US2081948A - Steam generator - Google Patents

Description

June 1, 1937.

F. MICHEL Er AL 2,081,948

STEAM GENERATOR A Filed April 1s, 193s 2 sheets-sheet 1 ng. 1 v #ggf .lu l

da* -mo Q4 i" WWE y NB r A 'u 'a' a //v S. M- .m CM ma l |50% 5m* |707 I mgeralure Mg. 2. ical' /fg 5W", mi f" I l7401 Wa 12a Il 100. *ML @o Il o a 10:0 rv r4.0 @31a .Jn/wa @am Jh/vW/I/P June 1 1937 F. MICHEL ET AL 2,081,948

STEAM GENERATOR Filed April 16, 19:56 2 Sheets-sheet 2 F' 1. 15 ogn F'N m I7 svncx 3 f f W l a aa 1,6 (ta) j l as 'F/Gr..

(P) ao m has FEED WATER Hein-R (t .5 T0 LORD a'7 L R INVENToRs Fl 5 1 3 CiNTHf Faison/:H MICHEL and Gf.- s o Hn/vs BCrLs/cHMH/vm l; mg Ran/HMT ce. Jb. 0W:

ATTORNEY LORD Patented t June 1, 1937 Y UNiTsDfsrAr-Es PATENT orrlcl:

s'rAM GENERA'ron "Friedrich Michel, Swarthmore, Pa., and Hans,

'Gleichmanm Falkenhain, near Berlin, Germany Application April 16, 1936, Serial No. 74,686

1 20 Claims. (Cl. 122-448) Our inventionrelates to improvements of steam It is, furthermore, an object of our -invention generators, and more-particularly to steam gento provide apparatus of the above character erators with forced passage of the operating wherein the supply of combustion media is conmedium. trolled jointly by means responsive to pressure 5 It is an object of our invention to provide a of working iiuid and means responsive to tem-v 5 forced-flow tubular steam generator having a perature of said fluid supplied to the third tubuzone wherein the working fluid is converted from lar element 01 Superheaiier. the liquid to the vapor state located in a por- These and other objects are effected by our tion Yof the heating space of such relatively low invention, as will be apparent'from the following '10 heat intensity that injury to the tubing of the descriptionand claims taken in connection with 10 conversion zone will be minimized, even though the accompanying drawing-S. fOrmmg a Dart 0f such tubing may contain salt deposits, together ihlsapplicatlcu, in Whieh with means responsive to a physical-character- Figs. 1 and '-are diagrams illustrative 0f theristic or characteristics ofthe working nuid to mal principles involved in our invention;

control application of heat to the generator in Fig. 3 is a diagrammatic view of a steam gener- 15 such manner as to prevent lsubstantial shifting atOl embOdying' -0111 improved control system; of the conversion zone, particularly under. vari- Fig- 4 iS a fragmentary diagrammatic View able load conditions. y j showing a second embodiment of our invention;

A further object of our invention is to provide and,

Va, furnace chamber having three heating zones, Fig- 5lS a diagramfirst, a zone subject mainly to radiant heat, sec- In accordance with our invention, we provide ond, a zone subject partly to radiant and partly a steam generator arrangement with forcedpasto contact heat, and, third, a. zone 'subject mainly sage oi' the operating medium for carrying out to contact heat; a tubular systemghavigtubular `lille methcd aS Set fOrth in impending applicaelements in said zones and so arranged thatvconl10n Serial N0. 691,349, led September 23. 1933. 25

version 'of rthe working iluid fromfthe liquid to which consists in operating the steam generator,`

the vapor state is completed inthe-tubular elein case of increase in load, with increasing presment of the third zone .andthe vapor received Sure and, in case of decrease in load, with defromthe last-named tubularxlem'ent is supercreasing pressure. In -order to carry out this heated in the tubular element of the second4 zone; meihcd With apparatus 0f this character. Special 30 and means responsive to." one or more physical Pmi/1510115 must be made S0 aS t0 er1-iur@ reliable conditions or the working nula for controlling andoontinnous operation of the plant.

the supply of combusidon vmedia "to the furnace 1 To' prevent deterioration of the tubes by salt O chamber in such manner as to restrict shifting delimita during Operatlcn. the heating Surfaces of said conversion zone, Y -v I "A further object of our invention is to provide. f takes Place musi be' as Particularly Set forth m apparatus offthe above character wherein the copending applications Serial Nos. 655,805 and superheater 'is so located` in the furnace that the 1 590,252, med February 2 1933 and September. 20-

quantityvofheat absorbed perv unit of weight is' 1933 respectively. subdivided into ltwo different 40 substantially constant-underyariable-l ad `and surfaces of 4dllel'euii ratei; 0f heat impact-i. ii-.140 pressure conditions .and :moans vgis," pro ded .to vinto a heating' surface portion (I) ci higher heatj ofsuch steam generators, in which evaporation 35 maintain :the outlet temperature of -gupers i impact, in which the percentage lof liquid of the heater substantisliyccnstant vunder v able load operating" medium with repeoi to the'tota'i exten-' conditiontheseztwothingsfnaniely; ocation 'f sion ofthe` heating surface portion (I) is greater y the superheaterfand cont liilot `autlisation.i0! :"than the percentage'. o f Ivapor'iphase Ifo! the' 145' i `heat so the'fsuperheater outlet# vpiodl'lction of, steam)` anditoa-sec'ond heating t,

