FLAME SAFEGUARn CONTRULS phần 3 pdf

REFERENCES •All Aboul Boilers,· Marine Engineering/Log, February 1974, pp. ~53. Bender, Rene J. (ed), ·Steam Generation,· Power, Special Report, June 1964, 48 pages. Burkhardt, Charles H., Domestic and CommerciaJ Oil Burners, 'Third Edition, New York et ai, McGraw-Hili Book CompanV. 1969, •Electrode Boilers Make sense.· Enert:t Marketing cover slory, Electrical World, 8ep1801ber " 1971. pp. 70-72. Faust, Frank H. and Kaufman, G. lheOOore, (ed.), Handbook of Oil Burning, Oil-Heat lnslilule of America, Inc., 1951. Griswold, John, Fuels. Combustion and FurnactJ$. Arst EdItion, ThIrd Impression, New York and l.onQ::ln, McGraw-HIli Book· Company, Inc., 1946. Guide for the Selection, Installation and Operation 01 Oil Burning Units, Newark, New Jersey, American Boiler Manufacturers Association, 1971. LeJdcon, Steam Generating Equipment, Third Edition, Artingta'l. Virginia, Arrllilrlcan Boiler Manufacturers Ass0- cIatiOn. 1974. North American Combustion Handbook, Firsl Edilion, Third Prlnling, Cleveland, Ohio, The North American Manufacturing Co., 1965. • Power From Coal" - Parts I, II, and Ill, Power, Special Repor1 t;7; the edllorsi, February, March, and April, 1974, 64 pages. Schaphorst, W., "ThouQhts About Fir&- Tube vs. Water-TUbe BoIiEll'S," Power, september, 1972, p. 167. SImpson., James H., -Conversion of Boilers to Dual· Fuel Systems." ASHRAE Journal. May 1973, pp. 46-54. Steiner, Kalman, Oil Burners, Third Edition, New York, Fueloil & 011 Heat, 1960. Trinks, W., and Mawhinney, M.H., Industrial Furnactls, Volume II, Fourth Edition, New York, London, Sydney, John Wiley & Sons, Inc., 1967. 70 • .~ PART I-TYPES OF FLAME DETECTION SYSTEMS The purpose of a flame detection system Is 10 delect the presence or absence 01 a safe flame so lhal bJrner 0p- eration may be conllnuedU condil1ons are safe. and Inler- fl.4'led if/hey are ~t FLAME CHARACTERISTICS USED BY FLAME DETECTION SYSTEMS All flames have certain characteristics In CCM1VT1OI'l in- ch.Jding Ihe following: ProducUO'1 of heal. Expansion 01 gases. Prod.!cllon' of by-products Emission of Ughl Onfrared 10 ullraviolet). Ionization of the atmosphere in and around the flame. Flame detection systems have been developed using several of these characteristics with Ihe flame detecting ponlon 01 Ihe system emitting a signal or originaJing soma physical action In Iha presence 01 Ihe detected characteristic. Many flame detection systems designed for use on cb- mastic healing systems use the thermal effect of/he flame as the method of detection. The detecting eiement must be healed by Ihe flame for operation 01 the system to continue. This ,Is true whelher Ihe heat is converted 10 a physical force, as in a bimetal or hydraulic pilot SElnsor, or to an electrical signal as in a Ihermocouple. Considerable lime )s required for the SElnsor to heal, and a similar time pericx:1 Is required for It to cool on toss or flame. Larger systems (commerCial and industriaQ require faster flame proving leChnlQJ8S. Fast responding systems have been devel~ that use Ih!I Ught emitted by the flame On1rared, Visible, or unraviolet) and the ionization characteristics of the flame. FLAME ROD VS THERMAL SENSORS Flame rod systems dppend on the abllily of the flame to conduct a CUrretlt when a potenltal Is awlied across il (flame lonizalion). The flame rod must be used wllh a suitable electronic flame safeo;uard control to al11=l1l1'1 the sig'\3l frcm lhe flame rod. The flame rod usually is used to detect a gas flame. 011 flames are not generally suitable for the awli- calion of a flame rcd because of their higher cperating temperatures. Flame rod defection systems have 4 ifTlXlrtant advan- tages over thermal type pilot sensors: , . .o.u !.CKAESPONSE TO FLAME FAILURE-The bimetal pilOI and the thermocQt.4lJe pilot have a response lime of up to 3 minutes. Rarely t:bes this type or pilot r&- spend In less than 1 minute. On domesllc Installations, wtlere these flame detection devices are normally em- ploved, low fuel consufT1)tion makes response time less 71 critical. Hence the maxil'l"lUTl r8SjX)1"1S8 timings for (his type at equipment have been eslabllshed at 3 miAJtes. Thermocouple systems are often used on larger installa· lions for gas pilot supervislO1 only, as an auxiliary 10 hl\1l speed rectifying flame rod systems. On larger installations, this slow response to flame fall· ure would be dangerous. For exarrple, on a typical larger Installation burning 600 cLblc feet at gas an hour, wring the minute or so It takes the flame sensing device to reccg- nlze (hal the flame has been /ost, at least 10 cLblc teet 01 gas can be Introduced Info the conbJslion ct\atrtle(. kr suming that natural gas is used. it will take an ad::filional 100 cubic feel of air for Pfoper corrbustlon. ThiS amounts 10 a tolal ot , 10 cLblc feet at cornbuslj~ mixture intra- wced into the combustion Chamber, 10000Ing for a means 10 be ignited. If delayed ignition takes place, lhal voll.lTle of fuel·air mixture COUld caUSEI a SElrious elCplosion. For thIS reason, larger jobs need electronic flame safE9J3rd systems that have a response timing of 2 to 4 SElcords. 