Experimental Study On Drying And Incineration Of Sewage Sludge In Fluidized Bed

Compared with the rapidly improvement rate of sewage treatment,the situation of sewage sludge disposal in China is very serious,only a few of them have been properly disposed of,while the rest of the sludge directly is discharged or piled up in the open air,posing a serious threat to the surrounding ecological environment.Sludge incineration,which has the advantages of high reduction rate,fast processing speed,can kill all pathogens and can recover energy,is the most thoroughly accepted disposal method at present.However,the content of nitrogen and sulphur in sludge is relatively high,and a large amount of NOx and SO2 gas pollutants will be produced when incineration,and HCl will cause high temperature corrosion of the heating surface,which also has an important influence on the formation of Dioxins.The sludge contains a lot of heavy metal,in the incineration process will cause migration,transformation,serious damage to the environment.In addition,the high cost of equipment investment and the large operating costs are also one of the factors restricting the development of sludge incineration technology.In this context,the experimental study of sludge drying and incineration was carried out.The effect of different sludge thickness,steam temperature and back mixing ratio on drying effect of sludge was studied by isothermal drying test on steam drying test rig.It is found that increasing steam superheat can reduce the adverse effect of partial steam condensation on sludge surface and shorten the time of sludge drying.Then with dry sludge as fuel,a series of incineration tests were carried out on the CFB incineration test bed,and the effects of different incineration temperature,excess air coefficient and sludge water content on the emission characteristics of NOx,SO2 and HCl were studied.It is found that the water content of sludge has little effect on SO2 emission during incineration,when the water content of sludge increases from 11% to 17%,NO emission is significantly reduced and HCl emission is improved.In the end,with the sludge multistage dry circulating fluidized bed incineration treatment process as blueprint,build sludge dry incineration treatment test bed,study the section of drying,burning and the operation mode of flue gas purification,which have laying the foundation for the process of popularizing.It is found that it is suitable for 15 Hz to choose the scraper motor frequency,and it can ensure that the water content of sludge in CFB incinerator is 15%~20%,and the temperature of the incinerator bed is easy to control in the 900 degrees centigrade.The leaching results of Zn,Cu,Ni,Cr,Pb,Cd and Hg in the sludge incineration ash residue are lower than the standard limit value of hazardous waste,and the flue gas purifying system has better effect on soot,SO2 and HCl removal.