US2316763A - Boiler apparatus - Google Patents

Description

April 20, 1943. H. J. KERR 2,316,763

' some: Arrm'rus Filed July 3, 1940 s Shun-shut 1 INVENTOR- Howa'rd J K err ATTORNEY.

April 20, 1943. H. J. KE

3? y 3. 1940 ///////////V//// V I5 Sheets-Sheet 2 Q/ZZ M'HHHHHHH O &

1N VENTQR. Howard J [1 err ATTORNEY.

April 20, 1943. H. J. KERR BOILER APPARATUS Filed July 3, 1940 3 Sheets-Sheet 5 INVENTOR.

7 BY Hz? ard JKer-r ATTORNEY.

maintained at proper temperatures.

Patented Apr. 20, 1943 BOILER APPARATUS Howard J. Kerr, Westfleid, N. J., assignor to The Babcock & Wilcox Company, Newark, N. J., a corporation of New Jersey Application July 3, 1940, Serial No. 343,715 16 Claims. :(Cl. 122-406) The invention herein disclosed relates to boilers and their operation, embracing for example a type of boiler wherein the flow of water or other liquid from which vapor is generated is maintained by natural circulation. In general such a boiler may include a system of heated upflow passages in which vapor is generated and from which vapor and unvaporized liquid are discharged into one or more upper drums, the vapor and liquid being separated and the liquid returned to the lower ends of the upflow passages through downflow passages, the column of liquid in the downflow passage establishing a hydraulic head which promotes and maintains a natural circulation of fluid in th boiler.

The demand for high steaming capacities and high boiler pressures has introduced various problems relating to the safety and efllciency of the units, among which are certain problems involving circulation which it is an object of this invention to overcome.

In a boiler employing natural circulation, it is essential that the fluid flow passages in both the upfiow and downflow portions of the circuit be so proportioned that under the most severe normal operating conditions, the hydraulic head differential between thecolumns of fluid in these two sets of passages will be such as to overcome the resistances to flow and set up an adequate flow of fluid so that the heat transfer surfaces will be This is of particular importance when the boiler is operated at high rates of heat absorption, and of more importance when the boiler is operated at high pressures. At elevated pressures, the high tem perature of the boiler liquid reduces the margin of safety between the temperature at which the metallic heat transfer parts must operate and the temperature at which such parts would become overheated.

With higher operating pressures. the circulatory conditions are affected, since the properties of the liquid from which the vapor is generated are such that the density of the vapor increases with pressure and the density of the liquid decreases until at some critical pressure the densities of the liquid and its vapor are the same; in the case of water, which is the liquid used in the majority of vapor generators, the density of the steam equals the density of the water at a critical pressure of approximately 3200 lbs. per square inch. Such a relation of densities is particularly pertinent to the design of natural circulation boilers which derive their circulating flow from the head differential which is a function of the difference in density between the water in the downtlow passage and. the water-steam mixture in the upfiow passage.

In the construction of a high capacity and high pressure boiler of the type under discussion, it is therefore essential that resistances and impedances to flow which use up an appreciable portion of the available hydraulic head that might otherwise be available for inducing and maintaining an active circulation and flow of liquid to the heat absorbing surfaces, be avoided or held to a minimum. In this respect, it is advantageous to use downcomers of large flow area from the elevated steam and water drum, and to locate the downcomers in unheated positions.

It has been found that with cylindrical downcomers of large diameter, particularly when connected to the end portions of the drum whereby an appreciable approach velocity occurs, a condition is provided which is conducive to vortex formation in the moving liquid at the entrance end of the downcomer. Such a vertical flow reduces the effective hydraulic head of the downflow water column and may be still further detrimental to good circulating conditions by causing the entrainment of vapor in the downfiow water stream.

Inhibition of a vortex therefore, eliminates a factor which contributes toward a reduction in the rate of boiler circulation. While it is important to prevent vortex formation in connection with a boiler at all operating pressures, the importance is emphasized particularly with reference to an upper operating range, for example, from about 1500 lbs. per square inch to 2500 lbs. per square inch. For such pressures, water at saturated temperatures of 597 F. and 669 F. respectively, has specific Weights of 42.5 lbs. per cubic foot and 34.7 lbs. per cubic foot, .while the steam has specific weights of 3.66 lbs. per cubic foot and 7.73 lbs. per cubic foot.

