ISO 13577-2:2014

INTERNATIONAL ISO
STANDARD 13577-2
First edition
2014-09-15
Industrial furnaces and associated
processing equipment — Safety —
Part 2:
Combustion and fuel handling systems
Fours industriels et équipements associés — Sécurité —
Partie 2: Équipement de combustion et de manutention des
combustibles
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 3
4 Safety requirements, measures and verification means . 3
4.1 General . 3
4.2 Gaseous fuels . 3
4.3 Liquid fuels .18
4.4 Multiple fuels .29
4.5 Oxygen or oxygen-enriched combustion air (OOECA) .30
5 Verification of the safety requirements and/or measures .32
6 Information for Use .37
6.1 General .37
6.2 Marking .37
6.3 Instruction handbook .37
Annex A (informative) List of significant hazards.40
Annex B (informative) Typical examples of fuels .42
Annex C (informative) Typical example of piping and components .43
Annex D (informative) Methods for burner start-up .55
Annex E (normative) Maximum allowed pressure .63
Annex F (informative) Examples for the determination of safety integrity level (SIL) using the risk
graph method .68
Annex G (normative) Requirements specific to Japan .79
Annex H (normative) Requirements specific to the USA .85
Annex I (normative) Requirements for Europe and associated countries .91
Bibliography .96
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 244, Industrial furnaces and associated processing
equipment.
ISO 13577 consists of the following parts, under the general title Industrial furnaces and associated
processing equipment — Safety:
— Part 1: General requirements
— Part 2: Combustion and fuel handling systems
— Part 3: Generation and use of protective and reactive atmosphere gases
— Part 4: Protective systems
iv © ISO 2014 – All rights reserved

Introduction
This document is a type-C standard as defined in ISO 12100.
The machinery concerned and the extent to which hazards, hazardous situations or hazardous events
are covered, is indicated in the Scope of this document.
When requirements of this type-C standard are different from those which are stated in type-A or -B
standards, the requirements of this type-C standard take precedence over the requirements of the other
standards, for machines that have been designed and built according to the requirements of this type-C
standard.
This part of ISO 13577 assumes that the equipment is not creating any potentially explosive atmosphere
and is located in a normally ventilated area.
Compliance with product standards e.g. ISO 22967 or ISO 22968 is not sufficient to ensure the minimum
safety requirements for industrial furnaces and associated processing equipment (TPE). This part of
ISO 13577 shall always have priority for TPE.
Industrial furnaces and associated processing equipment (TPE) generally consists of the following
components:
— processing chamber (e.g. steel construction with lining and/or refractory);
— heating systems;
— protective system;
— control and instrumentation system / operator-control level.
ISO 13577-1 provides the general safety requirements common to TPE. This part of ISO 13577 details in
addition specific safety requirements for combustion and fuel handling systems that are part of TPE as
listed in the Scope.
NOTE As stated in its scope, ISO 13577-1 does not cover blast furnaces, converters (in steel plants), boilers
and equipment not covered by ISO 12100.
The requirements for protective systems are specified in ISO 13577-4.
If a general requirement of ISO 13577-1 counters requirements in this part of ISO 13577, the requirements
of this part of ISO 13577 take precedence.
The requirements for reducing hazards from noise are given in ISO 13577-1.
It is assumed that TPE will only be operated and maintained by trained personnel.
INTERNATIONAL STANDARD ISO 13577-2:2014(E)
Industrial furnaces and associated processing
equipment — Safety —
Part 2:
Combustion and fuel handling systems
1 Scope
This part of ISO 13577 specifies the safety requirements for combustion and fuel handling systems that
are part of industrial furnaces and associated processing equipment (TPE).
NOTE The general safety requirements common to TPE are provided in ISO 13577-1 (See introduction).
This part of ISO 13577 deals with significant hazards, hazardous situations and events relevant to
combustion and fuel handling systems as listed in Annex A, when used as intended and under the
conditions foreseen by the manufacturer.
