Патент USA US2127787код для вставки
Aug. 23, 1938. 2,l27,787 M. SCHMIDT WATER TUBE STEAM GENERA'TOR Filed July 1'7. 1935 5 Sheets-Sheet 1 41 / ?/ 37 ?NVEN nw' > MAPT?N SCHM?DT AT ËORNEYS› Aug. 23, 1938. M. SCHMIDT WATER TUBE STEAM GENEHATOR . Filed July 17, 1955 5 Sheets-Sheet 2 #3 mio a 51 1// // // 7// //// /// / * ' .Se/miat ATT NEYS? , Aug- 23, 1938- ` . - M. SCHMIDT ` ‹ WATER TUBE STEAM GENERATOR Filed July 17, 1955 2,127,787 _ 5 Sheets›$heet 4~ Fig. 10. I I?vvE?vToRI MART?N ScHM?DT A T TORNEYS? ~ ' Gama-%ëma Aug.›23, 1938. 2,127,787 M. SCHMIDT WATER TUBE STEAM GENERATOR Filed July 17. 1935 5 Sheets-Sheet 5 fig. 17. ?NVENTOR? Mm?'??Sc??mor _' A an EY5~ Gush\ M 2 drums, but on the central-y, '?ows continuously and automatically either in each :individual cir culation unit or in indlviclual groups of such units, or again, through the entire tube system. The water must therefore always take a, de?nite path predetermlned by the constm?ctlcn so that a uniform cooling of all the tube& is assurecl. ` In all these cases, however, the disadvantage is present that the kinetic energy in the steam-water mixture at the upper end of the evaporatlng tube is dissipated. ? Such a loss of kinetic energy is disadvantageous. for example, if the water, more or less freed from steam, continues to círculate by being ledthrough downcomers hack to the evaporating tubes, be Since in the new boller, even under different 10 conditions of load and operation, for example, cause on account of the check to the circulation, the mass of water must be accelerated again. even with varyíng quantities oi' water_ in the ch' culation units, the riser parts of the circulatlcn the present invention is characterizecl by the fact units are well cooled, the heating surfaces can he worked at a high rating. The new hoíler comblnes the essential advan-? 15 tages of known ?ash hollers and water-tulle boilers witl?'?out the dlsadvantages mentloned above cu?'rlng in bollers of these types. ed with'the flash boller, the new Agnlshed particularly by its lower ul lncreaseol safety ln operation. 3, lt is especially suitable even for '37 virtue of_ its small weight, a& vantageonu h?re, and can in acloíitäon he aal lnllecl in 'power lnstallatlons aa nn auxíliary i" per-zl; leads. trucks an 'i .Also Wl , clly varv'íng leads, ene.: , in rail motor cars, a Safer operation without that, over a suñícíently long stretch of the ?ow path of the mixture, transfer ducts are provide& leading to a pipe or containe?' and connected, to the mixtnre tube, so that over this Stretch the gas or vapor can freely separate and pass into the connected plpe or container from the lic?uícl, which. continues to ?ow in the mixture tube. In consequence of this arrangement, no sepa 20, rator ccntainer is interposed in the ?ow-path of the mixture, and in addition the tube traversecl by the míxture cloes not pass through a con tainer. In contrast to the prccesses oí' separation 25 carriec? out in steam-separating drums and in known. steam driers, the separation of stearn and water according to this pari; of. the present in« vention is not brought about through stopping application of compllcateé. regulatins? anna› or interrnptlng the flow of water, preferably ,I is ensu?'ecl and; a further latitncle in the r- t" content is lcled so to prevent tl. hand uncle lvle loco of Water on the c assžstc-d by the action of impact, or hy sudclen hand an m in the circu. therehy a st?f?cient length of time, so- that the steam can escape freely from the water, which continues its course unchecl?ied. The *ation of the steam from the moving nisslhle eva-;meeting .. n unlts. 'the ' On account. of the lower degree of sensitiv * of the new hcller, the feed, as above rn n .-'` can he to certain extent acceleratccl, or t'a› steam~gene?atíng layed; in „ "ich, tuhes if the are feed not lmmecžlate 'evrop ,~ dangered. nalz??tme ls enectecl by connectíng a riser tube to .y r a section cí tube preferably running either hoti! 4 I -zrntclly or with a slight ävrclination. In this sec to provide eil'?cient appan “erancl efu leoo pipe is connecteà to issue holes or oncnings prcwícled in the neper wall of the mix 'for sem iG?' 'cart of example, the n'n??wre t???he into vllnch according to the present invent?on, it ic steam anti changes of direction, hut by proviçlžng a Sufiz cíentlv long stretch of 'the path of ?ow, and tion, It will he seen that in a waterutnhe "' ture _ tuhe. , able for the speci?c use referred to, la a › ce?ble generally ?for separa'ting gas &nel/or va_ from a mlxtnre of gas and/“or vapor and llom ? flowing through a tube, but for con * part of the invention will he descrlheo! helcw ^ stea?n can he separate& on the inner side of the cnrve since the water, under the action of cenn trlí” al force, moves in contact With the outer hall of the curvecl tube. › lít is already linomi to Wíthdraw steam on the `reíem?