EN 12952-9:2022

SLOVENSKI STANDARD
01-december-2022
Nadomešča:
SIST EN 12952-9:2003
Vodocevni kotli in pomožne napeljave - 9. del: Zahteve za gorilnike kotlov na
prašnata goriva
Water-tube boilers and auxiliary installations - Part 9: Requirements for firing systems for
pulverized solid fuels for the boiler
Wasserrohrkessel und Anlagenkomponenten - Teil 9: Anforderungen an
Staubfeuerungsanlagen für den Kessel
Chaudières à tubes d’eau et installations auxiliaires - Partie 9: Exigences pour les
équipements de chauffe pour combustibles solides de la chaudière
Ta slovenski standard je istoveten z: EN 12952-9:2022
ICS:
27.060.30 Grelniki vode in prenosniki Boilers and heat exchangers
toplote
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 12952-9
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2022
EUROPÄISCHE NORM
ICS 27.040 Supersedes EN 12952-9:2002
English Version
Water-tube boilers and auxiliary installations - Part 9:
Requirements for firing systems for pulverized solid fuels
for the boiler
Chaudières à tubes d'eau et installations auxiliaires - Wasserrohrkessel und Anlagenkomponenten - Teil 9:
Partie 9: Exigences pour les équipements de chauffe Anforderungen an Staubfeuerungsanlagen für den
pour combustibles solides de la chaudière Kessel
This European Standard was approved by CEN on 15 August 2022.

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 CEN-CENELEC 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 CEN-CENELEC Management
Centre has the same status as the official versions.

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, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12952-9:2022 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
1 Scope . 6
1.1 Firing systems . 6
1.2 Fuels . 6
1.3 Operation . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Fuel bunkers and conveying plant . 11
4.1 General. 11
4.2 Conveying plant . 11
4.3 Solid fuel bunkers . 11
5 Pulverizing system and pulverized fuel system . 12
5.1 Introduction . 12
5.2 Solid fuel feeders . 12
5.3 Mills . 12
5.4 Pulverized fuel bins . 13
5.5 Pulverized fuel supply pipes and shut-off devices . 13
6 Explosion prevention measures for pulverizing systems and pulverized fuel systems
................................................................................................................................................................... 14
6.1 General. 14
6.2 Plants operated without inert gas protection . 15
6.3 Plants operated with inert gas protection . 15
7 Equipment for air supply and flue gas discharge . 16
7.1 Air supply . 16
7.2 Air/fuel ratio . 17
7.3 Flue gas discharge . 17
8 Firing system . 17
8.1 General. 17
8.2 Burners for pulverized fuel . 18
8.3 Flue gas recirculation . 18
8.4 Monitoring and control . 18
8.5 Electrical equipment. 19
8.6 Safety precautions . 19
8.6.1 Purging of the flue gas passes and lighting-up . 19
8.6.2 Start-up . 20
8.6.3 Operation . 20
8.6.4 Shutting down of direct-firing systems . 20
8.6.5 Shutting down of indirect-firing systems . 22
9 Ash extraction plant . 23
10 Operation and maintenance . 23
10.1 General. 23
10.2 Operating instructions . 23
Annex A (informative) Operational requirements for permanently supervised firing system
for pulverized fuel . 24
A.1 General . 24
A.2 Operation . 24
A.3 Mills . 24
A.4 Air/fuel ratio . 24
A.5 Firing system . 24
A.5.1 Combustion residues . 24
A.5.2 Modification of the firing system setting . 24
A.5.3 Safety precautions . 24
A.5.4 Operation . 25
A.6 Operating and maintenance . 25
Annex B (informative) Significant technical changes between this document and the
previous edition . 26
Annex ZA (informative) Relationship between this European Standard and the essential
requirements of Directive 2014/68/EU aimed to be covered . 27
Bibliography . 28
European foreword
This document (EN 12952-9:2022) has been prepared by Technical Committee CEN/TC 269 “Shell and
water-tube boilers”, the secretariat of which is held by DIN.
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 April 2023, and conflicting national standards shall be
withdrawn at the latest by April 2023.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 12952-9:2002.
