US2316762A - Boiler circulation - Google Patents

Description

April 1943- E. G. BAILEY 2,316,762

BOILER C IRCULATI ON Filed July 3, 1940 3 Sheets-Sheet l n INVENTOR.

Ervin G. Bailey ATTORNEY.

April 20, 1943. E. G. BAILEY 2,316,762

BOILER CIRCULAYTION 3 Sheets-Sheet 2 7 Filed July 3', 1940 ATTORNEY.

April 20, 1943. E. s. BAILEY BOILER CIRCULATION Filed July 3, 1940 3 Sheets-Sheet 3 IN VENTOR.

- Evin G. Bailey ATTORNEY.

Patented Apr. 20, 1943 BOILER CIRCULATION Ervin G. Bailey, Easton, Pa., assignor to The Babcock & Wilcox Company, Newark, N. J a corporation of New Jersey Application July 3, 1940, Serial No. 343,707

20 Claims.

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 the boiler.

The demand for high steaming capacities and high boiler pressures has introduced various problems relating to the safety and efiiciency 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 the columns 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 maintained at proper temperatures. 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 temperature 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 downflow pas- Sage and the water-steam mixture in the upflow 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 tothe 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 vortical 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 downflow 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 7 development of certain devices which for convenience 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,-

' particularly to and through the return flow passages.

An additional object is to improve the flow conditions within an elevated boiler drum from which liquid is returned through a downcomer connection; also to inhibit or entirely prevent the formation of a vortex within such a drun at the entrance to such a connection.

The invention also contemplates the arrangement of specific devices within a boiler drum whereby the foregoing objects may be accomplished, such devices having a direct action on the flow of liquid into the downcomer passage to prevent the formation of a vortex and consequent impairment of boiler circulation.

These and other objects and features of the invention are more fully set forth in the ensuing detailed description and claims, particularly when read in conjunction with the accompanying drawings, of which the several figures are briefly described as follows:

Fig. l is a sectional side elevation indicatin a type of boiler favorable to utilization of the invention;

Fig. 2 is a sectional elevation of the boiler taken along line 22 of Fig. 1;

Fig. 3 is a partial section taken along line 3-3 of Fig. 1, indicating a side elevation of aform of vortex inhibitor in operative position within the boiler drum;

Fig. 4 is a planview of Fig. 3;

Fig. 5 is an end elevation, partly in section, taken along line 5-5 of Fi 3;

Fig. 6 is a partial section, similar to Fig. 3, indicating a modified form of vortex inhibitor;

Fig. '7 is a plan view of Fig. 6;

Fig. 8 is an end elevation, partly in section, taken along line 8-8 of Fig. 6;

Fig. 9 is a partial section, similar to Fig. 3, indicating an additional modification;

Fig. 10 is a plan view of Fig. 9;

Fig. 11 isa sectional elevation of Fig. 9 taken along line I I;

Fig. 12 is a partial section similar to Fig. 3, indicating a further modification;

Fig. 13 is a plan view of Fig. 12;

Fig. 14 is a sectional elevation of Fig. 12 taken along line l'4-|4; and

Fig; 15 is a plan view indicating a variation of the structure shown in Fig. 13.

The boiler indicated in Figs. 1 and 2 of the 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 have steaming capacities of several hundred thousand pounds of steam per hour, and operate at a gauge pressure of approximately 2500 lbs. per square. inch and 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 U. S. Patent 2,231,872 granted February 18, 1941, on application Ser. NO. 137,196 filed on April 16, 1937,

with the water supply header 20 at its lower end and with the steam and water drum 2| at its upper end. The downflow section comprises the downcomer pipes 22 connecting the ends of drum 2| with the ends of the header 29. One or more feed water connections such as 23 are made to the drum 2| at suitable locations for replacing water evaporated from the system and for maintaining a normal operating level of water within the drum between predetermined limits. In the drawings, the level of liquid is indicated at approximately the horizontal center line, but certain conditions might make it desirable to maintain a level either below or above the center line position. The necessary heat for vapor generation 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 hotproducts 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.

