Direct contact dryers are "a common convection dryer. The latent heat of steam in the dryer is not fully utilized and is discharged, resulting in a relatively low thermal efficiency of the dryer. Nevertheless, this type of dryer accounts for about industrial use. 85% of the total number of dryers. Although superheated steam has recently been used in some special occasions, which has higher thermal efficiency and can improve product quality, indirect or directly heated hot air is still common as a drying medium, so drying equipment is used If the product to be dried is not heat-sensitive or does not cause the product to burn, it can be directly heated with gas. In a direct contact dryer, the drying medium is in direct contact with the material, and convection provides heat for drying, while drying and evaporating The steam is carried out by the drying medium.

　　The gas temperature depends on the material, and the range can reach 50 N 400°C. For materials with strong heat sensitivity, dehumidified gas is required. When drying flammable, explosive, or solid materials that need to remove organic solvents, inert gas such as nitrogen is required. After the vaporized inert gas (containing solvent vapor) is discharged, the solvent can be recovered by recondensation, and then returned again. Heat in the dryer.