02 · Operations
Startup Procedure
A structured, phased approach to bringing a fired heater from cold or warm to full operation — covering pre-startup inspection, BMS permissive logic, furnace purge, controlled light-off, and gradual heat-up rate management. Follow all phases in sequence; do not skip or compress steps.
Life Safety — Read Before Proceeding
Fired heater startups are a leading cause of refinery fatalities. The risks are fuel accumulation, flashback, and uncontrolled heat-up causing tube failure. Every step in this procedure exists because someone was hurt when it was skipped. Verify each item independently — do not rely on the previous shift's walkdown.
Startup Phases Overview
Four sequential phases govern every startup. No phase may begin until the previous phase is fully complete and verified.
Phase 1
Pre-Startup Checks
Allow 2–4 hr
Phase 2
Furnace Purge
Min. 5 vol. changes
Phase 3
BMS Light-Off
Pilot → Main burner
Phase 4
Gradual Heat-Up
≤ 50 °C/hr typical
Phase 1 — Pre-Startup Checks
A complete walkdown of the heater, its piping, instrumentation, and utilities before any fuel gas is admitted. Issues caught here cost minutes to fix; issues missed here cost hours or lives.
Pre-Startup Inspection Checklist
01
Confirm PSSR / work permit clearance
All maintenance work permits must be closed and signed off. Pre-Startup Safety Review (PSSR) documentation must be complete and approved before any energisation begins. Check with the shift supervisor.
02
Verify all blinds / spectacle plates removed from process lines
Cross-reference the blind log sheet. Confirm each blind tag has been returned. Pay particular attention to heater inlet, outlet, pass-control, and bypass blinds. A live heater with a process blind in is a coking/tube-rupture event.
03
Check heater structure and casing for damage
Inspect casing panels, peepholes, explosion doors, and stack for physical damage. Confirm all access doors and peephole plugs are properly seated and latched. Open peepholes during operation create false air infiltration and draft readings.
04
Inspect refractory for cracks or spalling
Using a torch and peephole, look for visible cracks, fallen refractory tiles, or hot spots on the external casing. Any refractory damage must be assessed before firing — exposed tube supports or tube guides accelerate tube failure. Log findings.
05
Confirm process fluid flow is established through all passes
Minimum flow must be confirmed through every pass before ignition. Verify flow indicators (FI) on each pass are reading above minimum — typically
≥ 20–30% of design flow depending on unit. Dead-leg passes will overheat and coke rapidly on light-off.
06
Verify all pass flow controls and outlets are open and responsive
Stroke each pass-flow control valve and confirm movement at the valve. A valve that reads open on the DCS but is physically failed-closed will result in zero flow in that pass without an immediate alarm. Do not assume DCS indication is correct — physically verify.
07
Check fuel gas supply pressure and quality
Confirm fuel gas header pressure at burner manifold — typical range
0.5–2.5 bar g depending on design. Check that fuel gas is dry (no condensate in line — drain low points). High liquid content causes flame instability and potential flashback on light-off.
08
Confirm all fuel gas block valves in correct position
Main fuel gas ESDV (emergency shutdown valve) — confirmed closed. Burner isolation valves — confirmed closed. Fuel gas double-block-and-bleed (DBB) valves at burner fronts — both blocks closed, bleed open. Record valve positions on checklist.
09
Test all BMS permissive inputs — confirm no spurious trips
Walk through BMS screen on DCS. All permissive conditions (process flow confirmed, fuel ESDV closed, stack damper position, low-low flame detection reset) must show healthy. Any active trip must be investigated and resolved — do not bypass without engineering approval and PTW.
10
Verify all thermocouples and instruments reading plausible values
Crosscheck tube skin thermocouples (TIs), coil outlet temperatures (COT), bridgewall temperature, and flue gas temperatures against ambient or last-known values. A thermocouple reading
0 °C or -999 is failed — do not startup with a failed tube skin TC without supervisor approval.
11
Check combustion air supply — fans running, dampers operable
For forced-draft (FD) units: confirm FD fan running, outlet damper operational, air preheater rotating (if fitted). For natural-draft units: confirm stack damper is free to operate and set to correct startup position (typically
40–60% open). Test louver/register operation at minimum two burners.
12
Confirm steam/utility connections for sootblowers (if fitted)
Steam supply to sootblowers should be isolated and drained during startup. Sootblowers are not used during startup — but confirm steam traps on supply line are functional to prevent condensate accumulation.
13
Inspect burner assemblies — tips, registers, pilots
Visually inspect accessible burner tips for blockage, damage, or misalignment. Confirm pilot assemblies are installed and gas connections secure. Check that igniter electrodes are correctly positioned and leads connected. Dirty or blocked tips cause flame instability and excess CO on light-off.
