| Civil sewage sludge drying has been widely recognized as a volume reduction, harmlessness and resource-oriented approach. However, how to choose a reasonable drying process to improve the drying efficiency according drying characteristics, has long been one focus of the study. This article is a study on the sludge drying characteristics to guide drum drying and through a combination of sludge drying parameters on drum drying process simulation to optimize the drum drying.Moisture characteristic experimental study was carried out on thermogravimetry-differential thermal analysis (Netzsch STA409PC, Germany). The results show that more than 80% of the sludge bound water is capillary water, and mainly in micro-capillary. Micro-capillary structure makes the water within the sludge needs gasify internally firstly and then spread out in the form of steam, resulting in sludge particles occur hard outside and soft inside phenomena in drying process. Drying characteristic experimental study was carried out on moisture analyzer bench (DHS16-A). The results show that:increasing the drying temperature higher than boiling point can significantly improve the drying rate of sludge, but the improve rate of drying rate decrease with continue to increase the drying temperature; increasing the particle size will increase the resistance to heat and mass transfer lead to the drying rate decreased, and increase drying stress lead to the capacity reduction rate increased. Constant diffusion model (CDM) and simple variables diffusion model (SVDM) were gotten from a large number of drying experiments, to predict different drying temperatures, the particle size of sludge moisture content variation with time. And it was founded that simple variables diffusion model fitting experiment date at high precision, correlation coefficient was 0.99.Rotary dryer is suitable to be promoted for civil sewage sludge industrial drying, but the lack of model to direct the rotary sludge drying process to cause its further promote limited. The computer simulation method was used to investigate the rotary drier sludge process. First, building flights holds material model, MATLAB program was used to simulate the flight structure, installation angle and sludge particles repose angle on the law of scattering material, and found that:exhausting angle of the flights mainly influenced by the last segment of flight, the greater the angle between the dryer wall and the last flight segment the greater the exhausting angle, and exhausting angle will increase with the repose angle increasing; in the aspect of material spread uniformity, ordinary flights can't achieve spread amount proportional to drop space, but become reasonable with the decrease of material repose angle; spread amount is the most reasonable when material free surface length proportional to drop space, on the basis of this conclude, an optimizing model of flights was proposed and visualized by MATLAB. Secondly, mean residence time model of Rotary dryer was also introduced and simulated in this article. The influence of rotary speed, inclination angle, and radius were considered. It found that these factors have the similar influence on the sludge particles residence time, as they increase, the overall trend is gradually decreased, and the rate decrease of slowing down. Finally, the mean residence time model, drying Model of sludge particle, heat transfer and mass energy balance equations of the sludge particles in the rotary drum dryer were combined to get the heat and mass transfer model. then it was simulated and get the sludge particles temperature, humidity and air temperature distribution along the rotor axis. the result showed that when import air temperature is 650℃, sludge particles moisture content decreased, particle temperature can be divided to short-term temperature rise stage and continuous constant temperature stage, the final difference in temperature between hot air and particle maintained at about 140℃.
|
PDF Full Text Request