Bsi bs en 12952 8 2002

BRITISH STANDARD BS EN 12952 8 2002 Water tube boilers and auxiliary installations — Part 8 Requirements for firing systems for liquid and gaseous fuels for the boiler The European Standard EN 12952 8[.]

Water-tube boilers

and auxiliary

installations —

Part 8: Requirements for firing systems

for liquid and gaseous fuels for the

This British Standard, having

been prepared under the

direction of the Engineering

Sector Policy and Strategy

Committee, was published

under the authority of the

Standards Policy and Strategy

The UK participation in its preparation was entrusted to Technical Committee PVE/2, Water-tube boilers, which has the responsibility to:

A list of organizations represented on this committee can be obtained on request to its secretary

Cross-references

The British Standards which implement international or European

publications referred to in this document may be found in the BSI Catalogue

under the section entitled “International Standards Correspondence Index”, or

by using the “Search” facility of the BSI Electronic Catalogue or of British

enquiries on the interpretation, or proposals for change, and keep the

UK interests informed;

promulgate them in the UK

Amendments issued since publication

EUROPÄISCHE NORM May 2002

ICS 27.040

English versionWater-tube boilers and auxiliary installations - Part 8:

Requirements for firing systems for liquid and gaseous fuels for

the boiler

Chaudières à tubes d'eau et installations auxiliaires - Partie

8: Exigences pour les équipements de chauffe pour combustibles gazeux et liquides de la chaudière

Wasserrohrkessel und Anlagenkomponenten - Teil 8: Anforderungen an Feuerungsanlagen für flüssige und

gasförmige für den Kessel

This European Standard was approved by CEN on 15 May 2002.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E F Ü R N O R M U N G

Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2002 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members.

Ref No EN 12952-8:2002 E

Page

Foreword 3

1 Scope 5

1.1 Firing systems 5

1.2 Fuels 5

1.3 Operation 5

2 Normative references 5

3 Terms and definitions 6

4 Fuel supply 10

4.1 General 10

4.2 Fuel transfer and preparation 10

4.3 Fuel lines 10

4.4 Safety shut-off devices (Safety trip valves) 12

5 Equipment for air supply and flue gas discharge 13

5.1 Air supply 13

5.2 Air/fuel ratio 14

5.3 Flue gas discharge 14

6 Firing system 15

6.1 Burners 15

6.2 Flue gas recirculation 15

6.3 Control and monitoring 16

6.4 Electrical equipment 17

6.5 Safety precautions 17

6.6 Common stack for several firing systems 18

7 Operating manual 18

8 Particular requirements for firing systems burning gaseous fuels with high relative density 18

8.1 Main firing systems 18

8.2 Ignition burner systems 19

Annex A (normative) Chemical recovery boiler (black liquor boiler) 20

A.1 General 20

A.2 Additional requirements for the firing system for black liquor in the chemical recovery boiler 20

A.3 Special requirements for oil- or gas firing for chemical recovery boilers 21

Annex B (informative) Operational requirements for permanent supervised firing systems for liquid and gaseous fuels 22

B.1 General 22

B.2 Operation 22

B.3 Fuel preparation 22

B.4 Safety shutoff devices 22

B.5 Air/fuel ratio 22

B.6 Modification of firing, burner or air/fuel ratio setting 22

B.7 Control and monitoring 23

B.8 Purging, start-up and shut down 23

B.9 Emergency operation 23

B.10 Operating and maintenance instructions 23

B.11 Firing systems burning gaseous fuels with high relative density 23

Annex ZA (informative) Clauses of this European Standard addressing essential safety requirements or other provisions of the Pressure Equipment Directives 25

Bibliography 26

For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this standard.

This European Standard shall be given the status of a national standard, either by publication of an identical text or

by endorsement, at the latest by November 2002, and conflicting national standards shall be withdrawn at the latest

by November 2002

The European Standard EN 12952 concerning “Water-tube boilers and auxiliary installations” consists of thefollowing Parts:

Part 1: General

Part 2: Materials for pressure parts of boilers and accessories

Part 3: Design and calculation for pressure parts

Part 4: In-service boiler life expectancy calculations

Part 5: Workmanship and construction of pressure parts of the boiler

Part 6: Inspection during construction, documentation and marking of pressure parts of the boiler

Part 7: Requirements for equipment for the boiler

Part 8: Requirements for firing systems for liquid and gaseous fuels for the boiler

Part 9: Requirements for firing systems for pulverized solid fuels for the boiler

Part 10: Requirements for safeguards against excessive pressure

Part 11: Requirements for limiting devices of the boiler and accessories

Part 12: Requirements for boiler feedwater and boiler water quality

Part 13: Requirements for flue gas cleaning systems

Part 14: Requirements for flue gas DENOX-systems

Part 15: Acceptance tests

Part 16: Requirements for grate and fluidised bed firing systems for solid fuels for the boiler

CR 12952 Part 17: Guideline for the involvement of an inspection body independent of the manufacturer

Although, these Parts can be obtained separately, it should be recognized that the Parts are interdependent Assuch, the design and manufacture of water-tube boilers requires the application of more than one Part in order forthe requirements of the standard to be satisfactorily fulfilled

NOTE Parts 4 and 15 are not applicable during the design, construction and installation stages.

