Compressor dry gas seal
Thread Content
This post was last edited by 110120149 on 2019-10-29 at 17:56. The natural gas compression station is equipped with two compressors. The design pressure of the inlet pipelines for these compressors is 5.5 MPa, while the design pressure at the outlets is 10.0 MPa (the operating pressures at the inlets and outlets can initially be taken as the design pressures). The seal gas comes from either the outlet of each individual compressor or a collective pipe at the compressor outlets. During startup, a separate booster pump is used to increase the pressure of the seal gas, with a maximum pressure increase of 0.2 MPa. Does this pressure increase refer to an addition of 0.2 MPa on top of 5.5 MPa, or is it an addition of 0.2 MPa based on the actual outlet pressure of the compressors, within the range of 5.5–10.0 MPa?
It is sufficient that the pressure of the primary sealing gas is higher than the pressure in the balance line of the sealing chamber; a higher pressure ensures there will be flow. As for whether 57 kilograms is sufficient, it is best to consult the design institute or the compressor manufacturer. Even if they think it is acceptable, they are not responsible for this, so let them make the decision
May I ask what determines the pressure in the balance tube of the sealed chamber? Is it the inlet pressure of the compressor, or the outlet pressure?
You can take a look at the cross-sectional view of the compressor to understand this; there are labyrinth seals between the compressor’s inlet and outlet ports and the dry gas seal. The chamber located between the dry gas seal and the labyrinth seal is called the sealing chamber. The function of the balance tube is to equalize the pressures in the high-pressure and low-pressure sealing chambers. Once this equilibrium is achieved, the sealing gas in both dry gas seals can operate at the same pressure
Simply put, the pressure in the balance tube is close to the inlet pressure. A balance disk is installed on the outlet side of the compressor in order to counteract the axial thrust generated during operation; the leaked gas is sealed by this balance disk and then returns to the compressor’s inlet through the balance tube. Therefore, when the compressor just starts, with the return valve fully open, the outlet pressure is equal to the inlet pressure; thus, a booster pump is used to increase the gas pressure by about 0.2 Mpa above the inlet pressure.
There is another question regarding the amount of seal air required for the compressor that I would like to ask: does the mass flow rate of seal air needed by the compressor change as it moves from startup to its optimal operating condition? If the mass flow rate can change, under what conditions will the mass flow rate of the sealing gas reach its maximum?
As the operating conditions of the compressor change, the pressures at the inlet and outlet change as well, which in turn affects the force exerted by the sealing gas. Generally, dry gas seal manufacturers specify a minimum flow rate; as long as the flow rate is above this minimum value, you can adjust it as needed. .
Do you mean mass flow rate or volume flow rate by the flow rate you mentioned? Is the minimum flow rate of the sealing gas determined when the compressor outlet pressure is at its maximum, at its minimum, or when the compressor speed is at its highest?
Based on your target pressure and the actual pressure level, the booster pump will add an additional 0.2 Mpa to that value