Document dYeNna58Qy18jbb83gQgpGgKb

STEAM JETS: Simplified, Step-by-Step Procedure for Selectiol Stsom noul* die. In. Air volomt per lubs.sfm otTOT 005 0.1 013 0.2 03 60 100 600 300400 and Sizing to Get Effective Overfire Action in Stoker Furnaces Air injected per tube per hr with team jets can bo found from above Proper size of steam noztlo required comes from applying known olr weight per tube, steam pressure and tube site III: Pounds of Overfire Air Needed per Pound Cool Burned fur Different Smoke Densities tfHUng vefM / cm], She per 10,000 M,000 11,000 ti.000 14,000 Ht*n t.SS 1.45 >.47 1.10 1.70 I.S3 3.72 3.10 1.15 IV: Performance of Steam-Air let Couslitlng of 1-In. Air Tube Equipped With iVIn. Dia. Steam Nozzle Pmun T itdem upf/M < IfMIB IMflf*, piIf p*M|r*ffM f pt ilrwas, ft between (an discharge and air tubes to hold velocity down to about 2000 fpm under a pressure of 13 in. water. The formula is maximum output of fan in efm at 70 F (74d) x .072 and it equals S3.7 sq in.; the required eross-sectional ares. An 8-in. dis duet has a cross-sectional ares of 50.3 sq in. and a 9-in. duct has 63.6-sq-in. area. The first results in a top air velocity of 2137 fpm, and the second .1695 fpm. Either is satisfactory. Air tube and header duct may be constructed of standard pipe and fittings with no sharp bends or abrupt changes in cross-sections] ores. Fig. 5 shows o suggested assembly. Steam-Air Jets. So much for the blow er typo; now for the steam-sir Jets. Here we'll use e furnace 5 ft long with a grate 5 ft wide. We'll have coal of 13,500 Btu per lb, maximum coal burned per hr, 675 lb; smoke density, heavy; jets in the sidewall, and avail* . able steam pressure 50 psig. Our first four factors, Table V, are (1) maximum burning rate per sq ft per hr--675 lb coal per hr -+- 25 aq ft . grate area, 35 lb (2) overfire air re- qulied--from guide, p. 79,-30% (3) length of penetrotion--5 ft (4) heating value of coal--13,500 Btu per lb. Air-tube diameter comes from Fig. 2, dotted line, and is 1.5 in. Tube pacing shows oo Table 1, but this table applies only to the nearest inch. If air-tube dia from Fig. 2 .shows less than one in., use the alternate pro cedure to be discussed later. Our ex ample with a 5-ft penetration length and 1.5-in. lube dia (alls between 6 and 8 in., or 7 In. Number of air tubes Is arrived at just the same as above and it proves to bo 8: 5 ft x 12 in. per ft. - 1 = 7.57 7 in. lube spacing With sidewall location, put end jets in about one-jet spacing, 7 in. from the inside faces of front ond bridgewalls; then apaee remaining six at equal dis tances between them. An alternate .possibility if both sidewalls are acces sible is to locate 4 jets in each wall and stagger them with the opposite side. Fig. 6 employs penetration length and air-tube aixe to determine --5 weight,injected in the furnace per t!^ per hi--approximately 325 lb. Fig. 7 provides the guide for pt#3 steam-noxxle site. Using the vsriJJ figures for the example at bandit chart calls for a steam notsle^ lightly less than A in. dia. Rec mended choice is a A-ln. dia ne&lt] ovoid plugging, which may occur smaller-sized nozzle*. Steam consumption con be eslit with the aid of Fig. 8. As an eiapM consider the A-in. (.094 In.) no^ above. They use 50-psi steam add c some 23 lb per hr per nozzle- & eight this amounts to 184 lb per brjjj steam if jets'Operate continuously-' a coal-burning rate of 875- lb perftg the example given generates W of 7500 lb per hr of steam. This jets consume 2.5% of total outpotS they operate all the time. H aB work only 30% of the time theyj^ only 0.7S% of boiler output *vf Alternate Procedure. Where F1|l calls for an air-lube diameter of than one ioch a different procedural plies. Use only 1-in. dia tubes M (5)4). POWER Septsmb" j 8 Effect of different steam pressure! v\ flow through nozzles shows here I- Where olr-tubo length runs less than | A For turbulence glone steom-jet orwoll thickness, follow .this method * rongemeni shown is recommended V: To Choose Steam-Air left Property .a e. .Isilmeti Milaww turning rat* pi *a It # grats hn par hr h. CithMr* rh( p*rcatega of **arf!ta air r*fvlft4 . btlmat* Mngfh at paMtroil** tiikt A OttanalM htetlug vetaa of cool baraaS a. OrNmlar alr-laba SJflJMtrr gtikcd t. Dwnmb* a>-tcba ipactag rtqilrM S CakutoM number at olr tuba* ragalrad h. Cakatrtt nctghi at air par tvba I. 0*t*rnlM Ifci ilNi-utili dbwhr |. Mok* plr-tuba lauglb tatvaaa S and 10 lion IN 4ln*i*t*r L R**p nuzvt* ent*r*4 oid dignod vitti oli f alr.tub* 41a bach d thraat I. Arraag* far alo ta flav tat* air tuba et utMthly a4 ffto4ualty ai paoibl* n. D*tlgn nc*n a. Oan't all** any |*t t* lnpl*e* an th* far- mc* valli or bsrdag ml with A-ln.