This part of ISO 13577 covers:
— fuel pipework downstream of and including the manual isolating valve;
— combustion air supply (including oxygen and oxygen enriched combustion air) and flue gas system;
— burner(s), burner system and ignition device;
— functional requirements for safety related control system.
This part of ISO 13577 applies to any oxidation with air or other gases containing free oxygen of gaseous
and liquid fuels or any combustion of them to release thermal energy in TPE.
For thermal or catalytic post combustion and waste incineration, this part of ISO 13577 applies only to
auxiliary burners designed to start-up and/or support the process.
The pressure hazard of the piping and components covered by this part of ISO 13577 is within the
maximum pressure/size relationship of category I as described in normative Annex E.
This part of ISO 13577 also gives the necessary requirements regarding information for use.
This part of ISO 13577 does not cover hazards from heating generated by electricity.
This part of ISO 13577 does not deal with the hazards created by the release of flammable substances
from the products processed in the TPE.
This part of ISO 13577 is not applicable to combustion and fuel handling systems:
— of welding machines;
— up-stream of the TPE manual isolating valve.
This part of ISO 13577 is not applicable to electrical cabling and power cabling upstream of the TPE
control panel/protective system.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 7-1:1994, Pipe threads where pressure-tight joints are made on the threads — Part 1: Dimensions,
tolerances and designation
ISO 49:1994, Malleable cast iron fittings threaded to ISO 7-1
ISO 228-1:2000, Pipe threads where pressure-tight joints are not made on the threads — Part 1: Dimensions,
tolerances and designation
ISO 5817:2003, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding
excluded) — Quality levels for imperfections
ISO 7005-1:2011, Pipe flanges — Part 1: Steel flanges for industrial and general service piping systems
ISO 7005-2:1988, Metallic flanges — Part 2: Cast iron flanges
ISO 7005-3:1988, Metallic flanges — Part 3: Copper alloy and composite flanges
ISO 8434-1:2007, Metallic tube connections for fluid power and general use — Part 1: 24° cone connectors
ISO 8434-2:2007, Metallic tube connections for fluid power and general use — Part 2: 37° flared connectors
ISO 8434-3:2005, Metallic tube connections for fluid power and general use — Part 3: O-ring face seal
connectors
ISO 12100:2010, Safety of machinery — General principles for design — Risk assessment and risk reduction
ISO 13574, Industrial furnaces and associated processing equipment — Vocabulary
ISO 13577-1, Industrial furnaces and associated processing equipment — Safety — Part 1: General
requirements
ISO 13577-4, Industrial furnace and associated processing equipment — Safety — Part 4: Protective systems
ISO 19879:2010, Metallic tube connections for fluid power and general use — Test methods for hydraulic
fluid power connections
ISO 23551-1:2012, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 1: Automatic and semi-automatic valves
ISO 23551-2:2006, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 2: Pressure regulators
ISO 23551-3:2005, Safety and control devices for gas burners and gas-burning appliances — Particular
requirements — Part 3: Gas/air ratio controls, pneumatic type
ISO 23552-1:2007, Safety and control devices for gas and/or oil burners and gas and/or oil appliances —
Particular requirements — Part 1: Fuel/air ratio controls, electronic type
ISO 23553-1:2007, Safety and control devices for oil burners and oil-burning appliances — Particular
requirements — Part 1: Shut-off devices for oil burners
IEC 60204-1:2005, Safety of machinery — Electrical equipment of machines — Part 1: General requirements
IEC 60730-2-5:2009, Automatic electrical controls for household and similar use — Part 2-5: Particular
requirements for automatic electrical burner control systems
IEC 60730-2-6:2007, Automatic electrical controls for household and similar use — Part 2-6: Particular
requirements for automatic electrical pressure sensing controls including mechanical requirements
2 © ISO 2014 – All rights reserved

3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13574 apply.
