A laboratory study on the NO, NO2, SO2, CO and CO2 emissions from the combustion of pulverized coal, municipal waste plastics and tires

This is a laboratory study on the combustion emissions from pulverized solid fuels: NOx (NO and NO2), SO2, CO and CO2, Coal, waste tire crumb and waste plastics, such as poly(styrene), poly(ethylene), poly(methyl methacrylate), poly(propylene) and poly(vinyl chloride) (PVC), were burned in an electrically heated drop-tube furnace at high particle heating rates (10(4)-10(5) K s(-1)) and elevated gas temperatures (1300-1600 K). The fuel to air bulk equivalence ratio, phi, was varied in the range of 0.4-1.8. Air or a nitrogen-free mixture of O-2-CO2-Ar were used as oxidizing gases. Results showed that fuels which contain nitrogen generated the highest NOx emissions. Combustion of coal generated four times more NOx than combustion of tire crumb, in proportion to their nitrogen content, and ten times more NOx than that of the nitrogen-free plastics. The specific NOx emissions decreased dramatically (3-6 times) with increasing bulk equivalence ratio for all fuels. However, the NO2/NO ratio increased with the equivalence ratio in the fuel-rich region. Increasing the gas temperature, in the range 1300-1600 K, resulted in 10-25% more NOx, depending on the fuel. Atmospheric nitrogen contributed 20% of the total NOx emissions for coal, 308 for tires and 100% for the plastics. SO2 emissions of the particular coal and tire crumb tested were comparable. While absolute SO2 emissions of coal and tire increased with the equivalence ratio, specific emissions exhibited a mild downward trend. SO2 emissions were higher in the absence of atmospheric nitrogen, especially at fuel-rich conditions. Mild emissions of CO were encountered in the fuel-lean regions, but they increased exponentially in the fuel-rich region accounting for as much as 10% of the carbon at phi = 2. Overall, the CO2 emissions were proportional to the carbon content of the fuels. (C) 1998 Elsevier Science Ltd.