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'''~ Il""T <lAT1~ ~, FIG.51-VIBRATING GRATE. FIG. 52-RECIPROCATING GRATE. FIG. 53-OSCillATING GRATE. amplitude of motion that causes the grate sections 10 oscil· late. The entire assembly is inclined toward the discharge end of the bJiler to ensure movement of the coal and dumping of the ash. The TRAVELING GRATE (Fig. 54) is the most popular for spreader stokers feeding larger bJilers (over 75,000 pounds at steam per hour). The grate is made of overlap- ping clips or bars in the form of a wide, Elfldless, conveyor bell. It moves al speeds between 4 and 20 feet [1.2 and 6.1 metres] per hOur (depending on steam ~ loward the front end ot the bJller, discharging ash continuously Into a hOpper. II Is designed 10 handle a wide r.lnge of coals, as well as process wastes and municipal refuse. -'''EL'''~D c.~",~ TUVll _TOC.l'M(~ ~ I PLENUM CHAMBER CUTAWAY VIEW ASH - 'I, _~ SIMPLIFIED DRAWING FIG. 54-TRAVELING GRATE. CROSSFEED STOKERS (FIGS. 55 AND 56) Crossfeed slokers (otten called rnass.Qurning slckers) are well suited for a wide variety of solid fuels, including peat, lignite, subbltuminous, free-burning bituminous, an- thracite, or coke breeze. Their big advantage 15 thai lhey offer smoketess combustion al most loads. Coal is ted onto the grate from a hopper under control of a gate. The gate establishes the thickness of lhe fUel bee!. Furnace heat ignites the coal and dislillaUon begins. /As the fUel bed moves slowly. the coke formed is bumed. and the bed gets progressively thinner. By the time the far end is reached, nothing remains bul ash, which fallsortthe grate into a hOpper. Because of the variation In fuel{)ed thickness, airflow must vary along the bed. The grale surface is divided into a series of lOnes. each wilh Individual dampers tor close control 01 airflow. The furnace itself Is usually dBsigled with long, rear refraclory arches to direct the lean fUrnace gas fOlward, and to reflect heat 10 ignite the fUel qJickly. High-velocity averfire air jets, located in fronl or lhe fUr- nace above the grate. prlXllce the turbulence and mixing required for goocl combusllon. GRATE TYPES FOR CROSSFEED STOKERS (FIGS. 55 AND 56) Crossfeed stokers usually use traveling chain grates al- though an Inclined vibrallng grate is sometimes used The TRAVELING CHAIN GRATE (Fig. 55) is similar to the IraveJing grate described fo~ spreader stokers. except thai il is really a wide chain with grate bars forming lhe links. The linkS are slaggered and connected boI rods ex- tending across Ihe stoker width. A traveling gtate made with overlapping clips (lhe same as for a spraader stoker) Instead or a chain is somelimes used. This type has a chain drive althe side of lhe grate. 31 71-97556-1 UNDERFEED STOKERS (FIG. 57) In under1eed stokers, lhe coal is fed from the bottom or 6ide of the bed and Il'1e combustion zone propagales downward. The comt:l!Jslible gases from the Volatile mat· ter are passed through incandescent coke rather than through green coal (as in O'Ierleed stokers), resulting in more COf11,)lete combustion. The coal is pushed along in a feed trough, or retort. Urder pressure of fresh coal from behind, il rises, in the retort and spills over onto the bed at either side of lhe trough. No air is sUJ:Plled In the felort; II comes through ~nings, called ruyeres, in the grate sec- tions adjoining the trough. At the top of the retort, the in· coming air and furnace heat dry Il'1e raw coal. los the coal moves from the retort to the bed, ignilion occurs and distil· lation begins. The pressure 01' Ihe Incoming coal or the grate molion moves the blJrnlng coal to the oomping grates, where lhe astl is diSCharged. Underleed stol<ers in· elude single-retort and muJDple·retort stokers. FIG.57-UNDERFEED STOKER. SINGLE·RETORT STOKERS {FIGS. 58 AND 59) Single·retort stokers burn most bituminous coals as well as anthracile. Practical considerations limit their size, so they are used crlly in small plants. These slokers diNer in the method of feeding coal. One type has a reciprocat· ing ram and pusher block arrangement. The (am