US3256865A

US3256865A - Liquid-vapor separator

Info

Publication number: US3256865A
Application number: US341480A
Authority: US
Inventors: Thomas M Modrak; Marvin A Brahler
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1964-01-24
Filing date: 1964-01-24
Publication date: 1966-06-21
Anticipated expiration: 1983-06-21

Description

June 21, 1966 MODRAK ETAL 3,256,865

LIQUID-VAPOR SEPARATOR Original Filed Aug. 1, 1961 FIG.1

L INVENTORS 2 Thomqs M Modrak Y Marvm A. Brahler ATTORNEY 24% F|G.3 Kg

United States Patent 3,256,865 LIQUID-VAPOR SEPARATOR Thomas M. Modrak, Alliance, and Marvin A. Brahler, Louisville, (lhio, assignors to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Continuation of application Ser. No. 128,519, Aug. 1,

1961. This application Jan. 24, 1964, Ser. No. 341,480

Claims. (Cl. 122-491) This application is a continuation of application, Serial No. 128,519, filed August 1, 1961, now abandoned.

This invention relates in general to a liquid-vapor separator, and more particularly to an improved steam and water separating drum of a steam generator.

Heretofore, the drums of industrial type steam generators with steaming capacities of 14,000 to 60,000 pounds -of steam per hour have been generally provided with an internal bafile construction extending along the length of the drum for defining a compartment separated from the drum water space for receiving the steam and water mixture generated in riser tubes. In units wherein it was desirable, for reasons of economy or otherwise, to effect primary separation of the steam and water mixture by gravity, the compartment was generally formed with a co-extensive unobstructed outlet through which the steam and water mixture collected in the compartment was discharged directly into the steam space of the drum. In the steam space the heavy water particles of the mixture would be separated from the lighter steam particles by gravity as the steam particles would seek the steam outlet of the drum, the separated water being recirculated through the unit while the separated steam was taken off and delivered to a point of use.

In units of this type experience shows that, for various reasons, there is little likelihood that all of the riser tubes will deliver a mixture of the same quality into the mixture receiving compartment of the drum. For this reason a maldistribution of flow was likely which could result in operating difficulties, e.g., effecting undesirable water level gradients and/or effecting localized overloading or underloading of the secondary separating equipment, either of which could result in excessive moisture carryover.

Therefore, an object of the invention is to provide an improved arrangement whereby the distribution of the steam and water mixture received in the mixture receiving compartment of the steam and water separating drum is evened out and more uniformly distributed over the length of the drum.

Another object is to provide an internal drum arrangement in which-the steam and water mixture is discharged into the steam space of the drum at a relatively low velocity so as to enhance gravity separation thereof by increasing the amount of time available in which separation may occur.

Another object is to provide an improved drum internal construction which significantly improves water level stability throughout theoperating load range of the steam generating unit.

Still another object of the invention is to provide an improved drum internal construction wit-h the capacity to deliver satisfactory steam purity within the capacity range of a steam generating unit, and which is relatively inexpensive, easily constructed and installed, and which is positive in operation.

A feature resides in the provision that the improved drum internal construction of this invention minimizes carry-under, and thus enhances the delivery of solid water to the downcomer.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which we have illustrated and described a preferred embodiment of the invention.

In the drawings:

FIG. 1 is a front elevation view taken in section along the longitudinal axis of a steam and water separating drum;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1; and

FIG. 3 is a sectional view taken along line 33 of FIG. 1.

Referring to the drawings, there is shown in FIG. 1 a cylindrical, elongated, horizontally disposed steam and water separating drum 10 of the type used in industrial and marine boilers. In the illustrated embodiment, the drum 10 is arranged to operate with a water level 11 which defines the boundary between the lower water space 12 and the upper steam space 13. Several rows of high duty riser tubes 14 connect into the drum 10 for discharging thereinto the steam and water mixture, and several rows of downcomer tubes 15 serve to carry water away from the drum 10 to effect the circulation of the unit.

Arranged internally of the drum 10 is a longitudinally extending baffie 16 which is spaced from a circumferential wall portion of the drum and defines therewith a compartment 17 for receiving the steam and water mixture discharged by the high duty riser tubes 14 which have their respective discharge end portions collected under baffle 16. As seen in FIG. 1, the ends of the bafile are spaced inwardly of the ends of the drum 10, and end plates 18 close each of the ends of the compartment 17. The upper end 16A of the battle 16 extends to at least the water level 11 of the drum 10. Thus it will be noted that the mixture receiving compartment 17 is completely separated from the water space 12 of the drum 10.

