Module 02 · Operations
Normal Operations
What the operator monitors, adjusts, and records during routine steady-state running. Covers key parameters, combustion condition assessment, field walkround, and shift handover.
Key parameters to monitor
These six parameters define the health of the heater at any moment. Check them at every round and any time process conditions change. Values below are generic typical ranges — always refer to your unit's specific operating envelope.
Process
Coil Outlet Temperature (COT)
NormalUnit set-point ± 5°C
AlarmSet-point + 10°C
TripSet-point + 20°C
Firebox
Bridgewall Temperature
Normal750 – 870°C
Alarm> 900°C
ActionReduce firing immediately
Combustion
Stack O₂ %
Normal2 – 4 %
Too low< 1% — risk of CO, smoking
Too high> 6% — heat loss penalty
Firebox
Firebox Draft
Normal−2 to −5 mmH₂O
Positive draftHot gas leak risk
Excessive −veCold air ingress, O₂ % misleading
Process
Process Flow Rate
NormalAt design throughput
Low flow alarmUnit minimum flow
TripBelow minimum safe flow
Tubes
Tube Metal Temperature (TMT)
Normal< 600°C (CS/Cr-Mo)
AlarmMaterial-dependent limit
ActionReduce heat flux; investigate
Monitoring frequency
Log all six parameters at a minimum every two hours during steady-state operation. Increase to continuous observation during any process rate change, feed quality change, or burner adjustment.
Field walkround checklist
Complete this check every two to four hours, or as required by your site procedure. Use the peephole to observe each burner briefly — do not open inspection doors without following confined space or hot-work requirements.
Normal Operations Walkround
01
Check COT and flow at DCS
Confirm COT is at set-point ± 5°C and flow is above minimum safe flow before going to field.
02
Observe flames through peepholes
Each burner should show a stable, evenly-shaped flame. Note any burners with lazy, lifting, impinging, or visibly uneven flames — see combustion assessment section below.
03
Verify all burners are lit
Count lit burners against the expected number for current firing rate. An unlit burner with fuel valve open is a serious gas accumulation hazard — isolate immediately and follow flameout procedure.
04
Check for hot spots on casing
Run a thermal gun across the heater casing, especially around tube support zones and refractory seams. Any casing temperature above
~80–100°C suggests refractory failure and requires investigation before continuing operation.
05
Check draft gauge reading
Confirm firebox draft is in the normal range (
−2 to −5 mmH₂O). Positive readings mean hot gas can push out of the firebox — check damper and arch damper positions.
06
Inspect air registers
Confirm registers are in their set positions and have not shifted. Check for physical damage, debris blockage, or signs of air bypass around the register housing.
07
Check fuel gas header pressure
Fuel pressure should be steady at the design operating pressure. Fluctuating pressure causes unstable flames. A falling header pressure needs to be investigated at the source — do not compensate by opening more burner valves.
08
Check stack for smoke or colour
A clean stack should show heat haze only. Black smoke indicates incomplete combustion — insufficient air. White/grey plume during humid conditions is normal. Brown-orange tinge can indicate atomising steam issues on liquid fuel service.
09
Look and listen for unusual noise
Banging, rumbling, or pulsing from the firebox suggests combustion instability (pulsation). A high-pitched tone can indicate gas leaks near fittings. Clanging or creaking from the structure may be abnormal thermal expansion.
10
Check process pipe work and fittings for leaks
Walk the inlet and outlet manifolds. Use your nose as well as eyes — hydrocarbon smell near process piping requires immediate action. Report and isolate before continuing.
11
Check soot blower / steam condensate drains (if applicable)
Confirm steam traps on convection section soot blower headers are functioning. Wet steam in soot blowers can cause tube erosion and water hammering.
12
Log readings and note any deviations
Record time, COT, bridgewall temp, O₂%, draft, flow, and fuel pressure. Note any observations that differ from the previous round, even if still within limits — trends matter.
Reading combustion condition
The flame is the most direct indicator of combustion quality. Learn to read it through the peephole. You're assessing shape, colour, size, and stability — and cross-referencing with the O₂ analyser.
✓ Good combustion
Appearance
Compact, stable flame rooted at the burner tip. Blue/blue-orange on gas service. Consistent across all burners.
O₂ reading 2–4%. Steady, not hunting.
Action No adjustment needed. Log and continue.
O₂ reading 2–4%. Steady, not hunting.
Action No adjustment needed. Log and continue.
⚠ Rich / insufficient air
Appearance
Lazy, orange-yellow, luminous flame. Possibly smoky at peephole. Long flames touching or near tubes.
