Shell boilers - Part 12: Requirements for grate firing systems for solid fuels for the boiler

This part of this European Standard specifies the requirements for internal or external grate firing systems commencing at the fuel bunkers and ending at the ash extraction plant. For combination of various firing systems, the individual requirements of each system also apply.
If several fuels are burnt simultaneously or if a fuel quality varies considerably (e.g. moisture content), additional safety measures can be necessary, especially with respect to limitation of the fuel flow into the firing system and ensuring proper air supply to the individual fuels.

Großwasserraumkessel - Teil 12: Anforderungen an Rostfeuerungsanlagen für feste Brennstoffe für den Kessel

1.1 Feuerungsanlagen
Dieser Teil der Europäischen Norm legt Anforderungen fest für Rostfeuerungsanlagen, d. h. von den Brennstoffbunkern bis zu der Entaschungsanlage. Bei Kombination verschiedener Feuerungsanlagen gelten auch deren spezifische Anforderungen.
Wenn verschiedene Brennstoffe gleichzeitig verbrannt werden, oder wenn sich eine Brennstoffeigenschaft erheblich ändert (z. B. Feuchtigkeitsgehalt), können erhöhte Sicherheitsmaßnahmen nötig werden, vor allem im Hinblick auf die Begrenzung des Brennstoffstromes in die Feuerungsanlage und richtige Luftzuführung zu den einzelnen Brennstoffen.
1.2 Brennstoffe
Diese Anforderungen umfassen den Einsatz von festen Brennstoffen.
Erfasste feste Brennstoffe sind:
¾ Alle Kohlenarten, z. B. Lignit oder Braunkohle, hoch- oder niederflüchtige Steinkohle, Pechkohle, Anthrazit, Koks, Koksgrus, Kohlenschlamm;
¾ andere fossile feste Brennstoffe (z. B. Torf, Ölschiefer);
¾ feste Biomasse-Brennstoffe (z. B. Holz, Holzabfälle (Rinde), Zuchtpflanzen (Miscanth), Ernteabfälle (Stroh));
¾ feste städtische Abfallbrennstoffe (z. B. Müll, Klärschlamm, aus Müll gewonnene Brennstoffe (BRAM));
¾ feste Industrie-Abfallbrennstoffe (z. B. Petrolkoks, Ruß, Reifen, Papierabfälle, Späne von beschichtetem Holz, genutztes Holz, Schlachthofabfälle).
Brennstoffmischungen von einer oder mehreren dieser Gruppen (siehe 4.1.7) oder Brennstoffe ungewöhnlicher oder unbekannter Art können besondere Sicherheitsmaßnahmen erfordern, deren Eignung entweder durch praktische Erfahrungen, gewonnen mit vergleichbaren Brennstoffen, oder durch geeignete Versuche, z. B. nach EN 26184-1, bestätigt werden kann. Derartige Maßnahmen sind durch den Hersteller zu belegen.
Brennstoffe, auf denen die Auslegung basiert, sind in den Betriebsanleitungen (siehe 11.2) zu spezifizieren. Dies umfasst die Brennstoffdaten für 100 % Zufuhr des Grundbrennstoffes und alle Daten für Zusatz-brennstoffe zusammen mit ihrem maximalen thermischen Zufuhranteil.
1.3 Betrieb
Die Anfor

Chaudières à tubes de fumée - Partie 12: Exigences pour les équipements de chauffe à grille pour combustibles solides de la chaudière

1.1 Équipements de chauffe
La présente partie de cette Norme européenne spécifie les exigences pour les équipements de chauffe à grille interne ou externe commençant aux trémies de stockage du combustible et se terminant à l'installation d'extraction des cendres. Pour ce qui concerne la combinaison de différents équipements de chauffe, leurs exigences spécifiques doivent également être appliquées.
Lorsque plusieurs combustibles sont brûlés simultanément dans des équipements de chauffe, ou lorsqu'une qualité de combustible varie considérablement (par exemple la teneur en humidité), des mesures de sécurité supplémentaires peuvent se révéler nécessaires, notamment pour ce qui concerne la réduction du débit de combustible approvisionnant l'équipement de chauffe et la bonne alimentation en air pour les différents combustibles.
1.2 Combustibles
Les combustibles solides couverts sont :
¾ toutes les qualités de charbon, par exemple le lignite ou le charbon brun subbitumineux, le charbon bitumineux ou la houille, le charbon de brai, l'anthracite, le coke, la poussière de charbon, les résidus de charbon ;
¾ d'autres combustibles fossiles solides (par exemple, le coke de pétrole, la tourbe, le schiste bitumineux) ;
¾ les combustibles solides biomasse (par exemple, le bois, les déchets de bois [l'écorce], les plantes énergétiques [divers], les résidus de moisson [paille]) ;
¾ les combustibles solides de déchets urbains (par exemple des ordures, des boues d'eaux d'égouts, des combustibles dérivés des déchets [RDF]) ;
¾ les combustibles solides de déchets industriels (par exemple du coke de pétrole, de la suie, des pneus, des déchets de papier, des copeaux de bois revêtus, du bois usagé, des déchets de produits animaux).
Des mélanges de combustibles provenant de deux de ces groupes ou plus (voir 4.1.7), ou des combustibles d'une qualité inhabituelle ou inconnue peuvent nécessiter des mesures de sécurité particulières. Ce besoin peut être révélé par l'expérience pra

