Fired Heater Selection

Quick pick (TL;DR)

Fuel fired = absorbed duty ÷ thermal efficiency (≈ 0.85, or ~0.92 with an air preheater).
Pick the type by duty & service: vertical cylindrical for small/medium, cabin/box for large, reformer for special.
Keep the average radiant flux ~30–40 kW/m² to protect tubes, choose tube metallurgy for the temperature, fit low-NOx burners and O₂-trim combustion control, and always a SIL-rated burner management system (NFPA 85/86).

Step 1 — Heater type

Type	Use for	Note
Vertical cylindrical	Small footprint	Common
Cabin / box	Large duty	Horizontal
Reformer	High-temp	Special

Step 2 — Worked fuel firing

Process heater, 10 MW absorbed

Given absorbed duty Q = 10 MW thermal efficiency η = 0.85 Step 1 — Fuel fired fuel = Q / η = 10 / 0.85 fuel = 11.8 MW (fired) Step 2 — Losses stack + casing loss ≈ 1.8 MW (15%) add air preheater → η up to ~0.92 Step 3 — Radiant area flux ~30–40 kW/m² → set radiant tube area tube metallurgy for outlet temp (e.g. 9Cr) Answer → 11.8 MW fired, vertical, low-NOx, SIL BMS

Fired duty > absorbed (stack/casing loss). Flux ~30–40 kW/m² protects tube life.

Step 3 — Combustion & safety

O₂-trim & low-NOx burners.
Draft type for control & recovery.
SIL-rated BMS (NFPA 85/86) — mandatory.

Fuel firing calculator

Fuel input & radiant area

Fuel = duty ÷ efficiency; radiant area = radiant duty ÷ flux.

Absorbed duty (MW)

Efficiency

Radiant fraction

Flux (kW/m²)

Screening — flux ~30–40 kW/m² protects tubes; air preheater → η ~0.92.

Common mistakes

Fuel = absorbed duty (no efficiency).
Excess radiant flux.
No / inadequate BMS.

Requisition & datasheet

Service, duty, fluid, efficiency.
Fuel, type, flux, metallurgy, BMS.

Frequently asked questions

What should I know about Fired Heater Selection?

Fuel fired = absorbed duty ÷ thermal efficiency (≈ 0.85, or ~0.92 with an air preheater). Pick the type by duty & service: vertical cylindrical for small/medium, cabin/box for large, reformer for special. Keep the average radiant flux ~30–40 kW/m² to protect tubes, choose tube metallurgy for the temperature, fit low-NOx burners and O₂-trim combustion control, and always a SIL-rated burner management system (NFPA 85/86).

Which standards or codes apply?

API 560 (fired heaters), API 530 (tube thickness), API 535 (burners), NFPA 85/86 (combustion safety / BMS), API 556 (instrumentation).

Standards — API 560/530/535; NFPA 85/86; API 556.