Document 4aeN1ZnOzyeN1darvqLpvEjG1

TECHNICAL BRIEFS S Offals la you on: GAS TURBINES , ,, latest engineering developments ter busy power men FUELS AND FIRING For shaft speeds to 1750 RPM Johns-Manville Centripac seals better Flume con bo itabillicd by. swirl vonn or |et ImpIngcmM around tKa tube of gai turbine combuttor ihown et (rft Start-up data in graph shown above cover* 3-fn(IUon U] experience on reheat boilers with no ipeclal diiflcvlllot ] Let's Look at Gas Turbine Combustion Problems Some .Practical Aspects of Combustion in the Oat Turbine. By H R Hazard, BoiteUe Memorial /rutimie. Duraing fuel to produce heel and power has presented problem* since man'* fuel uaa of Are, and every typo of engine in use today ha* it* own combullion problem*. These may result from special properties of the fuel or lu ash or irons condition* surrounding combustion and will vary from failure of equipment *t one extreme to air pol lution st the other. The gas turbine has most of the problems common to other engines plus a few unique prob lems of it* own. Although solution of most of these problems I* the responsi bility of the development engineer, the operator should have a full understand ing of *11 the factors behind his own operating and maintenance require ments. In this paper some of tho prac tical aspects of combustion (n presentday gas turbines are discussed. Tho gas turbine differs from other engines In that fuel Is burned continu ously at high pressures to heal large quantities of air to only moderate tem peratures. Heat-release rotes are pro digious by boiler standards si small combustion volumes and relatively high pressure losses permit high turbulence levels. Combustors are really directfired air heaters In which the sir is heated only about 500 to 1000 degrees F, utilizing for combustion less than 20 percent of the available sir. Combus tion products ate mixed with excess air, Fig. 1, to heat entire mass to uni form temperature at turbine inlet. In several commercial gas turbines, combustor-inlet temperoture* range from about 275 F at idling to 500 F at full load, and eombustor-outlet tempera tures rsnge up to 1475 F. Changes in load are accomplished by changing compressor speed, which has the effect of increasing both air pressure and mass flow in such a relation that the air veloc ity through the combustors Is nearly constant regardless of load. The fuel rate Is increased approximately in pro portion to the olr weight, since fuel/air ratios do not vary greatly over the load rsnge except during acceleration or de celeration. Then a change in foel rste takes place immediately, but consider able time elapses before the new sir rste is established. Combustion pres sures vary from 15 psi at Idling to about 75 psi st full load in simple units, or may go as high as 120 pal in more com plex units. The two Important characteristics of the combustor that affect performance of the gas turbine ore combustion effi ciency and pressure loss. Law combus tion efficiency inoreases fuel consump tion only, but high pressure loss nol only Increases fuel consumption but re duces power output as well. A change of 1 per cent In pressure loss has ap*. proxlmotely the same effect on cycle aficiency as a change of 1.S per cent la I combustion efficiency. Tho only real," limit to heat-release rates In the is* ' turbine combustor is the pressure loss I required to force the air through tbs J combustor. This Increases as the com- ` bustor also is reduced. A usual value of pressure leas is about 5 per cent of*.. sialic pressure (about 20 in. water st; atmospheric pressure) with accompany ing heat-release rates of JA to 9.5 mil lion Btu per cu ft hr per atmosphere of * pressure. ARC Paper, no number. Corrosion Aspects of Bunkov C Combvs- . Non In Oat Turbines. By B 0 BoekUni . end C M Gardiner, General Electric Co. - The General Electric Company's Go* Turbine Deportment In Schenectady started testing a Bunker C-burnlng !* turbine at the factory Itto in 1947. Since that time, approximately 90,000 hours of Bunker C operation have been accumulated. This operating experience has shown that a basic corrosion prob? lem exists when bunting residual oil because slag-forming substance* th*1 are present will' very likely corrode the metallic parts. A great deal of progress has been made on the solution of this problem, end the work la continuing The present paper gives the history operating' experience and describes briefly the laboratory and shop tests (Continued on page 150) *EAD SERVICC SECTION rowa TEAR on centrifugal pump shafts as well as on oscillat ed rotating rods of other is minimised by J-M s&tripnc. This ts because the Bare cross section of this pack* jffift'provides the maximum connrafcutfsce*. Thus, it insures s gn^f jgs) with the least friction fftSMUod pressure. Because Centripac Is plaited Suite it retains its shape iodefnht*)y, thus maintaining msxi- frrito surface contact for iong wpod* of time. It is made from f|iongg--fuibperr asbestos y/ arn, thor oughly lubricated and graphited. It seals against fresh or salt, hot or cold water, oil, ammonia, brine, gasoline, and certain weak acids and other chemicals. Because of its wide application, it Isa favorite of plant men everywhere. For general service, Style #7 Centripac is recommended, ((con tains no wire, ts soft enough to conform-readily to the packing space, and itands up well in serv ice. It comes to coil form. Style #C-7 and Ring form, Style #R-7. Sixes'/w* and up. pr higher shaft speeds, J-M Plastic Packings iduce friction and scoring of shafts and sleeves R1 ` Highercentrifugal pump speeds make friction increasingly im portant in packing and shaft life. That is why J-M Plastic Packings have been designed to hsve the homogeneous struc ture and low friction so essen tial to tong packing life in this service. The exact composition of these packings varies according to the service conditions for which each particular style Is designed. AAst aarnt texample, one of these, Style No. 610 is an excedent general maintenance packing for tervice against steam, air, ammonia, gases, etc. up to 5SOF. It Is made of selected asbestos fiber minted with pure graphite and a small amount of non-friction metal, then bonded with a heat-resist ing compound to form a pliable coil or spiral. It U furnished in sixes of 14* and up. YOUR J-JM PACKING DfSTfilBUTOR will gladly recommend the right packing for your equip ment, and furnish it from stock fot your immedi ate requirements. Write Johns-Manville, Box fiO,. New York Id, N. Y. for his name and address. Jo Canada, 199 Day St., Toronto t, Ontario. Johns-Manville PACKINGS and GASKETS 5WEMU1 tU