4 Safety requirements, measures and verification means
4.1 General
The safety goals of this part of ISO 13577 shall include:
— choice of materials such that the construction and operation of the system are not detrimentally
affected. In particular, all the components of the fuel pipework shall be capable of withstanding the
mechanical, chemical and thermal loads to which they can be subjected during normal operation
and foreseeable abnormal operation (e.g. identified during a safety assessment);
— reliable and correct time for ignition of the air/fuel-mixture at the burner(s);
— prevention of unintentional release of unburned fuels;
— shut-off fuel-supply in case of relevant fault;
— protection of pipeline to preclude the propagation of flame in reverse direction;
— prevent firing when the evacuation of flue gas/combustion products is not ensured;
— prevent firing when the process conditions are not in the safe state.
Electrical circuits shall be designed in accordance with IEC 60204-1.
A risk assessment according to ISO 12100 shall be carried out. Safety function shall be designed in
accordance with ISO 13577-4, where the use of standards for functional safety IEC 62061, ISO 13849
(all parts), IEC 61511 (all parts) and IEC 61508 (all parts) is included. Informative Annex F provides
information for the determination of the SIL or PL of safety-related functions covered in this part of
ISO 13577.
Specific regional requirements are given in Annex G, Annex H and Annex I. The safety requirements of
these annexes shall ensure at least the equivalent level of safety to the requirements given in this part
of ISO 13577.
4.2 Gaseous fuels
4.2.1 Gas pipework
4.2.1.1 General
The pipework design shall take into account the composition and properties (e.g. pressure, temperature,
corrosiveness, specific gravity) of the fuel gas and the need for venting, purging and cleaning.
The pipework material shall comply with the relevant standards.
Due to durability, steel is the preferred material for pipes and components but where appropriate and the
same safety levels can be achieved then other materials may be utilized. Such materials and conditions
of service shall be specified in the instruction handbook. Oscillations which may cause damage to
pipework, components or safety systems shall be prevented (by firm anchoring and/or use of flexible
couplings).
4.2.1.2 Connections
Gas pipework connections shall be metallic and shall be of threaded, compression, flanged, welded or
brazed types. The number of connections shall be kept to a minimum.
Threaded connections shall be used only for the following pressure/diameter combinations:
— pressures up to 15 kPa, and diameters up to DN 100
— pressures up to 200 kPa, and diameters up to DN 50
— pressures up to 500 kPa, and diameters up to DN 25
— pressures up to 1 MPa, and diameters up to DN 15
For fittings according to ISO 49, the following limitations shall be observed:
— fittings must be class “A”;
— maximum allowed pressure is 50 kPa;
— for dimensions DN 25 or less, the maximum pressure is 500 kPa.
Where the equipment has a threaded connection, this thread shall comply with ISO 228-1 or ISO 7-1 as
appropriate. The use of threads complying with ISO 228-1 is limited to diameter up to DN 50. In case
of threads according to ISO 228-1, the tightness shall be ensured by a ring gasket. In case of threads
according to ISO 7-1 suitable sealants shall be used to ensure tightness. Hemp shall not be used in
threaded connections unless reinforced with a suitable sealant.
Other threaded connections may only be used providing they ensure tight connections and are suitably
identified.
The design of pipework shall be such as to avoid tensile loading of the joints.
Compression fittings shall comply with ISO 8434-1, ISO 8434−2 and ISO 8434−3 or ISO 19879. They shall
only be used for pressures up to 500 kPa and diameters up to 42 mm.
Any pipe passing through an unventilated space shall not have a connection except welded joints.
Flanges shall comply with ISO 7005-1 and ISO 7005-2 as appropriate.
Arc welding shall comply with ISO 5817, quality level C.
4.2.1.3 Unconnected pipework
Any unconnected pipework shall be plugged, capped or blank flanged by means of metallic parts.
4.2.1.4 Galvanic cells
The formation of galvanic cells shall be avoided by suitable choice of materials.
