Dry gas sealing technology and application

 I. Overview of Dry Gas Seals

The dry gas seal is a new type of non-contact seal developed in the late 1960s on the basis of the gas dynamic pressure bearing. The seal uses the principle of fluid dynamics to achieve non-contact operation of the seal end face by opening a dynamic pressure groove in the seal end face. After several years of research, John Crane in the UK pioneered the successful application of dry gas seals to gas transfer equipment on offshore platforms in the late seventies. The dry gas seal was originally developed to solve the problem of shaft sealing for high speed centrifugal compressors. As the seal is non-contact, the seal friction sub-material is largely PV independent and is particularly suitable as a shaft seal for high speed, high pressure equipment. With the increasing maturity of the dry gas seal technology, its application range is becoming wider and wider, at present, the dry gas seal is gradually being used in centrifugal pumps and agitators. In short, where mechanical seals are used, dry gas seals can be used. Compared with mechanical seals, dry gas seals have the following advantages: 1), long seal life, stable and reliable operation; 2), seal power consumption is small, only about 5% of the contact mechanical seal; 3), compared with other non-contact seal, dry gas seal gas leakage is small; 4), can achieve zero media escape, is an environmentally friendly seal; 5), the seal auxiliary system is simple, reliable, the use of no maintenance is not required.

Second, centrifugal pump with dry gas seal

 The medium conveyed by centrifugal pumps is liquid.

According to different working conditions, the following sealing forms can be used.

1, double-end dry gas seal; double-end dry gas seal can be used in most of the centrifugal pump shaft seal, it has the following characteristics: 1) "gas blocking" instead of the traditional "liquid blocking" principle, that is, with pressure sealing gas instead of pressure sealing liquid, to ensure (2) the whole set of seal non-contact operation, its power consumption is only 5% of the traditional double-end seal, the service life is more than 5 times longer than the traditional seal; (3) simple structure of the auxiliary system, to ensure that the process medium is not polluted and the process medium does not leak to the atmosphere, completely get rid of the traditional double-end mechanical seal The dependence on oil system. The sealing gas is industrial nitrogen or industrial instrument air, the pressure is higher than the medium 0.15-0.2MPa.

The shortcomings of the double-ended dry gas seal for pumps are: 1) a certain pressure of the gas source is required, and the pressure of the gas source is at least 0.2MPa higher than the medium pressure; 2) a trace of gas enters the process.

 2、 Tandem dry gas seal; Tandem dry gas seal for pumps has the following characteristics: 1) Dry gas seal and contact mechanical seal used in tandem, mechanical seal as the main seal, dry gas seal as the secondary seal; 2) dry gas seal and the main seal into the nitrogen gas, to ensure that the main seal has a certain back pressure, greatly extending the service life of the main seal; 3) main seal leakage of process media with the seal gas discharge into the torch, to ensure that the process (4) After the failure of the main seal, the dry gas seal acts as the main seal for a short period of time, preventing the process medium from leaking to the atmosphere. 5) The service life of this type of seal depends on the service life of the mechanical seal, generally around 2-3 years. 6) The seal is mainly used for volatile media, such as liquid hydrocarbon media; the seal gas pressure requirements are not high. Seal gas pressure requirements are not high.

 The shortcomings of the seal are: 1) The seal is not a dry gas seal in the full sense of the word, its overall performance is between the mechanical seal and the dry gas seal. 2) The seal is suitable for volatile media, the use of narrow range.