transfers coal from the h~r 10 the retort, where pusher blocks help dislriblJle il 10 the fuel bed. Another type has a relort with a sliding bottom on which are mounted auxiliary pusher blocks for advancing coal in the relort. Single-relort stokers may have stationary grares (Fig. 58), but many have moving grates to provide fuel-bed agio talion and 10 move the coal. An undulating grale (Fig. 59) produces a wave-like motion which breaks up the coke for· mations and keeps the fuel bed polOUS and free-burning. In addition, all single-relort stokers have dumping grates at the sides where the ash is discarded MUL nPLE-RETORT STOKERS (FIG. 60) Multiple-retort slokers are large-capacity units. They consist 01' a series of inclined, feeding relorts, extending from the 1ront to lhe rear ot the boiler, with tuyere sections between them. Rams push Ihe coal inlO the front end of the retorts below the fX>inl at air supply. Air is admilled lhrough the luyeres in the grate sec\ions between and al the top of the retorts. Incoming coal gradually forces its wey up under the fire. secondary distributing pushers move the whole mass slowly to the rear. The fuel bed is characterized tIy l'1ills directly over the retorts where the coat is coming in and by valleys (rela· , • -,' FIG. 55-CROSSFEED STOKER INSTALLATION WITH A TRAVELING CHAIN GRATE. The INCUNED VIBRATING GRATE (Fig. 56) consists of a grate surlace mounted on, and in intimate contact with, a grid of water lubes. These lubes are connected to the boiler circulatory system to ensure positive cooling. Waler cooling prevents grate deterioration, minimizes clinker formation. and protects the grate from radiant heat when auxiliary oil or gas firing is used. '''D9D~ '''Ln FIG. 56-CROSSFEED STOKER INSTALLATION WITH AN INCLINED VIBRATING GRATE. The entire structure is supportedtly a number of flexing plates, allowing the grate 10 move freely in a vibralory mode. Intermittent grate vibration moves the coal from the feeding h~ onto the grate and graooal1y down the in- clined surlace. Ashes arB discharged aulomalicaHy into an ash pit. A liming device regulates the frequency of the vibratory periods. FIG. Sg-SECTIONAL VIEW OF A SINGLE- RETORT STOKER WITH UNDULATING GRATES. (Courtesy of Detroit Stoker Company, Monroe, Michigan.) FIG.S9-SECTIONAL VIEW OF A SINGLE·RETORT STOKER WITH STATIONARY GRATES. (Courtesy of Detroit Stoker Company, Monroe, Michigan.) • . ' FIG. SO-MUL TIPLE·RETORT STOKER (SECTIONAL VIEW OF 1 RETORl). lively thin sections at fuel baa) over fhe tuyere zones keeps the fuel bed porous. Dumping grates atlhe rear get where the air is entering. The valleys form aseries at paral· rid at the ash. leI, active burning lanes down the tength of the stoker. The multiple-retorl slake' was a nalural extension of The reciprocating grate is built in sections. Adjacent the single-relor! idea. HOWElWJr, its pq:l'Jlarily has waned sections move in q::lposile directions to cause stroking ac- 10 lhe poinl where only one or two are sold each year lion-when one section is moving forward, the other is Ihrou;tloul (he enlire industry. The multlple-relort s1ok.er moving backward. This reciprocating movement distrib- was usacl eXlensively tot' burning caking coals, tor which it utes coal over the grate surface and at the same time is WEIll adapled. Recant successes in this same area by 33 71-97558-1 , -;. •• over1eed stokers, which are much less costly to malnlain, have just aoout obsoleled multlple-reton stokers. SUSPENSION FIRING In susp80Slan firing, pulverized !powdered) coar is transported to the furnace in an air slream and injected into the combuslion cl'larrt)er, along with primary air, (hrou~ 8. nozzle. The nozzle IS usually horizontal, and is surroune!ed by art. air register Itlrou~ which secondary air Is admitted. . Within a fractioo of a IIbcbndafter a fine panicle ofpow- dered coal enters the combustion chamber, the heat pre- sent raISes 1m lerrperature and distills aI'I' lhe volatile maUer. The volatiles, moslly hydrocartlOns, Ignile more easily than the carbon c~1 of lhe COllI. While the volatiles bum, they heat the remaining