Development And Test Of Stirring Dryer For Sewage Sludge With Superheated Steam

With the development of urbanization level in China, The discharge municipal wastewater increase more and more in recently years. As the accessory of wastewater treatment, the production of sewage sludge increase rapidly. The sewage sludge contains a lot organic pollutants, heavy metals, virus, microorganism and so on. The misconduct of it will cause serious environmental pollution and become harmful to human health. Meanwhile, Reasonable treatment and disposal may change waste into valuables because sewage sludge has complicated composition. The article introduces common treatments, including concentration, digestion, mechanical dewatering and disposals such as landfill treatments, desiccation and incineration, composting, brickmaking.Drying technology is key step before reasonable disposal to be widely studied at home and abroad. Traditional drying technology can be divided into three groups: direct drying, indirect drying, and combined drying while new drying includes solar drying, oil-frying drying and so on. Each drying technologies have own advantages and disadvantages to be worth learning. Due to so many advantages with saving, high heat transfer coefficient, no transfer quality resistance and good quality of drying production, superheated steam drying is paid much more attentions today. The article give two examples about superheated steam drying with superheated steam fluidized bed and two-stage combined drying process which will be used in preparing sludge granulated fertilizer.A superheated steam mixing and drying equipment is designed for sewage sludge in this paper. Key parts is described in detail including screw feeding device, stirring paddle rachis components and practical installation, shell weldment, top head and so on. Besides, control cabinet, inverter, design of control system are introduced at the same time. To improve test-bed and process design matching mixing and drying equipment, automatic electric heating steam boiler, heater, gas heat exchanger, pipeline, fan and some other components were connected compactly together. Then the preliminary test and study for drying property were began on the test-bed under the same steam flow, 30 min for drying time, 200℃ for superheated steam temperature, 10kg/h for feeding speed. Different spindle speeds were changed into 300r/min, 450r/min, 600r/min for making drying tests. The moisture of discharging drying sludge was measured and its apparent forms were observed.The result showed that when the spindle speed reached 300r/min and 450r/min, the moisture of drying sludge would be 29.91% and 37.45%. The drying effect was evident. It is obviously that the higher spindle speed adjoint the smaller sludge particle by the apparent forms of discharging drying sludge. But the moisture of drying sludge get too high to be 53.40% when the spindle speed is 600r/min and the result is poor. When the spindle speed is 300r/min, the drying sludge become too large and its average diameter is about 10 mm. So the spindle speed is suitable to be about 450r/min when the condition is set at 30 min for drying time, 200℃ for superheated steam temperature, 10kg/h for feeding speed. The equipment and preliminary test are objective to provide a refence for the design of superheated steam multi-effect combined drying technology for sewage sludge.