The solution of this problem has entailed the development of certain devices which for col.- venience of identification are known as vortex inhibitors, their purpose being to prevent the formation of a vortex and thereby permit the maintenance of a high rate-of natural circulation.

An object of the invention is therefore to utilize to the fullest extent the available hydraulic head in a natural circulation boiler operating at high capacities or high pressures, or at high capacities and high pressures.

A further object is to improve the characteristics of fluid flow in a natural circulation boiler,

the drum between predetermined limits. In the particularly to and through the return flow pas sages. a

An additional object is to improve the how conditions within an elevated boiler-r cm: from which. liquid is returned through a downcomer connection; also to inhibit or entirely prevent the forma= tion of a vortex within such a drum. at the entrance to such a connection.

ings, of which the several figures are briefly described as follows:

Fig. l is a sectional side elevation indicating a type of boiler favorable to utilization of the iii-=- vention;

Fig; 2 is a sectional elevation of the boiler taken along line 2-2 of Fig. 1;

Fig. 3 is apartial section taken along line 3-3 of Fig. 1 indicating in plan a form of vortex inhibitor in operative position within the boiler drum;

Fig. 4 is an end section taken along line 6-53 of Fig. 3;

Fig. 5 is a side elevation ing a. modification;

Fig. 6 is an end section taken along line fi-t of Fi 5;

Fig. 7 is aside elevation partly in section show ing an additional modification:

Fig. 8 is an end section taken of Fig. 7. i

The boiler indicated in Figs. 1 and 2 of the partly in section showalong line 8-8 drawings is a boiler of the natural circulation type capable of generating vapor at high rates and at high pressures and temperatures: for example, such a boiler may haveste r capac-= ities of several hundred thousand pounds of steam per hour, andoperate at ggauge pressure drawings, the level or liquidis indicated at ap proximately the horizontal center line, but certain conditions might make itdesirable to aintain a level either below or-above the center line position. The necessary heat for vapor genera tion is supplied by a two stage furnace having a primary stage A which is fired by suitable burners B, and a secondary stage C which receives hot products of combustion from the primary stage. The heating gases pass from the secondary stage C to a convection passage D and finally'leave the setting through gas outlet E. 1

The vapongenerating elements of the boiler comprise a plurality of groups of tubes which in the main define the primary and secondary stages A and C of the furnace and thus are subjected to intense heat oif radiation from the burning fuel ciatedwith the passage 1) are heated mainly by convection, being exposed to combustion gases.

which have been cooled in their passage through the preceding two stages of the furnace.

The tubes associated with the primary stage A include the floor tubes 26 which are connected at of approximately 2500 lbs. per-square inch and 1 a corresponding saturation temperature of approximately 669 F. Such a boiler. together with its furnace and other related parts is included in the subject matter of '0'. S. Paten 223L872 granted February 18, 1.941, on app ation Ber. No. 137,196 filed od-April 16, 193?, asthe joint application of E. G. Bailey and others. It is to be understood that the boiler illustrated, and described herein is broadly representative of the type of bbiler in which the subject invention may be' utilized, and that its specific characteristics,

such as the form and arrangement of its component parts, may be variously modified.

The boiler as shown comprises a plurality of I groups of steam generating tubes winch with their connections constitute the upfiow section of a natural circulation system having connections downcomer pipes 22 connecting the ends of drum 2| with the ends of the header 20. One or more ,'.feed water connections such as 23 are made to the drum 2! at suitable locations for replacing their lower ends to the water supply header 2c, the front wall tubes 25 which are connected to flour tubes 26 by means of the ntermediate header 2t, and the side wall tubes 7 which are connected at their lower ends to side wall headers 28. The tubes 25 and 27 are connected at their upper ends to headers 29 and 8@ respectively, the headers Sfibeing suitably connected to the drum 2! through riser tubes 3 i 4 The tubes associated with the secondary stage 0 include the rear wall tubes 32 which extend upwardly from header 33 to the drum 2i,'and side wall tubes 3% which extend upwardlyirom lower side wall headers 35 to upper side wall headers 3d, the latter having suitable connections 3? also to the drum 2i.