2. PRQVES FLAME AT IGNmON POINT With the bi- melal pilot and Ihe thermocouPle pilaf, the pilot is essentially proved at the source. BecauSEI of lhe flexibility of poslllonlng a flame rod, a pilot flame can be proved aJ the point of interseclion with the main flame. 3. PROTECTS ITSELF AGAINST FAILuRE OF ITS CQM.!'ONENT PARTS A bimetal pilot or lherrTlOCOl.ple pilot Installed on a large burner Is 5/.bjec1 to the intense heat of the corTt:Iustion c/1aIrt:ler and reflected h&aI frcm radiant brickwork:. This heal can cause melal f~, lead- ing 10 Sluggish operation, nuisance shuldJwns, or eYElrt failure or the sansing element. In some cases, the bimetal pilot has actually failed In the -on- posllion. This, Of courSEl, causes a hazardouS condition by allowing lhe main gas valve to remain open or be opened with no real proof that a pilot flame is present Wflh eleclronic flame safeg.Jllfd systems, a checking circuit can be built into the syslem. If abnOrmal cordlJons occur In the flame delee/or circuit-SUCh as c:pen circuits, shOrt circuits. or leakage resistance to grOU'"d-they simulate absence. not presence, at flame and cause the system to fail safe. 4. LONG WFE Of CQNSISTE!'lT OPERATION-As pointed out abOve, the intense heat encot.rIlered on larger installations causes metal fatig.Je in thermocouple pilots and bimetal pilots. With electronic flame safE9J3rd syslen'lS, hoW8\'8r, a flame rod or photocell is the flame sensing device TIle flame rod normally has a temperature raUng In excess or 2,000 degrees, so it can withsland the hi\1l 1Iame lempel'alures. 71-97558-1 FLAME CONDUCTIVITY VS FLAME RECTIFICATION SYSTEMS There are 2 basic principles In flame rod delecllon systems-flame conductivity and flame rectification. Conduc- tivity systm are, for the mOSI part, no longer used. Eilher lype of system depends on the ab.lllty at the flame 10 conduct current when a voltage Is applied across The ac VOltage ~Iied 10 the electrodes looks like this: In a 60 Hzsyslem, II changes its direction /polarity} 120 times a second. At one instant, one of the electrodes is positive, and 1/120 01 a second later it is negaliva. /J.s the voltage Changes polarity, the flame current (ion flow) will Change direction. For a CondJClivity system, the areas 01 the 2 electrodes (called flame and ground electrooes) are equal and the flame current between them is the same In both directions. This is the principle 01 a conduclivity system, When an ac voltage is applied across the flame electrode and the ground electrode, alternating currenl proportional to the awtled voltage flows through the flame. Because the flame current in a conductivity system Is ac, this system cannot differentiate between a leakage current and an actual flame current. It i!$ possible for the. system to falsely indicate the presence 01 a flame (with possibly dangerous results) if the flame electrode is shQrted to grcx.nd through a leakage circuit with about the same resistance as the impedance of a flame. A carton depOSit on the base of the flame electrode could form a very effective leakage path and cause a false flame indica- lion. (A direct short of low impedance would, 01 course, make the system Inoperative.) lhe flame rectification system also uses 2 electrooes, bul with 1 irfllortant difference-lhe grOUnd eleclrode is + ~ y > 6 - , L.c . ~UU£NT Feow _£M , 2 eleclrlXies in the flame. Heat frem the flame causes !!lQIawJ~ be~weE!ln the electrOCies 10 colli.de wllh each other so forcibly as to knock; some electrons out of the ai- oms, proC:liClng ions. ThiSts called flame Ionization. Posi- tively Charged·,1ons flow to the negatively charged electrocJe; negatively charged electrons flow to the positively charged eleclrode. always designed to be much larger than the flame elec· trode (flame r~. FOI" effective operation, the area of the ground electrode must be atleasl4 limes thai 01 the flame rod. Usually, the ground electrode will be the burner head. Because of the difference In electrode size, more current flows In one direction than In the other. When the flame rocl is positive, more current flows. : f ' '~ When the flame rod is negative. less current flows. 