Introduction:
Pressure Regulating Stations (PRS) also known as “Gas Trains” are required to supply a certain quantity of gas at different operating pressures. The PRS meets both maximum & minimum inlet pressure requirements. It restricts downstream pressure to predetermined set level, thus, ensuring safety. PRS are installed at various stages of the gas pipeline.
Typically,
1st Stage PRS: installed at the Supply or Source point of Gas.
2nd Stage PRS: installed near or at the junction of multi utility point.
3rd Stage PRS: installed at every utility point.
The design features of a Pressure Reduction Station are:
- The PRS shall be designed for maximum working pressure.
- The PRS must contain safety devices as mentioned in the scope.
- The PRS station shall be capable to cater towards the maximum flow rate and lowest differential pressure.
- End connections should be flanged end either ANSI 150 or ANSI 300 with raised face with metallic gaskets.
- The PRS must have pass/parallel stand by line to get uninterrupted gas supply in case of maintenance and other miscellaneous activates.
- All equipment installed in PRS should have an identification plate which would display the manufacturers name, serial number, capacity, set pressure, working pressure, flow rate and gas.
When designing a Pressure Reduction Station, the following parameters are essential:
- Type of Gas
- Maximum flow rate
- Accuracy and lock up class
- Maximum and minimum inlet pressure
- Maximum and minimum outlet pressure
- Maximum and minimum operating temperature
Installation Practices:
- PRS should set / handled by a trained personnel only.
- Skid should be placed and fastened on concrete platform.
- PRS direction L to R / R to L (as per arrow marked on PRS).
- Safety Relief Valve should be vented well above the roof height.
- Breather hole provided on bonnet should remain clean and clear.
- The vapor line should come from bottom and upward towards PRS.
- All ball valves should remain open during normal operating condition.
The Pressure Reduction Station consists of:
a) Ball Valve: To isolate the system from main supply or to isolate the either side of PRS the ball valve are being used.
b) Pressure gauge: To monitor upstream and downstream pressure of regulator, the pressure gauges are installed. Isolation Valve is provided with each pressure gauge for easy replacement of pressure gauges in case of failure.
c) Filter: A filter protects the rest of station from any debris or dust that may be carried with gas stream. Debris may consist of parts accidentally left in the pipe during construction. It could also result from swarf from drilling holes and taps, welding bends, sand from construction, fine iron oxide dust and so on.
d) Safety Shutoff Valve: This normally remains open. If the outlet pressure of the regulator rises than the permissible limit, the safety shutoff valve senses it via the impulse line and instantly shuts off the supply to the downstream system.
e) Pressure Regulator: Pressure regulator is a device, which design to maintain downstream pressure at certain quantity of gas, irrespective of variation in upstream pressure for maximum to minimum limit. To reduce the pressure from upstream to downstream, spring loaded or pilot operated pressure regulators are used. Pressure regulators do not require any external source of power to operate.
f) Safety Relief Valve: A slight weeping of the pressure regulator result in increasing the downstream pressure to dangerous levels, such creep pressure is blown off through safety relief valve.
g) Flame Arrestor: Flame arrestors are used to arrest the flame from reaching the highly dense area of fuel, in case of backfire and thus avoid accident and explosions. The flame arrestor has an in built non – return valve.
PRESSURE REDUCING STATION SINGLE STAGE
PRESSURE REDUCING STATION – DOUBLE STAGE
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