The'vapor generating 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 of radiation from the burning fuel and products of combustion. The

tubes associated with the passage D areheated 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 24 which are connected at their lower ends to the water supply header 29, the front/wall tubes 25 which are connected to floor tubes 24 by means of the intermediate header 26, and the side wall tubes 21 which are connected at their lower ends to side wall headers 28. The tubes 25 and 21 are connected at their upper ends to headers 29 and 30 respectively, the headers 30 being suitably connected to the drum 2| through riser tubes 3|. The tubes associated with the secondary stage C include the rear wall tubes 32 which extend upwardly from header .33 to the drum 2|, and side wall tubes 34 which extend upwardlyfrom lower side wall headers 35 to upper side wall headers 36, the latter having suitable connections 3'! also to the drum 2 I.

Water or other liquid for vapor generation is distributed from header 2!) to the lower side wall headers 28 and 35, and to the rear wall, header 33, through connections 38, 39 and 49,'respec-' tively.

A division wall 4| between the two furnace stages is formed of tubes 42 which extend upwardly from header 20 to header 29 and have portions 43 within the furnace arranged to provide outlets 44 for products of combustion passing from the primary to the secondary stage.

The tubes associated with the convection passage D include the bank of tubes 45 extending upwardly from header 29 to the upper drum 2| and transversely of the flow of heating gases. Additional tubes 45 which extend from header 29 to the drum 2| have their end portions arranged along the walls 41 and 48 of the passage D and their intermediate portions 49 arranged across the passage in transverse relation to gas flow. Other heating surface associated with the passage D includes a superheater 59 and an economizer 5|.

' In the arrangement shown and described, all tubes forming the upfiow section of the system derive their total supply of liquid either directly or indirectly, from a lower header such as 20, and all tubes discharge their total contentfof heated liquid, or liquid and vapor mixed, into a common upper drum such as 21. The individual connections from the upfiow section to the drum 2| are made at successive longitudinal positions, as shown in Fig. 2 for tubes 32 and 31, occupying the major central portion of the drum length and leaving the end regions for connection of the downcomers 22 which are disposed exteriorly of 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 upflow 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 any tube 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 undue limitations to other factors of the unit. The location of such downcomers relative to the entrances for liquid into drum 2| 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 twofold efiect ont he 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 Figs, 3 to 14, inclusive. are installed in a boiler drum in the vicinity of the downcomer to counteract and prevent the vortical action at the point of discharge. In gen eral, these devices comprise a combination of plate elements or battles in an arrangement providing passages whereby the body of circulating liquid is subdivided and directed into the downcomer with a minimum loss of velocity head. The

individual plate members are disposed in a substantially upright position and may be entirely submerged at normal operating levels of liquid within the drum, the plates preferably extending upwardly within the drum to a height correiii) sponding substantially to the minimum operating level.

In Figs. 3, 4, and 5 the vortex inhibitor comprises a plurality of substantially rectangular plates arranged in intersecting planes to form a cross; for convenience of construction, a plate 53 having attached thereto the plates 54 at opposite sides. The device is installed in the drum 2| with the intersection 55 of the planes substantially coincident with the axis of the downcomer pipe 22, and preferably with the plane of one of the plates extending longitudinally of the drum in the direction of the approaching liquid. The plates have portions 56 extending into the outlet opening 51 to further the inhibiting action within the downcomer and to provide a support for the device. The outer portions of the plates may extend beyond the diameter of outflow opening and be bolted or otherwise secured to clips 58 welded to the drum shell as a further means of support.

It will be noted that by this arrangement there are four passages 59, 60, BI and 62 formed at the entrance to the downcomer, each passage converging toward the axisof the downcomer, thus causing the main body of liquid to be directed into the downcomer in a plurality of streams from different directions, and effectively inhibiting the formation of a vortex. A further advantage is that each plate has a portion extending transversely of the path which a vortex might follow and thereby provides an additional hindrance to vortical action.

