What is lignite dryer?
, also known as coal dryer
, is a machine and equipment mainly used for drying lignite coal
, etc. The rotary lignite dryer
adopts low temperature four-stage drying process to evaporate the moisture of lignite to less than 13% water content while ensuring the quality of the lignite being dried remains unchanged. The first-stage drying area removes most of the water at 400℃ under high humidity to ensure that the chemical composition of lignite does not change and it is not easy to burn; the second-stage drying area has a room temperature of 300℃ and removes water at high output through medium temperature strong induced air to ensure that the lignite does not coke; the third-stage drying area has an indoor temperature of 120℃-210℃ and uses the crushing device in the drum to repeatedly hit and break up the materials and dry them in the downstream; the fourth-stage drying area is High exhaust area, room temperature 60℃-80℃, relying on the low-temperature hot airflow with negative pressure of the induced air system to eliminate water.
What is lignite used for?
Industrial uses of lignite in lignite plant include combustion for power generation, which generates harmful substances after direct combustion and pollutes the environment; lignite pyrolysis can yield gas, tar, phenolic products, coke or semi-coke products; lignite can also be used for coking, and after lignite is processed into coking type coal according to the requirements of coking, it can be industrial coke and crude gas by high temperature coking furnace and carbonization in the carbonization chamber; lignite can also be chemically converted from solid to liquid state. The products of direct liquefaction of lignite include high quality gasoline, jet diesel, diesel fuel, LPG, etc.; lignite can also be gasified to produce gas for drying gases.
Working principle of lignite dryer
The previous drying method generally uses centrifugal mechanical dewatering, with expensive equipment, low capacity and small dewatering range, usually only about 10% water reduction at a time. There is still 15 --- 20% water content. The lignite dryer, which adopts the new technology of crushing and dispersing lignite first and then thermally drying it, makes the drying treatment of materials continuous, industrialized and automated. The moisture of wet lignite can be reduced from 25% to 30% to less than 13% after being treated by lignite slurry drying process, which can be used as fuel coal and improve the coal washing process, with good economic, social and environmental benefits.
Coal dryer, under the condition of ensuring the quality of lignite being dried remains unchanged, adopts low temperature four-stage drying process to evaporate the moisture of lignite to less than 13% water content. The first-stage drying area removes most of the water at 400℃ under high humidity to ensure that the chemical composition of lignite does not change and it is not easy to burn; the second-stage drying area has a room temperature of 300℃ and removes water at high output through medium temperature strong induced air to ensure that the lignite does not coke; the third-stage drying area has an indoor temperature of 120℃-210℃ and uses the crushing device in the drum to repeatedly hit and break up the materials and dry them in the downstream; the fourth-stage drying area is High exhaust area, room temperature 60℃-80℃, relying on the low-temperature hot airflow with negative pressure of the induced air system to eliminate water.
Drying technology of lignite dryer
Vibration mixed flow drying method
Vibration mixed flow drying method can remove about 10% of moisture from lignite and raise the calorific value to about 3500 calories. The drying capacity of a single unit is larger and can reach 3 million tons per year, but the dehydration rate is low.
Its principle is to crush raw coal to 35-50mm and dry it through hot air dryer. The dryer is an airtight box with 4-5 layers of "zigzag" type vibrating inclined screen. The high temperature hot air produced by the hot air furnace is mixed with the cold air to about 230C° to form a medium temperature hot air passing through the drying box from bottom to top. The coal particles pass through the vibrating screen surface from top to bottom, and the fine particles leak down from the mesh and finish drying quickly, while the coarse particles roll down slowly through the screen surface and get dried through heat exchange between the hot air and the coal blocks. The drying process varies from 10-60 minutes depending on the dehydration rate required. If needed, the dried coal can also enter the coal separator for sorting to discharge gangue and mud lumps, so that the calorific value of lignite can be further improved.
Belt furnace drying and quality improvement technology
Belt furnace drying and quality improvement technology can reduce the moisture of lignite to less than 10% and increase the calorific value to more than 5000 calories. Its principle is similar to that of vibrating bed drying, both of which use hot air to dry, but the hot air temperature used in this technology can be as high as 300C°. Using the preheating, drying and cooling process, besides drying the lignite, it can also modify and improve the quality - it decomposes the oxygen-containing functional groups and makes some oxygen atoms precipitate out, thus making the dehydration rate higher. The lignite is placed on the mesh heat-resistant metal belt for conveying, and the strong wind generated by the fan passes through the mesh of the mesh conveyor belt and the gap between the lignite and the hot air for heat exchange, so that the lignite is dried and modified and refined. The large amount of water vapor evaporated during the drying process can also be recovered by condensation.
This technology can adjust the drying time and the process can be controlled, but there is no very mature technology in China yet, but the technology has high technological content and its prospect is promising.
Drum drying technology
Drum drying technology can reduce the coal moisture content to about 15%, with high dewatering rate and increase the calorific value to about 4500 calories. The principle is to put the material coal into the drum filled with high temperature hot air of about 500C° after crushing to 0-50mm. In the tilted rotating drum of coal dryer system, the lifting plate on the wall of the drum makes the lignite form a full-break fabric curtain in the drying cylinder with a stable stroke, so that the flue gas and the raw coal can fully exchange heat, and the exchange time is about 30 minutes, so that the lignite can be dried.
Compared with the vibrating bed drying technology, the processing capacity of a single unit of drum drying technology is relatively small. Moreover, due to high drying temperature, lignite is prone to spontaneous combustion or even explosion, high lignite crushing rate and difficult operation.
Feature of lignite dryer
a. The lignite dryer has low drying cost, large processing capacity, strong overload resistance and low fuel consumption.
b. Adopting downstream drying method, the flue gas and wet materials enter the dryer from the same side, which can use high temperature flue gas to obtain high evaporation intensity, low dryer outlet temperature and high thermal efficiency.
c. The operating parameters can be changed according to the nature of different materials, so that the materials in the dryer barrel can form a stable full break fabric screen, and the quality of heat exchange more fully.
d. The new feeding and discharging device in the drum dryer eliminates blockage, discontinuity, unevenness and backflow of materials and reduces the load on the dust removal system.
e. The new internal structure strengthens the cleaning and heat conduction of dispersed materials, eliminates the phenomenon of sticky inside the cylinder wall, and has stronger adaptability to the moisture and viscosity of materials.
f. The coal dryer realizes "zero horizontal thrust", which greatly reduces the wear and tear of the retaining pulley, and the cylinder runs smoothly and reliably.
g. The lignite dryer adopts "centering type pallets device", which makes the pallets and rollers always have linear contact, thus greatly reducing the wear and power loss.
h. The size and moisture of the product can be controlled according to the user's requirements, and the moisture of the product can be less than 8% when drying coal slurry, and the size can be controlled to less than 8mm.
Application of lignite dryer
a. Drying of coal slurry, raw coal, flotation fine coal, mixed fine coal and other materials in the coal industry.
b. Drying of blast furnace slag, clay, bentonite, limestone, sand, quartzite and other materials in the construction industry.
c. Drying of various metal concentrates, waste slag, tailings and other materials in mineral processing industry.
d. Drying of non-thermally sensitive materials in the chemical industry.
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