Chemical Process Machinery Area: [Weekly Topic] Compressor dry gas seal issues? (2011.5.30~6.5)
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Many large compressors these days use dry gas seals; please share your respective information on dry gas seals with us, and it would be best to discuss any problems encountered in production. First, I would like to discuss the dry gas sealing issue in our facility: when the chillers’ compressors stop operating due to accidents, the pressure inside the unit is around 10 Bar, while the pressure of the sealed nitrogen supply from outside is only up to 7 Bar. Moreover, the pressure booster pump does not have a self-start function; therefore, we carried out technical modifications to connect a separate high-pressure nitrogen supply for sealing purposes. Also, I’m not sure how your booster pumps are activated when the unit is shut down? I hope everyone will discuss and share information related to their own departments. Those who post excellently will receive an additional reward of 10 to 50 wealth points or an equivalent amount of charm points.
The booster pump should be activated automatically. Our booster pump has a power air source at the front; once the pressure difference drops, the power air is activated. This air enters a pneumatic directional valve, which is connected to a booster cylinder, thereby increasing the pressure of the isolating gas.
This question is quite simple. For ordinary electrical appliances, slight interlocking with the main unit can enable automatic start and stop.
The dry gas seal of our turbine CO2 compressors relies primarily on the CO2 drawn from within the compressor itself for sealing, which is simply referred to as self-sealing. During parking or driving, due to the relatively low pressure of its own gas, instrument air is used for sealing; once the compressor is operating normally, the use of instrument air is stopped.
The primary seal vent of our dry gas seal is discharged directly to a higher point, to prevent tripping caused by excessive backpressure in the flare line； Our booster pump starts automatically, and after it begins operating, the differential pressure between the sealing gas and the balance pipe is around 0.05 MPa.
I’m wondering how your company’s booster pump achieves automatic startup? Please provide a detailed answer.
Set up interlock: the booster pump starts automatically when the differential pressure between the seal gas and the balance pipe is below 0.05 MPa, and it stops automatically when this pressure is above 0.1 MPa
There are mainly two schemes for the automatic start-up of a dry gas seal booster: First, the booster starts automatically when the pressure difference between the main seal gas and the balance line is less than 0.2 MPA; the booster pump stops when this pressure difference exceeds 0.25 MPA； 2. Start the turbocharger based on the main seal gas flow rate and the pressure difference between the inlet and outlet of the turbocharger
1. Dry gas sealing requires that the seal gas be supplied to the unit before lubricating oil is introduced. Moreover, the pressure of the seal gas (main seal gas) must not be lower than the pressure in the unit’s balance line; otherwise, the seal surfaces will be contaminated and the seal will be damaged. Since the dry gas pressure in the plant cannot be maintained during production fluctuations or in the event of accidents, whereas the demand for gas used for dry gas sealing is relatively stable and low, most sealing media have now been switched from dry gas to nitrogen; it is recommended to replace dry gas with nitrogen as the sealing medium. II. There are mainly two schemes for the automatic start-up of the dry gas seal booster: 1. The booster starts automatically when the pressure difference between the main seal gas and the balance tube is less than 0.15 MPa; the booster pump stops (manually) when the pressure difference exceeds 0.25 MPa. 2. Start the turbocharger based on the main seal air flow rate and the pressure difference at the inlet and outlet of the turbocharger. The above suggestions are for reference only
Our unit uses a catalytic cracking rich gas compressor, with nitrogen as the sealing medium. The problem is that salt deposition has occurred at the labyrinth seals of the compressor, which prevents nitrogen (used as a buffer gas) from entering the interior of the compressor; as a result, the pressure difference between the main sealing gas and the buffer gas is low. We connect the upper and lower balance pipes to reduce the pressure and increase the pressure difference.
Reply to 9# jwg70128: Our unit is new and not yet in operation; we are currently carrying out pre-commissioning tasks. We are now performing oil circulation, and test seals have been installed. The lubricating oil has been introduced into the unit. Is there any problem? It’s an ammonia compressor. Also, I don’t see a pressure booster pump on our seal disk! ! ! Please give help!