Abstract
Use of municipal solid waste (MSW) as fuel for electricity generation reduces landfill disposal and can mitigate air quality degradation associated with combustion of conventional fossil fuels. Co-combustion is a waste-to-energy technology that can use MSW and coal as co-fuels, offering potential energy recovery and reduced air emissions. This research discerns how MSW composition influences the heating value and air pollution for the co-combustion of coal with MSW using five MSW composition scenarios, four of which were derived by a reduction of plastics, organics, paper, or a combination thereof, as compared to the national average MSW composition. Numerous combustion products could be evaluated; this study focused on five high impact air combustion products: SO2, CO, CO2, NO, and NO2. The moisture content was varied from similar to 10% (considered dry) to 404 (average MSW Moisture). AspenPlus software was used for the deterministic simulation modeling of incineration (MSW only) and parallel co-firing (co-combustion of coal and MSW) to determine theoretical heating values and pollutant effluent concentrations. The United States Environmental Protection Agency (U.S. EPA) models WAR and WARM were used to determine the potential environmental impacts (PEIs) and greenhouse gas emission equivalencies, respectively, for each MSW scenario. For the WAR model, values for each impact category parameter can vary, but each parameter is weighed equally. Of the MSW scenarios studied, the national average held the highest heating value with 8519 MBtu/lb and the lowest occurred for the MSW Scenario with recycled paper and composted organics, with 8251 MBtu/lb. Results show that SO2, CO, CO2, NO, and NO2 flue gas concentrations (and therefore PEIs) depend upon the composition and moisture of the MSW, in addition to the MSW/coal ratio. Approximate ranges for the WAR results (PEI/h) are 7410-7663 for NO, 4-8 for NO2, 18 105 for CO, 30-46 for CO2, and 89-2152 for SO2. WARM results show lower net CO2 emission equivalents to landfill MSW with reduced paper and,organics, while combustion is preferred for MSW with paper reduction, organics reduction, and plastics reduction. The results for the national average MSW were independent of the disposal processing method. Reduction in pollutant concentrations did not yield overall cost savings for the electricity producer, as profit was reduced by similar to 20-30%. There are savings associated with emission costs using MSW in lieu of coal: up to similar to 3.3% for NO, similar to 20-47% for NO2, and similar to 95% for SO2. A hypothetical carbon dioxide tax was also imposed to realize the potential cost savings by reducing CO2 emissions. In summary, the measurable impact MSW composition and moisture had on pollutant concentration, heating value, and economic parameters was important.