Vacuum rake dryer is a horizontal intermittent vacuum drying equipment, which has the characteristics of low drying temperature, high drying rate, energy saving, good equipment sealing, and easy solvent recovery. It is particularly suitable for materials that are not resistant to high temperatures, are prone to oxidation at high temperatures, or are prone to powder production during drying (such as various dyes). However, the efficiency of the rake dryer is low, the structural design is not very reasonable, and it is difficult to meet the requirements of large-scale production. There is still a certain gap in technical level compared to foreign countries, and special types of rake vacuum dryers still need to be introduced from abroad.
In recent years, with the rapid development and increasing scale of the chemical industry, equipment has been continuously developing towards large-scale series, and the heat exchange area required for increased production has correspondingly increased. The specifications have become larger, and the required motor power and land area have increased, leading to an increase in production costs; The increase in production requires a corresponding increase in the pressure and temperature of the heating medium, resulting in thicker walls of the equipment cylinder and jacket, increased production costs, but reduced heat transfer efficiency. Therefore, a new type of nitrogen closed-loop circulation rake dryer was born.

Changzhou Baide's development of a new type of nitrogen closed-loop circulation rake dryer is based on a thorough understanding of customer needs, combined with the advantages of various existing dryers, to develop a new type of dryer. The new dryer should have a wide range of process applicability and solve new problems raised by modern production processes. The new equipment is designed to meet the needs of powder drying processes in the chemical and feed industries, providing a highly efficient and energy-saving composite heat transfer drying equipment with a wide range of powder applications and high drying effects.

Working principle of nitrogen closed-loop circulation rake dryer
The new nitrogen closed-loop circulation rake dryer is a composite conductive contact drying equipment designed for powder drying processes. This type of equipment consists of a cylinder, a mixing shaft assembly, a driving component, a discharge valve, and a dust removal system. The equipment needs to be used in conjunction with air heating and dehumidification treatment equipment during production. The outer surface of the cylinder is equipped with steam or thermal oil jacket, which can be heated up to 300 ℃.
When the equipment is working, high water content materials enter the equipment through an external quantitative feeding device. Under the high-speed rotation of the mixing shaft, the materials are stirred and thrown up by many straight blades and are in a centrifugal state. At the same time, they fully contact and transfer heat with the inner wall of the cylinder, and gradually move towards the discharge end. Throughout the process, the moisture of the material is gradually evaporated to achieve the ultimate drying effect. The evaporated water vapor is driven by the dry hot air inside the equipment, and after passing through the filtering device for dust removal, it enters the recovery system for secondary recycling. The entire device fully utilizes the advantages of conductive contact heat transfer and convective heat transfer, while utilizing heat recovery to achieve energy conservation and emission reduction.

Structure of nitrogen closed-loop circulation rake dryer equipment
(1) The equipment cylinder adopts a slender circular cylinder structure, which can increase the heat transfer area per unit volume. An integral jacket is attached to the outer layer of the cylinder, which can be heated by thermal oil or steam.
(2) The equipment adopts a high-speed flat blade mixing structure
The spindle is made of thin-walled hollow tube, which can meet the requirement for shaft rigidity under the condition of slender cylinder. On the surface of the shaft, there are multiple sets of flat propellers evenly distributed along the axial direction. When the main shaft rotates at high speed, it can carry the animal material to rotate along the circumference of the cylinder to obtain centrifugal force, which enables sufficient heat transfer of the material and rapid drying. Each flat blade adopts an adjustable and replaceable design. According to the process requirements, the horizontal angle of the flat blade can be freely adjusted to fully mix and loosen the material.
(3) The equipment discharge end is equipped with a dry hot air inlet, and the appropriate air volume should be selected according to the drying process requirements; The entry of hot air can quickly remove the water containing gas evaporated from the material, thereby improving the drying efficiency of the equipment.
(4) The feeding end of the equipment is equipped with a pulse trap, which is used to filter dust in the gas, so that the hot air coming out of the equipment can be dehumidified and heated for secondary use, achieving the goal of energy conservation and emission reduction.
(5) The equipment is equipped with a planetary discharge valve at the discharge port, and the discharge speed can be controlled through motor frequency conversion to ensure the drying efficiency of the material.

Application of nitrogen closed-loop circulation rake dryer process
The process control of the new rake type closed-loop drying machine is flexible, which can meet the needs of continuous production processes and has excellent energy-saving and emission reduction performance. The process flow of the equipment is:
(1) Start the heating cycle device connected to the cylinder jacket at the beginning of the work, so that the cylinder reaches the required process temperature for drying;
(2) Activate the air dehumidification and heating device to keep the equipment cylinder in a state of hot air convection circulation; After the temperature inside the equipment cylinder is measured by a thermometer and meets the process requirements, it enters the next program;
(3) Activate the device driver device;
(4) After the equipment rotates smoothly, start the feeding conveyor and let the material enter the equipment through the feeding port for drying;
(5) The material undergoes circular spiral motion around the cylinder under the action of numerous flat blades, and moves from the inlet to the outlet direction. During the movement, it uniformly contacts the cylinder wall to form contact heat transfer, and evaporates the moisture or solvent in the material into a gas state, condensing at the center of the cylinder;
(6) The hot air at the center of the cylinder, under the circulating convection wind speed, forms convective heat transfer with the material on the one hand, and absorbs and carries away the water vapor evaporated from the material on the other hand, accelerating the contact heat transfer process of the material to achieve the goal of improving efficiency;
(7) When the material is continuously moved to the discharge end of the cylinder under the action of the flat blade, it is continuously discharged through the discharge device;
(8) To control the drying yield and drying effect, the equipment speed and the angle of the flat blade can be adjusted to achieve flexible process control.

In the field of powder drying production, the application of the new rake type closed-loop dryer technology in the material drying production process is effective and feasible. It combines the advantages of both conductive contact heating and convective heating devices to achieve the high drying efficiency required by customers; In addition, the process application of the new rake type closed-loop dryer can also change the angle of the straight blade relative to the axis by adjusting the bolts, thus meeting the needs of different processes and production volumes. In addition, the driving device can be used in conjunction with a variable frequency motor for more flexible speed control. In terms of hot air, water evaporation emissions, and recycling, it can achieve energy-saving and emission reduction effects, which is in line with the national plan for innovative development.