6 • ~ • ~ ~I ~_"~O· ,, 'pO ". With the current In one direction so much larger than the current In the other direction, the resultant currenl is, effectively, a pulsating dIrect current which operates the electronic netWork. The flame relay pulls in, indicating the presence of a flame and allowing the bUrner sequence to continue. The larger the ratio of ground area to flame elec· trode area, the greater the flow of current in the proper direction-in other words, a reclified current. Only the ionized path through a flame and the different sized electrodes can provide the rectified current required for the operation of the electronic network in a rectification system. Should a high resislance leakage to ground occur in the flame circuit, it senc:ls an ac signal Into the network, and lhe system shuts down safely. The rectification system does re'Cognize the difference between a high resis· tance leakage to ground and the presence of a flame. 72 - - PART II-REQUIREMENTS FOR FLAME ROD RECTIFICATION SYSTEMS The 'requirements thai must be satisfied when applying a recUfying flame rod are: 1. Stable flame - The name 10 be proved must be stable-continuously in contact with Ihe flame grounding area. We are primarily concerned with pUOI flames since 1beS8 are the most common and the most difficult awllcalions. 2. Adequate ground area. 3 Flame rod prq)9rly located in the flame envel~. 4. A clrcuillo carry the flame signal 10 the amplifier in the primary control. These 4 requirements will be covered In detail in the sections thai follow. REQUIREMENT l-STABLE (PILOT) FLAME The pilot to use if the pilot is 10 be proved by a flame rod should have the following characteristics. 1. 11 shoold be a premixed pilot 2. tt should be a strong pilot. 3. II should be poSitioned where it will smoothly ignite the main burner. USE A PREMIXED PILOT Prembred pllots are recommended beCause the stronger flame anel greater speecl 01 flame propagation contribute to go::id contact with the ground area ana to stability with respeclto the flame electrode. Raw gas pilots are generally difficult to Slfl9rvise elec- tronically because of the difficulty in securing a slable flame ground. In ad:l'ilion, lheflame o1a raw gas pilot may fluctuate excessively and changeposilion in response to minor draft variations, cOrTJlllcaling the prd:llem 01 flame rod location. - . Fig. 1 shows the 2 types of pllots. Note, with the raw gas pilol, how the Insulaling layer of raw gas keeps the flame from contacting the groond area until near the end. With the raw gas pilot reaching oul for the air necessary for combusllon, even this small contact is uncertain. Com- pare this with the flame-l<>groond-area contact in Ihe premiXed plio!. USE A STRONG PILOT Make the pilot flame strong enough to be reasonably stable under the most adverse conditions of draft and modulation. If the pilot flame leavElS the flame electrode for a period longer than the flame relay liming, nuisance shut- downs are sure to result. Increase the gas pressure to the pilot, or enlarge the pilot orifice_if necessary to provide a stronger flame. Increasing the gas pressure tends to harden and lengthen the pilot flame, increasing ils stability under adverse conditions. This stability is especially necessary when the main burner fires with hl~ pressure gas. Adjust the air mixer 10 reduce traces 01 yellow in the pilot to a minimum. POSITION THE PILOT WHERE IT WILL SMOOTHLY IGNITE THE MAIN BURNER Follow the burner manufacturer's recommendations on pilotlocauon, if available; if not, Iry to find the location most favorable to the smooth ignition 01 main flame. For example, with a mullJple-head or multiple-Jet burner,the ideal location isat U1epolnt where gas first emerges from bJrner ports, aM a point near the LpSheam ed;J:I of the burner (with respect to the direction of the drafl). The pilot can normally be mountec;l yertically between bu'ner heads as shawn in Fig. 2 wilh the pilol flarne playing up- ward across the junction of the gas slreams coming from al I6ast 2 heads. Fig. 3 shows a satisfaclory pilot installation on an inspirator or venturi type burner. The pilot is firing in the general direction of the main flame. The pilot is strong enough to intersectlhe main flame envelCf.lE!, aM the flame rod is Iocatea where it can prove both the pilol and main flames simultaneouSly. Fig. 3 is a QOOd example o1a pilot that is in a p::lSition 10 smoothly igdte the main burner. Fig. 4, however, shows an exaggerated pcx:lr installation. Here the pilot has been located so that no part of II comes near intersecting the main burner envelCf.lE!, and the Rame rectifier is positioned where a lazy pilol flame ~jr ing at low gas pressure) can still coolacl it. Obvioosly this installation can only result In delayed ignition and ro Ql starts. On radiant type burners, t~ pilot is often ITlOl.nted alongside the burner or fires throogh one of the b.Jrner c:penings In the radiant burner block as shown in FlO. 5. TOP VIEW IlISIJLn,~~ lAYU ~l'~f CO~T'CT ~IT~ OI'R""'\ ""(JJ~C oRE_ SIDE VIEW AG. 1- FLAME CONTACT WITH GROUND AREA-RAW GAS PILOT VERSUS PREMIXED PILOT. 