Study On Pyrolysis And Incineration Of Medical Waste Including The Numerical Simulation Of Three-stage Rotary Kiln Incinerator

The amount of medical waste(MW) increases as the development of the economy, which contains a great quantity of bacteria and viruses. Among current technologies, thermal treatment especially the incineration has been found to be widely used in China. At the same time, rotary kiln is used as an important kind of incinerator due to its flexible feedstock capability.Funded by National High Technology Research and Development Key Program of China(2007AA061302) and Important Project on Science and Technology of Zhejiang Province of China(2007C 13084), the study of pyrolysis and incineration of MW, including numerical simulation of three-stage rotary kiln system, were carried out. Based on the pyrolysis and incineration mechanism of MW(TG-FTIR), numerical simulation on three-stage of rotary kiln system was studied by FLUENT. Finally, a new three-stage rotary kiln incinerator system for MW pyrolysis and incineration was put forward, and experiments on this disposal system were carried out.Experimental investigate of pyrolysis and incineration characteristic of MW is introduced in PartⅠ. Pyrolysis and incineration kinetics also volatile releases of seven typical components of MW were thoroughly studied through complex chemical equilibrium analysis and TG-FTIR system. The products of MW under pyrolysis, gasification and incineration were got by chemical equilibrium analysis. According to the investigation of pollutant product from Cl, N and S, HCl concentration was higher than N and S pollutant, the HCl in the flue gas could meet the need of National standard without scrubber, when less than 0.1% of Cl in MW. At the same time, Cl2 formatted when MW with high Cl composition incinerated at low temperature.The distribution of volatile release of MW was got by TG-FTIR. All volatile from cellulose released before 520℃, including CO2, CO, H2O, acid such as acetic acid, aldehyde such as benzaldehyde, ketone such as 2-butanone, and also hydrocarbon. All volatile from plastic released before 570℃, mainly including hydrocarbon, except HCl released from PVC pyrolysis and incineration. All volatile from tissue released before 620℃, including NH3, HCN, acid, CO2 and hydrocarbon. The kinetic mechanism of seven components of MW was got through TG and distributed activation energy model was set up for volatile release.For the mixture of MW, the effect on PVC to cellulose and tissues was greater than that to plastic. On one hand, from to the chemical equilibrium analysis, HCl in flue gas would exceed the need of National standard when more than 0.1% of Cl in MW. On the other hand, HCl is harmful and corrosive, either directly or indirectly formation highly toxic dioxins and furans in the furnace effluent. Thus, the pyrolysis and incineration of PVC and MW was timely and continuous analyzed, HCl removal efficiency and Ca-based additives were quantitatively studied.Numerical simulation of three-stage rotary kiln system is introduced in Part II. After reviewed the motion of particle in the transverse plane of rotary kiln, including the effect of wall friction, filling ratio and Froude and its functions. The effect of rotate speed, friction angle of wall of the active layer and velocity of particle were studied through Euler-Euler model. From the computation result, the height, slope and area of active layer increased as the increase of rotation speed and friction angle. The particle velocity increased as the increase of rotation speed, and the maximum speed was found at the surface of active layer.A physical-chemical process inside three-stage rotary kiln incinerator was performed with Computational Fluid Dynamics(CFD) code(FLUENT). Standard k-εturbulent model, finite rate/eddy-dissipation reaction model and P1 radiation model were chosen, as well as the char burnout were consider through UDF. From the analysis of the three-stage incinerator, the highest temperature appeared at the connection between rotary kiln and secondary chamber, the effect of leak air from the head of kiln, as well as secondary air and fluidized air to the whole system were analyzed, the fitting arrange of secondary air and the suitable ratio between secondary air and fluidized air were got.Introduce the engineering project of three-stage incinerator system is introduce in PartⅢ, the system was developed by State Key Laboratory of Clean Energy Utilization in Zhejiang University, which linked rotary kiln with secondary chamber. Experiments on this disposal system were carried out, including the characteristic of flue gas, fly ash, bottom ash, heavy metal and dioxin. From the experiment results, we could found that this three-stage incinerator system was suitable for medical waste incineration. According to the analysis of relation among the operation parameters, temperature was the most important parameter to the whole system.