Switching conditions for the primary dry gas seal of a turbine-driven ammonia compressor

Reply to 1# 654262293: The switch can be made safely once the pressure of the process gas is higher than that of nitrogen when the compressor is running.

It is necessary to pre-heat the process dry gas seal to prevent ammonia gas from condensing in the dry gas seal pipeline due to low pipe temperatures when switching to the ammonia process medium. Liquid in the dry gas seal can, at best, affect its sealing performance, and at worst, damage the dry gas seal.

The last edit to this post was made by 654262293 on 2010-10-14 at 12:35, with a reply to 2# sjxx30: The pressure of medium-pressure nitrogen is between 1.6–2.0 MPa, while the outlet pressure of the ammonia chiller does not exceed 1.66 MPa. According to what you said, the dry gas seal cannot be switched when the outlet pressure of the ammonia chiller is at 0.8 MPa. But in reality, it is usually necessary to switch to the primary dry gas seal when the outlet pressure of the ammonia chiller is between 0.8–1.0 MPa; otherwise, more nitrogen will leak into the system, resulting in an excessive amount of non-condensable gas in the system.

The last edit to this post was made by 654262293 on 2010-10-14 at 12:36. Reply to 3# sun0225: The process gas that reaches the dry gas seal comes from the outlet of the third stage of the compressor; the temperature at that outlet is around 130 degrees, so there is no risk of ammonia vapor condensing into liquid ammonia. However, sometimes, during switching, the flow rate at each stage of the dry gas seal fluctuates greatly, and in some cases, there is no flow at all. Such situations indicate that the switching cannot be completed. At this point, the switching is forced to be paused; after adjusting the process, switching is attempted again. So there must be some issues when switching, have you encountered that? How do you switch?

The process gas inlet for the primary seal does not have a temperature indicator. There should be a length of 15 to 20 meters from the compressor’s main outlet pipe to the inlet of the compressor’s primary seal gas. The dry gas seal station is definitely not insulated, while other sections may or may not be insulated. The flow rate of the dry gas seal is also low; if the system is operated in winter, the low temperature in the pipes combined with heat loss will cause ammonia to condense into a liquid inside the pipes. In particular, there is no flow in the pipeline of the previous sealing process before switching; high pressure combined with heat dissipation causes ammonia to condense into liquid ammonia even before it reaches the dry gas seal station. If switching is carried out carelessly without taking these factors into account, this liquid ammonia will enter the dry gas seal, which could lead to a situation similar to that on the 5th floor: no flow, forcing a return to the previous setting. If this happens, the consequences will be severe.