US2003419A

US2003419A - Boiler

Info

Publication number: US2003419A
Application number: US581347A
Authority: US
Inventors: Artsay Nicholas
Original assignee: Individual
Current assignee: Individual
Priority date: 1931-12-16
Filing date: 1931-12-16
Publication date: 1935-06-04
Anticipated expiration: 1952-06-04

Description

June 4, 1935. N. ARTsAY 2,003,419

BOILER y Filed Deo. le, 1951 7 sheets-sheet 1 sPHl 5mm-umm vAvomzA- saouomzen snee vAPomLA-now sua: sms non snes s-rAa:

s 41 n .gx E L v wif x sm. vAPon. izlmou 1PA. vAPon lzAnoN sconomze'n.

STAGE STAG: S'I'ME .STAGE Y STAnE INVENTOR ATTORNEY Jllne 4, 1935.a Y N, ARTSAY 2,003,419

BOILER Filed Deo'. 16, l1931 7 sheets-sheet .2

VAPORIZATION STAGES ECONOMIZER.

STAGE SPH. STAGE VAPORAIZATCN ECONOMiZEBv STAGE STAGE SPH. vAPomzm-wrq snee .STME 1 QNVENTQR EY @j ATTORNEY `lune 4, 1935. N, ARTSAY 2,003,419 n BOILER Filed Deo. 16, 1951. '7 Sheets-Sheet 3 ATTORNEY June 4, 1935.

BOILER Filed Dec 16, 1931 Sheets-Sheet 4 |NV-ENTOR- BY f, m

ATTORNEY June 4,' 1935.

N. ARTsAY BOILER Filed Dec. 1.6; 1931 OOOGGO OOOOOO @uw '7 Sheets-Sheet .5

000000 o@ oo lNVENTOR ENQ/2@ ATTORNEY June 4, 1935. N. ARTsAY 2,003,419

BOILER Fi1edDeo. 16, 1931 '7 Sheets-Sheet 6 ATTORNEY N. ARTSAY June 4, 1935.

BOILER Filed Dec. 16, 1931 INVENTOR BY Q ATTORNEY Patented 'Xl-lune 4,A

PATENT oFFicE nonna Nicholas Artsay, New York, N. Y. Application December 16, 1931, Serial No. 581,347

.somma 'I'he invention relates to steam boilers or steamv generators of the so-called ilash type and has for its purpose the provision of an improved form and operation of such boilers. 'I'he detailed points of improvement over prior boilers o! this type will be clear from a reading oi' the following specication.

The invention is illustrated in the drawing iiied herewith. In these drawings Figs. 1`, 2, 3 and 4 are diagrams used in the discussion of the theory of. the invention; Fig. 5 illustrates a` vertical longitudinal section more or less diagrammatic of a boiler in accordance with my invention; Fig. 6 is a section on line 6-,5 of Fig. 5; Fig. '7 "is a section on an enlarged scale on line 1--1 of Fig; 5; '7a is anenlarged sectional view 'on line 'laf-1a of Fig-7; Fig. 8 is a section similar to that of Fig.` 'lshowing a modification; Fig. 9

is a vertical section on line 9 9 of Fig. 6; Fig. 10 is.a section on line Ill-LII! of Fig. 9; Fig. l1 is a diagrammatic view.-on an enlarged scale of a detail of the boiler; Fig. 12 is a view similar to Fig. 11 of a. variation; Fig. 13 is a diagrammatic showing, of my boiler arrangement illustrating particularly the .connections between the several tubular parts or elements; and Fig. 14 is a diagrammatic view of the boiler with its controls.

In water tube Aboilers of the coil or flash type as hitherto built, there is no natural thermal orv gravity circulation of the water, all of the water nwhich is to be converted into steam entering the boiler at one end of vthe coil, or at one end of. the coils when there area number of them in parallel, and emerging at the other end as steam. The rate at which the water or steam and water mixture er steam moves at any point in the coil is always equal to the rate at which the boiler is being'ied. The' coil itself comprises several more or less distinct stages. The first of vthese inthe path of the water motion is the feed water heating stage sometimes called the economiser stage, this being followed by the evaporating stage where the` water is gradually converted into saturated steam., and ^in most'cases the steam generating stage is' followed by a superheating-stage where the steam generated is heated up to the desired temperature. v

On the gas sideA of the boiler, all of the gas.

produced by combustion nrst gives up some of its heat by radiation in a radiant heat zone which is followed byeI firsthot convection zone, next by a convection zon'e yof medium .gas temperature, and nnally by a colder convection 4zone where the residual heat is partially recovered by so-called economizers or by air preheaters.

