The Mechanism Analysis Of Mixed Waste Plastics And Pulverized Coal Combustion In Grate-Kiln Pelletizing Process

The behavior and mechanism of mixed waste plastics and pulverized coal(PC for short) in flight combustion process was studied in this paper, which could provide a theoretical basis and technical support for injecting waste plastics in grate-kiln pelletizing process. Combustibility index and ignition characters index of PC and three plastics(PE, EVA and ABS) have been compared by means of thermogravimetry. Co-injection combustion experiments of waste plastic and PC were conducted in a horizontal combustion furnace. Afterwards the temperature field in furnace and the composition of exhaust were analyzed. The established that gas-solid flow, heat transfer and combustion of mixed pulverized coal and waste plastics digital model was used by the simulation software in the rotary kiln, Afterwards the temperature field, the gas concentration field, the composition of exhaust and the concentration distribution of Volatile in furnace of the geometric model were analyzed systematically. The behavior and mechanism of mixed waste plastics and pulverized coal in flight combustion process was revelation.Combustibility and ignition characters index of the plastic was up to one order of magnitude of that of PC, Moreover, combustibility and ignition characters index of PE was the highest, The apparent activation energy of waste plastics is markedly lower than that of pulverized coal. Moreover, The reaction order of waste plastics was obviously higher than that of the pulverized coal.With the addition of 10 %-20 % plastic in PC, the highest temperature positions shift towards the fuel imports in the furnace, indicating that the plastic could effectively promote the combustion of PC and improve its combustion rate. When the addition of plastic was over 20 %, the highest temperature positions shift towards exhaust outlet in the furnace and the temperature in furnace decreased obviously.The combustion of PC was suppressed by the plastic and the rate of PC combustion was significantly decreased. The concentration of CO was decreased and the proportion of CO2, NOx and SO2 was increased in exhaust gases with the plastic addition increased from 10% to 30%, the concentration of SO2 in the exhaust was decreased from 40 ppm to 10 ppm.With the addition of plastic in PC, the highest temperature positions shift towards the fuel imports in the furnace, When the addition of plastic was over 20 %, pulverized coal combustion was restrained by waste plastics. results of combustion experiments shows different slightly. The concentration distribution of CO, CO2 and H2 O was more than pulverized coal combustion in the process of mixed fuel combustion. The produced vapor quality score of mixed fuel combustion was more than that of the pulverized coal.The dynamics analysis of pulverized coal binding plastic, the volatilization of pulverized coal and fixed carbon touch oxygen each other was blocked by plastic droplet, the fixed carbon combustion was hindered by plastic droplet. The fixed carbon combustion was jammed in the anaerobic area of Plastic droplet.When the oxygen mass fraction of plastic was less than that of the fixed carbon combustion needed. Fixed carbon combustion rate of pulverized coal will be reduced.The thermomechanical analysis of pulverized coal binding plastic indicate that, Pulverized coal and plastic combustion were priority to CO2 generated in the process of low temperature and CO generated in the process of high temperature. When the temperature was raised to 616℃, CO and H2 was generated primarily by CH4 combustion. The incomplete combustion of CH4 was played dominant roles with increasing temperature. Fixed carbon combustion in coal was restrained. For gasification reaction of the fixed carbon in coal, the gasification reaction of fixed carbon was promoted by combustion of pulverized coal and waste plastics.