Detailed introduction to the structure, working principle, and usage precautions of glass-lined reaction vessels

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Since reaction vessels are widely used in the chemical industry, it is essential for us to understand their basic structure and working principle. Today, Xiao 7 will use a glass-lined reactor as an example to explain things in detail for everyone. 　　Basic Structure 　　(1) The reaction vessel consists of a reaction container, an agitator and transmission system, a cooling device, safety devices, a heating furnace, etc. 　　1. The vessel body and the lid are made of stainless steel; the vessel body is connected to the flange via threads, while the lid is a flat lid with a regular shape. The two are fastened together using main bolts and nuts arranged evenly around the perimeter. 　　2. The main sealing surface of the autoclave uses a type A double-line seal, while the other sealing points employ a sealing mechanism based on linear contact between an arc surface and a flat surface, or between two arc surfaces. Good sealing performance is achieved thanks to the high precision and smoothness of these contact surfaces. 　　3. A barrel-shaped silicon carbide furnace core is installed outside the furnace body; the electric furnace wire passes through this core, with its ends extending out from the lower part of the furnace shell. The wire is connected to the controller via wiring studs and rubber-sheathed cables. 　　4. The kettle lid is equipped with a pressure gauge, a burst disk safety device, a vapor-liquid phase valve, a temperature sensor, etc., to facilitate monitoring of the reaction taking place inside the kettle at any time, to adjust the ratio of the substances within the kettle, and to ensure safe operation. 　　5. The coupling is mainly composed of a pair of inner and outer magnetic rings with strong magnetic force, with a pressure-bearing spacer in between. The mixer is driven by a servo motor through a coupling. By controlling the speed of the servo motor, it is possible to control the stirring speed. 　　6. A tachometer coil is installed at the upper part of the spacer; when the mixer, which is integrated with the inner magnetic ring, rotates, this tachometer coil generates an induced electromotive force. This electromotive force is proportional to the mixing speed, and it is transmitted to the tachometer, allowing the mixing speed to be displayed. 　　7. A cooling water jacket is installed between the magnetic coupling and the kettle lid; cooling water should be circulated when the operating temperature is high, to prevent demagnetization due to excessive temperature of the magnets. 　　8. The bearings are made of stainless steel or high-strength electrographite, offering resistance to wear and a long service life. 　　(II) Controller 1. The enclosure is made of a standard aluminum alloy chassis, with the upper cover that can be pulled back for easy maintenance and repair. The panel is equipped with a digital temperature display, voltmeter, tachometer, as well as control switches and adjustment knobs for the operator to use. 　　2. Electrical principle: The electronic components of the stirring control circuit are all mounted on a single circuit board. It employs a dual-loop control system, which offers high speed regulation accuracy, stable rotation speed, and strong resistance to interference. It also features comprehensive protection functions such as over-speed and over-current protection. By adjusting the “speed control” knob, the DC voltage of the DC motor can be changed, thereby altering the motor’s rotation speed and achieving control over the stirring speed. 　　3. Solid-state relays (commonly known as voltage regulators) are used in the heating circuit to regulate the voltage, thereby simplifying the circuit. The heating power can be adjusted by simply turning the “voltage regulation” knob. Additionally, the control unit of the heating circuit is equipped with an intelligent digital display, which allows the heating temperature to be adjusted as needed according to the requirements of the manufacturing process, while ensuring extremely high precision in temperature control. 　　4. All external leads pass from the rear panel, via waterproof connectors, to the terminal blocks inside the controller. 　　Working principle: The temperature control system for glass-lined reaction vessels surrounds the reactor with a jacket, and is equipped with a steam control valve connected to the steam generation device, as well as a cooling water control valve connected to the cooling water supply. 　　The temperature measurement equipment detects the real-time temperatures inside the reactor and the jacket; the temperature control equipment uses appropriate control methods to regulate the temperature in the jacket, thereby ending the temperature control of the glass-lined reactor. 　　When the temperature measured by the temperature sensing device is below the set value, open the steam control valve to increase the water temperature inside the jacket, thereby raising the temperature of the material in the reaction vessel as well ； When the temperature measured by the temperature sensing device is higher than the set value, the cooling water control valve is opened to lower the temperature of the water inside the cooling jacket, thereby reducing the temperature of the material in the reactor. This helps to keep the temperature within a specified range, ensuring that the reaction can proceed smoothly. 　　