Annex A of this European Standard is normative and Annex B is informative

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain,Sweden, Switzerland and the United Kingdom

NOTE 1 This standard is not applicable to coil type boilers (flash boilers/small boilers) that use burners in accordance with

EN 12953-7 apply for single burner installations

1.2 NOTE 2 This standard is not applicable to the storage of liquid fuels and to transfer

stations of long-distance gas pipelines Fuels

This Part of this European Standard specifies requirements, which cover the use of liquid and gaseous fuels asdefined in this standard Fuels deviating from standardized commercially available types may require additional oralternative safety measures For black liquor these safety measures are given in Annex A

1.3 Operation

This Part of this European Standard specifies requirements for operational equipment in clauses 4 to 8 which apply

to steam boilers and hot water generators with permanent supervision by properly trained personnel familiar withthe special conditions of the firing system and the type of fuel being fired

2 Normative references

This European Standard incorporates by dated or undated reference, provisions from other publications Thesenormative references are cited at the appropriate places in the text and the publications are listed hereafter Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision For undated references the latest edition of thepublication referred to applies (including amendments)

EN 161, Automatic shut-off valves for gas burners and gas appliances

EN 264, Safety shut-off devices for combustion plants using liquid fuels — Safety requirements and testing

EN 287-1, Approval testing of welders — Fusion welding — Part 1: Steels

EN 751-1, Sealing materials for metallic threaded joints in contact with 1st, 2nd and 3rd family gases and hotwater — Part 1: Anaerobic jointing compounds

EN 751-2, Sealing materials for metallic threaded joints in contact with 1st, 2nd and 3rd family gases and hotwater — Part 2: Non-hardening jointing compounds

EN 751-3, Sealing materials for metallic threaded joints in contact with 1st, 2nd and 3rd family gases and hotwater — Part 3: Unsintered PTFE tapes

EN 1044, Brazing — Filler metals

pressure parts of the boiler

EN 13480-2, Metallic industrial piping — Part 2: Materials

prEN 50156-1, Electrical equipment for furnaces and ancillary equipment — Part 1: Requirements for applicationdesign and installation.

EN ISO 3677, Filler metal for soft soldering, brazing and braze welding — Designation (ISO 3677:1992)

ISO 7-1, Pipe threads where pressure-tight joints are made on the threads — Part 1: Dimensions, tolerances anddesignation (ISO 7-1:1994)

ISO 228-1, Pipe threads where pressure-tight joints are not made on the threads — Part 1: Dimensions, tolerancesand designation (ISO 228-1:2000)

3 Terms and definitions

For the purposes of this Part of this European Standard and the following terms and definitions apply

3.1

black liquor

spent liquor from the pulp cook

3.2

black liquor gun

device for the introduction of the black liquor as a spray of droplets into the furnace The black liquor gun is not aburner

3.3

high volume low concentration odorous gas

mixtures of air and a low concentration of odorous gases collected from the pulp mill processes, where theconcentration of the combustible odorous gas is always kept below the lower explosion limit

chemical recovery boiler start up burner

oil- or gasfired burner mainly intended for the initiation of the black liquor combustion process The chemicalrecovery boiler start up burners are located in and integrated with a combustion air register, like the primary or thesecondary air register of the furnace Thus they have no individual air supply and no individual combustion aircontrol

burner which maintains a proper permanent ignition source for one or a group of other non-monitored burners

burner group

burners operated in unison and controlled jointly One of the burners can be a master burner

3.6

burner management system

system that performs a predetermined sequence of actions and always operates in conjunction with a flamemonitor that reacts to signals from control and safety devices, gives control commands, controls the start-upsequence, supervises the burner operation, and manages controlled shutdown and lockout

3.7

firing system

total equipment required for the combustion of fuels including the installations for the storage, preparation, andsupply of fuels, the combustion air supply, the burner(s), the flue gas discharge, and all related control andmonitoring devices A flue gas recirculation system can be an integral part of the firing system

