Analysis and Application of Sludge Low Temperature Heat Pump Drying Technology
Sludge is a by-product of the process of sewage treatment and water purification, and its main components include floccules composed of various microorganisms and organic and inorganic particles.
The vast majority of sludge has the value of resource reuse. In 1995, the World Water Environment Federation (water environmental feder-action WEF) renamed the sludge as biosolids (biosolids), which is a city rich in organic matter that can be effectively utilized. pollutants. The original sludge has a high moisture content (98%~99%), which leads to its huge mass and volume, which is not conducive to transportation and disposal. Dewatering and drying of sludge are important prerequisites for sludge stabilization, reduction and resource utilization. Generally, the moisture content of mechanically dewatered sludge discharged from sewage plants is still as high as 60%~80%, and the disposal methods such as composting, incineration and landfilling of sludge require further drying of the moisture content of sludge to 40%~50%, or even lower.
The principle of sludge solar drying is mainly to use the radiant heating function of solar energy and the water absorption capacity of unsaturated natural wind to evaporate and dry the water in the sludge. According to whether the sunlight directly shines on the sludge, solar drying technology can be divided into greenhouse type and concentrated type.
Heater type. Sludge, as a by-product of sewage treatment, has the characteristics of high organic content, prone to corruption, may cause epidemics, high moisture content, and difficult dehydration (due to the influence of colloidal structure). Landfill, composting, etc. Although these methods can alleviate the problems of large sludge output and difficult disposal, they have hidden dangers of secondary pollution and are not a long-term solution, and have been gradually abandoned in developed countries.
In Germany, methods such as landfilling and composting of sludge have been gradually banned. Therefore, it is imperative to find a safe and economical development path for sludge disposal. There are three mainstream sludge treatment and disposal routes in my country, namely, land use after anaerobic digestion, land use after aerobic fermentation, and building materials use after drying and incineration. The first two treatment methods will have certain effects on the land. The risk of secondary pollution, and because the sludge itself is composed of a large amount of organic matter, the calorific value of the sludge after drying is equivalent to lignite, so the most thorough method for sludge treatment is drying and incineration.
Sludge has the characteristics of high moisture content and large volume, and the primary premise of sludge incineration is sludge drying. Sludge drying technology is a method that uses thermal energy to evaporate the moisture in the sludge to facilitate subsequent sludge treatment. In the past period of time, the treatment process of sludge reduction in my country is mainly divided into two categories: direct drying and indirect drying. Direct drying means that the wet sludge is in direct contact with the high temperature gas, the high temperature gas provides the heat required for the evaporation of the water in the sludge, and then the evaporated gas is taken away by the high temperature gas for further processing. The characteristics of direct drying are high heat transfer efficiency and good drying effect. Common direct drying methods are drum drying, flash drying and belt drying. Indirect drying means that the sludge is not in direct contact with the heat source, and uses the heat conduction effect to contact the outer wall of the metal pipe into which the high temperature heating medium (usually steam or heat transfer oil) is passed to evaporate the water in the sludge. At present, most of the domestic sludge drying projects use indirect drying methods, such as paddle drying, disc drying and thin-layer drying.
Today, the application field of heat pump drying equipment has expanded to various industries, such as leather processing, food processing, tea drying, tobacco drying, vegetable dehydration, fish drying, ceramic baking, sterilization and drying of pharmaceuticals and biological products, Sludge treatment, chemical raw skin and fertilizer skin drying and other fields. In recent years, it has also been used in the engineering practice of sludge drying treatment. The low-temperature drying of sludge is a specific form of belt drying. Its drying temperature is between 40 and 75 °C, which can be adjusted according to the operating environment to meet the requirements of different drying processes. The wet mud (with a moisture content of about 80%) is cut into strips by the slitter and then enters into the steel belt in the belt dryer, and is transported forward at a certain speed (with a frequency conversion motor, in actual operation, it can be processed according to the processing requirements. Adjust the speed of the steel belt), and at the same time, the hot air provided by the dehumidification heat pump is fed into the belt dryer through the circulating fan to dry the wet mud. The dried sludge particles are discharged from the bottom discharge port, and can be directly sent to the storage bin through the transportation equipment. At the same time, the moisture in the drying process enters the heat pump system for dehumidification and reheating, completing one cycle and entering the next cycle for reuse. Although the condensed water during the drying process is clear, it contains a variety of pollutants and needs to be discharged. To the sewage treatment center, it can be discharged only after the treatment reaches the standard.
The use of biological filter technology in waste gas purification treatment in urban sewage treatment plants can not only effectively achieve the purpose of waste gas purification, but also fully utilize biological resources, and ultimately achieve the fundamental goal of maximizing economic and environmental benefits. In the actual use of biofilter technology, the relevant designers need to fully combine the actual situation, strictly abide by the relevant regulations, reasonably select the biofilter, scientifically select the filter material, and accurately set the environmental temperature, humidity and other important parameters. At the same time, attention is paid to the daily operation and maintenance management of the biological filter to ensure that a more ideal exhaust gas purification effect can be obtained after giving full play to its effective function.
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