Water or other liquid for vapor generation is distributed from header 20 to the lower side wall headers 28 and 35. and to the rear wall header 33. through connections 38, 39 and M, respectively.

A division wall ti between the two furnace stages is formed of tubes 42 which extend upwardly from header 20 to header 29 and have portions 63 within the furnace arranged to provide outlets it for products of combustion passing from the primary to the secondary stage. i 1

The tubes associated with the convection passage D include the bank of tubes at extending upwardly from header 29 to the upper drum 2! and transversely of the flow of heating gases. Additional tubes as which extend from header 23 to the drum it have their end portions arranged along the walls ti and d8 of the passage D and tubes forming the upfiow section of the system derive their total supply of liquid either directly or indirectly, from a lower header such as 26, and all tubes discharge their total content of heated liquid, or liquid and vapor mixed, into a common upper drum such as 2i. vThe individual connec water evaporated from the system and for main- I taining a-normal operating level of water within downcomers 22 which are disposed exteriorly" of I j Z the setting walls 52 and thereby shielded from heat of the furnace.

The downcomers 22 as shown, are circular conduits of relatively large internal diameter to provide adequate flow area for the total quantity of liquid which must be returned to the lower part of the upi-low section at a high rate to maintain the desired high rate of vapor generation. The flow area provided by any downcomer is greater than the flow area of anytube discharging into the drum, but for practical considerations the total downflow area is only a fraction of the combined flow area of all such discharging tubes. The total flow area afforded by the downcomers may also represent only a fraction of the transverse cross section of the normal liquid content of the drum. It is desirable for economic reasons to keep the diameters of drums and downcomers down, where it can be done without involving un- .due limitations to other factors of the unit. The

location of such downcomers relative to the entrances for liquid into drum 21 throughout its central portion requires that the liquid attain a high velocity of flow longitudinally of the drum in its approach to the downcomer, and an accelerated velocity as the direction of flow is changed and the liquid enters the downcomers; furthermore, such conditions are conducive to the formation of a vortex in the body of liquid above and within the downcomer. Thus, there is a two-fold effect on the amount of hydraulic head available for maintaining circulation, first a loss due to the acceleration of velocity at the entrance, and second, a further loss due to the formation of the vortex. The vortex under certain conditions may be hollow and penetrate to a considerable distance below the upper surface of the liquid within the drum, and in some instances may actually extend within the downcomer; in such cases the effect of the vortex is accentuated and entails a further loss in hydraulic head due to the presence of vapor or gas which reduces the density of the descending column of liquid.

The conditions described have led to the development of certain devices known as vortex inhibitors which, as shown in the copending applications of E. G. Bailey, Serial No. 343,707, filed July 3, 1940, and R. M. Hardgrove; Serial No. 343,-

' 725, filed July 3, 1940, both of which applications are assigned to the assignee of the present invention, are incorporated in the circulatory system of a boiler for counteracting and preventing vortical action of the fluid in the downflow section. Figs. 3 to 8, inclusive, of the present application illustrate further developments in connection with this same general problem, each specific embodiment being shown in association with a downcomer from a boiler drum for inhibiting vortical action in the descending column of fluid. In general, such devices divide the body of circulating liquid into a plurality of streams and direct the flow of individual streams toward the downcomer connection.

grating may be formed of a plurality of spaced bars 51 with other bars 58 of serpentine formation undulating across the spaces between successive bars 51 to provide a plurality of channels or passageways 59 and in cellular arrangement throughout the length and breadth of each grating. The individual passages are indicated as being of substantially triangular cross-section, but other shapes might be found suitable and could be formed by suitable selection and arrangement of the bars. shown, of non-circular, irregular polygonal crosssection, have a greater dimension longitudinally of the drum than transversely, and are closed peripherally by the bars 51 and 58 which thus determine the paths which individual streams of liquid must follow. Since the passageways extend from one face of the grating to the other, the length of each passageway is determined by the width of the bars 51 and 58, and a greater length is readily obtained by utilizing a plurality of gratings 54 and 55 as shown. one superimposed upon the other and preferably with the corresponding passageways 59 and 60 of the gratings in register. The spaced bars 51 and undulating bars 58 are suitably connected at intervals 'as at 6|, and the entire unit of one or more gratings supported at each end by a transverse angle bar 52. The unit is preferably held in spaced relation to the inner wall of the drum as at 63 and may be conveniently supported in relation to the downcomer opening by attachment of the end bars 62 to clips 64 which are fixed to the drum.