Disposed between the rows of downcomer tubes 15 and high duty riser tubes 14, there may be provided other tubes 19 which function either as lower duty riser tubes or as downcomers depending upon the amount of heat absorbed thereby.

According to this invention, a thin, substantially planar, perforated baflie or plate 20, having an open area of approximately 51%, is connected to the upper end of the compartment baflle 16 along substantially the entire length of the drum 10 to form an upright extension, of the baffle. Preferably, the open area of the plate 20 is attained by numerous closely spaced small holes or perforations 21 having a cumulative cross-sectional flow area sufficient to provide an evenly and widely dispersed slow moving outflow from the perforations 21 to enhance gravity separation of water particles in the steam space 13 wherein a significant portion of the vapor/liquid 3 separation takes place. It has been found that if the perforations 21 in the plate 20 are A diameter holes on A" spacing, the open area will be suflicient to effect the desired results.

The perforated bafile 20 is connected in overlapping spaced relationship to the upper end 16A of the bafile 16 by means of suitable fasteners 22 extended through spacer sleeves 23 at longitudinally spaced intervals. By this construction an opening or outlet 24 is defined between the bottom end 20A of the perforated plate 20 and the upper end 16A of baffle 16 at approximately the normal water level height. As shown, the perforated plate 20 is preferably angled inwardly of drum 10 so as to form an acute angle with respect to the water level. While not necessarily restricted thereto, a 30 inclination from the vertical has been found to give satisfactory results as will be herein described.

Extending between the upper end B of the perforated plate 20 and the adjacent wall portion of the drum 10 is a top plate which closes the upper end of the compartment 17. Thus, the steam and lower density portions of the incoming steam-water mixture collected in the compartment 17 are constrained to flow through the perforations 21 in the baffle 20, in passing from the compartment 17 to the steam space 13 of the drum 10, while the higher density portions of the incoming steamwater mixture pass directly from the compartment 17 into the water space 12.

In operation, any maldistribution resulting from the discharge of any steam and water mixtures of different qualities into the compartment 17 is evened out behind the

bafiles

16 and 20. This is effected for the reason that the varying qualities of the respective mixtures discharged by each of the riser tubes are collected in a relatively large plenum which enables a remixing of the mixture to occur along with some natural separating taking place Within the compartment 17. This remixed mixture is then evenly distributed over the length of the drum 10 by the perforated plate bafile 20. The separated steam and lighter mixture within compartment 17 flows out through the perforations 21 in the top portion of the bafl'le 20 as the heavier separated water flows out through the lower portions of the baffle 20 and slot 24, formed between

baffles

16 and 20.

Because the perforated plate 20 is angled downwardly, the steam-water mixture discharging therethrough leaves in a direction substantially normal to holes 21 and thus the mixture has imparted thereto a component directed downwardly toward the water level 11. Thus the fluid outflow from the perforations 21 in the baflle 20 is directed away from the entrance to the steam scrubbing apparatus 26 (or outlet from the steam space 13) to effect a sweeping U-shaped path of flow whereby entrained water is separated from the fluid outflow by gravity within the steam space 13.

While some steam carry-under may occur, it is confined near the surface 11 of the drum water, and thus can be naturally separated by the steam bubbling up through th water. Because the steam carry-under is near the surface, there is little or a negligible amount of steam entrainment in the downcomers 15. Consequently, the less steam entrained with the water in the downcomers 15, the more circulation through the steam generator is enhanced in a natural circulating unit.

The slot 24 formed between drum baffles 16 and perforated baffie 20 is especially of advantage during low load circulation as it permits any water separated upstream of the perforated plate 20 to be discharged directly into the water space 12 of the drum 10 without going through the perforated plate 20. During boiler start-up, it is desirable to have the least restriction possible on the riser circuits for holding the pressure drop to a minimum in order to permit some circulation through the boiler circuits which is necessary to prevent overheating of the tubes.