3.8

firing system heat input

heat input into the combustion chamber according to the mass flow of the fuel supplied multiplied by the netcalorific value

flue gas recirculation

return of flue gas from downstream of the flame zone or from the flue gas exit by hydrodynamic pressure difference

or a separate fan into the air register of the burner or directly into the combustion chamber

3.11

implosion

unintentional instantaneous negative pressure build-up caused, for example, by an explosion in a confined space,

by rapid closing of dampers, or by rapid reduction in temperature (flame out)

master fuel trip

device for rapid automatic shut-off of all fuel supplies to the boiler area and electrical igniters in the event of dangerwhich may act by automatic, manual or emergency switch initiation even if a possible electrical or mechanical faultoccurs

3.15

maximum heat input of the firing system

heat input including the reserve required for load control at which the boiler can be safely operated

3.16

maximum firing rate of the burners

firing rate at which the burner may be operated

monitor

limit transducer, which senses the reaching of a fixed limit value and initiates an alarm and/or a cut out The outputsignal is only cancelled if the cause of the alarm has been removed and the value has returned to within its fixedlimits

3.18

multi-fuel firing system

firing system where, in a common combustion chamber, more than one fuel can be burnt simultaneously oralternately by separate or multi-fuel burners

3.19

purge of burner guns

carried out after shutdown of a burner to ensure the removal of residual fuel by the introduction of steam orpressurized air into the fuel lines downstream of the shut-off devices

3.20

purging of the flue gas passes

forced flow of air through the combustion chamber, flue gas passes, and associated ducts which effectivelyremoves any gaseous combustibles and replace them with air

3.21

quick-acting shut-off device

safety trip valve which closes within 1 s

with relative density below 1,3 e.g natural gas, coke-oven gas, blast-furnace gas

NOTE Natural gas in accordance with ISO 6976

safety shut-off device

safety trip valve

valve which automatically and totally cuts off the fuel supply

ignition time: When starting-up the burner, the period of time between the first fuel entering the combustion

chamber and the first indication of the flame by the flame monitor

3.28.2

ignition safety time: When starting-up the burner, the period of time between the first fuel entering the combustion

chamber and the de-energizing of the quick-acting shut-off device if the flame monitor does not indicate a flame

3.28.3

main burner safety time: When there is an ignition safety time applicable to an igniter burner only the period of

time between the first fuel of the main burner entering the combustion chamber and the de energizing of the quickacting shut-off device of the main burner if the flame monitor does not indicate a flame

3.28.4

extinction safety time: During operation of the burner the period of time between the extinction of the flame and

the de-energizing of the quick-acting shut-off device

3.29

transfer station

one or more lines each including a pressure control valve and a quick-acting shut-off device for the protection of thedownstream supply lines and the connected appliances against overpressure The transfer station may comprise ofheating and filtering equipment for the gas supply, measuring equipment for flow and calorific value and noiseabatement devices

4 Fuel supply

4.1 General

For multifuel firing systems using separate or combined burners these requirements shall apply to the oil and/orgas firing part involved

Where several fuels are burnt simultaneously, improved safety measures can be necessary, especially in respect

to limitation of heat input into the firing system and proper air supply to the individual fuels

4.2 Fuel transfer and preparation

4.2.1 The fuel supply line shall be equipped with a reliable quick-acting safety shut-off device (master fuel trip)which shall be positioned in a safe location It shall reliably cut off the fuel supply to the boiler room or the boilerarea and shall be operable manually or by remote control or by an emergency switch (see 6.5)

4.2.2 Some liquid fuels, such as heavy fuel oil, require preheating to achieve the viscosity required for properatomisation Where national oil quality standards are in existence, these shall be observed

Any heat source other than open flames, that can be cut off immediately if required, and the rating of which can beautomatically controlled, shall be used for oil preheating

In the unpressurized condition the fuel oil temperature shall not attain the fuel oil flash point and in any case shallnot exceed 90 C

To attain the temperature for the required atomisation viscosity, pressure type preheaters shall be used Themaximum temperature shall be at least 5 C below the boiling temperature of water in the oil at the connectedpressure

Each fuel oil preheating system shall be automatically temperature controlled A temperature indicator shall befitted downstream of the preheating system Oil temperatures below the temperature prescribed upstream of eachburner or burner group shall shut off the burner or burner group

Oil temperatures above the temperature prescribed upstream of the burners shall shut off the heat supply of thepreheater or other suitable measures shall be taken

For pressurized preheaters, the requirements for pressure vessels shall be applied Functioning of the necessaryoverpressure protection shall be ensured by suitable temperature control Any escaping oil shall be safelydischarged

