Key points to note in the design of mechanical seals for reaction vessels

Due to the gradual development of reaction vessels towards high pressure and large diameter, and the lower rotational speed than the mechanical seal used in the vessel, the following points should be noted in the design:
1. Material selection of mechanical sealing ring for kettle
Due to the fact that most reaction vessels are sealed with gas, the selection of materials should not only consider the corrosiveness of the medium, but also the leakage of the material itself. When the diameter is large, integral surface composite materials should be used; When the pressure is high, it is advisable to use high PV value matching materials with high mechanical strength. When the medium pressure is below 10MPa, it is recommended to use hard alloy or silicon carbide and carbon graphite materials for matching. When the medium pressure is greater than 10MPa, it is recommended to use cemented carbide and cemented carbide, cemented carbide and copper alloy, and silicon carbide and copper alloy. The selection of friction materials should not only consider pressure and circumferential velocity, but also take into account all conditions such as shaft diameter, temperature, lubrication, and cooling method.
However, high-pressure large-diameter seals and friction pair end faces are prone to deformation, especially with the increase of medium pressure, the starting torque tends to increase. Therefore, the sealing ring should be made of materials with high strength and good rigidity.

2. Design of mechanical seal structure for kettle
In the design, double-sided sealing should be used for high-pressure large-diameter seals to ensure reliable sealing. Usually, the atmospheric end is sealed and designed to be balanced due to the large pressure difference; Due to the sealing fluid inside the sealing chamber, the pressure difference on both sides of the sealing end face of the middle end seal is very small, and it can be designed as a non-equilibrium type; But when the pressure of the medium inside the kettle is unstable or the pressure of the sealing liquid inside the sealed chamber is unstable and causes pressure fluctuations during operation, it can also meet the requirements and should be designed as a balanced type. In some imported equipment, the sealing under low pressure is also balanced. This is to reduce the frictional heat on the end face, prevent the evaporation of the end face liquid film, and thus achieve a longer service life. When the pressure inside the kettle exceeds 10MPa, it is recommended to use a multi-stage mechanical seal device.

3. Determination of geometric dimensions
In the design of mechanical seals for high-pressure reactors, the shape and support method of the sealing ring should be fully considered. The bending caused by pressure and the moment caused by the eccentric force on the center of rotation of the cross-section will have a significant impact on the sealing characteristics. Due to the size limitation of the kettle flange, the radial space of the fixed ring is generally not too large. So it is necessary to fully consider the shape of the ring, the support method, the position of the sealing ring, etc., so its pressure resistance and deformation are small. To avoid deformation caused by pressure, thermal stress, and unbalanced forces, the shape should be as symmetrical and simple as possible. It is also recommended to contact the back of the support method. Special attention should be paid to the rounded corner R at the connection of the end face convex platform. The rounded corner R should be as large as possible, and other chamfers should also be taken with appropriate values, without sharp angles. The friction width varies with the shaft diameter and appropriate strength coefficient.