The slot 24 between

baffles

16 and 20 and the large open area of baffle 20 also minimizes the pressure drop through the drum internal baffle construction. Maintaining the pressure drop through the drum internals as small as possible therefore enables either a reduction of the height required for natural circulation, or a higher circulation rate for a given capacity. Actual test in a p.s.i. installation has indicated that the pressure drop, over the capacity range of the unit, will not exceed .03 p.s.i. This has been found to be considerably less than the pressure drop of other known internal bafile constructions.

A further advantage afforded by the use of a perforated baffle 20 as herein disclosed, is the small amount of drum water volume and end flow area that is taken up by the described construction. Thus the larger the amount of water storage space available in a given drum, the smaller will be the shrink and swell of the drum Water during swings in the load to effect in a more stable or less fluctuating water level. Further, since the end flow area is not materially reduced by the perforated baffle construction of this invention, the water level gradient from one end of the drum to the other will be maintained to a minimum. Actual tests have shown that water level fluctuation during steady load operation was only about /2 inch.

With the primary or main separation of the mixture discharged into the steam space 13 is effected by gravity as described above, a steam scrubbing apparatus 26 may be arranged across the vapor outlet 31 of the drum to further remove the final amounts of moisture carried by the steam before leaving the drum 10. The scrubbing apparatus 26 preferably is formed of closely spaced corrugated elements 27 constructed and arranged somewhat as disclosed in the patent to Fletcher 2,007,966. This scrubber device 26 removes the last particles of water carried by the separated steam so that essentially dry steam is delivered to the steam outlet 31. Included as part of the scrubber apparatus 26 is a suitable drain 28. Completing the makeup of the drum are the usual safety valve nozzle connections 29.

In accordance with the invention, it will be noted that the entrance 30 to the steam scrubber 26 is positioned at the furthest removed point possible from the perforated bafile 20. This is to provide the mixture discharged into the steam space 13 with the greatest time and travel possible in which to effect gravity separation in the steam space 13.

Thus it will be noted that while the perforated baflle 20 is not by itself a separating device; nevertheless, it provides an internal drum construction with. a capacity to deliver satisfactory steam purity within the capacity range of the boiler incorporating the same. Further the perforated baflle construction in accordance with this invention enhance-s circulation by minimizing carry-under, stabilizing water level, and breaking localized concentration of steam and water mixtures to more evenly disgribute the steam and water mixture over the length of the rum.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form and mode of operation of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed with out departing from the spirit of the invention covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. In a natural circulation vapor generator, a cylindrical elongated vapor-liquid separating drum having therein a liquid level defining the boundary between a liquid space and a vapor space, generating tubes opening into said drum for discharging a liquid-vapor mixture thereinto, and a partition longitudinally dividing said drum into a receiving chamber wherein said liquid-vapor mixture is discharged and a main separating chamber including a substantially unobstructed major portion of said vapor space wherein a significant portion of the vapor/liquid separation takes place, said partition including a submerged baflie enclosing the discharge ends of said generating tubes, and an upwardly extending substantially planar plate connected with said baflie and formed with perforations along its length and so arranged relative to the remaining portions of said partition that the vapor and lower density portions of the liquid-vapor mixture are constrained to flow through the perforations in passing from the receiving chamber directly into the main separating chamber, the perforations of said plate' having a cumulative cross-sectional flow area sufiicient to provide an evenly dispersed slow moving fluid outflow from the perforations along substantially the entire length of the drum to enhance gravity separation of the liquid particles from said outflow within said main separating chamber, said partition being formed at approximately the height of the liquid level with opening means through which liquid passes directly from said receiving chamber to said liquid space, said opening means extending substantially the entire length of the partition' 2. In a natural circulation vapor generator, a cylindrical elongated vapor-liquid separating drum having therein aliquid level defining the boundary between a liquid space and a vapor space, generating tubes opening into said drum for discharging a liquid-vapor mixture thereinto, a partition longitudinally dividing said drum into a substantially unobstructed receiving chamber on one side of the drum wherein said liquid-vapor mixture is discharged and a main separating chamber including a substantially unobstructed major portion of said vapor space wherein a significant portion of the vapor/liquid separation takes place, said partition including a substantially planar plate extending upwardly from said liquid level and being formed with a uniform pattern of perforations along its length and means mounting said planar plate relative to the remaining portions of said partition so that the vapor and lower density portions of the liquid-vapor mixture are constrained to flow downwardly through the perforations toward said liquid level in passing from the receiving chamber directly into the main separating chamber, the perforations of said plate having a cumulative crosssectional flow area suflicient to provide an evenly dispersed slow moving outflow from the perforations along substantially the entire length of the drum to enhance gravity separation of the liquid particles from said outflow within the main separating chamber, and means defining a vapor outlet communicating with said main separating chamber and disposed near the top of and on the side of said drum opposite said receiving chamber, said outlet cooperating with said plate to effect a sweeping U-shaped path of all of the vapor discharged through the perforations in said plate whereby entrained liquid is separated from the vapor within said main separating chamber.