The technical modifications in comparison with the previous edition are listed in Annex B.
The EN 12952 series concerning water-tube boilers and auxiliary installations consists of the following
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 using liquefied pressurized ammonia and ammonia
water solution;
• Part 15: Acceptance tests;
• 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
manufacturer.
• Part 18: Operating instructions
Although these parts can 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.
This document has been prepared under a Standardization Request given to CEN by the European
Commission and the European Free Trade Association, and supports essential requirements of EU
Directive(s) / Regulation(s).
For relationship with EU Directive(s) / Regulation(s), see informative Annex ZA, which is an integral part
of this document.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: 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, Türkiye and the United
Kingdom.
1 Scope
1.1 Firing systems
This document applies to pulverized fuel firing systems of steam boilers and hot water generators and
commences at the filling equipment for the boiler bunkers or for the pulverized fuel storage system and
ends at the ash extraction plant. For multifuel firing systems using separate or combined burners, these
requirements apply to the pulverized fuel firing part involved. For other fuels or firing systems used in
combination, other requirements apply, e.g. EN 12952-8:2022.
1.2 Fuels
These requirements cover the use of pulverized fuels (e.g. coke, anthracite, bituminous coal or hard coal,
lignite or brown coal, petrol coke, oil shale and pulverized bio mass) ranging from low to high volatile
matter content.
1.3 Operation
Requirements for operational equipment apply for steam boilers and hot water generators with
permanent supervision by properly trained persons.
As firing systems using pulverized fuel can be designed either as direct-firing or as indirect-firing
systems, operational requirements have to be differentiated. Annex A summarizes the operational
requirements for firing systems including the pulverizing system.
2 Normative references
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 1127-1:2019, Explosive atmospheres - Explosion prevention and protection - Part 1: Basic concepts and
methodology
EN ISO 4126-1:2013, Safety devices for protection against excessive pressure - Part 1: Safety valves
(ISO 4126-1:2013)
EN 12952-8:2022, Water-tube boilers and auxiliary installations — Part 8: Requirements for firing systems
for liquid and gaseous fuels for the boiler
EN 12952-18:2012, Water-tube boilers and auxiliary installations - Part 18: Operating instructions

As impacted by EN ISO 4126-1:2013/A1:2016 and EN ISO 4126-1:2013/A2:2019.
3 Terms and definitions
For the purposes of this document the terms and definitions given in EN 12952-8:2022 and the following
apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
back-up firing system
separate firing system to maintain safe ignition and stable combustion of the pulverized fuel
3.2
burner group
burners operated in forced unison and controlled jointly and the burners supplied by the same mill or
the same pulverized fuel feeder
3.3
burner management system
system which performs a predetermined sequence of actions and always operates in conjunction with a
flame monitor
Note 1 to entry: It reacts to signals from control and safety devices, gives control commands, controls the start-up
sequence, supervises the burner operation, and causes controlled shutdown and lock-out.
3.4
carrier gas
transport medium for pulverized fuel through mill, classifier, and pulverized fuel lines
Note 1 to entry: It can consist of primary air and/or inert gas.
3.5
clearing
removal of accumulation or settlement of pulverized fuel in the case of insufficient purging of the
pulverizing system
3.6
bunker
bunker for the storage of raw fuel for an individual mill
3.7
fuel feeder
installation for the extraction of fuel from the fuel bunker and the controlled feeding of fuel into the mill
3.8
combustion air
total air supplied to the firing system for combustion
3.9
conveying plant (fuel handling plant)
installation for conveying and distributing raw fuel to the individual fuel bunkers
3.10
direct-firing system
system where the fuel is ground and dried in the mill and then is fed directly to the burners
3.11
explosion
unintentional instantaneous combustion phenomenon occurring in a confined space with considerable
pressure build-up
Note 1 to entry: A weak explosion is called puffing.