14
Check steam/condensate systems to heater (if applicable)
Confirm steam injection lines for atomisation (if fuel oil capable) are drained, pressured, and at temperature. Confirm convection section steam coils (if fitted) are in service or correctly isolated. Steam leaks into the firebox cause false flame signals and refractory damage.
15
Confirm oxygen analyser / flue gas analyser in service
O₂ analyser in the flue gas duct must be in service and reading plausible ambient values (~
20.9% O₂) before light-off. It is the primary excess air control tool. A failed or bypassed O₂ analyser means operating blind on air/fuel ratio during heat-up.
16
Confirm CO / combustible gas detectors functional
Test CO and LEL detectors in the heater house and near burner fronts using test gas or bump test. Confirm alarm setpoints are active in the control room. A detector that fails on startup but shows healthy should be treated as non-functional until investigated.
17
Confirm no hot work or open ignition sources within 15 m of heater
Radio to area supervisor and confirm all hot work permits in the heater area are suspended during startup. Check for grinding sparks, vehicle exhausts, or temporary equipment that could act as an ignition source during furnace purge when fuel vapour may be present.
18
Supervisor sign-off — Phase 1 complete
Phase 1 must be countersigned by the shift supervisor before proceeding to furnace purge. Record time of completion in the heater logbook. Do not proceed without this sign-off even under production pressure.
Phase 2 — Furnace Purge
Before any ignition attempt, the firebox must be purged of any residual fuel gas or combustible vapour. This is the single most critical act in preventing a furnace explosion on startup. The purge is non-negotiable — NFPA 86 and most refinery standards require a minimum of five firebox volume changes with fresh air.
Never Skip or Shorten the Purge
A furnace explosion from an undetected gas pocket is not survivable at close range. The purge timer must be confirmed from measured airflow — not estimated from experience or clock time. If air supply is interrupted during purge, restart the purge timer from zero.
Furnace Purge Procedure
01
Confirm all burner fuel valves are closed and pilots de-energised
Every burner block valve and pilot gas valve must be physically confirmed closed at the burner front. Walk the entire burner deck — do not rely on DCS valve status alone. Bleeding (venting) all DBB valves between the block valves confirms no through-flow.
02
Open stack damper to maximum position
Drive the stack damper to
100% open. On natural-draft units this maximises draught for purge airflow. On forced-draft units, confirm the FD fan is running at maximum speed for purge. Record stack damper position on DCS and confirm against field indicator.
03
Open all burner air registers / dampers to maximum
Fully open primary and secondary air registers on all burners to maximise air flow through the firebox. On FD units, confirm air header pressure is established. On natural-draft, confirm ambient draught conditions — purge flow is lower on calm, high-humidity days; allow more time.
04
Start purge timer — record start time and airflow rate
Record the start time in the logbook. Calculate required purge time:
t = (5 × V_firebox) / Q_air where V is firebox volume (m³) and Q is airflow (m³/min). If airflow is not known, use minimum 15 minutes as a conservative default — never less. Some unit-specific procedures require 30 minutes.
05
Monitor flue gas for combustible gas during purge
If a portable LEL meter is available, sample from peepholes and the base of the stack during the purge. Any LEL reading above
0% means residual fuel is present — extend purge and investigate source before continuing. Do not crack open access doors to check "by smell."
06
Confirm purge complete — record end time
Record end time. Confirm calculated volume changes achieved. Purge is complete only when the required number of volume changes AND minimum time have both been met. Sign off in the logbook. The BMS permissive "Purge Complete" must be acknowledged in the DCS before proceeding.
07
Set air registers and stack damper to light-off position
After purge, reduce stack damper to startup draft setting — typically
–0.05 to –0.15 in WC (–12 to –37 Pa) at the bridgewall. Set burner air registers to approximately 50–60% open for light-off — enough excess air to establish stable flame without excessive windage that lifts the flame off the tip.Phase 3 — BMS Light-Off Sequence
The Burner Management System enforces a strict permissive logic before allowing fuel to the burners. Each permissive must be satisfied in sequence — the BMS will not allow the next step until the prior step is confirmed. Operators must understand what each permissive means, not just click through the DCS.
BMS States During Startup
Idle / Locked Out
No permissives satisfied. System awaiting operator initiation.
Purge Ready
All pre-purge permissives met. Purge timer can be started.
Purge In Progress
Purge timer running. Light-off not permitted.
Light-Off Permitted
Purge complete. Pilot gas available. Ignition enabled.
Pilot Established
Flame scanner confirms pilot. Main fuel valve may open.
