Bench-Scale Biomass/Coal Cofiring Studies

    Research output: Contribution to conferencePaper

    Abstract

    The threat of increased global warming has subjected fossil fuels to increasing scrutiny in terms of greenhouse gas and pollutant emissions. As a result, using renewable and sustainable energy resources, such as biomass, for electricity production has become increasingly attractive. Cofiring biomass at low percentages in coal-fired power plants could dramatically increase the use of sustainablefuels for power production without large capital investments, takes advantage of the high efficiencies obtainable in coal-fired power plants, and provides fuel diversity. Cofiring can also be viewed as a way to mitigate CO2 emissions because CO2 is consumed during plant growth. Several utilities have tested biomass/coal cofiring in utility boilers and issues remain regarding how blending biomassand coal will affect combustion performance, emissions, fouling and slagging propensities, corrosion, and ash saleability. In and effort to further address issues biomass/coal cofiring faces, representatives from NREL, Sandia National Laboratories Combustion Research Facility, and the Federal Energy Technology Center have embarked on a collaborative effort to study many of the fireside issuespertaining to biomass/coal cocombustion. This paper describes bench-scale biomass/coal cofiring experiments that support this effort. The combustion behavior, gaseous emissions, and alkali metals released during the combustion of several biomass/coal blends were investigated using a direct sampling, molecular beam mass spectrometer system (MBMS) in conjunction with a high temperature quartz-tubereactor. Experiments were performed with Pittsburgh #8 and Eastern Kentucky coals blended with various biomass samples such as red oak wood chips, imperial wheat straw, Danish wheat straw, and switchgrass. Pittsburgh #8/biomass blends contained 15% biomass on an energy input basis. Eastern Kentucky/biomass blends included three blends with 15% biomass on an energy input basis, one blend with 5%imperial wheat straw on an energy input basis, and one blend with 25% red oak on an energy input basis. Each of the pure fuels and blends were subjected to combustion in 20% O2 in helium at a furnace temperature of 1100 deg. C and the products were monitored with the MBMS. The products of interest included NOx, SOx, chlorine, and alkali metals. The amounts of NO and SO2 detected during thecombustion of the coal/biomass blends suggested that any change was the result of diluting the nitrogen and sulfur present in the fuel blend. The chlorine released during the combustion of the coal/biomass blends, however, did appear to be affected by blending the two fuels beyond just a dilution effect. The amount of hydrochloric acid detected during the combustion of the coal/wheat strawblends was higher than expected based on the combustion results for the pure fuels. Conversely, the amounts of potassium chloride and sodium chloride detected during the combustion of the coal/wheat straw blends was lower than expected. It appears that blending coal and high chlorine and alkali containing fuels affects the chlorine partition- ing in the gas phase in such a way that cannot beexplained based on just mixing of the pure fuels. At the present time, this effect is not fully understood, however, equilibrium calculations and fuel and blend compositional analyses will help confirm and understand this interesting chemical effect. Contact (e-mail): david_dayton@nrel.gov
    Original languageAmerican English
    Pages569-579
    Number of pages11
    StatePublished - 1999
    EventImpact of Mineral Impurities in Solid Fuel Combustion: Engineering Foundation Conference on Mineral Matter in Fuels - Kona, Hawaii
    Duration: 2 Nov 19977 Nov 1997

    Conference

    ConferenceImpact of Mineral Impurities in Solid Fuel Combustion: Engineering Foundation Conference on Mineral Matter in Fuels
    CityKona, Hawaii
    Period2/11/977/11/97

    NREL Publication Number

    • NREL/CP-430-23582

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