TOXIC GAS PHASE EMISSIONS FROM THE COMBUSTION OF PULVERIZED COAL MIXED WITH POWDERS OF WASTE PLASTICS OR TIRE CRUMB

摘要

This paper presents results on the gas phase emissions from the combustion of coal and alternative waste fuels (plastics and automobile tires). The plastics examined were poly(ethylene) and poly(styrene). All fuels were burned in powder form. Mixtures (50-50 by weight) of the above waste fuels with coal were also burned. Results are reported on the SO_2, NO_x, CO and CO_2 emissions. For a limited number of cases results are also presented on the release of organic air toxics, in particular the polynuclear aromatic hydrocarbons (PAHs). Experiments were conducted under well-controlled conditions in bench-scale laboratory facilities. Coal particles, ≈100 μm, and particles of pulverized alternative fuels, ≈200 μm, were injected and burned in an electrically-heated drop-tube furnace. The furnace temperature was set to 1250℃. The residence time of the gas was 1 s. Experiments spanned a range of fuel-lean (φ < 1), stoichiometric (φ = 1) and fuel-rich (φ > 1) conditions. Results showed that (a) the NO_x emissions of tires were a few times lower than those of coal and those of plastics were even lower. Thus, blending these alterative fuels with coal drastically reduced NO_x emissions. NO_x emissions of all fuels decreased drastically with the increasing equivalence ratio, (b) the SO_2 emissions of tires were comparable or a little higher than those of coal, meanwhile there were negligible SO_2 emissions from burning plastics. Generally, specific SO_2 emissions decreased mildly with increasing equivalence ratio. The CO emissions from all fuels increased sharply with the equivalence ratio, in the fuel-rich region only. CO emissions were the highest poly(ethylene) and poly(styrene) followed by tire crumb and then coal. The specific CO_2 emissions were proportional to the carbon content of the fuels and decreased with increasing equivalence ratio. PAH emissions of tires were higher than those of coal. Combustion of coal blended with tire crumb or powdered plastics drastically reduced the NO_x emissions. The SO_2 emissions of coal were also reduced in the case of blends with plastics only. Blending with the alternative fuels somewhat increased the CO emissions of coal in the fuel-rich domain. Blending with plastics increased the CO_2 emissions, while blending with tire decreased the CO_2 emissions of coal. Blending with tire mildly increased the PAH emissions of coal.