OISD

OISD-111 Amended edition FOR RESTRICTED CIRCULATION

PROCESS DESIGN AND OPERATING PHILOSOPHIES ON

FIRED PROCESS FURNACE

OISD-STANDARD-111

First Edition, March 1989

Amended edition, August, 1999

Oil Industry Safety Directorate Government of India

Ministry of Petroleum & Natural Gas

OISD

OISD-STANDARD-111 First Edition November 1988

Amended edition, August, 1999 FOR RESTRICTED

CIRCULATION

PROCESS DESIGN AND OPERATING PHILOSOPHIES ON

FIRED PROCESS FURNACE

Prepared By:

COMMITTEE ON PROCESS DESIGN AND OPERATING PHILOSOPHIES

OIL INDUSTRY SAFETY DIRECTORATE 2ND FLOOR, “KAILASH”

26, KASTURBA GANDHI MARG

NEW DELHI - 110 001.

NOTE

OIL publications are prepared for use in the Oil and gas industry under Minstry of Petroleum and Natural Gas. These are the property of Minstiry of Petroleum and Natural Gas and shall not be reproduced or copied and loaned or exhibited to others without written consent from OISD. Though every effort has been made to assure the accuracy and reliability of data contained in these documents, OISD hereby expressly disclaims any liability or responsibility for loss or damage resulting from their use. These documents are intended only to supplement and not replace the prevailing statutory requirements.

Note 1 in superscript indicates the changes / modifications / additions as approved

in 17th Safety Council Meeting held in July, 1999.

OISD

III

FOREWORD

The Oil Industry in India is nearly 100 years old. Because of various collabortion agreements, a variety of international codes, standards and practices have been in vogue. Standardisation in design philosophies and operating and maintenance practices at a national level was hardly in existence. This, coupled with feed back from some serious accidents that occurred in the recent past in India and abroad, emphasized the need for the industry to review the existing state of art in designing, operating and maintaining oil and gas installations. With this in view, the Ministry of Petroleum and Natural Gas, in 1986, constituted a Safety Council assisted by Oil Industry Safety Directorate (OISD), staffed from within the industry, in formulating and implementing a series of self regulatory measures aimed at removing obsolescence, standardising and upgrading the existing standards to ensure safer operations. Accordingly, OISD constituted a number of Functional Committees of experts nominated from the industry to draw up standards and guidelines on various subjects. The present document on “Fired Process Furnaces” was prepared by the functional committee on “Process Design and Operating Philosophies”. This document is based on the accumulated knowledge and experience of Industry members and the various national and international codes and practices. It is hoped that provisions of this document, if implemented objectively, may go a long way to improve the safety and reduce accidents in Oil and Gas Industry. Suggestions are invited from the users after it is put into practice to improve the document further. Suggesstions for amendments to this document should be addressed to :

The Co-ordinator, Committee on

“Process Design and Operating Philosophies”, Oil Industry Safety Directorate,

2nd Floor, “Kailash” 26, Kasturba Gandhi Marg

New Delhi-110 001.

FUNCTIONAL COMMITTEE ON

PROCESS DESIGN AND OPERATING PHILOSOPIES

LIST OF MEMBERS

Name Designation / Organisation Status

1. Sh. T.C. Varghese DGM (TECH), HPCL,

Member Leader

2. Sh. V.S. Save Sr. Manager, HPCL

Member

3. Sh. G. Raghunathan Sr. Manager, HPCL

Member

4. Sh. S.V. Puthli Sr. Manager, HPCL

Member

5. Sh. N. Lal

Dy. Gen. Manager, ONGC

Member

6. Sh. V.K. Ramesh Dy. Suptd. Engr., ONGC

Co-opted Member

7. Sh. N. N. Gogoi Dy. Gen. Manager, OIL

Member

8. Sh. A. Sinha

Dy. Ch. Engr. OIL

Co-opted Member

9. Sh. M.A. Sreekumar

Sr. Manager, CRL

Member

10. Sh. A. Varadarajan

Sr. Manager, MRL

Member

11. Sh. B.K. Trehan Addtl. Director , OISD

Member Coordinator

In addition to the above several experts from theindustry contributed in the preparation, review and finalisation of the document.

