JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION
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(c) A stoker boiler (103.5 MMBtu/hr) burning 80% wood bark and 20% deinking sludge (mass basis), equipped with an electrostatic precipitator control. (d) A stoker boiler (349.2 MMBtu/hr) burning 71% bark and 29% wastewater residuals (mass basis), equipped with an electrostatic precipitator (ESP) control. (e) A fluidized bed boiler (210 MMBtu/hr) burning 76% bark, 21% sludge (municipal solid waste), and 3% gas (mass basis), equipped with a baghouse control. Compilation of “air toxic” and total hydrocarbon emissions data for pulp and paper mill sources: a second update (Technical bulletin no. 973) The data reported in technical bulletin no. 973 is based on 64 wood-fired boilers, all of which burn inland wood residues (NCASI 2010). In their analysis, NCASI applied advanced statistical techniques to detect outliers, which were then excluded from the reported data. The bulletin does not provide raw data, and only a summary was available. The bulletin contains data on emissions of more than 75 different air toxics. Among these emitted air toxics, the predominant pollutant species are acetal- dehyde, formaldehyde, and benzene. The emissions from this source are shown as “NCASI Pulp and Paper” in Figure 3. Summary of emission factors from NCASI technical bulletins Figure 3 shows the emission factors for air pollutants from statistical analysis of several sources along with specific emission factors associated with boilers that burn a combination of unconventional fuels. As shown in Figure 3, the emission factors reported by NCASI across several technical bulletins vary con- siderably for all pollutants. One explanation for the large variations could be that NCASI reports average numbers based on detailed statistical procedure applied to the data from boilers of several facilities, whose fuel compo- sition information is not always available. Depending on the blend of the fuel (amount of sulfur, nitrogen, ash, etc.) and the boiler type, the emissions of pollutants vary significantly. When fuel composition data for individual facilities are available, it helps us identify factors that may have caused the variations in the emission factors. For example, the highest emission factor for PM is reported for facilities that burn the maximum propor- tion of wood in the fuel mixture (i.e., 100% bark and wet wood or 71% wood and 29% wastewater residuals), mainly due to the high ash content. For NO x and CO, the emission factors reported in MACT/CISWI testing were the highest, followed by boilers burning 49% wood
biomass fuels. Below subsections provide an overview of each NCASI technical bulletin, followed by a summary in Section 4.3.4. Comprehensive compilation and review of wood-fired boiler emissions (Technical bulletin no. 1013) NCASI technical bulletin no. 1013 summarizes emission factors developed from statistical analysis of stack test data and associated laboratory reports (NCASI 2013). The majority of data was drawn from (1) EPA-mandated major source boiler maximum available control technol- ogy (MACT) and commercial and institutional solid waste incineration units (CISWI) testing conducted in 2009 and 2010, (2) testing conducted by individual facil- ities from 2009 to 2012, and (3) some pre-2009 emission factor data not previously available in the technical bulletins. The emission factors are believed to best char- acterize pollutant emissions from industrial wood-fired boilers operating in the 2009–2012 timeframe and can be considered to be replacements of the existing emis- sion factors in EPA’s AP-42 Chapter 1.6. The data uti- lized to develop the emission factors include boilers burning biomass fuels or combinations of biomass and fossil fuels. The biomass fuels include bark, hog fuel, wood chips, sawdust, sanderdust, and planer shavings, which are similar to the biomass fuels represented in EPA’s AP-42 Chapter 1.6: “Wood Residue Combustion in Boilers.” Comprehensive compilation and review of combination wood-fired boiler emissions (Technical bulletin no. 1026) NCASI technical bulletin no. 1026 summarizes emis- sion factors for boilers that burn wood in conjunc- tion with at least one other nontraditional fuel, such as tire-derived fuel, petroleum coke, dewatered pulp mill sludge, or old corrugated container recycling rejects (NCASI 2015). The bulletin contains informa- tion on emission factors from individual facilities’ stack testing data. From this bulletin, we chose to analyze the relevant emission factors for five facilities that either burn 100% nontraditional fuel (e.g., sludge) or burn wood in conjunction with other fuels in a boiler. These boilers include: (a) A fluidized bed boiler (78.7 MMBtu/hr) burning 100% wastepaper sludge, equipped with bag- house and SNCR controls. (b) A stoker boiler (160.4 MMBtu/hr) burning 39%– 59% bark (mass basis), with the remaining fuel being deinking sludge and mechanical pulping sludge, equipped with a wet scrubber control.
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