Msw Direct Gasification And Melting Incineration Process Applied Basic Research

The direct gasification & melting incineration of municipal solid waste(MSW) can decrease the pollutions of heavy metals and dioxins in incineration residue and avoid the synthesize reaction of dioxins in MSW incineration.The technology has ecologically and satisfying purpose of reducing the volume and the weight,harmless and resource.The technology is considered as terminal way of MSW management by environmentalists after it had been studied and experimented.This technology was deemed to be an ideal realized technology in 21century.Therefore,the direct gasification & melting incineration of MSW becomes one of the most significant research communities.The emphasis of this study is on the fundamentals of the direct gasification & melting incineration of MSW in according to the characteristic of MSW in China. It is useful in innovate the thermal treatment technology of MSW.Firstly,it was studied that the heat rate and atmosphere effect on the characteristic of MSW gasification and combustion.The results show:the transformation of MSW gasification and combustion is distinct in different temperature region.The reaction products of MSW gasification and combustion have strong orientation,such as CO,CO₂,H₂ and CH₄.The gasification rate of MSW is mainly determined by temperature and detention time.The volume of MSW instantaneous gasification is influenced by the varieties of heat rate. When the concentration of oxygen increase,the volume of MSW instantaneous gasification increase,too.Whereas the variety trend is similar.The TG-DTG thermal analysis showed that the dry MSW include the stage of pyrolysis and gasification in low temperature and the stage of char combustion in high temperature course.The temperature range of thermal process is diverse due to the difference of heat rate and detention time.The finally trend of thermogravimetric analysis are invariability with the speeding up of heat rate. Increase in oxygen concentration,enhance the combustion reaction.The kinetic model of raw MSW gasification and combustion is built according to TG-DTG data with the method of Doyle integral.The mechanism equation of first stage is f(a)=3/2(1-a)^4/3((1-a)^1/3-1)^-1,the mechanism equation of second stage is f(a)=3(1-a)^2/3in 10%oxygen,f(a)=2(1-a)^3/2in 21%oxygen and f(a) =(1-a)² in 56%oxygen.The Kinetics parameters of raw MSW gasification and incineration were obtained in different heat rate and atmosphere.Secondly,the melting mechanisms of MSW incineration were investigated. Incinerator residue normally has CaO,SiO₂ and Al₂O₃ as major constituents. The thermodynamics of incineration residue,such as composite reaction,Gibbs and balance constant of CaO-SiO₂-Al₂O₃ system were characterized during melting process.The characteristics of incineration residue melting were experimented,we also analyze how the content of CaO,SiO₂,Al₂O₃ and the condition of the experimentation impact the characteristics of fusion on solid residues.The experimental results show:it should be controlied that the content of CaO is 33%by weight,ache-alkalinity is 1 and the melting atmosphere is tiny deoxidize atmosphere in order to reduce the melting temperature of incineration residue.In addition,the kinetics model of incineration residue melting transition was regressed from the experimental data of DSC.The kinetics parameters of incineration residue melting transition were obtained.The aforementioned results and model of incineration residue melting form the basic fundamentals for the practical engineering and optimal design of the direct gasification & melting incineration process.Subsequently,migration characteristics of heavy metals(cadmium,chromium, nickel,lead,copper and zinc)in the gasification and melting incineration system of MSW were investigated by experiments.Effect of several factors such as temperature,melting time and atmosphere on the volatilization of heavy metals were discussed in details.The results show that cadmium and lead are volatile metals,while chromium,nickel and cooper are refractory volatility heavy metals.Vitrification of the residues inhibited slightly heavy metals vaporization from MSW gasification and melting incineration,however,the volatility of heavy metals was variational for different compound species.The volatilization rate of heavy metals was fluctuating with the increasing of temperature.The limited zinc was vaporized since a substantial amount of the zinc was converted into ZnO in high temperature oxidation atmosphere.The vaporization percentage of heavy metals vaporization was stable over 30 minutes of melting time.The influence degree of the added HCl and SO₂ on each heavy metal was different.HCl will enhance the vaporization of heavy metals, but the effect of SO₂ on vaporization percentage of heavy metals was not obvious.The mechanisms of desulphurization was studied during the direct gasification & melting incineration of MSW.The influences of operational conditions on the desulphurization efficiency such as reaction temperature,ratio of Ca/S,resident time and absorbents were investigated.The results shown that the CaO has been good at desulphurization,when the reaction temperature is 800～900℃and the ratio of Ca/S is 2.5～3.The desulphurization sorbent of CaO added Fe₂O₃ or plant ash can enhance the desulphurization efficiency of sorbents.Finally,the Semi-pilot scale test was studied in two self-developed direct gasification & melting incineration system,one capacity is 1 t/d,and another capacity is 10t/d.The process of direct gasification & melting MSW incineration was analyzed,and combustion efficiency,chamber temperature distributing and the factors that influence the emissions of NO_x,HCI and SO₂ were studied.The results of experiment demonstrate:when the ability of incinerator is ideal and the run is steady-going,combustion efficiency is more than 95%.The content of heavy metals were less than the rule of environment law in the flue gas,the leaching content of heavy metals were also meet with environmental criterion in melted slag,flue gas is 0.072 ng-TEQ/Nm³,melted slag is 0.001ng-TEQ/g.The emission content of NO_x is added up rapidity with temperature increasing in chamber.Increasing second air or excess air coefficient significantly increased the sulfur-retention efficiency of CaO,and decreased the emission content of SO₂ in flue gas.However,the effect of excess air coefficient on HCl concentration is inconspicuous in flue gas in MSWI. Therefore,this technology can simultaneously realize low emissions dioxin, high efficiency of electric power generation,obtaining stable and useful vitrified slag and reducing in the amount of exhaust gas.Therefore,the process of direct gasification & melting incineration is a feasible method to realize harmless disposal of municipal solid waste(MSW). The technology has advantages of simple structure and harmless treatment thoroughly.Direct Gasification & Melting technology is tacking with the development of environment-friendly technology and its products are harmonious with the external environment.