Cement Mill
Product Description
The coal slime dryer is a new dedicated coal-slime drying machine developed by our company on the basis of existing dryers. It is equipped with a de-agglomeration mechanism, movable grate-type lifting flights, a cleaning device and an impact-crushing scattering device, enabling it to dry viscous materials that ordinary rotary dryers cannot handle, and it is a product specially developed and designed for sticky filter-cake materials.
The coal slime dryer belongs to the rotary-drum dryer category and is suitable for drying coal slime and sludge in the coal-mining industry, magnetic, gravity and flotation concentrates of metallic and non-metallic ores, clay in the cement industry and many other sectors. Its features are high productivity and ease of operation. The drum is a horizontal rotating cylinder, inside which various lifting flights of different angles are welded in a staggered arrangement from front to rear; at the feed end a ring stopper and spiral lifting flights are provided to prevent the material from flowing back. It offers advantages such as a rational structure, fine workmanship, high output, low energy consumption and convenient operation. Coal slime itself has high moisture and high stickiness, and traditional dryers fail to address this characteristic. The dedicated coal slime dryer adopts a unique scattering device that breaks up the agglomerated slime before drying, increasing the contact area between the coal slime and the hot air and greatly improving heat utilization. After drying, the moisture of the coal slime can be reduced to below 12% in a single pass, and the dried coal slime can be used directly as fuel, turning waste into a valuable resource.
Working Principle
Coal slime is conveyed by belt conveyor or bucket elevator to the hopper, then enters the feed end through the hopper feeder and the feeding pipe. The slope of the feeding pipe must be greater than the natural angle of repose of the material so that the material flows smoothly into the coal slime dryer. The drum of the coal slime dryer is a rotating cylinder slightly inclined to the horizontal; the material is fed from the higher end while the heat carrier enters from the lower end and contacts the material counter-currently, although there is also a co-current arrangement where the heat carrier and the material enter the drum together. As the drum rotates, the material moves under gravity toward the lower end, and during its forward movement inside the drum the wet material receives heat directly or indirectly from the heat carrier, so that the wet material is dried; it is then discharged at the discharge end by a belt or screw conveyor. Lifting flights are installed on the inner wall of the coal slime dryer drum; their function is to scoop up and scatter the material, increasing the contact surface between the material and the airflow so as to raise the drying rate and promote the material forward. The heat carrier is generally hot air, flue gas, etc. After the heat carrier passes through the dryer, a cyclone dust collector is usually required to capture the material carried in the gas; if it is necessary to further reduce the dust content of the exhaust gas, it should pass through a bag dust collector or a wet dust collector before being discharged.
Process Flow
The process flow of the coal slime dryer is as follows. Because coal slime has a certain stickiness, after the wet coal slime enters the dryer it passes through the following working zones during drying:
- Material-guiding zone: the wet coal slime enters this zone and rapidly contacts high-temperature hot air, so that moisture evaporates quickly; under the agitation of the large-lead-angle lifting flights the material is guided into the next working zone without forming agglomerations.
- Cleaning zone: in this zone the wet coal slime is scooped up by the lifting flights to form a material-curtain state, and when the material falls it tends to adhere to the drum wall. Because the equipment is designed with a cleaning device, the cleaning device very reasonably cleans the material adhering to the inner wall; in this process the cleaning device also crushes material lumps and agglomerates, thereby increasing the heat-exchange area and raising the drying rate.
- Inclined lifting-plate zone: in this zone the wet coal slime is already in a low-moisture loose state and no longer exhibits adhesion; after heat exchange the material reaches the required moisture state and enters the final discharge zone.
- Discharge zone: in this zone the drum has no lifting flights, and the material rolls and slides to the discharge port, completing the entire drying process.
Coal slime drying equipment has already been put into use in many coal-slime washing enterprises in Henan, Anhui, Heilongjiang, Guizhou and elsewhere, creating considerable economic benefits.
Uses
With the increasing mechanization of coal mining, the proportion of pulverized coal and fine coal in raw coal is growing ever larger, which greatly increases the amount of primary coal slime at steam-coal washing plants and flotation tailings at coking-coal washing plants. As a by-product of the washing process, coal slime has the characteristics of fine particle size, strong water retention, high ash content and a relatively large amount of clay, which brings many inconveniences to its comprehensive utilization. Most of the coal slime from washing plants is sold cheaply to local farmers, which both pollutes the environment and wastes resources, so the value of coal slime is not truly realized. The coal slime dryer system that was developed is intended to solve the problem of coal slime being unusable for comprehensive utilization due to its high moisture content (20%–30%). This process adopts a new technology of first crushing and dispersing the coal slime and then thermally drying it, making the treatment of coal slime continuous and industrialized; after treatment by this process the moisture of the coal slime can be reduced from 25%–28% to about 12%. Because a pre-scattering device is introduced into this process, the drying efficiency of the coal slime is greatly improved. After drying treatment, the coal slime can mainly be used in the following ways:
- As a raw material to process coal-slime briquettes for use in industrial boilers or for residential life;
- As power-plant fuel, reducing production costs;
- As a brick-plant additive, improving the quality of bricks;
- As a cement-plant additive, improving cement performance;
- Coal slime containing certain specific components can be used as a chemical raw material.