Important components inside the reactor: 1. Agitator; 2. Enameled temperature gauge sleeve. As the name implies, the temperature gauge sleeve is a device used in reaction reactors to measure the immediate reaction temperature of the materials inside. 　　It is generally installed on anchor-type or frame-type glass-lined mixers, and can also be used with paddle-type or impeller-type mixers. Its nominal pressure is 0.6 MPa and 1.0 MPa, while the medium temperature typically ranges from -20°C to 200°C. 　　The structures of glass-lined thermometer casings generally fall into two types: Type A and Type B. Type A is a glass-lined thermometer casing without a temperature sensing element, with a nominal diameter of 32~80 mm. Type B is a glass-lined thermometer sleeve equipped with a temperature probe, with a nominal diameter of 50–80 mm. 　　There are Type A and Type B installation methods for glass-lined thermometer casings. Type A is used with frame-type glass-lined agitators, with an installation angle of 0°, while Type B is used with anchor-type glass-lined agitators, with an installation angle of 7°. 　　The glass-lined finned thermometer sleeve is a thermometer sleeve used for glass-lined reaction vessels equipped with paddle and impeller agitators, with a nominal pressure of 0.6 MPa and 1.0 MPa, and a medium temperature range of -20 to 200°C. 　　Different types of stirring devices in reaction vessels require different types of thermometer sleeves in order to accurately and timely measure the reaction temperature of the materials inside the vessel, thereby enabling timely temperature control and ensuring the smooth progress of the reaction. 　　Installation Notes The quality of installation for glass-lined equipment directly affects its service life and performance; failure to pay attention during installation can lead to malfunctioning of the equipment and damage to it. 　　1. Handling 　　During handling, only the supports, tank body, and lifting lugs should bear the load; the tank must be moved smoothly. Rolling or tipping it is not allowed, and vibrations and collisions must be avoided. It is strictly prohibited to subject vulnerable components such as connections and clamps to stress. 　　2. Lifting 　　When lifting, steel wires must be attached to the designated points (such as lifting lugs); lift carefully and place the item gently, using soft materials as padding underneath. 　　3. Inspection before assembly 　　Before assembly, wash the glass-lined surface with water, and wear clean soft-soled rubber shoes to check whether the glass lining is in good condition. 　　4. Interface Installation 　　When tightening the bolts, do so in pairs along diagonal lines, tightening them gradually while applying even force to avoid excessive stress in certain areas that could damage the enamel coating. 　　5. Agitator 　　(1) After the agitator is assembled with the reducer, anti-loosening components such as lock nuts should be used ； 　　(2) Ensure that the installation surface of the mechanical seal is level, the kettle mouth is level, and the cylinder is vertical, in order to guarantee the performance of the mechanical seal ； 　　(3) During manual trial operation, no abnormalities were observed; the operation was smooth, and the verticality and radial runout met the design requirements ； 　　(4) Pay attention to the rotation direction; if it runs in the reverse direction, the wiring must be rewired, otherwise it will affect the mixing effect and may even cause the mixer to fall and damage the enamel. 　　6. Gaskets: Select gaskets based on the properties of the medium; replace them promptly if they lose their elasticity after being removed. 　　7. Welding 　　(1) Welding is strictly prohibited on the surface of glass-lined equipment ； 　　(2) When welding pipes and supports to the jacket, electric welding should be used along with cooling measures; gas welding is not permitted ； 　　(3) When welding in the area near the glass-lined surface, it is necessary to cover that surface to prevent welding slag from splashing and damaging it. 　　8. Hydrostatic test 　After the equipment has been installed and inspected to ensure there are no errors, a hydrostatic test is conducted. The equipment is then tested with water for half an hour; it can only be put into use once it operates properly. 　　Operating Procedures A glass-lined reactor is a composite material product formed by lining the inner surface of a steel container with glass containing high levels of silica, which is then fused to the metal surface through high-temperature treatment. Therefore, it combines the stability of glass with the strength of metal, making it an excellent corrosion-resistant material. The following provides a detailed overview of the operating procedures for glass-lined reaction vessels: 1. Operating pressure: 0.2–0.4 Mpa. 　　2. The following media cannot be used: (1) Hydrofluoric acid and fluoride-containing media ； 　　(2) Phosphoric acid, with a concentration of over 30%, at a temperature higher than 180℃ ； 　　(3) Sulfuric acid, concentration 10%–30%, temperature above 200℃ ； 　　(4) Alkaline solution, pH ≥ 12, temperature above 100°C. 　　Additionally, for applications with high requirements, these can be met through special design. For example, the design temperature of low-temperature glass-lined reactors can reach -45℃ ； The design pressure of the medium-pressure glass-lined tank is 116 MPa, and it can be designed as a coil-type jacketed vessel ； When the operating pressure of the inner cylinder is less than 0.11 MPa, the operating temperature range of a glass-lined tank designed for temperatures of 0–200°C can be extended to -10–200°C. 　　3. Operating temperature: When the metal carcass material is Q235-A or Q235-B, the design temperature is 0～200℃ ； When the metal core material is 20R, the design temperature is -20 to 200°C. 　　4. Porcelain layer thickness: The porcelain layer thickness in glass equipment is 0.8–2.0 mm, while that in accessories for enamel-coated equipment is 0.6–1.8 mm. 　　5. Voltage resistance: Enameled glass possesses good insulating properties; when the enamel layer is tested with 20 KV high-frequency electric sparks at a specified thickness, these sparks are unable to penetrate the enamel layer. 　　