Application examples of double end gas film mechanical seal-

Application example of double end gas film mechanical seal

　2018-11-08　　

Application examples of double end gas film mechanical seals:

The liquid ammonia pump of the synthetic ammonia plant of the fertilizer department of a branch of Sinopec is an imported horizontal single-stage cantilever centrifugal pump. Two sets are installed on site, one for each. Its function is to transport liquid ammonia from the spherical tank to the high-pressure ammonia pump of the urea plant. The operating conditions of the liquid ammonia pump are: medium temperature -4~0℃, medium population pressure 0.435MPa, outlet pressure 1.755MPa, working speed 2950r/min.

The original shaft seal of the pump adopts tandem mechanical seal, the inner mechanical seal adopts liquid ammonia self-flushing, and methanol is used as buffer between the inner seal and the outer seal, and the off-position tank and external nitrogen supply are used to realize the cyclic flushing of methanol. . As a result, the sealing effect is poor and leakage is frequent. It is designed to adopt a manifold type double-end gas film seal (as shown in Figure 4-20), and a good sealing effect has been achieved. 261-60 mechanical seal

Figure 4-20 Double-end gas film seal

In this double end gas film seal, two sets of single end seals are arranged back to back. In order to save axial space, the inner seal and the outer seal share a transmission sleeve and spring seat. The moving ring is made of imported carbon graphite, which is connected with the spring as the shaft. The compensation ring and the static ring are made of cemented carbide, and micron-level spiral grooves are engraved on the cemented carbide. The complete set of sealed rotating components are integrated with positioning blocks for stationary components and sleeve positioning rings to ensure accurate positioning during on-site installation and quick installation. It is required to pass clean nitrogen with 0.2-0.3MPa higher pressure than liquid ammonia in the sealed chamber between the inner and outer seals. According to the inlet pressure and outlet pressure of the pump and the balance method adopted by the impeller, the normal pressure of the gas film seal is determined to be 1.25MPa , This can ensure zero leakage and zero escape of the sealed liquid medium, and at the same time control the amount of nitrogen entering the pump cavity to be very small. The trace nitrogen leaked through the outer seal enters the environment. This part of the gas is pure nitrogen without any ammonia, which fully meets the requirements of environmental protection.

The auxiliary system adopts a container structure, which is light in weight and occupies a small area. The auxiliary system mainly has the following three functions: one is to provide a clean and stable air source, this part of the function is mainly realized by the filter unit, the pressure regulating unit; the other is to monitor the operation status of the seal, this part of the function is mainly by the metal rotor flow The third is to provide an alarm function when the air supply pressure and sealing leakage are abnormal. This part of the function is mainly realized by the pressure switch and the flow switch. The principle of the auxiliary system is shown in Figure 4-21. The nitrogen from the nitrogen pipeline or the nitrogen bottle is reduced to about 1. The pressure is reduced by the pressure regulating valve, and the impurities above 1um are removed by the filter, and then enters the sealed cavity through the one-way valve; the sealing operation status is monitored by the flowmeter, if it leaks If the amount exceeds the standard, start the flow report; the air supply status is monitored by the pressure gauge and pressure switch. Once the air supply pressure is lower than the set minimum value, the pressure alarm is started.

Figure 4-21 Schematic diagram of gas film seal auxiliary system

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