HRSG Duct Burner & Supplemental Firing Calculator

Calculate supplemental duct burner fuel firing duty (MMBtu/hr and MWth), turbine exhaust gas temperature rise, and added steam generation per ASME PTC 4.4.

Turbine Exhaust Gas (TEG) Flow

TEG Mass Flow Rate (kg/s): e.g., F-class or H-class turbine

Unfired TEG Temperature (°C):

Target Fired Temperature (°C): Duct burner exit temperature

TEG Inlet Oxygen Conc (% O₂):

Firing Duty & Added Steam

Duct Burner Heat Input:

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Fuel Firing Duty (MMBtu/h):

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Natural Gas Fuel Flow:

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Incremental Steam Production:

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Residual Exhaust Oxygen after Firing:

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Frequently Asked Questions

Why do HRSG duct burners not require external combustion air fans?

Gas turbine exhaust contains 12% to 15% unused oxygen by volume. Duct burners fire directly into this hot, oxygen-rich exhaust stream, acting as a massive preheated combustion air supply.

What is the maximum allowable duct burner firing temperature?

Standard HRSGs limit firing to 750°C–850°C without requiring specialized refractory lining. Beyond 900°C, carbon steel casing and superheater tube alloy metallurgy must be heavily upgraded.

What is the efficiency of supplemental firing in a combined cycle plant?

Supplemental duct firing converts fuel energy into steam at nearly 100% incremental thermal efficiency because the turbine exhaust gas is already at 500°C–600°C, eliminating standard combustion air preheat losses.