serving 'm surface 'portion in) vor lower' heat, l n v of -thegsaltj-deposit-fzone, so th`t which'thejpercentagefof vapor-is tter' intp 'temperatura fthe'percenta'ge of. liquid (phase 1I otthepronjj nt'ionistoorcvide rface portion (mi, ext to tnesinface or -whereinthe eration, `in which portion the vapiaufis.v super- SuPDly, of combustion media is .controlled by 'a heated to a given degree (phase III ofl the produc? thermostat respcnsiveftofthe temperature" ci'" su- 1 tion of. steam),'also formi:Y preferably n. heating duction or steam). 'me :mst supcrneating imr- '50 A' working duid super-heater, surface portion of'ltwver heat ixnpschthat i's-to. l v v .i

in the rst aforesaid copending application, i. e.,

if the operating pressure varies with Varying load of the boiler. The object of the present invention is to provide means whereby it is possible that said phases IIV and III- the position of which is above all essential during operation-adjust themselves' continuously within the predetermined heating surface portions II and III independently of fluctuations of pressure and load.

Since phase II ends upon the attainment of the state of dry saturation characterized by the upper limit curve of the heat-temperature diagram and since phase III- begins upon the attainment of said state, it is practically sufficient to initiate, if possible, the generation of steam in such a manner that this state adjusts itself in operation continuously at the same region of the heating surface.

To prevent shifting of said region or the zone where change of state is completed, two measures are proposed according to the invention. The first measure consists in maintaining the temperature` of superheat constant independently of the pressure. In applying this measure, determinations at different operating pressures are made with the aid of the diagram Fig. 1- (Mollier diagram), which shows the quantity of heat in calories required to superheat a kilogram of steam to a constant temperature of superheat, for instance, of 400 C.; and, if these values are plotted against pressure, the diagram of Fig. 2 is obtained. The latter diagram indicates that the heat of superheat per kilogram of steam with a constant temperature of superheat is suinciently y constant within wide pressure limits. Consequently, if the superheater is arranged in such a manner that it always takes up per kilogram of steam the same quantity of heat, the state of dry saturation with a constant temperature of superheat must necessarily be always obtained at the same point of the heating surface.

The second measure consists in inserting in the path of the-flue gas the superheater at. a point where the absorption of heat per kilogram of steam always remains actually the same. If a steam generator, with a heating surface in a radiation heating chamber and a heating surface in a contact heating chamber, isassumed, and,

if the load of the generator is increased, the absorption of heat of the contact heating surface per kilogram of steam increases, whereas vthe absorption of heat of the radiation heating surface per kilogram of steam decreases. The reverse is the case with a decrease of load. It is apparent that there is a point in the path of the flue gas in each steam generator at which fluctuations of load have no influence upon the absorption of heat per kilogram of steam.

The second measure, to be simultaneously applied with the ilrst in solving the problem consists, therefore, according to the invention in the fact that the superheater is inserted in the path of the ue gas at a neutral point. By simultaneously applying bot-h measures, it is, consequently, possible to maintain the position of the zone, in which the state of dry saturation occurs always at the same point of the heating surface.

As above stated, the phase of production of steam .'III as well as phase II should adjust themselves within the contact heating surface. Phase III lasts from the beginning of the superheating up to a certain degree of superheating. Referring again to the diagram of Fig. 1, that would mean that the phase III of the generation of steam at a pressure of 60 atmospheres ends, for instance, at the point A. This point lies about 16 units of heat above the corresponding point of the upper limit curve (line a). These 16 units of heat are. consequently, taken up b'y a contact heating surface, whereas the remaining units of heat (line b) will be taken up by the next superheater disposed at the above-mentioned point. 'Ihis quantity of 110 units of heat is to be supplied if the superheating is continued up to 450 C. and maintained constant at this temperature. Since the absorption of heat of the superheater per kilogram of steam remains always constant in operation on account of its being arranged in the path of the flue gas at the neutral point, thel point A at a pressure of, for instance, 225 atmospheres would correspond to the point B. This point B is obtained by drawing from point B1 a line v,c equal to line b. If the values for different pressures and temperatures of superheat are plotted in a corresponding manner the curves I and 2 will be obtained. The design of the heating surfaces must be carried out according to these curves in such a manner that the curve to be obtained at different pressures should have the desired minimum distance (a) in units of heat from the upper limit curve in the case of the lowest pressure and of the lowest temperature 0f feed water. If the point B is taken first, measured a distance a above the upper limit curve, it will be obvious that the line or curve I in the direction of A would enter the region o1 wet steam. The latter conditionmust be avoided and this is done by starting with a point such as A located on the lowest pressure line. If the minimum distance a would not be fixed at the lowest inlet temperature of the feed water, it may also happen that the curve upon a decrease of the inlet temperature of the feed water during the operation wanders later in part or wholly into the zone of the wet steam.