OISD

PROCESS DESIGN AND OPERATING PHILOSOPHIES

ON PROCESS FURNACES

CONTENTS

SECTION

1.0 INTRODUCTION 2.0 Scope 3.0 LOCATION 3.1 General 3.2 Safe Distance from Roads 3.3 Wind Direction 3.4 F.D. Fan Location 4.0 CLEARANCES/ACCESSABILITY 4.1 Bottom Fired Furnaces 4.2 Multifloor Side Fired Furnaces 4.3 Valves 4.4 Dampers 4.5 Explosion Doors 5.0 BASIC DESIGN CRITERIA 5.1 Cenfiguration 5.2 Materials of Construction 5.3 Heat Flux 5.4 Corrosion Allowance 5.5 Ladders/Platforms 5.6 Personnel Protection 5.7 Peep Holes 6.0 PROCESS SYSTEM 6.1 Pass Flow Control 6.2 Pressure Monitoring 6.3 Temperature Monitoring 7.0 FIRING SYSTEM 7.1 Burner Mounting 7.2 Pilot Burners 7.3 Burner Lighting 7.4 Fuel Gas Control Valve 7.5 Blinding of Fuel Gas/Oil 7.6 Knock Out Pots 8.0 UTILITY SYSTEM 8.1 Coil Purge 8.2 Box Purge Steam

9.0 Safety Instrumentation 9.1 Indications 9.2 Alarms 9.3 Shutdown System 9.3.1 Shutdown Action 9.4 Typical 10.0 Operating Checks 10.1 Pressure Survey 10.2 Safety Audit 11.0 FLOW MEASUREMENT 11.1 Temperature Measurement 11.2 Monitoring of Decoking 11.3 Quench Pot for Decoking 11.4 Tests after Decoking 11.5 Decoking Schematic 12.0 SAFETY IN FURNACE OPERATION 12.1 Display Board 12.2 Check-List for Furnace Lighting 12.3 Precautions in Shutdown 12.4 Tube Failure 13.0 GENERAL 13.1 House-Keeping 13.2 Safety Shower 13.3 Fire Fighting Facilities 14.0 REFERENCES ATTACHEMENTS ANNEXURES I Typical Arrangement for coil purge steam/inert gas to a four pass furnace II Safety Instrumentation for a four pass furnace III Decoking system for a four pass furnace

OISD 1

PROCESS DESIGN AND OPERATING PHILOSOPHIES ON FIRED PROCESS FURNACE

1.0 INTRODUCTION

Fired Process Furnaces are usually component parts of process plants. These are primarily use to beat hydrocarbons of all types, from heavy crude oils and asphalt to the l ightest hydrocarbon liquids or gases. These may also be used to heat other substances such as air or steam.

A fired process furnace consists of three basic parts; a heating coil, a setting and a stack. The heating coil consists of length of tubing connected together which carry the material being heated. The setting is a suitable housing for firing. It is connected to a stack by means of a duct. The furnace may be fired by oil or gas burners. Instruments are generally used to control rate of firing and flow through coils to maintain desired operat-ing conditions. The design, type, size and other similar design aspects of any individual furnace are based on and determined by various factors such as operating process, size of the unit, space available, economics etc. However safety and operational efficiency should be the primary factors in design consideration for furnace.

2.0 SCOPE

This document covers safety provisions in

fired process furnaces in Petroleum and Natural Gas Industry. These shall be the minimum requirement and additional safety features have to be provided depending on individual situations. This does not include boilers and direct fired furnaces like direct fired air heater of FCCU and sulphur reaction furnace since they are specialty items.