Figs. 6, 7 and 8 illustrate a form of inhibitor in which an upright plate 63 extends across the downflow passage in a longitudinal direction and plates 64 are symmetrically arranged at opposite sides. Each of the plates 54 is of angular formation or V-shaped as shown and is spaced from the central plate 63 to provide passages 65 at both sides. The plates may have lower portions 66 extending into the out-flow opening 51 as in the form previously described, and may also have additional support for example by attaching outer portions of the plates to clips 6'! which are welded to the drum. The plates may be further supported by means of a ring 68 secured to their upper edges. In this specific arrangement there are also a plurality of converging passages formed about the axis of the downcomer, those formed by the angular plates as at Y59, and those formed between the angular plates and the central plate as at 'lll, the passages 10 which are adjacent the longitudinal axis being in communication in pairs longitudinally of the drum by reason of the passages 65.

Figs. 9, 10 and 11 Show a form of inhibitor in which a plurality of plates II are utilized, each disposed in an upright position and spaced from the adjacent plate and extending in a direction paralleling the longitudinal axis of the drum 2!. The plates as shown are of successively decreasing heights at each side of the central plate 12 and each is of semicircular formation at its upper edge. As in the other forms, the plates may extend into the outflow opening 57 as at 13 and may be secured to the drum by means of clips 14. Additional support for the plates may be had from spacer rods 15 as shown. This arrangement of plates presents a plurality of passages for the flow of liquid into the downcomer 22 whereby the main stream is subdivided into a plurality of smaller streams, each of which'is confined to a relatively narrow path in a vertical plane parallel to the original direction of flow.

Furthermore each plate provides an obstruction in the path of any vortex that might tend to form.

The form of inhibitor shown in Figs. 12, 13 and 14 utilizes a plurality of upright plates 16 which as seen in Fig. 13 are spaced apart at their upstream edges 11 relative to the direction of flow of liquid longitudinally of the drum, and converge toward alocation 18 beyond the rearward margin of the downcomer passage 22 where the plates are in contact with one another; thus forming a plurality of separate passages 13 converging in the direction of the downcomer with each passage of decreasing cross-section in the direction of flow. Individual plates may be recessed as at 80 along their bottom edges, leaving the end portions 8| and 82 of full height and in contact with the drum wall. The plates may be reinforced for example by rods such as 83, and the entire assembly held in position in the drum by bolted connections to clips 84. The device may include a relatively coarse screen 85 of wire mesh entirely enclosing the plate assembly except at the bottom where the plates are contiguous to the drum wall, the effect of the screen being to reduce turbulence in the body of liquid and provide smoother flow into the passages 19. The plates-are so proportioned and assembled that when the device is installed in a drum, the

outlet opening 51 is entirely spanned by the assembly, or substantiallyso, in order that the plates will have their maximum directional effect on the total quantity of liquid entering the downcomer.

This form of inhibitor similarlydivides the returning liquid into a plurality of relatively small streams and positively directs each stream through a relatively long tapering passageway 19 into a different flow area unit of the downcomer passage. Since the individual passages 19 are of gradually decreasing ,flow area, the effect on the flowing liquid is to gradually build up its velocity as it approaches the downcomer passage so as to avoid an otherwise abrupt increase of velocity and consequent loss of head at the entrance to the downcomer.

It is understood that modifications of the device are permissible without interfering with its inherent function as a vortex inhibitor; for example, under certain conditions of liquid flow the plates 1t, which in Fig. 13 are represented as being equally spaced and having their leading edges 11 in alignment transversely of the drum, may be unequally spaced and, irrespective of the particular spacing, certain of the plates extended beyond others in the direction of the oncoming fluid. Fig. 15 represents a variation such as described wherein the side plates are extended upstream as at 85 to bring their leading edges in advance of the leading edges of the intermediate plates 76 and closer to the side walls of the drum than the corresponding edges of the side plates shown in Fig. 13, thus increasing the overall width of entrance into the inhibitor over that provided in Fig. 13, the extended side plate portions' 86 serving to positively direct a greater proportion of the main stream of liquid toward,

and into the passages 19.

Additional embodiments of the invention are contemplated, and these and others which may be devised are fully embraced by the scope of this invention as defined and limited only by the appended claims. Certain examples of such related developments are disclosed in the copending applications of H. J. Kerr, Serial No. 34 ,71

filed July 3, 1940, and R. M. Hardgrove, Serial No. 343,725, filed July 3, 1e40, both of which applications are assigned to the assignee of the present invention.