73 71·97558-1 Here the pilot fires In the dlrec:lion of draft and provides a flame which readily Inl9rwcls with t!"le main burner flame. Fig!. 6, 7, 8, and 9 smw recomlTlElOdad pilolloc:ations on other burner types. PosmON THE PILOT $0 rr FIRES IN THE GENERAL DIRECTION OF THE DRAFT Fig. 315 an 8l1:C9l1enl BlI:arrple at a piJOllhai is localed 10 1Ire In the direction at t!"le drall. Obviously, drall etfecl would not pull. th8 piiOI away from lhe main 11am&. In fact, prevailing draft would anecl both pilOl and main flames in FIG. 2-TYPICAL MOUNTING OF FLAME RECTIFIER' P·ILOT ON MUlTIPLE HEAD GAS BURNER. 11=j):::1!yP'LOl lkd=j FIG. 3-RECOMMENDED PILOT INSTALLATiON ON AN INSPIRATOR OR VENTURI TYPE BURNER. the same manner. Any drilllrlQ of one flame would be ac- companjedbya almUaralfling 0' l!"le other. The result will be smooth reliable Ignition. Never instalilhe plio! burner so thallhe pilot flame can st1i1l Joaposiflon whete il will not positively IglU8lhe main burner, but can still make conlact wilh the flame electrode. For ell:atJl)le, i1 the pliol burner Is installed horizontally or inclined. the flame electrode must NOT fie along the lop of (he pilot burner assembly where a weak or ~Iazy' pilot PILOl FIG. 4-INSPIRATOR OR VENTURI TYPE BURNER WITH EXAGGERATED POORLY POSITIONED PILOT AND FLAME RECTIFIER. TDP VIEW "" J ' FIG. 5-TYPICAL MOUNTING OF FLAME RECTIFIER PILOT ON RADIANT INSHOT TYPE BURNER. 74 flame, inadequate to liQht the main burner, can curl up around lhe shank 01 lhe 1lame eleclrode. PROTECT THE PILOT FROM THE EXTREME HEAT OF THE COMBUSTION CHAMBER AND RAOIAnON 00 not locale the pilot burner nozzle where the main 11ame will impinge on il under any f1rinQ conditions. tf p0s- sible, keep the pilot oorner below or behind the main burner ,(as in F(Q. 3) so Ihat the burner frame and refractory help aiDE VIEW BV~~ER "" "" FIG. 6-POSSIBLE MOUNTING OF PILOT AND FLAME ELECTROOE ON RING TYPE BURNER. FLAIoIC RECTIFlU TOP VIEW FIG. 7-POSSIBLE MOUNTING OF PILOT AND FLAME ELECTRODE ON TUNNEL BURNER, 75 10 shield the pilot burner. Locating lhe pilot In the secon- dary air stream will also provide a cooling effect. KEEP THE PILOT VENTURI ACCESSIBLE AND AWAY FROM HIGH TEMP1::'AATURE AREAS The pilot venturi /TILlS! be accessible 10 make air adjust- ments 10r the proper amount of premi:Jclng. Preferably, the venturi ml:lCer should be localed outside the combustion chamber and usually outside of any wind boll; area. Fig. 2 shows the venturi located where il is readily accessible. Hi.;;tl-temperature locations should be avoided because Changes in air temperature al the pilol mi:lCer may pr~ce undesira changesble In the pilot flame characteristics. POSlllVE COMBUSTION CHAMBER PRESSURES Positive combustion charrtler pressures are caused t¥ lhe rapid expanSion of lhe fuel mixture in the oorner. One result is pilot instability, causing erratic flama prO\ling. In severe cases the pressure may be emugn to snuff oullhe pliol. It may be necessary to relocate the pHot venturi where the pressure will be equaliZedbetween it and lhepilotnoz- zle; e.g., below lhe oorner bed on an ~hol burner. SIDE VIEW FIG. 8-TYPICAL MOUNTING OF PILOT ASSEMBLY ON MULTIPLE HEAD INSHOT BURNER. PILcr TOP VIEW FIG. 9- TYPICAL MOlJNTING OF PILOT ASSEMBLY ON SINGLE- PORT INSHOT BURN.ER. 71-9755&-1 REQUIREMENT 2-ADEQUATE GROUND AREA ,,,. • Ensure that the ground area In contact with the flame exceeds the area of the flame rod normally In COTllact with the flame by a raUoOf alleast 4 10 1. This ratio Is sufficienlly large 10 prevern grOUnd area. problems regardless Of the pas/lion of lh". rod in the flame. WHAT IS GROUND AREA? Ground area is any malerial In contact wllh (he flame that will carry the flame currenl10 ground. Grourd area Is dasignecHnto the buTner ItseH. In ad::Iition, melal burner or COrnbusl.ion chamber pal1&, refractory, and other maleri· als In contact with the flame all act as pan 01 the ground area. (Refractory does conliJcl once It Is healed· this Is why the flame rod must not be In contact with refractory.) A typical method of pro iding ground area tor a pilO! flame is shown in Fig. 10. Ground area is provided on the C7005 Rectifier Pilot by "bomb fin" grOUrd plales that are part of the burner noz- ·l.