Pipe Dimension And Piping Information

Piping and Instrumentation Diagram (P&ID) of Fuel Gas Compressor

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Introduction

A Fuel Gas Compressor (FGC) boosts low-pressure fuel gas to the stable pressure and quality required by prime movers (e.g., gas turbines, engines) or process users. The P&ID defines process flow, auxiliaries (lube oil, seal gas), anti-surge protection, safeguarding, and tie-ins to utilities and flare—crucial for design, operations, and maintenance.

1) Process Overview

  • Fuel Gas Source → Suction Conditioning (filter/coalescer, KO drum) → Compressor (centrifugal or screw) → Aftercooler → Fuel Gas Receiver/Manifold → Users (Turbine/Heaters).

  • Controls: suction pressure control, discharge pressure control, anti-surge recycle to suction, unit permissives/trips via PLC.

  • Safety: PSVs to flare/vent, high-high temperature/pressure trips, fire & ESD tie-ins.

2) Major Equipment on the P&ID

  • V-101 Suction KO/Separator with demister, level instrumentation, drain to closed drain.

  • F-201 Fuel Gas Filter/Coalescer (duplex optional) with ΔP indicators.

  • K-301 Fuel Gas Compressor (centrifugal or screw).

  • E-401 Aftercooler (air or water cooled) + condensate pot & drain.

  • V-501 Fuel Gas Receiver/Surge Drum (optional) for damping transients.

  • Seal Gas Panel (for centrifugal, dry gas seals) or Distance Piece Vent (for screw/recip).

  • LO-Skid: Lube oil reservoir, main/aux pumps, cooler, filters.

  • Anti-Surge Recycle Line with control valve back to suction.

  • Flare/Relief Header connections from PSVs, blowdown valves, and vent pots.

3) Key Piping & Valves

  • Inlet Isolation: MOV-101 at battery limit; BDV-101 for depressurization to flare.

  • Bypass/Start-Up: Manual bypass around filters; optional around compressor (for maintenance).

  • Anti-Surge Loop: FCV-AS-301 from discharge to suction, sized for full recycle at surge conditions; NRV to prevent reverse flow.

  • Discharge Isolation: MOV-301; PCV-302 to maintain header pressure or protect users.

  • PSVs: On V-101, K-301 casings (if applicable), aftercooler outlet, V-501; relief to flare with tailpipes and thermal reliefs on blocked-in segments.

  • Drains & Vents: Low-point drains to closed drain; high-point vents for commissioning.

  • Sample Ports: Gas quality, dew point, and calorific value (if analyzer provided).

  • Check Valves: At user manifold to avoid backflow.

4) Instruments & Typical Tags

  • Pressure: PIT-101 (suction), PIT-301 (discharge), PDIT-201 (filter ΔP).

  • Temperature: TIT-101 (suction), TIT-401 (aftercooler outlet), bearing metal temps (TIT-B1/B2).

  • Flow: FIT-301 (through compressor), FIT-AS-301 (anti-surge loop).

  • Level: LIT-101 on KO drum with LSH/LSL tied to trips/alarms.

  • Vibration/Speed (centrifugal): VIB-K-301, SPT-301 (speed), combined into machine protection system (MPS).

  • Controls:

    • PIC-301: Discharge header pressure control (may trim anti-surge bias).

    • SIC-301: Surge control using flow vs. head map (via ΔP across orifice or flowmeter and speed).

    • LIC-101: KO drum level to drain valve LV-101.

  • Analyzers (optional): Moisture analyzer (AIT-M), H2S/CO2 (if required), CV/BTU analyzer for turbine specs.

5) Control Philosophy (Simplified)

  • Start-Up:

    1. Suction and discharge MOVs open on permissives;

    2. Recycle FCV-AS-301 opens (minimum flow);

    3. Lube oil system running & pressures OK;

    4. Seal gas pressure > process by set margin;

    5. Ramp to speed/flow while staying right of surge line.

  • Normal Operation:

    • PIC-301 holds discharge header setpoint.

    • Anti-Surge adjusts FCV-AS-301 to maintain surge margin using flow-head map; fast-acting with open-bias on trips.

  • Shutdown/Trip:

    • On trip, FCV-AS-301 goes open (fail-open), suction/discharge isolate as logic dictates, BDV-301 opens to flare if ESD.

    • Cool-down run if specified.

6) Typical Design/Operating Parameters (tune per project)

  • Suction Pressure: 3–10 barg (fuel gas header).

  • Discharge Pressure: 15–35 barg (as required by users).

  • Gas Specs: Dew point below minimum metal temperature; particulates/oil mist within compressor limits.

  • Temperatures: Suction 20–45 °C; discharge limited by compressor map/materials; aftercooler outlet ≤40 °C typical.

  • Materials: Piping CS/SS; instrument tubing SS316; elastomers fuel-gas compatible.

  • Area Classification: Class/Zone hazardous; use Ex-rated instruments, junction boxes, and motors.

7) Safety, Relief & ESD

  • PSVs sized for fire case, thermal expansion, blocked-in scenarios; discharge to flare with appropriate backpressure checks.

  • Blowdown: BDV-301 to flare for ESD; tie-in location shown on P&ID.

  • Seal Gas: Maintain clean, dry seal gas > process pressure; include filter, regulator, flow indicator and differential alarm.

  • Lube Oil: Dual filters with ΔP alarm; low LO pressure trip; high bearing temperature trip.

  • Gas Detection: Fixed detectors near seals/vents; interlock to alarm/ESD as per HAZOP.

  • Fire & Gas: ESD pushbuttons; fire detectors may drive unit trip and blowdown.

8) Utilities & Tie-Ins

  • Instrument Air: for control valves (anti-surge CV, PCV, drain valves).

  • Cooling Water or Air: for E-401 aftercooler & lube oil cooler.

  • Power: MCC/UPS for PLC, MPS, auxiliaries.

  • Closed/Open Drain, Flare Header, Nitrogen (purging/maintenance).

9) Cause & Effect (Excerpt)

  • LSH-101 (KO Drum High-High) → Trip compressor; open BDV-301; alarm.

  • PSH-301 (Discharge High-High) → Open FCV-AS-301; if persists, trip.

  • Low LO Pressure → Immediate trip; permissive block for restart.

  • High Vibration → Trip via MPS; open recycle; alarm.

  • Gas Detected in Enclosure → Alarm; on Hi-Hi → trip and blowdown.

  • ESD Pushbutton → Isolate, recycle open, BDV to flare, safe stop.

10) Deliverables & Download

  • P&ID Files: DWG (compressor train, auxiliaries, flare tie-ins).

Conclusion

This Fuel Gas Compressor P&ID template captures the essential process path, conditioning, anti-surge protection, and safety systems required to deliver clean, stable fuel gas to users. Customize setpoints, equipment selections, area classification, and materials to your project standards and HAZOP results.

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