3.12
explosion pressure resistant design
installation that is dimensioned so as to withstand the maximum explosion pressure without substaining
permanent deformation
3.13
explosion pressure shock resistant design
installation that is dimensioned so as to withstand the pressure surge occurring during an explosion
without rupture although permanent deformation can occur
3.14
firing rate during start-up
firing rate of a burner or a burner group forming part of a pulverizing system of a direct-fired system
during start-up
3.15
firing system
equipment for the combustion of fuels, including the installations for the storage in the boiler house,
preparation and supply of fuels, the combustion air supply, the burner(s), the flue gas discharge, and all
related control and monitoring devices
Note 1 to entry: A flue gas recirculation system can be installed as an integral part of the firing system.
3.16
firing system heat input
heat input into the combustion chamber
Note 1 to entry: Firing system heat input is normally calculated as the mass flow of the fuel supplied multiplied by
its net calorific value
3.17
flame monitor
device that detects the presence or absence of the flame and transmits a signal to the control device
Note 1 to entry: For a pulverized fuel firing system the flame can be defined as:
•  an individual flame of a single burner,
•  the flame of a burner group for instance all burners connected to a pulverizing system,
•  the flame of all burners in one combustion chamber.
3.18
flame-resistant material
combustible only when subjected to a continual supply of heat energy and extinguishes upon removal of
the ignition source
3.19
flue gas recirculation
return of flue gas from downstream of the flame zone or from the flue gas exit
Note 1 to entry: This can be achieved by pressure difference or the use of a separate fan or fans into the pulverizing
system, the air register of the burner, or directly into the combustion chamber.
3.20
implosion
unintentional instantaneous negative pressure build-up
Note 1 to entry: This can occur as a consequence of an explosion in a confined space, by rapid closing of dampers,
or by rapid reduction in temperature, e.g. flame out.
3.21
indirect-firing system
system where the fuel that has been ground and dried in the mill is intermediately stored in bins and the
vapours are separated
Note 1 to entry: The pulverized fuel is extracted from the bin and fed to the burners.
3.22
inerting
dilution of the oxygen content of an air/fuel mixture by the addition of an inert gas or steam to a level
where it is no longer ignitable
3.23
lighting-up equipment
facility to achieve safe ignition of pulverized fuel at the burner
Note 1 to entry: It may also be used for the provision of heat to initiate the drying process during start-up of a mill
in a direct-firing system.
3.24
limiter
transducer, which, on reaching a fixed value (e.g. pressure, temperature, flow, water level) is used to
interrupt and lockout the energy supply and requires manual unlocking before restart
3.25
lockout
interruption of the energy supply
Note 1 to entry: Manual unlocking is required before restart.
3.26
master fuel trip
device for rapid automatic shutoff of all fuel supplies to the boiler area and power to the electrical igniters
in the event of danger
3.27
maximum heat input of the firing system
maximum heat input including the reserves required for load control at which the firing system can be
safely operated including all reserves
3.28
mill
installation for grinding and drying the raw coal or bio mass and for classifying and conveying the
pulverized fuel
3.29
minimum heat input of the firing system
minimum heat input at which the firing system can be safely operated
3.30
monitor
limit transducer that 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
returned to within its fixed limits.
3.31
multi-fuel burner
burner in which more than one fuel is burned either simultaneously or alternately
3.32
multi-fuel firing system
firing system where, in a common combustion chamber, more than one fuel can be burned
simultaneously or alternately by separate or multi-fuel burners
3.33
primary air
part of the combustion air flow fed to the mill for the drying and conveying of pulverized fuel. This
primary air may be mixed with flue gas
3.34
pulverized fuel bin
bin (silo) for the intermediate storage of pulverized fuel
3.35
pulverized fuel burner
device for the introduction of fuel and air into a combustion chamber at required velocities, turbulence,
and local fuel concentration in order to establish and maintain proper ignition and stable combustion of
the fuel
3.36
pulverized fuel feeder
device for the controlled feeding of pulverized fuel from the pulverized fuel bin into the pulverized fuel
supply lines to the burners or other equipment
3.37
pulverizing system heat input
firing system heat input is the sum of the heat input from the single pulverizing systems
3.38
purging of the flue gas passes
flow of air through the combustion chamber, flue gas passes and associated ducts, which effectively
removes any gaseous combustibles and replaces them with air
3.39
purging of the pulverizing system
removal of any accumulation or settlement of pulverized fuel from inside the pulverizing system
3.40
safety time
time period during which the effectiveness of the safety device may be inhibited without a hazardous
condition occurring
4 Fuel bunkers and conveying plant
4.1 General
4.1.1 The conveyance of solid fuels, temporary storage in bunkers, and extraction shall be arranged
such that the flow of the fuel is ensured as far as possible.