~( ~lECTIItlDE x" FIG. 10-C7005 FlAME RECTIFIER PILOT. zle. This type of pilot will rarely present ground ralio ptcblems. It is not usually necessary to provide special grounding a.sserrtlIles for main burner flames-the flame COntact with the walls of the cont:ustion cham/::le( and wllh burner parts is generally sufficiant 10 provide' an acceptable ground-lo-flame-rod ratio. ADDING GROUND AREA TO EXISTING BURNERS PILOT BURNERS If the existing pilot bJrner does not proviae sufficient ground area for the flame, it may be replaCed with a rectifier pilot like the C7005 which does have sufficienl ground. II may also be filted wilh a special ground assembly, if available; or grOUnd area may be added to the pilot USing one ot the methods Sl'lJwn below. • FLAT PLATE MULTIPLE ROD TIle flat plale asserrbly is similar to the type at ground area used on the C7005. It may be construc.led simply by welding together pieces of high-temperature steel. The assembly is then welded 10 the burner head. TIle multiple rod assembly is constructed b\' welding plecesofflame rod loa melal strap. The slrap is then fitled around lhe burner head and welded In position. TIle rods may also be welded directly to the burrier head, or the head may be tapped and the rods screwed Into the tapped holes. MAIN BURNERS If gtwnd area musl be added 10 a main burner flame, add rods or pipe grOUnded 10 the boiler or furnace wall and projecting Inlo the flame al all times. RODS VS FLAT PLATES FOR GROUND AREAS A curious phenornenal will be noted when using flal metal surfaces as a grounding medium in lhe flame envelope. Allhc>lJl;t1 the metal may bEl complelely Immersed In the flame, effective ground area In contacl with the flame wlllex:lsi only around lhe edgeS of the tlal metal surface. A thin layer of unburned gas tends 10 insulate the center por- tions of (he flal surface from the burning fuel and IonIzed gases adjacent 10 lhe ftame. This condition Is present, but to 8 much lesser degree, when rod materials are used for flame grounding. 76 Rod materials also offer a much more flexible means of accompliShIng grounding, as they may be mounted In any number and In any pattern necessary to Insure contact wilh the flame under all conditions of varyIng drafts. The qusstlon 01 flash-over does not enler the picture with rod grounding either, as II may with f1afplate ftame groundlng. Protel;tion from flame snuffing In strong drafts Is perhapS even grealer with rod grOLrlding than II Is with flat plate groundino. The flame will liang behinc:l a rod, whereas lhe plate lends tpblock the air flow, Ihus wiping the flame from Ihe surface , EFFECT OF SOOT OR SCALE BUILDUP Soot or scale buildup on a flame rod can rasull in reduc- tion of the grOUnd-te>-flame-rod-area rallo to IBS5lhan the 4 to 1 rEQJired for prc:per rectiflcallon and'flame currenr. Un- - ,,',. der -no flarne-, condltions, sool and' scale are nonconduc- tors of eleClricity. However when flame is awlied, they actually become condJclors. The problem Is In the addi· tlonal area acX1ed 10 the flame red by fhis bui~. Ad:fI- tlonal surface area provided by Ihe hills and valleys of lhe buildup material can easily cb.bIe or triple the flame rod area. Too much buildup can decrease the flame currene below the value required to hold in Ihe flame relay, and burner shuldown will occur. This points out Ihe necessity of inspecting and Cleaning the flame red periedically. PROVING ADEQUATE GROUND AREA (FLAME SIGNAL MEASUREMENlJ The best inc:licator or adequate ground area is a flame signal reading of prq:>er size and steadiness. The flame signal is measured with a dc microammeter (Honeywell W136A or equivalent) connected in series with the F lead. Most HoneY'N8l1 conlrols have a meter jaCk which aute>- malically places Ihe meter in serles with the flame rod. Refer to the inseructions paCked with the flame safeguard control for Ihe exact flame slglal measurement procedure. WlIh most Honeywell conlrols, the flame siliT'i!l should be at least 2 microart'f.lElres and s1eadj. The reading 00- '\ained on self-Checking systems will be much higher-re- ter to the controllnsfrucfions. If the flame signal reading is not correct, the ground area shOuld be the firsl ilem checked. If In doubt, ~ more ground area 19lTIpOfarily and recheck the flame slglal. tt a satlsfacfory reading is obtained, adj permanent ground area. REQUIREMENT 3-PROPER LOCATION OF THE FLAME ROO IN THE FLAME ENVELOPE , The location of the flame ro:::l In the flame en'l9lc:pe must meel the following requirements. ,. The location must provide the req.Jlred type of flame s~rvrsion. 