Effect of coal minerals on chlorine and alkali metals released during biomass/coal cofiring

The combustion behavior, gaseous emissions, and alkali metals released duri ng the combustion of several biomass/coal blends were investigated using a direct sampling, molecular beam mass spectrometer (MBMS) system in conjunct ion with a high-temperature alumina-tube now reactor. Pittsburgh No. 8 and Eastern Kentucky coals were blended with various biomass samples such as re d oak wood chips, Imperial wheat straw, and Danish wheat straw. The coal/bi omass blends were 15% biomass on an energy input basis. All pure fuels and blends were subjected to combustion in 20% oxygen in helium at a furnace te mperature of 1100 degrees C, and the products were monitored with the MBMS. The amounts of NO(g) and SO2(g) detected during the combustion of the coal /biomass blends suggested that any change was the result of diluting the ni trogen and sulfur present in the fuel blend. The amount of HCl(g) detected during the combustion of the coal/wheat straw blends was higher than expect ed based on the combustion results for the pure fuels. Conversely, the amou nts of KCl(g) and NaCl(g) detected during the combustion of the coal/wheat straw blends was lower than expected. Chemical equilibrium calculations ind icated that the amounts of condensed alkali species were significantly enha nced, usually in the form of Sanidine (K2O*Al2O3*6SiO(2)) and Albite (Na2O* Al2O3*6SiO(2)). Therefore, the lower-than-expected amounts of gas-phase pot assium chloride detected during combustion of the wheat straw/coal blends w as likely the result of potassium being sequestered in the condensed phase by the clay minerals in the coal.