Problems with the dry gas seal of syngas compressors

Synthesizer compressor dry gas seal leakage: 1 Judged from the dry gas seal flow rate； 2. Judging from the temperature of the leaking gas, the dry gas seal is damaged, resulting in an increased leakage rate and a rise in temperature ；

The nitrogen pressure should be subject to interlock protection for the dry gas seal system: (1) Introduction. A dry gas seal is a non-contact mechanical seal that combines dynamic and static pressure mechanisms along with air film lubrication; it is primarily used in rotary machinery such as turbine compressors and turbine expanders in industries like natural gas pipelines, refining, petrochemicals, and chemicals. Dry gas seals were originally developed from helical groove gas bearings. Compared with other mechanical seals, their main difference lies in the shallow grooves engraved on the end faces of the rotating or stationary ring (or on both end faces simultaneously). When the seal is in operation, an air film is formed on the sealing end faces, preventing contact between them; as a result, almost no wear occurs on these end faces. It features high reliability, a long service life, low leakage of sealed gas, extremely low power consumption, no oil contamination in the process circuit, and the process gas does not contaminate the lubricating oil system either. (2) Process flow and description: (a) Nitrogen flow: Nitrogen is drawn from the nitrogen tank, passes through a coarse filter and a fine filter; after achieving a filtration precision of 1u, it is divided into four streams. Two streams of pre-sealing gas (buffer gas): one stream enters the high-pressure side sealing chamber via an orifice plate, while the other stream enters the low-pressure side sealing chamber via an orifice plate. The nitrogen introduced into the pre-sealing chamber is primarily used to prevent the gas contained within the machine from contaminating the sealing surface, with an orifice plate being used to control the amount of nitrogen consumed. Two main sealing gas circuits: one enters the main sealing chamber on the high-pressure side via a flow meter, while the other enters the main sealing chamber on the low-pressure side via a flow meter. When the compressor is operating, the pumping action of the spiral grooves engraved on the rotating ring opens the sealed end face and provides lubrication and cooling. The normal nitrogen consumption for a set of main seals is ≤1 NM3/h. (b) Instrument air system: The instrument air is drawn from the plant’s instrument air network, passes through a filter to achieve a precision of 3μm, and then goes to the dry gas seal cabinet to serve as isolation gas. Two circuits of rear seal gas (isolation gas): one circuit enters the rear seal chamber on the low-pressure side via an orifice plate, while the other circuit enters the rear seal chamber on the high-pressure side via an orifice plate. The instrument air that enters the rear sealing chamber is primarily used to prevent lubricating oil from contaminating the sealing surfaces, with orifice plates being used to control the consumption of this instrument air. (3) Alarm interlock instructions: The normal value for the pressure difference between the main sealing air and the pre-buffer air pressure is ≥0.3 Mpa ； Underreporting: 0.1Mpa ； Underreported value: 0.05 Mpa. (4) Operating procedures for putting the dry gas seal into use: (a) Before operation, the pipelines must be thoroughly purged to prevent impurities such as welding slag from entering the sealing chamber; ensure high cleanliness, and close all valves to put the system in standby mode. (b) At least ten minutes before the unit starts operating, the rear isolation gas must be supplied first, and this supply must not be interrupted during the unit’s operation. Before air is introduced into the unit, a buffer gas should be activated; once air begins to flow into the unit, the pressure of the front sealing gas should be 0.05 Mpa higher than the pressure at the balance pipe. (c) The main seal gas must be supplied before starting up. Dry gas seal deactivation: (a) After the compressor is stopped, the pressure in the lubricating oil main line must be reduced to prevent lubricating oil from entering the seal chamber and causing damage to the seal. (b) After the compressor stops operating normally, the buffer gas and main sealing gas cannot be shut off immediately; they must be stopped only after there is no pressure left inside the machine and the medium gas has been completely replaced. (c) After the compressor stops normally, the back-seal isolation gas must not be turned off until ten minutes after the lubricating oil circulation has ceased. Commissioning of the precision flow meter: Sequence of commissioning: Open the flow meter’s bypass valve – open the valve downstream of the flow meter – open the valve upstream of the flow meter – close the flow meter’s bypass valve. (5) Daily operation requirements: The differential pressure across the filter is used to determine whether the coarse filter and the fine filter are clogged; an alarm is triggered when the differential pressure reaches 60 Kpa, at which point it is necessary to replace the filter elements ； Before replacing it, open the valves before and after the other filter first, then close the valves before and after the clogged filter; once the pressure is released, the replacement can be carried out. (6) Handling of dry gas seal failures: Stop the nitrogen supply; this will trigger the interlock that shuts down the dry gas seal, and the unit should be handled as in an emergency shutdown scenario.

It is best to contact the host and the sealing supplier to conduct a joint diagnosis in order to resolve the issue; otherwise, if a problem arises over time, it could turn into something serious.

I would like to ask what effect temperature has on dry gas seals, especially on the primary seal gas Some units apply electric heating at the primary inlet – why?

What you mentioned is that the leakage at the non-driving end is relatively high; in other words, the leakage through the first-stage seal of the cylinder body is significant, which indicates that the first-stage seal is severely damaged. Next, check the amount of leakage from the second stage to determine the condition of the second-stage seal.

Whether at the drive end or the non-drive end, as long as the air volume for primary sealing exceeds the interlock value, the system will shut down. The seal must have failed. But it is also necessary to check whether the back pressure of the vent pipe has decreased.

Our compressor also tripped due to high pressure in the flare gas discharge; later, we changed the pressure threshold from 0.4 to 0.6 MP, and then there were no more issues. So it cannot be judged solely based on pressure and flow rate! ?

Thank you to all the sea friends. The seal was indeed damaged, and it has now been repaired. Thank you all for your help. ‘

The problem lies at the primary stage; the dry gas seal on the non-driving side has been replaced