4.2.1.5 Flexible tubing and couplings
Flexible tubing shall comply with the general requirements of 4.2.1.1, together with the following:
— shall be as short as practicable;
— shall be suitable for the maximum and minimum working (fuel and ambient) temperatures;
— shall be suitable for a pressure 1,5 times the working operating pressure (with a minimum of
15 kPa), at the maximum and minimum working temperatures;
— shall have a directly accessible, upstream manual shut-off valve;
4 © ISO 2014 – All rights reserved

— shall be mounted in such a way as to avoid distortion, whiplash and damage;
— shall have end fittings as integral parts of the tubing;
— shall be constructed from suitable material both metallic and/or non-metallic selected for the
application duty and not be easily damaged.
Couplings for removable equipment shall ensure a gastight connection with the equipment connected
and disconnected.
4.2.1.6 Marking
The pipework shall be identified as gas pipework.
NOTE Identification of gas pipework is dealt with by national regulations.
4.2.1.7 Soundness/tightness
The gas pipework shall be tight and shall be designed to withstand the internal pressure. After assembly,
the gas pipework shall be submitted to its test pressure and tested for tightness. The test pressure shall
be not less than 1,1 times the maximum working pressure at any point with a minimum of 5 kPa.
The external leakage rate shall not give rise to a dangerous condition, flammable and/or toxic, in the
foreseen circumstances of the equipment installation. The frequency of testing to determine the external
leakage shall be specified in the instruction handbook.
NOTE It is generally agreed that an external leak rate of ≈ 1 dm (n)/h will not give rise to a dangerous
condition in typical ventilated industrial installations. The actual leak rate will depend upon the volume, number
of connections, test gas, number of valves and component parts contained.
The external leak rate test method shall take into account the volume, number of connections, test gas,
number of valves and component parts contained and temperature. Methods of testing shall include
spray bubble leak identification and/or pressure decay test.
4.2.1.8 Condensate drains
In cases where condensates can create a hazard, means shall be provided at the lowest points of the
equipment for draining any condensate. When moist gases are being used, condensate drains of a
suitable type shall be installed. Any condensate drains, siphons, etc. shall be in a position such that they
can be easily checked. Flammable condensates shall be collected by an appropriate means (e.g. piped
into a container).
Valves in condensate drains shall be suitably plugged, capped or blank flanged by metallic parts.
4.2.1.9 Purge points
Means shall be provided to facilitate purging of the gas system during commissioning and maintenance
to prevent the build-up of flammable substances.
4.2.1.10 Blow-off and breather pipes or conduits
Where blow-off or breather pipes or conduits are fitted on regulators or relief valves or vent valves,
adequate means shall be provided to facilitate the venting of gas from the system to a safe discharge
area.
In case breathers or blow-off pipes are gathered, the cross section of the collector shall be suitable to
evacuate simultaneously total flow rates of the exhaust sources.
In case breathers are gathered with blow-off pipes, non-interaction of the collected lines, valves and
instruments shall be verified.
4.2.1.11 Pressure relief devices and flame arrestors on pipework
For equipment designed for situations in which flashback can occur, flame arrestors and/or pressure
relief devices shall be fitted.
Pressure relief devices shall be designed to yield at a pressure below the design pressure of the pipework
and shall be positioned such that the discharge flow and the pressure relief device does not constitute a
risk to the equipment, personnel or third parties.
A flashback at least shall trigger an alarm. The required measures after a flashback shall be described
in the instruction handbook.
4.2.1.12 Pressure oscillations
The gas pipework shall be designed so as to avoid the possibility of gas velocities and pressure
fluctuations causing oscillations which could cause damage to pipework, components or safety systems
(e.g. by designing the correct sizing of pipe, using pressure regulator,).
4.2.1.13 Equipment supplied with different fuel gases
Where a burner is intended for alternating use with more than one gaseous fuel, means shall be provided
to ensure that the supply pipework of the gas not being fired is positively isolated.
