HCl emission characteristics and BP neural networks prediction in MSW/coal co-fired fluidized beds

The HCl emission characteristics of typical municipal solid waste(MSW) components and their mixtures have been investigated in a Φ150 mm fluidized bed. Some influencing factors of HCl emission in MSW fluidized bed incinerator was found in this study. The HCl emission is increasing with the growth of bed temperature, while it is decreasing with the increment of oxygen concentration at furnace exit. When the weight percentage of auxiliary coal is increased, the conversion rate of Cl to HCl is increasing. The HCl emission is decreased, if the sorbent(CaO) is added during the incineration process. Based on these experimental results, a 14×6×1 three-layer BP neural networks prediction model of HCl emission in MSW/coal co-fired fluidized bed incinerator was built. The numbers of input nodes and hidden nodes were fixed on by canonical correlation analysis technique and dynamic construction method respectively. The prediction results of this model gave good agreement with the experimental results, which indicates that the model has relatively high accuracy and good generalization ability. It was found that BP neural network is an effectual method used to predict the HCl emission of MSW/coal co-fired fluidized bed incinerator.

Effect of Atmosphere on HCI Releasement during MSWI Fly Ash Thermal Treatment

Municipal solid waste incineration(MSWI)fly ash constitutes a hazardous waste.Melting disposal has been verified to be prospective for stabilizing heavy metals and dioxins.Release of contaminant HCl during MSWI fly ash thermal treatment leads to potential environmental risks.The behavior and transformation of chlorine are critical to the disposal strategy of MSWI fly ash.In this study,the pathway of HCl formation in MSWI fly ash thermal treatment under complex atmosphere was revealed.Results show that CaOHCl in fly ash was first decomposed to CaCl_(2),CaO and H_(2)O below 550°C,which provides H for HCl generation.Then,CaCl_(2),NaCl or KCl were reacted with H_(2)O to release HCI,during which process H_(2)O and O2 promote HCl formation,CO inhibit HCl production since H_(2)O is consumed in water-gas reaction.The initial temperature of HCl generation affected by the concentration of H_(2)O in the atmosphere.When temperature up to 1250°C,almost all NaCl or KCl were volatilized,HCl mainly from the reaction of chlorine-containing minerals with H_(2)O,such as Ca_(19.2)Mg_(2.8)(Si_(0.75)Al_(0.75))8 O36Cl_(2),Ca4(SiO4)(SO4)Cl_(2)and Ca10(SiO4)3Cl_(2)in N_(2),CO and air atmosphere separately.Moreover,in a reducing atmosphere,metals are more easily chlorinated by HCI,resulting in further consumption of HCI.The order of atmosphere for reducing HCl emissions should be CO>N_(2)>Air>>H_(2)O.