Emergency Trip
Safety trip active. All fuel valves closed. Investigate before reset.
Light-Off Sequence — Burner by Burner
On multi-burner heaters, light off burners one at a time starting from the bottom-most row (for vertical cylindrical heaters) or working symmetrically from one end (for cabin heaters). Never light two burners simultaneously — the resulting heat and draft changes can destabilise adjacent pilots.
| Step | Action | BMS Permissive / Verify |
|---|---|---|
| L-01 | Confirm BMS in "Light-Off Permitted" state BMS | Purge complete flag active in DCS. All trip conditions clear. Main ESDV confirmed closed by BMS. |
| L-02 | Select Burner #1 for ignition on BMS | BMS enables pilot gas solenoid for selected burner only. All other burners remain isolated. |
| L-03 | Confirm pilot gas pressure at burner front | Typical pilot gas pressure: 0.1–0.3 bar g. Too high = flame blow-off. Too low = ignition failure. Confirm with local gauge. |
| L-04 | Energise igniter — initiate pilot spark BMS | Spark timer active (typically 10–30 s). Operator watches peephole for pilot flame. Flame scanner signal should activate within 5 s of pilot establishment. |
| L-05 | Confirm pilot flame on scanner AND visual CRITICAL | Both BMS flame scanner AND visual confirmation via peephole required. A scanner signal without visual confirmation may indicate scanner fault — do not proceed on scanner alone. |
| L-06 | Open main burner block valve — low fire position only | BMS permits main fuel valve to crack open (~5–10% of max) only after pilot confirmed. Listen and observe for stable combustion. No "whomp" or delayed ignition — if occurs, close immediately and repurge. |
| L-07 | Confirm main flame — stable blue/yellow flame, no lifting CRITICAL | Check through peephole. Flame should be attached to burner tip, not floating. Adjust air register if flame is lifting (reduce air) or impinging (increase air). A lifted flame is unstable and can extinguish silently. |
| L-08 | Repeat L-02 through L-07 for each subsequent burner | Light burners in the designed sequence (see unit-specific procedure). Allow 2–3 minutes between each burner lighting to allow draft and temperature to stabilise before adding the next heat source. |
| L-09 | Once all burners lit — verify symmetric heat distribution | Monitor tube skin temperatures across all passes. No single pass should be more than 25–30 °C above others at low fire. Uneven heating at startup accelerates differential thermal stress in headers and fittings. |
| L-10 | Trim excess air to 15–25% excess at low fire BMS |
Target flue O₂: 3–5% at low fire. Use O₂ analyser — not draft gauge alone. High excess air at low fire chills the firebox and increases CO risk if a burner trips. Confirm CO reading is < 50 ppm in flue gas. |
Failed Ignition — Mandatory Wait
If a pilot fails to light within the BMS spark timer window, the BMS will lock out that burner. Do not immediately retry. Close all fuel valves, wait a minimum of 5 minutes to allow any accumulated gas to disperse, then re-initiate the purge sequence from Phase 2 before attempting re-ignition. Repeated failed attempts without re-purging are a leading cause of furnace explosions.
Phase 4 — Gradual Heat-Up
Once burners are lit and stable at low fire, the heater must be brought to operating temperature slowly and under close control. Heat-up rate limits protect the refractory lining (thermal shock causes spalling), process tubes (differential thermal expansion), and the process fluid (avoiding localised overheating and cracking before steady-state flow is established).
Standard Heat-Up Rate
≤ 50 °C/hr
Coil outlet temperature rise. Applies from light-off to normal operating temperature for most crude, vacuum, and process heaters.
Post-Refractory Repair Rate
≤ 20 °C/hr
After any refractory repair or new castable placement. Slow rate drives out moisture without steam-cracking the refractory.
Maximum Allowable Rate
> 80 °C/hr
Do not exceed. Rapid heat-up causes refractory spalling, tube-to-fitting stress, and process-side vapour locking in liquid-full systems.
Soak Hold (new refractory)
1 hr per hold
Hold at 150 °C, 250 °C, and 450 °C to allow moisture to escape and thermal equilibration before continuing ramp. Refer to refractory cure curve.
Gradual Heat-Up Checklist
01
Record initial COT (coil outlet temperature) and all pass TIs
Log the baseline temperatures on all passes and the bridgewall immediately after stable combustion is established. This is time zero for heat-up rate calculation. All subsequent rate checks are relative to this baseline.
02
Set fuel firing rate to achieve target heat-up rate
Use the heater's firing rate controller (FRC) or manually adjust the fuel gas pressure control valve. Target COT rise of
≤ 50 °C per hour. In practice, check every 15 minutes and adjust — do not set and leave during heat-up.