3.0 LOCATION

The following factors should be considered

while locating a fired process furnace: 3.1 GENERAL

Furnace should be located only at edges of the process units to limit the hazard of open flame to only the small part of the plant facing the furnace and also to facilitate easy fire fighting operations in case fire breaks out in the furnace. Also the furnace should be at least 15 meters away from the nearest process equipment handling hydrocarbon, with no sewer boxes, sampling points etc. in between, form where hydrocarbon could emit vapours when the furnace is on.

3.2 SAFE DISTANCE FROM ROADS There should be a minimum distance of 15

meters form the periphery of the furnace to the edge of any road with vehicular traffic.

3.3 WIND DIRECTION Furnaces should always be located upwind or

sidewind form the rest of the plant. 3.4 F.D. FAN LOCATION F.D fans wherever applicable should be

located at grade. Air intake to the FD fan, should be from a safe location so that no hydrocarbon can be sucked into them.

4.0 CLEARANCE/ACCESSIBILITY 4.1 BOTTOM FIRED FURNACES There should be a minimum of 1.75 meters of

headroom for the bottom fired furnace floor including plenum chamber, if any, above grade for operational conveniences and safety.

4.2 MULTIFLOOR SIDE FIRED FURNACES For multifloor side fired furnaces, 1.0 meter

wide platform and 2.0 meters high headroom should be provided.

4.3 VALVES

2 OISD-111

Unless remote operated, valves on the fire box purging and coil purging steam lines should be located atleast 15 meters away from the furnace in the form of a manifold and distinctly marked for easy identification.

4.4 DAMPERS Dampers should be operable from ground.

Position of damper while in operation should be distinctly visible from ground.

4.5 EXPLOSION DOORS Explosion doors shall be provided for all

furnaces to release accidental over press-ures. Explosion doors should be located in such a way that the discharge is directed to a safe area.

5.0 BASIC DESIGN CRITERIA 5.1 CONFIGURATION The selection of the configuration of furnace,

viz. vertical, horizontal, bottom fired, side fired etc. should be judged from various design consideration like heat duty, service etc. and safety consideration like layout limitations, accessibility etc.

5.2 MATERIALS OF CONSTRUCTION The selection of materials for various parts of

the furnaces should be done depending on:

a) Temperature b) Type of process Fluid c) Type of fuel used 5.3 HEAT FLUX The burners should be designed & spaced in

such a way that heat flux on to the tubes of the furnace at any point does not let the skin temperature go above the allowable limit for the material of the tubes at the maximum allowable design conditions.

5.4 CORROSION ALLOWANCE

Depending on the material of construction of the tubes and the type of process fluid handled, adequate corrosion allowance

should be given to the tubes so that failure of the tubes due to corrosion does not occur. In case the furnace handles different types of process fluid, the corrosion allowance should be decided on the assum-ption that it handles the most corrosive fluid at all the item.

5.5 LADDERS/PLATFORMS A minimum of tow ladders or staircase

should be provided for reaching the various elevations of the furnace. At any elevation, access to both ladders should be available. Platforms Provided at various elevations should be sufficient to carry out operating checks and routine maintenance jobs during the run. If cat / monkey ladders are provided, provide safety chain / rod at the entrance. Note 1

5.6 PERSONNEL PROTECTION If the shell temperature at any point on the

furnace is above 55 Deg.C suitable protect-ion of personnel should be provided.

5.7 PEEP HOLES Irrespective of the type of furnace, peep

holes should be provided both at the furnace floor and sides so that the operator can have a fair view of all the radiant tubes, bottom row of convection tubes and burner patter. Air screens should be provided at these peep holes when the furnace is pressurised.

6.0 PROCESS SYSTEM 6.1 PASS FLOW CONTROL & MONITORING It is necessary to provide flow-control on

each pass of the furnace to avoid unbalancing of the flow due to coking or partial vapourisation and thus to avoid overheating of tubes. The individual pass flow of the furnace should have recorders, low flow alarms and fuel cut-off at low coil flow.

6.2 PRESSURE MONITORING

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Pressure gauges shall be provided at the inlet and cross over of each pass. A common pressure gauge shall be provided t the common outlet of the furnace.