It has hitherto been believed by the majority of those working in this art that the solid water even moving slowly in tubes is the most effective cooling medium for the metal of the tubes. The usual arrangement of boilers of this type has .5 thereforemeen to preheat the water, usually to a point approaching the boiling point, and then to "lead it into the zone of most intense heating eifect, that is, the hot radiant heat zone and then letting it now successively through coils in cooler l0 zones. Yaporization with such an arrangement begins in the intensely yhot radiant zone and ends in the main convection zone. Where the steam after generation is to be superheated, this is arrangedl for in a number of different ways as f ar'as the ltemperature zone is concerned in which the superheating is done. Quite commonly the steam generating coil is split or divided and superL heating surface inserted at one or more points.v

One of the important phases of my invention relates to the vaporization stage. To explain it, tuse will be made of Figs. 1 to 3. Referring to `Fig. 1, this iigure represents athe usual arrangement of heating stages as related to the several heating zones. The base 1 2 of the diagram represents Hthe full length ofthe coil, or of one of the parallel-coils where there are several in parallel, and the ordinates from this line to the curve 3 represent the rate' of heat absorption perunit length of the coil. The area under the curve 3 therefore corresponds to the total heat absorbed by the coil per unit of time. The hot gasesmove from left to right. The high fiat part of the curve 3 corresponds to the radiant zone where 'the heating byy radiation is. most intense. The vertical dotted lines indicate the divisions between the several stages. The broken line 4 represents the water or steam containing. surface. The portions of this. line lying above the line 4i--2 represent tubes exposed to the heating effect in the respective zones while the portions under the baseline I--2 represent outside con. f nections between the stages.' Water enters the economizer stage 4a and after being heated is led to the evaporating stagelb in the radiant zone. I'he conversion of 'water into steam is finished in .the main convection zone in the `stage 4c. Stage l4d is the ,'superheatingstage `lin the example nin Fig. 1 this is split up into twopats illustrated one-of which is located in the convection sone' and been heated in this stage flows into the first part lof the evaporating stage VB which lies in the velocity an intimate emulsion-like mixture ofsteam and water) before admitting it to the zone of most intense heat absorption, taking into account/ the lrise of boiling point due to pressure increase caused by frictional resistance to the flow. The evaporation is completed in 4C and the steam then` superheated in the superheater 4D. In boilers of the coil type as built in thepast, the tubes have been f relatively small diameter so that the segregation of steam bubbles and their collection at the sides of the tubes was not likely to occur. If coil boilers are to be built with tubes of diameter suftlcient'to allow an effective cleaning, this bubble segregation becomes an important factor and is likely to result in localized over; heating and damage to the tube and in their bursting. In a. coil boiler with stages of vaporization arranged as I have described in connection with Fig. 2, the dangerous Amoment of the rst formation of the steam-bubbles and their natural segregation due to their buoyancy is relegated to the' colder convection zone where the temperature of the gas is too low to endanger the tube even if part of the surface is blanketed by a layer of steam and therefore not adequately cooled by the moving water.

Fig. 3 is inserted to bring out more clearly the novelty of my invention. In this figure the superheating zones are omitted and it will be understood that they can be inserted in any zone, for example, as illustrated in Fig. 2. In this Fig. 3 the curve of heat absorption rate 3 is similar to that of Figs. 1 and 2. The arrangement usedrin the past and my arrangement are both drawn in in this figure for comparison. The heavy dotted line indicates the usual arrangement while the full heavy line indicates my arrangement. An inspection of the figure will make it clear that with the old arrangement of vaporization stages in the convection zone the flow of the fluid to be heatedand evaporated is parallel to the gas iiow while with my arrangement these -two are for the larger part in countercurrent. As far as I am aware, such a substantial degree of vaporization preliminary to entering the radiant zone has never `-been used heretofore and my theoretical investigations show that very beneficial results l follow from the change introduced by me.