' As it is necessary with'a boiler of the present type to maintain the temperature of superheat constant, we have a thermostat subject to the outlet temperature of the superheater and controlling the supply of combustion media to the furnace chamber in such manner that the temperature of the superheated steam is maintained substantially constant, it being remembered that, referring to the aforesaid description and to Figs. 1 and 2, the heat absorbed per pound o'f steam is substantially constant over a wide range of pressure and load conditions. Accordingly, if the heat supplied to the generator is so controlled as to keep the superheat temperature substantially constant, and the superheater is so located in the furnace that the quantity o1' heat absorbed per pound of steam passing through the superheater remains the same over a wide load range, it will be apparent that thermal conditions of the working uid in tubular elements of the generator immediately preceding l the superheater Will be such as to restrict or limit shifting of the conversion zone and, therefore, of the salt-deposit zone. While this method of control is suilicient to prevent substantial shifting of the conversion zcne, with load fluc- 'shifting of that zone into portions 3of heating tuatons, nevertheless, it is subject to the objection of uctuations caused by delay or lag. For

example, if the temperature of the superheated steam should drop and if the control apparatus is, in consequence, adjusted to supply Van increased quantity of combustion media, the tem perature oi the superheated steam would, after case, as will be apparent from Fig. 1, the temperature should not be regulated to a constant value, as in the case where the thermostat responds to the temperature of superheated steam, but temperatures corresponding to diierent pressures must be maintained and which are prescribed by the behavior of curves I or 2 of Fig. 1. Consequently, if the regulating impulse for control is taken from a point in front of the superheater, Whose outlet is to be maintained at 450 C., the control apparatusmust regulate the supply of combustion media so as to maintain a temperature of 305 C. in front of the superheater at aA pressure of atmospheres, a temperature of 330 C. at a temperature of 120 atmospheres, and a temperature of 4355" C. at a pressure of atmospherea these temperatures for these partlcular loads being determined from curve I of Fig. 1.

In order that the temperature impulses de- A rived from a thermostat located in front of the superheater may be utilized'to give results corresponding to temperatures related to the pressures, as indicated by curvevl of Fig. 1, it is necessary to use a pressure impulse in conjunc' tion with the temperature impulse, the two im@ pulses working together to secure control suchv that the thermostat. is compensated tof secure the properoperation for variable load conditions; If variation in feed water temperature should be a disturbing factor, then an impulse maybe e provided and dependent on feed water temperature, this impulse being used in conjunction with the temperature impulse in front vof the superheater andthe pressure impulse of the working fluid to control the application of heat to the boiler so as to maintain the outlet temperature of the superheater substantially constant.

To summarize in general, in all forms of the invention, location of the superheater soas tov absorb substantially the same quantity of heat per unit of weight of workingeuid .passing therethrough and being superheated is essential, for, with this feature, the control apparatus-may be controlled by the various temperature and pressure characteristics pointed out in order to maintain the outlet temperature of the superhater substantially constant, the condition of constancy of the superheater outlet temperaturev and location of the superheater providing for such thermalg and working iluid state conditions in tubular elements of the boiler preceding the superheater that the salt deposit zone may bee held within narrow limits and consequently We prefer to avoid space. of relatively. high heatl intensity may be avoided under a'wide range of loads.

- In Fig. 13, We show an embodiment of ourl invention wherein the furnace I0 is providedwith `a chamber II having a rst zone, atv I2, heated mainlyl by radiant heat, a second zone,` atl I3, heated'partly by radiant heat and partlyv by contact or convection heat, and a third or convection zone, at I 4, heated mainly by contact. Combustion media, for example, fuel' and air,

' are supplied in a regulated manner by the apparatus including a motor I6 "for delivering fuel I land a motor I1 for delivering air. The steam generator comprises a tubular system including a rst tubular element I8, a second y,tubular element I9, and a third tubular element 20, the element I8 being located in the rst Zone I2, the element I9 in the third-zone I4, and th element 20 in the second 'zone I3. i

As heretofore pointed out', the phase I of steam generation occursv in the first tubular element, at I8, andthe phases II and III of steam generation occur in the second` tubular element I9, phase II of steam generation representing'the completion of conversion from the liquid to the vapor state, and phase III representing superheating. After leaving the tubular velement vI9 with the relatively small amount of superheat, the

vapor goes to the tubular element 20 where it is superheated. O

As heretofore pointed out, and as will be-apparl ent from Fig.1, the amountof heat absorbedl per pound of steam in carrying vout vthe superheating of phase III is kept-,at aminimum, the object' being, as hereinbefore stated,to locate the lines I or 2,.as the case may be, of Fig. 1, in such manner that, in operating over a wide pressure range,

the control apparatus will not be subject to' thetemperature of wet steam.

In Fig. 3, we show the tubular systemsupplied with water as Working fluid .by means of a pump 22, the workingY fluid ilowing once through the tubular vsystem and undergoingV the physical changes just indicated. The pressure of working uid is due entirely to said pump 22.

-As pointed outin the aforesaid application, l l

Serial No. 691,439,.variable-'pressurecycle opera- I tion of the plant may be secured byhaving the feed pump responsive to a load. effect such as speed, that is, with an increase in load, the

feed pump is controlled to increase the pressure of working fluid and vice versa. AIo'this end, in Fig. 3,- we show `the tubular system of the steam generator supplying,` superheated steam to the turbine` 23, having-algovernor `24 which controls the speeds ci. the'motorsvv 25, I6, andV I1 supplying feed water.!,uel, andzair respectively, to the bonen i s l .r y., v

'f As' pointed outvin'V said application, Serial No. 691,439, feed weten-fuel and' air vare supplied in such manner'as Yto secure steam delivery from the boiler at a pressure dependent upon the load. l

Also, irrespective of operating pressure, the outgoing steam temperature is held constant. Ac-

eordingly, we show a thermostat 28, which exerts a correcting `iniiuezice on the fuel and air supply motors I 6 and .II in such manner that the latter operate to secure the heat release required to keep the temperature of steam approximately constant.