I claim:

1. In a boiler having an elevated horizontally disposed drum adapted to contain circulating boiler liquid under pressure during normal operation, a plurality of vapor generating tubes having connections with said drum from their upper ends, means for conducting liquid from said drum to the lower ends of said tubes including a cylindrical conduit member in direct communication with the lower portion of said drum, means for maintaining a rate of flow into and through said conduit member conducive to vortical movement of the liquid entering said member from said drum, and means associated with the entrance to said conduit member from'said drum for dividing said liquid into a plurality of streams for inhibiting said vortical movement.

2. A vapor generator having a circulatorysy'sterm for boiler liquid including a plurality of vapor generating tubes and an elevated drum, means for maintaining a level of boiler liquid within said drum during normal operation, downcomer means for supplying the preponderance of liquid required for vapor generation within said tubes from said drum under conditions conducive to gyratory movement of the liquid entering said downcomer means from) said drum, and means within said drum adjacent the entrance to said downcomer means for inhibiting said gyratory movement, said last named means forming multiple flow paths below said liquid level for directing liquid toward said entrance in a plurality of streams.

3. In a boiler having a system of vapor generating tubes exposed to heat of combustion, an elevated boiler drum to which upper ends of said tubes are connected whereby during normal operation unvaporized'liquid is discharged into said drum from said tubes, means for conducting liquid from said drum to lower ends of said tubes including a downflow connection from said drum below the normal level of liquid therein, said downflow connection having a fiow capacity suflicient for the formation of a vortex in said level of liquid, and means within said drum, adjacent 7 said downfiow connection forming multiple flow paths below said liquid level for directing liquid into said connection in a plurality of streams to different cross-sectional areas of said connec-' tion, the'combined cross-sectional areas of said streams substantially equaling the total cross sectional area of said connection.

4. In combination with a pressure vessel adapt- -means including members having portions below said liquid level for dividing the body of liquid 7 being withdrawn into a plurality of streams and zontally disposed, a plurality of .vapor generating tubes, means for delivering liquid to said drum during normal operation including connections from the upper ends of said tubes to said drum, means for conducting liquid from said drum to the lower ends of said tubes including a downflow conduit having its upper inlet end connected to said drum below the normal level of liquid therein, said conduit having its connection with said drum so arranged relative to said drum and to said connections from said tubes as to cause liquid entering said drum from said tubes to flow longitudinally of said drum toward said conduit connection and to flow in a transverse direction to enter said conduit, said change of direction combined with the rate of flow longitudinally of said drum and into said conduit contributing to a vortical disturbance in said liquid adjacent the entrance to said conduit, and means for reducing the extent of energy loss otherwise resulting from said vortical disturbance comprising a device within said drum in proximity to said downcomer connection for subdividing the liquid flowing toward said connection into separate streams and for directing each of said streams separately into said conduit,

6. In a boiler having an elevated drum adapted to contain circulating boiler liquid during normal operation, a plurality of vapor generating tubes having connections with said drum from their upper ends, said drum having its longitudinal axis horizontally disposed and said connec.. tions being made with said drum throughout an intermediate portion of its length, means for conducting liquid from said drum to the lower ends of said tubes including a downflow conduit having its upper inlet end connected to an end portion of said drum below the normal level of liquid therein, said conduit having a flow area sufficient for a vortical disturbance to be set up within liquid flowing from said drum into said conduit, and means for inhibiting said vortical disturbance comprising a plurality of upright plates at least partially submerged in said liquid and mutually forming channels opening downwardly toward said conduit connection.

7. In a boiler having an elevated drum adapted to contain circulating boiler liquid during normal operation, said drum having its longitudinal axis horizontally disposed; a plurality of vapor generating elements having connections from their upper ends to: said drum throughout an intermediate portion of its length, said elements being exposed to heat resulting from the combustion of fuel within a furnace, downcomer means shielded from said heat for conducting liquid from said drum adjacent its end to the lower ends of said vapor generating elements, said downcomer means having a flow capacity suflicient for a vortex to be formed therein, and means within said drum in the region of said downcomer means and submerged at least in part in said liquid for directing liquid from said drum into said downcomer means in a plurality of separate streams.