-nce to a míxture of steam anal water ex_ cent where otherwise indicatecl. Hitherto the separation of steam from e accorclži?rg From a mžxture to this ?owing part through the present a curved "wen on inventlon denis with apparatus which, :a migu› r ture of steam and water produced in ever-lo tubes, has been commcnly e?ected in. a stcarn evaporating and-water drum tubesinto deliver. which the open encls of If the dlscharge of these tulles lies below the 50 surface of the water, the steam generate& _ then force its way through the snperincomh layer and in consequence must entraln a ?wm?tíoy chargeinto of water, butthe even steam if thespace evapomtlng of the (ir-nm, 'cases the steam must stlll contain a large pronart-lon of water because, in the mixture ejected, the stearc and water are in a state of relative turhule-nce and so prevent the desh-ed sudden separation ci” 70 In contrast, to such arrangements, this part oi Inner of a curvecl tul?eírom a mixt??re of &team and. ?owing the?'ethrough. With this object, a tuhnlar connection is introduce& into the curveíl ”tulle from the cuter side of the bend, which provided. near the inner wall of the cirrvecí tube on the side turned away from the cli rectlon ol flow with e small. inlet opening for the steam. !a substantiel separatlon of steam from the mov GO ing water cannot, however, he eflected_ in this man??er. In contrast thereto, according to this part oi' the present invention. as great as possible a sep~ araticn of steam ls eífected by connecting to the 65 lnner side of the curved tubeja lead-off pipe, into _which an elcngated clischarge opening, compris ing perforatícns provided in the inner Wall of the the steam and water particles. For such reasons, in order to obtaín dry steam, steam separators or driers have been constructecl which for the separation of the steam and water rely either on the impact prlnciple, or on› the action of centriíugal force, or on sudden changes description, particularly when taken in conjunc tion with the accompanyíng drawings which form o! direction. a part thereoi. ` bend over a suf?cic-ntly long Stretch, discharges. ?m'thot oh?šects and advantages of the inven tion will appear' more fully from the following ta. aroma-7 In the drawings: curs through suction due to other steam-gener ‹ Figure 1 shows a diagrammatic view of a cir ating tubes. culation unit according to the invention, Figura 2 is a cross section, on a larger scale, of the upper part of the unit showing one form'of apparatus for separating the steam generated from the circulating water. i. Figure '3 shows diagrammatically ,one form› of a group of circulation units connected in series 10 to form a coil with a horizontal axis. Figura 4 shows a modification having a plu rality of circulating units fed from a reservoir. ' Figure 5 shows diagrarnmatically, in vertical section. a further example of the new water-tube 35 boiler. t Figure 6 is a diagram of a part of the same in plan View. 20 tion of the new boiler. I' Figure 10 is a vertical section through yet an 'other form of the invention. Figura ll is a diagram of a part of the same in planvview.` elevation and partly in section. Figura 18 is a cross 'section on the line iB-IS of Figure 17. in the circulation units shown in Figures 1 to 4, the heated riser or steam generating tube is in dicated at i, and the unheated or only slightly heated downcomer at 2. In the upper part of the unit, the riser is connected to the.downcorner by a bend having a large radius of curvature and at the bottom by a bend with a smaller radius of curvature, sudden changes of directionbeing thus avoided throughout so 'that a circulation unit is provided with a closed circulating path free from obstruction. i _ › ` By means of a pipe 3, feed water is fed into the downcomer 2 in the same direction as the?ow therein. the steam 'generated in the riser part being led oiT at the upper intermediate part of 46 the unit where the riser connects ,with the down comer. ' With this object, a lead-off pipe 8 is connected to the intermediate tube l which is provided with ` holes or slits 5 opening thereinto. In. addition, a connecting pipe 'lis provided between the steam outlet duct B and the downcomer 2, so that water condensed or entrained can 'escape into the down comer. › group closed in_ itself. The ?rst riser l is con nected to the next downcomer 2, this downcomer to the second riser, this again to the next down-i comer, this downcomer to the third riser and this to the thirri downcomer, which is connected 10 back to the ?rst riser. . The unit is red through thepipe &into the downcomer i which delivers into the first riser I only. On the other hand, steam .is withdrewn through a lead-od pipo t provided at the upper 15 part oi each individual circula'tion unit forrned ? By virtue of the bend of large