Research On Process Parameters Optimization For Superheated Steam Drying Sludge

With the development of economic and urbanization in our country, the number of urban sewage treatment plants and production daily also become more and more big. A large amount of accumulated sludge not only occupy vast farmland area, and the harmful composition for the sludge which is a pathogen, volatile matter and ash and toxic substances in the integration of high moisture content of solid sediment has become one of a public nuisance for the influence of modern urban public environmental health. For now land using, building materials and burning and other processing mode were becoming the main way of sludge disposal, but the moisture content of sludge must conform to the corresponding disposal standards in the process of sludge, so reducing the sludge moisture content is to realize the first premise of sludge reduction, harmless and recycling treatment. Because it is a high-energy consumption for working of the steam generating system and drying medium heating system and long time drying in the Superheated steam sludge drying process, so how to economic and efficient sludge drying become the main problem facing.Drying is one of an effective way to reduce the sludge moisture content, and superheated steam drying is particularly suitable for dry sludge of high moisture content and low value-added materials because the superheated steam drying had some advantages which hot air drying does not, such as low energy consumption, high efficiency, safety and environmental friendly, etc. According to project requirements, test conditions and purpose, a sludge atmospheric pressure superheated steam drying test-bed was designed and produced. And it is completed the installation and commissioning test bench successfully. The test-bed had strong applicability and practicability for its achievement control of superheated steam temperature, steam flow and test data real-time transmission.For the study of the process parameters of superheated steam drying on the sludge to influence of the drying properties, the influence of the superheated steam temperature, the mass of sludge and steam flow were studied as impact factors, and there were two parameters as dry performance index which were the relative of unit energy consumption and average intensity of drying. In order to investigate the relationship between the process parameters of superheated steam drying on the sludge and the drying properties, the single factor experiment and quadratic orthogonal rotation combination test were carried out respectively. Through the analysis of test data, the results showed that:The mass of sludge, steam temperature and steam flow were the main factors influencing on the drying performance of superheated steam drying sludge. With the increasing of steam temperature and steam flow, the decreasing of the mass of sludge, the drying rate was increased gradually. With the increasing of steam temperature and steam flow, the relative of unit energy consumption value was to decrease after the increase, and average intensity of drying has been increased. With the increasing of the mass of sludge, the relative of unit energy consumption value was to decrease after the increase, and average intensity of drying has been decreased.According to analysis of the regression equation and experimental factors on the drying performance index of the response surface and contour shows that the impact of three factors on the two evaluation indexes of order were : the mass of sludge>superheated steam flow>superheated steam temperature. The optimum parameter of relative unit energy consumption was: steam temperature was 215℃; The superheated steam flow was 30 m3·h-1; the mass of sludge was 26g(8mm thickness approximately). In this condition, the predicted relative unit energy consumption was 281.313kJ/g. And the actual relative unit energy consumption was 280 kJ/g in validation tests. By comparing the theoretical predictions and the actual results, the relative error was 0.467%. A valuable reference for the parameter optimization and equipment design of sludge superheated steam drying was provided by the experimental results.