OCR Text |
Show 2 combustion and fuel conditions on the emissions. Even with the more prevalent fuels, the importance of fuel composition and combustion stoichiometry is relatively poorly understood. As other types of biomass materials enter the fuels market, and more advanced conversion technologies develop, the potential environmental impacts and emission control requirements become less clearly defmed. During a laboratory study investigating the inorganic transformations and ash deposition characteristics of biomass fuels in steam boilers (Miles, et al., 1994; Baxter, et al., 1993; Jenkins, et al., 1994), measurements were made of uncontrolled pollutant concentrations for various species under variable stoichiometry. Concentrations were converted to emission factors or emission indices giving mass ratios of emitted pollutant to dry fuel consumption for the purposes of normalizing the results. These uncontrolled emission factors indicate how certain fuel characteristics may impact pollutant emission control measures, as, for example, in the case of nitrogen species where ammonia injection for NOx control is routinely employed in commercial biomass-fueled units. Predictions of the injection rates for ammonia (itself a greenhouse gas and important in the formation of aerosols and in acid deposition) to avoid excess slip Ooss of unreacted ammonia through the stack) require knowledge of the NOx production rates in the furnace. Non-catalytic NOx reduction by ammonia injection also tends to increase the emission of N20, which is an important greenhouse gas (Becker, et al., 1992). Biomass materials contain variable amounts of nitrogen, sometimes in quite large concentrations, but the conversion fractions of fuel nitrogen to NOx as a function of fuel nitrogen concentration are largely unknown (Grass and Jenkins, 1994). Although the measurements described here were not capable of distinguishing NOx from thermal, fuel, or prompt mechanisms, total NOx emission was obtained over a wide range of fuel nitrogen concentrations and air-fuel ratios. Also reported are emission factors for S02, CO, and total hydrocarbons. Methods Concentrations of NO, NOx (as N02), S02, CO, total hydrocarbons (THC as Cf4), C02, and 02 were monitored by continuous analyzers sampling the exit gas from the Multifuel Combustor (MFC) at the Combustion Research Facility, Sandia National Laboratories, Livermore, California. This laboratory unit was originally designed to simulate pulverized coal combustion in utility coal-fued furnaces, but has subsequently been used with solid biomass fuels and biomass-derived liquids. The combustor, depicted in Figure |