In the form shown, the spaced bars ,{51 are parallel and extend longitudinally of the drum 21; however, this specific arrangement while convenient and desirable is not a fixed essential, nor is the general rectangular outline of the structure to provide the plurality of passageways such vanes to the flowing body of liquid, whereby the In Figs. 3 and 4 a vortex inhibitor 53 is shown as comprising a plurality of gratings 54 and 55 arranged horizontally above the entrance of a downcomer 22, the gratings extending both transversely and longitudinally beyond the rounded periphery of the outlet opening 56 within which i the downcomer 22 is received. The extent of overlap may be varied to suit different conditions, for example, the relative sizes of the downcomer and drum, as well as the normal rates of circulation of boiler liquid and the normal operating levels of such liquid within the drum. Each liquid is subdivided without appreciable loss of energy and the plurality of streams separately guided along confined paths of substantial extent toward and through the outlet and into the downcomer 22.

It has been found that this form of inhibitor is adapted to the successful prevention of vortical disturbances in th discharging liquid under a variety of operating conditions, and moreover is a form which may be procured or constructed with facility at relatively small expense. The inhibiting action of such a device is probably due to the division of the liquid into a plurality of streams and to the disposition of the flow-directing eleinents, such as the bars 51 and 58, in edgewise relation to the outlet openin and thus in transverse relation at intervals to the course of any rangement to gratings 54 and 55 of Figs. 3 and 4..

A similar grating 66 is arranged at the upstream end of the gratings 55 in an upright position and transversely of the drum 2|, thus providing a primary division of the circulatin liquid into a plurality of streams, the bars 51 and 58 of The passageways as this grating also presenting edge portions to the on-coming liquid whereby the division is accomplished without appreciable energy loss, and the walls of the passageways 59 and 6b are of sufiicient depth to provide a substantial directional eflect on the flowing liquid. An inclined grating Bl, also of the character of gratings d and 55, is arranged at the downstream end of gratings 65, its upper portion 68 being extended above the level of the upper gratin 65 and its lower portion 69 extended below the level of the lower grating 65 to a point adjacent the inner wall of the drum, in this particular embodiment, the portion 69 having its end supported on the drum wall. The gratings 65 may be suitably positioned and supported relative to the outlet 56 by means of angle bars 62 and clips 56 as in the case of the embodiment hereinbefore described, and gratings 66 and El suitably supported in the desired position relative to the gratings B5. The gratings 65 and 66 as shown are of substantially the same width transversely of the drum while the inclined grating 67 disposed nearer the end wall In is of a smaller width dimension. A narrower and less extensive grating is suitable rearported relative to the outlet 56 in the manner A curved hood provided for other embodiments. or deflector i2, suitably formed from a flat plate if desired, is positioned above and to the rear of gratings II and suitably supported by clips 13 and I4 fixed to the drum. Referring to Fig. 7 the deflector has its leading edge 15 preferably below the horizontal axis of the drum and approxitions in structure are fully included within the scope of the invention as defined in the appended claims.

I claim:

1. A vapor generator having a circulatory system for liquid including a pluralityof vapor generating tubes and an elevated drum, downcomer means for supplying the preponderance of liquid required for vapor generation within said tubes from said drum, means for generating vapor within said tubes at a rate requiring a rate of supply of liquid through said downcomer means means for supplying the preponderance of liquid mately at the normal operating level of the circulating liquid. The upper portion 16 of the plate is inclined downwardly toward the end wall 10 of the drum and continued in a curved portion 11 rearwardly of the gratings and then forwardly a short distance to a location 18 adjacent the drum wall. The form of the deflector 12 as seen in projection in Fig. 8, is substantially a segment of a circleof smaller radius than the internal radius of the drum 2!, the upper edge portion 19 being straight and horizontally disposed, and the curved edge portion 80 being spaced from the inner wall of the drum at graduated distances throughout its height as at 8!. The formation of the vane is such as to gradually deflect the circulating liquid from its longitudinal cours in the direction of the outlet to the direction in which it must flow to pass through the passages 59 and 66 in the gratings H and, since the inclination and curvature of the vane is gradual, such deflection is accomplished without appreciable loss of velocity head. Liquid which flows beyond the vane l2 into the space between the vane and the end wall ill may return through the spaces 8! for flow into the downcomer 22, thus substantially equalizing levels at opposite sides of the deflector and preventing liquid from becoming pocketed within the closed end of drum.