radius, the steam water mixture in the riser I is transrerred with out 'substantial resistance to flow into the more or less horizontal length 4. in which it can continue ?owing at a high velocity. In this length of tube i a comparatively long path is provided in which steam can separate by passing through the open ings 5' into the steam lead-off pipe 8. The length within@ which the separation of steam from the continuously moving water is completed is indicated in Figurez by a. v _ The circuiation in an individual unit is in th?s form no longer completely independent of the circulation in the other units. but the advantage 20 is Secured that the total circulaticn is divided into individual circulations and each circuiation unit contains only a small mass of water, though variable between wide limits. and that at no point of the boiler can a large mass of _water accumu Figures 12 to 17 show different forms of con ` struction of the' separating apparatus, partly in 40 3, three circulation units. each comprising a riser and a downcomer, are connected into a. of a riser and a downcomer. ' 'Figuresm 8 and 9 are diagrammatic vertical sections through three further forms of construc %E I I In the :form of the invention shown in Figure `. In this modi?cation, the individual circulating units, each iorrned of riser and downcomer parts. are independent from one another so that the ä?te which by its inertia could check the circula 25' on. As a modified iiorm, however, each downco?ner .of a group may he ieri. as will be described be low. . ' so' Fie i shows circulatina units with a reser voir ti arranged in the feed pine, the water level in this reservoir being lower than the points where the steam is led o? and lower aiso than the upperrnost heated sectionsoi' the risers i of the 85 circulatin'g its. ` ' ` From the lower part of the reservoir, feed pipes il lead to the downcomers 2 oi 'the circula tion units, while steam lead-of! pipes t deliver steam into the upper part of the reservoir. The 4.0 feed water which ?ows into the reservoir after passing through a trickle preheater in, for ex- ' ample, is heated by the steam in the reservoir 8. The feed pine is indicated at i2, and the steam pipe leading to theyplace of consumption at !3. 45 This reservoir is then connected with the cir' culating units by the water inlet tubes which de liver into the downcomers. The feed is delivered into this reservoir and from it each unit takes the feed water required. In consequence. the 50 water content in the tubes even with irregular feed or load varias less rapidly. The water content of the boiler is in this way increased without exercising a disturbing in- i fiuence on the circulating system. such a reser voir, to which a water-level indicator can be ?t ted, is advantageously applied to larger boilers with several circulating systems connected in par ailel. “The water lever in the reservoir can., moreover, be subjected to larger variations or 60 leveLvwithout endangering the cooling of the in-' dividual units. It is, therefore, possible with a new boiler pro videdwith this arrangement to withdraw sud denly, in a. manner known in itself, larger quan 65 tities of steam, without the necessity of imme-. diateiy adjusting the firing and feed. since even with smaller water content o! the circulating' circuiation of the individual small quantities of units. the upper -heated parte of the steam-gen water likewise takes place with complete inde erating tubes arestill well cooled. on the other 70 pendence in each unit. This Construction has hand, the possihility exists of reading boilers with reservoirs only'frqrn time to time. the advantage that the circulation is not dis turbed by steam-generating processes working› g `Obviously it is not necessary that all the steam` pipes _of the circulation units should be led to the under other conditions of circulating and- heat reservoir. Ailthat is necessary is that a balance 75 ' ing, so that no de?ection of the ?ow of water oc 76 4 of pressure should be established between the reservoir and the 'circulation units, and for this purpose a connection of any sort between the steam lead-oil' sections of the circulation unit and the upper part of the rese?'voir is suf?cient. In Figures 5 and 6, the risers I. of the circula tion units lie close together and form the wall of the combustion chamber |5, the circulation units being connected in series as already described 10 with reference to Figure 3, in the case of a circu tion group comprising three units. The groups of units are connected in a set to form an annular coil closed upon itself, water be ing fed into each third downcomer, or one of each 16 group, in the direction of the ?ow of ?uid therein. The feed water is fed into a ring !6, from which feed pipes IT lead to the proper downcomers. The steam generated in the risers