6. Impact resistance: The lower the internal stress in the glass layer, the better its elasticity; the greater its hardness, the higher its bending and compressive strength, and thus the better its impact resistance. In some factories, when a steel ball with a diameter of 30 mm and a weight of 112 g is used to impact the glass layer within the specified thickness, the impact energy generated is 282×10-3 J (the standard for top-quality products is 260×10-3 J). 　　Precautions during use 　To ensure the proper use, maintenance, and cleaning of glass-lined reactors, to standardize and regulate all operations, to extend the equipment’s service life, and to guarantee safe production and consistent product quality, the following suggestions are provided regarding how to use glass-lined reactors correctly: 　1. It is strictly prohibited to strike the glass-lined surface or its outer shell; care must be taken to prevent hard objects from falling into the reactor and damaging the glass lining. 　　2. During operation, try to avoid contact between the reactor shell and corrosive liquids such as acids and alkalis; if any material comes into contact with it, clean it immediately with a cloth. 　　3. It is prohibited to wash the equipment with water to prevent damage to the insulation layer. 　　4. When the minimum temperature is ≤ 0°C, the water remaining in the jacket should be drained after use to prevent damage to the equipment due to freezing. 　　5. For reaction vessels equipped with mechanical seals, the sealing area must be kept clean. 　　6. If the bottom of the tank becomes blocked during discharge, do not use metal tools to break it open; instead, use a bamboo pole, plastic rod, or wooden stick to gently push it aside. If glass lining debris is found during discharge, the tank should be opened immediately for inspection; it must be repaired before use again. 　　After introducing these main components, let’s take a look at the heating methods for glass-lined reaction vessels and the ways to improve heat transfer performance. 　　Heating method: The operating temperature of the reactor is relatively high; chemical reactions generally require specific temperature conditions to take place, so the reactor has to withstand both pressure and temperature. The common methods for achieving high temperatures are as follows: 1. Water heating – This can be used when a high temperature is not required; its heating systems come in open and closed types. The open-type design is simpler; it consists of a circulation pump, a water tank, pipes, and control valves. When high-pressure water is used, high mechanical strength is required for the equipment. Coils are welded to the outer surface of the reaction tank, and there is a gap between these coils and the tank wall, which increases the thermal resistance and reduces the heat transfer efficiency. 　　2. Steam heating 　 When the heating temperature is below 100°C, steam at a pressure lower than one atmosphere can be used for heating ； Within the range of 100~180°C, use saturated steam ； At higher temperatures, high-pressure superheated steam can be used. 　　3. Heating with other media 　If the process requirements dictate operation at high temperatures, or if it is desired to avoid using high-pressure heating systems, other media can be used in place of water and steam, such as mineral oil (275–300°C), biphenyl ether mixtures (boiling point 258°C), molten salts (140–540°C), liquid lead (melting point 327°C), etc. 　　4. Electric heating: The resistance wire is wound around the insulating layer of the reactor cylinder, or installed on a special insulator placed at a certain distance from the reactor. Therefore, a small spatial gap is formed between the resistance wire and the reactor body. 　　To achieve high temperatures using the first four methods, it is necessary to add a jacket to the reactor vessel; due to the large amplitude of temperature changes, the jacket and shell of the reactor are subjected to thermal stress resulting from these temperature variations. When electric heating is used, the equipment is lightweight and simple; the temperature is easy to control. No pumps, furnaces, chimneys, or other such devices are required, and it is very simple to operate. The level of risk is low, and the costs are low as well. However, the operating expenses are higher compared to other heating methods, and the thermal efficiency is below 85%. Therefore, it is suitable for applications where the heating temperature is below 400°C and electricity is relatively inexpensive. 　　How to improve heat transfer performance: 1. To withstand the corrosiveness of various solutions, glass-lined reactors are sometimes equipped with linings made from different materials, such as lead or ceramic tiles; even the reactor body itself may be made of steel or cast iron. 　　2. By using screw-type and anchor-type impellers with scrapers in viscous liquids, the power required is doubled; at the same time, the heat transfer coefficient also increases by almost a factor of two. Therefore, it is practical to use scrapers to improve heat transfer in viscous materials. 　　