carbon particles to IncandesC8flG8. SecCl'ldary air sweeps past and &Crltls the hoi carb::ln partiCles, grackJally burning them. Pulverized coal installatiOnS have lhe high heal effi- Ciency and quick regulation dJlainable wilh gas and oil, which are olher examples of suspension firing. They also represent an efficient method of burning a Cheaper fuel. The major disadvantage is the expensive pulverizing and handling equipment required, which results In a relatively hi~ ~raling cost for mechanical power. They also re- quire dusl. calchers or precipitalors near urban areas to keep fly ash from settling oyer the area. Pulverized coal units are economically feasible only for plants consuming more lhan a ton 01 coal per hour. These inslallations handle any type of bituminous coal. They can handle coke or anthracite in special cases, but it takes much more power to grind these hard coals. The power re- quirement also increases rapidly with moisture conlenl, so the coal is dried as much as possible before pulverizing. THE DIRECT·FIRING SYSTEM A variety ol equipment is used to grind and lransp:ln the coal and inject it into the furnace. Originally, the prepa- ration pnase was entirely'separate. The central system (or tin system) consisted of a large pulverizer supplying a nLR1t:ler 01 furnaces, and had a bin or bunker for sloring ltie coal 10 await demand. II could operale al optimum ca- paCity wilhout the need for a back~ pulverizer In case of an emergency. The coal was a constant.gradeofflneness, and the burners could be cOntrolled separately with ease. HOW8ller, the central system had lwo big disadvantages: 1. The storage bin was a potential fire hazard Sponta- neCJl.JS iglitlon almost always occurs jf a binful of pow- dered coal is left undisturbecl for several days. 2. After Sloring the coal for a few hours, caking occurs due to surface o:.cidation and the coal no 10nQlir flows fteely. In the direct·firing system now used, the pulverizer SLP- piles only one furnace, and has no storagebin. Since there Is no slorage capaCity, pulverizer operation fluctuates with load demand ThIs system is simpler, involving less equip- menl, so It rl!ldJces capltal outlay. II also avoids lhe poten- lIal fire hazard and caking of lhe bin. The quantity of pulverized coal in the mill never exceeds a minimal amount, and piping belween the mill and furnace is short. The flexibility needed 10 handle a wide range of coal and load conditions is built into leday's dlrect·firlng systems. The pufverizing mlJlls the hean of the direct-firing sys. tem. The funclions of amlll are (1) feeding raw coal at the proper rate, (2) grinding the COlli to the desired fineness, and (3) classifying the finished product so oversized parti- cles are returned to the mill's grincing zone. In most mills, air performs three functions: (1) it dries lhe coal. (2) II helps Classify the pulverized coal leaving the grinding elements, and (3l1t Iransports the finished prc:xj uct to the burners. The air is si.Wled by tarceck:lrafl or negative pressure. In (he fOlCed-dlalt. arrangement, a fan outside the mill ~lIes air under &nOl (tl pressure to perform these 3 functions. tr 8 separate air heater is provided, the fan can be located on the Inlet side 01 the heater and will handle cold air. When aU combuSlioo air cemes from a single air heater (general practice in aU but large, central stallons), the fan moves only heated air. and its size and power re- QUirements are mUCh greater. In both cases, the fans han- dle air only, whiCh Is an advanlage, but the pulverizer mUSl be kepi airtj~1. In the negative pt&ssure arrangement, an exhauster fan rl!ldJces lhe air prBSSLl'e on the mill so that internal at- mospheric pressure can be used. The fan may be com- bined with the pulverizer proper, or il may be mounled ellternally. However, il has 10 handle air laden with coal, so it must be rl.lQQQCl to resist wear. PULVERIZING MILLS (FIGS. 61 THROUGH 66) In a typical pulverIzing mill (Fig. 51), a feeder moves the raw coal from a hopper into a pulverizer at a definite. ad justable rate. The feedet mechanism can be a