In this disclosure of the invention the description and illustrations have necessarily been restricted to certain selected embodiments but it is to be understood that the practical application of the invention may involve apparatus of different form and appearance, and that such variarequired for vapor generation within said tubes from said drum, said downcomer mean comprising a conduit of several times greater flow area than any One of said tubes connected at its upper end to a lowerportion of said drum below the normal liquid level, means for generating vapor within said tubes at a rate requiring a rate of supply of liquid through said downcomer means conducive to gyratory movement of the liquid entering said conduit from said drum, and a grating in the path of said entering liquid for inhibiting said gyratory movement.

3. In a boiler, in combination witha pressure vessel thereof having a downflow connection through which unvaporized boiler liquid is withdrawn for delivery to vapor generating tubes, said downflow connection having a flow capacity large enough for a vortex to be formed in the liquid being withdrawn, means within said vessel for preventing said vortical disturbance comprising a grating fronting the entrance tosaid connection and spaced throughout from the inner wall of said vessel, the bars of said grating being relatively thin in a transverse direction as compared with their depth in the direction of liquid flow.

4. A vapor generator having a circulatory system for liquid including a plurality of vapor generating tubes and an elevated-drum, a downcomer connection for supplying the preponderance of liquid required for vapor generation within said tubes from said drum, means for generating vapor within said tubes at a rate requiring a rate of supply of liquid through said downcomer connection conducive to gyratory movement of the liquid entering said downcomer connection from said drum, and a grating of substantially rectangular outline disposed in the path of liquid entering said downcomer connection for inhibiting said gyratory movement, said grating extending across the marginal outline of said downcomer connectionin all directions and being formed of elements constituting blades for direct-' ing the liquid downwardly toward separate units units of flow area of said downcomer connection.

5. In combination with a vessel adapted to contain liquid during normal operation, downcomer means for continuously withdrawing liquid from said vessel in a substantially circular stream at a rate conducive to vortical action of the liquid entering said means, means for continuously replenishing said vessel with liquid at substantially the rate at which liquid is withdrawn whereby the level of liquid within said vessel is maintained between predetermined limits, and means adjacent the entrance to said downcomer means for dividing the liquid being withdrawn into a plurality oi non-circular streams and for guiding said streams through peripherally closed flow paths in the direction of said entrance.

6. Boiler apparatus comprising a drum having an outlet through which a column of liquid is discharged downwardly during normal operation, said outlet having a flow area sufiicient for the formation of a vortex within the upper portion of said column, and means in the path of said liquid for maintaining said column of discharging liquid substantially free from cavitation, said means comprising a grating formed of bars defining a. plurality of cellularly arranged flow-direct- I ing channels of polygonal cross-section.

'7. In combination, a boiler drum having its longitudinal axis horizontally disposed in normal operation, said drum having an outlet through which boiler liquid is discharged in a downward direction, said outlet having a flow capacity sufflcient for a vortex to be formed in liquid being discharged therethrough, and means within said drum forming separated flow paths for liquid flowing toward said outlet, said flow paths being of irregular polygonal cross-section and of greater dimension longitudinally of said drum than transversely. Y

8. In combination with a boiler drum adapted for operation in a substantially horizontal position, said drum having a downwardly discharging outl t for circulating boiler liquid flowing longitudinally of said drum, said outlet having a flow capacity sufiicient for the development of a vortex in said circulating liquid in the vicinity of said outlet, means adjacent said outlet forming channels for directing liquid into said outlet, and means arranged forwardly of said outlet forming other channels for th longitudinally flowing liquid.