4.1.2 Coarse solid fuel lumps, foreign matter, and tramp metal shall be removed to avoid damage or
blockage of the pulverizing system.
4.1.3 Dangerous areas of the fuel handling plant shall be marked by warning signs.
4.2 Conveying plant
4.2.1 Automatic facilities for the conveyance and distribution of solid fuel into the bunkers shall only
be started if visual and/or audible warning signals have been given beforehand. Precautions necessary
for the protection of personnel against injury by moving components shall be taken. Sufficient waiting
time between warning signal and start-up shall be provided (see A.4).
4.2.2 Several continuous conveyors arranged in series to form one conveying line shall be interlocked
such that the normal operation of any conveyor is possible only if the downstream conveyors are in
operation and the storage facility is ready to accept the fuel.
4.3 Solid fuel bunkers
4.3.1 The solid fuel bunkers shall be built to achieve uniform discharge by the selection of proper shape
and design in order to ensure a continuous uniform flow of the fuel and to avoid segregation.
4.3.2 To avoid ingress of hot air/gas into the bunker or the suction of leakage air into the pulverizing
system, a minimum fuel level shall be maintained in the bunker, unless other suitable measures are taken.
Monodisperse solid fuels like pelletized bio mass or biomass shells have very poor sealing behaviour. The
minimum fuel level is several times higher compared to coal. A decoupling element like a rotary gate
valve in the fuel down pipe between feeder and mill is recommended.
4.3.3 The minimum filling level of solid fuel bunkers shall be monitored and the feeder downstream of
the bunker shall be automatically stopped if the level falls below the predetermined level.
4.3.4 The inner surface of the solid fuel bunker roof shall be designed so as to avoid the accumulation
of dust and gas in dead pockets.
4.3.5 Bunker charging openings shall be guarded to prevent personnel from falling in (see A.5).
4.3.6 Fuel bunkers shall be equipped with fire fighting or fire prevention equipment.
5 Pulverizing system and pulverized fuel system
5.1 Introduction
5.1.1 The pulverizing system shall be readily accessible to enable cleaning operations to be carried out.
Pressurized systems shall be dust-tight and gas-tight.
5.1.2 All practicable steps should be taken to eliminate sites in the pulverizing system where pulverized
fuel and raw fuel can become lodged.
5.1.3 If there is a possibility of settlement of pulverized fuel on components that have become hot
during operation, facilities shall be provided for purging and clearing after shut-down.
5.1.4 To avoid the build up of electrostatic charges, all components shall be earthed unless forced and
faultless earthing is inherent in the design.
5.2 Solid fuel feeders
5.2.1 Solid fuel feeders and chutes shall be designed to provide a uniform flow of fuel into the mill.
5.2.2 Means shall be provided for monitoring the flow of fuel. In the event of loss of flow the conveyor
shall be automatically stopped (if necessary time delayed).
5.3 Mills
5.3.1 Mills shall be designed to withstand the mechanical and thermal loadings which occur during
operation.
Manufacturers of pulverised fuel systems shall follow the requirements of EN 1127-1:2019, where
applicable to ensure that the risks from dust explosions are eliminated or properly controlled.
5.3.2 The temperature downstream of the mill or classifier shall be continuously measured. If the
allowable operating temperature is exceeded, this shall be annunciated by an optical and/or accoustic
alarm. Suitable automatic devices shall prevent the upper temperature limit from being exceeded.
5.3.3 The allowable operating temperature and the upper temperature limit depend on design, mode
of operation and type of fuel. These temperatures shall be determined by the manufacturer upon
agreement with the user of the plant.
5.3.4 A means for inerting the pulverizing system shall be provided unless the risk of explosions and
fire hazards are prevented by other means, which are also valid in the case of upset conditions.
