First, an overview of dry gas seal
Dry gas seal is a new type of non-contact seal developed from the foundation of gas dynamic pressure bearings in the late 1960s. The seal utilizes the principle of fluid dynamics to realize the non-contact operation of the sealing end surface by providing the dynamic pressure groove on the sealing end surface. After years of research, the British company John Crane took the lead in the late seventies to apply dry gas seals to gas delivery equipment on offshore platforms and achieved success. Dry gas seal was originally developed to solve the shaft seal problem of high-speed centrifugal compressors. Due to the non-contact operation of the seal, the friction material of the seal is basically not limited by the PV value and is particularly suitable as a shaft seal for high-speed and high-pressure equipment. With the increasingly mature dry gas sealing technology, its application is also more and more broad, at present, dry gas seal is gradually being applied in centrifugal pumps and blenders. In short, where the use of mechanical seals can be used dry gas seal occasions. Compared with the mechanical seal, dry gas seal has the following advantages:
1, long sealing life, stable and reliable operation;
2, the sealing power consumption is small, only about 5% of the contact mechanical seal;
3, compared with other non-contact seals, dry gas seal gas leakage is small;
4, can achieve zero escape of the medium, is an environmentally friendly seal;
5, seal auxiliary system is simple, reliable, use does not require maintenance;
Second, the centrifugal pump with dry gas seal
Centrifugal pump transport medium is liquid. According to different working conditions, the following types of seals can be used:
1, double-sided dry gas seal
Double-sided dry gas seal can be used in the vast majority of centrifugal pump shaft seal, it has the following characteristics:
1) Replace the traditional "liquid blockage" principle with "gas blockage", that is, replace the pressured sealing liquid with pressurized sealing gas to ensure "zero escape" of the process medium;
2) The entire seal non-contact operation, the power consumption is only 5% of the traditional double-sided seal, the service life of more than 5 times longer than the traditional seal;
3) A simple auxiliary system to ensure that the process medium is not contaminated and the process medium does not leak to the atmosphere, completely get rid of the traditional dual-end mechanical seal on the oil system. Sealed gas using industrial nitrogen or industrial instrumentation, the pressure is higher than the medium 0.15-0.2MPa.
Pump double-sided dry gas seal is inadequate is:
1) gas source that requires a certain pressure, gas pressure at least higher than the medium pressure 0.2MPa;
2) a trace of gas into the process.
2, series dry gas seal
Pump series dry gas seal has the following characteristics:
1) dry gas seal and contact type mechanical seal used in tandem, the mechanical seal is the main seal, the dry gas seal is the secondary seal;
2) Dry gas seal and the main seal between the access to nitrogen, to ensure that the main seal has a certain back pressure, greatly extending the life of the main seal;
3) Leakage of the main seal of the process medium with sealing gas into the torch to ensure that the process medium does not leak to the atmosphere, is an environmentally friendly seal;
4) After the failure of the main seal, the dry gas seal plays a main role of sealing for a short period of time to prevent a large amount of leakage of the process medium to the atmosphere.
5) The life of this type of seal depends on the service life of the mechanical seal, which is usually about 2-3 years.
6) The seal is mainly used for volatile media occasions, such as liquid hydrocarbon media; less demanding on the seal gas pressure.
The inadequacies of the seal are:
1) The seal is not yet a perfect dry gas seal, its overall performance is between the mechanical seal and dry gas seal.
2) The seal is suitable for volatile media occasions, the use of a narrow range.