A second important phase of my invention re-` lates to the troublesome effects of high concentration of dissolved and suspended matter in the boiler water. y i A In the 'usual boilers with thermal circulation the small amount of salts and dirt introduced with the feed Water stays in the boiler and the concentration gradually increases, its bad effects .being somewhat lessened by a periodical or continuous blow-down and the substitution of fresh feedfwater. Besides troubles in the boiler proper vdue-to scale formation steam separated in the drum and delivered to the superheater carries with it a small amount of entrained moisture with the dissolved concentrated salts in it. Even these smallamounts of salts have been found very harmful to superheatei's. steam reheaters and turbines. In the case of coil boilers as usually constructed, all the salts and dirt introduced with the feed water will pass to the superheater and the turbine or other engine as there is no such blowdown possible as in boilers of the type first referred to. My invention is designed to remove or at least to mitigate this evil. For this purpose I propose to withdraw near the end of the vaporization all of the steam-water mixture from the 10 coil, to pass it through a steam separator, such for example as a. centrifugal separator, to return the steam to the coil, and to dispose separately-of the concentrated solution separated out. 'I'he withdrawal should be made at a point near the 15 end of vaporization where only approximately 5 to 10% "of the water is left unconverted into steam. Preferably, in the interest of uniform regulation, I substitute an amount of fresh feed water of low initial concentration for the concen- 20 trate Withdrawn.

In order to carry out this proposal it is necessary to keep the point of total vaporization at approximately the same spot in the coil-so that.

the percentage of water withdrawn will not vary 25 greatly when the rate of steaming and firing is varied. That this is entirely feasible 'will be clear from the following considerations.

Referring to Fig. 4, thecurve 3a shows the heat absorption rate per unit length of coil and C per unit weight of steam output at normal operation. Curve 3b shows it at aA lower boiler output. 3c shows it'for an overload operation. When the steaming rate increases, theproportion of heating eiect by radiation decreases, while 33 the proportion of heating by convection increases. These opposing characteristics of the two zones make it possible to select superheating surfaces in such a way that the loss of heating effect in the convection part of the superheater is bal- 40 anced by the increased heating effect in its radiant part as shown by the shaded areas. A result, important forl the present invention, follows from this characteristic of superheating surface so arranged. The usual aspect of this is that 45 with varying loads on the boiler and superheater the final superheat remains constant. In connection with my invention it is interesting t6 put this in the converse form, i. e., that if the final superheat is kept constant, the amount of superm heating surface will also remain constant, or in other words the point where evaporation is complete is fixed. It will further be obvious that if the distribution of superheating surface between that part which is heated by vradiation and that 55 part which is heated by -convection is judiciously. made, not only will the point f total evaporation remain fixed, but 'the pointat which any given percentage, for example 95%, of the water has been evaporated also remains substantially fixed. G0

It therefore becomes possible to withdraw unevaporated water in a constant desired proportion or in other words at a desired concentration of salts in it. v

`In case it is not desired to use superheat'but c5 to use the steam in saturated condition, the rate of ring is regulated to deliver steam at some low superheat which always is of some advantage and then the point of total vaporization will also be in a denite spot oi' the coil making the with- 70 drawal ,of the concentrate i'r proper quantities possible.

A complete boiler in accordance with my invention is illustrated in Fig. 5. 4This figure shows a steam generator of large capacity and of a form 5 suiteb1y insulated on the outside as at Il. 'nie roof of the furnace is also lined with tubes connected to-headers and included inthe tubular System.-

Burners i 2 are placed in both sides of the sloping roof and they are connected with the primary air supply I2. 'I'he spaces between the burners are cooled by tubular elements Il connected in series with the atubular elements of the roof or, if desired, with elements of the upper part of the furnace envelope. If preferred, these spaces may also be closed by suspended refractory ipanels. Secondary air for completing the combustion is admitted by the duct 33 and the nozzles 24. These nozzles 24 are placed on the four walls o f the furnace, the tubular envelope of the furnace being interrupted for this purpose. Preferably the axes of the nozzles are so placed as to cause a rotary motion to the llame. It is within the scope of the invention to arrange auxiliary cross burners to accelerate the ignition of the mainl coal jets in case coals are used which are slow to ignite. Such auxiliary burners can take the place of some of the secondaryair nozzles, without affecting in substance the features f the preferredi form described They are indicated at I2b. when fuels are used that areeasily ignited, it is not necessary to provide the secondary air nozzles 34, all the air necessary for combustion being in that case supplied atthe burners.

The bottom 25 of the furnace is arranged to have the slag accumulate on it in a molten state. Such slag is then removed by tapping. If preferred, this can be modified by having a tubular slag screen at the bottom.

