Experimental Study Of The Effects Of Atmospheres On MSWI Process And Heavy Metals Behaviors

With the increasing of municipal population and improving of life level, the generation, organic composition content and heat value of municipal solid waste (MSW) also increase. Large number of MSW has led to enormous damages for people and environment;then how to realize harmless, volume reductive and resourceful treatment of MSW has become world research problem. Incineration plays an important role in the disposal and utilization of MSW. More recently, the development of municipal solid waste incineration (MSWI) technology has more mature;however the environmental requirements have become stricter, correspondingly MSWI technology, incineration efficiency and the second pollution (especially for the release of toxic substances such as heavy metals and dioxins) have become stricter. This paper starts with complex atmospheres in incinerator, and studies on the effect of these atmospheres on incineration process and heavy metals behaviors.Firstly, the thermal gravimetric experiments were done to analysis thermal decomposition (reductive atmosphere) and combustion characteristics (oxidative atmosphere) of six representative compositions of MSW. Comparing the former with the latter condition, volatilization of volatiles and combustion of fix carbon process under thermal decomposition lag behind under combustion;through mixing these thermal gravimetric curves, the properties of these compositions in MSW during thermal decomposition and combustion respectively can be obtained;the thermal decomposition and combustion characters of wood, paper and textile are resemble, the same to rubber and food residue. The plastic waste shows higher thermal decomposition temperature and narrower thermal, decomposition temperature range. Meanwhile, it was proved that the thermal decomposition/combustion characteristics of mixed compositionscould be thought as the sum of the ones of several single compositions and little effect among them.According to select proper reaction kinetics equations and calculate the kinetics parameters—apparent activation energy Em, it is known that the different reaction extent of every composition can be gained under two conditions;Under thermal decomposition condition the order of compositions from difficult to easy is rubber, food residue (vegetables), textile, paper, wood and plastic;under combustion condition the order is textile, plastic, wood, paper, rubber and food residue, which has theory instructing meaning for selecting MSW treatment methods. The conversion rates calculated by mechanism reactions tally with ones by experiments, which shows the chose reactions can reflect the practice reaction process.The effects of atmospheres on heavy metals vitalization characters are studied on a suit of equipment designed by myself. The results show that the reductive and oxidative atmospheres have greater effect on Ni, Cu and Cr;generally, heavy metals under reductive atmosphere have higher volatilization character than under oxidative atmosphere. The increase of HC1 content would lead to different extents volatilization increase of heavy metals, and the exist of HC1 changes the distribution of heavy metals, makes the distribution tend to transfer from bottom ash to flue gas, more apparently are Pb, Zn and Cd. Setting Cd as an example, if the remaining time is enough long, there is little effect of the atmospheres on CdCl2, and only some effects on volatilization rate. Whereas, short remaining time would affect the volatilization of heavy metals greatly. The temperature also in some extent affects the volatilization of heavy metals. Furthermore, the increase of moisture in waste would affect the heavy metals. For Cu, the presence of moisture depresses the volatilization of oxides, and increases that of chloride and the metallic species, while in contrast, the volatilization of both Pb and Zn is always depressed, regardless of the chemical forms used.The transformation and evolvement of six heavy metals different forms are studied through HSC thermodynamics calculate software and database,the calculate results show the effect of different atmospheres on transformation of different forms. Comparing the transformations and distributions in bottom ash and flue gas of heavy metals under reductive atmosphere with ones under oxidative atmosphere, there is a great effect on Cd, Cr and Cu, and different forms appear in different atmospheres, next there is small effect on Ni and Zn, all transformation forms are same and the temperature starting to transform under oxidative atmosphere is lower than under reductive atmosphere, while for Pb, there is no effect on it.Subsequently, the comparative studies on effects of atmospheres on incineration and pollutants control is very meaning, and it is worthy to study further intensively.