O₂ reading Below 1.5%. Stack may show black smoke.
Action Open air registers incrementally. Increase arch/stack damper opening. Verify O₂ rises before making further adjustments.
O₂ reading Below 1.5%. Stack may show black smoke.
Action Open air registers incrementally. Increase arch/stack damper opening. Verify O₂ rises before making further adjustments.
⚠ Lean / excess air
Appearance
Short, hard, blue-white flames. Burners may appear dim. Possible lifting off the tip at extremes.
O₂ reading Above 5–6%. Stack heat loss is elevated.
Action Close air registers slightly. Check for air infiltration through door seals or casing. Balance fuel/air ratio to bring O₂ to target band.
O₂ reading Above 5–6%. Stack heat loss is elevated.
Action Close air registers slightly. Check for air infiltration through door seals or casing. Balance fuel/air ratio to bring O₂ to target band.
✗ Flame impingement
Appearance
Flame contacting the process tube directly. May see localised glowing or discolouration on the tube.
Risk Rapid tube overheating. Hotspot, creep damage, and tube failure.
Action Reduce firing on that burner immediately. Adjust register and tip orientation. Do not restore full firing until cause is identified.
Risk Rapid tube overheating. Hotspot, creep damage, and tube failure.
Action Reduce firing on that burner immediately. Adjust register and tip orientation. Do not restore full firing until cause is identified.
✗ Flame lifting / instability
Appearance
Flame detaches from tip, appears to flutter or root intermittently. Pulsing sound may accompany.
Risk Precursor to flameout. Unburnt gas can accumulate.
Action Check fuel pressure and tip condition. Reduce excess air if lifting due to high velocity. If instability persists, shut that burner down via normal flameout procedure.
Risk Precursor to flameout. Unburnt gas can accumulate.
Action Check fuel pressure and tip condition. Reduce excess air if lifting due to high velocity. If instability persists, shut that burner down via normal flameout procedure.
O₂ analyser limitations
The O₂ analyser samples at one point in the flue gas path and can be fooled by air infiltration through casing leaks. Always correlate O₂ readings with visual flame observation and stack appearance — don't rely on the analyser alone.
Responding to heat duty changes
When feed rate or target COT changes, the operator must rebalance the heater. The principle is simple: fuel and air must change together, and changes should be made in small steps with time allowed for the system to stabilise.
Heat Duty Change — Operator Response Guide
| Scenario | Initial indicator | First action | Follow-up check |
|---|---|---|---|
| Feed rate increase | COT falling below set-point | Increase fuel flow gradually to restore COT. Adjust air in proportion. | Confirm O₂% stays in 2–4% band. Check draft has not gone positive. |
| Feed rate decrease | COT rising above set-point | Reduce fuel flow. Reduce air proportionally to maintain O₂ target. | Confirm minimum process flow is maintained. Never reduce flow below minimum safe flow. |
| Feed quality change (e.g. lighter crude) | COT response change for same fuel rate; possible flame appearance shift | Allow COT controller to compensate. Monitor O₂ and flame stability. | If auto-control cannot hold set-point, make manual trim. Notify shift supervisor. |
| Fuel gas composition change (e.g. lower calorific value) | COT begins to fall; flame may appear lazier | Increase fuel flow to compensate. Open burner valves evenly across all burners. | Check fuel header pressure has not dropped. Monitor flame stability closely. |
Always adjust in small steps
Large, rapid fuel or air adjustments cause combustion instability, O₂ swings, and can lead to flame-outs. Make one adjustment, wait for the system to respond (typically 2–5 minutes depending on heater size), then assess before making the next change.
Shift log and handover
A good handover is the most important thing you do for the next operator. The heater has no memory — your log is the continuity.
What to record every shift
COT, bridgewall temp, O₂%, draft, flow, fuel pressure — values and times, not just "normal".
Any adjustments made — what changed, when, and what the response was. Include air register or damper moves.
Burner status — how many on, any taken out of service, any relights performed.
Visual observations — flame appearance, stack colour, anything unusual seen or heard on the round.
Alarms received — time, parameter, value reached, and action taken. Even nuisance alarms.
Any deferred maintenance or known defects — list what's outstanding, not just what went wrong today.
What the incoming operator needs to watch — a trend developing, a burner that's been unstable, a process change expected next shift.
Trends are more important than single readings
A COT at set-point but rising 2°C per hour is more significant than a COT 3°C above set-point and stable. Always note direction of travel, not just the current value.