The connection and difference between low temperature sludge drying and sludge drying
The sludge drying technology has an early origin. In the early 19th century, the Germans invented the world's first plate and frame filter press. Today, after two hundred years of development, various types of filter presses have been born for different scenarios.
The domestic sludge drying industry started late, sprouting in the period of reform and opening up in the late 1970s. Due to the restrictions of heavy water and light sludge, the domestic large-scale sludge filter press manufacturers have only started from 90 years It can be seen from the gradual establishment that sludge drying has never been developed.
In fact, the policy of heavy water and light sludge was gradually changed in China since 2010. A large number of water treatment and environmental protection exhibitions covering the drying of sludge appear in the country every year, and we can see the vigorous development of various environmental protection companies.
'Sludge drying' is no longer an unfamiliar industry for some friends in the industry or even outside the industry. After nearly ten years of technological development, many technologies including low-temperature drying of sludge have been urged. The following will understand the connection and difference between them, and let the users establish a deep understanding of sludge drying through process comparison.
Sludge classification and its drying technology.
- According to the source, it can be divided into: water supply sludge, domestic sewage sludge, industrial wastewater sludge.
- According to the composition and nature, it can be divided into: organic sludge (hydrophilic), inorganic sludge (hydrophobic)
- According to the treatment process, it can be divided into: primary sludge, excess sludge, digested sludge, chemical sludge
- According to the generation stage, it can be divided into: raw sludge (primary settling + secondary settling), concentrated sludge, digested sludge, dehydrated sludge, dried sludge
Sludge drying can be divided into two major 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 Original disc dryer. Thermal drying, as the name implies, uses a heat source to directly or indirectly carry out water evaporation and drying of sludge. The cost of directly manufacturing a heat source is usually higher than that of mechanical drying.
According to the physical structure of the dryer, it can be divided into:
- Hot water drying technology, that is, plate and frame filter press-hot water vacuum drying technology;
- The use of steam film drying, including disc dryer, hollow paddle dryer, turbo dryer;
- Electricity drying technology, that is, belt dryer.
In addition, it also includes stacked screw dehydrator, centrifugal dehydrator, etc.
Features of hot water sludge dryer: Good stability, easy operation, low running cost, suitable for large long mining enterprises with rich hot water.
Steam film dryer features: simple equipment, good stability, large operation flexibility, high efficiency, suitable for large steam-rich long mining enterprises.
Furnace flue gas waste heat dryer: The equipment is more complicated, the efficiency is high, the initial investment is relatively high, if there is a heating furnace in the enterprise, the running cost is low.
Electrical energy sludge dryer: simple structure, easy operation, high efficiency and good operating environment. Representative equipment: Shincci sludge heat pump low temperature dryer.
Solar sludge drying plant: It occupies a large area and has low energy consumption. It is suitable for areas with sparse sunshine and dry climate.
The meaning and mainstream technology of low temperature sludge drying
In the existing deep sludge dewatering technology, low temperature drying is an effective method that can evaporate all the capillary water, adsorbed water and part of the combined water of the sludge. The so-called low-temperature drying of sludge is the process of evaporating the water in the sludge by an external heat source lower than the burning point of the sludge. However, sludge drying is a process of net energy consumption. The energy consumption cost 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 , So that the operating cost of sludge treatment is greatly reduced.
In the past few years, our country introduced the coal-to-electricity policy. Heat pump equipment is widely used in various scenarios in life and industry. The introduction of environmental protection policies has accelerated the development of low-temperature drying of sludge heat pumps. It has distinctive features of economy, reliability, and environmental protection. Has become the mainstream technology representing low-temperature drying of sludge on the market today.
The connection between low temperature sludge drying 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 introduced above. Low temperature drying of sludge is a subdivision technology of sludge drying. The main drying temperature is below 90 degrees, which belongs to low temperature drying. Among them, heat pump low temperature drying is a typical representative. After the sludge is dried, in-depth treatment to achieve the closed loop of its environmental protection treatment is called sludge treatment, such as dry sludge blending, soil for building materials, etc.
Advantages of sludge drying at low temperature:
Sludge evaporation and dehydration drying is divided into high temperature drying and low temperature drying. High temperature drying will cause the harmful substances in the sludge to evaporate, and the high temperature equipment has poor stability and safety, and has been gradually eliminated. Low temperature drying is the use of circulating hot air (about 70 degrees) to evaporate sludge moisture. Due to the low temperature, harmful substances are not decomposed and cannot be volatilized, and the stability and safety of equipment are greatly improved.
The sewage condensed by the sludge drying process at low temperature is directly returned to the original sewage tank to avoid the environmental problems caused by direct discharge. The water content of dry sludge can be reduced to a lower water content than other mechanical dewatering, and the volume of sludge is greatly reduced, which can save considerable environmental protection costs for sewage disposal units that have skyrocketed solid waste disposal costs.
Comparison of Low Temperature Drying of Sludge Heat Pump and Plate / Frame / Snail:
- The frame / stacked snail adopts a mechanical method to filter the sludge to squeeze out the water in the sludge. The water content after extrusion is generally between 60% and 85%;
- The low-temperature drying of sludge adopts low-temperature heat pump dehumidification technology. The sludge evaporates the moisture of the sludge through the circulating hot air, and the water content can be reduced to below 30%;
- The low-temperature sludge drying equipment is the back-end equipment of the plate frame / stacked screw equipment. The feed requirement is solid (non-drip) sludge, and the sludge moisture content is generally less than 85%. The feed of the plate / frame screw equipment is a solid-liquid mixture, and the sludge moisture content is generally above 90%.