4.2.1.14 By-pass
By-passes shall not be fitted in parallel with any item of safety equipment.
This requirement shall not apply to valve proving systems (see ISO 23551-4) on automatic shut-off valves.
4.2.1.15 Isolation of required safety devices
Required safety devices (e.g. pressure switches, relief valves) shall not be isolated from the equipment
they protect during start-up or operation of the burner. In case isolating valves cannot be avoided and
are mounted between these required devices and the main lines, these isolating valves shall be locked
in the open position during operation of the equipment by adequate means (e.g. manual lock).
4.2.2 Required safety devices
4.2.2.1 Manual isolating valve
A manually operated isolation valve shall be fitted upstream of the first control device in the gas circuit.
Manual isolation valves shall be so designed or positioned as to prevent inadvertent operation but shall
be easily accessible and capable of rapid operation when required.
They shall be so designed that the “OPEN” and “CLOSED” positions are readily distinguishable (e.g. a 90°
turn valve if applicable and available).
4.2.2.2 Filter/strainer
Special care shall be taken to prevent the ingress of particles, either from the pipework or from the
gas, which would be detrimental to the operation of the equipment by the incorporation of a suitable
filter or strainer immediately downstream of the first manual isolating valve of the TPE. Additional
filters/strainers may be required (e.g. immediately upstream of the automatic shut-off valve). The filter
and/or the strainer shall be positioned in such a way that periodic servicing remains easy. The filtering
capacity of the filter/strainer has to be chosen according to the requirements of downstream equipment.
NOTE Normally safety and control devices for gas burners and gas-burning appliances require upstream
filters with filtering capacity ≤ 50 µm. Strainers with larger mesh size are only suitable for primary cleaning.
6 © ISO 2014 – All rights reserved

In case of the installation of a by-pass to the filter/strainer, an identical filtering device shall be installed
on the by-pass line.
The intervals for checking the filter and/or the strainer shall be specified in the instruction handbook.
4.2.2.3 Gas pressure regulator
A gas pressure regulator shall be incorporated where this is necessary for control of the pressure and
the flow rate.
Gas pressure regulators when fitted shall comply with ISO 23551-2 as appropriate.
If the outlet side of the gas pressure regulator and/or the following line section with equipment up to
the burner is/are not designed for the maximum supply pressure (inlet pressure upstream to the gas
pressure regulator under fault conditions) an over pressure cut-off device shall be installed upstream of
the gas pressure regulator shutting off the gas supply before an excessively high pressure occurs.
The over pressure cut-off device shall be:
— a mechanical valve which measures the gas pressure downstream of the gas pressure regulator by
means of an impulse line and closes by spring force in case the pressure exceeds the set response
pressure, or
— an automatic shut-off valve according to ISO 23551-1 actuated by an overpressure detector installed
downstream of the gas pressure regulator. The overpressure detector shall comply with IEC 60730-
2-6 or be evaluated to ensure appropriate reaction time and accuracy. In this case, signal processing
has to fulfil the requirements of a protective system according to ISO 13577-4.
A small capacity relief valve (token relief valve) shall always be applied downstream of the gas pressure
regulator, if an over pressure cut-off device is installed to vent small leakages of the high pressure cut-
off.
Pressure adjustment on the gas pressure regulator shall only be possible with a special tool provided
for the task.
Where the gas for the pilot burner is taken from upstream of the gas pressure regulator to the main
burner(s), the pilot burner shall be equipped with a separate gas pressure regulator.
4.2.2.4 Low gas protection
Low gas pressure protection shall be fitted. The low gas pressure protection device has to provide
satisfactory and reliable proof of the pressure for all operation conditions.
The system shall prevent start-up or cause safety shut-down and lock-out in the event of pressure
falling below a pre-determined value. This function shall meet a requirement of the protective system
according to ISO 13577-4.
Gas pressure detectors shall comply with IEC 60730-2-6 or shall be evaluated to ensure appropriate
reaction time and accuracy.