Referring now to the more `detailed c'enstruc` tion `of the tubular envelope of the furnace chamber Il, attention is directed to Fig. 7 showing a section on line 1 1 of lil'ig. 5. The tubular structure shown covers the entire perimeter of the furnace. Pairs of columns 2 2, 22 are installed at the corners of the furnace. In the form shown there are four pairs of such columns, the horizontaiprojection of the furnace'l being rectan-l guiar. The numbermay be varied and the shape of the furnace may be made other than rectangular. The paired columns are connected by several small horizontal plates lOl-IM, Fig. 7a, on which short headers 24, 2i rest., Each pair of columns 23 therefore supports several short headers in a vertical row. The total i'iow of the steam and water mixture is divided between the two sets of

vertical headers

24 and 25, and fur- `t'ber subdivided between tbe panna tubes respectively connecting these two'sets of headers,

the steam and water mixture flowing through them in parallel. The. respective -levels of the 'headers and the inclination of the tubes is such that after a complete. circuit varound the furnace the parallel tube connect into the header placed in the same vertical row immediately below the initial header. There are thus two parallel paths v for the steam and water mixture each comprising short headers placed at diagonally Opposite corners and parallel tubes connecting these headers.`

'Ihe clearance b'etweenvthe tubes of one set of headers is made substantially equal to the tube diameter or slightly larger, and the tubes of the second set occupy the spaces between the tubes "of .the Afirst set. The side': of' the furnace thus present 'a completely water cooled tubular envelope. With such a construction it will be unnecessary to have the usual solid brick setting, andinexpensive thermal insulation il will be sumcient. The

headers

24, 25 may safely'be anchored between the columns, the thermal expansion of the tubes being taken up by bending of the tubes at the corners as at21. In the case of large or high pressure boilers.4 itis advisable to anchor only one half of the headers, the othe` half being allowed to slide on the supporting plates joining the columns 23.- The vertical thermal expansion of the furnace envelope is reduced in this construction to the vertical expansions of the separate lvertical header and this is not cumulative, some clearance being provided for this purpose between the header tops and the supporting plates as at' I I2, Fig. '7a. Theposition of the columns gives the necessary accessibility to the header hand holes' 24a, 25a. .provided for inspection, cleaning, .and rolling in` of the tubes. In practice, the headers will of course be suitably insulated and access doors provided to the hand holes.

As a variation, in the case of steam generators of small output. the shortvertical headers vcan if desired be fitted with flanges andk bolted together to make up the vertical columns. The

variety in shape of the headers is not limited in tical assemblies ofv steel boxes connecting one or more pairs of tubes and welded to the vertical columns can be also used instead of the short headers just described. In these cases,I al1 the outside piping and casing should provide for the total vertical thermal expansion.

InFig. 8 is shown a variation for cases where it is thought necessary to arrange one wall of the furnace for a refractory lining-or where itis desired to leave it, or a portion of it, open for a stoker. In this case there are two sets of headers each comprising three series of headers. The-two sets are designated 2lb and 25h respectively and together. with the connecting tubes furnish continuous covering for the'three furnace walls.A The tubesv of the two sets of headers are lnterspaced as in the case described in connection with Figs, 'I and 7d. To provide the necessary return flow at the 'ends of thewater cooled furnace covering, successive' pairs of headers at these points are made in one piece.

Referring further now to Pig. '5 the casing e.

encloses the convection heating surfaces.' This includes the yconvection superheater 31, the

economiser 22, the last vaporisation stage 2.9 'and the nrst vapor-ization stage 42. An air preheater Il is also preferably arranged succeeding the steam-generatingstages in the path of the gases. l

'Ihe connections of the various cmnponent parts of the tubular system-of the boiler will be 'explained below, where reference will be made toFig'. 13.

-.The gasesgenerated' in the furnace usually entrain small particles of molten slag which settleentbenntrenetbouertubeaeleggingtnem by gradual-accumulation. This is a common from the tube itself where the latter is nearly horizontal or from the underlying slag accumulations on nearly vertical tubes. In my arrangement I provide a plurality of widely spaced horizontal water cooled tubes 4I at the point where the gases leave the furnace, the ow of gas across these tubes also being horizontal. The advantage of thisv arrangement is that the slag which usually settles in formations extending along the line or gas flow, gets no support and the accumulation breaks of its own weight. The remaining entrained particles of slag solidify after passing the water cooled slag screen 4| and will not clog the iirst rows of tubes in the convection zone but will settle in large part in the ash pocket 42, being separated out of the gas by the sharp upward turn of the gasl flow at this point.

As far as the convection surface is concerned, its construction ds not present anything radically new over established practice except that 1 the tubes are laid out mostly horizontally for the best utilization of spacethere being no necessity to allow for natural gravity circulation. Figs. 9 and 10 show vertical sections at right angles to each other of the convection tube bank. Good heat transfer requires certain velocity of the water and steam mixture in the tube. Theheat transfer increases with the-velocity but the frictional resistance to the ow increases very rapidly with an increase in the velocity. It is therefore necessary to increase the number` of tubes arranged in parallel as the evaporating water increases in volume. Instead o f increasing the number of tubes arranged in parallel the size of the tubes could be increased but this is less desirable.