8. In a boiler having a drum adapted to contain circulating boiler liquid during normal operation, a plurality of vapor generating tubes exposed to a temperature sufiiciently high to cause liquid contained therein to be vaporized, downflow connections between said drum and tubes for deliveringliquid from said drum to said tubes for vapor generation, said downflow connections each having a flow capacity sufficient for a vortex to be formed in liquid flowing thereinto from said drum, up-fiow connections between said drum and tubes for returning unvaporized liquid from said tubes to said drum, and means for maintaining a higher density of fluid in said downfiow connections than in said tubes and upfiow connections, said means including means shielding said downflow connections from the temperature to which said tubes are subjected and means for inhibiting the formation of said vortex in liquid flowing from said drum into each of said downflow connections, said last named means having channels formed therein for directing different units of the circulating liquid into different units of flow area of each downflow connection.

9. In a boiler, in combination with a pressure vessel thereof having a downflow connection through which unvaporized boiler liquid is conducted to vapor generating tubes, means for maintaining a level of liquid within said drum over the entrance to said connection under conditions conducive to the formation of a vortex in said liquid, a vortex inhibitor within said drum having means for directing the flow of liquid into said downflow connection comprising a plurality of upright plates having edge portions below said liquid level extending transversely of the entrance to said connection in planes intersecting adjacent said entrance.

10. In a boiler, in combination with av pressure vessel thereof adapted to contain circulating boiler liquid during normal operation and having an outlet through which boiler liquid is withdrawn from said drum for delivery to vapor generating tubes, the flow capacity of said outlet and the rate of flow therethrough being such that a vortex tends to develop in the liquid being withdrawn, a vortex inhibitor within said drum comprising plates having portions below the normal liquid level disposed in planes intersecting substantially in alignment with the central axis of said outlet.

11. In a boiler, in combination with a horizontally disposed drum thereof adapted to contain circulating boiler liquid during normal operation, said drum having an outlet below the normal liquid level through which boiler liquid is withdrawn in a downward direction for delivery to vapor generating tubes, said outlet having a flow capacity sufficient for liquid to flow therethrough at a rate contributing to the development of a vortical disturbance in said liquid, means for inhibiting said vortical disturbance and thereby decreasing the resistance to the flow of said liquid into and through said outlet comprising a plurality of spaced plates having submerged portions arranged edgewise of said outlet in planes substantially parallel to the longitudinal axis of said drum.

12. In a boiler, in combination with a drum thereof adapted to contain circulating boiler liquid during normal operation, said drum having an outlet below the normal liquid level through which boiler liquid is withdrawn for delivery to vapor generating tubes, said outlet having a flow capacity suflicient for liquid to flow therethrough at a rate contributing to the development of a vortical disturbance in said liquid,

means for inhibiting said vortical disturbance and thereby decreasing the resistance to the flow of said liquid into and through said outlet'comprising a plurality of spaced plates arranged edgewise of said outlet in planes substantially parallel to the longitudinal axis of said drum, successive plates terminating inwardly of said drum at different distances relative to said normal liquid level.

13. In a boiler, in combination with a drum thereof adapted to contain circulating boiler liquid during normal operation, said drum having an outlet below the normal liquid level through which boiler liquid is withdrawn for delivery to vapor generating tubes, said outlet having a flow capacity sufficient for liquid to flow therethrough at a rate contributing to the development of a vortical disturbance in said liquid, means for inhibiting said vortical disturbance and thereby decreasing the resistance to the flow of said liquid into and through said outlet comprising a plurality of spaced plates arranged edgewise of said outlet in planes substantially parallel to the longitudinal axis of said drum,

successive plates terminating inwardly of said drum in edge portions curved in said planes at different distances relative to said normal liquid level.