4.2.2.5 High gas protection
High gas pressure protection shall be fitted in all circumstances except when:
— the equipment supply pressure does not exceed 10 kPa, and
— regulator failure does not result in an unsafe start-gas rate being obtained.
Where high gas pressure protection is required, the system shall prevent start-up or cause safety shut-
down and lock-out in the event of a pre-determined pressure being exceeded. This function shall meet
the requirements of a protective system according to ISO 13577-4.
Gas pressure detectors shall comply with IEC 60730-2-6 or shall be evaluated to ensure appropriate
reaction time and accuracy.
4.2.2.6 Automatic shut-off valves
The gas supply to each burner or group of burners shall be under the control of two automatic shut-off
valves in series in the gas pipework in accordance with the following subclauses of ISO 23551-1:2012:
— for general requirements: subclause 7.1;
— for leak tightness: subclause 7.2;
— for durability: subclause 7.5;
— for the closing function: subclause 7.6.101;
— for the closing force: subclause 7.6.104;
— for the closing time: subclause 7.6.106.
The sealing force for automatic shut-off valves shall be equal to or greater than 15 kPa.
For natural draught burner with a controlled capacity below 70 kW the sealing force for automatic shut-
off valves shall be at least 5 kPa.
The automatic shut-off valve shall endure the intended number of cycles in the TPE.
Valves construction and materials shall be suitable for the used gas composition.
Automatic shut-off valve shall be capable of withstanding all upstream pressures, backpressure and
differential pressure under all process circumstances.
High cycling applications over 100 000 cycles/year, (e.g. pulse firing, regenerative burners) shall use
only valves that are declared capable of the intended number of cycles and on/off cycling rate.
The instruction handbook shall specify the need to check automatic shut-off valves for correct operation,
the procedure to be adopted and the intervals at which this should be carried out and the requirements
for replacement. Means to permit the operator to determine when automatic shut-off valves require
replacement shall be supplied.
NOTE It is commonly agreed that valves are to be tested annually unless longer testing intervals can be
justified by the risk analysis.
All systems shall have the ability for manual leak testing of the automatic shut-off valve.
Control valves may be used as safety shut-off valves provided they are designed as both safety shut-off
and modulation valves and tested for concurrent use.
The automatic shut-off valves shall not open or shall shut off the fuel to the burner when the limit of any
safety condition is reached. In this case, the relevant automatic shut-off valves shall be de-energised by
a protective system according to ISO 13577-4.
NOTE Examples for safety related conditions to be considered are (but not limited to): minimum and/or
maximum gas flow, minimum and/or maximum gas pressure, minimum and/or maximum air flow, minimum
and/or maximum air pressure, failure of power supply and/or other utilities (e.g. compressed air, steam), failure
of heat transfer fluid, fume extraction malfunction, minimum and/or maximum operation temperature, minimum
and/or maximum combustion chamber pressure, flame failure, failure of valve proving as referred in 4.2.2.7,
incorrect air gas ratio as referred in 4.3.3.3.
It shall only be possible to manually reset (locally or remotely) the lock out of a closed automatic shut-off
valve.
8 © ISO 2014 – All rights reserved

Flame failure or process control shut down shall cause the closing of two automatic shut-off valves piped
in series except in the following cases where closing a single individual burner shut off valve is sufficient:
— in case of high-temperature equipment;
— in case of low-temperature equipment where the individual burner automatic shut-off valve is
fitted with proof of closure according to ISO 23551-1, and the protective system closes an upstream
automatic shut-off valve (header valve) if one of the individual burner valve is not proven closed by
the prove of closure switch.
Flame failure or process control shut down of radiant tube burner system shall cause the closing of
two automatic shut-off valves piped in series except in the following cases where the closing of a single
individual burner shut off valve is sufficient:
— each radiant tube burner system is explosion resistance and the exhaust system dilutes the ignitable
fuel-air-mixture from leaking gas valves inside the exhaust system below 25 % of the LFL.
