Rotary dryer can dry and dehydrate wet materials with high water content to achieve the specified water content. It plays an important role in modern industry. When it comes to the rotary dryer, as the name suggests, we generally think of the cylindrical shape. Today, we will talk about the rotary dryer from three aspects to help you have an in-depth understanding.
1、 Drying process - step by step
If you want to understand the rotary dryer, you have to start with the drying process. The whole drying process is roughly divided into three stages.
In the first stage, after the wet material enters the cylinder, in the process of moving forward, it is directly or indirectly heated by the heat carrier, the temperature of the material rises rapidly, and the surface moisture evaporates rapidly.
In the second stage, the water inside the material evaporates stably to the surface. During this time period, the material temperature is constant and the evaporation rate is also constant.
In the third stage, the material temperature continues to rise and the evaporation rate decreases. At this time, the water content of the material has decreased significantly and the evaporated water has decreased.
2、 Heating method - multiple options
1. Direct heating
The heat transfer is carried out by convection in the dryer. The drying speed is fast, the thermal efficiency is high, and the gas is in full contact with the material with less dust. According to the flow direction of hot air, it is generally divided into counter flow type and forward flow type.
2. Indirect heating
In contrast to direct heating, when the rotary dryer is heated indirectly, the heat carrier does not directly contact the material. All the heat required for material drying is transmitted to the material through the heat transfer wall. When drying materials, a concentric cylinder is arranged in the rotating cylinder, the hot gas passes through the inner cylinder, and the materials pass through the annular space between the two cylinders. This heating method increases the heating area of materials and accelerates the drying speed.
3. Compound heating
When the rotary dryer is used for combined heating, there are both direct heating and indirect heating, and a concentric cylinder is also set in the rotary drum. Part of the heat required for material drying is transferred to the material by heat conduction through the heat transfer wall of the inner cylinder by hot air; The other part is transmitted to the material by convection heat transfer through countercurrent contact between the hot air and the material in the annular space between the two cylinders.