The convection bank of tubesmay be arranged in many ways known to the art. As the increase 1in the specic volume proceeds, due to the forma- -tion of steam, the number of parallel coils should be increased. Figs. 9 and 10 show one of the possible ways inwhich square headers are stacked up.

The bank consists of several rows of tubes, eight tubes in each row for instance. The flow starts in four parallel tubes, thus having cross-over headers and cross-down headers as shown in the upper part of Figs. 9 and 10. When the number of tubes connected in parallel should be increased, for instance doubled, the cross-over headers are eliminated and only cross-down headers are used,

-as shown in the middle part of Figs. 9 and l0. 'When the next doubling of the number of parallel .tubes is required, Athe 'short vertical ycross-down headers are used as shown in thedower part oi' Figs. 9 and 10. Instead of headers, so-called U bends, or connecting boxes may be used and the tubes supported on drilled plates according to the established economizer construction practice. This part of the description is' intended to series with the coils as described further lon in Y' connection with Fig. 13.- The purpose of Athis arch 1s two fold. First itis intended to reduce the '.wear onthe refractory portions ofthe arch by' the erosive slag contained in the hot gases which pass this point at high velocity. In the second place the arch by suitably deflecting the flow of 'gas reduces the stratiilcation, thereby producing a more even heating eiect in the first convection rows'of tubes, which is very important in the case l' the water is shown divided into four parallel coils forming 4the evaporating stage 59, the outlets from the header 48 being controlled by individual valves. At some point in this first vaporization stage the number of v coils is duplicated in accordance'with the showing of Figs. 9 and 10.

The six parallel coils emerging from the .'drst vaporizing stage 49 connect into header 50 arranged preferably in a horizontal position, thisheader being connected by pipes 5| to the inlet 'headers of the two sets of headers and tubes con-- stituting vthe furnace envelope a's'shown and described in vconnectionwith Fig. 5. The number of parallel coils in each set is, forexample, six, makingfa total'of twelve.

After passing through the furnace envelope,

-the water and steam is delivered by' these twelve coils into the slag screen 4l. In flowing through this slag screen, the mixture of steam and water crosses the gas passage several times, for example, four times as shown in Fig. 13. After completing the passage through the slag screen, the steam and Water mixture enters the header 52 which forms the inlet header for the arch 44. The steam and water mixture is next delivered into several steam separators I3 arranged in parallel .as shown diagrammatically'in Fig. 13. In these separators the unevaporated portion of the water, which is a concentrated solution of the salts inthe water, is separated out to be withdrawn. Fresh water is added to replace the withdrawn concentrated solution, and the new mixture of the dry steam with the fresh water that has. been newly added is led to th-e nalvaporization stage 39. The detail of 4the separators is shown in Fig. l1 to be referred to hereafter. Y A

After a complete vaporization has occurred, the steam is carried to the radiantr heat part 54 of the super-heater placed at the top of the furnace in- .cluding the roofand thence into the nal convection part 3l of the superheater and thence to the steam main. illustrate the preferred way of changing -the numv It will be understood that the radiant part of the superheater may, if desired, be placed lower vdown in the path of iiame instead of at the top as shown and described.

As will be clear from what was said above, the amounts of heating surface in; y the different heating zonesare so proportioned that after the mixture has passedthrough thearch only a sm'all percentage of the total weight is still in the form..

In the case of an outdoor installation, such as shown in Fig.'5, all of the columns which support the various mentioned parts of the steam generator are fitted with consoles cn which th'e light outer casing- 55 is hung. yThis outer casing is.

l preferably mostly'glasswindows and is intended to protect the steam generator and the operating -personnel against the weather and to provide a sheltered spacel for the operators control ,in' struments, piping, etc.

coil; Such bends are shown, for example, in the., .pipes 5I connecting the section I9 to the furnace envelope. These U-bends act duringv stoppages like air seals and, if required, `suitable piping with' the necessary valves will .be provided to y' break these air seals, the valves being either operatedby hand or automatically. This being a if well-understood feature, it will be unnecessary to erator. At such times these valves make it posillustrate it.