Mnogovodni kotli - 12. del: Zahteve za kurilne sisteme na trdna goriva z zgorevalno rešetko

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Status
Published
Publication Date
16-Sep-2003
Current Stage
9092 - Decision on results of review/2YR ENQ - revise - Review Enquiry
Completion Date
04-Jun-2021

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Großwasserraumkessel - Teil 12: Anforderungen an Rostfeuerungsanlagen für feste Brennstoffe für den KesselChaudieres a tubes de fumée - Partie 12: Exigences pour les équipements de chauffe a grille pour combustibles solides de la chaudiereShell boilers - Part 12: Requirements for grate firing systems for solid fuels for the boiler27.060.30Grelniki vode in prenosniki toploteBoilers and heat exchangersICS:Ta slovenski standard je istoveten z:EN 12953-12:2003SIST EN 12953-12:2004en01-junij-2004SIST EN 12953-12:2004SLOVENSKI

STANDARD
SIST EN 12953-12:2004

EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12953-12September 2003ICS 27.060.30; 27.100English versionShell boilers - Part 12: Requirements for grate firing systems forsolid fuels for the boilerChaudières à tubes de fumée - Partie 12: Exigences pourles équipements de chauffe à grille pour combustiblessolides de la chaudièreGroßwasserraumkessel - Teil 12: Anforderungen anRostfeuerungsanlagen für feste Brennstoffe für den KesselThis European Standard was approved by CEN on 12 June 2003.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards 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 translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and UnitedKingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36

B-1050 Brussels© 2003 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12953-12:2003 ESIST EN 12953-12:2004

EN 12953-12:2003 (E)2ContentsPageForeword......................................................................................................................................................................31Scope..............................................................................................................................................................41.1Firing systems................................................................................................................................................41.2Fuels................................................................................................................................................................41.3Operational equipment..................................................................................................................................42Normative references....................................................................................................................................43Terms and definitions....................................................................................................................................54Fuel bunkers with conveying plant..............................................................................................................64.1General............................................................................................................................................................64.2Conveying plant.............................................................................................................................................74.3Fuel bunkers...................................................................................................................................................74.4Fuel bins.........................................................................................................................................................85Fuel treatment................................................................................................................................................85.1General............................................................................................................................................................85.2Size reduction of the fuel..............................................................................................................................85.3Drying of the fuel............................................................................................................................................86Fuel feeding....................................................................................................................................................97Explosion prevention measures...................................................................................................................98Equipment for combustion air supply and flue gas discharge...............................................................108.1Air supply......................................................................................................................................................108.2Combustion air/fuel ratio............................................................................................................................108.3Flue gas discharge......................................................................................................................................109Firing system................................................................................................................................................119.1General..........................................................................................................................................................119.2Control and monitoring...............................................................................................................................119.3Electrical equipment....................................................................................................................................119.4Safety precautions.......................................................................................................................................119.4.1General..........................................................................................................................................................119.4.2Purging of the flue gas passes....................................................................................................................129.4.3Lighting-up...................................................................................................................................................129.4.4Start-up.........................................................................................................................................................129.4.5Shutting down..............................................................................................................................................139.5Common stack for several firing systems................................................................................................1310Ash handling and extraction.......................................................................................................................1311Operation and maintenance........................................................................................................................1411.1General..........................................................................................................................................................1411.2Operating instructions................................................................................................................................14Annex A (informative)

Operational requirements for permanently supervised firing systems for solidfuels on grate firing systems......................................................................................................................15Annex ZA (informative)

