Centrifugal Compressor Dry Gas Seal Supply System
Dry Gas Seal is the internal parts of the Centrifugal Compressor. I am going to write a short note about the Centrifugal Compressor Dry gas seals system.
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| Centrifugal Compressor |
GE and Man-turbo Manufactured Multistage Centrifugal Compressors being like bearing between Compressor style. So we can differentiate the sides of the compressor based on Drive end side and Non-Drive end side. Dry gas seals are placed in both drive end and non-drive end sides to prevent the leakage from the rotor shaft.
Drawing Video
The compressor discharge gas which comes out between the balancing drum and labyrinth enters into the chamber and returns to the compressor suction through an external connection called a balancing gas pipeline. After the Balancing drum, we have inner Labyrinth in the chamber. Next to the Inner Labyrinth Seal, the Dry Gas Seal unit is Started. The dry gas seal is separated by chambers. Drive end side separated by 6 chambers. and Non-drive end side separated by 5 chambers. Dry Gas seals are Double mechanical gas seals and it is segmented as 3 units called Primary Seal, Secondary Seal, and Territory Seal. Primary seals and Secondary seals are combined in a set of units and it is called by Cartridge type. This type of Mechanical gas seals is made by cartridge type seal with Assembly bar. Next to the secondary seals, a territory seal is take placed. it is not a Mechanical gas seal. It is just a couple of labyrinth seals assembly.
See this video for full details
Primary gas seals consist of a set of the seal ring, mating ring, primary Sleeve, primary Housing, primary retainer, primary dich elements, and springs
. and Secondary gas seals consist of a set of the seal ring, mating ring, secondary Sleeve, secondary Housing, secondary retainer, secondary dich elements, and springs. This set of Seals is placed the same in both drive end and non-drive end side.
To prevent the process gas from escaping through the chamber and inner labyrinth every individual chamber is pressurized by process gas or external source gas. For primary seal, the process gas is used to pressurize from the compressor final discharge. It is Called as Seal Gas. Initially seal gas supplied from an external source is added to the process gas. For secondary seal, nitrogen gas used to pressurized as a buffer gas. Because it is an inert gas. So it acts as the backup for the primary seal. For territory seal, instrument air is used to flushing the territory seals. The schematic flow Diagram for the dry gas seals and supply system is shown in the figure.
Now we will see the Supply of Seal gas from the primary seal. To be sure that the seals operate with condensate-free clean gas, filtered gas is injected at a pressure slightly higher than the suction pressure. For example, assume compressor suction pressure is 1 bar means the primary seal gas pressure needs to maintain from 1.5 to 3 bar. Now the supplying seal gas wants to preheated by the electric heater for a certain specific temperature to get lean seal gas. Then Preheated seal gas is passed through the filter for the process of removing foreign particles, dust, and minor carbon particles from the gas. This is the Replaceable cartridge type twin gas filters. These filters are piped in a parallel arrangement using a continuous flow transfer valve. Normally any one of the filters is being online and another one is standby. If the filter differential pressure is getting high means that active filter got choked. And it is showing the alarm signal from the DCS. Then we need to change over the filter with help of continuous flow transfer valve and equalizing or bypass valve. After that, we can change the filter element from the existing choked filter. This filtering element size is 2 to 5 microns.
Then Cleaned seal gas is injected to the primary seal chambers on Drive end and Non-drive end side through the Orifice. The seal gas pressure is controlled and maintained by the pressure differential control valve. Then seal gas that returns from primary seal chambers, directly sent to the flare system to burn through a flow control valve and flow orifice valves through lines called primary vent lines. A differential pressure transmitter is installed between the upstream and downstream of the flow orifice valves. The pressure transmitter provides for an alarm signal and tripping the unit in-case of high pressure.
Next, we will go for secondary seals. For Secondary seals Nitrogen gas (N2) is used to pressurized. The inlet pressure of the Nitrogen gas is 8 bar. Nitrogen gas is passed through the filter for the process of removing foreign particles, dust, and minor carbon particles from the gas. This is the Replaceable cartridge type twin gas filters. These filters are piped in a parallel arrangement using a continuous flow transfer valve. Normally any one of the filters is being online and another one is standby. If the filter differential pressure is getting high means that active filter got choked. And it is showing the alarm signal from the DCS. Then we need to change over the filter with help of continuous flow transfer valve and equalizing or bypass valve. After that, we can change the filter element from the existing choked filter. This filtering element size is 2 to 5 microns.
Then Cleaned Nitrogen gas is injected to the Secondary seal chambers on Drive end and Non-drive end side through the Orifice. The seal gas pressure is controlled and maintained by the pressure control valve. Then Nitrogen gas that returns from secondary seal chambers directly sent to the atmosphere in a safe area. It is called Secondary vent lines. These Secondary vent lines are monitored by one or more flammable gas detectors. It is provided for an alarm signal and tripping the unit in case of flammable gas leaks coming from primary seal gas.
Finally, we will go for a territory seal. For Territory seals, Instrument air is used to flush the seals. Inlet pressure of the Instrument air is 8 bar. The first instrument air is passed through the filter for the process of removing foreign particles, dust, and minor carbon particles from the gas. This is the Replaceable cartridge type twin gas filters. These filters are piped in a parallel arrangement using a continuous flow transfer valve. Normally any one of the filters is being online and another one is standby. If the filter differential pressure is getting high means that active filter got choked. And it is showing the alarm signal from the DCS. Then we need to change over the filter with help of continuous flow transfer valve and equalizing or bypass valve. After that, we can change the filter element from the existing choked filter. This filtering element size is 2 to 5 microns.