By way of example, we show the thermostat 28 operatively associated with contacts, at 29, controlling the reversible motor 3U for operating the rheostat 3| in the circuits of the motors I 6 and I1. As already indicated, the governor 24 controls the speeds of the feed water motor 25, the fuel supply motor I6, and the air supply motor I1, whereby, incident to load change, the feed pump speed is changed to change the operating pressure and the fuel and air supply motors have their speeds changed in a direction generally suitable to the change in feed water supply. For example, we show the governor -24 operatively associated with the rheostat 24a in the circuits of the motors. In order that a predetermined outgoing superheat temperature may be maintained, it is necessary to apply a correcting influence to the suppliesof fuel and air; and, for this reason, the thermostat 28 is employed for controlling the fuel and air supply motors I6 and I1.

As hereinbefore indicated, to avoid'lag effects and consequent shifting of the conversion zone, additional controlling elements are employed. In Fig. 3, a thermostat 3| is arranged in front of the superheater 20 and a pressure responsive device 32 is associated with the tubular series-flow passage, the thermostat and the pressure responsive device operating in any suitable manner to impose an additional controlling effect on the reversible motor. One example of a way in which the thermostat and the pressure responsive device may be used for this purpose is shown diagrammatically in Fig. 3 wherein the thermostat 3l is operatively connected to the responsive element 33, and the pressure responsive device to the responsive element 34. The responsive elements 33 and 34 have their movements transmitted in any suitable manner to the contacts, at 29, for controlling the reversible motor.

In Fig. .4, there is shown an arrangement similar to Fig. 3 except that there is an additional temperature impulse used, a thermostat 36 being associated with the series-ow'tubular surface in front of the surface I8 and sensitive to feed water temperature changes. The thermostat 36 operates an element 33, which, in conjunction with the elements 31 and 34 serve to control the contacts, at 29.

Thus, it will be seen that, in Figs. 3 and 4, thermostats are employed which minimize lag difficulties and limit shifting of the conversion zone, because such thermostats are sensitive to temperature changes in advance of the thermostat 28.

As hereinbefore indicated, an important feature of the present invention is location of the supern heater, it being necessary that it shall be so located as to absorb substantially the same quantity of heat per unit'of weight of vapor passing therethro-ugh and being superheated under Variable load conditions, variation in load,` of course, introducing variation in pressure. With the variable pressure cycle of operation, the quantity of radiant heat absorbed per unit of weight of under varying load conditions is concerned.

motive fluid being superheated diminishes with increase in load and pressure and vice versa. This is indicated diagrammatically in Fig. 5 by the curve R. On the other hand, the quantity of contact heat absorbeai per unit of weight of working fluid being superheated increases with increase in load and pressure and vice versa, this being indicated by the curve C on Fig. 5. Accordingly, the superheater is so located in the heating space as to be subject both to radiant and to contact heat so that it has a neutral location insofar as absorption of heat per unit of weight In other words, irrespective of variations in load and pressure, the heat absorbed per unit of Weight of vapor passing through the superheater and being superheated is substantially constant. With such location of the superheater and with control of the application of heat so as to maintain the superheater outlet temperature substantially constant, it will be apparent that means' are provided to restrict shifting of the salt deposit zone, for these conditions impose. such thermal conditions on the Working fluid that the conversion zone of the boiler is held lwithin fairly narrow limits under variable load and pressure conditions.

In connection with Figs. 3 and 4, it will be apparent that the thermostat and pressure control devices may be used in any suitable manner to bring about adjustments in fuel and air supplies. To this end, and by way of example, in Fig. 3, we

vshow the actuated elements 33 and 34 connected to the ends of a floating lever 40 operatively connccted, through a dash pot at 4I, to one end of the lever 42, the other end of the latter lever carrying a Contact 43 arranged between the contacts 44 and 45 of the contact device, at 29. As shown, the contacts 44 and 45 are positioned in response to the thermostat 28. The lever 42 tends to be maintained in a central position by means of springs 46, movement of the lever for this purpose being provided by the dash pot, as the dash pot has suitably small openings 41 in its piston which cause the dash pot to function as a link to transmit motion of the elements 33 and 34 to the contact 43, but which permit of relatively slow movement vof restoration of the lever 42 to central position. With this arrangement, it will be apparent that the thermostat 28 controls the contacts 44 and 45 so as to secure supplies of fuel and air in such a manner as to maintain the outgoing steam temperature approximately constant. Also, the thermostat 3| and the pressure responsive device 32 operate through the intermediary of suitable mechanism to control the contacts in such manner as to minimize lag effects. The operation of the apparatus shown in Fig. 4 is similar except that an additional temperature impulse is taken into account.

