Study On The Drying Methods Of Municipal Sludge

As the ratio of sewage water treatment in our country increases year after year, municipal sludge volume brought by the sewage treatment process grows larger, thus sewage pollution results in the formation of sludge pollution. Sludge treatment and disposal has become one of the most important tasks for environmental protection in order to prevent consequent pollution and make effective use of municipal sludge. There are three sludge disposal methods currently used, which is recycling in agriculture, land filling and incineration. Each of them needs the drying technology. How to dry the municipal sludge economically and efficiently has become an important topic in the science field.The paper mainly targets at investigating municipal sludge drying technology which was efficient, economical. Using the drying box heating system studies on the factors influenced over the drying efficiency of municipal sludge drying, explores the mechanism of sludge drying, and calculates the energy consumption of the sludge drying system. In addition, using home-made solar drying device studies on the factors influenced over municipal sludge drying, and which were based on improving a series of equipment for designing more rational solar sludge drying device, and calculates the relevant operating parameters and drying costs. The following is the main conclusion of the research:(1) During the course of drying sludge by the drying box, the drying rate can be divided into three phases: acceleration phase, constant rate drying phase and falling rate drying phase, the phase of distinctive characteristics: constant rate drying phase accounts for more than 50 percent of the total drying time, the acceleration phase accounts for only 15 percent, so moisture content removal of the municipal sludge mainly in constant rate drying phase.(2) During the course of drying sludge by drying box, when the drying temperature is the same, the thinner thickness of the municipal sludge, the faster drying rate, 1.0cm thickness of the mud cake, the drying effect is best; the smaller diameter of the sludge particle, the faster drying rate, 1.0cm diameter of the sludge particle, the drying effect is best. When the drying temperature is different, come to 1.0cm diameter of the sludge particle on condition that the drying temperature of 120℃, the drying effect is best and the most economical. (3) During the municipal sludge Solar drying experiment, the higher the drying temperature and the lower the humidity, the higher the efficiency of drying. To the 2.0cm thickness of the mud cake for example, the summer (solar radiation intensity of 14.8 kcal per square centimeter) and the winter (solar irradiance of 7.5 kcal per square centimeter) of the maximum rate of drying were respectively 45g per hour and 6g per hour, the drying rate in summer was significantly higher than it in winter, achieving the same effect of drying (moisture content 60%) time were respectively 1.2 days and 7.2 days.(4) Using drying box and solar-hot exhaust joint drying sludge device, to achieve the same effect of drying (60% of moisture content), respectively the cost is 187.5 Yuan per ton, 2.4 Yuan per ton, the cost of solar-hot exhaust joint drying sludge far less than the drying box drying.Results above provided scientific basis for engineering practice of sludge heat-drying and solar energy drying, and has some guided significance.