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HISTORY BACKGROUND DOCUMENT IP 15-1-1 H

Instrumentation for Fired Heaters Page 1 of 2

Rev. 2 June 2000

THIS INFORMATION FORAUTHORIZED COMPANY USE ONLYEXXON RESEARCH AND ENGINEERING COMPANY FLORHAM PARK, N.J.

INTERNATIONAL

PRACTICE

BACKGROUND HISTORY DOCUMENTATIONFOR CORRESPONDING PARAGRAPHS OF IP 15-1-1 (REV. 2)

S,E [H] 4.2 Proper fuel/air ratio control is required to prevent substoichiometric burner operation which can lead toburner flame out, accumulation of unburnt fuel and air in a hot firebox and a potential explosion.

S [H] 5.2 High pressure in the firebox will force hot flue gas out openings and create a potential hazard for personnelin the area. Pressure switches are not allowed since their accuracy is not good for measuring pressures

just slightly above atmospheric pressure.

S,E [H] 5.3 Same considerations as Par. 4.2 above. The oxygen sensor helps prevent substoichiometric burneroperation while the combustibles sensor detects when it has occurred due to some sort of systemmalfunction.

E [H] 5.4 Environmental compliance for combustion emissions is done though testing so sample ports are needed.

S,O [H] 5.8 Forced draft heaters with downstream induced draft fan and heat recovery device (e.g. air preheater) canbe overpressure if induced fan fails or blockage occurs. Therefore need fast acting relief damper whichopens unrestricted discharge of flue gas to atmosphere.

S [H] 6.3 Loss of flow in a heated coil will cause the coil to overheat and fail. Locating the FLCO on the inlet avoidsflow measurement difficulties often incurred at the outlet (e.g., high temperature and/or two phase flow).

S [H] 6.4 This avoids potential for flow going though the FLCO flow meter indicating no problem, even though therereally is no flow through the heater coil.

S [H] 6.7 High coil outlet temperatures indicate the heater may be over-fired leading to high tube metal temperatures,increased coking, reduced run length, etc. Therefore it is critical this be detected and alarmed soimmediate corrective action can be taken.

S,O [H] 6.10 Avoids inadvertent loss of flow due to instrument malfunction.

S [H] 7.4 The pilot is a constant source of ignition which avoids accumulation of unburnt fuel and potential for afirebox explosion. Therefore if the pilot is out (no gas pressure), all fuels are shut off to avoid potential forunburnt fuel accumulation.

S [H] 7.5 Liquid carryover from the fuel gas knockout drum can cause burner flames to be extinguished. High levelalarm will give warning.

S,E [H] 7.6 Loss of atomizing steam can result in fuel oil dripping out the bottom of the burner. If the oil has a low flashpoint it will vaporize in the atmosphere and can be easily ignited resulting in a significant fire under theheater.

S [H] 8.1 Needed to ensure fuels to heater can be stopped from remote locations during an emergency.

S [H] 8.2 Ensures fuel valves will not close and then reopen in uncontrolled manner during temporary loss ofinstrument air.

S,O [H] 8.3 This prevents damper from moving in uncontrolled manner following correction of fault which causedprotective system to move damper to a predetermined fail safe position.

S [H] 8.4 Helps avoid mistakes by use of one standard system.

S,O [H] 8.5 Two detectors and self checking enhances reliability of system by reducing potential for nuisance trips.

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IP 15-1-1 H HISTORY BACKGROUND DOCUMENT

Page 2 of 2 Instrumentation for Fired Heaters

Rev. 2 June 2000

THIS INFORMATION FORAUTHORIZED COMPANY USE ONLYEXXON RESEARCH AND ENGINEERING COMPANY FLORHAM PARK, N.J.

INTERNATIONAL

PRACTICE

S [H] 8.6 Ensures majority of pilots are lit before main fuel is introduced in cold firebox during startup. Past incidenthistory has shown many firebox explosions were due to introduction of main gas fuel into firebox with fewor no pilots in service.

S [H] 8.7 Having a large number of very small burners with pilots has been found to cause operational problems.

Main fuel PLCO prevents accumulation of unburnt fuel in the firebox if main fuel control valve shouldsuddenly close and reopen.

S [H] 9.1 Ensures these special cases are carefully reviewed.

S,O [H] 9.2 Prevents possibility of continuing to put fuel in the heater at low/no air flow which could case burner flameout and firebox explosion.

S [H] 9.4 Protects against high firebox pressures in event induced draft fan fails.

S [H] 9.5 If natural draft backup option is not provided, loss of induced draft fan will cause low air flow and potentialfor accumulation of unburnt fuel in firebox and explosion. Shutdown of heater prevents this possibility.

Notes:

(1) Each paragraph to identify the Purpose Code(s) of the corresponding paragraph number of the applicable International Practice (IP).

(2) The symbol [H]is used to denote all History Background Paragraphs which are for INFORMATION ONLY.

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