Relationship between this European Standard and the Essential Requirementsof EU Directive 97/23/EC.............................................................................................................................17Bibliography..............................................................................................................................................................18SIST EN 12953-12:2004

EN 12953-12:2003 (E)3ForewordThis document EN 12953-12:2003 has been prepared by Technical Committee CEN/TC 269 “Shell and water-tubeboilers”, 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 orby endorsement, at the latest by March 2004, and conflicting national standards shall be withdrawn at the latest byMarch 2004.This document has been prepared under a mandate given to CEN by the European Commission and the EuropeanFree Trade Association, and supports essential requirements of EU Directive(s) (Pressure Equipment Directive97/23/EC) [1].For relationship with EU Directive(s), see informative annex ZA, which is an integral part of this document.The European Standard EN 12953 concerning shell boilers 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:Workmanship and construction of pressure parts of the boiler Part 5:Inspection during construction, documentation and marking of pressure parts of the boiler Part 6:Requirements for equipment for the boiler Part 7:Requirements for firing systems for liquid and gaseous fuels for the boilers Part 8:Requirements for safeguards against excessive pressure Part 9:Requirements for limiting devices of the boiler and accessories Part 10:Requirements for feedwater and boiler water quality Part 11:Acceptance tests Part 12:Requirements for grate firing systems for solid fuels for the boiler Part 13:Operating instructionsCR 12953 Part 14: Guideline for the involvement of an inspection body independent of the manufacturer (TR)Although these Parts may be obtained separately, it should be recognized that the Parts are interdependent. As such,the design and manufacture of shell boilers requires the application of more than one Part in order for therequirements of the European Standard to be satisfactorily fulfilled.The annex A of this European Standard is informative.This document includes a Bibliography.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, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,Slovakia, Spain, Sweden, Switzerland and the United Kingdom.SIST EN 12953-12:2004

EN 12953-12:2003 (E)41 Scope1.1 Firing systemsThis part of this European Standard specifies the requirements for internal or external grate firing systemscommencing at the fuel bunkers and ending at the ash extraction plant. For combination of various firing systems,the individual requirements of each system also apply.If several fuels are burnt simultaneously or if a fuel quality varies considerably (e.g. moisture content), additionalsafety measures can be necessary, especially with respect to limitation of the fuel flow into the firing system andensuring proper air supply to the individual fuels.1.2 FuelsThe solid fuels covered are: all coal qualities, e.g. lignite or brown coal, sub-bituminous or hard brown coal, bituminous coal or hard coal,pitch coal, anthracite, coke, coal culm, coal sludge; other fossil solid fuels (e.g. petrol coke peat, oil shale); biomass solid fuels (e.g. wood, wood wastes [bark], energy plants [miscanthus], harvest wastes [straw]); municipal waste solid fuels (e.g. garbage, sewage sludge, refuse derived fuels [RDF]); industrial waste solid fuels (e.g. petrol coke, soot, tyres, paper wastes, coated wood chips, spent wood, animalproduct wastes).Fuel blends from two or more of these groups (see 4.1.7), or fuels of unconventional or unknown quality canrequire special safety measures which can be proved either by practical experience gained from comparable fuels,or by suitable tests, e.g. in accordance with EN 26184-1. Such measures should be documented by themanufacturer.Fuels on which the design is based should be specified in the operating instructions (see 11.2). This should includethe fuel data for 100 % input of the basic fuel and the data for any supplementary fuels together with their maximumthermal input percentage.1.3 Operational equipmentThe requirements for operational equipment in clauses 4 to 10 apply to steam boilers and hot water generators withpermanent supervision by properly trained personnel familiar with the special conditions of the firing systems and thetype of fuel.Annex A contains the operational requirements for permanent supervision.2 Normative referencesThis 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 12952-8:2002, Water-tube boilers and auxiliary installations – Part 8: Requirements for firing systems for liquidand gaseous fuels for the boiler.EN 12952-9:2002, Water-tube boilers and auxiliary installations — Part 9: Requirements for firing systems forpulverized solid fuels for the boiler.EN 12953-7, Shell boilers — Part 7: Requirements for firing systems for liquid and gaseous fuels for the boiler.SIST EN 12953-12:2004