variable- stroke plunger, a re1iOlving screw, or a rotaling table. A crusher-dryer removes surtace moislure from high mois- ture coals before they get 10 the pulverizer. The pulverizer ilself crushes Ihe coal into a powder, usually by grinding. STOR"GE"'N "O'PER~ COA~ PIPING TO BuRNERS FEEOER CRuS"ER· DRYER C~"SS'F'ERS Pu~YER'lER FIG. 61-TYPICAL PULVERIZING MILL. 34 but also by impact and attrition (wearing away by friction). drum, typically a steel barrel with a cast alloy·steelliner. Air carries the pulverized coal to a cla::isi(ief, which deter- Steel or special·alloy balls, about 1 fa 2 inches [25 to 50 mines the fineness 01 the coal going to the burners and re- mm] in diameter, occupy about one-third 01 the drum vol- turns the ov~rsize particles to the pulverizer. Finally, an air ume. As the drum rotates, the balls are carried part of the stream carries the classified coal to the burners through way around it and then slide or drop back toward the bot· pipes. tom. Coal is fed in at both endS at the drum and intermin· There are several types of pulverizers. Table IV lists gles with the balls. Impact from the 1alllng balls and typical characteristics 01lhe most common types, which attrition and crushing from the sliding mass pulverize Ihe will now be·described. -; coal. The pulverized coal exits 1rom txlth endS of the drum, BALL M1L,L (FIG. 6f) as shown. (In another design, the raw coal enters one enc:t A baO mill (or tube mill) consists at a horizontal, rotaling and the pulverized coal leaves at the other end.) ,- . ' TABLE IV -lYPICAl PULVERIZER CHARACTERISTICS PULVERIZING MILL TYPE • SPEED (RPM) CAPACITY (TONS OF COAL PER HOUR) PRINCIPAL APPLICATION FIGURE NO. Ball Slow 20-25 4.so Abrasive coals. 62 Bowl (SuctionB-) Medium 75-225 4·20 Industrial steam- generaling systems. 63 Ball-and-Race Medium 75-225 4·20 IndUstrial steam· generating systems. 64 Roll-and-Race Slow 2().75 55·70 Gentral-station txlilers lor utilities. 65 Altrition High above 225 6-32 Nonabrasive coals; txllh industrial plants and utility staliOtlS. 66 , ",- • a Pressurized txlwl mitis are manufactured in larger sizes, up 10 100 tons 01 coal per hour, for the electric utility industry. Ball mitis use more power and are noisier than other types at pulverizers. However, tJ:ley can handle abrasive coals at less than halt the malnt~ance costs. l BOWL MILL (FIG. 63) A bowl mill is usually a suction machine. An exhauster keeps the txlwl under slight negallve pressure to draw In the raw coal Md convey pulverized coal 10 the burners. /4s the txlwl rolates at a constanl speed, coal Is drawn Into II and ground between the rollers and grlndlng 00wl. The exhauster is a ruggedly buill steel-plale tan de- signed tor handling abrasive materials. A semishrouded tan wheel wilh so-called ·Whizzer ft blades handles lhe coarser coal particles. This herps !o increase the life ot the maIn exhauster blades, sInce Ihey only have to corrveythe finer coal particles. Bowl mills are also manufaclured for pressurized, rather than suclion, operation. TIle pressurized mills are built in larger sIzes (LP to 100 tons ot coal per hour) tor the electric utility industry. In lhese mills, the rollers are In- clined more 10 the horizontal than they are in lhe suction FIG. 62-BALl MILL PULVERIZER. design. 35 71-97558 1 PULVEI'lIZEO·COAL DELIVEI'lY PIPE FIG. G3-BOWL MILL PULVERIZER. BALl-AND-RACE MILL (FIG. 64) A ball-and-race mill has 1 stationary top ring. 1 rotating bottom ring. and 1 set of balls that comprise the grinding elements. Each ring has a groove (race) 10 keep the balls in place. The oollom ring is driven by a yoke allached 10 the verlical main shatl of the uni\. MAIN SHAFT CLASSIFIER '~J:ciIONARY DRIVING YOKE 'SURNER,PIPE ' SHUTOFF VALVE ~, FIG. 64-BALL-AN[)"RACE PULVERIZER. This mill is designed for pressurized operation. Raw coal Is fed into the grinding zone to mix with partially ground coal. Primary air causes the coal 10 circulate through the grinding elements, where some of it is pulver- Ized in each pass between the rings and balls. A$ the coal becomes fine enough 10 be picked ~ by the air. it is car ried 