Appropriate precautions shall be adopted under these circumstances.
WARNING — If the pulverizing system cannot be made inert after an emergency shutdown, there will be
a risk of explosion during the shutdown period if the mill is disturbed, e.g. by opening of the mill, starting
the primary air supply, or starting the mill motor. Suitable inerting mediums are inert gases (e.g. flue gas
with low oxygen content) or preferably steam.
5.3.5 A fire-extinguishing system shall be provided.
5.3.6 To isolate the mill for repair purposes during boiler operation, appropriate shut-off devices shall
be provided upstream and downstream of the mill.
5.4 Pulverized fuel bins
5.4.1 Pulverized fuel shall only be stored in a dust-tight bin (silo). Charging and extraction devices shall
be designed to prevent the formation of a direct pathway between the contents of the silo and the
atmosphere during charging and extraction operations.
5.4.2 Pulverized fuel bins shall be readily accessible and shall be designed to aid discharge by the
selection of adequate shape and design. The design of the bins and their internals shall be such as to
prevent any inadmissible dust deposits from occurring. Bins and accessories shall be designed to prevent
the escape of pulverized fuel and inerting gas into the surrounding operating areas.
5.4.3 On completion of erection of the plant, a leakage test shall be performed by the manufacturer.
5.4.4 Access doors shall be secured against unintentional opening.
5.4.5 Pulverized fuel bins shall be protected against inadmissible heating from the outside. Negative
pressures which can occur shall be taken into account in the design.
5.4.6 Pulverized fuel bins shall be equipped with a connection for protective equipment, e.g. for the
introduction of inert gas or fire extinguishing foam.
Pulverized fuel bins shall be automatically monitored for interior fire, e.g. by gas measurements, unless
they are operated under inert conditions, or fire hazards are excluded by other means.
5.4.7 When a pulverized fuel bin is equipped with an additional discharge system, this system shall
only be designed as a closed system.
5.4.8 The filling level of the pulverized fuel bin shall be monitored.
5.4.9 With regard to fuel feeding into the burners the requirements given in 5.2 shall be applied
accordingly.
5.4.10 Shutoff devices shall be provided at the extraction points of pulverized fuel bins. The gaskets shall
be made of flame resistant material.
5.5 Pulverized fuel supply pipes and shut-off devices
5.5.1 Pulverized fuel shall only be conveyed in closed pipes which shall be dust-tight if operated under
internal pressure.
5.5.2 The transport velocities in the pulverized fuel pipes on a running mill shall be sufficient to
minimize deposition of pulverized fuel in the pipes and to avoid unsteady pulverized fuel delivery to the
burner.
This shall also apply to installations where the pulverized fuel flow is directed into multiple pipes.
5.5.3 All piping system components shall be capable of being purged of pulverized fuel.
5.5.4 Pulverized fuel pipes shall be manufactured using appropriate materials so as to withstand
mechanical and thermal stresses occurring under all operating conditions.
5.5.5 Devices shall be installed to isolate idle pulverized fuel pipes or pulverizing systems from the
furnace.
If one device is used to isolate more than one pulverized fuel pipe, means shall be provided to prevent
circulation between the different pulverized fuel pipes across the burners.
5.5.6 Stoppage of pulverized fuel supply to all burners associated with a mill shall be effected by the
controlled shut down of the associated fuel feeder, and primary air supply.
The shut down of the primary air supply shall be achieved by
• stopping the primary air fan, and/or
• closing the damper in the primary air supply duct.
For tube bore mills, closing of dampers in one or more pulverized fuel lines directly on top of mills is
acceptable, provided no pulverized fuel can accumulate, and no excess pressure can occur in the
pulverizing system.
The primary air supply and the fuel feeder shall be capable of being stopped even in the event of loss of
control power.
5.5.7 For mills which generate their own carrier flow, e.g. fan type, beater mill, stopping only the fuel
feeder shall be sufficient.
