Drying Technology
Keywords: sludge treatment technology、sewage treatment plants
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Sludge reduction, harmlessness, and resource utilization are the topics of sludge treatment today, but the problem of excessive sludge moisture content seriously restricts the development of sludge treatment technology. Through the description of the status quo of sludge heat pump drying technology, its working principle, air treatment process and general design points of drying equipment are systematically introduced. The expansion design of sludge dehumidification and drying in the development of new network billing system and magnetic levitation large-scale high-efficiency machine is introduced, and the proposed direction of sludge drying equipment standard specification is proposed.
Activated sludge method is currently the treatment method used by 90% of sewage treatment plants in the world. This method will generate a large amount of sludge. If the sludge is not properly disposed of, it will cause secondary pollution to spread to the environment, causing harm to human health and ecological safety. Threats, bringing high potential environmental security risks and hidden dangers. The main hazards caused by sludge are as follows: ① The landfill disposal of sludge consumes a lot of land resources. ② A large number of pathogens (including various heavy metals, trace highly toxic organic substances, a large number of bacteria and parasite eggs, etc.) grow in the sludge. ③ endanger the safety of groundwater sources. ④ bring air pollution. The so-called "control of water but not mud, great transfer of pollution". Sludge reduction, harmlessness, and recycling are the topics of sludge treatment today. However, sludge with high moisture content is very inconvenient during storage, transportation, loading and unloading, etc. Therefore, it is necessary to find efficient and green sludge dryers. Chemical processing technology is imperative.
Classification of sludge drying equipment
The main purpose of sludge drying is to reduce the amount of sludge, and the drying equipment can be divided according to the method of contact between the drying medium and the sludge, the form of the equipment, and the type of heat source. Among them, solar energy sludge drying and electric energy sludge drying are the main applications, and electric energy sludge drying is currently the most widely used and plays an irreplaceable role. Evaporation, dehydration and drying of sludge are divided into high temperature drying and low temperature drying. High temperature drying will cause the volatilization of harmful substances in the sludge, and the high temperature equipment has poor stability and safety, and has been gradually eliminated. Low-temperature drying means that the temperature of the circulating drying hot air is below 90°C, which can effectively avoid the generation of odorous gases such as NH3 and H2S. Dehumidification heat pump low-temperature drying equipment is a typical representative.
Principle and application of dehumidification heat pump low temperature drying equipment
Air circulation: Through the action of the circulating fan, the dry and hot air in the drying box and the wet sludge on the mesh belt form convection heat exchange, so that the moisture in the wet sludge is transferred to the air, and the wet sludge becomes dry sludge. Then the air becomes moist and hot air, which flows through the heat pipe evaporator (the state changes to b) and the evaporator, and is absorbed by the refrigerant in the evaporator to cool the air and separate out condensed water, which is treated uniformly through the drain pipe. After passing through the heat pipe condenser, the air becomes low-heat dry air at this time, and then heated by the condensation heat released by the condenser of the heat pump system, it becomes high-temperature dry hot air, and then flows over the wet sludge surface for circulation. The addition of heat pipe evaporator and heat pipe condenser is to improve the energy efficiency ratio of the system. Exhaust gas treatment devices can also be added to purify the circulating air.
Sludge conveying: Wet sludge with a moisture content of 50%~80% reaches the mesh belt conveying system of the drying box through the conveying device (generally, it will be formed before reaching the mesh belt system to improve the drying efficiency). Dehumidification and drying of the air, the hot dry air rises at a relatively fast speed from the bottom of the mesh belt, and the sludge is dried in the process of contacting with the sludge. The system can reduce the moisture content of the sludge to 10%~50%, drying After the sludge is picked up and transported, the subsequent resource recycling is carried out.
The current sludge drying equipment adopts a modular splicing design, which can be freely combined, and there is no large-scale and efficient equipment. Magnetic levitation and frequency conversion technology are currently rapidly rising in the field of HVAC. The magnetic levitation centrifugal compressor starts at low frequency and low voltage, and the compressor has a long life and is intelligent.
high degree of chemistry. Major equipment manufacturers of magnetic levitation compressors have begun to apply them in a wide range of refrigeration fields, actively exploring the development of various high-efficiency chillers, and after improving the performance of the units, they can replace traditional screw and scroll compressors, and sludge based on magnetic levitation compressors. Drying dehumidifiers are more energy-saving than conventional equipment, have a high degree of intelligent control, and are more integrated with the new networked charging system, which can provide customers with convenience and economic benefits.