l From the foregoing, it will be apparent that we have devised a steam generator of the seriesflow type wherein the operating pressure is dependent upon the feed pump and the turbine governor is employed to control, not only the feed pump, but also the `supplies of fuel and i air. A correction impulse is derived from the thermostat 28 associated with the outgoing steam line to control supplies of fuel and air so as to maintain the outgoing steam temperature approximately constant. of devices, providing a variable pressure steam generator arranged to supply steam at approximately constant temperature irrespective of pressure, it is desirable to incorporate the aforementioned features of control to minimize shifting of the conversion zone, such measures of control being the location of the superheater 20 in such manner as to absorb the same quantity of heat per pound of steam at different loads and the features which operate to give an anticipating effect, the latter features including the thermo-stat 3l and the pressure responsive device 32 of Figs. 3 and 4 as well as the thermostat 36 of Fig. 4 and these 'devices providing for relatively quick response vand reduction in lag. In other words, the location of the superheater and the supplementary and anticipatory controlling devices cooperate to keep the conversion zone restricted to relatively narrow limits irrespective of With this arrangement operation of ditions. y y While We have shown' our invention in two forms, it will be obvious'v to those skilled in the art that it is not so limited,vv but is susceptible Y of various other changes and modifications with` out departing from the ,spirit thereof, and we desire, therefore, that vonly such limitations shall` be placed thereupon vas, are imposed by `the -prior art or as are specically s et forth in th'e-r ap pendedclaims. .Y p i What we claim is: y 1. In a generator lsupplied with liquida'slwork-r ing fluid andtransfo'rmingit intosuperlieated vapor, a vfurnace chamber includinga 'Contactl heat zone anda combined radiant and, contact heat zone, a tubular system comprisingftubularrr heat-absorbing elements arranged 'in' said cham-'- ber and includingy tubular heat-'absorbing ele' ments in said zonesf, fmeans forysecu'ring forced ow of working iiuid through the tubular sys tem and under pressurede'pending upon the load,v the. tubularheat-absorbing element or elements f preceding inthe directionof Vworking fluid iiciavlvA Athe eienient in thecontact zone and` the latter, 1 being lso-'farranged' andheat being sotabsorbedn .l thereby that the. vsolid or scale-depositzone due A to conversion ofthe worldng'fluidffrom theliquid to the vapor state is `located intubing of the element inthe contact zone-subjectto heatoi such l. relatively low intensityAthatfirijmy"to r,such tubing 4win beminimizd ei/enf though it contains `solid orscalev-deposits andthe tubularelementv in saifd combined r'aniianijf.l and Vfccj'n'tac jlieatfzone servingv to supe'rheat vvanrreceivedffrom'thetub- A ular element in the :contact z'one,l andr'ea'n's' for Y ',lres'tricting shifting ofjsaidfs'olidor scale-deposit zone `i'l'clurlir'ig the, .tubular 'heat-absorbing'. ele- "mentso' locatedrv 'inthe combined' radiant and contact' heat zonetliat .the'qu'antity o f heatv ab- 1 lsorbed per unit jofwei'ghtof Avapor passing 1 ments in n Vsaid zones.; means flowof'working' uid through he tubular system through and `being sulperheatetiv Vis'. substantially constant under variablejload conditions'.

2. In al generator. supplied with liquid as and unnerpressre depending-unen tHe-mamme 'heatl soabsorbed thereby scalefd'eposit; zone due 'to v.con-

the element in the" 1 zonein-ksucngmannerctnat the'q'uannty or heat absorbed" per for weight or vapor' passing .A therethroughand being superheated -is substantially, yconstant` under variable conditions -the t boiler" under Ivariable loadg'cnm v Y working Vfluid and transforming it into-,superheated 1" vapor",` a 'furnace I chamber including ja' vcontact j heat zone and -a' lcomliined radiant and contact j jheat zone,.a tubuiar 'system"`comprising' tubular f heat-absorbing elements arranged inl said chainer-sn ,mueven or scale; and means for restri ting shifting o1' saidA-v vsolid for scalegdeposit zone including'the location-oi said third tubular element functioning and meansfor controlling the application of heat to the heat-absorbing elements of the generator so as to maintain the temperature of superheated vapor leaving the generator substantially constant.

3. In a motive uid generator, a furnace having a heating chamber including a rst zone wherein heatingoccurs due mainly to radiation, 1 -a secondzone wherein heating occurs partly due tofracliation and partly' due to contact or confvection, and a third zone'wherein heating occurs mainly due to` convection; a tubular system including Aiirst; third-and second tubular elements arrangedfin saidyrsu second, and third zones,

' respectivelygand the first, second, and third tubular elements being vconnected in series; means for supplying liquid as working uid to the tubu- VAlarfsystemY forfforced flow therethrough under pressure depending upon the load; the first and 'second tubular elements being constructed and -arrar'iged so that the'solid or scale-deposit zone due to conversionofthe working iluid from the yliquid-to thle"vapor-state is vlocated in tubing of vthe-:'s-:cond'ftubulaii element Aarranged in a part I if1'said y,tl'iirdgzonevoi-such lrelatively low heat Vintensity-thatkinjury '-to such tubingv will be minimi'ined;A .even though-'containing deposits of so1ids' 'or", scale;A ai'idmeans 'for restricting 4shiftn-Ving'of soli `rqrigscale-deposit zone including the-:location o 4said third tubular elementfunctioning f as ansuperheater in such manner that the? duantityof' heat absorbed per unit of weight o igvaporpassing therethrough and being superheatlfedrisv substantially constant under .variable application of' heat tothe tubular elements so fas tofmaintain the temperature of superheated vapor leaving the third tubular element substantially constant.

