Cogeneration Gas Turbine: NFPA 37, Enclosure Cooling and CO2 Protection

Cogeneration/trigeneration plants run natural-gas turbines (heavy-duty frame and industrial units). On 50-100 MW class units, lube oil, fuel gas and high ambient temperatures create three separate fire risks. NFPA 37 (Stationary Combustion Engines and Gas Turbines) defines enclosure ventilation, CO2 protection and gas-detection rules.

Enclosure Ventilation

• Normal: 30-50 ACH for cooling
• Maximum: increase fan speed when the internal temperature exceeds 55°C
• Emergency: close dampers just before CO2 release, otherwise the gas escapes
• Purge: 30 ACH mandatory after CO2

CO2 Total Flooding

• Concentration: 50 percent (gas turbine)
• Hold time: 20 min
• Discharge: 1 min (surface fire)
• Reserve: 100 percent reserve cylinder bank; optional under NFPA 37, but treated as mandatory in the field
• Alarm: 20 sec pre-discharge warning

Lube Oil System

• Tank: 1,500-3,000 L, bearing cooling
• Pump: AC + DC emergency pump
• Level alarm: low-level shutdown
• Fire detection: linear heat cable, IR3 flame detector
• Water spray: over the lube oil tank and cooler; an NFPA 15 water spray system is the alternative

Natural Gas Regulator

• Pressure reduction: 70 bar -> 30 bar -> 5 bar (turbine inlet)
• ESDV: dual Emergency Shut-Down Valves
• Gas detector: 20 percent LEL alarm, 40 percent ESD
• PSV: over-pressure vent to safe location
• Filter separator: removes liquid/solid particulates

Detection and Interlock

• UV/IR3 flame: detects within 3 sec
• Vibration: bearing/compressor fault
• Exhaust temp: alarm above 650°C
• Hot gas path inspection: every 8,000 hours
• Trip logic: the turbine is shut down as soon as CO2 activates

Gas turbine with MEP Calc

MEP Calc sizes gas turbine enclosure ventilation, CO2 total flooding and gas regulator per NFPA 37.

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