6.3 TEMPERATURE MONITORING Temperature indicators shall be provided at

Control Room for the cross over, outlet of each pass and the common outlet of all passes.

7.0 FIRING SYSTEM 7.1 BURNER MOUNTING The burner mounting should be such that

there is no impingement of flame on the tubes.

7.2 PILOT BURNERS Each burner shall be provided with a gas pilot

burner, with fuel gas supplied at steady pressure and condensate free. The pilots shall be kept always on when the furnace is in service. Liquid fuel operated pilot burners are not recommended as those are not reliable.

7.3 BURNER LIGHTING Lighting ignitors to light up the pilot burners

are recommended Alternatively, LPG torch may be used to light the burners. The use of acetylone torch/oil soaked torch to light the burner should be avoided. Main burners should be lighted only from pilot burners. Lighting a main burner from the heat of adjacent burner is unsafe and should not be practiced. LPG cylinder used for the torch should be removed from the vicinity of the furnace after lighting up the furnace.

7.4 FUEL GAS CONTROL VALVE In some existing furnaces, double diaphragm

control valve with fuel gas itself acting against instrument air to compensate for pressure variations are used. In order to avoid the danger of fuel gas coming out through the vent going into instrument air system if the diaphragm ruptures, the use of such valves is not recommended. An automatic vent valve

should be provided to release the trapped gas between the process control valve and the shutdown valve.

7.5 BLINDING OF FUEL GAS/OIL Fuel gas lines should have provision for

blinding off adjacent to the burners & down-stream of the control valve with spectacle blinds, who position is visible at all times. Main fuel oil line and main fuel gas line to the furnace should also have provision for blinding at the down-stream of control valve and at the return line. It should be possible to blind fuel gas to pilot burners also. Fuel gas lines should be kept blinded of when the furnace is not in operation.

7.6 KNOCK OUT POTS The fuel gas lines should be provided with

knock-out pots so that condensate will not get into the burner lines. Knock-out pot for each furnace should be located 15 M away form it and its drain should be connected to the flare. Gauge glass and a high level alarm should be provided for the knock-out pot should be steam traced. The fuel gas lines to/from knock-out pot should be slopped towards the knock-out pot.

8.0 UTILITY SYSTEMS

8.1 COIL PURGE Purge steam or inert gas connections shall be

given to the inlets of all furnace passes. Wherever steam injection cannot be done (for e.g. Reformer heater) inert gas connect-ion shall be give. The inert gas should be cut in automatically by solenoid valves, actuated by safety shutdown system. Alternatively, manually operated valves located 15 meters away from the furnace or control valves remotely operated form Control Room should be provided. Non-return valves (flanged) should be provided downstream of these valves to prevent backing up of oil. Pressure gauges should be provided on the individual coil purge lines downstream of the block valves/control valves and upsteam of non-

4 OISD-111

return valves. A typical sketch for such an arrangement is attached as Annexure-I

8.2 BOX PURGE STEAM Box purge steam connections shall be

provided to the furnace to ensure furnace purging before lighting up and also to create an inert atmosphere in the fire box during a fire emergency. Wherever purging connect-ions are given to both radiant and convection sections, there should be independent lines for those, with separate control points. Steam purging connections should be provided with capacity sufficient to permit displacement of the furnace volume within ten minutes at the available steam pressure. Purging connections should be arranged in such away that they cover the entire floor of the furnace leaving no pockets.

Opening of the fuel gas supply control valve

may be interlocked with the purging system so that the valve does not open till purging is compete.

9.0 SAFETY INSTRUMENTATION Following minimum safety instrumentation

for indication / recording / alarm / shutdown should be provided for all furnaces.