Where steam heating coils for oil preheating are installed and the condensate is returned to the boiler, the heatingcoils shall be safely dimensioned and tested to ensure that no oil can escape into the condensate A means ofchecking the condensate for oil content shall be provided When steam lines are connected to fuel oil lines forpurging purposes or for steam assisted atomisation, the line shall be protected against back flow from the higherpressured fluid

4.2.3 For gaseous fuels, a pressure controller shall be provided in the supply line to each firing system unlessthis task is performed by the transfer station

The reliability of the gas pressure controller and its related safety device shall be proved by component testing or

an individual test within the system acceptance test

4.3 Fuel lines

4.3.1 Fuel lines, including gaskets and valves shall be designed and laid out to withstand the mechanical,chemical and thermal loads to which they are exposed in service Only fire resistant piping material shall bepermitted

4.3.2 The fuel lines shall be tight and properly fixed In systems subjected to vibrations the resulting stressesshall be minimized to avoid leakage

4.3.3 Connections shall preferably be welded or brazed Threaded joints or bolted flanges shall also be used.Welded joints shall only be made by welders approved to the appropriate standards (see EN 287-1).

Brazed joints shall be permitted in oil lines for pipe diameters < DN 25 and/or operating pressure < 10 bar providedthe brazers shall be approved and the filler materials have been certified, e.g by a certificate of a specializedmanufacturer (see EN ISO 3677 and EN 1044) They shall also be permitted in gas lines for pipe diameter < DN 80and/or operating pressure < 5 bar

For threaded joints the requirements of ISO 7-1 and ISO 228-1 shall apply Thread joints shall be used up to DN 50and shall be sealed by metal to metal contact, or sealed by non-hardening sealing materials Hemp shall only beused as a sealant support The use of PTFE sealing materials shall be restricted as indicated in EN 751

Compression-type fittings in accordance with appropriate standards may be used up to DN 25, provided they shall

be not to be dismantled for maintenance purposes

Flanged connections on apparatus, equipment and valves shall be permitted for all diameters

Material shall be in accordance with EN 13480-2

4.3.4 Flexible lines shall be used for connecting the burner to the fixed piping For fuel oil in the preheated stateonly jacketed metallic hoses shall be permitted

Furthermore, flexible lines may be used instead of expansion joints at protected locations For oil, these linesshould be jacketed metallic hoses, otherwise they shall be provided with a protective device consisting of e.g adouble line with an oil monitor which switches off the oil supply pump in case of an oil leakage For gas, these linesshall be corrugated steel pipes

All flexible lines shall be as short as possible, be readily visible, and shall be installed with adequate bending radii.The flexible lines and the connections shall carry the manufacturer's symbols and indication of the nominalpressure The design pressure shall be at least 1,5 times the maximum allowable pressure The lines shall beprotected against unacceptable external heating

4.3.5 To protect fuel lines against unacceptable high pressure, automatic control and safety devices shall beprovided For oil lines, pressure relief valves shall be installed Protection of oil pumps and the effect of pressurerise in lines between closed shut-off devices due to heating shall also be taken into consideration For gas lines thenecessary protection against overpressure shall be performed by a safety shut-off valve plus a pressure reliefvalve

4.3.6 On completion of installation, all fuel piping including valves and other equipment within the fuel lines up tothe burner nozzles shall be cleaned to remove any weld spatter, corrosion products and foreign matter The typeand performance of the cleaning process shall also be recorded In addition leakage testing and strength testing inaccordance with a good engineering practice shall be performed

For oil and gas, each safety shut-off device shall be subject to internal leakage testing, to confirm that fuels doesnot leak through the device

After any welding work or replacement of components on fuel lines, the aforementioned tests shall be repeated.The performance of the tests shall be authenticated by certificates recording the test procedure, the medium used,the test pressure and the test results obtained

The certificates shall be issued by the person responsible for the testing

4.3.7 Gas escape lines for intermediate venting and for purging or charging shall be arranged such, that theescaping gas is either reliably ignited and burnt off with a flame trap installed in the pipe where the gases aretransferred to the burning device or is safely discharged to the atmosphere if unburnt The joining together of theselines shall only permitted if no dangerous operating conditions are expected When necessary, gas escape linesshall be equipped with the necessary draining facilities Connections for test devices shall be provided so that theadequacy of venting can be checked