For typical examples of piping and components see informative Annex C.
4.2.2.7 Valve proving
Automatic shut-off valves controlling capacities higher than 1 200 kW shall be proved closed at each
start-up of the TPE. In case where the valve is not proved closed, the current start-up shall be stopped
and the system shall go to lock-out. The valve proving procedure and the action after such failure shall
be specified in the instruction handbook (e.g. replacement of valve).
NOTE It is generally agreed that a leak rate of the valve(s) below 0,1 % of the maximum gas flow into the
combustion chamber during operation is considered as proved close valve. In case of preheated gas and/or oxygen
or oxygen enriched combustion this value has to be readjusted accordingly.
For a TPE intended to be started up more than two times a year, the automatic shut-off valve(s) shall be
proved closed by an automatic system.
Automatic valve proving shall fulfil the requirements of a protective system according to ISO 13577-4.
In multiple burner systems with two automatic shut-off valves for each burner, automatic testing does
not have to prove each burner valve individually (see Figure C2b). The testing of the individual burner
valves shall be specified in the instruction handbook.
4.2.2.8 Individual manual shut-off valves for burners
For burners which are independently ignited, each individual burner shall be fitted with a manual shut-
off valve suitable for the type of gas.
However, if the installation of such a manual valve affects the mixing characteristics of mixing devices
(e.g. venturi mixers), then the shut-off valve shall be installed upstream of any such device.
For multiple burners in which cross-ignition from burner to burner occurs by design, the complete group
of burners shall be fitted with at least one manual shut-off valve.
4.2.3 Combustion air and air/fuel ratio
4.2.3.1 Combustion air system
The pipework design shall take into account the properties of combustion air (e.g. pressure, temperature).
The location of the combustion air intake shall be such as to prevent entry of impurities (e.g. dust) and
flue products, unless provided for by the design (e.g. for reduction of emission of nitrogen oxides NO ).
x
The ventilation of TPE shall be such as to allow an adequate supply of process air and combustion air to
reach the burner(s) under all conditions.
Attention should be paid to sufficient air supply to the TPE. For many applications, it is recommended to
install an air inlet filter with filter monitoring to achieve reliable operation of the installation.
The combustion air system shall be designed in a manner that prevents the back-flow of furnace
atmosphere through combustion equipment.
The air circuit shall be designed so as to avoid oscillations that may lead to material defects.
4.2.3.2 Air flow and pressure detectors
TPE fitted with forced or induced draught burner(s) shall be fitted with devices for proving adequate air
flow during ignition and operation of the burner.
Air flow failure at any time during the pre-purge, ignition or operation of the burner shall cause safety
shut-down and shall cause a lockout. This function shall meet the requirements of a protective system
according to ISO 13577-4.
The air-proving device shall be checked in the “no flow” state prior to start-up [e.g. by stopping the
combustion air supply or by interrupting the air signal to the device(s) in such a way as to simulate
stopping the combustion air supply]. Failure to prove the device in the “no flow” condition shall prevent
start-up.
Air flow shall be monitored:
— by pressure detectors or
— by flow detectors.
It shall be shown that any of these devices provide satisfactory and reliable proof of the flow for all
operating conditions.
This requirement shall not apply to portable gas burners, work station burners and equipment-integrated
burners with open flame, supervised continuously by trained operators, and having a maximum burner
input rating below 70 kW.
Air pressure detectors shall comply with IEC 60730-2-6 or shall be evaluated to ensure appropriate
reaction time and accuracy. They shall be suitable for the number of operations foreseeable for the
application.
4.2.3.3 Air/fuel ratio
The air mass flow shall always be in a ratio with the gas mass flow in order to ensure safe ignition
and that throughout the operating range, a stable and safe combustion is maintained at each individual
burner. The ratio does not need to be the same value at all operational conditions.