10 the classifier. Oversize coal is removed and r& turned to the pulverizer. Maintenance on this type of mill depends on the abrasiveness of the coal being burrl8d. Grinding elements might have to be replaced annually, or they might last len years; the average is two years. ROLLAND-RACE Mill (FIG. 65; A roJ/-and-race mill has 3 large diameter, loroidal rolls equally spaced around Ihe mill. The rolls are mounted on axles and IiI inlo a concave grinding ring. The roll assem. blies are allached, by a pivoted connection, 10 an over· head stalionary Irame. which maintains their posilion, (in anolher design, the rolls are not1ixed in position, but rA- volve about the axis 01 the mill in planetary fashion.) Springs apply force 10 the roll axles, thus Supplying grind- ing pressure. I LLr" PIPES I.,' CO"L 1 -'" 'U"'CY 'I' PIPE PULVERIZED_ : -COAL II' , ,r~OELIVERY FIG, 65-ROLl-AND-AACE PULVERIZER. The grinding ring rOlales at a slow speed. This motion is transmilled 10 lhe foils, which rolate about their own axes. Grinding occurs under the rolls in lhe replaceable grinding ring. There is no metal-lo-metal conlact between grinding elements as each roll rides on a thick layer ot coal. This 1ealure minimizes maintenance. Circulation of the coal IS the same as described for the bali-and-race mill. This Iype of mill is bum in large sizes for use in utility industries. The mill shown weighs 150 tons and stands over 22 teet [6.7 metres) high, Each roll assernbly weighs 10 tons. The diameter of lhe grinding rillQ is 89 inches 12.26 metres]. ATIRITION MILL (FIG. 66) An attrition mill is a high-speed machine that combines impact and allrition forces 10 pulverize coal. (Attrition is the process of wearing away by friction.) Coal and primary air enter the crusher-dryer section where the coal is reduced by swing hammers and an adjustable crusher-tJlock as- sembly. Here. also, flash drying and turbulenl action 36 I £)(HAUSTER SECTION Jj -_.,~ .j;.~ ~41, CRUSHER· I ORYER SECTION : REJECTOR ASSEMeLY I ~ GRIO I~MOVING .• ~Iil~~\"" .:;.i . ". . I ~ II"' I ~, ''"1 ~ " "" , ., ~ STATIONARY IMPELLER PE:G "" FIG. 66-ATTRITION PULVERIZER. remove surface moisture1rom the coal. Dried, granulated coal then passes through a grid section which removes oversize particles for recnJshing. In Ihe pulverizing section, the impeller pegs, statiOllary pegs, ard moving pegs are all tungsten·carbide-1aCed for exlreme hardness. The coal is pulverized by (1) impact of the coal on the impeller pegs. (2) rubbing between the sta· tionary pegs and moving pegs. and (3) rubbing of coal on coal. A classifier assembiy returns the coarse particles for further pulverization. The integra' exhauster draws in coal of the desired fineness and delivers the coal-air mixture 10 the burners. The allrition mill has these advantages: 1. Low capital cost per unit 01 output. 2. Minimum space requirements. 3. Direct drive (no speed reduction) between the prime mover and the pulverizer. 4. Quiet operation. 5. Lightweight parts to facilitate maintenance. 6. Small coal inventory within the mill. The main disadvantage of an attrition mill is the high main- tenance cost incurred wilh abrasive coals. PULVERIZED-COAL BURNERS (FIG. 67) Burners for pulverized coal are comparatively sirrple. Usually the coal is simply blown into the furnace through a horizontal nozzle by the same air wnich has passed through the pulverizer and has transported the coal to the burners in pipes: this is the primary air. SE!con::lary air is usually preheated and SUl=Plied by forced·draft through a "windbox" opening around the burner. • .;- WITH STUODEO TueES HOfUZONfAlllURNER CIRCULAR REGISTER BURNER INTERVANE BURNER FIG. 67-TYPICAl PULVERIZEO-COAl BURNERS. Internal ribs or vanes in the nozzle, in lhe format rifling, heip 10 control air turbulence and the resulling lIame impart a rotary motion to the mixt\Jre of coal and primary shape. air. This provides fuel·air premixing and considerable tur· Most industrial pulverized-coal burners fire info lhe bulence, which are required 10r efficienl combustion. M combuslion chamber horizontally from one 01 the