How to deal with the secondary pollution caused by garbage incineration?

Conventional treatment methods of municipal solid waste include landfill, incineration and composting. Garbage incineration has attracted much attention because of its advantages of complete harmlessness, large capacity reduction, short treatment time, heat energy recovery and small occupied area. Since the Eleventh Five-Year Plan, China has built more than 50 domestic waste incineration power plants, and Zhuhai, Shanghai, Beijing, Guangzhou and other places are also actively preparing for large-scale waste incineration plants.

The core of incineration technology is the reasonable organization of combustion and the prevention of secondary pollution. The secondary pollutants of garbage incineration to the environment mainly come from the flue gas produced during incineration. Incineration flue gas contains a large number of acidic gases (hcl, so2, hf, hbr, nox, etc.). ), organic pollutants (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, etc. ), particulate matter and heavy metals. On the basis of introducing the generation and discharge process of various pollutants in the incineration process, this paper puts forward the measures to control the secondary pollution of garbage incineration.

1? Formation and harm of flue gas pollutants from garbage incineration

1. 1? acidic gas

The acid gases in the incineration flue gas are mainly composed of sox, nox, hcl and hf, all of which come from the combustion of corresponding garbage components. Sox is mainly composed of so2, which is produced by incineration and oxidation of sulfur-containing compounds. Nox includes no, no2, n2o3, etc. It is mainly caused by the decomposition and transformation of nitrogen-containing compounds in garbage or the high temperature oxidation of nitrogen in the air during combustion. Hcl comes from chlorides, such as nacl and kcl in pvc, rubber, leather and kitchen waste. The concentration of hcl gas in incineration flue gas is relatively high, often 400 ~ 1200? One in a million. The concentrations of sox and nox are relatively low. There are two reasons why the garbage incinerator produces dioxins: one is that the garbage itself contains a small amount of dioxins, and the other is that the incinerator produces dioxins during the combustion of garbage. There are three formation mechanisms: (1) high temperature synthesis. In the initial drying stage of garbage entering the incinerator, except water, low-boiling organic substances containing hydrocarbon components volatilize and react with oxygen in the air to generate water and carbon dioxide, forming a temporary anoxic state, so that some organic substances react with hydrogen chloride to generate dioxins; ? (2) Ab initio synthesis. Through de? The new synthetic reaction forms dioxins. That is, at low temperature (250~350℃), macromolecular carbon (residual carbon) reacts with organic or inorganic chlorine in fly ash matrix to generate dioxins; ? (3) precursor synthesis. Incomplete combustion and heterogeneous catalytic reaction on the surface of fly ash can form a variety of organic gas phase precursors, such as polychlorinated phenol and polyvinyl chloride. In the combustion process, precursor molecules generate dioxins through chemical reactions such as rearrangement, free radical condensation and dechlorination.