Existing drying equipment, the most is convection heat transfer drying. Such as hot air drying, hot air and the material to be dried in contact with heat exchange to evaporate moisture. Convection dryer representative of the common types of equipment air suspension dryer, such as fluidized bed dryer, flash dryer, air dryer, spray dryer, ventilated dryer, flow dryer, air rotary dryer, stirring dryer, parallel flow dryer, rotary dryer and so on.
The actual application, there are single machine use, there is a combination of machine use, there are also deformed models and so on. Air flow dryer, fluidized bed dryer, spray dryer, etc. are hot air as the heat carrier, in drying at the same time, also completed the transfer of materials. Such dryers are mainly characterized by the absence of transmission parts.
The most common way to dry powder, granule and flake materials is to apply hot air or gas flow on the surface of the granule. The passing gas stream transfers heat to the material, causing the water to evaporate. The evaporated water vapor goes directly into the air to be taken away, to the drying system commonly used drying media are air, inert gas, direct combustion gas or superheated steam.
The method makes the hot air and material direct contact, while heating and removing water. The key is to improve the contact area between the material and the hot air to prevent the hot air bias flow. The temperature of the material during the constant speed drying is almost the same as the wet bulb temperature of the hot air, so the use of high temperature hot air can also be used to dry heat-sensitive materials. This drying method drying rate is high, less investment in equipment, but the thermal efficiency is low, the following is the basic situation of various types of convection drying equipment.
(1) Box-type drier
It is one of the oldest dryers. The material is loaded with the plate, the plate is placed in the frame car layer by layer discharge into the steam or electricity as a heat source, the hot air in the box can be circulated and part of the discharge, in order to make the drying more uniform. Although the thermal efficiency is low, but still in a large number of use, but also continue to manufacture, because the structure is simple, the operation is not often care no obvious problems. But a lot of material drying to turn over the plate, turn over the powder, heat-sensitive materials are often easy to discoloration, but also does not apply to the drying of materials with solvents. Due to the accumulation of materials, the inner layer of heat transfer, mass transfer is poor, and thus the drying rate is low.
(2) Tunnel type drying room
The material tray is placed on a special car, which can be intermittently in and out of the tunnel, in order to increase the output and improve the thermal efficiency. Other structures are similar to the box dryer.
(3) Mesh belt dryer
Can be used for drying corn, grains, vegetables and so on. This machine is equipped with stainless steel wire mesh transmission belt, the material moves with the belt, can be heated in sections. The device to each section 1.8 ~ 2m long as a unit, the longest can be connected to 40m, the hourly capacity can be as high as 4t. Constant rate of drying stage of the hot air temperature up to 130 ℃, exhaust relative humidity up to 85%.
(4) Multi-layer turbine dryer
Its structure is a vertical garden cylinder, equipped with a number of layers of turntable, the material can be added from the top, layer by layer down to the bottom of the release. Hot air from the bottom of the introduction, set up in the center of the cylinder by a number of blower turbine impeller segmentation cycle air, and the corresponding height of the inner wall of the heater to supplement the heat of the air to improve thermal efficiency and drying rate. However, the equipment is not easy to clean, for the production of many varieties and the requirement of clean materials is more difficult.