walls. justable vanes in the secondary air regislef, or wil"'d:x:lx, These burners generally are arranged In a maTVler 10 pro- 37 71-97558·1 mote turbulence. Two methods used 10 increase turbu- bustion chalTtler throw their flames against each other. In lence are opposed firing and tangeflfjal firing. tangential firing, the burners throw their tlames inlo the In opposed /iring, bumefS In ~lfe walls of the com· corners of the C~I, COMBINATION BURNERS DEFINITIONS burner is one that is capable 01 burning two fuels at Ihe same lime. There are prd:lably as many Iypes of col'Tbina- Comtination,burners, also:callad multlfuel burners, are tion burners as there are combinations of the different gas, burners that.are capable 9t burning gas or oil, or even pul- oil, and pulverized-coal bJrners. Table V shows the most verb:ed coal. They can Oe 'divided Inlo two classes-con- common combination gas-oil bumers, which are now the version burn'f!tS and simultaneous burners, A conversion most prevalent of the modern bJrners. burner, also called a dual-fuel burner, is a combination bJrnel that is designed 10r rapidly and conveniently CONVERSiON BURNERS changing from one fuel 10 another by automalicaly or Periodic changes in the fuel sLWly and price picture manual,ly qJeninl;j and closing valves. A Simultaneous often make it adVisable 10 change fuels. Therefore, by tar "'- TABLE V-COMMON TYPES OF COMBINATION GAS.OIL BURNERS TYPE Of CONVERSION BURNER TYPEOf 0" BURNER TYPE OF Oil BURNEll ""IR_ATOMIZINO STEAM_ lOW PRESSURE HIGH PRESSURE ATOMIZlNO IIIEC10CAIUCAl ATOMIZINCl HORIZONTAL ROTARV 3-f'IPE PRE~IXING (ASPIRATING) Easlly llOapleC or merl/ng 3-W/ll'fva {Figs Be and BB), - - - - [}A,S "lING (NOZZLE MIXING) - - - W~Jy ,,"C'. paCllaOle<:l (20 10 '~BoHP). also SllIULTA,NEOUS IFI"", 70 acd 7\) In OIOor b.rn" , nO, ACI popJlilf lor modarn l:>u,nal"S (Fig ", H"IPE PRE~IXING (ASPIRATINGI Raql.l~85 aTh Inl,,! 10 bl.ltner. al'lO SI· IoIULTANEOUS (IOlgs, 13 and 14), - - - - GA,S FliNG /NOLlLE" ~IXIN)'I - WIcIoIy "'"C', pac~aOllC' (60 10 YCO BOHP), also SI~ULTANEOUS (FIG,151 Widely usod, p.C~AOIed :60 10 1CO BOHP!, also SI~ULTA,NEOUS (Fill '" - - 2 SEPARATE BURfolERS IN t ASSEMBLY SEVERAL TypeS - - - Fa~1y a:.mmon_ In <><100, Inat&II&I'on~. nol 80 papular 10' rr>r>De1ll ~rs (F"'_ 18). the rrosl prevalenttypEl of burner is the conversion ldual- tueO burner thai turns aUher gas Of oil. These burners are typically used on steam generators rated between 20 and 700 boiler horSBlXlwer output (840 thousand to 29.3 mil- lion 8tuh input at 80 percent efficiency). Most mOdern gas burners are deSigned so thallhey can be adapted to con- version burners by the addition of oil controls, and vice- versa. Packaged combination burners, which Include all necessary conversion com~nents and automatic con- trols, are also available. Combination gas-oil burners can be divided inlo 3-ptpe or 4-pipe burners, depending on the number 01 inlets to the burner. J-PIPE CONVERSION BURNERS As the name implies, these conversicn burners require three pipes to deliver (1) primary comb Jstion air, (2) oil, and (3) gas. Low pressure air-aulomizing, meChanical at- omizing, and horizontal rotary oil burners are adaptable to 3-pipe systems. LOW PRESSURE AIR-ATOMIZING OIUPREMIXING GAS BU RNERS (FIGS. 68 and 69) The low pressure air·atomizing oil burner is readily adaptable as a convarsi::m burner because gas may be fed through the alomizirlg air passage. This requires only the insertion 01 a 3-way valve. Although there are really four pipes, the atomizing air and gas p:pes are connected 10 the 3-way valve, so there are only three pipes actually con- nected to the burner. Therelore this system is commonly referred to as a 3-pipe conversion burner. To burn oil, the 3-way valve is positioned to shut off the gas and admit atomizing air. When the valve is Iurned 10 38 FIG.S8-LOW PRESSURE AIR-ATOMIZING OIL/PREMIXING GAS, 3-PIPE CONVERSION BURNER (PIPING ARRANGEMENT). (From Combustion Handbook by North Amen'can Mfg. Co" Cleveland, Ohio.) • ~'O"'l'~" ~~"t' .