2. The flame rod must be In conlact at all times with the flame fo be proved. 3. The rod must b& located so lhat II c8/TlOt defect the pllof flame if il becomes too small to Ignite the main bumer flame (pilot proving aw1icatlons only). 4. The locatron should prevent changes In the flame ro:::l posillon or al leasl eliminate the PJSSlblllty of any change causing a dangerous situation. TYFES OF FLAME SUPERVISION The flame rod may provide any Of 3 possible types of flame supervision: Pilot anc:l maIn flame slmultaneoosly. Pilot flame only. Main flame only. BOTH PILOT AND MAIN FLAME SUPERVISED If at all possible, the flame rod should be Iocaled af the intersection of the pilot and main flames. This type 01 awlj- cation proves lhalthe plloe Is adecp.Ja.le for main flame ignition anc:l proves lhe main flame COO!lI1l.OJSIy dJring the run cycle. Figs. 3, 6, 7, and 8 show flame rods awlied fa supervise the pitof flame at the poinl of intersection with Ihe main flame. PILOT FLAME ONLY SUPERVISED On some installations it may be Impossible to prO'fflthe pilot and' main flames SimUltaneously because of vari· ations in the main flame envelq:::.e al different tiring rates. Where II is not possible to prove lxlth pilot anc:l main flames, proving the pilot only is the nexl best q:ltion. Fig. 11 shows a mechanical fan type burner where the gas pressure rotates Ihe fan blades 10 provide torced draft for the burner. [n this burner, the flame position varies with the firing rate, making illmpossible to prOl/e lxlth pilo!. anc:l main flames. Alsa, b&cause Of the design of the cermus- tion chamber, It Is Il'fl)OSSible fa check the main flame and pilot flame without sub~ !!.ng the pilot asserriJlv to the In- tanse combustion chamber temperature. Proving the pilol only is also ckJne on con1:linatlon IOJ2S" oil burners, particularly on the horizontal (otary type wllh the gas ring added. When proving a pilot closer 10 Its source than at the ignl. tion point for the main flame, we can sHI! prove the presence of an adequate pilol flame by supervising the pilot gas prBS5ure. Fig. 12 shows a raverse acting gas pressure switch used to intern pt the circuli to the main gas valve whenever the pilot pressure drops below the point at which rell· able ignllion would occur. MAIN FLAME ONLY SUPERVISED When only the main flame is to be supervised, the flame ro:::l must be located where It will remain in the flame eovelq:::.e during atl variations In firing rates and draft ad- jusfments. On larger burners, special conslc:leratlon mUSl bEl given to main flame welq:::.e changeS that occur 0'l9f T7 71-97558-1 considerable distances wllh variations In firing rates. certain ring and gun burners produce regular fluctuations in flame loCation, even during steady firing. AWlicalions or this kind shouldJ)e carefully checl<ed under all possible draft cerdtions and LKlder all firing rates before the instal- latioo is considered complete. ENSURE THAT THE FLAME ROO REMAINS IN CON· TACT WITH'THE FLAME UNDER ALL CONDITIONS , aiDE VIEW FIG. 11- MECHANICAL FAN-TYPE BURNER IN WHICH PILOT FLAME ONLY IS P VEN ~:::"T"'" l~R "CO ;-;OVALV "" • PilaT ~ W " " PILOT 8UllNER llJ"I'LT '" ~ - L:: RfvfR5f: ACTlt,»l PRE 5SURE , • L MAIN Cl)/HlQ GAl IlIlh~1 ClllCun 10 III VALvE VALVf lENP1LOT G PREl~RE DROP.; ~. GAl I> 6:: ] .~, FIG. 12- METHOD OF PROVING AN ADEQUATE PILOT. Main flame posilion and Siability are important on lhose appllcalions where II is necessary to supervise both pilot and main flame simultaneously or when the main flame only Is supervi&ed. If both pilol and main flame are 10 be supervised, then the flame roo must be located so thai It remains in contact with lhe main flame under as wIde a range of draft and burner I'TlOdLIlation conditions as possible. If the main 11ame only Is to be supervised. then the flame roo must stay in the flame envelqJ6 under all COl'ldi- tions of draft and rnoclllation. AVOID LOCATION THAT ALLOWS FLAME ROO TO BE IN PILOT FLAME WHEN PILOT CANDLES Avoid locating lhe rod Immediately aoove the pilot flame (see Figs. '3 and 14). If the plio! pressure Is rEdJC8d for any reason, the pilot flame would obViously decrease in its int9l"\!'lJty, and a candling effect would be noliceable. If the flame rod Is localeo: immediately above the pilot, this candling could allow the flame rod to sense the pilot even lhough the pilot flame is in no posilior'lto smoothly or sa/ely ignjte the main burner. Bringing the roo In from the side or from undemealh the pilol flame avoids the POSSibility that lhe flame roo will cootac! the pilot flame under a low pressure condition where the pilot is incapable of prO\lidlng safe ignition. LOCATE THE FLAME ROD TO PREVENT DANGEROUS CHANGES IN POSITION Keep the flame roo short, avoiding bends i1 possible. Fig. 15 is an e.:ceilent example 01 an application that meets this r9CIuirement. Nole how the flame roo is brought PILOT 8U~N,~ .RONG PO~TIIl< Of ~O~ FIG. 13-IMPROPERLY POSITIONED FLAME ROD MAY PROVE AN INADEQUATE PILOT FLAME. NOTE· INE fLANE H!CTIlOOE INOI.JLO 6E LOCA TED ON EIT~!