Spray drying has been developed into the most successful technology for powder drying in the pharmaceutical, food, chemical, and metallurgical industries since the development of the drying technology for skimmed milk in Europe in the early 20th century. Especially in recent years, spray drying is a dry form that directly forms a liquid slurry into a powdery material and is the most widely used in other industries. Spray drying is a drying process in which a raw material liquid is atomized into droplets and hot air (or other gas) is directly contacted with the droplets to perform heat transfer and mass transfer heat exchange to obtain a powdery granular product. The raw material liquid may be a solution, an emulsion or a suspension, or may be a melt or a paste. The dried product may be powdered, granulated, hollow spheres or pellets as required. From the point of view of the spray dryer: According to the direction of the air flow, there are parallel flow (forward flow type), counter flow type and mixed flow type; according to the form of atomizer, there are centrifugal type, pressure type, air flow type; According to the production process, there are two kinds of open and closed loops (subdivision and self-inert loop and semi-closed loop). This article mainly starts from the characteristics and differences of the two kinds of centrifugal spray dryer system of open type and closed type, and combines the safety features of the closed type centrifugal spray dryer. It can be said that the explosion proof type developed by Changzhou Pilot Drying Equipment Co., Ltd. Centrifugal spray dryer is designed for the safety and reliability of many kinds of oxygen-sensitive and explosive materials.

1. Characteristics and differences between open and closed-cycle centrifugal spray dryer systems
1.1 Features of Open Centrifugal Spray Dryer System
At present, most of the spray dryers used in China are mostly centrifugal in terms of the form of atomizers. Most of the spray dryers used in the production process are open-ended. The characteristics of the open centrifugal spray dryer system: The heating medium can only be used once in the system to be discharged into the atmosphere, and can not be recycled. Therefore, it can only be applied to the exhaust gas with high moisture content, non-toxic and odorless gas. , and when discharged into the atmosphere does not affect environmental pollution.
Although the equipment flow of open centrifugal spray dryer system is relatively simple, air (or other carrier) is sucked by the fan through the filter, sent to the heater and heated into hot air, and evenly flowed into the tower through the hot air distributor at the top of the drying tower. However, the main disadvantages of this system are as follows: First, the consumption of heating medium is large and energy is wasted; second, there is a great potential safety hazard when the organic solvent or the easily oxidized and easily explosion-proof materials are dried.

1.2 Features of closed-cycle centrifugal spray dryer system
Closed-cycle centrifugal spray dryer system is rarely used in the domestic pharmaceutical industry. Its characteristics: The heating medium forms a closed loop in this system, which is beneficial to save heat carrier, recover organic solvents, and prevent toxic substances from polluting the atmosphere. The feed liquids used in the general pharmaceutical and chemical industry are often materials containing organic solvents, or are easily oxidized, flammable, and explosive materials, and some may also be toxic materials. When using a closed cycle system, most of the heating medium uses inert gas (such as nitrogen, carbon dioxide, etc.), so that the exhaust gas from the drying tower removes fine particles from the cyclone and wet scrubber and then enters the condenser and condenser. The role is to condense the solvent (or moisture) in the exhaust gas. The condensation temperature must be below the dew point of the maximum allowable concentration of the solvent to ensure the condensation effect. After dehumidification, the exhaust gas is boosted by a fan, and then it enters an indirect heater and turns into hot air. This cycle is repeated.

1.3 Comparison of Open and Closed Cycle Centrifugal Spray Dryer Systems
(1) Closed circulatory system is far less than open heat carrier and is energy-saving;
(2) Closed-cycle systems can suitably contain organic solvents, easily oxidized, flammable, explosive materials, or toxic materials. The scope of application is that open systems cannot be achieved; they are safe;
(3) The closed-loop system has more than one organic solvent system for recycling than the open-type one, which is environmentally friendly;
(4) The open-type drying tower needs to maintain a certain negative pressure, while the closed-type drying tower needs to maintain a certain positive pressure value.

2. The composition and operating mechanism of explosion-proof closed-cycle centrifugal spray dryer system
The explosion-proof closed-cycle centrifugal spray dryer recently developed by Changzhou Pilot Drying Equipment Co., Ltd. combines the concept of energy conservation and environmental protection of closed-cycle systems with the concept of explosion-proof safety. The organic combination of these two concepts is this The R&D foundation of the equipment system.

2.1 The system composition of explosion-proof closed-cycle centrifugal spray dryer
Explosion-proof closed-cycle centrifugal spray dryer system (Fig. 1) consists of a main body of a centrifugal spray dryer, a heater with an air filter, a blower, a gas-liquid separator, a size condenser, a spray tower, an exhaust fan, and a cyclone Separator, two-stage cyclone separator, pump, oxygen meter, pipeline and control valve.