Overview of closed cycle spray dryer
The closed cycle spray dryer is a closed cycle spray drying process specially used for the suspension made of ethanol, acetone, hexane, gas oil and other organic solvents, and the products with inert gas (or nitrogen) as the drying medium. The entire process is oxidation free, the medium is recyclable, and the inert gas (or nitrogen) can be recycled. The closed cycle system designed for organic solvent recovery has extremely high requirements for explosion-proof control, high system self-control performance, and strict GMP requirements. It is commonly used for spray drying of precision ceramics, pharmaceuticals, battery materials, hard alloy (Wc. Fe) powder.
The explosion-proof closed cycle centrifugal spray dryer system is composed of the centrifugal spray dryer host, heater with air filter, blower, gas-liquid separator, large and small condensers, spray tower, exhaust fan, primary cyclone separator, secondary cyclone separator, pump, oxygen detector, pipeline and control valve.
As a special equipment for drying organic solvent slurry, the nitrogen closed cycle spray dryer uses nitrogen as the drying cycle gas. During the drying process, materials can be prevented from oxidation and organic solvents can be recovered at the same time. It is suitable for drying the powder of slurry prepared with ethanol, acetone, hexane and other organic solvents. The equipment is explosion-proof designed, and the drying process is safe and environmentally friendly.

Working principle of closed cycle spray dryer
The closed cycle spray drying equipment works in a closed environment. The drying medium is inert gas (or nitrogen), which is suitable for drying materials containing toxic gas or materials prone to oxidation during the drying process; The system uses inert gas as the circulating gas, which has a protective effect on dry materials. The circulating gas undergoes processes of moisture loading and dehumidification, and the medium can be reused; After being heated by the heater, nitrogen enters the drying tower, and the liquid material is transported to the centrifugal nozzle by the screw pump. The liquid is atomized into powder material by the high-speed circulating atomizer and discharged from the bottom of the tower. The evaporated organic solvent gas, under the negative pressure of the fan, condenses the powder dust trapped in the gas into liquid through the cyclone separator and spray tower dust removal. The non condensable gas medium is continuously heated and reused as a drying carrier in the system. The conventional conventional centrifugal spray drying achieves the purpose of moisture removal through continuous air supply and exhaust, which is also an obvious difference between explosion-proof closed centrifugal spray drying equipment and conventional centrifugal spray drying equipment; The drying system operates under positive pressure internally, maintaining a certain positive pressure value. If the internal pressure drops, the pressure transmitter automatically controls the inflow to ensure system pressure balance.

Process Flow Diagram of Closed Cycle Centrifugal spray Dryer

Process design of closed cycle spray dryer experimental equipment
1. Drying system form: closed cycle system
2. Drying medium: nitrogen
3. Atomization method: centrifugal atomization
4. Contact mode between fog droplets and hot air: parallel flow
5. Liquid supply method: Peristaltic pump with stepless speed regulation, stable feeding
6. Heating method: Explosion proof electric heating
7. Dust removal method: cyclone separator+pulse bag filter
8. Solvent recovery: Condenser recovery

Main technical parameters of closed cycle spray dryer experimental equipment
1. Equipment model: BLPG-5 closed cycle centrifugal spray dryer
2. Drying room: Φ 1220 × H1220mm
3. Drying main tower: Φ 1400 × H3100mm
4. Solvent evaporation rate: 5kg/h
5. Inlet air temperature: 140~180 ℃, adjustable temperature
6. Air outlet temperature: 70-90 ℃, adjustable temperature
7. Exhaust oxygen content:< 0.3%
8. Solvent recovery rate: ≥ 95%
9. Installed power:~ 50kw
10. Nitrogen consumption: pressure 0.3-0.5MPa, flow rate 0.3Nm3/h

Main features of closed cycle centrifugal spray dryer
1. The connection of each pipeline in the closed system adopts a unique sealing structure with good sealing performance, which can ensure that the system has no leakage under a pressure of 0.5MPa and high thermal efficiency;
2. Using inert nitrogen as the drying medium gas, it is resistant to poisoning, oxidation, and explosion. The gas can be reused after being loaded and dehumidified;
3. The condensation system and recovery system equipped with a solvent for drying the material liquid in the system can enable the solvent in the drying material liquid to be recycled through secondary treatment. The drying of the material (solvent removal) is completed in a closed state and nitrogen environment in a hot state, and the solvent is recovered through the condenser. The safety of the whole machine is high. At the same time, the equipment is designed to be fully enclosed, with a high material recovery rate. The high yield of this equipment system cannot be achieved by other types of dryers. Main technical indicators: dry powder material recovery rate ≥ 95%, product residual solvent ≤ 2%, thereby greatly reducing production costs;
4. The drying speed is very fast. After spray, the surface area of the feed liquid increases. In the high temperature airflow, 95%~98% of the water can be evaporated instantly. The drying time is generally only about 5~40see;
5. Spray drying is usually used to deal with solutions with moisture content of 40%~60%, which can be dried into powder products at one time. Most products do not need to be crushed and screened after drying, thus reducing the production process and simplifying the production process. At the same time, the product has good dispersibility, flowability, and solubility. Due to the drying process being completed in air, the product naturally maintains a spherical shape similar to droplets and has good flowability;
6. The equipment is equipped with a system pressure online testing device, an oxygen concentration online detection and control device, and an in-situ cleaning device;
7. The equipment control system adopts a human-machine interface, namely PLC+touch screen control, and the process flow chart is dynamically displayed. The particle size, bulk density, and moisture content of the product can be adjusted by changing the operating conditions within a certain range, which is relatively easy to control.

Applicable scope of closed cycle spray dryer
1. Solids containing organic solvents that need to be recovered or in contact with air may pose a risk of combustion or explosion.
2. Dry, toxic, and odorous products.
3. Dust can form explosive mixtures in the air.
4. The finished product should avoid contact with oxygen, otherwise it will oxidize and affect the quality of the product.