Seals commonly used in industrial compressors are labyrinth seals, floating ring oil film seals, mechanical contact seals and dry gas seals. 2 .1 labyrinth seal The internal seal of the compressor is typically a labyrinth seal, such as a seal on a wheel cover, a spacer sleeve and a balance disc. The labyrinth structure commonly used in compressors is a zigzag type, a smooth type, a step type, and a honeycomb type. The principle of the labyrinth seal is that the gas flows from the high pressure end to the low pressure end under the action of the pressure difference between the front and the back of the seal. When the gap between the tooth and the shaft is sealed, the air flow speed is increased, the pressure and the temperature are lowered, and the gap flows into the interdental cavity. The area suddenly expands, and the airflow forms a strong vortex. At this time, the airflow speed is almost zero, the kinetic energy is completely changed into heat, and the gas itself is heated, so that the gas enthalpy remains equal to the front tooth enthalpy. For the ideal gas, the gas temperature rises again to the inflow. The temperature before the gap, but the pressure in the cavity rises very little, it can be considered that the pressure remains unchanged, this process can be considered as a throttling process. The gas flows from this space through the gap between the next sealing tooth and the shaft, and flows into the next interdental cavity, repeating the above process. This flows through each tooth and finally flows out of the entire seal. Each time the gas flows from a large interdental cavity through a small gap between the teeth and the shaft, and then flows into the other large interdental cavity, the pressure is reduced once, and as the specific volume of the flowing gas increases, The speed through the gap is constantly increasing, so that the pressure that passes through one tooth downstream is reduced more. The labyrinth seal is the effect of reducing the amount of leakage by using the throttling phenomenon. According to the flow calculation formula, the air leakage can be seen. By setting the sealing device, the clearance between the sealing teeth and the shaft can be much smaller than the gap when the seal is not provided, and the flow area is reduced. F, due to the throttling, the pressure difference between each tooth before and after the tooth is much smaller than the pressure difference between the front and the rear of the sealing device, the pressure difference is reduced, the flow rate is reduced, and the air leakage is reduced. 2. 2 floating ring oil film seal The floating ring oil film seal is a kind of wet mechanical seal. The seal form can form an oil film in the gap between the ring and the shaft, and the ring itself can freely float radially. As shown in the structure, the ring on the high pressure side is called the high pressure ring, the low pressure side is called the low pressure ring, and the middle ring between the high pressure ring and the low pressure ring. The working principle is that the sealing oil is injected into the sealing chamber at a pressure higher than the pressure of the process gas, and one way flows to the high pressure side through the gap between the high pressure ring and the shaft, forming an oil film in the gap to seal the process gas; the other is by the low pressure ring and The gap between the shafts flows out. The principle that the floating ring can float freely is the same as that of the bearing. The buoyancy generated by the oil film is used to bear the load. The difference is that the object to be floated is different. It is the shaft that floats on the bearing, and the bearing pad is fixed. Although the floating ring is sealed, the floating ring and the rotating shaft are not fixed, but the floating ring is much lighter than the rotating shaft, so that the floating ring is floating, and the shaft is not moving. Due to the buoyancy generated by the oil film, the float ring and the shaft are automatically maintained in alignment, which is a prominent feature of the floating ring structure. This feature can greatly reduce the seal gap value, thereby reducing the oil leakage rate. From the structure of the floating ring, more L-shaped rings and rectangular rings are used. L-ring oil film seal shows that the working condition of the high-pressure side float is much worse. Firstly, the pressure difference between the two sides of the floating ring is small. Secondly, the gap is generally reduced as much as possible. Therefore, the oil leakage on the high-pressure side The amount is much smaller than the low pressure side. A large amount of heat cannot be taken away by the oil, so that the temperature of the ring and the oil is high, and it is easy to cause the suspension shaft to damage the floating ring. In order to solve this problem, the cooling of the high pressure side ring must be strengthened. For example, drill some cooling holes in the high-pressure ring, let the oil wash the outer wall of the high-pressure ring first, and then most of the oil flows through the cooling holes from the high-pressure side ring, which enhances the cooling effect. In order to improve the wear resistance of the shaft at the seal, a bushing is generally added, and a wear-resistant material is applied to the bushing. 2 .3 mechanical contact seal Mechanical contact seals, also known as end seals, are characterized by a low leakage rate of the sealed medium. Therefore, in a compressor, it is often used when the compressed gas is not allowed to leak outward. Mechanical contact seal structure of the compressor. The seal is sealed by end faces (moving ring 1, static ring 2, etc.), floating decompression carbon ring 5, spring loading device (spring 4 and spring seat 3 with comb seal) and auxiliary seal (static ring seal) 8, moving ring seal ring 6) and other components, in order to drive the moving ring is also equipped with a drive pin 7. The moving ring and the static ring end face are smooth and straight, under the action of the spring force, close to each other, and relative rotational motion . A thin oil film is placed between the end faces to seal the process gas, which is a dynamic seal. The increase in the temperature of the friction surface of the mechanical