After saying so much, Xiao 7 will now summarize for everyone the advantages of glass-lined reaction vessels as well as the quality requirements. 　　Advantages of the equipment 　　Due to their unique advantages, glass-lined reaction vessels have replaced equipment made of stainless steel, non-ferrous metals, plastics, and other materials in many applications; therefore, it is important to have a comprehensive and systematic understanding of them. Enameled equipment is made by spraying a glassy glaze with a high silicon content onto the surface of a metal substrate, followed by multiple high-temperature firing processes at 920–960°C to ensure that the glaze adheres tightly to the metal surface. As a result, it possesses the dual advantages of glass-like chemical stability and the good mechanical properties of metals: 1. Corrosion resistance – It can resist most inorganic acids, organic acids, organic solvents, and weak bases; it exhibits excellent corrosion resistance, especially in mediums such as hydrochloric acid, nitric acid, and aqua regia. 　　2. Non-stick property: The smooth glass surface does not stick to the medium and is easy to clean. 　　3. Insulation Suitable for applications where static electricity is likely to be generated during the production process of the medium. 　　4. Isolation: The glass layer isolates the medium from metal, making it difficult for iron ions to dissolve into the medium. 　　5. Freshness retention: The glass layer provides excellent freshness retention for the medium. 　　Quality requirements: Glass-lined reaction vessels must be designed by units with the appropriate qualifications for designing pressure vessels, manufactured by units that hold the necessary certifications for manufacturing pressure vessels, and the glass lining must be applied by units with a license for producing glass lining ； The design and manufacture of the metal shell must comply with the GB150 standard for steel pressure vessels, the enamel shall meet the requirements specified in HG2432-2001 \"Technical Requirements for Enamel-Coated Equipment\", and it is also necessary to satisfy the provisions of the \"Regulations on Safety Supervision of Pressure Vessels\". 　　1. Insulation: The glass layer must pass a 20kV high-voltage test; it is considered qualified if it does not conduct electricity ； 　　2. Impact resistance The index for mechanical impact resistance is 220×10-3J ； 　　3. Temperature resistance: The glass surface’s ability to withstand sudden changes in temperature; the heat shock threshold is 120°C, while the cold shock threshold is 110°C℃ ； 　　4. The thickness of the glass layer is 018–210 mm ； 　　5. Surface The glass layer has a smooth and glossy surface, free of spots or scratches ； 　　6. Documentation 　Since low-pressure and medium-pressure glass-lined equipment fall under category II and category III pressure vessels respectively, the documents accompanying the equipment at the time of delivery must be complete and valid, such as product inspection certificates, approval certificates issued by the vessel inspection authority, and as-built drawings stamped with the seals confirming design and manufacturing qualifications. 　　Glass-lined reactors, which are widely used in the chemical industry, often suffer various types of damage due to factors such as the corrosiveness of the media, fluctuating reaction conditions, transportation issues, usage problems, and human error, resulting in unnecessary production interruptions. It is therefore particularly important to know how to maintain it effectively. So what should we pay attention to? 　　1. Feeding 　　(1) It is strictly prohibited to have metals or foreign substances present in the material, and large, hard pieces of material must not be added directly ； 　　(2) Prevent hard objects such as metals from falling into the container and damaging the enamel surface ； 　　(3) Reduce the temperature difference between the material and the tank wall, avoiding heating material in a cold tank or adding cold material to a hot tank, so as to prevent internal stresses caused by large temperature differences from affecting the service life of the equipment. 　　2. Temperature rise and fall 　　(1) When heating, the temperature should be increased gradually, with the pressure increase rate in the jacket controlled at 0.11 MPa/min ； 　　(2) Prevent sudden cooling during temperature reduction to avoid stress-induced ceramic cracking. 　　3. Discharging 　　If the discharging valve or pipes are blocked, non-metallic tools should be used to clear them; forceful hitting is not allowed. 　　4. Jacket medium 　　It is strictly prohibited to allow acids to enter the jacket, in order to prevent hydrogen absorption by the metal in the enamel layer, which could lead to spalling of the enamel lining. 　　5. Two maintenance sessions per year 　In accordance with the specified maintenance cycle for glass-lined reaction vessels, maintenance is carried out twice a year, usually around the Spring Festival and during major overhauls. 　　6. Inspection of thermometer sleeves The thermometer sleeves and air inlet pipes of the glass-lined reaction kettle are removed for inspection only around the Spring Festival each year. 　　7. Impeller inspection: During the annual major maintenance, in addition to checking the thermometer casings and air inlets, it is also necessary to inspect the impellers, perform pressure testing on the reactor jacket, change the oil in the reducer, and check the anti-corrosion measures as well as the insulation properties of the reactor. 　　8. Others: The regular maintenance of glass-lined reactors with agitators is carried out according to specific circumstances.