is separated at the upper .part of each circulation unit and led 20 off through ducts IS to the collector ring ia. From this ring I& steam passcs through a pipe 20 to a superheater 2! which is arranged in a fiue 22 connected to the combustion chamber, while in the ?ue 22 above the superheater 2i a feed-water heater 23 is provided, from which a pipe 24 leads to the feed-water ring IE. By thus connecting the new circulation units in series in such a way that the water content of the riser of a circulation unit, after separation of the steam, always fiows into the downcomer of the next unit and the downcomer of the last unit is connected with the riser, oi the ?rst unit, the sets of unit groups form a coil with horizontal nxis which can be closed upon itself. In th?s way. a, tube boiler is obtained which units the char acteristics of the coil boiler with vertical rising axis and of the tube boiler with a number of comparatively short riser tubes at a considerable angle. In Figure '7, the feed-water heater is indicated at 25 and is formed as a pre-evaporator. The tubes leading the steam-water mixture from the › preheater 25 are indicated at 26, the steam be ing .separated in these tubes and led through steam pipes 21 to the risers i of the circulating units. Beyond _the points where the steam pipes branch off, the tubes 28. connected to the tubes 25, contain water free from steam which is led into the downcomers 29 of the circulation units in the direction of the ?ow therein. The circulation units can, by way of example, be arranged in an annulus as in Figures 5 and 6 or they can be arranged in any other suitable fashion. y The steam generated in each circulation unit is led off from its upper part to a steam collector 30. In F'igure 8, the wall surrounding the combus tion chamber is formed of steam generating tubes arranged in a helieal coil having the form of a six-threaded screw, the individual coils or tubes of the wall being indicated by the numerals 3l to 36. Each of the six coils, according to the in vention, is connected by an unheated downcomer to a circulation unit, ior example, the coil 3! is connected with the downco?ner 21. The upper most part of the coil passes without any sudden change of direction into the downcomer 31, which is so bent down at its lower end that it leads with 70 out sudden change of direction to the lower end of the coil 31 forming its inlet. In this way each coil forms the riser OT a cir culation unit, the steam generated in this riser being led off at the upper end of the unit from the zone ot transition between the riser part and the downcomer part. The steam lead-off pipe of the unit to which the riser 3l corresponds is in dicated at 38. To the steam lead-off pipes of the six circulation units, tubes are connected in which the super heating is en'ected. The superheater tube con~ nected to the pipe 38 is indicated at 39. The superheater 40 formed of convolutions of these connecting tubes, lies, in the example illustrated, in a ?ue 4l connected to the combustion chambe?'. v The steam led off from the circulation units of the steam-generating system ?ows therciore di rect to the superheater. ' In this form of the new boiler, notwithstanding the fact that the steam-generating tubes lie close together so as to form a wall, the boiler as com pared with the single threaded coil has the ad vantage that it comprises only comparatively short tubes at a eonsiderable anglc with only a small resistance to ?ow. Also, in such a coil sys ??U tem, the water ?ows in parallel through the short circulating paths. Only the steam generated is led off and as much water is fed into the system as is with drawn in the form of steam. The circulating . system remains the same, with the exception that the steam-generating tubes are substantially longer than the downcomers. I_ In Figures 9 and 10, circulation units highly heated to different degrees are connected in ; series. . In Figure 9 coiled tubes serve as risers, these tubes being wound, as in Figure 8. in the form of a six-threaded helix. The most highly heatcd coils 44 form the wall of the combustion chamber _ 43. Beyond the set of circulation units ?'ompris ing these highly-heated risers, two other sets of circulation units are arranged whose risers 45, 45 are concentric with the tubes 44 and at a certain distance therefrom. The risers 44 of the ?rst 40 circulation units are connected to downcomers 41 which lead to the risers 45 of the second circu lation units. These in turn are connected with downcomers 48 which lead to the risers 46 of the third circulation units; and these again are con- _ I nected to the downcomers 49 which are led back to the risers 44 of the ?rst circulation units. For the sake of clearness in the drawings, the downcomers 41, 48 and 49 are shown only by single lines, although actually six risers