Document n9D7M94e5ykEN3Ek9KJ5aOvaG

ROTARY-CUP AND COMBINATION GAS-AND-OIL BURNERS Coot bunker Pulverized fuel to burner Pulverized fuel Bnto burners>. iy Cup revolving ieuiit*rilihb briakt up oil flbn of rim by renMfugol forco owl discharger Into clockwise olr atroom |0 Built-In fun rotating ' motor-speed lapplloa primary aW |u behind the atomising ell cup. Air catcboa op fine el) spray Isovlng at cup edge Ihi (his putvarlsed-cool firing system, pulveriser ts hsld radar positive priimri by far*ad-draft fen, must bu tight tahoustur fan puts nogetfvu pressure on mill but requires that special precautions he taken against severe fan wear lg Bolt driven rotary-cup burner tarries a loot-oil reaervolr to Inavre pealtlve " teed, end e aubmerQod electric hooter to held oil et correct temperature. Oet pilot mounted overhead, together with low-voltage ayatem, aervea to Ignite the ell 20 ComWnatlo geo and c either fuel or befh together* saws^,regbter regulates primary air supp#ftf* to storage tank or pump suction. (2) Fuel enters the dosed circuit at the some rate it is burned, simplifying fuel metering and combustion control. (3) Pump may be used to boost pressure on existing oil-burner systems. Retary-Cup Burners. Third major class of oil burners, the horizontal rotary cup, atomises fuel oil by literally tear ing it into tiny droplets. A conical or cylindrical cup rotates et high speed (usually about 3500 rpm if motor-driv en). Oil moving along this cup reaches the rim where centrifugal force flings it into an air stream. Fig. 17. This system of atomising requires no oil pressure beyond that needed to bring oil to the cup, and proves attrac tive in installations where only lowpressure steam is available. High oil preheat temperatures must be avoided aince gasification may develop. The rotary cup can satisfactorily atomise oils of high viscosity (300 ssu), how ever, and hot a wide range, about 16 to 1. Fig. 16 shows a burner with a builtin driving motor, while Fig. 19 shows, one with a belt drive. It also indicates provision for swinging the burner out of the furnace. Gas end oil burners are often com bined, as in Fig. 20. Designs of such combinations vary widely, both in nature of oil unit and gas unit. Their ability to handle either of the two fuels, or both at once, proves desirable In locations where both ore available. Burner Mofatanance. Properly main tained; modem oil burners give highly satisfactory service. For peak perform- once, make sure that the burner uniformly free-flowing oU, clear sediment that clogs burner noxri*vV. This means avoiding sludge bulldupjg-sj in storage tanks and keeping stralM^^Xj: in good condition. Preheat temperature)?;-.,, must be right for fuel and burner typAjav^ and must be uniform. . Keep burners in good condition watching for weor caused by abrasion of 8tb in fuel, and for carbon buildup . ,,, In rotary-cup burners, worn rims poor atomisation. If cups are properly protected after being off. carbon forms on the rim- burner is shut down always the cup and insert a flame shield- W or carbonised mrahanleal-atonMrtfjsr nozsles play hob; replace worn vo&.^ ' ond keep them clean. BB (7S2) POWER Orodnd to the fineness of flourj coal inflows In pipes and handles in a furnace' mueh as does oil. The job requires ft equipment for drying and pulverising jktbc coal, transporting it to the furnace frla aa sir stream and injecting it along jtifwith the air needed for combustion. vipenilen Burning. Within a fraction ^ of e second -alter one of these minute ? particles enters the fumocc and is ex- ji Paced to radiant heat, its temperature s rises and the volatile matter distills l`ofl. Enough olr (primary air) is Intro* Induced at .the burner, intimately mixed fttfUh the stream of cool particles; to L-bum (ss resulting from separate diajutUlitfon 0f ^{-1, particle in the stream. volatiles, mostly hydrocarbons, yifnite more easily than the carbon re- j?**n*n* *n particle and beat the Incandescence. Secondary air, ^introduced around the burner, sweeps PP**t the hot carbon particles and grod^t-'ielly bums with them in a flame sev$*1 feet long. ^job of grinding, transporting t co* *nt0 *** fumce may In a number of ways. riVn preparation phase was **Part*- *n tbc so-called bin cool was dried, pulverised, sep- from '*** *r u,e<* *n the Pu*ver* "till, ond stored to await demand. Being divorced from furnace operation, this system could operate at best ca pacity with constant fineness. Storage reduced need for spare pulveriser ca pacity. Burners eould be controlled separately with ease. Unit System. The direct-firing, or unit, system Is now almost universally used In new plants. In it. pulverisers feed burners directly. There is no storage; pulveriser operation thus 'fluctuates with steam demand. This system is not only simpler, involving less equip ment, but it avoids storage-bin' fire hazard as quantity of pulverised eoal never exceeds that in the mill and In the short lengths of piping to the burn ers. Elimination of a separate mill house, pulverised coal storage, con veyors and feeders reduces capital outlay. Built into today's systems is the flexibility needed to handle various functions under a wide range of lood end coal conditions. Heart of the unit system is the pul veriser. with its equipment for feeding raw coal at the proper rate, grinding the eoal to desired fineness, classifying the finished product so ovenired par ticles are returned to the mill, and delivering the coal in its transport air. Basic Arrangements, In most mills, air performs three functions, it dries the coal, classifies the pulverised fuel leaving the grinding elements end transports the finished product to the burners. The mill end its associated fan can be arranged in either of two bosie ways. In one, a forced-draft fan outside the mill supplies it with sir under enough pressure to carry out the joba to be done in the mill and to transport the coal to the furnace. The tan handles air only, which is an ad vantage, but the pulveriser must be kept tight In the second scheme, the mill is under negative pressure developed by en exhauafer fan, which may be com bined with the pulveriser proper, or mounted externally. Since it handles sir laden with coal, It must be designed to resist wear. Pig. I and 2 show typical layouts of each type. Cue! Preparation. Before taking a look at pulveriser construction, let's consider tome factors that affect op eration. First comes the matter of raw. coal size. Many plants receive, either regularly or occasionally, run-ol-mlne coal. While the usual feeder provides for rejecting oversized pieces, it is well to take os much load off the mill as possible. Thus some form of coolcrushing equipment represents a good investment A further precaution for an ' December IP4B PSJ) S9