The difference between open spray drying system and closed spray drying system of spray dryer

The closed spray drying system of the spray dryer is also called a closed cycle spray drying system. Its characteristic is that the system forms a closed circulation loop and the heat carrier can be recycled. For the drying of materials whose volatile substances are organic chemical solvents, are toxic or can cause harm to people and the environment after escaping, and the organic solvents or products contained in the feed liquid are easily oxidized, flammable or explosive materials, under normal circumstances, it is necessary to The materials used in this process cannot come into contact with oxygen, so most of the heat carriers use inert gases (such as nitrogen, carbon dioxide, etc.). The tail gas discharged from the dryer has to go through the condenser to recover the solvent or remove the moisture after gas-solid separation. It is then heated by the heater and then enters the dryer for recycling using the organic solvent spray dryer. This type of dryer needs to add refrigeration equipment to the system, which has higher operating costs and higher air tightness requirements for the equipment. Normal pressure or slightly positive pressure is mainly used in the dryer to prevent air from entering the system.
In the open spray drying system of the spray dryer, hot air only passes through the system once and is no longer recycled. This process is mainly suitable for exhaust gases with high moisture content, non-toxic volatiles, no odor, and discharge into the atmosphere. An occasion that cannot cause any pollution.
Since most of the volatile components in spray drying are water, this process is also the most commonly used solution. The air is heated by the fan and enters the dryer after heat exchange. After drying, it enters the dust removal system together with the evaporated water vapor and powdery products for gas-solid separation, and then the high-humidity and low-temperature gas is discharged into the atmosphere. The advantages of this system are simple process, small equipment investment and low operating costs. The disadvantage is that it consumes a lot of air and wastes a lot of energy. For a system with an optimal temperature of about 180°C, the heat taken away by the exhaust gas accounts for about 33% of the total heat consumption.