and six downcomers would be provided. The device then consists of a set of six groups of units, each group comprising oneunit in each coil. The steam generated in the individual circula tion units is led off at the upper part of each unit ; as indicated by the arrows 50, 5I, 52. Feed water is introduced only into the most highly heated circulation units, and preferably into the downcomers 49 which lead back to the, risers 44, whereby the eflicient cooling explained in the (SO introduction to this speci?cation is Secured with respect to the most highly heated tubes. The point of introduction of feed water to the circula tion units is indicated at 53. ' The hot gases at the upper end of the combus tion chamber 43 pass under a cover 54, and thence in a downward direction through a ?ue 55 to the lower end of a ?ue 56 which at its upper end is connected with the uptake 51. It will be seen that the risers 44 of the ?rst set of circulation units, which form the wall of the combustion chamber, are heated to the greatest extent and that the risers 45 of the second set of units, which form a wall separating the ?ues 55 56 are heated to a less extent; and that. 5 ?nally, the outermost risers 45 of the third set ot length a. in the tube 69 pass through openings 13 circulation units are_ heated to a still less extent in the upper tube wall to a lead-'off pipe-IL ` by the already largely cooled combustion gases. `~ The individual openings through which y the In the form oi the invention shown in Figures 10 and 11,- three groups of risers heated to dii ferent degrees are provided as before, these risers being connected with their corresponding down steam separated from the moving_ waterpasses from the mixture tube into the lead-off pipe could be replaced „by any other suitable arrangement comers to form circulation units. Therisers are arranged round a combustion chamber so that at points spaced along the length of the tube. In certain circumstances, a lengthwise section 10 the hot gases, therein rising rrom below, ?ow ever series of tubes formed hy the risers.` The risers ti lying nearest to the axis of the combus tion chamber; are the most highly heated; the risers 62, next in order being heated less highly; 15 and the risers '63, lying iurthest from the axis, i are heated to the least extent. The correspond ing downcomers connected at their 'lowest ends with the rlsers `_GL M* W are indicated at tnt, Et, which would provide open space in the tube wall of the tube may be provided with an enlarged 10 cross-section, in such a way that the steam may íreely separate from the stream of i water over a sumciently long Stretch to a space inside the tube section, from which it passes to the lead-off tube. such a form of Construction is shown in Figura 15 13. 'The section of tube whose cross-section is greater than the cross-section of 'the inlet tube 'iii and of the water-receiving tube 'it is indicated at li. 20 All the risers and downcomers are connected in series, in a manner that will he cbvicus ironi Fig ure 11, so as to form sets of unit groups which in effect comprise one continuous cell. Feed-water › - a Along the length a, steam from the stream of 20 miitture can freely separate to` the space provided in the upper part of the tube _section 'li and from this space can iiow into the lead-off pine lE. v 'in Figure 14, the separation of the steam from is_ ied into the downcorners ti& which lead to the the mixture is completed along the length a, of a 25 25 most highly-heated risers ti', so that these, as above explained, contain the largest quantity oi _ section of tube 'H of gradually increasing cross section connected to the inlet tube lt. At the end of the length in which separation is , From each circulation unit iormed ci a rise?' `and' downcomer, stea'm is led off at the upper part eitected, the tube il forks into a tube “lt and a tuhe W. The water, without any change in its 30 30 and separated' from the stream of water. such a steam lead-off pipe is indicated in Flgure lil at ti, direction of ?ow, passes into the tube “it, and the and thefeed pipe connected to adowncomer tt at separated volatile constituerits are led o? through water. %35 ` _ _ tt. The circulation units ti and tel are arranged at a somewhat higher level than the units ta, BE the pipe lt. and these again somew?hat higher than the units of the steam from the mixture is likewise eiiected 35 along the length a 'of a tube section ll' of increas ta, tt. The apex of the circulating path of the most highly-heated_ unit thus lies at a somewhat higher level than that of the succeeding less highiy-heated unit in which the steam-water mix 40 ture 'is raised to a somewhat less extent. in this way, consideration is taken of the fact that the circuiating force is strongest in the riser which is› heated to the greatest extent. With individual circulating units thua con 45 nected in series to form a group, an advantageous form of the invention is obtained, inasmuch as the circulation units are heated less and less strongly according to their successive positions in series. the feed_ water being introduced into the unit 50 heated to the highest extent. The largest quan tity of ?uid ?ows through the mest' highly heated riser so that an especially e?lcient'cooling of the tube heated to the greatest extent, and conse quentiy mostexposed to damage, is Secured. 