~ ToU FIG. 59-LOW PRESSURE AIR-ATOMIZING OIL/PREMIXING GAS, 3-PIPE CONVERSION BURNER (SECTIONAL VIEW). (From Combustion Handbook by North American Mfg. Co., CJevelsnd, Ohio.) the opposite position, II shuts off the atomizing air and ad- mils gas. The gas enters [he burner lhrOLQ'l the same an- nular space used for atomizing air when burning oiL This system cannot be used for simultaneous burning of gas and oil. A premixing gas burner of lho asplraUng type Is used, and the corri:lustion air draws In the gas by venturi action. The gas Is usually supplied at at~rjc pressure (zero gas). Masl at lhese burners have a retractable oil nozzle. Retracting the nozzle enlarges the atomizing air passage so ellOlJgh gas can pass throu~ ii, even at zero gas pressure. MECHANICAL·ATOMIZING OIUGAS RING BURNERS (FIGS. 70 AND 71) The adaptallon of a mechanical atomlzing oil burMr 10 a conllersiCYl b.Jmer is easily accomplished a.; ack:Iing a circular manilold carrying the gas orifices. The gas ling is hinged SO that it can be swung out 01 firing p:.lSiUon for in- spection and cleaning. The general shape and location oflhe gas ring cause the entering air to swirl thrCll.q1 lhe space between the out- side of the ring and the air regisler, and belween the inner surface of the ring and the flame cone. This causes a lur· b.Jlence of air and gas lor intimale mixing, as welt aspanly inducing a sucllon of gas into the combustlCYl chamber. The gas ring can sometimes be moved forward and back· ward with respect to the wall of the combustlCYl chamber to facilitate optlmum positioning for the desired <::peration. Generally, the same controls can be used to regulate the gas flow, oil flow, and airflow. SO gas and oil can be b.Jrned simultaneously as well as separately. This type of conversion burner Is widely used and is available as a paCkaged automatic burner. Fig. 70 shows an internal view of one modal as II looks from inside the comb.JsliCYl chamber. Four oil nozzles are in a cluster in the cenler 01 the b.Jrner, and the gas pans are evenly dis- tributed arounc:lthe burner. A blower Slq)lies corrbustiCYl air. Fig. 71 shows a similar modal as it looks from outside the corrtluslion chamber. It has been swung <::pen CYl its hir'l',JEl to reveallhe oil nozzles. Both of the packaged mcx:l- els shown have nozzle mixing gas b.Jrners and lorced draft from a blower. They can b.Jrn gas or liQhI oil, or both simultaneously. The Model 119 is rated for 20 to 70 boiler horsepower, ana the Model 120 is raledlor 50 to 125boiler horsepower. HORIZONTAL ROTARY OIUGAS RING BURNERS (FIG. 72) A gas ring can also be added to a horizontal rotary b.Jrn- er, b.Jt the oil b.Jrner has to be swung oul from its pan when gas is used. For Ihis reason. it Is nol as popular as Ofhl:lrs for combination b.Jrners. Obviously, gas and oil cannot be b.Jmed simultaneously. Normally, gas pressure is about 1 psig, b.J1 some mcx:l- els <::perale with hiQher gas pressures. Some of these b.Jrners have their own coobusliCYl chatrtler and are Mpust't-~. unlls completely assembled at the factory; Ihey are pushed ~ to a Scotch marine or similar type 01 boller, essentially making a steam generatOl. CapaCilies -range from alx:lul 1010 380 boiler horsepower OUlput {420 thouSand to 15.9 million Btuh inpul at 80 percent efficiency). 4-PIPE CONVERSION BURNERS These conversion b.Jmers require four pipes 10 deliver (11 primary combusllon air, (2) afomlzlng air or steam, (3) oir, and (4) gas. Generally, anoll b.Jmer Is made Inloa c0n- version burner a.; adding a founh connectiCYl for the gas. 39 71-9755&-1 FLAM!!: ELECTRODE FORWARD GAS PORTS BURNtll. TILE ORI1'ICE PL"TE A55El,IBLY D1LNDlZLE5 RADIAL GAS PORTS NORTH AMERICAN MOD£l119 PACKAGEO AUTOMATIC IlIUIllN£Il , FIG. 70-MECHANICAL-ATOMIZING OIL/NOZZlE NIXING GAS RING. COMBINATION BURNER (INTERNAL VIEW). (Courtesy of Notl.fl American Mfg. Co., Cleveland, onio.) Low pressure air·atomizing, high pressure air-atomizino, and steam-alomizing oil burners are adaplable to 4-pipe systems !l is also sometimes possi:;'!e to add an atomizer 10 a gas burner to ~ke It a conversion burner. LOW PRESSURE AIR-ATOMIZING OIUPREMIXING GAS BURNERS (FIGS. 73 AND 74) This burner is sir'QUar to Ihe 3-pipe burner (Figs. 68 and 69) except that it has. a separate gas inlet, so the 3-way valve is nol reqUired, TIle metal We support shown in Fig. . 