The separators Il referred to above. and shown in Fig. 13 are each preferably arranged as the one shown in Fig. 11. In this gure only one separator is shown, it being understood that the others are duplicates; I0 is one end of the coil interrupted at the withdrawal point, II being the end of the coil where the steam returns tothe coil after the concentrate has been eliminated. The admission of the substitute lfresh feed water is controlled by the valve I2. I3 is a centrifugal steam separator although it will 4be understood that, if preferred, some other type of separator may be used. 'I'he concentrated salt solution' that is`separated out is withdrawn through the trap I4 and may be allowed to go to waste. However, when high steam pressures are used, the I heat in this concentrate may be a fairly large quantity and in such cases I prefer to employ a heat saving device to reclaim at least part of this vheat.4 Before sending the water to the heat reclaiming device, I prefer to flash a part of Ait into steamby reducing the pressure and to use this steam in a feed water heater. This flashing is done in the centrifugal separator I8, the water owing first through the valve 22 Vand lthen through the reducing nozzle 22a. The steam formed is led into .the feed water heater I1 containing coils through which the feed water flows. l' I'he condensate formed is removed through the trap Isa. The water separated `out in theseparator I8 is withdrawn through the trapII.

upon starting and-shutting down the steam gensible to cut out this concentrate separating device.

Instead of flrstflashing a portion of the water withdrawn from the system into steam as just described, I may, as illustrated in-Fig. 12,- use a heat exchanging device where all of the 'water flows in contact withthe coil I1a earryingthe feed water to the boiler. 2

By the separation of scribedv into two separate Aparallel constructions, expensive suspension of the heavy parts on columns is avoided. The furnace is supported by the four pairs of evenly loaded columns described above and the heavy convection bank of tubes of Fig. 5. The valves 2l and .2I--2I are provided for use the furnace and the con-V Vectionstages .0I the boiler inthe manner dei.

5 the sost of tneboner setting.' mtrouhie from slagging of the ilrstrowsof'thetubesofthiecoxi-A path necessary for complete combustion especially in connectionvwith opposed nrlng from the burners and additional turbulenceprovided by `the tangential iets of secondary air: The long straight path ofthe flame" eliminates the danger of direcgfiame impingement on thetubes which loften* produces blistering. The rectangular form of the furnace, tending to-break up the rotary motion produced by the tangential jets of secondary air increases the vturbulence and thereby promotes combustion.

sure of the steam are diagrammatically illustrated in connection th the boiler. This will best be explained by In Fig. 14 the means for the output of the generator and the temperature and pres- 4 t stating the general principle of operationifas follows: l'irst, the amount of vwater fed per unit of time into the generator and the amount of fuel redper unit of time are con'- trolled by the demand of steam as indicated by the changes of steam pressure in the mains.

This simultaneous control of feedwater flow and of the rate of combustion is well known inits application to coil boilers and infact this principle follows naturally from the operation of a coil boiler not having any considerable water storage.

When this problem is studied, however, in connection with boilers of large -outputandlong coils theinsluiiliciency of this simple scheme becomes apparent. Methods in actual use provide 4an intermittent control and alsodo not take' care of f differences between the actual performance of the performance theoretically set the boiler and yby the'positions of thecontrqls. In long coils this may involve surges, wateri hammer, uneven quality of steam especially if the quality of fuel and eiliciency of combustion is variableand of:

course beyondrcontrol, or when the resistance in tubes is variable due to clogging, different inlet feed water temperatures, improper functioning of the feedpump, and Vso forth. In large coil boilers the secondary factorsare becoming of great 4importance and this led me to the invention of the dierential control, the scheme'of .which isshown in Fig. 14.V The boiler shown 'diagrammaticallyinthisflgureisthesameasthat- The control system has been shown in a separate nguresmerelv -for'puiposes of clarity.

58 is a feed pump which forces the water into the economiser section 3l. 'Ihe water then passes successively, as described before, through the first vaporizati'on section ,'the' second vaporization stage2linthe furnace,theslagscre `enli,the arch Il. the steam separator I), the last vapori-v -zation lstage 39 where freshv vwater is added through the valve I2, the radiant heat superheater Il, and the convection superheater 31, be-: ing finally delivered to the main Il. The course ofV the'fiame and hot gases is shown by the lin'es v s.. n y

Before starting, the steam filling, the boiler isthoroughly vented at any vplaces where air may collect. 5 Next, the full pres-l discharge lwater into the open Amake-up water ,pmx u. The museum sans@ mesu generator shouldbe i full-of water. It-will be understood that during.

40 regulator l61.

and 54 which are exposed to direct radiation, and water from the vaporization stages 4|, 44, 39 and superheater stages 54 and 31 is quickly expelled into the tank 6|. Any steam generated at this period is led into the water of the tank 6| and is there'condensed until the temperature of this water reaches about 212 deg. F., after which the steam passes into the water without, condensing and to the air through the open vent 82. After 10 an interval the lagging heating eiect'in the convection surface will producethe proper proportions of the steam and water in the several stages corresponding to the established flow and rate of firing judged by the `attainment of normal l5 steam temperature, and then' the boiler can be connected to the main by opening the non-return ,and stop valves 63 and 64 respectively. During the starting up period, the xed rate of feed is maintained by the feed by-pass valve 65 while the main feed controlling valve 66 is kept closed.