~ ~IO[O~ 8ELOW T~[ PI~OT WRONG FIG. 14-IMPROPER POSITION OF FLAME ELECTRODE ON C700S FLAME RECTIFIER PILOT. 78 do n vertically Irom the Iq') of the burner assembly. This llame rod will not sag and dTOCP away rrom the location where il can properly supervise the pilol and main flame. Had the flaiile fOCI been broughl In from behind, it would have required a longer flame rod with a bend. The longer, bent flame ro:! could drocp out 01 p::sition and no longer provide proper supervision of the pilot Other argu~ls in favo~.at a ShOrt flame rod without bends are: (1) a shorterro:!lessens the chance of excess flame rod area distortinQ the rCJd.area-lo-grouroarea ratio upon which uame rectiticatio:n depends, and (2) straight flame rodS are easier 10 replace than rlXiS that musl be bent to reach the flame-proving point. LOCATE THE FLAME ROD 6aOW OA BESIDE THE FLAME IF II CANNOT BE APPUED VEATICALLY It the flame, rod cannot be positioned SO lhat it comes down from directly above the flame as in Fig. 15. locate it below or bes~ the piiOI flame. FIg.13 Shows how a flame rod may plCve an Inadequate pilot if it is lX'SifiOMd along the top o1lhe pilot burner. In ad1ition, the ro:! must not be located where II can drocp Into a position where it mighl be able to prove an unsafe pilot. If the rod is lOCated beside or below the pilot, it will, if affecled by excessive heat condi· lions, drcq::l away rrom the pilot flame and cause a sate shutdown. UNUSUAL APPLICATIONS RUNNEA PILOT INSTALLATION Fig. 16 shows a burner with mullip/e firing ports iglited by a runner type pilotlhat is proven at the extreme encI at - o o o FIG. 15-INSTALLAnON WIlli SHORT, STRAIGHT FLAME ROO. 79 the runner. This application Is used on many cast Iron sec- lional bollars, and is ideal for the flame rectification sys. tam, The sna.ll, constantly burning pilot may be proved by a thefmOcQ1 1)le IypQ assambly, The constanlly burning pl. lat ignites the runner pilot and that, In turn, fires each oftha burner ports. The rUMer pilol is checked at the1ar end of the runner, A runner piiOI or this type should have adeq.ele grounding area (the small flame al each runner port Is grounded), Ar'rof recbJClion in pressure would make ilself lell flrst at the far end of the runner. Therefore, in lhe event of pilot r9liJclJon. the flame rod would no longer be able 10 prove Ihe pilot at lhe end afthe runner ar'd would not allow the main burner valve to open. MULTIPLE PILOT INSTALlATION If the runner typepilot is nol salisfactory lor thepartieu- Iar installation, end it It is necessary to have more than 1 pilot assen'tlly within a burner for safe i~llIon. !hen sach pilol should be SlCle/Vised by its own flame ro:! an::! flame safeguard control. With the RA890 Primary Controls, this individual supervision can be accompliShed wil.toJl aUlfjl- iary equipment. Fig. 17 ShOws one RA890 and one flame rod asserrbly for sach pilot being- proven. The Interconneclion is SirTlJfe because of tne fleXibility of the RA890. The control circuit can be isolaled from the electronic network. After the first pilot haS been prOViEln, terminal 5 of the first relay provides the power to the control circuit at the relay checking !he second pilot. It the second pilot is also proven, power Is made available to operate the main burner valve. With this arrange- menl, it makes no difference wheth9r Ihe p~ots are intermittent, Igli!ad for eaCh burner operallon, or c0n- stantly burning. In any case, they would haY8 to be pfO'f91 separately or the main burner vaNe could nol be ener- gized. If either pilot fails, the bUrner Is IrTlITtIilCiaIely sh.rt down. - - 0 I~ .c WULTIPlE Olltll~ ~~ PIlRfll(rl(l<[lIPllOf>, ~I r [Ii N III ElOIIIl[1I /' flAW[ 1100 I'll BUIiHEIl o~ ~~AI"_M£1I ",JoHIFClLO NOZZLES FIG. 15-FLAME ROD PROVING RUNNER TYPE PILOT. 71-9755&-1 ()<\ T JoHT PILor - [...]... (INCHES) 1 2 3 4 5 6 7 8 DISTANCE FROM END OF PIPE TO SIGHTED AREA 6 6 .3 3.5 2.6 2.1 1.8 1.6 1.5 1.4 12 18 11.9 17.6 6 .3 4.4 3. 