Introduction

A Fuel Gas System supplies clean, pressurized gas to fired equipment such as gas turbines, heaters, boilers, and process furnaces.
The Piping and Instrumentation Diagram (P&ID) shows the essential flow of gas from the source through treatment, pressure control, heating, and distribution — along with key instrumentation, valves, and safety features.

Understanding this P&ID helps engineers design, operate, and maintain a safe and reliable fuel supply network.

1. Process Overview

Typical flow sequence:

Fuel Gas Source → Filter/Separator → Pressure Control → Heater → Distribution Manifold → Users

The system ensures:

• Continuous and stable gas pressure

• Filtration to remove solids/liquids

• Temperature control to prevent condensation

• Automatic shutdown on high/low pressure or emergency events

2. Main Equipment on the P&ID

Optional:

• Analyzer (AIT-801) for BTU, moisture, or H₂S content

• Flow Transmitter (FIT-301) on main supply

• Temperature Indicator (TIT-401) after heater

• Dew Point Monitor (DPIT-501) for gas quality assurance

3. Key Valves and Control Loops

a) Pressure Control Loop

• PIC-301 senses downstream pressure and adjusts PCV-301.

• If upstream pressure fluctuates, control valve modulates to protect burners or turbines.

• Bypass line with manual valve HV-301B allows maintenance on PCV.

b) Temperature Control

• TIC-401 monitors gas outlet temperature from heater.

• Modulates heating element or glycol flow via TCV-401.

• Low temperature alarm (TAL-401) prevents cold gas supply.

c) Shutdown & Protection

• ESDV (SDV-501) — closes automatically on high-high pressure, low pressure, or external trip.

• BDV-502 — opens to flare for controlled depressurization.

• PSV-701 — mechanical relief on overpressure.

• All interlocks handled via PLC / ESD system.

4. Instruments and Typical Tags

🧠 Tip: Use standardized ISA tagging in your AutoCAD legend (PT, TT, FT, LT, etc.) for clarity and automation compatibility.

5. Typical Control Philosophy

1. Normal Operation:

   • Fuel gas flows through filters → pressure control → heater → users.

   • PCV-301 keeps downstream pressure constant.

   • TIC-401 maintains outlet temperature (~40–60°C).

2. Startup:

   • Line-up valves open gradually; purge with nitrogen if required.

   • Heater energized when minimum flow is achieved.

3. Shutdown:

   • On ESD: SDV-501 closes, BDV-502 opens, venting to flare.

   • Heater and analyzer isolated.

4. Trips & Alarms:

   • High Pressure (PSH-301) → close ESDV; alarm.

   • Low Pressure (PSL-301) → trip user (turbine/furnace).

   • High Temp (TSH-401) → shutdown heater.

   • Gas Detection near skid → close ESDV, alarm control room.

6. Design and Operating Parameters (typical values)

7. Safety and Flare Integration

• PSV-701, BDV-502 discharge to flare header via knockout pot and seal drum.

• Thermal Relief Valves (TRV) on blocked segments.

• Fire & Gas Detectors located around heater, skid, and filter section.

• ESD Pushbutton near access point for emergency isolation.

8. Lines and Legend

Piping Material: Carbon Steel or SS316 (depending on gas quality)
Flanges: ASME Class 300 or higher as per design pressure
Instrument Air: Dry, 6–8 barg

9. Deliverables & Download

Included Files:

• P&ID (DWG)

Conclusion

A Fuel Gas System P&ID defines every critical element of a plant’s gas supply — from filtration and pressure regulation to temperature control and safety isolation.
It ensures safe delivery of fuel gas to turbines, heaters, and boilers while meeting reliability and safety standards.