Experimental Study On Sludge Combustion Characteristics And Chlorine Release

Sludge is a solid by-product of sewage treatment,which contains a large amount of water,pathogenic microorganisms and a variety of pollutants.It must be properly disposed of to protect environment.Incineration treatment can decontaminate the sludge and minimize its volume,which makes the proportion of sludge incineration in various countries increases year by year.However,the chlorine in the sludge will release at high temperature,causing adverse effects such as high temperature corrosion and ash corrosion.So,the law of chlorine release during the combustion has received extensive attention.In this paper,waste sludge and municipal sewage sludge were chosen because they are typically suitable for incineration and they contain certain chlorine.The combustion characteristics and combustion products of the samples were detected by the TG-FTIR system;the incineration treatment was carried out by the static combustion system,and the residual chlorine content of the ash was detected by potentiometric titration and ion chromatography.These experiments can help to confirm the law of chlorine release,the conclusions are as follow:(1)The sludge sample has high volatile content with many types,leading the combustion process,while coal mainly consists of coke.So,the sludge combustion performance is better than coal.Under anaerobic conditions,coal burnout rate and combustion products are greatly reduced;while oxygen has little effect on that of sludge samples.As the oxygen concentration increases,the ignition and burnout temperatures of all three samples decrease,and the maximum rate of combustion also increases.(2)The chlorine content and morphology of the three samples are different.The chlorine content of the waste sludge is the highest,reaching 2.3%,and the sewage sludge is 0.159%.The chlorine in these two sludges mainly occurs in an inorganic form,and more than 95%of the chlorine in the sludge can be extracted in the form of chloride ions by leaching.The chlorine content of coal is 0.086%,most of which is organic chlorine,the inorganic chlorine only accounts for 32.6%.(3)The chlorine of the three samples release in the form of HC1 or alkali metal chloride.For the two sludges,HCl release from 200 ℃ to 600℃ and the coal from 300℃to 700℃.The temperature of HCl release corresponds to the temperature of the CO2 release.Under anaerobic conditions,the HCl release of coal,waste sludge and sewage sludge decreased by 68%,83%and 53%respectively,indicating that the participation of oxygen has a positive effect on the release of HCl.However,when the oxygen concentration is greater than 20%,the increase of oxygen concentration has no effect on the total amount of HCl release.From 800 ℃ to 1000 ℃,the chlorine in the sludge mainly releases in the form of alkali metal chloride,and the release rate has little to do with the presence of oxygen,indicating that this process does not require the participation of oxygen.By comparing the residual chlorine in HCl and ash,it was found that the chlorine in sewage sludge and coal was mainly released by HCl,while the chlorine in waste sludge release in the form of alkali metal chloride.(4)In this paper,a smoke model is established,and a chemical thermodynamic equilibrium software was used to simulate three inorganic chlorides and different ash contents during the incineration.After the main components of the sludge were studied by many tests,the chlorine release law of sludge was discussed through the simulation of these sludge components.