9.1 INDICATIONS/RECORDING

a) Flow for each pass and total flow b) Inlet pressure to each pass c) Common outlet pressure of all passes

together "Outlet pressure indication for all passes for heavy feed stock service" should be provided. Note 1

d) Outlet temperature of individual pass e) Transfer line temperature f) Pressure and temperature at cross-over g) Fire box pressure (draft gauges) h) Pressure of oil and gas downstream of

respective control valves. I) Differential Pressure between oil and

atomising steam j) Stack temperature k) Fire box temperature at selected points at

the radiant sections.

l) Fire box temperature at the arch level (below convection section)

m) Skin temperatures for each pass n) The indications of FD/ID fans (whether

running or not) o) Smoke density indicator/Oxygen analyser

(Optional) p) Indication for flame detector q) Local draft gauge for furnace fire box, arch

and stack.

9.2 ALARMS

The following alarms should be provided:

a) Low flow for each pass b) High Stack temperature c) High/Low differential pressure between oil

and atomising steam d) Low fuel gas pressure downstream of control

valve and for pilot e) Low fuel oil pressure downstream of control

valve. f) High fire box pressure g) High smoke density(optional) h) Gas detector high hydrocarbon (20% of the

explosive limit) at FE fan suction. I) Pilot flame failure where flame detector is

provided. j) High skin temperature. Note 1 k) High arch pressure. Note 1

9.3 SHUTDOWN SYSTEM 9.3.1 Parameters for Shutdown

The shutdown system should get actuated when any of the following happens:

a) Low pass flow in minimum tow passes or low total flow for a multi pass furnace. In the case of catalytic process furnaces like Reformer employing a liquid hydrocarbon feed and recycle gas steam, the furnace shutdown should get actuated when recycle gas failure occurs.

b) Fuel gas/fuel oil low pressure.

c) ID/FD fan failures if drop out doors are provided and do not open within specified time.

d) FD fan failure when drop out doors are not provided.

OISD 5

e) High fire box pressure.

f) Flame failure wherever flame detectors are provided.

g) High high coil outlet temperature. Note 1

9.3.2 Shutdown action. On being actuated by any of the conditions

as per 9.3.1, the furnace shutdown system should initiate the following action immediately :

a) cut off fuel gas and fuel oil b) open stack damper wide c) opening of drop out doors if provided.

If required the above action should be manually supplemented. Cut in of purging steam or inert gas as necessary to be manually done (Ref.8.1)

9.4 TYPICAL FURNACE INSTRUMENTATION.

A typical sketch indicating safety instrumen-tation on furnace is attached as Annexure-II

10.0 OPERATING CHECKS

Sufficient facilities should be incorporated in the design for operating personnel to have satisfactory checks of the equipment.

10.1 PRESSURE SURVEY Local draft/pressure gauges should be

provided to measure the pressures at various locations in the furnace like below convection zone, air preheater inlet/outlet, etc.

10.2 SAFETY AUDIT Apart from routine checks carried out by the

operating staff, independent checks by Process Engineers/Safety Engineers should be carried out and reports sent to the operating staff periodically. All safety shutdown systems should be checked regularly and records maintained. Prior to cold start up, all safety shutdown systems should be checked for their correct operation before firing the furnace.

11.0 DECOKING SYSTEMS

Furnaces handling heavier feed stocks tend to lay down coke inside their tubes during operation. This results in hot spot and consequent failure of tubes. For such furnaces, it is necessary to decoke the tubes periodically. Decoking is done when skill temperatures and coil inlet pressure go high. Decoking is done generally using steam and air.

11.1 FLOW MEASUREMENT There should be provision for measurement of

flow of steam/inert gas and air to each pass of the furnace to be decoked.

11.2 TEMPERATURE MEASUREMENT There should be provision to measure the

temperature at various locations in the coil like convection, convection/radiant transition, radiant and radiant outlet or each pass. The tube skin temperature also should be measu-red at these locations. It is recommended to have provisions for recording of all these temperatures during decoking operation.

11.3 MONITORING OF DECOKING. As decoking is both by burning and spalling,

safe progress of both must be observed by the nature of dust discharged at the coil outlet and colour of the coil itself together with the temperature readings throughout the coil. Very careful observation must be made of red spots in the coil to prevent overheating and consequent burning or damage to the tubes. it is recommended to have maximum coke removal by spalling. It is preferable to have decoking in the reverse direction to ensure better spalling.

