Document jykbLKjLL7G6yN4LbKEwBkEL5

,;tauu a?;- tnwi6 w wol biiiciviu uvenire nvkiwii m wivnvi S' hi iKlvvO ftoeing coupling rfx/frtaochp .coopting Sample stoker-fired boiler, above, w((| hove jets mounted in front wall i Applying the first four foctors In Toble II to this chort ' gives olMube dlo required for o, blowefiupplled jet How Overfire Jets Cal Be Made to Cut Smoke" Loeott oir tubos on tube spacing above bod; aim 6 In. above on back Here's an eafty*ta>fpllew procedure that gets results in cutting down smoke from old boilers. AH the details you need to build a set of workable steam or air (eft-diameter spacing, number, capacity of the tubes--are discussed and explained By l N ROWLEY, Managing Editor, and i C McCABE, Associate. Editor >A RELATIVELY INEXPENSIVE, quickly and additional air depending upon lo . available tool (or cutting down smoke cation of steam nozzle in air tube. in m old boiler sounds like magic. As far as selection of type goes , Yet Bituminous Coal Research, lne has blowers have cheaper operating costa as .bees running a aeries of jet clinics air movers than do jets. Where a across the country to show combustion' boiler operates with little or no makeup engineers where just such e tool has blowers are almost the obvious choice. been put to work. This tool is an Steam jets apply where (1) there are overfire jet. no blowers (2) initial cost of blowers Let's first look at (he function per seems prohibitive (3) only turbulence formed by this jet, end then leam how is needed. to moke and apply one. Smoke, as As for service, no overfire jet can ' distinguished from cinder and flyoib, ' overcome poor firing practice. They consists of .finely divided carbon and are no cure-all. But as o supplementary soot particles. These .particles come tool or a. source of auxiliary overfire Into being when decomposed hydrocar- air they prove most helpful. "boas issuing from the fuel bed fail to General Operation. Bear this in mind. burn completely because of (1) insuf Installing jets is useless unless-one of ficient orygen (2) inadequate turbu the following conditions applies: (1) lence or mixing (3) a combination of reliable sutomotic jet controls--prefer , 1 and 2. Here is where, overfire jets ably electronic (2) e situation requir get in their work. ing continuous operation of jets (3) a There are (wo types depending on convenient indication for acquainting where they draw their primary force: the fireman with the density of fine gas. (1) blowers to give both additional No fireman will or could be expected air and turbulence (2) steam jets to to operate jets only as needed. give turbulence only, or both turbulence Now let's got about the job of choos ing a jet-system design (or a -boiler, Fig. 1. Tables 1) am the steps but well follow ihro need to know (1) maximum' rate per sq ft of grate area- per percentage of overfire sir requi distance from walla that je to penetrate smoking are length of penetration (4) I of coal. Maximum burning rate . observing hourty rate of coal < Uon under peak load and dit grate area in sq ft For our it is 2000 lb coal per hr 80 sq ft "* ; or 2$ lb per hr per sq ft. Second, the percentage of KftWfift) U Smiopad Tram ftehnti MOHrtal laitttel*, tad W 6 Mi>r, S ft (Sill I: fester-line Spicing cf Sir fates " / - * 'SlMvS* fanwitf, In.. II: To fltossi Blower Overfire Sir /els 0. bUmatt matlnram brains i*t* pentll grat* era* pr Sr S. btWnat* Mrn1*e *1 *rttr air rtgulrtd . EilimoH hagO* **lfll**i r*lra4 4. Oetemhn booling voIm of caaf-b>md . OtttmlM air-tab* dlan*tr t. D*lmtlM olr-lab* ipoel'B g. CaUvtot* moSw *1 *lt (iWt r*Wd b. D*t*n*hit vttgM of air par tvb t. D*l*rmi *le gmtor* (*r blown J. Cokuk*l* l*t*l t* It elr an all I* la]l lot* far*ec* D*t*rniiiit (r*ti-MCIIM> r*0 *f doctw*rk MtOri t. Don't 1st Obi |tt Inslug* W lontfc* vail r IW* cmI %required: Here a guide chart based on .^experiment* comes to aid. U shows the ''following: density Estimated percentage overfire air needed' Light ..............................10 Moderate........................ 20 Heavy ............................30 j. Only in cases of extreme smoking is y>mcre than 30% overfire air needed>As much as 35% overfire air is not too much if dense but infrequent smoke develops when, for intisnee, the fuel *bed it manually disturbed during cleani?l- But the larger the percentage of excess air needed the mote Important rjkai the jets operate only as long ns needed. Tor our example, we'll as* a moderate smoke and 20% overfire a|r. -?hitd point--length 61 penetration `nslly equals grate length if overfire v.Ve *n the front wall; grata width .side wall*. Our cose has them E&WtR Sp|mber 194$ In the front wall of furnace, and length of penetration is 10 ft. Heating value of coal comes from (l) recent analyses of eoel burned (2) typical analyses of coals from the same mine or bed (3) coal suppliers.' Out example uses 13,000 Biu per lb co*L Fig. 2, solid line, employs the four points (Table H, e-d) we have just 'determined to give air-tube diameter. Table t gives recommended center-line spacing of air tubes. But how many tubes do we need? This is determined by dividing the in side length of the furnace wall in inches by - distance. of air-tube spacing end subtracting one. Convert fractions into nearest whole number. Example: 8 ft x 12 in. per It . ... 13-id tube spacing - Fig. 3 takes into account the length of penetration and tire air-tube die to give the lb per hr of air to be delivered by each tube--560 lb per hr. Fig. 4 uses these same lectors-to determine air pressure required at air-tube en trance, 13 In. of water; Total air-weight requirements of all tubes must be converted to the some terms by which fan and blower menulecturers rate equipment. By use 'of a conversion factor .222 in a formula, this can be done. For example: No. of air lubes x weight of air per tube per hr x .222 equals cu ft of air per min ute at 70 F,.or 746 ctm in oar case. The eir pressure,'13 in. of water, re quired at the air-tube entrance may also be used for blower discharge pres sure. But duct velocity must not greatly exceed 2000 (pm (or this to be true, and there can't be any sharp bends or abrupt area changes in .the duct work. Again, an established formula employing a conversion factor of .072; comes to the rescue to give the required cross-sectionol area of the duct-' ISJJ) 79