(87a) Holistic Analysis of Emissions from a Small, Modular Fast Pyrolysis System for Conversion of Biomass and Mixed Waste

Authors: 
Schwartz, N. R. - Presenter, Mainstream Engineering Corporation
Blaise, M. J., Mainstream Engineering Corporation
Wagner, A. L., Mainstream Engineering Corporation
Yelvington, P. E., Mainstream Engineering Corporation
Total emissions for a small-scale (45 kg/hr, nominally 1 ton/day), transportable pyrolysis system, including on-site utilization of the fuels and byproducts, were determined from measured burner emissions using pyrolysis bio-oil, char, and gas fuels derived from mixed solid waste (MSW) and biomass. Fast pyrolysis provides an alternative to open burn pits that have been used at remote bases, and emit harmful gaseous emissions and particulate matter. By comparison, fast pyrolysis can convert MSW into useful heat and power while producing sterile ash and relatively clean combustion products. Combustion of pyrolysis byproducts (i.e., char and gas) was required to generate process heat for drying the feedstock to the required moisture content (<10%) and to achieve the desired volumetric waste reduction target (>95%). Utilization of byproducts was especially important for these small-scale systems where heat losses and parasitic power draws became more challenging as the surface-to-volume ratio of the unit operations increased. Emissions were measured from a process gas burner, bio-oil burner, and char burner that compose the fuel utilization section of a pilot-scale pyrolytic solid waste remediation system (py‑SWRS), and the emissions were compared to the relevant standard set by the U.S. Environmental Protection Agency (EPA). The gas burner was evaluated using propane (LHV of 47 MJ/kg) and a surrogate process gas (LHV of 8 MJ/kg) with a molar composition of 16% CH4, 39% CO2, and 45% CO. Several 80% (m/m) ethanol and 20% (m/m) bio-oil fuel blends were prepared to measure the CO2, CO, NOx, THC, and PM emissions of a heated, air-atomizing bio-oil burner. Fast pyrolysis char produced from pine feedstock was combusted with a pilot-scale fluidized bed reactor to demonstrate the feasibility of process heat generation. In the char burner, the fluidizing gas flow rate, gas inlet temperature, excess air, and reactor temperature were varied to determine the effects on emissions and combustion efficiency. Based on the emissions of each burner, the total emissions for CO, NOx, SO2, and total PM were determined for the pilot-scale py‑SWRS and compared to the EPA standard for other solid waste incinerators (OSWI), which regulates nine pollutants. Of the four common pollutants, CO, NOx, SO2 met the EPA OSWI standard, while total PM (32.6 mg/dscm) was slightly over the 30 mg/dscm limit. The bio-oil burner contributed the most to the total PM emissions, based on the tested burner conditions. We postulate that the PM could be reduced below the limit by tailoring the fuel-air equivalence ratio of the bio-oil burner. The other five pollutants included in the OSWI standard (dioxins, cadmium, lead, mercury, and HCl), which depend primarily on the feedstock composition, were also considered. The total emissions data were fed into a decision support model for waste remediation at remote locations, which considered environmental compliance as one of the performance metrics.