74 is used only when the burner ls installed in a thin metal wall-not when itls installed In a relractof)' wall. Sincelhis burner has separate alomizing air and gas inlets, il may be used 10 !x.lrn oil alone, gas alone, or 011 and gas simUltaneously. HIGH PRESSURE AIR- OR STEAM-ATOMIZING OIU GAS RING BURNERS (AG. 75) An oil burner using high pressure air or steam 10r atomi- zation can be simply adapted to a conversion burner by mounting a ported, ring-shaped gas manifold around the all burner nonla{s). This is the sarne merhod used to adapt a mechanical.alomizing oil burner 10 a conversion burner (FiQS. 70 and 71). Gas and oil can be burnedsimul- taneously as well as separately. This type of conversion burnel is well-suiled for burn- ing heavy oil and is generally buill in larger sizes. II is widely used, and available as a packaged aulOTlalic burner. The MOdel 121 (shown) has a nozzte mixing gas burner. TIle all burner is equipped with a tip emulSion '0 atomizer in which either compressed air 0' steam serves as the atomizing medium. The blower provides 10rced draft. This model can burn gas, light oil, heavy oil, combi· nation gas and light oil, or combination gas and heavy oil. 11 is raled lor 60 10 700 boiler oorsepower. GAS BURNER PLUS ATOMIZER II is sometimes poS5ible to ad::J an atomizer to a gas burner to make ~ into a 4-pipe conversion burner. An aspi· rating Iype of premixing gas burnet using a disptacement rod 10 adjust its capacity (Fig. '5) can be easily adapted to a conversion burner by' simply removing Ihe rod and re- placing II with an oil atomizer. Many modern gas burners are simply combination bumers with the atomizer omitted; this facilitates Conversion to oillaler. OTHER TYPES OF CONVERSlON BURNERS (FIGS, 76 AND 77) SEPARATE BURNERS IN ONE ASSEMBLY Two separate bumers are sometimes built into one as- sembly. Fig. 76 Shows a hOrizontal rolary oil burner com- bined with a Websler Kinetic forCed-draff gas burner. Each burnar haS its own pilot and Is supervised sepa. rately.TIle oil burner can burn all grades 01 fuel oil; the gas burner uses low pressule gas. Only one of the burners Is q:)Elrateel at a time. capacities range from 75 to 300 boilgr horsepower. Other combinations of mechanical-atomiz- Ing oil burners with separafe gas burners ate fairly common. [...]... L4l 1 027 0 to 9.300 " '" """" PaClr1 ~n.".N.b1s II S " c:rllieal P'fl8II""S syslsms, al:o.< 30!0U .2 ~", '6 ~ 91·94 " ~.~ ~,~ ", ,~ '" 1 '2, 1\3 11'.118 111· '20 JIOOr ~ ... 1 ,25 mlNlon 10 ,00 million 2lJ 10 23 00 1.000 10 eo,lXXl Stq>A8IIsrrt:NCl '2. 5 million (0 25 0 million 2ElO 10 !IllOO 10.lXXl 10 aX!.lXIIJ FI.Id-EroK:Jed ,8.6 mlI'l IQ 27 0 BoHP (11.3 million Btuh inpul) for field-assembled boilers A cast·iron seclional b:::liler lFigs 81 and 82) is corn­ posed 01 casHron secllons lhal fil together... 120 BaH P (5 mIllion Btuh input) may require field installation of refractory and insulatioo for the furnace floor II is avail· able as a pa.ckaged boiler-burner in sizes up to 600 BaHP (25 million Btuh il'l'Ul) The tirebol boiler can be used to generate either hoi water or steam The maximum hot water le~rature is 25 0 F [ 121 C) , and the maximum operating pressures are 160 psig for hal water and 20 0... 600.000 ~p '08.900 31010 '38,000 "" '''0 "" I"""" ~ , , ,,~ a For a boaS' sllll:l.nC)/ 01 tlO per""nl, _lch Is c:oTImoo, b Avan.Dls CNo as 81. 62 420 Il'IOuSancllO 31 million {HAT) Bf1C1 . FIGURE NO. Ball Slow 20 -25 4.so Abrasive coals. 62 Bowl (SuctionB-) Medium 75 -22 5 4 20 Industrial steam- generaling systems. 63 Ball-and-Race Medium 75 -22 5 4 20 IndUstrial steam·. P.draQ8d 1 ,25 mlNlon 10 ,00 million 2lJ 10 23 00 1.000 10 eo,lXXl "" ~,~ W.l •• _T o. eflnl· , Stq>A8IIsrrt:NCl &apos ;2. 5 million (0 25 0 million 2ElO 10 !IllOO. weighs 150 tons and stands over 22 teet [6.7 metres) high, Each roll assernbly weighs 10 tons. The diameter of lhe grinding rillQ is 89 inches 12. 26 metres]. ATIRITION MILL (FIG.