-dia steam nozzles, Table'lV. quired is determined by dividing total Let's set up an example: Take a weight of overfire air (above) by Maker-fired hrt boiler with a grate 5 ft weight of air injected per tube per hr, k>g by 3 It, 6 in. wide and a furnace or 683 -f- 143 gives 5 tubes. .height of 3 ft burning 350 lb of 13,000 If all five lubes go in on one side `Iha ms] per hr at moximum^ating and they should be'equally spaced with . tiring off e moderate smoke. Available end tubes at least 6 In. from the ad tfesn pressure is 50 psig. jacent end walls. The five tubes coold -..Calculate total weight of overfire air be put in both walls, 3 on one side, two Required Pr hr by multiplying (1) on the other, end staggered with the maximum coal burned per hr (350) by (2) lb of overfire air required per i'bof coal burned, from Table III (195) opposite side tubes. Canrtraction Datalli. Fig. 9 shows the important features of construction of a e find 683 lb of overfire air steam-air jet Air tube can be made of ^"ired per Hr. standard pipe. The smooth, rounded or. w Next, determine weight of air (ejected funnel-shlkped approach to the air tube * furnace per lube per hr if can be formed of plastic refractory or 1,e Pieced in the sidewall to give a pipe coupling, reducing from at least 6-In. length of penetration, and two sixes larger than tbe air tube down V- ^Fplied to the nozzle is at 20 to air-tube size. , one-in. lube, air injected ; i t* fumtee from Table IV hy inter'li ft 0a,^^ ^e 143 lb per hr per tube. U. i!I'i u ,0 at (bit point that ' b`* Icam pressure is higher ?4v*J..\oal` retfu^r<** reducing 4* ""<1"pp'v lhe 1#w Hern, tiol*t dumber of oir tuboi i The steam nbzxle may be made from o standard pipe cap or plug. A drilled hole forms the noale boro and should be countersunk to provide smooth flow into tbe nozzle. Alloy cast iron or heattreated high-chromium, medium- or high-carbon steel makes a nozzle ma terial that resists erosion ond givqs long life under this service. Proper control and operation depends upon building into the system valves and steam gages. They provide a ready means of holding steam pressure to the desired point and shutting off jets when not needed. Hand-controlled purging valves or traps remove moisture from the lines. Unmuffled stesm jets give, off s dis turbing noise. There are several de signs of mufflers both concentric and suspended that have been worked up to reduce this nuisance. In our next article, in. an early issue, on the appli cation of overfire jets to particular de signs of furnaces and stokers we will illustrate some of these muffler arrange ments. Where only turbulence fits the bill, steam nozzles may discharge directly into the firebox instead of into the throat of the air tube. .And here's how that fi accomplished. Ordinarily the steam noale dis charges directly into the firebox instead of the throat of an -air tube. It gives nearly as much penetration without an air tube os with. it. But it is not practicable to install jets with air tubes and then stop the air inlet if it is found later thot air is unnecessary. A vacuum forms in the air tube and penetration becomes al most nil. In a case like this extend the steam line through the air tube so the nozzle discharges near the air-tube outlet. Whatever small amounts o( air Bow through the air tube, under natural draft, keep the steam nozzle cool when not in use. Fig. 10 shows just such a noale assembly. Our next article discusses the recom mended application points for various stoker arrangements. spf*mber l?4B (575) 31