Principle of Closed Loop Boiling Drying Machine

The closed-loop boiling dryer is a closed-loop system. At the beginning, start the fan, open the exhaust valve, close the switching valve, input inert gas (usually nitrogen), and replace the existing air in the system. When the oxygen content in the system reaches the predetermined target, close the exhaust valve and open the switching valve. Nitrogen in the system serves as a medium for heat and mass transfer, achieving the purpose of drying wet materials. After the organic solvents contained in the wet material are vaporized, they enter the condenser together with nitrogen gas to condense the solvents into liquid and flow into the storage tank. Nitrogen gas, due to its low boiling point, cannot liquefy and enters the next cycle driven by the fan. The drying device in the closed-loop circulating vibrating fluidized bed dryer system can be selected from cylindrical boiling dryers (also known as high-efficiency boiling), box type boiling dryers, vibrating fluidized bed dryers, and even air flow dryers according to the material state and requirements. As these dryers are fluidized drying, the drying rate is high and the drying time of the material is short.

Characteristics of Closed loop Boiling Drying Machine

1. The system is fully enclosed and has almost no oxygen (content self-control). As mentioned above, the system of the closed-loop boiling dryer operates in a fully enclosed state, with neither (nor allowed) external leakage nor (not allowed) internal leakage. For this purpose, it is necessary to ensure that all parts of the system, whether it is pipeline interfaces or the inlet and outlet ports of the box; Whether in the positive pressure zone or the negative pressure zone; Both static and dynamic parts must be strictly sealed. The oxygen content in the system does not exceed the process requirements, ensuring the safety of explosion and flame prevention, and providing reliable assurance for oxygen sensitive materials.

2. Zero emissions. If the system operates continuously, there are basically no exhaust emissions

3. Solvent recovery. If the system can operate continuously, the solvent recovery rate will be very high (up to over 98%), and its economic significance is self-evident.

4. High degree of automation. Our company has set up automatic control and over limit alarm devices for three parameters including temperature, oxygen content, and system pressure in the system, using PLC control, which is easy to operate, safe, and reliable.

Application scope of closed-loop boiling dryer

Granulation in the pharmaceutical industry: tablet granules, granule granules, capsule granules.

Food industry granulation: cocoa, coffee, milk powder, granulated fruit juice, seasonings, etc.
Granulation in other industries: pesticides, feed, fertilizers, pigments, dye chemicals, etc.
Drying of wet materials in powder or granular form.

Coating: granule, pill protective layer, color preparation, sustained-release, film, enteric coating, etc.

Technical Description of Closed loop Boiling Drying Machine Equipment

The closed-loop boiling dryer is composed of a drying machine, heater, condenser, bag filter, fan, and material bin. The entire drying process is carried out in a sealed environment under nitrogen protection, and the discharge is carried out in a sealed environment, which has the characteristics of no dust and high safety.

Before use, the closed-loop boiling dryer uses nitrogen to replace the air in the system, so that the oxygen content in the system reaches the safe concentration of the solvent. Wet materials enter the drying machine through the feeding port on the equipment in a sealed container. The air supply fan sends filtered nitrogen gas, which is heated by a heater to the temperature required for the drying process. It then enters the boiling bed to perform heat and mass transfer (drying) on the material added through the differential feeding port. After the feeding is completed, it is dried to the desired final humidity of the material. During the drying process of the closed-loop boiling dryer, the humid and hot gas carries a small amount of micro powder and passes through the dust collector to separate all micro powders above 2um into gas-solid in the dust collector. Solid dust is collected in the dust collector, and the gas enters the multi-stage condenser (finned condenser has low pressure drop and good condensation effect) to condense the solvent in the humid and hot gas. The condensed solvent is collected in a collection tank and stored (zero emission to air, recyclable). After condensation and dehumidification, the dry nitrogen gas is then sent to the heater for circulation through a blower. After the closed-loop boiling dryer completes the drying process, the materials on the hot air distribution plate are placed into the lower cylinder by the flipping mechanism, and then input into a sealed container for storage and packaging through a vacuum pump or airflow conveying system (both incoming and outgoing materials are operated in a sealed environment, and there is no dust in the workshop).

Advantages of Closed Loop Boiling Drying Machine

1. After being dried by a closed-loop boiling dryer, the hot and humid gases containing solvents enter the condenser to condense the solvents in the gas (with a solvent recovery rate of over 95%), which can both recover solvents and condense dehumidified dry gases. The recovered solvent can be recycled again, which can save costs and will not cause environmental pollution due to exhaust emissions. Hot and humid gases undergo condensation dehumidification, resulting in lower absolute humidity inside the gas (compared to ordinary boiling drying), stronger drying ability, and better adaptability to moisture absorbing materials that are affected by humidity environments.

2. The closed-loop boiling dryer is a fully enclosed structure, and the equipment is filled with inert gas (such as nitrogen) inside. When drying anaerobic materials or materials containing flammable and explosive solvents, there is no oxygen in the gas, making it impossible to burn or oxidize. This can effectively prevent equipment from catching fire or exploding during production, making it safer than ordinary equipment.

3. When the closed-loop boiling dryer is working, the internal air pressure required is low, and only a slight positive pressure is needed. Therefore, the power of the fan equipped with the equipment is reduced because during positive pressure, the hot air blows upward from the lower part of the hopper mesh plate, and the penetration force of the wind is strong. Although the boiling height of the material is not high, the contact between the hot air and the material is more complete, and the drying rate is faster. After the fan power of the equipment is reduced, the noise of the equipment decreases, while also saving energy.