EN 12953-12:2003 (E)5EN 26184-1, Explosion protection systems — Part 1: Determination of explosion indices of combustible dusts in air(ISO 6184-1:1985).prEN 50156-1, Electrical equipment for furnaces and ancillary equipment — Part 1: Requirements for applicationdesign and installation.3 Terms and definitionsFor the purposes of this European Standard, the following terms and definitions apply.3.1back-up firing systemseparate firing system to maintain safe ignition and stable combustion. The lighting-up equipment can be used forthis purpose3.2basic firelayer of glowing fuel, fire bed or flame of the fed fuel. The basic fire can also perform the duty of the lighting-upequipment, or the back-up firing system (mostly air)3.3carrier gastransport medium for pneumatic conveying3.4combustion airtotal air supplied to the firing system for combustion3.5firing systemscan be distinguished in accordance with the type and structure of the fuel, the feeding procedure and the processof combustion. Fuel and air can be introduced in the combustion chamber in different ways to establish andmaintain proper ignition and stable combustion. Combustion of

the fuel

is performed on grates3.6fuel binsilodust-tight container for temporary storage of combustible solids in the boiler room3.7fuel bunkeropen storage of solid fuel3.8fuel feeding systemdevice to transport fuel into the combustion chamberNOTEThis can be effected directly by feeders through ports in the furnace walls, by means of chutes or through thebottom grate3.9fuel handling plantinstallation for conveying, mixing and distributing solid fuels to the individual fuel bunkers or fuel bins3.10grate firing systemfuel is burnt in a layer supported by a system of firebars which may have a cooling systemNOTEThe firebars should be so spaced as to admit the undergrate combustion air supply in proper distribution. Othermeans of admitting and distributing the combustion air supply can be provided.SIST EN 12953-12:2004

EN 12953-12:2003 (E)63.11indicatormeasuring instrument which indicates a variable value (e.g. pressure, temperature, flow, level). It can be equippedwith an annunciator3.12lighting-up equipmentfacility to achieve safe ignition of the feed fuel3.13limitertransducer, which, on reaching a fixed limit value (e.g. pressure, temperature, flow, level) is used to interrupt andlockout the energy supply and It requires manual unlocking before restart3.14lockoutinterruption of the energy supply. Manual unlocking is required before restart3.15master fuel tripdevice located at a safe place for rapid automatic shutoff of all fuel supplies to the grate and electrical igniters in theevent of danger3.16maximum continuous rating (MCR)allowable heat outputsteam boiler or hot water heat output that can be generated during continuous operation and at which the steam orhot water generator may be operated, taking the specified steam condition or hot water condition (water mass flowtimes the difference between outlet and inlet enthalpy) into consideration3.17monitortransducer that senses the reaching of a fixed limit value and initiates an alarm and/or a shut-down. The output signalonly reverses if the causing value has changed at a defined range3.18purging of the flue gas passesflow of air through combustion chamber, flue gas passes, and associated ducts

including flue-gas treatment systems,which effectively removes any gaseous combustibles and replace them with air3.19start-up conditionthe plant can be started cold (temperature of ceramic lining is at ambient value); hot (temperature of ceramic lining is above the minimum ignition temperature of the basic fuel); or warm (temperature of ceramic lining in between the ambient and minimum

ignition temperature)4 Fuel bunkers with conveying plant4.1 General4.1.1All facilities shall be designed so as to withstand mechanical and thermal stresses. Fuel shall not be heatedto an unacceptable level. Sites where fuel may accumulate shall be avoided.4.1.2Conveyance, temporary storage, and extraction of the fuel shall be arranged such that sufficient flow of thefuel and additives is ensured.SIST EN 12953-12:2004

EN 12953-12:2003 (E)74.1.3The fuel storage capacity shall be determined in accordance with the fuels used.NOTEIt is recommended that the storage of fuel within the boiler room itself is minimized.4.1.4Measures to prevent fire, explosion and injuries to personnel shall be provided for volatile fuels and thosecapable of pyrolysis in the absence of external heating. As an example wet sludges can have an inherent explosionrisk due to the release of volatiles (e.g. methane)when stored. Dried sludges have a fire and dust explosion risk.4.1.5Sludge storage in bins shall be preferred to storage in bunkers (see 4.4.1).4.1.6The storage of fuels supplied in small grain sized particles or fibres which can be stirred up and becomeairborne shall only be permitted in bins (silos).4.1.7If different types of fuels are used, dangerous operating conditions due to blending shall be excluded, e.g.by the use of separate bunkers or bins and separate feeding systems.4.1.8If there is a risk of blockage of conveying systems or firing systems by coarse lumps of fuel, foreign matterand tramp metal, then means for the removal of

