(2) Belt drying technology-lignite is evenly distributed on the conveyor belt from the feeding end through the feeding device. Conveyor belts are usually made of perforated stainless steel sheets, driven by motors through gearboxes, and the speed can be adjusted. The most commonly used drying medium is hot air or hot flue gas.
(3) Airflow drying technology-Airflow drying, also known as "instantaneous drying", is the application of fluidized dilute phase transportation in drying; According to the difference of drying medium and operating temperature, airflow drying can be divided into straight tube and bed mixed type.
(4) Fluidized bed drying technology-lignite fluidized bed drying equipment developed and applied in industry, which mainly uses superheated steam or air as the fluidized medium (or drying medium) and has a heat exchanger inside the fluidized bed; Lignite fluidized bed drying technology mainly includes superheated steam fluidized bed drying technology and steam-air combined drying technology.
(5) Vibration drying technology-Vibration drying is to realize the flow of solid particles in the dryer through mechanical vibration, and at the same time realize the drying process under the action of drying media (such as hot flue gas). Lignite vibration drying equipment mainly includes vibration mixed-flow dryer and vibration fluidized bed dryer. Rotating tube drying technology is the most mature lignite dehydration and drying technology in industry at present.
(6)K- fuel technology-the most non-evaporative drying technology. This technology uses the direct contact between raw coal and steam in the upgrading device, and removes the moisture in raw coal in the form of liquid water by adjusting the three factors of time, temperature and pressure, thus "squeezing out" the moisture in coal, changing the pore structure and hydrophilicity of coal, and improving the quality of low-rank coal. In Wyoming, USA, there is an upgrading plant with an annual processing capacity of 750,000 tons.
(7) High temperature fluidized bed drying technology
(1) Brief introduction of high temperature fluidized bed coal drying technology
Fluidized bed drying of coal drying started around 1955, and gradually became the first choice for coal drying. In 1958, there are 6 rotary dryers, 64 vibrating fluidized bed dryers, 44 pneumatic dryers and 6 vibrating fluidized bed dryers for coal drying in the United States. To 196 1, there are 1 1 rotary dryers, 66 vibrating fluidized bed dryers, 40 pneumatic dryers and 23 vibrating fluidized bed dryers. By the end of 1980, there were more than 170 fluidized bed dryers for coal drying. Some of these dryers have been in operation for more than 30 years. Mainly because the fluidized bed dryer used for coal drying has the following advantages: it can use high temperature air intake, up to 950 degrees; Due to the adoption of high-temperature air intake, the equipment is compact, the investment is low and the energy consumption is low; Single machine output is large: the maximum water evaporation that has been put into production can reach 150 tons/hour (the fluidization area is 33 square meters, and it can reach 100 square meters as required); Can directly dry wide screen materials: 0-2(0-50 mm); Dry and separation of coarse and fine particles can be realize. (2) Coal drying explosion.
As we all know, the Kst of pulverized coal is around 80, which belongs to the dust with slight but destructive explosion. Pulverized coal explosion is the first safety problem to be solved in coal drying. Because the dust explosion triangle (lignite is easier to explode, its oxygen concentration: 7-8%) is: 1) and the temperature is 600 degrees; 2) Oxygen concentration:11%; 3) Dust concentration: 80g/m3. Therefore, in the design and operation, at least one side of the dust explosion triangle should be removed. According to the investigation of dust explosion of fluidized bed coal dryer by relevant departments, the results show that about 60% of the explosion is caused by improper human operation; About 40% of the explosions were caused by incorrect operation specifications. Therefore, the automatic control of fluidized bed coal dryer can avoid dust explosion caused by improper operation. In addition, all equipment start-up procedures, equipment interlocking, emergency stop procedures, HAZOP analysis of drying process and important instruments must be carefully, strictly and regularly checked, so as to completely put an end to dust explosion caused by incorrect operation specifications. Design and installation of system explosion relief device. According to the practical operation experience, the explosion problem of fluidized bed coal drying can be completely solved.
process flow
The coal (0-50 mm) to be dried is added into the wet coal bunker, and enters the interior of the fluidized bed dryer (that is, the upper part of the bed plate) through the feeder, where it is heated and dried by the high-temperature flue gas (500- 1000 degrees) from the combustion chamber: coarse particles (0.5-50 mm). Fine particles (0- 1mm) are taken to the dust collector by hot air for separation, and then discharged from the rotary discharge port at the bottom; The tail gas is discharged after further dust removal by bag filter or scrubber.
(4) Design points of high temperature fluidized bed dryer.
Because the lower part of the bed plate (combustion chamber and pipeline system) is lined with refractory cement, its working temperature can reach 1200 degrees or above; The upper part of the bedplate (about 50mm), that is, the temperature inside the drying chamber is about the outlet temperature (60- 100 degrees). The design of high-temperature fluidized bed dryer only needs to solve the high-temperature design of 50 mm- 100 mm bed plate and its upper part. The air distribution plate made of high-temperature resistant materials used in aero-engines has been proved for many years that it can work for a long time below 1000 degrees.