| In recent years,the annual sludge output of China's urban sewage plants is growing at a high speed,and it is estimated that the sludge output in China will reach55.5 million tons in 2020.At present,the problems of short life,high energy consumption,unstable operation effect and high failure rate in the core area of the equipment are common in domestic sludge treatment system.Therefore,the research and development of a safe,economical and efficient sludge drying process that can not only meet the requirements of sludge treatment and disposal,but also be conducive to the subsequent resource utilization has become a topic of keen discussion among the practitioners in the field of sludge drying.This paper mainly studied the basic characteristics and drying characteristics of municipal sludge.Firstly,the industrial composition,element content and apparent viscosity of sludge samples from three municipal sewage treatment plants in Zhenjiang city were analyzed,and then a small test device for sludge drying was designed to conduct debugging experiments.The main research contents are as follows:1.Industrial analysis,content detection of non-metallic elements,content detection of conventional metals and content detection of some heavy metal elements were conducted on three kinds of sludge,and the results showed that the moisture content of the three kinds of sludge was higher than 80%;The content of volatilization and fixed carbon in the sludge in Zhengrunzhou and Jingkou areas was higher,and the content of C and H was significantly higher than that of Jianbi sludge.The volatile and fixed carbon content of Jianbi sludge was lower and the ash content was higher.In the detection of metal element content of sludge,Al,Fe,Ca,K,Zn and Cu in heavy metals are the ones with high content of conventional metal elements.2.The apparent viscosity of sludge in Jingkou area was measured under different water content,temperature,rotating speed,mixing ratio and CaO adding ratio.The results showed that the sludge with different water content showed the characteristics of pseudoplastic fluid at lower shear rate,Newtonian fluid and Bingham fluid at higher shear rate.The power function model of shear rate and sludge apparent viscosity was obtained;As the temperature increased from 20?to 80?,the apparent viscosity of sludge decreased gradually,and the shear rate and the apparent viscosity of sludge were fitted into the S-function model.The difference between the flow curve of sludge with CaO addition and that without CaO addition was great.After mixing,the rheological curve of sludge has little difference from that of mixing sludge.3.The design of the low temperature vacuum drying device and device processing out,according to actual situation of sludge in different drying temperature,thickness,ventilation,air volume,CaO and mixing rate is studied in this series of conditions,it is concluded that the corresponding effect of drying curves and drying rate curve,the results show that the sludge drying rate will experience major endothermic,fast,slow down and low speed;The drying rate of sludge was positively correlated with the drying temperature and negatively correlated with the sludge thickness.By comparing the consumption time and power consumption of semi-drying,it is concluded that under the conditions of thickness of 4 mm,drying temperature of 80?and air volume of 156 m~3/h,adding 2.5%CaO and 10%mixing of dry sludge is the optimal semi-drying and full-drying conditions in a series of drying experiments,respectively. |
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