prEN 12952-8

SLOVENSKI STANDARD
oSIST prEN 12952-8:2020
01-marec-2020
Vodocevni kotli in pomožne napeljave - 8. del: Zahteve za gorilnike kotlov na
tekoča in plinasta goriva

Water-tube boilers and auxiliary installations - Part 8: Requirements for firing systems for

Chaudières à tubes d'eau et installations auxiliaires - Partie 8 : Exigences pour les

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

Chaudières à tubes d'eau et installations auxiliaires - Wasserrohrkessel und Anlagenkomponenten - Teil 8:

Partie 8 : Exigences pour les équipements de chauffe Anforderungen an Feuerungsanlagen für flüssige und

pour combustibles gazeux et liquides de la chaudière gasförmige Brennstoffe für den Kessel

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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 CEN-CENELEC

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 12952-8:2020 E

European foreword ...................................................................................................................................................... 4

1 Scope .................................................................................................................................................................... 6

1.1 Firing systems .................................................................................................................................................. 6

1.2 Fuels ..................................................................................................................................................................... 6

2 Normative references .................................................................................................................................... 6

3 Terms and definitions ................................................................................................................................... 7

4 Fuel supply ...................................................................................................................................................... 11

4.1 General.............................................................................................................................................................. 11

4.2 Fuel transfer and preparation .................................................................................................................. 11

4.3 Fuel lines .......................................................................................................................................................... 12

4.4 Safety shut-off devices (Safety trip valves) .......................................................................................... 13

5 General.............................................................................................................................................................. 15

5.1 Air supply ......................................................................................................................................................... 15

5.2 Air/fuel ratio .................................................................................................................................................. 16

5.3 Flue gas discharge ......................................................................................................................................... 16

6 Firing system .................................................................................................................................................. 16

6.1 Burners ............................................................................................................................................................. 16

6.2 Flue gas recirculation .................................................................................................................................. 17

6.3 Control and monitoring .............................................................................................................................. 18

6.4 Electrical equipment.................................................................................................................................... 19

6.5 Safety precautions ........................................................................................................................................ 19

6.6 Common stack for several firing systems ............................................................................................ 20

7 Operating manual ......................................................................................................................................... 20

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

density .............................................................................................................................................................. 20

8.1 Main firing systems ...................................................................................................................................... 20

8.1.1 Supply of gases ............................................................................................................................................... 20

8.1.2 Safety shut-off device ................................................................................................................................... 20

8.2 Ignition burner systems ............................................................................................................................. 21

Annex A (normative) Chemical recovery boiler (black liquor boiler) .................................................... 22

A.1 General.............................................................................................................................................................. 22

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

recovery boiler .............................................................................................................................................. 22

A.3 Special requirements for oil- or gas firing for chemical recovery boilers ............................... 23

A.3.1 General.............................................................................................................................................................. 23

A.3.2 Special requirements for start-up burners ......................................................................................... 23

A.3.3 Special requirements for the firing of odorous gases ...................................................................... 24

Annex B (normative) Gas turbines in combination with heat recovery steam generators ............ 25

B.1 General ............................................................................................................................................................. 25

B.2 Additional requirements for gas turbines in combination with heat recovery steam

generators ....................................................................................................................................................... 25

B.2.1 Safety shut-off devices ................................................................................................................................ 25

B.2.2 Electrical equipment ................................................................................................................................... 25

B.2.3 Bypass operation of the heat recovery boiler .................................................................................... 25

B.2.4 Switching from gas turbine operation to fresh air operation at secondary firing ................ 25

Annex C (informative) Operational requirements for permanent supervised firing systems

for liquid and gaseous fuels ...................................................................................................................... 27

C.1 General ............................................................................................................................................................. 27

C.2 Operation ......................................................................................................................................................... 27

C.3 Fuel preparation ........................................................................................................................................... 27

C.4 Safety shutoff devices .................................................................................................................................. 27

C.5 Air/fuel ratio .................................................................................................................................................. 27

C.6 Modification of firing, burner or air/fuel ratio setting ................................................................... 27

C.7 Control and monitoring .............................................................................................................................. 28

C.8 Emergency operation .................................................................................................................................. 28

C.9 Operating and maintenance instructions ............................................................................................ 28

C.10 Firing systems burning gaseous fuels with high relative density ............................................... 28

Annex D (informative) Significant technical changes between this document and the

previous edition ............................................................................................................................................ 30

Annex ZA (informative) Relationship between this European Standard and the essential

requirements of Directive 2014/68/EU aimed to be covered ..................................................... 31

Bibliography ................................................................................................................................................................. 32

This document (prEN 12952-8:2020) has been prepared by Technical Committee CEN/TC 269 “Shell

EN 12952 series “Water-tube boilers and auxiliary installations” consists of the following Parts:

• Part 6: Inspection during construction, documentation and marking of pressure parts of 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 14: Requirements for flue gas DENOX systems using liquefied pressurized ammonia and ammonia

• Part 16: Requirements for grate and fluidized-bed firing systems for solid fuels for the boiler;

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

Although these parts may be obtained separately, it should be recognized that the parts are inter-

dependent. As such, the design and manufacture of water-tube boilers requires the application of more

than one part in order for the requirements of the document to be satisfactorily fulfilled.

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

This European Standard has been prepared under a mandate given to CEN by the European

Commission and the European Free Trade Association, and supports essential requirements of

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

This document specifies requirements, for liquid and gaseous fuel firing systems of steam boilers and

These requirements also apply to firing systems of chemical recovery boilers (black liquor boilers) with

These requirements also apply to gas turbines in combination with fired/unfired heat recovery steam

generators with the additions and amendments specified in Annex B of this document.

