Dry gas seal issues

III. Single-face dry gas seal: It is suitable for situations where a small amount of process gas leaking into the atmosphere poses no hazard, as shown in Figure 6. Figure 6. IV. Series dry gas seal: It is suitable for situations where a small amount of process gas leaking into the atmosphere is acceptable, as shown in Figure 7. Figure 7 A series of dry gas seals can be considered as two or more dry gas seals connected end to end in the same direction. Similar to the single-end face structure, the gas used for sealing is the process gas itself. Typically, a two-stage structure is employed: the first stage (the primary seal) bears all or most of the load, while the second stage, acting as a backup seal, bears no pressure drop or only a minor one; the process gas that leaks through the primary seal is directed to a flare for combustion. The extremely small remaining amount of unburned process gas leaks through the secondary seal and is introduced into a safe area for discharge. When the primary seal fails, the secondary seal can act as an auxiliary safety seal, ensuring that the process medium does not leak in large quantities into the atmosphere. V. Series dry gas seal with intermediate air intake: It is suitable for applications where neither the process gas nor the sealing gas is allowed to leak into the atmosphere, as shown in Figure 8. Figure 8: In scenarios where it is not allowed for the process medium to leak into the atmosphere, nor for the seal gas to leak into the process medium, a labyrinth seal can be added between the two sealing stages of the series configuration. It is used for flammable, explosive, and highly hazardous gas media, ensuring complete prevention of any external leakage. Such as H2 compressors, natural gas compressors with high H2S content, ethylene and propylene compressors, etc. In addition to the process gas itself, another supply of nitrogen is required as the sealing gas for the second stage in this structure. The process gas that leaks through the primary seal is entirely introduced into a flare for combustion using nitrogen. All that leaks into the atmosphere through the secondary seal is nitrogen. When the primary seal fails, the secondary seal also serves as an auxiliary safety seal. VI. Double-end dry gas seal: It is suitable for applications where it is not permissible for process gas to leak into the atmosphere, but it is allowed for a sealing gas (such as nitrogen) to enter the machine, as shown in Figure 9. Figure 9: A double-end face seal is equivalent to two sets of single-end face seals arranged face to face; sometimes, each of the two seals uses its own moving ring. It is suitable for situations where torch conditions are not available, and a small amount of blocking gas is allowed to enter the process medium. Nitrogen is introduced between the two sealing layers as a blocking gas, thereby creating a reliable blocking seal system. The pressure of the nitrogen is controlled to remain at a level 0.2–0.3 MPa higher than the pressure of the process gas; this ensures that any leakage from the sealing gas occurs in the direction of the process gas and the atmosphere, thus preventing the process gas from leaking into the atmosphere.

I’m sorry; I can’t upload my images. I think that by considering the above dry gas seal structure along with your factory’s design, you will be able to understand the principle, and then your question will have an answer； If you want to see the pictures, you can leave your email address ； Also, I think finding the compressor PID diagram will be very helpful for understanding

We usually refer to the so-called primary seal as the pre-seal gas, and the secondary seal gas as the main seal gas. In fact, the content is the same: the pressure of the primary seal gas is the pressure of nitrogen that has been regulated and supplied to the dry gas seal chamber; since this gas is part of the seal chamber, its pressure is considered to be the pressure of the seal chamber itself. When the pressure of the secondary seal exceeds the set value, the check valve closes down.