4.4 Safety shut-off devices (Safety trip valves)

4.4.1 The fuel supply line shall be equipped with two safety shut-off devices arranged in series immediatelyupstream of each burner, or burner group One of these safety shut-off devices shall be of quick-acting design, andcorrespond with group A of EN 161 The second safety shut-off device may also be used as a fuel mass flowactuator for the control of the firing rate of the burner, but its closing time shall not exceed 5 s For gas, thesedevices shall also correspond with group A of EN 161

The fuel supply lines shall be provided with devices for removing those impurities from the fuel which may impairthe functioning of the safety shut-off devices

The safety shut-off devices shall automatically and reliably cut off the fuel supply to the burner An adequateauxiliary power source, e.g a spring, shall be permanently available to assure this occurs The reliability of theautomatic shut-off devices shall be proved This proof shall be performed by component testing as specified in

EN 264 for liquid fuels or in EN 161 for gaseous fuels

Leakage testing of each of the safety shut-off devices shall be possible in its installed condition at regular timeintervals For gas, the connection line between these two safety shut-off devices shall be equipped with anintermediate venting or a leakage detection device

Oil burners of special design such as return-flow atomizers, burners with a tip shut-off device etc., using return-flowlines shall be provided with additional double shut-off valves in these lines

For gaseous fuels with low calorific value and with very low supply pressure, e.g below 200 mbar, the duty of theaforementioned safety shut-off devices may be performed by equivalent devices, e.g rotary slide valves withsealing water, or double-seat valves with an intermediate venting

4.4.2 The fuel supply shall not be released during the start-up operation until

a) the ignition device is ready for ignition (see 6.1.5);

b) purging is completed (see 6.5.2 and 6.5.3) or there is fire in the combustion chamber;

c) the minimum preheating temperature required for the oil has been reached;

d) the safety shut-off devices proved to be closed or the leakage test proved to be successful;

e) the fuel control valve(s) and the air damper(s) are in the start position;

f) functional control of the flame monitor proves no defect to be present, and in the case of individual flamemonitoring detects there is no flame present prior to ignition

4.4.3 The automatic safety shut-off devices shall be operated such that they do not release the fuel supply to theburners during the start-up operation, and cut it off during operation whenever

1) the control power for the safety devices fails;

2) the flue gas damper is not fully open or the induced draught fan fails, or the combustion chamber pressure is tohigh;

3) the combustion air fails to be supplied (see 5.1.1);

4) the combustion air flow is insufficient (see 5.2);

5) the pressure is:

a) the pressure of the atomising medium is less than that required (for steam and pressure-air atomizers),b) the fuel pressure is less than the minimum pressure (for gas burners, and oil burners with pressureatomizers),

c) the maximum fuel return flow pressure is exceeded (for oil burners with return-flow atomizers),

6) the speed of rotation of the atomising cup is insufficient (for oil burners with rotary atomizers) Where theatomising cup is on the same shaft as the fan, it will suffice to monitor the fan air pressure

7) there is an unacceptably high fuel flow rate in the burners; if necessary cut-off may be effected with a delay intime;

8) the ratio of flue gas recirculation flow/burner firing rate is unacceptable (see 6.2);

9) the flue gas recirculation fan, if fitted, fails and the ratio of flue gas recirculation flow/burner firing rate isunacceptable (see 6.2);

10) cut off switches are actuated;

11) the emergency switch is actuated (see 6.4.3);

12) any of the limiters responds (e.g for water level, temperature);

13) burners (also burner guns) which can be swung out or retracted without the aid of tools are swung out orretracted;

14) the flame monitor responds due to the absence or extinction of the flame

4.4.4 As soon as the causes for conditions a) to f) of 4.4.2 and 1) to 9) of 4.4.3 have been removed, the burnersmay automatically restart by following the regular start-up programme if this shall be permitted for the plant

Where the conditions 10) to 14) of 4.4.3 apply, lock out shall always occur Restarting shall only be possible bymanual intervention

Where plants have multiple burners, if the conditions mentioned in 1), 3), 4), 5), 7), 8), 9), 10) and 14) of 4.4.3occur only on one burner or one burner group, it shall suffice if the fuel supply to the respective burner or burnergroup is not released during start-up and is interrupted during operation This shall also apply to 12) of 4.4.3 if ahazardous escape of flames and flue gases is prevented

4.4.5 One manually operated emergency shut-off device shall be arranged immediately upstream of the burner,

or each burner group A manually operated emergency shut-off device is for example:

4.4.6 All safety related valves shall be durably marked with regard to their intended use

5 Equipment for air supply and flue gas discharge

5.1 Air supply

5.1.1 The combustion air fan shall be monitored by the air flow and one of the following criteria:

a) speed of the forced draught fan;

b) pressure downstream of the forced draught fan;