. The test results showed that sodium is the major alkali-vapor species present in the PFBC flue gas of these coals and that there is a positive linear relationship between the level of sodium-vapor emission with both Na and Cl contents in the coals. This suggests that the sodium-vapor emission from these coals is a result of direct vaporization of NaCl present in the coals. The measured alkali-vapor concentration (Na + K) ranges 67 to 90 ppbW and is more than 2.5 times greater than the allowable alkali limit of 24 ppb for an industrial gas turbine. It is concluded that utilizing these coals in the PFBC for power generation may require a method to control these alkali vapors.