-load-conditions and means for controlling the 4.; Ina motive fluid generator, a furnace having a heating 4chamber includinga iirst zone Y .wherein lheating occurs due mainly to radiation, agsecond zone wherein heating'occurs partly due to: radiation andpartly due tov contact or convec-`- tion, andathirdl zone 'wherein vheating occurs 'f 'mainlydue tocon'vection; a tubular system including lfirstQthird, and second tubular'elements garrangedfin said firstJ second,l and third zones. grespectively, and the iirst, second, andv third tubu- -lar elementsfbeing connected in series; means for tsupplying liquid asv working uid to the tubular system for forced-flow therethrough under'presune dependingupon :the'loadthe first and sec- And tubular 'elements-being constructed and ar- 'fran'ge'd so' thai-.the solid miscele-deposit zone due to conversion 'ftheworking iluid `from the liquid to the 7vapoxstate isflocated inV tubing of the second tubular velement arranged in a part of saidthi'rdf zone of suchrelatively low heat inftensity thatimuryfto suchv tubing w111 be mm1- mized evfen though containing eposits of solids as a superheater in such manner that the quan- .5 vtityof heatabsorbed per unit of weight of vapor passing therethrough and being super-heated is i substantially constant under variable load condiftionsand mechanism for maintaining the temperature 'of superheated vapor leaving the third clement substantially constant, said mechanism finoludingmeans responsive to the temperaturev of vapor supplied t the third tubular elenient and to the pressurev of working -iluid for lar elements.

5. In a steam generator, a furnace having a heating chamber including a rst zone wherein heating occurs due mainly to radiation, a second zone wherein heating occurs partly due to radiation and partly due to contact or convection, and a third zone wherein heating occurs mainly due to convection; a tubular system including rst, third, and second tubular elements arranged in said first, second, and third zones, respectively, and the rst, second, and third tubu- -lar elements being connected in series; means for supplying liquid as working fluid to the tubular system for forced iiow therethrough under pressure depending upon the load; the first and second tubular elements being constructed and arranged so that the solid or scale-deposit zone due to conversion of the working fluid from the liquid to the vapor state is located in tubing of thesecond tubular element arranged in a part of said third zone of such relatively low heat inf tensity that injury to such tubing will be minimized even though containing deposits of solids or scale; and means for restricting shifting of said solid or scale-deposit zone including the location of said third tubular element functioning as a superheater in such manner that the quantity of heat absorbed per unit of weight of vapor passing therethrough and being superheated is substantially constant under variable load conditions, means providing an impulse depending upon the temperature of vapor` Supplied to the third tubular element, means providing an impulse depending upon the temperature of vapor leaving the third tubular element, means providing an impulse depending upon the pressure of working uid, and means for utilizing said impulses to control the application of heat to the tubular elements.

6. In a steam generator, a furnace having a heating chamber including a rst zone wherein heating occurs due mainly to radiation, a second zone wherein heating occurs partly due to radiation and partly due to contact or convection, and a third zone wherein heating occurs mainly due to convection; a tubular system including first, third, and second tubular elements arranged in said first, second, and third zones, respectively, and the rst, second, and third tubular elements being connected in series; means for supplying liquid asworking fluid to the'tubular system for forced flow therethrough under pressure depending upon the load; the first and second tu lar elements being constructed and arranged that the solid or scale-deposit zone due to conversion of the working fluid from the liquid to the vapor state is located in tubing of the second tubular element arranged in a part of said third zone of such relatively low heat intensity that injury to such tubing will be minimized even though containing deposits of solids or scale; and means for restricting shifting of said solid or scale-deposit zone including the location of said third tubular element functioning as a superheater in such manner that the quantity of heat absorbed per unit of weight of Vapor passing therethrough and being superheated is substantially constant,

under variable load conditions, means providing a first impulse depending upon the temperature of vapor supplied to the third tubular element, means providing a second impulse depending upon the temperature of the liquid supplied to the first tubular element, means providing an controlling ythe application of heat to the tubuimpulse depending upon the temperature of working fluid leaving the third tubular element,

A means providing an impulse depending upon the pressure of the working Huid, and means utilizing said first, second, thirdV and fourth impulses to control the application of heat to the tubular heat absorbing elements.

7. In a steam generator, a furnace having a heating chamber including a combustion space; a tubular system including first, second, and third tubular elements arranged vin said chamber and connected in series, means for supplying water as working fluid to the tubular system and for securing forced flow through the latter of the working iiuid; means responsive to the load condition of the generator for causing the pressure thereof to increase with increase in load and vice versa; the rst tubular element being arranged in said combustion space, the rst and second tubular elements being constructed Vand arranged so that the salt deposit zone due to conversion of the working fluid from the liquid to the vapor state is in tubing of the second element located' in a portion of said chamber of such relatively low heat intensity that injury to such tubing containing salt deposits will be minimized, and the third tubular element being arranged in said chamber so as to absorb heat and superheat the vapor delivered thereto by the second element, combustion apparatus for the combustion space; means for supplying combustion media to the combustion apparatus; and means for controlling the lastnamed meansr` to vary the rate of supply of combustion media so that the temperature of the superheated working fluid leaving the third element may be maintained substantially constant.

8. In a steam generator, a furnace having a heating chamber including a iirst zone wherein heating occurs due mainly to radiation, a second zone wherein heating occurs partly due to radiation and partly due to contact or convection, and a third zone wherein heating occurs mainly due to convection; a tubular system including iirst, third, and second tubular elements arranged in saidv rst, second, and third zones, respectively, and the first, second, and third tubular elements bein-g connected in series; means for supplying water as Working fluid to the tubular system and for securing the forced ilow through the latter of the working iiuid; means responsive to the load condition of the generator for causingv the pressure thereof to increase with increase in load and vice versa; the rst and second tubular elements being constructed and arranged so that the salt deposit zone due to conversion of the working fluid from the liquid to the vapor state is located in tubing of the second tubular element arranged in a part of said third zone of such relatively low heat intensity that injury to such tubing containing salt deposits will be minimized; combustion apparatus for the rst zone of the heating chamber; means for supplying combustion media to the combustion apparatus; and means controlling the last-named means so that combustion media is supplied to the combustion apparatus in such manner that the superheated working fluid leaving the third tubular element is maintained at substantially constant temperature under variable load conditions.