55 While one form of Separator suitable'Ior use with water-tube boiiers in accordance with the present invention has been described with refer ence to Figure 2, it will be understood that many other constructional forms embodying the_ sanie 60 principle of' maintaining the velocitycf ?ow of w in the form shown in Flgure 15, the separation ing cross-section connecting to the inlet tube 16. The tube. section ll" passes, at the end of the length in which separation is ei'fected, into the tuhe 'lt in which the water continues to flow with cut change of direction. 40 ` The volatile constituents separated in the sec tion 'il' of the tube 'it are on the other hand led\` of! through the pipe lt' bra'nching off in a reverse 45 direction from the section ll'. While in the constructional forms of the ex ample described, it is assumed that the voiatile constituents pass ireelyupwards from the moving inixture and the water continues to ?ow in the lower part of the tube, Flgure 16 shows another term of construction in which the separation of the volatile constituents of the mixture flowing'in a curved tube takes place on the inner side thereoi'. The 'tube bent into a circular are, for example, one convolution of a coil evaporator, is indicated 55 by the numeral 80. - Under the action of centrifugal force, the iiquid is compelled to move to the outer side of the tube while the steam collects along the inner wall, separation being e?écted along the length a. 50 At this point, a lead-off pipe Bi is connected to Thus, in the form shown in Figura 12, the the tube 80 on its inner side, into which issue length of tube 89 in which the separation of the t holes 82 provided in the innerwali of the bent the water are possible. ` v ` steam is completed from the moving mixtu?'e, is 65 arranged horizontaliy. . . tube co. . Figures 17 and 18 show a constructional form 65 In orderto faciliate the separation ci' the steam, in which steam is separated from the water ?ow the cross-section of the tube G@ is enlarged as' ing through a tube and passed into a connected compared with 'the cross-section ci' the tuhes lt and 12. ` container, two mixture tubes connected to a com mon container 83 being shown in the example ii 70 The mixture, for example; any heated llc?uid \ iustrated. As the regions of separation are similarly ar ranged, it will be su?icient to describe one of them. The riser tube 84 passes at it's upperend into e. straight length of tube 85, which, is con for further use or treatment. 76 The volatile constituents separated ;along the nected through a bend 86 to a downcomer 81. which contains volatile particies, ?ows through the tube 10, while the liquid !read from such particles ?ows through the tube 12 to any point, 4 „sa 6 i 2,127,787 The upper wall of the length of tube 85 enters a slot provided in the wall of the container 83, upper header, means connecting said lower header to a plurality of said units, and means to feed water to said lower header. 5. A water tube steam generator, which, in addition to the quantity of water continuously 5 ?ed in and evaporated during one passage through the boiler, contains a small additional quantity of the connection being made water-tight by _a welded seam 88.‹ In the upper wall of the length of tube 85, holes or slits 89 are provided which open into the container 83. il) . ' The steam separated from the ?owing mixture along the length a can pass freely through the slits 85 into the container 83, While the water outside the container continues its course through the tube 85 and the bend 85 to the downcomer 81.' water, comprising steam-generating tubes, and downcomer tubes, means connecting said steam generating tubes and said downcomer tubes to 10 form circulating units, in which the circulating water content of the steam generator is divided into a plurality of circulating units, means in said connecting means to separate the steam irom the water-steam mixture produced in said While I have described herein certain forms of my invention, I wish it to be understood that I do not intendito limit myself thereby except with in the scope of the appended claims. steam-generating tubes, whereby the water in I claim: downcomer tubes, means connecting said _steam eenerating tubes and said downcomer tubes the steam-generating tubes of each circulating unit being continuously connected with the down said mixture after the separation of steam there from may continue to flow through said down comer tubes, said units being disposed around an axis, upper and lower annular headers, means 20 connecting the steam separating means of a plu rality of said circulating units to said upper header, means connecting said lower header to a plurality of said units, and means to feed water to said lower header. 