those objects shall be provided, preferably before entering thebunker.4.1.9Dangerous areas accessible to personnel shall be marked with warning signs.4.1.10Outdoor storage facilities and fuel bearing components as well as buildings for indoor installation shall beequipped with a lightning protective system in accordance with relevant European Standards.4.2 Conveying plant4.2.1Several continuous conveyors arranged in series to form one conveying line shall be interlocked such thatthe normal operation of

any conveyor is possible only if the downstream conveyors are in normal operation and thestorage facility is ready to accept the fuel.4.2.2Precautions shall be taken for the protection of personnel against injury from moving components.Sufficient time shall be provided between the warning signal and starting of the plant.4.2.3If the type and format of the fuel requires bins (silos) for temporary storage in accordance with 4.1.5 or4.1.6, subsequent conveyance shall be performed in a closed system, which shall be gas-tight if operated underinternal pressure.4.2.4Piping used for conveyance shall be designed with a high resistance to wear.4.2.5For conveyance of fuel in closed pipes, deposition shall be prevented by sufficient velocity of the carriergas depending on the type and format of the fuel.4.2.6All piping system components of a conveying system shall be capable of being purged of fuel.4.2.7If multiple lines are installed, devices shall be provided to isolate idle conveying lines from the downstreamstorage facility or the furnace.4.3 Fuel bunkers4.3.1Fuel bunkers shall be built to achieve uniform discharge by the selection of proper shape and design, inorder to ensure a continuous fuel flow and to avoid segregation.4.3.2To avoid ingress of hot air/gas into the bunker, a minimum level of fuel shall be maintained and monitoredin the bunker, or other suitable measures shall be taken, see also 6.1 and 6.4.4.3.3The inner surface of the fuel bunker roof shall be designed so as to avoid the accumulation of dust and gasin dead pockets.4.3.4Bunker charging openings shall be adequately guarded to prevent personnel from falling in.SIST EN 12953-12:2004

EN 12953-12:2003 (E)84.3.5Fuel bunkers shall be equipped with fire fighting or fire preventing equipment. Fire fighting by sprinklersystems is

allowed but the use of

concentrated water jets is prohibited. Bunkers may be emptied by use ofemergency chutes.4.4 Fuel bins4.4.1Some fuels according to their type and format shall be stored in dust-tight bins (silos). The requirements forpulverized fuel bins specified in 5.4 and 6.2.2 of EN 12952-9:2002 apply accordingly.4.4.2The permissible maximum storage temperature shall be specified for each single fuel and fuel blends andshall be monitored in the freeboard during the storage, if there is a risk of self-ignition4.4.3If combustible gas emanation from the fuel cannot be prevented, silos shall be equipped with suitable gasmonitoring and safe venting devices, otherwise an explosion-proof silo or inert gas protection shall be provided.4.4.4Fuels as specified in 4.1.4 require bins to be equipped with a stationary nonfreezing fire extinguishingsystem to enable fire to be fought without opening access doors. The extinguishing compound shall be evenlysprayed and well distributed across the entire cross sectional area of the bin. Spray nozzles shall be protectedagainst blockage by the ingress of dust. Where stationary spray-type extinguishing systems are operatedautomatically, manual initiation shall be possible.5 Fuel treatment5.1 General5.1.1The equipment shall be designed so as to withstand mechanical and thermal stresses. It shall be soarranged as to be readily accessible to enable cleaning operations to be carried out. The total system shall be gastight if operated under internal pressure.5.1.2Practicable steps shall be taken to minimize sites in the plant where combustible dust or fuel may becomelodged.5.1.3Facilities shall be provided for purging and clearing components which are hot during operation. If there isa possibility of settlement of combustible dust on components that have become hot during operation, facilities shallbe provided for purging and cleaning after shut down.5.1.4Mechanical equipment for fuel treatment shall be designed and operated such that no unacceptableheating of the fuel occurs.5.1.5The system shall provide the operator with adequate information about significant operating conditions,both normal and abnormal.5.1.6To avoid the build-up of electrostatic charges, all components shall be earthed unless forced and faultlessearthing is inherent in the design.5.2 Size reduction of the fuel5.2.1If size reduction of the fuel is performed by crushers in the boiler house with the application of hot gas asthe carrier gas for combined grinding and drying process, the necessary explosion prevention measures shall begiven.5.2.2For eventual intermediate storage after size reduction, 4.4 applies.5.3 Drying of the fuelWhen drying fuel prior to combustion, the maximum permissible temperature in accordance with 4.4.2 shall be moni-tored. The vapours shall be discharged in order to prevent the risk of explosion. For the combined crushing and dryingprocess, 5.2.1 shall apply.SIST EN 12953-12:2004