11.4 QUENCH POT FOR DECOKING The spallings at the coil outlet should never be

let-off directly to atmosphere, but always be let-out only through a quench pot where they will be washed down with water. This is to prevent hot particles flying around which may pose a safety hazard. The coil outlet to quench pot should not have pockets and should be free flowing to quench pot.

6 OISD-111

11.5 TESTS AFTER DECOKING Rigorous inspection and hydrostatic test with

water should be done on the furnace coils after every decoking operation and records kept.

11.6 DECOKING SCHEMATIC A typical system for decoking line up is

attached as Annexure-III

12.0 SAFETY IN FURNACE OPERATION 12.1 DISPLAY BOARD Important operating procedures including

lighting, startup and shutdown procedures to be followed should be listed and displayed at the prominent location for the operators.

12.2 FURNACE LIGHTING A check-list should be prepared to avoid

missing of any step during lighting a furnace. Following key points should be ensured:

a) L i s t a l l dampers which are to be

opened. b) Check fuel supply and return pressure. c) Drain condensate from fuel gas/knock-

out pot. d) Purge the furnace thoroughly with

steam till steam comes out on top of stack. Additionally, samples from the fire box may be taken for checking the presence of hydrocarbon before attempting to light the furnace.

e) Light the pilots first by electric

ignitors. If LPG torch is use, place it at the burner before gas is turned on. Close the gas supply torch while it is kept on the burner. Remove the gas cylinder from the vicinity of the furnace after lighting.

f) Should fires go out while lighting, turn

off gas and purge the furnace thoroughly before attempting to relight the burners.

12.3 FURNACE SHUTDOWN In case shutdown system is actuated or the

furnace fire have to be taken out, ensure that:

a) Fuel is cut-off to the furnace b) Stack damper is wide opened c) Drop out doors wherever provided are

opened d) ID fan is tripped. e) Steam or inert gas to the coil is cut in If the furnace has to be down for a long time,

fuel lines to the furnace should be blinded. 12.4 TUBE FAILURE In the case of tube failure of the furnace, the

following action should be taken in addition to the actions listed under 9.3.2:

a) Cut off feed to the coil b) FD fan is tripped c) Fire box purge steam is opened.

d) If furnace is serving vacuum column, the vacuum should be broken and column should be brought under slight fuel gas pressure.

e) Keep pilot burner running near failed tube. Note 1

13.0 GENERAL 13.1 HOUSE-KEEPING Perfect house keeping should be ensured in

the vicinity of the furnace. Utility points with provisions to take steam and water should be provided in the vicinity of the furnace.

13.2 SAFETY SHOWER

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A safety shower should be provided in the vicinity of the furnace.

13.3 FIRE FIGHTING FACILITIES Adequate number of monitors with

pressurised hydrant should be provided around the furnace so that the shell and the supporting structure may be kept cooled in the event of a fire emergency. Alternatively, a sprinkler, system may be provided which may be actuated from a distance. Adequate number of DCP tenders and hose reels should be located at strategic locations to help the operators fight a fire in the vicinity of the furnace.

Training/regular drill of operating personnel

on fire fighting and first aid may be carried out.

14.0 REFERENCES 1. OISD-STD-118 on Layouts for Oil and Gas

Installations.

8 OISD-111

ANNEXURE I

TYPICAL ARRANGEMENT FOR COIL PURGE STEAM / INERT GAS TO A 4 PASS FURNACE

PASS IN LET TO FURNACE

COIL PASS-1

COIL PASS-2

COIL PASS-3

COIL PASS-4

(MIN

TY

PE

)

NON RETURN VALVE (TYP)

BLOCK VALVE OR CONTROL VALVE (TYP)

LEGEND PI – PRESSURE GAUGE ST – STEAM TRAP ONLY IN (CASE OF STEAM)

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OISD 11

NOTES

12 OISD-111

NOTES

OISD 13

NOTES

14 OISD-111

Ref. No. 11—111—01

OISD 15

10—1998—01—1000