4. The closed-loop boiling dryer is equipped with a flap mechanism, which enables discharge under fully enclosed conditions, greatly reducing the labor intensity of workers and ensuring that there is no dust in the operation workshop. The workshop environment is good and the degree of automation is high.

5. The main unit of the closed-loop boiling dryer uses a pulse dust removal system, which has high dust removal efficiency. The dust does not stick to the filter cartridge and is easy to disassemble and clean.

Characteristics and advantages of closed-loop boiling dryer equipment

secure

The closed-loop boiling dryer is a fully enclosed structure, and the equipment is filled with nitrogen inside. When drying anaerobic materials or materials containing flammable and explosive solvents, there is no oxygen in the gas, making it unable to burn or oxidize. This can effectively prevent equipment from catching fire or exploding during production, making it safer than ordinary equipment.

Efficient

The main unit of the closed-loop boiling dryer uses a bag pulse dust removal system, which has high dust removal efficiency. The dust does not stick to the filter cartridge and is easy to disassemble and clean. And using the whole machine back blowing technology (patented technology), the equipment is subjected to a whole machine back attack after the closed-loop boiling dryer is dried, and its dust removal is thorough. After using this technology, the bag cleaning frequency of the equipment is extended from the original 1-2 days to 12-15 days. The closed-loop boiling dryer is located at the bottom of the main unit and can be evacuated to the material storage device, reducing the workload of workers and improving efficiency.

environment protection

After being dried by a closed-loop boiling dryer, the hot and humid gases containing solvents enter the condenser to condense the solvents in the gas (with a solvent recovery rate of over 95%), which can both recover solvents and condense dehumidified dry gases. The recovered solvent can be recycled again, which can save costs and will not cause environmental pollution due to exhaust emissions.

energy conservation

When the closed-loop boiling dryer is working, the internal air pressure required is low, and only a slight positive pressure is needed. Therefore, the power of the fan equipped with the equipment is reduced because during positive pressure, the hot air blows upward from the lower part of the hopper mesh plate, and the penetration force of the wind is strong. Although the boiling height of the material is not high, the contact between the hot air and the material is more complete, and the drying rate is faster. After the fan power of the equipment is reduced, the noise of the equipment decreases, while also saving energy.

broad-spectrum

The hot and humid gases inside the closed-loop boiling dryer are condensed and dehumidified, resulting in lower absolute humidity and stronger drying ability, making it more suitable for moisture sensitive materials. For materials with finer particles: Due to low air pressure, the escape rate of the material is small, and it can be fully recovered in the secondary dust removal process.

The closed-loop boiling dryer operates in a fluidized state during the drying process, where the material undergoes extensive gas-solid contact with hot air, resulting in high drying intensity and efficiency. Moreover, as the equipment size increases and the fan airflow increases, the equipment's operational efficiency can still be guaranteed; Unlike static vacuum drying systems, their drying efficiency decreases as the equipment increases. The material in the closed-loop boiling dryer drying process is fluidized, avoiding other adverse situations such as local material overheating and deterioration caused by direct contact between the heating surface of the material and the material in the vacuum drying system.

Process flow diagram of closed-loop boiling dryer

Structure of closed-loop boiling dryer equipment

The closed-loop boiling dryer consists of an air filter, air heater, drying bed, separation chamber, filtration chamber, air duct, circulating fan, control system, etc.

1. Host: The host consists of a bottom inlet chamber, a drying bed, a separation chamber, and a filtration chamber.

2. Air filter: filtered by primary and medium efficiency air filters to ensure the cleanliness of the incoming air.

3. Air heater: Using stainless steel tubes wrapped around fins, it improves the heat transfer coefficient of the heat exchanger while ensuring no rust or foreign objects fall off.

4. Exhaust system

Equipped with exhaust ducts, circulating fans, and isolated installation from the main unit, the noise level is ≤ 80 decibels. The air volume can be controlled by frequency conversion, and the fluidization state can be continuously adjusted. Therefore, this machine is suitable for a wide feeding range and can also adapt well to the air volume requirements of different material conditions.

5. Mixing mechanism

The use of a built-in rake tooth mixing mechanism in the material truck can assist in fluidization, prevent the phenomenon of dead bed caused by material flow in the drying process, maintain a stable fluidized state, and ensure uniform moisture content of the material after drying.

Technical characteristics of closed-loop boiling dryer

1. PLC touch screen operation, easy to operate, stable, with strict interlocking function, will not cause human error.

2. The cleaning method is pulse bag cleaning, with continuous offline cleaning and dust removal during operation. The cleaning effect is much better than the cylinder shaking bag cleaning method, avoiding material bed death during drying.

3. Equipped with a pull-out hard skeleton cloth bag, it ensures the bag area and cleaning effect while reducing the poor working environment for workers when dismantling and washing the bag. It is easy to remove the cloth bag from the equipment without drilling into the cylinder.

4. The equipment achieves automatic closed discharge through an automatic discharge device, reducing cross contamination of materials and labor intensity for workers.

5. The equipment contains a mixing structure that can prevent material trays and dead beds. Make the material fluidized and boil for better drying effect.

6. The equipment adopts a closed circular structure, with no dead corners, easy and rapid cleaning, and no cross contamination

7. After docking with the pneumatic conveying system, it can achieve fully automatic continuous operation function without human control (optional).

8. There is a drainage device at the bottom of the host, which can quickly drain the accumulated water during machine cleaning;

9. The entire equipment is easy to operate, disassemble, and clean;

10. The whole machine has good sealing and operates under negative pressure

11. Pulse bag filter (or stainless steel blowback filter can be used if there are special requirements) and equipped with pressure difference detection function to ensure reliable sealing. The exhaust duct is designed with temperature sensors and interlocked with the PLC control system to ensure product safety during the production process.