9. In a steam generator, a furnace having a heating chamber including a rst zone heated mainly by radiant heat, a second zone heated partly by radiant and partly by contact heat, and

la third zone heated mainly by contact; a tubular system including first, third, andv second tubular elements arranged in said first, second, and third`zones, respectively; means for supplying water as Working fiuidto the tubular system and securing forced flow through the latter of the working fiuid; means providin-g for variation in the pressure of the Working fluid in accordance with the load; the first and second tubular elements being constructed and arranged so that the salt deposit zone due to conversion of the Working fluid from the liquid to the vapor state is located in tubing of the second element in a part of said third zone of such relatively low heat intensity that injury to such tubing containing salt deposits will be minimized, and the third tubular element serving to superheat vapor delivered thereto by the second tubular element; combustion 'apparatus for said first zone, means for supplying combustion media to the combustionV apparatus; said third tubular element being so located in the second zone that the heat absorbed per unit weight of steam passing therethrough is substantially constant under variable load conditions; and mechanism including means responsive to temperature of the working fiuid in the vapor state and to pressure of the Working uid for controlling the combustion media supply means so as to keep the temperature of steam leaving the third tubular element substantially constant.

10. In a steam generator of the series-flow tubular type for supplying steam under variable pressure, a feed pump for supplying water to the generator and determining the operating pressure; means for supplying fuel and air to the generator; controlling means for the feed pump operating in response to load to provide a pump outlet pressure which increases with increase of load andvice versa; and thermostatiforv controlling the fuel and air supply means 'to maintainthe outlet steam temperature approximately constant.

'11'. In a steam generator of the series-fiow tubular type and including a superheater for supplyingsuperheated steam under -pressure which varies ldepending upon the load, a feed pumpfor supplying Water to the generator and determining the operating pressure; means for supplying fuel and-air to the generator; controlling means for the feed pump operating in response to load to supply .feed waterunder pressure which increases with increase in loadand vice Versa; a first thermostat associated with the outlet steam line for controlling the fuel and air supply means ter as operating medium-for passage throughthe tomaintain the outlet steam temperature approximately constant; and a second thermostat associated with the tubular surface of the generator ahead of the superheatervfor exerting an additional controlling effect upon the fueland air first, second, and third heating surfaces'. in series; means for supplying fuel andv air to lthe radiant zone for combustion therein; lsaid first;

second, and third heating surfaces being constructed and arranged so that vaporization is completed in said second heating surface and superheating is effected in said third heating surface; driving means for the feed pump and the fuel and air supply means; and means for controlling sai'ti driving means and including means responsive to the temperatures of medium leaving the second and third heating surfaces and to the operating pressure of the medium for exerting a controlling effect on the driving means for the fuel and air-supply means. l

13. In a steam generator, a furnace chamber including a radiant heat zone, a combined radiant and contact heat zone, and a contactl heat zone; a series-flow tubular system including a first heating surface in the radiant zone, a second heating surfacein the contact zone, and a third heating surface in the combined radiant and contact zone; a feed pump for supplying water as operating medium forV passage, through the first, second, and third heatingsurfaces in series; means for supplying fuel and 'air to the radiant zone for combustion therein; said first, second, and third heating surfacesl being constructed and arranged `so that vaporization is completed in. said second heating surface and superheating is effected in said third heating surface; driving means for the feed pump and the fuel and air supply means; and means for controlling the driving means for the fuel and air supply means in response to the temperature of medium ahead of and after the superheater and to pressure of the operating medium. Y,

14. In a steam generator, a furnace chamber including a radiant heat zone, a combined radiant and contact heat zone, and a contact heat zone; a vseries-flow,tubular system including-aI first heating surface in the radiant zone, a second heating surfacein the contact zone, and a third heating surface in the combined radiant and contact zone, al feed pump for supplying water as operating medium for passage through the first, second, and third heating surfaces in series; means for 'supplying fuel and air to the radiant zone for combustion therein; said first, second, and third heating --surfaces beingl constructed and arranged so that vaporization is completed -in said second heating surface and superheating is effected in said third heating surface; driving means for the feed pump and the fuel and air supply means operating in response Ito load to provide steam under pressure Ywhich increases with increase in load and vice versa; and means for controllingthe'driving means for the fuel and air supply means in response to the temperatures existing at separated points ahead of and after the superheater and in response to the operating pressure.

15. In a steam generator, a furnace chamber vincluding a radiant heat zone, a combined radiant and contact heatzone, and a contact heat zone;

a series-flow tubular system including a first heating surface in the radiant zone, a second heating surface in the'contact zone, and a third vheating `surface ,in the combined radiant and second `heating surface and superheating is ef- `-fected in said third heating surface; driving means for the feed pump and the fuel and air supply means operating in response to load to provide steam under pressure which increases with increase in load and vice Versa; means responsive to temperature of superheated steam leaving the generator for controlling the driving means for the fuel and air supply means so as to maintain the outgoing steam temperature approximately constant; and additional means for controlling the driving means for the fuel and air supply means in response to temperature of water supplied to the first heating surface, to the temperature of medium passing kfrom the second heating surfaceto the third heating surface and to the pressure of operating medium.