5 2.9 2.8 2 .3 2.1 9.1 6 .3 4.9 4.1 3. ' 3. 1 2.8 24 23. 2 30 36 28.4 34 .' 11.9 14.8 8.2 6 .3 5.2 4.4 10.1 7.8 6 .3 3.9 3. 5 '.4 4.7 4.2 89 INCHES 42 48 17.6 20.4 23. 2 26.0 26.9 31 .7 34 .' 11.9 12.9 15.7 17.6 19.5 21 .3 23. 2 9 , 10.6 11.9 13. 4 14.8 16.2 17.6 7.' 6 .3 5.5 4.9 8.6 7 .3 6 .3 5.6... 10 3. 2 6.1 8.8 4.8 9.5 2 .3 3.4 4.6 5.6 6.8 1.6 3. 2 4.8 1.1 2.1 0.050 2 1.2 tess 3 ""'n 1 1.5 2 .3 3.0 3. 8 4.8 4 - 1.2 1.7 2 .3 2.' 3. 5 5 - 1.4 1.' 2 .3 2.8 1.2 1.5 2 .3 Less than 1 6 1.9 Less 8.1 7.6 8.8 2.5 3. 2 4.2 5.2 8.1 IIOT RffIU.CTORY 'V': !'- /1»: '" r ;'1 8.2 7.8 9.5 4.8 5.8 7.0 1.9 2.5 3. 2 3. ' 1.1 2.1 2.9 3. ' 4.6 5.6 1.6 2.1 2.• 3. 2 1.0 1.7 2.5 3. 2 4.0 4.' _ IIOT PILOT RH~"'CTORY ;'1 ": 1 "l... ,",co - - - 01101' OOT FIG 30 -FLAME CURRENT VS, FLAME SIGNAL FLAME SIGNAL MEASUREMENT The besl indicator 01 a proper detector a~llcatlon is a flame currenl is essentially stable regardless of Increases in flame signal Assume thatlhere is a variat~ In flame sigl8l 8Q.l31 to the width of range A When the flame signal traverses the A variation, there is no sig!ificanl change in flame current It would be... pipe REFER TO THE HONEYWEll FLAME SAFEGUARD CATALOG FOR DETAILS OF EACH MODEL B3 71-97558-1 CHECKLIST FOR FLAME ROD APPLICATIONS o Flame rocl remains in gcxx:l contact with flame under all normal firing conditions o Flame rod iS~ as short as possible -preferably applied from below or beside the flame proved o Ground area is alleasl 4 limes the area of (he rod in the flame o Flame lead has Insulation... C7011A The flame rod used should be as short as possible for the flame to be proved Most flame rod holders may be fit led wllh a threaded pipe to add ~rt to the long flame rod rltesung indicates that the rod musl be supported TYPES OF FLAME RODS Whenever the flame rod extends into the main flame envelope, the temperatures encountered may have some effect on the type of rod selected Most Honeywell flame. .. firing rates 1, Pilol1lame only-the smallest pilot flame thai can be sighted must be capable 01 reliably Igniting the main burner 2 Main llame only-sIght the first 1 /3 of the flame near esllhe burner nozzle, at a point where the flame is presenl for all firing rates 3 PlIol and main flame- sighting must be at Junction 01 ooth flames The smallest pilot flame that can be sig,tad must be capable of igniting... 11.9 13. 1 14.2 9.1 10.1 11.0 11.9 8.0 7.1 8.7 7.7 9.8 8.5 10.4 6 .3 60 I 66 '4 0",,40 72 9.1 71·97558-1 TABLE II-DIAMETER OF AI1EA SIGI-fTED THI10UGH ORIFICE IN INCHES CELl-TO-_ ORIFICE DISTANCE ONeHES) 12 24 J6 1 2 .3 4.6 66 ORIFICE DIAMETER INCHES 0.125 0.250 DISTANCE FROM ORIFICE TO SIGHTED AREA INCHES 48 80 72 12 24 36 48 60 I 72 12 24 36 48 60 Over 10 Over 10 6.8 Over 10 3. 2 6.1 8.8 4.8 9.5 2 .3 3.4... flickering flame, they will simulate flame and will hold In the flame I'8lay after the actual burner flame has been extin FIG 10- METHOgS OF RESTRICTING THE DETECTOR'S VIEW , '. The area viewed by the cell dePends an 3 things: 1 The diameter of the opening in front of the cell 2 The distance from the cell to the opening 3 The distance from the opening to the area interk:led to be vlewecl Fig 10 shows 3 ways... sensing tlba in.the Minipeeper flame delectors (C7027A, C703SA, arid C7044A) is called a UV PJWElr tube When salurated with ultraviolet radiation, this tube delivers aoout -;/10 Wau to the flame signal amplifier The flame relay requIres aoout 31 4 wall to pull in, so mUe power ~lification is required The sensing tube in lhe a~justable se.nsitivity (C7076s) and Purple Peeper flame detectors (C7012s) is... the flame safeguard control Instructions for the flame signat current required and tor exact test procedures In applying or serviCing the flame defector, the primary goal should not be 10 achieve a flame currenl of maximum strength, but a gocx:l steady sig\al above the minimum acceptable current The reaSOn for trying to achieve a steady flame Signal current beccmes apparent from the graph in Fig 30 . 28.4 6 .3 17.6 23. 2 34 .' 2 11.9 14.8 17.6 20.4 3. 5 6 .3 9.1 23. 2 26.0 26.9 31 .7 34 .' 3 10.1 11.9 12.9 15.7 17.6 19.5 2.6 4.4 6 .3 8.2 21 .3 23. 2 4 9. , 11.9 13. 4 14.8 17.6 2.1 3. 5. 17.6 2.1 3. 5 4.9 6 .3 7.8 10.6 16.2 4.1 6 .3 8.6 9.7 10.7 11.9 13. 1 14.2 5 1.8 2.9 5.2 7.' 6 1.6 4.4 6 .3 7 .3 8.2 9.1 10.1 11.0 11.9 7 2.8 3. ' '.4 3. 1 4.7 5.5 6 .3 7.1 8.7. TYFES OF FLAME SUPERVISION The flame rod may provide any Of 3 possible types of flame supervision: Pilot anc:l maIn flame slmultaneoosly. Pilot flame only. Main flame only. BOTH

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