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Reactors are often used in petrochemical, rubber, pesticide, dye, pharmaceutical and other industries to complete sulfonation, nitration, hydrogenation, hydrocarbonation, polymerization, condensation and other processes, as well as reaction equipment for many other processes of organic dyes and intermediates. Low-pressure reactor generally refers to a reactor below 1.6MPa. Due to different process conditions and media, the material selection and structure of the reactor are also different, but the basic components are the same, including transmission device, heat transfer and stirring device, kettle body (upper cover, cylinder, bottom), process nozzle, etc. The appearance size of the equipment is generally taken as the effective height of the reactor Hgz/the inner diameter of the reactor Di=1.0~1.2. If Hgz/Di>1.5, the number of blades needs to be added. The blade diameter di is usually taken as 1/3/Di, and the distance between the upper and lower blades should be slightly larger than the blade diameter. Necessary heat transfer and stirring devices are installed in the structure of the equipment to enhance the reaction process. The reactor body is generally made of steel (or lined), cast iron or glass-lined. The materials, stirring devices, heating methods, shaft seal structures, volume sizes, temperatures, pressures, etc. used in the reactors all have similarities and differences, and there are many types. Their basic characteristics are described below.: 1. Structure The structure of the reactor is basically the same. In addition to the reactor body, there are also transmission devices, stirring and heating (or cooling) devices, etc., which can improve heat transfer conditions and control the reaction temperature more uniformly without intensifying the mass transfer process. 2. Operating pressure The operating pressure of the reactor is relatively high. The pressure inside the kettle is generated by chemical reactions or temperature rise. The pressure fluctuates greatly, and sometimes the operation is unstable. The sudden pressure increase may exceed the normal pressure several times. Therefore, most reactors are pressure vessels. 3. Operating temperature The operating temperature of the reactor is relatively high. Usually chemical reactions need to be carried out under certain temperature conditions, so the reactor can withstand both pressure and temperature. Methods to obtain high temperatures usually include the following: 1. Water heating can be used when the temperature is not high. There are two types of heating systems: open type and closed type. The open type is relatively simple. It consists of a circulating pump, a water tank, a pipe and a regulator that controls the valve. When high-pressure water is used, the mechanical strength of the equipment is required to be high. A coiled tube is welded on the outer surface of the reactor. There is a gap between the coiled tube and the kettle wall, which increases the thermal resistance and reduces the heat transfer effect. 2. Steam heating When the heating temperature is below 100°C, steam with a pressure below atmospheric pressure can be used for heating. ； Within the range of 100~180℃, use saturated steam ； When the temperature is higher, high-pressure superheated steam can be used. 3. Use other media for heating. If the process requires operation at high temperatures or you want to avoid using a high-pressure heating system, other media can be used to replace water and steam, such as mineral oil (275~300℃), diphenyl ether mixture (boiling point 258℃), molten salt (140~540℃), liquid lead (melting point 327℃), etc. 4. Electric heating wraps the resistance wire around the insulation layer of the reaction kettle body, or installs it on a special insulator at a certain distance from the reaction kettle. Therefore, a small space gap is formed between the resistance wire and the reaction kettle body. The first three methods to obtain high temperatures all require adding a jacket to the kettle body. Due to the large range of temperature changes, the jacket and shell of the kettle are subject to temperature changes and generate temperature difference pressure. When electric heating is used, the equipment is lighter and simpler, the temperature is easier to adjust, and there is no need for pumps, furnaces, chimneys and other facilities. It is also very simple to start, is not dangerous, and has low cost. However, the operating cost is higher than other heating methods, and the thermal efficiency is below 85%. Therefore, it is suitable for places where the heating temperature is below 400°C and the price of electricity is low. 4. Stirring structure Chemical reactions are usually carried out in the reactor. In order to ensure that the reaction can proceed evenly and quickly and improve efficiency, a corresponding stirring device is usually installed in the reactor, which brings about the problem of dynamic sealing of the transmission shaft and prevention of leakage. 5. Working of the reactor Most reactors are operated intermittently. Sometimes, in order to ensure product quality, they need to be cleaned after each batch of materials is discharged. ； The top of the cauldron is equipped with quick-open manholes and hand holes for easy sampling, volume measurement, reaction observation, and access to the equipment for internal maintenance. 6. Chemical production requirements and development trends for reactors 1. Large volume, which is an effective way and development trend to increase output, reduce quality errors between batch production, and reduce product costs. Most reactors used in dye production in China are below 6000L, and some in other industries are as large as 30m³. ； In foreign countries, the capacity in the dye industry is 20,000 to 40,000L, while in other industries it can reach 120 m³. 2. The stirrer of the reactor has been developed from a single stirrer to a double stirrer or an external pump for forced circulation. Abroad, in addition to installing a stirrer, the kettle body is also rotated along a horizontal line to increase the reaction speed. 3. Use production automation and continuity to replace cumbersome intermittent manual operations. If program control is used, it can not only ensure stable production, improve product quality, increase profits, reduce physical labor, but also eliminate environmental pollution. 4. Utilize heat energy rationally, select the best process operating conditions, strengthen insulation measures, improve heat transfer efficiency, minimize heat loss, and fully utilize waste heat or heat energy generated after reaction. The application of heat pipe technology will be the direction of future development