16. In a steam generator, a furnace chamber including a radiant heat zone, a combined radiant and contact heat zone, and a contact heat zone; a series-flow tubular system including a first heating surface in the radiant zone, a second heating surface in the contact zone, and a third heating surface in the combined radiant and contact zone,

, a feed pump for supplying water as operating medium for passage through the first, second, and third heating surfaces in series; means-for supplying fuel and air to the radiant zone for combustion therein; said first, second, and third heating surfaces being constructed and arranged so vthat vaporization is completed in said second heating surface and superheating is effected in said third heating surface; driving means for the feed pump and the fuel and air supply means operating in response to load to provide steam under pressure which increases with increase in load and vice versa; means responsive to temperature of superheated steam leaving the generator for controlling the driving means vfor the fuel'and air supply means so as to maintain the outgoing steam temperature approximately constant; and

additional means for controlling the driving means for the fuel and air supply means in response to temperature of medium ahead of said third heating surface and to the pressure of medium.

17. In a motive fiuid generator, a furnace having a heating chamber including a first zone wherein heating occurs due mainly to radiation, a second zone wherein heating occurs partly due to radiation and partly due to contact or convection, and a third zone wherein heating occurs mainly due to convection; a tubular system including first, third, and second tubular elements arranged in said first, second, and third zones, respectively, and the first, second, and third tubular elements being connected in series; means for supplying water as working fiuid to the tubular system for forced flow therethrough; the first and second tubular elements being constructed and arranged so that the solid or scale-deposit Zone due to conversion of the working fluid from the liquid to the vapor state is located in tubing of the second tubular element arranged in a part of said third zone of such relatively low heat intensity that injury to such tubing will be minimized even though containing deposits of solids or scale; and means for restricting shifting of Ysaid solid or scale-deposit zone including the location of said third tubular element functioning as a superheater in such manner that the quantity of heat absorbed per unit of weight of vapor passing therethrough and being superheated is substantially constant and means for controlling the application of heat to the tubular elements and responsive to the temperature of superheated working fiuid and to a temperature of the working fluid ahead of the superheater.

18. In a motive fiuid generator, a furnace having a heating chamber including a first zone wherein heating occurs due mainly to radiation, a second zone wherein heating occurs partly due to radiation and partly due to contact or convection, and a third zone wherein heating occurs mainly due to convection; a tubular system including first, third, and second tubular elements arranged in said first, second, and third zones, respectively, and the first, second, and third tubular elements being connected in series; means for supplying water as working fiuid to the tubular system for forced fiow therethrough; the first and second tubular elements being constructed and arranged so that theA solid or scaledeposit zone due to conversion of the working fiuid from the liquid to the vapor state is located in tubing of the second tubular element arranged in a part of said third zone of such relatively low heat intensity that injury to such tubing will be minimized even though containing deposits of solids or scale; and means for restricting shifting of said solid or scale-deposit zone including the location of said third tubularelement functioning as a superheater-in such manner that the quantity of heat absorbed per unit of weight of vapor passing therethrough and being superheated ls substantially constant and means for controlling the application of heat to the tubular elements and responsive to the temperatures of working liquid between the second and third tubular elements and following the third tubular element.

19. In a motive fiuid generator, a furnace having a heating chamber including a first zone wherein heating occurs due mainly to radiation, a second zone wherein heating occurs partly due to radiation and partly due to contact or convection, and a third zone wherein heating occurs mainly `due to convection; a tubular system including first, third, and second tubular element-s arranged in said first, second, and third zones, respectively, and the first, second, and third tubular elements being connected in series; means for supplying water as Working fiuid to the tubular system for forced flow therethrough; the first and second tubular elements. being constructed and arranged so that the solid or scaledeposit zone due to conversion of the working fluid from the liquid to the vapor state is located in tubing of the second tubular element arranged in a part of said third zone of such relatively low heat intensity that injury to such tubing will be minimized even though containing deposits of solids or scale; and means for restricting shifting of said solid or scale-deposit zone including the location of said third tubular element functioning as a superheater in such manner that the quantity of heat absorbed per unit of weight of Vapor passing therethrough and being superheated is substantially constant and means for controlling the application of heat to the tubular elements and responsive to the temperature of feed water supplied to the first element, the temperature of working fiuid passing from the second tothe third tubular elements and to the temperature of working fiuid leaving the third tubular element.

20. In a motive fiuid generator, a furnace having a heating chamber including a first zone wherein heating occurs due mainly to radiation, a second zone wherein heating occurs partly due to radiation and partly due to contact or convection, and a third zone wherein heating occurs mainly due to convection; a tubular system including rst, third, and second tubular elements arranged in said rst, second, and third zones,

respectively, and the first, second, and third tubular elements being connected in series; means for supplying Water as working uid to the tubular system for forced flow therethrough; the rst and second tubular elements being constructed and arranged so that the solid or scaledeposit zone due to conversion of the working iuid from the liquid to the vapor state is located in tubing of the second tubular element arranged in a. part of said third zone of such relatively low heat intensity that injury to such tubing will be minimized even though containing deposits of solids or scale; and means for restricting shifting of said solid or scale-deposit zone including the location of said third tubular element functioning as a superheater in such manner that the quantity of heat absorbed per unit of weight of vapor passing therethrough and belng superheated is substantially constant and means for controlling the application of heat to the tubular elements so as to keep the temperature of superheated steam leaving the third tubular element substantially constant.

FRIEDRICH MICHEL. HANS GLEICHMANN.

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