EN 12953-12:2003 (E)96 Fuel feeding6.1Shutoff device shall be installed within the fuel feeding system. This shutoff device shall be closedautomatically if the minimum height of the fuel column is lost when mechanical feeding.Shut off devices need not to be installed if it can be ensured that negative pressure is maintained in the fuel feedingsystem or a minimum column of fuel (4.3.2) is maintained in the fuel bunker.6.2It shall be ensured that after shut-off of

the firing system and during outage, no fuel can enter the furnace.6.3The feeding of fuel shall be cut off in the event of loss of control power (see 9.2.2), under the start-upconditions in accordance with 9.4.4.1 a), or under shutting-down conditions in accordance with 9.4.5.1 a).6.4Fuel feeding systems shall be provided with appropriate sealing which prevents the back flow of hot gasesfrom the boiler, flash-back by flame, or flying sparks or backfire. Egress of hot gases into the boiler house shall beprevented.6.5Depending on the type of fuel, fire fighting equipment shall be installed. This equipment shall be activated,when set temperature has been exceeded in the fuel supply equipment. Equipment for monitoring and fire fightingshall be placed in such a way that a fire can be extinguished quickly. The equipment shall be easy to test.7 Explosion prevention measuresCombustible dusts have different propensities to ignite and can form explosive mixtures with air.A hazard of combustible dust explosion exists, if the dust is dispersed in a confined space containing air or oxygen inconcentrations within the upper and lower explosion limits, and if an ignition source exists. For primary prevention ofexplosions, at least one of these conditions shall be safely excluded at all time.Individual components of a firing system require specific protective measures. By preference, explosion protectivemeasures shall be inherent in the design of the components, e.g. the avoidance of leakages, the prevention ofdeposits, and the exclusion of external heating. For easy reference, an overview of important prevention measures forthe different operational areas is given below in Table 7-1:Table 7-1 — Overview of important prevention measures for different operational areasOperational areaFor explosion prevention measures see clause(s)Fuel properties1.2 (see EN 26184-1), 4.1.4 to 4.1.7Fuel bunkers4.3.3Fuel bins5.4.2, 5.4.5, 5.4.6, 6.2.2 of EN 12952-9:2002, and 4.4.3Fuel treatment plant5.1.2 to 5.1.4Size reduction of fuel5.3, 6, 8.7.2.2 and 8.7.4 of EN 12952-9:2002Drying of fuel5.3Combustion monitoring9.2Purging9.4.2Start-up, operation, and shutting down of thecombustion process9.4.3 to 9.4.5All operating areasA.6SIST EN 12953-12:2004

EN 12953-12:2003 (E)108 Equipment for combustion air supply and flue gas discharge8.1 Air supply8.1.1Air 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.8.1.2Air ducts shall be gas-tight.8.1.3For firing systems with both underbed and overfire air supply which are regulated by manually orautomatically controlled dampers, the air distribution shall be monitored.8.1.4A shut-off device shall be installed within the combustion air supply line. Shut-off devices in the air ductsshall be protected against unintentional maladjustment.8.1.5Unrestricted air intake shall be ensured.8.1.6The fan shall be monitored by the air flow and one of the following criteria:a) speed of rotation of the forced draught fan;b) pressure downstream of the forced draught fanc) air flow

indicatord) power circuit breaker of the forced draught fan motor.8.2 Combustion air/fuel ratio8.2.1The air/fuel ratio shall be monitored, e.g. by flue gas analysis.8.2.2Allowable values, including corresponding safety margins, of the air/fuel ratio shall be given in theoperating instructions (see 11.2.2 f)) by the manufacturer of the firing system.8.2.3An air/fuel ratio lower than that allowable shall be annunciated.8.2.4In the case of an air/fuel ratio lower than required for safety reasons, the firing system shall be cut offmanually or automatically.8.3 Flue gas discharge8.3.1Flue gas discharge shall be monitored to ensure it is not unnecessarily restricted. This shall be performedby:a) monitoring

the position of the damper(s) during start-up;b) monitoring of the induced draught fan operation and combustion chamber pressure;c) monitoring of the flue gas discharge temperature;d) limiter for the flue gas discharge temperature when exceeding 300 C.8.3.2The induced draught fan shall be monitored in accordance with 8.3.1 b) and one of the following criteria:a) speed of the induced draught fan;b) pressure upstream of the induced draught fan;c) power circuit breaker of the induced draught fan motor.SIST EN 12953-12:2004

EN 12953-12:2003 (E)119 Firi
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