During starting the steam separators are cut out as explained above, the by-pass valve 20 bcing open and the valves Zl-Zl being closed.

After running conditions have been attained, the steam' separators are put on the line by opening the valves.2l-'2l and closing the valve 20 and opening` the valve I2 for adding the fresh feed water'. The master regulator 61 through relays 68'and 69 respectively controls the feed group of $0 apparatusand the combustion group of appal ratus. The rst group consists of feed pump speed regulator 11i-and of the feed Valve regulator 1|. The second group consists of the fuel feed regulator 12 and regulatorsfor the induced forceddraft fans and primary air fan respecto the master regulator, for instance, by means of floating levers with adjustable arms, which are shown in Fig. 14 or by other means known to the art. According to my invention the differential regulator 16 of the feed group is actuated by the 60 diierence between the actual rate of heat liberation and the rate of 'heat liberation -set by the master regulator, this difference being preferably .taken by a device 18 made sensitive to the total rise of steam temperature between the inlet and outlet headers of the superheaters, because of its insignicant time lag -in respect to combustion. So, for instance in case of suddenly poor fuel the rate of feeding water into the boiler will be reduced by lesser superheat to correspond to the actuar heat liberation. Similarly the difieren--A tial combustion regulator 11 is actuated by the difference between the actual flow of water and the flow as set by the master controller. This difference is taken at the feed valve by device 19 as difference between the static head in the valve or pipe and the dynamic head in the throat of the valve, as shown diagrammatically on a somewhatenlarged scale on Fig. 14. Thus said differential regulator 11- will not operate if saiddifference in hydraulic heads and hence the vev locity atfthe feed valves is normal. In case, for

'instance, of clogging of tubes and increased total.

resistance to the ow, the flow' and the velocity .through the valve will decrease, hence the hy- 75 draulic head diiferencewill also decrease and the regulator 11 will decrease the rate of combustion thus restoring the proper relation of water iiow to combustion rate. The action of differential regulators will affect the output of the boiler which will be corrected by the next movement of the mastervregulator 61. as compared with the main effect given by the master regulator will be achieved by a lesser range and amplitude of movement of the relays by the differential regulators. In the scheme as invented by me the chances of regulation hunting are not only reduced but `also means in the form of differential regulators 16 and 11 are provided to dampen the hunting if such arises. For proper functioning of the control system the substitute water valve I2 is controlled by a device 80 which acts in response to the rate of concentrate discharge from separator I3.4 Devices diagrammatically shown in Fig. 14 and referred to in the description of that figure are all commercial devices obtainable on the market. For boilers of this type, designed to have a very large output, it will be necessary to have toward the end of the apparatus as many as thirty to forty parallel coils and it becomes neeessary to ensure uniformity of water distribution among these coils.. For this purpose a series of fil The differential effect valves B I-Bl Ais inserted in the connection of the economizer stage and the rst vaporization stage where the number of coils is not yet large. Preferably these valves have associated with them ow indicators. The valves are preferably manually operated to effect an even distribution of water among the initial coils, but an automatic operation known to the art may also be resorted to.

The proper behavior of a steam generator built in accordance with my invention during emergencies such as failures of the regulating system itself, requires also the provision of a minimum flowof water through the tubes and a minimum amount of combustion, these two being so proportioned that the minimum deliveries of water and fuel maintain theproper distribution of water and steam in the coils. These flows of water and fuel must of course be independent of the regulating system and are provided in the following manner: The minimum combustion is obtained from one or more suitably placed burners in continuous operation at a uniform rate. The minimum v:flow of water is arranged also for emergencies when the main stopvalve or the non-return valve are closed. For this purpose a by-pass outlet into the feed water tank 6| is arranged 4and its valve 82 besides being loaded to open at excess pressure is interlocked `with the main stop and non-return valves as indicated in Fig. 14 so that when the latter.Y are Iclosed, the by-pass valve is opened. The b'y`` pass inlet is by valve 65, already described."J` This minimum ow of water and fuel is preferably also used during so-called banking periods when the boiler is maintained in a state of readiness to be brought up to substantial steaming capacity from its practical minimum. f

, The novel features of this/control of operation for coil boilers without water storage or natural circulation maybe summed up as follows:

With the usual methods of coil boiler control,

when the demandrfor steam'changes, the feed water verte, 'me fuel 'feeding and draft devises are set in new positions to handle the required changed amounts of water, fuel and gas. 'ghe usual methods ldo not go beyond thisv and with their application the temperature ofsteam is vafil riable. I am proposing to use this regulation only as a first approximation and for the final mutual adjustment of the water feed, fuel feed and gas movement I am using additional devices, differentially introduced, so that the rate of water feed'is adjusted by the difference between the actual rate of heat liberation and the rate of heat liberation necessary for the uncorrected water feed. In this scheme the additional differential device will operate until the proper balance is reached and said difference in heating rates becomes zero. fuel is adjusted by the additional differentially introduced device made sensitive to the difference between the actual velocity of water through the feed valve opening and the velocity at which the valve operates correctly with the master regulator. In other words the rate of feeding fuel, whichv is first set to correspond to the rate of feeding water, is further corrected to correspond to the amount of water actually delivered'to the boiler. In this scheme the additional differential device will operate until the proper balance is reached. By making said differential devices sensitive to the differences between the rates of feeding waterI and fuel as actually obtained and as set by the master regulator and by connecting them as described I am avoiding regulation hunting when both corrections or adjustments are made simultaneously.

Good performance of large coil boilers depends upon continuous maintenance of proper proportions of steam and water in evaporating coils at all steam demands. With the usual methods of control this is possible only at steady loads, clean boiler, uniform fuel, i. e., in conditions rarely met in actual operation and the consideration of these actual conditions led me to the invention of the differential control. With such controlas described any sudden irregularity in the water feed or in the combustion will automatically correctJ combustion or water feed respectively and the' danger of flooding the coils or overheating them will be eliminated.

Under usual type of control a coil boiler would maintain steam pressure (deliver proper quantities cf steam) but the temperature of superheated steam will be variable, while a coil boiler having the differential control invented by me will deliver proper' amounts of steam at uniform both pressure and temperature.

What I claim is:

1. A steam generator of the class described comprising a furnace whose walls are lined with water tubes, means to feed fuel adapted to be burned in suspension from points adjacent to the top of the furnace, a separate vertical bank of substantially horizontal tubes, a gas passage to carry the products of combustion from the lower end of the furnace to the bottom of the separate bank of tubes, an off-takev for the gases at the top of said separate bank of tubes, a slag screen in said passage comprising a plurality of hori- Similarly the rate of feeding zontal tubes set across the gas flow, said tubes all being connected to present a closed path through which the water to be vaporized travels unidirectionally.

2. A steam generator according to claim 1, and including in addition an arch above the slag screen to protect the roof of the said gas passage, said arch comprising tubular elements connected to form part of the said closed path.

3. The method of generating steam comprising forcing the water to be evaporated through a tubular structure in a continuous stream from inlet to outlet, heating the water first in a zone of low heating effect to a point where a substantial part of the water has been evaporated thereby accelerating the rate of flow, thereafter heating the mixture in zones of most intense heating effect until all but a relatively small part of the water has been evaporated, withdrawing said small part of unevaporated water from the boiler and replacing it by a similar amount of fresh feed water.

4. Themethod according to claim 3 and further comprising automatically regulating the rate of adding the fresh feed waterresponsively to the amount of concentrate removed to make the two equal.

5. The method according to claim 3 and further comprising superheating the steam, and regulating the rate of fuel feed to keep the final steam temperature constant, whereby the fraction of water remaining unevaporated at the point of withdrawal remains substantially constant.

6. The. method according to claim 3, and further comprising superheating the steam' in part in the zone of low heating effect and in partr in the zone of intense heating effect so as to keep substantially constant the proportional part of the coil used for superheating, and regulating the rate of fuel feed to keep the final temperature constant.

7. In a boiler of the vclass described, the com'- bination of an assembly comprising two tiers of short vertical headers at opposite corners of the furnace, the several headers of one tier being staggered relatively to those of the other tier, tubes connecting the headers serially and together with them forming a continuous closed path, there being a plurality of parallel tubes connecting each header with thel next lower opposite header, the tubes extending along the furnace wall, and a second assemblysimilar to the first the two tiers of headers of the second as sembly being at the other two corners of the furnace and the tubes of the second assembly being arranged to occupy spaces between the tubes of the first assembly.

8. Apparatus in accordance with claim 7, and further comprising vertical columns adjacent to the tiers of headers and shelves secured-to the columns upon which the headers rest, there being some clearance between each header top and the shelf above it.

NICHOLAS ARTSAY.