If the variation of pressure and/or temperature of air and fuel gas affect the safety and combustion
stability, then correction for pressure and/or temperature is required.
The design of the air/gas ratio control has to consider process conditions as well as fuel and combustion
air properties. Defect or malfunction should effect that the system will tend towards higher excess air
or proceed to lockout if the air/gas ratio results in an unsafe condition.
Pneumatic gas/air ratio controls shall comply with ISO 23551-3, if applicable.
Electronic gas/air ratio controls shall comply with ISO 23552-1, if applicable.
To ensure their reliability, air/gas ratio controllers according to ISO 23551-3 or ISO 23552-1 shall be used
in conditions (temperature, pressure, flow rate) for which they have been designed. These conditions
and instructions for maintenance shall be specified in the instruction handbook.
In case other methods/technologies are used for the ratio control and depending on the combustion
air and fuel gas properties, additional protective measures shall be applied according to the results
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of the risk assessment (e.g. air/fuel ratio monitoring by protective system according to ISO 13577-4).
The method/technology and the procedure for the functional test shall be described in the instruction
handbook.
4.2.4 Supply of pre-mixed fuel gas/air
4.2.4.1 Mixture pipework
The mixture pipework volume shall be minimized to reduce risk in the event of flashback, but shall not
compromise pressure and flow distribution needed for stable burner operation. The system shall be
designed so as to provide a sufficiently high mixture flow velocity such that flame propagation upstream
cannot occur, or shall be fitted with flame trap(s)/arrestor(s), pressure relief devices or blowout devices
to prevent damage in the mixture pipework and mixing equipment.
Flame trap(s)/arrestor(s) if used shall be located as close to the burner(s) as practicable.
Alternatively, the system shall be fitted with a sensor which causes lock-out in the event of the flow
velocity falling below a pre-determined limit or a temperature sensor which causes lock-out in the event
of flashback. This function shall meet the requirements of a protective system according to ISO 13577-4.
These devices are not required for burners where the manufacturer can demonstrate that flashback
cannot occur in any circumstances (e.g. pilot burners with their own mixing devices).
4.2.4.2 Air and gas supply to the mixture circuit
The presence of fuel gas/air mixture in the pipework supplying either fuel gas or air to the mixing device
(e.g. due to reverse flow of the mixture) shall be prevented.
If a non-return valve is used for this purpose and if it is not resistant to flashback, then an additional
high gas pressure switch located downstream of this non-return valve shall be incorporated to shut
off the flow of fuel gas to the equipment by means of the relevant automatic shut-off valves specified in
4.2.2.6 in the event of a flame flashback.
A flashback shall trigger an alarm. The required measures after a flashback shall be described in the
instruction handbook.
4.2.5 Burners
4.2.5.1 Main burners
All burners shall be suitable for the working conditions and shall provide operating safety for:
— the fuels used (type, pressure, etc.);
— the operating conditions (pressure, temperature, atmosphere, etc.);
— the nominal input rate and range of regulation (maximum and minimum capacity);
— ease of visual monitoring (sight glasses, sight holes, etc.).
4.2.5.2 Radiant tube burner systems
Radiant tube burner systems shall be suitable and allow safe operation. They shall:
— be constructed of suitable materials for the thermal input rate, temperature and furnace atmosphere;
— minimize the probability of combustion products having contact with the furnace atmosphere.
4.2.5.3 Ignition device/pilot burner
The ignition device shall be reliable and of sufficient capacity, so that immediate, low noise and smooth
ignition is obtained. Detail verification procedure for use in commissioning, operation and maintenance
shall be included in the instruction handbook.
Any direct ignition device or combination of the ignition device and the pilot burner in automatic
installations shall form an integral part of the main burner system.
The construction and location of a pilot burner shall be such that, under all operating conditions, the
pilot flame remains stable and of such a shape that the main flame is ignited.
For safety requirements, pilot burner(s) shall be treated as main burners and 4.2.2.3, 4.2.2.4
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