03
Monitor all pass flows continuously — confirm no pass starvation
As temperature rises and process fluid begins to change phase (particularly in crude units), flow distribution can shift. A pass showing
> 15% flow deviation from others requires immediate rebalancing via pass-flow controllers. A starved pass at elevated temperatures will coke in minutes.
04
Check tube skin temperatures every 15 minutes
Monitor all tube skin TIs (TIs on radiant coils). No tube skin temperature should exceed the maximum allowable metal temperature (MAMT) for the tube metallurgy. Typical MAMT: CS =
400 °C, 9Cr = 600 °C, 321SS = 650 °C. Report any unexpectedly hot spot immediately.
05
Adjust excess air as firing rate increases
As fuel rate rises, the burner air registers may need to be opened to maintain target flue O₂ of
3–4% at normal operation. Trim air in small increments. Watch for CO breakthrough — CO > 200 ppm in flue gas indicates insufficient combustion air and must be addressed before further heat-up.
06
Adjust stack damper to maintain target furnace draft
Bridgewall draft should be maintained at
–0.05 to –0.1 in WC (negative — slight suction) during heat-up. As temperature rises, natural draft increases; the stack damper will need to close slightly. A positive pressure firebox causes puffing from seals and potential fuel gas release at burner fronts.
07
Check for refractory hot spots on external casing
During the first heat-up, walk around the heater exterior with a hand on the casing (or use IR thermometer). The casing should feel warm but not hot to touch — a local hot spot indicates refractory thinning or cracking behind it. Typical casing temperature:
50–80 °C max at any point.
08
Confirm process outlet conditions reaching design range
As COT approaches the target process temperature — e.g.
350–380 °C for atmospheric crude — confirm that downstream equipment (fractionator, transfer line) is ready to receive. Coordinate with the board operator on when to transition control from manual heat-up ramp to normal DCS temperature control.
09
Transition to automatic COT control — confirm controller response
Transfer from manual firing rate to automatic COT temperature controller. Confirm the controller is tuned correctly — a poorly tuned controller on transfer can cause an overshoot of
20–50 °C beyond setpoint, potentially triggering a tube overtemperature trip on the first transfer. Monitor closely for 10 minutes post-transfer.
10
Confirm all alarm setpoints active and BMS in normal operating state
Check that all high-high temperature alarms, low-low flow alarms, and BMS trip setpoints are set to their normal operating values (some may have been raised for startup). Restore any alarms that were temporarily suppressed with shift supervisor approval, and confirm suppression log is cleared.
11
Conduct post-startup walkdown — check all burner fronts
Physically inspect every burner front for fuel gas leaks (use detector or soapy water). Check that all burner peepholes are plugged. Confirm no unusual noise from any burner (roaring = too much air, hissing = gas leak, chugging = unstable combustion). Log observations.
12
Declare heater in normal operation — complete startup log
Record start time, end time, final operating parameters (COT, fuel pressure, flue O₂, draft), and any observations in the heater logbook. Notify the shift supervisor and board operator. Hand over the heater formally in the shift handover notes — startup is complete.
Key Startup Parameters — Quick Reference
Startup Operating Parameters
| Parameter | Startup Target | Normal Operation | Do Not Exceed | Notes |
|---|---|---|---|---|
| COT heat-up rate | ≤ 50 °C/hr | — | 80 °C/hr | Reduce to 20 °C/hr after refractory repair |
| Flue gas O₂ (light-off) | 5–8% | 3–4% | < 2% (O₂ low) | High O₂ at startup = safe; reduce as load increases |
| Bridgewall draft | –0.05 to –0.15 in WC | –0.1 to –0.2 in WC | Positive (+ value) | Positive firebox = puffing, seal failure risk |
| Process pass flow deviation | < 10% | < 5% | > 20% | Rebalance passes before continuing heat-up |
| Tube skin temperature | Monitor closely | Varies by metallurgy | MAMT (see tubes) | Hot spots indicate coking or flow imbalance |
| CO in flue gas | < 50 ppm | < 200 ppm | > 500 ppm | High CO = incomplete combustion, add air |
| Purge volume changes | ≥ 5 complete changes | — | Cannot skip | NFPA 86 minimum. Restart timer if purge interrupted. |
| Failed ignition wait | ≥ 5 min before retry | — | Cannot shorten | Full re-purge required before second attempt |
Warm Start vs Cold Start
A warm start (heater shut down < 4 hours, firebox still > 200 °C) still requires a full BMS purge sequence but may allow a faster heat-up ramp back to operating temperature — consult unit-specific procedures. The pre-startup inspection checklist must always be completed in full regardless of outage duration.