Research On Drying Characteristics And Process Of Sewage Sludge

With the continous increasing of the wastewater discharge and its treatment rate, the sewage sludge volume seems to be growing rapidly in China. Whether adopting which method to dispose sewage slduge, reducing the moisture content of sewage sludge is a necessary intermediate treatment process. Sewage sludge thermal drying to reduce moisture content has been proved to be a very effective method for reducing the volume and weight, eliminating the hazard and recycling as resource. Experiment study on drying characteristics of sewage sludge was investigated in this dissertation.After introducing the constitution and basic characteristics of sewage sludge, the common disposal methods and their developing trend were discussed, and the necessity and importance of sewage sludge drying was explained. Then the study progress on sewage sludge moisture distribution, drying chacteristics and the apparent morphology were discussed. The research content of this dissertation was brought out.The thermal drying experiments of a typical sewage sludge were done on the convective drying equipment. The differential of drying rate to dry base moisture content was brought out to analyze the sewage sludge moisture distribution. The content of free water, interstitial water, surface water and bound water in sewage sludge was given. Then the relationship between sewage sludge moisture content and viscosity was discussed. Kinetic analysis of sewage sludge drying process was done, then the reaction mechanism equation and drying activation energy was calculated.The sewage sludge drying characteristics was studied through convective drying experiments, and the relationships among water content, drying rate and drying time were given. Then the influence of drying temperature, hot air velocity, hot air relative humidity and sludge shape on drying characteristics was discussed. The drying kinetic models were fitted to experiment data to find the best sewage sludge drying model, and the expression between model parameters and drying conditions was analyzed.Sewage sludge apparent images under various experiments conditions were screened by digital camera and microscope. Image analysis was done through image processing technology, and the change law of sewage sludge apparent morphology during drying process was studied. Approximately calculation methods of sewage sludge volume, porosity and fractal dimension through image analysis were brought out. The change law of volume, porosity and fractal dimension during drying process was found out, and their influence factors such as drying temperature and hot air velocity were discussed.Coal, biomass and dry sewage sludge were used as additive to change sewage sludge character, then convective drying experiments of the mixture were done. The moisture distribution, reaction mechanism equation and drying activation energy of the mixture were discussed. The influence of additive kind, addition proportion, granule size and addition time on the drying characteristics were discussed. The mixture volume, porosity and fractal dimension during drying process were calculated for finding their changing law.Sewage sludge drying system with the capacity of 20t/d was introduced, and the mass and energy balance in the system was analyzed. Drying experiments of sewage sludge mixed with additive were done, and the influence of addition proportion, addition position on drying effect was discussed. Then the improvement methods for the drying system were brought out.General summary of this paper and further research was presented at the last chapter. It is beneficial to for the further studying.