Sludge drying technology originated earlier. At the beginning of the 19th century, the Germans invented the world's first plate and frame filter press. After two hundred years of development, various types of filter presses used in different scenarios have been born.
The domestic sludge drying industry started relatively late. It sprouted during the reform and opening up period in the late 1970s. Due to the inherent policy constraints of heavy water over sludge, large domestic sludge filter press manufacturers have only started in the nineties. It can be seen that sludge drying has never been developed.
In fact, the domestic policy of focusing on water rather than mud has been gradually changed since 2010. There are a large number of water treatment and environmental protection exhibitions covering sludge drying in the country every year, and we can see the vigorous development of environmental protection companies.
"Sludge drying" is no longer an unfamiliar industry to the industry and even some outsiders. After nearly ten years of process technology development, in addition to many technologies including low-temperature sludge drying, the following editor will understand the connections and differences between them, and let users establish a deep understanding of sludge drying through process comparison . Sludge drying can be divided into two types: mechanical drying and thermal drying. Mechanical drying is a process of physical drying through mechanical dehydration equipment. Because of its long history of development, plate frames, paddles, and The original disc dryer. Thermal drying, as the name implies, uses a heat source to directly or indirectly evaporate and dry the sludge. The cost of direct production of a heat source is usually higher than that of mechanical drying. Meaning and mainstream technology of sludge drying at low temperature
In the existing sludge deep dewatering technology, low-temperature drying is an effective method that can evaporate all the capillary water, adsorbed water and part of the bound water of the sludge. The so-called low-temperature sludge drying is the process of evaporating the water in the sludge through an external heat source lower than the burning point of the sludge. However, sludge drying is a process of net energy consumption. Energy consumption usually accounts for more than 80% of the total cost of sludge treatment. If the waste heat of flue gas is used for sludge drying, the energy consumption bottleneck of sludge drying can be completely overcome. , Which greatly reduces the operating cost of sludge treatment.
The country introduced a coal-to-electricity policy in the past few years. Heat pump equipment is widely used in various scenarios in life and industry. Together with the introduction of environmental protection policies, the industry has accelerated the development of the low-temperature drying of sludge heat pumps. It has the distinctive characteristics of economy, reliability and environmental protection , Has become the mainstream technology representing low-temperature sludge drying in the market today.
The relationship between low temperature drying of sludge and sludge drying
Sludge drying belongs to the category of sludge treatment and is one of various treatment methods, which includes the various process methods described above. Low-temperature sludge drying is a subdivision technology of sludge drying. The main drying temperature is below 90 degrees, all of which belong to low-temperature drying. Among them, heat pump low-temperature drying is a typical representative. After the sludge is dried, advanced treatment is called sludge disposal in order to realize the closed loop of environmental protection treatment, such as mixed burning of dry sludge and soil for building materials.
Advantages of low temperature drying of sludge
Sludge evaporation, dehydration and drying are divided into high temperature drying and low temperature drying. High temperature drying will cause harmful substances in the sludge to volatilize, and high temperature equipment has poor stability and safety, and has been gradually eliminated. Low temperature drying is the use of Xunhua hot air (about 70 degrees) to evaporate the sludge water. Because of the low temperature, harmful substances are not decomposed and cannot be volatilized, and the stability and safety of the equipment are greatly improved.
The sewage condensed from the sludge through the low-temperature drying process is directly returned to the original sewage tank to avoid the environmental protection problem of secondary pollution caused by direct discharge. Compared with other mechanical dehydration, the moisture content of dry sludge can be reduced to a lower moisture content, and the volume of sludge is greatly reduced. This can save considerable environmental protection costs for sewage disposal units due to soaring solid waste disposal costs.
Comparison of low-temperature drying of sludge heat pump and plate and frame/stacked snails
1. The frame/stack snail is a mechanical method to filter the sludge to squeeze out the water in the sludge. The moisture content after extrusion is generally between 60% and 85%;
2. Low-temperature sludge drying adopts low-temperature heat pump dehumidification technology, the sludge evaporates the sludge moisture through circulating hot air, and the moisture content can be reduced to below 30%;
3. The low-temperature sludge drying equipment is the back-end equipment of the plate and frame/screw stacking equipment. The feed requirement is solid (non-dripping) sludge, and the sludge moisture content is generally less than 85%. The feed of the plate and frame/screw stacking equipment is a solid-liquid mixture, and the water content of the sludge is generally above 90%.