6 Explosion prevention measures for pulverizing systems and pulverized fuel
systems
6.1 General
6.1.1 Pulverized fuels have different propensity to ignition and can form explosive mixtures with air.
A pulverized fuel explosion is to be expected, if pulverized fuel is dispersed in a confined space containing
air or oxygen in concentrations within the upper and lower explosion limits, and if an ignition source is
present. For primary prevention of explosions, at least one of these conditions shall be safely excluded at
any time. If this cannot be accomplished completely, one of the following protective measures to restrict
the effects of an explosion shall be applied in the order of preference given:
• the operation with inert gas protection in accordance with 6.3;
• the restriction of the effects of explosions. Any endangered components shall be designed to resist
the explosion pressure or the explosion pressure shock;
• the reduction of the blast pressure of an explosion by pressure relief vents. Only automatically closing
pressure relief devices shall be used. Escaping gases shall be safely discharged into the open
atmosphere outside the boiler house.
• Explosion suppression systems;
The prevention of explosion propagation into other components shall be done by isolating devices e.g.
quick-acting shutoff devices, rotary feeders, or automatic fire extinguishing equipment.
NOTE Further information is given in EN 1127-1:2019.
6.1.2 Electrostatic ignition sources shall be avoided; see 5.1.4.
6.1.3 Protective measures as specified in 6.2 and 6.3 may be waived for fuels with low K -values
St
(defined by EN 14034-2:2006+A1:2011) e.g. fuels with a volatile matter content lower than 10 % on dry
and ash free basis or as long as a water content higher than 45 % is maintained during process.
6.2 Plants operated without inert gas protection
6.2.1 For direct-firing systems with pulverizing systems normally not being operated under inert
conditions, primary prevention of explosions shall be achieved, if purging and starting-up is performed
in accordance with 8.6.2.2. With these provisions it shall suffice, if the following components of a hard
coal grinding system are of explosion pressure shock resistant design for a gauge pressure of at least
1 bar:
• fuel feeders and chutes upstream of the mill;
• mills, classifiers, mechanical separators, and other components connected to the gas side;
• pulverized fuel pipes including installed valves and expansion joints;
• air ducts and installed equipment upstream of the mill for a length of at least 8 times the hydraulic
diameter. (Hydraulic diameter is four times the cross-section area of the duct divided by the
perimeter of the duct.).
For pulverized bio mass firing systems it shall be ensured, that despite of the changed self-ignition and
explosion attributes of the high-volatile fuel dust the above mentioned measures are sufficient for a safe
pulverizer operation. It can be necessary to include additional safety measures like pressure relief
equipment or explosion suppression systems.
6.2.2 Pulverized fuel bins, and pulverized fuel separators directly attached to them, shall be of
explosion pressure shock resistant design for a gauge pressure derived from the dimensioning of the
automatically closing pressure relief devices in accordance with the relevant standards (e.g.
EN ISO 4126-1:2013 ).
Electrostatic precipitators shall not be permitted for pulverized fuel separation.
6.2.3 For tube ball mills the requirements of 6.2.1 and 6.2.2 may be waived, if due to special measures
taken or implied by the inherent properties of the system, a critical explosion pressure cannot occur.
6.3 Plants operated with inert gas protection
6.3.1 For the purpose of explosion prevention, the atmosphere shall be regarded as inert if a mixture
of pulverized fuel/air cannot be ignited. Under normal atmospheric conditions, the oxygen limit
concentrations are 14 % by volume for hard coal and 12 % by volume for brown coal.
With regard to the above, the following oxygen concentrations measured by volume in humid conditions
shall be allowed:
• 12 % for hard coal;
• 10 % for brown coal pulverized in fuel bins; and
• 12 % for raw brown coal in fan type mills;
For other fuels than coal, e.g. biomass, the oxygen limit concentration shall be determined. The
operational oxygen limit concentration shall be 2 % below the determined oxygen limit concentration.
6.3.2 The oxygen concentration shall be continuously monitored, if inert conditions cannot be ensured
as inherent to the system.
6.3.3 When the allowable oxygen concentration is exceeded, it shall immediately be diminished
automatically to an allowable value, e.g. by steam injection. If the oxygen concentration fails to be reduced
to a permitted level, the plant shall be shut down automatically within a predefined time.
