Theoretical and experimental study on the emission characteristics of waste plastics incineration by modified O 2/RFG combustion technology

Abstract

For mitigating the emission of greenhouse gas CO 2 from general air combustion systems, a clean combustion technology O 2/RFG is in development. The O 2/RFG combustion technology can significantly enhance the CO 2 concentration in the flue gas; however, using almost pure oxygen or pure CO 2 as feed gas is uneconomic and impractical. As a result, this study proposes a modified O 2/RFG combustion technology in which the minimum pure oxygen is mixed with the recycled flue gas and air to serve as the feed gas. The effects of different feed gas compositions and ratios of recycled flue gas on the emission characteristics of CO 2, CO and NO x during the plastics incineration are investigated by theoretical and experimental approaches. Theoretical calculations were carried out by a thermodynamic equilibrium program and the results indicated that the emissions of CO 2 were increased with the O 2 concentrations in the feed gas and the ratios of recycled flue gas increased. Experimental results did not have the same trends with theoretical calculations. The best feed gas composition of the modified O 2/RFG combustion was 40% O 2 + 60% N 2 and the best ratio of recycled flue gas was 15%. As the O 2 concentration in feed gas and the ratio of recycled flue gas increased, the total flow rates and pressures of feed gas reduced. The mixing of solid waste and feed gas was incomplete and the formation of CO 2 decreased. Moreover, the emission of CO was decreased as the O 2 concentration in feed gas and the ratio of recycled flue gas increased. The emission of NO x gradually increased with rising the ratio of recycled flue gas at lower O 2 concentration (<40%) but decreased at higher O 2 concentration (>60%).