25 6. A water tube steam generator comprising a comers of the next unit, to form a group of units circulatory system of steam generating tubes, having a substantially closed circulating path, downcomer tubes, connecting means for said generator tubes and downcomer tubes. feed water tubes for said downcomer tubes, steam and water 30 sepa?'ating means in said connecting means, and means to conduct separated water to said down l. A water-tube steam generator, which in ad dition to the quantity of water continuously fed in and evaporated during one passage through the boiler, contains an additional mass of water, units comprising steam-generating tubes and and means in said connecting means to separate 30 the steam from the water-steam ?nixture pro duced in said steam-generating tubes, whereby the water in said mixture after separation of steam thereirom may continue to ?ow through said downcomer tubes. comer tubes, said feedtubes being connected to the lower portions only of said downcomer 2. In a steam generator as claimed in claim 1, means to introduce feed water into a piurality of said units, . ' ` 3. A water tube steam generator, which, in addition to the quantity of water continuously i ed in and evaporated during one passage through the boiler, contains a small additional quantity in said downcomer tubes and the velocity of' separated water past said separating means is substantially retained in said circulatory system. 7. A water tube-steam generator comprising a of water, comprising steam-generating tubes, and furnace, steam generating tubes in said iurnace, 40 downcomer tubes outside of said furnace, tubes connecting said generator tubes and said down downcomer tubes, means connecting said steam generating tubes and said downcomer tubes to iorm circulating units, means in said connecting ing tubes to separate water from a steam-water mixture, steam collecting means connected to means to separate the steam from the Water stcam mixturevproduced in said steam-generating tubes, whereby the water in said mixture after the separation of steam therefrom may continue to flow through said downcomer tubes, means to collect the steam separated by said separating means, and means independent of said collecting means to introduce feed water into the lower por tion of at least some of said' circulating units. 4. A water tube steam generator, which, in addition to the quantity of water continuously fed in and evaporated during one passage through the boiler, contains a small additional quantity of water, comprising steam-generating (JO tubes whereby low water columns are maintained tubes, and downcomer tubes, means connecting said steam-generating tubes and said downcomer 'tubes to form circulating units, in which the cir culating water content of the steam generator is divided into a plurality of circulating units, means in said connecting means to separate the (35 steam from the water-steam mixture produced in said steam-generating tubes, whereby the comer tubes, separating means in said connect said separating means, means to conduct the 45 separated water into said downcomer tubes, and means to introduce feed water into said down comer tubes. A 8. A water tube steam generator as in claim 7, wherein the feed water tubes are separate from 50 said steam collecting means and are connected to the' lower portions of said downcomer tubes. 9. A water tube steam generator, which, in ad dition to the quantity of water continuously fed in and evaporated during one passage through 55 the boiler, contains a small additional quantity of water, comprising steam-generating tubes wound in the form of a multi-threaded coil, and downcomer tubes, means connecting said steam generator ,tubes and said downcomer tubes, means 00 in said connecting means to separate the steam from the water-steam mixture produced in said steam-generator tubes, whereby the water in said mixture after the separation of steam there from may continue to ?ow through said down 65 comer tubes, means to conduct off the steam water in said mixture afterthe separation of separated by said separating means, and means steam therefrom maycontinue `to ?ow through unconnected with said conducting means to in said downcomer tubes, upper and lower headers, troduce water into at least some of said tubes. means connecting the steam separating means 70 oi a plurality of said circulating units to said` MARTIN som/mar.