6.3.4 The inert gas protection shall be maintained during start-up and shutdown periods as long as
pulverized fuel is present.
6.3.5 If flue gases or steam are used as a medium for inert operation, the temperature of the medium
should be maintained above dew point in order to maintain the inert gas protection.
6.3.6 Fuel feeders and chutes serving pulverizing systems under inert gas protection need not be
operated under an inert atmosphere unless the raw fuel contained is not explosive, see 6.1.3. The
requirements of 6.2.1 shall not apply to these fuel feeders and chutes.
7 Equipment for air supply and flue gas discharge
7.1 Air supply
7.1.1 Air ducts shall be capable of withstanding the mechanical and thermal stresses occurring during
operation e.g. gauge and vacuum pressures resulting from closed dampers, implosions and rapid
temperature changes.
7.1.2 Air ducts shall be gas-tight.
7.1.3 Where the air flow is directed into multiple ducts or a common windbox, the system shall be such
as to divide the flow into the proper ratio among the various ducts or burner air ports.
7.1.4 For boilers with several burners to which combustion air is supplied by a common control device,
each burner or burner group connected to a unit pulverizing system shall be equipped with a shut-off
device (e.g. damper).
7.1.5 If there is an interruption of the fuel supply to the burner or the burner group of a pulverizing
system, this shut-off device shall also cut off the air supply automatically. Where required, the shut-off
device shall permit a minimum air flow.
7.1.6 Shut-off devices in the air ducts shall be protected against unintentional maladjustment. Open
and start-up positions shall be capable of being recognized, checked and monitored.
7.1.7 The combustion air fan shall be monitored by the combustion air flow and one of the following
criteria:
a) speed of the forced draught fan;
b) pressure downstream of the forced draught fan;
c) differential pressure at the forced draught fan;
d) power input of the forced draught fan motor;
7.1.8 During start-up of the pulverized fuel firing system, a minimum combustion air flow shall be
maintained in accordance with the requirements given by the manufacturer in the operating manual.
7.2 Air/fuel ratio
7.2.1 The air/fuel ratio shall be controlled automatically. Allowable values including safety margins
shall be given by the manufacturer of the firing system in the operating manual (see Clause 10).
7.2.2 The air/fuel ratio shall be monitored, e.g. by flue gas analysis.
7.2.3 An air/fuel ratio which is lower than the allowable shall be annunciated both optically and
acoustically (see Annex A).
7.2.4 When an air/fuel ratio occurs which is lower than that required for safety reasons, the firing
system shall be cut off either manually or automatically.
7.3 Flue gas discharge
7.3.1 Unrestricted flue gas discharge shall be monitored. This shall be performed by the following
measures:
a) checking the position of the damper(s) during start-up;
b) monitoring of the induced draught fan operation and limiters for the combustion chamber pressure.
If the relevant combustion chamber pressure is exceeded, the firing shall be cut off and locked out.
7.3.2 The induced draught fan shall be monitored in accordance with 7.3.1 b) and one of the following
criteria:
a) speed of the induced draught fan;
b) pressure upstream of the induced draught fan;
c) differential pressure at the induced draught fan;
d) power input of the induced draught fan motor;
8 Firing system
8.1 General
8.1.1 The firing system shall be suitable for the respective steam boiler or hot water generator. It can
consist of several pulverizing systems or several pulverized fuel feeders feeding several burners each.
8.1.2 The firing system shall be equipped with lighting-up equipment and monitoring equipment.
If the lighting-up equipment is operated with oil or gas, it shall comply with EN 12952-8:2022.
NOTE If other fuel is burnt by the lightning-up equipment, e.g. pulverizes fuel stored ready to use, the design
and operation of the equipment the appropriate clauses of EN 12952-8:2022 can also be applied.
8.1.3 To permit visual observation of lighting-up equipment and main burner flames, inspection
openings shall be provided at suitable locations on the combustion chamber and the burners.
8.1.4 For the injection of matter, other than the main fuel into the combustion chamber, see A.5.1.
A device to perform controlled injection, e.g. a rotary
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