Application of clean coal drying equipment in lignite drying

The dryer for coal drying can be divided into direct heating type and indirect heating type. The drying medium is flue gas or steam. Because coal is not afraid of flue gas pollution, does not react with flue gas, and does not shrink, so direct heating convection dryer with flue gas as drying medium is commonly used, such as rotary dryer, air dryer, fluidized bed dryer with spouted bed, vibrating fluidized bed dryer, grinding dryer and vertical shaft dryer. Steam heating dryers such as drum dryer, tray dryer are mainly used for briquetting lignite drying.

1、 Rotary drum dryer

Rotary drum dryer is mainly used for drying flotation clean coal and flotation tail coal. This kind of dryer usually adopts parallel flow operation to avoid the possibility of ignition. The drying medium can be hot air or flue gas produced by combustion of natural gas or coal. Figure is a schematic diagram of a typical rotary drum dryer. The steel cylinder of the dryer is made of refractory material and supported on the roller by the rolling ring installed on the cylinder body. The cylinder body is usually driven to rotate by a gear transmission device. The axis of the cylinder inclines 2 ° to 5 ° from the horizontal. The inner wall of the cylinder is provided with a copy board. When the cylinder rotates, the coal material is picked up by these plates and gradually sprinkled into the hot gas flow along the axial direction in the cylinder.

2、 Rotary tube dryer

Rotary tube dryer is widely used for lignite drying in block plant. It can also be used to dry hard coal. This is an indirect heating dryer with saturated steam (pressure of 0.15-0.55mpa) as heating medium. Seamless steel pipes with a diameter of 120-108mm are fixed on the tube plates at both ends of the inclined drum

The cylinder body is supported on the roller through the rolling ring, and the transmission device drives the cylinder to rotate through the gear. The heating steam enters the tube through the hollow shaft to heat the steel pipe. The wet coal is fed into the steel pipe from the high end. Due to the inclination, the coal will gradually move from the high end to the low end during the rotation. Dry coal is collected from the collection chamber and discharged from the lower end. In order to prevent the coal from moving too fast in the pipe, the variable pitch guide screw is installed in the steel pipe. The condensate is discharged through a hollow pivot at the low end of the drum.

In lignite briquetting plant, this kind of dryer uses waste steam from briquetting machine as heating steam. It is also beneficial to the utilization of heat energy, but the oil droplets from the waste steam will be carbonized and deposited on the pipe wall. Trichloroethylene at 70-80 ℃ can be used for cleaning for about 3 h to remove the sediment on the pipe. The used trichloroethylene is recycled by distillation.

3、 Chamber dryer with agitator

This kind of dryer is usually used for the drying of flotation clean coal. Parallel flow operation is adopted. The drying chamber is divided into several small chambers by a partition board. Under the chamber are two mixing shafts with opposite rotation direction and blades on them. The hot flue gas is introduced by the duct and contacts with the wet coal added from the duct for mass and heat exchange. Coal is lifted by paddle agitator and thrown from inlet to outlet chamber by chamber. The waste steam is discharged from the pipe. The agitator can also break up any caking coal that may form.