Drying Technology
Keywords: activatedsludgesewagetreatment sewagesludgedewatering
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The production volume is also increasing sharply. A large number of pathogenic microorganisms, heavy metals, parasite eggs and other toxic and harmful substances are enriched in the sludge. If not properly handled, it will cause secondary pollution to the environment and seriously endanger the health of animals, plants and human beings. The sludge has a high moisture content and is bulky, making it inconvenient to store and transport. Drying and dehydration is the key process in sludge treatment, which can reduce the volume and increase the calorific value, and realize the resource utilization of sludge. Sludge drying treatment mainly includes mechanical dehydration and thermal drying.
The mechanical dehydration of sludge is to remove a large amount of water in the sludge of sewage treatment plants with mechanical devices and reduce the volume. Common mechanical dehydration equipment includes vacuum filter dehydrator, centrifugal dehydration The cost of mechanical dehydration is far lower than the cost of thermal drying treatment, but the moisture content of sludge after mechanical drying is still high, and thermal drying equipment needs to be used for further treatment. deal with. Thermal drying technology is to use high temperature flue gas, steam or heat transfer oil and other heat medium to remove the moisture in the sludge through the heat transfer between the sludge and the heat medium. After thermal drying treatment, the moisture content of sludge can be reduced to 10%~40%, which can realize semi-drying or full-drying of sludge, and greatly reduce the volume of sludge. Belt dryer is one of the thermal drying equipment, and it is also widely used in sludge drying.
The belt dryer can be divided into different types according to the flow form of the drying medium, the number of layers of the conveyor belt, and the temperature of the heating medium. According to the flow form of the drying medium, it can be divided into a through-flow belt type and a horizontal airflow belt type. According to the different number of conveyor belt layers, it can be divided into single-layer belt type, multi-layer belt type and multi-level belt type. The multi-layer belt dryer is a commonly used belt dryer, and the number of layers is usually 3 to 5 layers. It is usually used for low drying speed requirements, long drying time, and process operating conditions (such as drying Medium flow rate, temperature and humidity, etc.) can be kept constant. According to the temperature of the heating medium, it can be divided into low temperature belt type and medium temperature belt type. When the belt sludge dryer was first popularized, it basically adopted the low-temperature drying method. Due to the low drying temperature, a large amount of air needs to be blown in during operation, the floor space is large, and the power consumption of the blower is large. With the continuous research and development of belt dryer technology, the medium temperature belt type has begun to occupy the market. The new belt sludge dryer on the market basically adopts the medium temperature drying method, usually the temperature is higher than 100 ℃.
The belt dryer has high safety performance and low risk of dust incineration. During drying, the material is slowly conveyed through the belt, and is not affected by mechanical extrusion, friction and cutting, and generates little dust; the sludge has wide applicability and equipment Stable operation, high utilization rate, various heat sources are used, including natural gas, fuel oil, steam, hot water, heat transfer oil, and even cooling water and exhaust gas of gas engines; no need for dry mud back mixing, it can achieve semi-drying of sludge Drying or full drying, the moisture content of the mud can be freely set, and the use is flexible; it has a wide range of uses. Since the 1990s, belt dryers have been increasingly used for drying biological solids, such as granular and strip. , drying processing of flake, block, block, stalk, slag and other materials.
The key factors affecting the processing efficiency of the belt dryer are the circulating air volume in the dryer and the residence time of each layer of mesh belts. The sludge is in direct contact with the internal circulating air in the dryer, and the size of the circulating air volume affects the final moisture content of the sludge. , found that the larger the circulating air volume, the lower the moisture content of the mud, and the better the drying effect. In addition to the circulating air volume, the residence time of the mesh belt is also a key factor affecting the efficiency of belt drying. In theory, the longer the sludge stays in each layer of mesh belts during drying, the longer the contact time with hot air, but the slow-running mesh The belt will lead to an increase in the accumulation of sludge, a decrease in the surface area, and a decrease in the drying rate, which is not conducive to drying. Some scholars have studied the effect of residence time on the drying effect of the multi-layer belt dryer, and they believe that the sludge residence time in the second layer of mesh belt is more conducive to sludge drying.