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

NOTE 2 This standard is not applicable to the storage of liquid fuels and to transfer stations of long-distance

This document specifies requirements, which cover the use of liquid and gaseous fuels as defined in this

standard. Fuels deviating from standardized commercially available types may require additional or

alternative safety measures. For black liquor these safety measures are given in Annex A.

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

EN 161:2011+A3:2013, Automatic shut-off valves for gas burners and gas appliances

EN 751 (series), Sealing materials for metallic threaded joints in contact with 1st, 2nd and 3rd family

EN 16678:2015, Safety and control devices for gas burners and gas burning appliances - Automatic shut-

EN ISO 23553-1:2014, Safety and control devices for oil burners and oil-burning appliances - Particular

prEN 12952-5:2020, Water-tube boilers and auxiliary installations — Part 5: Workmanship and

EN 50156-1:2015, Electrical equipment for furnaces and ancillary equipment - Part 1: Requirements for

EN ISO 3677:2016, Filler metal for soldering and brazing - Designation (ISO 3677:2016)

EN ISO 9606-1:2017, Qualification testing of welders - Fusion welding - Part 1: Steels (ISO 9606-1:2012

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

EN ISO 228-1:2003, Pipe threads where pressure-tight joints are not made on the threads —

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

device for the introduction of the black liquor as a spray of droplets into the furnace

mixtures of air and a low concentration of odorous gases collected from the pulp mill processes, where

the concentration of the combustible odorous gas is always kept below the lower explosion limit

devices (including main or igniter burners) for the introduction of fuel and air into a combustion

chamber of a steam generator at required velocities, turbulence and local fuel concentration to establish

oil- or gasfired burner mainly intended for the initiation of the black liquor combustion process

Note 1 to entry: The chemical recovery boiler start up burners are located in and integrated with a combustion air

register, like the primary or the secondary air register of the furnace. Thus they have no individual air supply and

burners in which more than one fuel is burned either simultaneously or alternately

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

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

system that performs a predetermined sequence of actions and always operates in conjunction with a

flame monitor that reacts to signals from control and safety devices, gives control commands, controls

the start-up sequence, supervises the burner operation, and manages controlled shutdown and lockout

total equipment required for the combustion of fuels including the installations for the storage,

preparation, and supply of fuels, the combustion air supply, the burner(s), the flue gas discharge, and all

Note 1 to entry: A flue gas recirculation system can be an integral part of the firing system.

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

device which detects the presence or absence or break-away of the flame and transmits a signal to the

control device, and generally consists of a sensing device (with amplifier if necessary) and switching

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

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)

transducer, which, on reaching a fixed value (e.g. pressure, temperature, flow, water level) is used to

interrupt and lock-out the energy supply, and requires manual unlocking before restart

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

limit transducer, which senses the reaching of a fixed limit value and initiates an alarm and/or a cut out

Note 1 to entry: The output signal is only cancelled if the cause of the alarm has been removed and the value has

firing system where, in a common combustion chamber, more than one fuel can be burnt

carried out after shutdown of a burner to ensure the removal of residual fuel by the introduction of

forced flow of air through the combustion chamber, flue gas passes, and associated ducts which

safety trip valve which closes within 1 s according to EN 161:2011+A3:2013 or EN 264

ratio of the density of the gas to the density of dry air under equal conditions of pressure and

fuels include light fuel oils, and heavy fuel oils which need preheating for proper atomisation. For

improvement of atomisation, emulsions of heavy fuel oil with water may be used with appropriate

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

with relative densities exceeding 1,3 e.g. liquefied petroleum gases, the main components of which are

operation where fuel supply shut-off is initiated within 1 s at the latest after extinction of the flame

during operation, and a directly following attempt of re-ignition is automatically made in compliance

Note 1 to entry: This operation ends with the operating condition being reached or, if the flame is not ignited after

oil burners, where a portion of the quantity of oil supplied to the burner via the flow line does not flow

from a burner gun vortex chamber into the combustion chamber, but flows backwards into the storage

time taken from the occurrence of an unsafe operating condition (for example, flame interrupt during

Note 1 to entry: The reaction time of the actuating element is to be considered separately.

when starting-up the burner, the period of time between the first fuel entering the combustion chamber

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

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 quick acting

shut-off device of the main burner if the flame monitor does not indicate a flame

during operation of the burner the period of time between the extinction of the flame and the de-

one or more lines each including a pressure control valve and a quick-acting shut-off device for the

protection of the downstream supply lines and the connected appliances against overpressure

Note 1 to entry: The transfer station may comprise of heating and filtering equipment for the gas supply,

For multifuel firing systems using separate or combined burners these requirements shall apply to the

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.

4.2.1 The fuel supply line shall be equipped with a reliable quick-acting safety shut-off device which

shall be positioned in a safe location. It shall reliably cut off the fuel supply to the boiler room or the

boiler area and shall be operable by remote control or by an emergency switch (see 6.4.2).

4.2.2 Some liquid fuels, such as heavy fuel oil, require preheating to achieve the viscosity required for

proper atomisation. 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

In the unpressurized condition the fuel oil temperature shall not attain the fuel oil flash point.

To attain the temperature for the required atomisation viscosity, pressure type preheaters shall be

used. The maximum temperature shall be at least 5 °C below the boiling temperature of water in the oil

Each fuel oil preheating system shall be automatically temperature controlled. A temperature indicator

shall be fitted downstream of the preheating system. Oil temperatures below the temperature

prescribed upstream of each burner 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

For pressurized preheaters, the requirements for pressure vessels shall be applied. Functioning of the

necessary overpressure protection shall be ensured by suitable temperature control. Any escaping oil

Where steam heating coils for oil preheating are installed and the condensate is returned to the boiler,