Energy & Fuels 1997, 11, 439-446
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Effects on SOx and NOx Emissions by Co-Firing Straw and Pulverized Coal L. S. Pedersen,*,† D. J. Morgan,‡ W. L. van de Kamp,‡ J. Christensen,§ P. Jespersen,§ and K. Dam-Johansen† Department of Chemical Engineering, Building 229, Technical University of Denmark, DK-2800 Lyngby, Denmark, International Flame Research Foundation, P.O. Box 10000, 1970 CA IJmuiden, The Netherlands, and SK Power Company, Lautruphøj 5, DK-2750 Ballerup, Denmark Received July 17, 1996X
The effect of co-firing straw and pulverized coal has been investigated in a 2.5 MWt pilot-scale burner and a 250 MWe utility boiler. In the 2.5 MWt trial the straw was chopped and fed separately to the burner, whereas in the full-scale experiment the straw was preprocessed as pellets and ground with the coal in the mills. Straw fractions in the range of 0-20% on a thermal basis were used in the full-scale experiment and 0-100% on a thermal basis in the pilot-scale experiment. Two low-sulfur coals and one high-sulfur coal were used in the pilot scale, whereas a high-sulfur coal was used in full scale. Results from both tests revealed that an increased fraction of straw in the fuel blend resulted in a reduction of NO and SO2 emissions. The lower SO2 emission was partly due to a lower sulfur content of the straw and partly due to retention of sulfur in the ash, probably present as solid alkali sulfates. The reduction of NO emissions was due to lower conversion of the fuel-bound nitrogen. Increasing the straw fraction results in a larger release of volatiles including NO precursors, leading to conditions that can suppress formation of NO from fuel nitrogen.
Introduction Thermal conversion of biomass has until now primarily been restricted to grate-fired boilers or fluidized beds. Bio fuels such as sawdust,1 straw,2 and sewage sludge1,2 have been reported co-fired with pulverized coal in pilot scale. A test in a conventional 54 MW pulverized coal fired unit using 40% wood thermally has also been reported.3 In Denmark, straw has for some years been used in small-scale grate boilers (