contact seal moving ring and the static ring will destroy the oil film and increase the wear of the moving and stationary rings. For this reason, oil washing is used to remove the heat generated by the friction, so that the temperature is kept within a certain range, and at the same time, the accumulation of impurities near the end faces can be prevented. The moving and stationary rings work under high friction conditions. Therefore, reasonable selection of materials for moving and static rings has a great influence on the sealing performance and life. 2 .4 dry gas seal The seal has the advantages of less leakage, less wear, long service life, low energy consumption, simple and reliable operation. It has been widely used in centrifugal compressors in the petrochemical industry. The dry gas seal has a similar cross-sectional shape to the mechanical contact seal, and the seal is realized in a plane perpendicular to the rotational phase. The structure of the spiral groove type gas seal is mainly composed of two parts, dynamic and static. The stationary part consists of a static ring (main ring) sealed by an O-ring, a stainless steel clamping sleeve that is loaded with a spring and a fixed static ring (fixed in the compressor casing), and a moving ring (also called a mating ring). The sleeve and a locking nut (maintaining axial positioning) are mounted on the rotating shaft and rotate with the shaft at a high speed. The moving ring is generally made of tungsten, silicon carbide with high hardness, rigidity and wear resistance. Dry Gas Sealing Structure The spiral groove gas seal works on the balance of hydrostatic and fluid dynamics. The sealing gas is injected into the sealing device, so that the moving and stationary rings are subjected to hydrostatic pressure. The static pressure is present regardless of whether the mating ring rotates or not, and the dynamic pressure of the fluid is generated only when the shaft rotates. The spiral groove on the mating ring is the key to generating fluid dynamic pressure. When the moving ring rotates, the gas in the spiral groove is sheared from the outer edge to the center, generating dynamic pressure. Due to the static pressure, the sealing enthalpy flows out to the gas. Inhibition, gas flow is blocked, gas pressure is increased, this elevated pressure separates the static ring and the moving ring of the flexible installation. When the gas pressure is balanced with the spring restoring force, a minimum gap is maintained to form a gas film. , sealing the process gas. Due to the structural requirements, the gas seal has two tasks: First, to prevent the main ring and the mating ring from contacting during the rotation, to avoid friction and heat generation; and when the shaft does not rotate, the seal should be zero leakage. Therefore, firstly, the main ring and the mating ring should be finished and finely mounted to maintain the flatness requirement of the contact surface on the optical strip. Since the spiral groove on the sealing surface is only a few microns deep, it must be cleaned with a very clean gas. Generally, the gas injection upstream of the seal is very clean. After strict filtration, the seal gas can be used as a peripheral gas source or a process gas from the compressor outlet. 3 comparison The main features of the shaft end seal of the high speed turbo compressor are summarized, and the four types of seals are compared. High-speed turbo compressor shaft end seal comparison seal type advantages Disadvantages Labyrinth seal non-contact type, long life; simple structure, low manufacturing cost, easy maintenance. Large leakage, high operating and maintenance costs; there is a danger of environmental pollution. The floating ring seals non-contact type and has a long service life; it has a wide range of use of speed and pressure. The leakage amount in the sealing oil is large; the oil system is complicated, the investment is large, the floor space is large, and the operation and maintenance cost is high; the danger of the sealed oil contaminating the process gas circuit is large. The mechanical contact seal has a low leakage amount, and the sewage system is relatively simple; the oil pressure difference is large, the control is relatively easy, and the high oil tank can be eliminated. It is a contact seal; there is a danger of internal leakage and contamination of the process gas circuit. Dry gas seal non-contact type, long life and high reliability; no need to seal oil system, no oil pollution; low power consumption, low operation and maintenance costs. The price is higher; it needs to be promoted. 4 Conclusion The development trend of the shaft end seal of the high-speed turbine compressor for the process gas in the petrochemical industry is the labyrinth pumping inflatable seal floating ring seal mechanical float ring combination seal dry gas seal. Soda Maker Machine,Fountain Soda Machine,Water Carbonator Machine,Carbonated Drink Machine Suzhou Puretal Electric Co.,Ltd , https://www.puretal.com
1Because the rotor and stator of the compressor rotate at a high speed and the other is fixed, there must be a certain gap between the two parts, so there must be gas leaking from one part to another in the machine. Leak outside the machine. In order to reduce or prevent these leakages of gas, a sealing device is required. The compressor seal is divided into an internal seal and an external seal. The internal seal is generally labyrinth type. For the external seal, if the compressed gas is non-toxic and harmless, a small amount of gas leakage is allowed. A labyrinth seal can be used. If the compressed gas is toxic or flammable, it is not allowed to leak out of the machine. Mechanical seals such as liquid seals, mechanical contact seals, suction seals or air seals must be used. With the application and development of mechanical seals, the mechanical seals are newly classified. According to whether there is any additional liquid between the friction faces of the seal faces, the mechanical seals can be divided into dry seals (DGS) and wet seals (WS). Sealed Nitrogen and other inert gas seals are sealed Process gas seals Fully gasified Sealed Solid Lubrication Seals Wet seals Seals (floating ring oil film seals) Mechanical contact seals Process liquid seals 2 Seal type