Then Cleaned Instrument air is injected to the Territory seal chambers on Drive end and Non-drive end side through the Orifice. The seal gas pressure is controlled and maintained by the pressure control valve.
Then Instrument air that returns from the territory seal chambers directly sent to the lube oil tank. Because next to the territory seal the bearing units are started. Instrument air acts as a barrier for lube oil and lube oil vapors coming from the bearing units. it is not allowing the lube oil and lube oil vapors to enter into the mechanical gas seals. It is carrying the lube oil and lube oil vapors draining from the bearing units and leaving them into the lube oil tank.
This is the concept of the Centrifugal compressor dry gas seals supply system.
To prevent the process gas from escaping through the chamber and inner labyrinth every individual chamber is pressurized by process gas or external source gas. For primary seal, the process gas is used to pressurize from the compressor final discharge. It is Called as Seal Gas. Initially seal gas supplied from an external source is added to the process gas. For secondary seal, nitrogen gas used to pressurized as a buffer gas. Because it is an inert gas. So it acts as the backup for the primary seal. For territory seal, instrument air is used to flushing the territory seals. The schematic flow Diagram for the dry gas seals and supply system is shown in the figure.
Now we will see the Supply of Seal gas from the primary seal. To be sure that the seals operate with condensate-free clean gas, filtered gas is injected at a pressure slightly higher than the suction pressure. For example, assume compressor suction pressure is 1 bar means the primary seal gas pressure needs to maintain from 1.5 to 3 bar. Now the supplying seal gas wants to preheated by the electric heater for a certain specific temperature to get lean seal gas. Then Preheated seal gas is passed through the filter for the process of removing foreign particles, dust, and minor carbon particles from the gas. This is the Replaceable cartridge type twin gas filters. These filters are piped in a parallel arrangement using a continuous flow transfer valve. Normally any one of the filters is being online and another one is standby. If the filter differential pressure is getting high means that active filter got choked. And it is showing the alarm signal from the DCS. Then we need to change over the filter with help of continuous flow transfer valve and equalizing or bypass valve. After that, we can change the filter element from the existing choked filter. This filtering element size is 2 to 5 microns.
Then Cleaned seal gas is injected to the primary seal chambers on Drive end and Non-drive end side through the Orifice. The seal gas pressure is controlled and maintained by the pressure differential control valve. Then seal gas that returns from primary seal chambers, directly sent to the flare system to burn through a flow control valve and flow orifice valves through lines called primary vent lines. A differential pressure transmitter is installed between the upstream and downstream of the flow orifice valves. The pressure transmitter provides for an alarm signal and tripping the unit in-case of high pressure.
Next, we will go for secondary seals. For Secondary seals Nitrogen gas (N2) is used to pressurized. The inlet pressure of the Nitrogen gas is 8 bar. Nitrogen gas is passed through the filter for the process of removing foreign particles, dust, and minor carbon particles from the gas. This is the Replaceable cartridge type twin gas filters. These filters are piped in a parallel arrangement using a continuous flow transfer valve. Normally any one of the filters is being online and another one is standby. If the filter differential pressure is getting high means that active filter got choked. And it is showing the alarm signal from the DCS. Then we need to change over the filter with help of continuous flow transfer valve and equalizing or bypass valve. After that, we can change the filter element from the existing choked filter. This filtering element size is 2 to 5 microns.
Then Cleaned Nitrogen gas is injected to the Secondary seal chambers on Drive end and Non-drive end side through the Orifice. The seal gas pressure is controlled and maintained by the pressure control valve. Then Nitrogen gas that returns from secondary seal chambers directly sent to the atmosphere in a safe area. It is called Secondary vent lines. These Secondary vent lines are monitored by one or more flammable gas detectors. It is provided for an alarm signal and tripping the unit in case of flammable gas leaks coming from primary seal gas.
Finally, we will go for a territory seal. For Territory seals, Instrument air is used to flush the seals. Inlet pressure of the Instrument air is 8 bar. The first instrument air is passed through the filter for the process of removing foreign particles, dust, and minor carbon particles from the gas. This is the Replaceable cartridge type twin gas filters. These filters are piped in a parallel arrangement using a continuous flow transfer valve. Normally any one of the filters is being online and another one is standby. If the filter differential pressure is getting high means that active filter got choked. And it is showing the alarm signal from the DCS. Then we need to change over the filter with help of continuous flow transfer valve and equalizing or bypass valve. After that, we can change the filter element from the existing choked filter. This filtering element size is 2 to 5 microns.
Then Cleaned Instrument air is injected to the Territory seal chambers on Drive end and Non-drive end side through the Orifice. The seal gas pressure is controlled and maintained by the pressure control valve.
Then Instrument air that returns from the territory seal chambers directly sent to the lube oil tank. Because next to the territory seal the bearing units are started. Instrument air acts as a barrier for lube oil and lube oil vapors coming from the bearing units. it is not allowing the lube oil and lube oil vapors to enter into the mechanical gas seals. It is carrying the lube oil and lube oil vapors draining from the bearing units and leaving them into the lube oil tank.
This is the concept of the Centrifugal compressor dry gas seals supply system.
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