9. In combination with a boiler drum adapted for operation in a substantially horizontal position, said drum having an outlet for circulating boiler liquid flowing longitudinally of said drum, said outlet having aflow area sufllcient for the development ofa vortex in said liquid at relatively high rates of flow therethrough, a grating substantially horizontally disposed above said outlet and below th minimum operating level of said liquid, and a grating arranged forwardly of said outlet in an upright position.

10. In combination with a boiler drum adapted for operation in a substantially horizontal position, said drum having an outlet for circulating boiler liquid flowing longitudinally of said drum, said outlet having a flow area suflicient for the development of a vortex in said liquid at relatively high rates of flow therethrough,'a grating substantially horizontally disposed above said outlet and below the minimum operating level of said liquid, and a second grating arranged in oblique relation to said first grating.

11. In combination with a boiler drum adapted for operation in a substantially horizontal position, said drum having an outlet for circulating boiler liquid flowing longitudinally of said drum, said outlet having a flow area suflicient for the development of a vortex in said liquid at rela- 12. In combination with a boiler drum wherein during normal operation boiler liquid is circulated longitudinally of said drum for discharge through a submerged outlet in a transverse direction, said outlet having a flow capacity suflicient for a vortex to be formed in the discharging liquid, a grat ing within said drum across the entrance to said outlet, the bars of said grating being of substantially greater depth than thickness, and means adjacent a marginal portion of said rating for deflecting longitudinally circulating boiler liquid into passages formed between bars of said grating.

13. In combination with an elevated drum having horizontally spaced inlet and outlet means for liquid whereby during normal operation liquid received through said inlet means is caused to flow longitudinally of said drum in the direction of said outlet means, said outlet means having its axis of flow directed downwardly from said drum, said outlet means having a flow capacity suflicient for the development of a vortex in said liquid substantially about said axis, means for discharging liquid through said outlet means with minimum turbulence and loss of velocity head comprisin a system of blades or vanes arranged 'edgewise of said outlet means for dividing the body of discharging liquid into a plurality of streams, and means extending transversely of said drum into proximity with opposite wall portions thereof for arresting longitudinal flow of undivided liquid substantially at the downstream margin of said outlet means.

14. In combination with a boiler drum adapted for operation in a substantially horizontal position, said drum having a downwardly dischargin outlet for boiler liquid adjacent a closed end thereof whereby circulating boiler liquid flowing longitudinally of said drum toward said outlet is tively high rates of flow therethrough, a grating substantially horizontally disposed above said caused to flow transversely of said drum to pass through said outlet, said outlet being large enough in flow area for liquid to flew therethrough under conditions conducive to the formation of a vortex adjacent said outlet, a grating substantially horizontally disposed above said outlet, and a member arranged marginally of said grating for deflecting longitudinally f1 owing boiler liquid into passages formed between bars of said grating, said member being curved upwardly from a position rearwardly of said grating adjacent the closed end of said drum to an advanced position above said grating.

15. In combination with a boiler drum adapted for operation in a substantially horizontal position, said drum having an :outlet for boiler liquid opening laterally thereof whereby boiler liquid flowing longitudinally of said drum toward said outlet is caused to flow transversely of said drum to pass through said outlet, said outlet being large enough in flow area for liquid to flow therethrough under conditions conducive to the formation of a vortex adjacent said outlet, a grating above said outlet and spaced from the walls oi said drum, and a deflector of generally segmental formation arranged transversely of said drum for directing boiler liquid through said grating, said deflector terminatin in a substantially horizontal upper edge portion above an intermediate portion of said grating and having adjoining curved edge portions spaced from the inner wall of said drum.

16. In the circulatory system of a vapor generator, an elevated drum, downcomer means for supplying the preponderance of liquid required for vapor generation from said drum, said downcomer means having a flow capacity sufiicient for supplying said liquid under conditions conducive to vertical movement or the liquid entering said downoomer means iroxn said and means for inhibiting said vertical movement comprising astructure in the nature or a grating fronting th entrance to said downcomer v7.4" said grating being formed or relatively thin stripdike elements arranged edgewise to the flow or said liquid to divide said liquid into a plurality of c section to include a plurality of peshaving outlets distiibuted throughout the projemed area of the entrance to said downccmer ,HOWARD J.

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