14. In a boiler, in combination with a drum thereof having an outlet for circulating boiler liquid at one location and inlet connections for boiler liquid at a location longitudinally spaced therefrom whereby liquid entering said drum through said inlet connections is required to flow longitudinally of said drum toward said outlet, said outlet having a flow capacity sufflcient for liquid to flow therethrough at a rate contributing'tothe development of a vortical disturbance in said liquid, means for inhibiting said vortical disturbance and thereby increasing the rate of flow of said circulating boiler liquid through said outlet comprising a plurality of plates arranged longitudinally of said drum in edgewise relation .to said outlet, said plates having upstream edge portions spaced transversely of the drum for dividing the body of longitudinally flowing liquid into separate streams and for forming separate passageways between adjacent plates for liquid flowing into said outlet, said passageways opening downwardly to substantially the entire cross sectional area of said outlet and being closed at the downstream edge portions of said plates.

15. In combination with a horizontally disposed boiler drum wherein during normal operation boiler liquid is circulated longitudinally of said drum and caused to flowthrough a submerged outlet adjacent an end wall thereof, said outlet having a flow capacity sufiicient for the development of a flow condition conducive to the formation of a vortex in said liquid, means for inhibiting the formation of said vortex and thereby promoting the flow of boiler liquid through said outlet comprising spaced plates arranged longitudinally of said drum in edgewise relation to said outlet for directing said circulating liquid into said outlet in a plurality of separate streams, said plates converging longitudinally of said drum from a location in advance of said outlet to a location at least beyond the central axis of said outlet, the passages formed between adjacent plates opening downwardly toward said outlet beneath the normal operating level of said liquid.

16. In combination with a horizontally disposed boiler drum wherein during normal operation boiler liquid is circulated longitudinally of said drum and caused to flow through a submerged outlet adjacent an end wall thereof, said outlet having a flow capacity sufficient for the development of a flow condition conducive to the formation of a vortex in said liquid, means for inhibiting the formation of said vortex and asiedca thereof adapted to contain circulating boiler liquid during normal operation, said drum having its longitudinal axis horizontally disposed and having inlet and outlet means for circulating boiler liquid at longitudinally spaced locations, said outlet means having its axis of flow at said drum in transverse relation to the drum axis whereby liquid delivered to said drum through said inlet means and flowing longitudinally of said drum toward said outlet means is caused to change its direction of flow 'to enter said outlet means, means for operating said boiler at a capaoity causing boiler liquid to flow longitudinally of said drum and into and through said outlet means at a rate conducive to vortical movement of said liquid entering said outlet means, means for inhibiting said vortica1 movement comprising a plurality of upright plates presenting spaced upstream edge portions to the approaching liquid and forming passages opening downwardly toward said outlet means, and means for screening the entrances to said passages 7 18. In combination with an elevated drum arranged horizontally and having inlet and outlet means for liquid displaced longitudinally thereof, a downcomer extending downwardly from said outlet means, said outlet means and said downcomer having flow capacities suflicient for the development of a vortical flow condition adjacent said outlet means, and means for inhibiting the development of said vortical flow condition by directing liquid received through said inlet means toward and into said downcomer in a plurality of streams, said directing means comprising spaced p-lates having adjacent end portions extending longitudinally of the direction of fiow of liquid approaching said outlet means and having portions arranged edgewise of said outlet means whereby multiple flow passages are provided for liquid flowing toward and into said downcorner, said passages having entrances between said adiacent end portions at an upstream location relative to the flow axis of said outlet means, some of said plates extending upstream a greater distance than other plates.

19. In combination with a longitudinally extended drum arranged horizontally and adapted to contain a body of circulating liquid during normal operation, said drum having a submerged outlet adjacent one end whereby liquid is re quired to flow longitudinally of said drum for subsequent discharge downwardly through said outlet, said outlet having a flow area sufficient for the development of a vortex in liquid flowing therethrough, a vortex inhibitor within said drum having channels formed therein for directing said liquid toward said'outlet in a plurality of streams,

the walls of said channels including portions extending longitudinally of said drum to define entrances to said channels, and including other portions at a downstream location arranged to limit the longitudinal flow of said streams.

flow characteristics of said circulating fluid by 10 inhibiting the development of said vortex and thereby increasing the efiective hydraulic head of the downflow column of fluid, which comprises, dividing the fluid approaching the upper end of the downflow column into a plurality of streams, and directing each stream separately toward a difierent cross sectional unit of said downflow column.

ERVIN G. BAILEY.

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