3. In a natural circulation vapor generator, a cylindrical elongated vapor-liquid separating drum having therein a liquid surface defining the boundary between a liquid space and a vapor space, generating tubes opening into said drum for discharging a liquid-vapor mixture thereinto, a partition longitudinally dividing said drum into a receiving chamber into which said liquid-vapor mixture is discharged and a main separating chamber including a substantially unobstructed major portion of said vapor space wherein a significant portion of the vapor/liquid separation takes place, said partition including a submerged baffle enclosing the discharge ends of said generating tubes, and an upwardly extending substantially planar plate formed with perforations along its length and so arranged relative to the remaining portions of said partition that the vapor and lower density portions of the liquid-vapor mixture are constrained to flow throughv the perforations in passing from the receiving chamber directly into the main separating chamber, the perforations of said plate having a cumulative cross-sectional flow area suflicient to provide an evenly dispersed slow moving outflow from the perforations to enhance gravity separation ofthe liquid particles from said outflow within the main separating chamber, and means connecting said baffle and said plate in overlapping spaced relationship at approximately the height of said liquid surface to form an opening immediately adjacent said plate through which the liquid collected on the upstream side of the plate passes directly from said plate to the liquid space.

4. In a natural circulation vapor generator, a cylindrical elongated vapor-liquid separating drum having therein a liquid level defining the boundary between a liquid space and a vapor space, generating tubes opening into said drum for discharging a liquid-vapor mixture thereinto, a partition longitudinally dividing said drum into a receiving chamber on one side of the drum wherein said liquid-vapor mixture is discharged and a main separating chamber including a substantially unobstructed major portion of said vapor space wherein a significant portion of the vapor/liquid separation takes place, said partition including an upwardly extending planar plate formed with a multiplicity of closely spaced perforations along its length and so arranged relative to the remaining portions of said partition that the vapor and lower density portions of the liquid-vapor mixture are constrained to flow downwardly through the perforations toward said liquid level in passing from the receiving chamber directly into the main separating chamber, the perforations of said plate having a cumulative cross-sectional flow area suflicient to provide an evenly and widely dispersed slow moving fluid outflow from the perforations to enhance gravity separation of liquid particles from said outflow within the main separating chamber, means forming an opening in said partition immediately adjacent said plate through which the liquid collected on the upstream side of the plate passes directly from said plate through said opening into said liquid space, and means defining a vapor outlet communicating with the main separating chamber and disposed near the top of and on the side of the drum opposite said receiving chamber, said outlet cooperating with said plate to effect a sweeping U-shaped path of all of the outflow from the perforations in said plate, whereby entrained liquid is separated from the outflow within said main separating chamber.

5. In a natural circulation vapor generator, a cylindrical elongated vapor-liquid separating drum having therein a liquid level defining the boundary between a liquid space and a vapor space, generating tubes opening into said drum for discharging a liquid-vapor mixture thereinto, a partition longitudinally dividing said drum into a receiving chamber on one side of the drum wherein said liquidvapor mixture is discharged and a main separating chamber including a substantially unobstructed major portion of said vapor space wherein a significant portion of the vapor/liquid separation takes place, said partition including a submerged baflie enclosing the discharge ends of said generating tubes, and an upwardly extending substantially planar plate inclined with respect to the liquid level and formed with a multiplicity of closely spaced perforations along its length and so arranged relative to the remaining portions of said partitionthat the vapor and lower density portions of the liquid-vapor mixture are constrained to flow downwardly through the perforations toward said liquid level in passing from the receiving chamber directly into the main separating chamber, the perforations of said plate having a cumulative cross sectional flow area sufiicient to provide an evenly and widely dispersed slow moving outflow from the perforations to enhance gravity separation of the liquid particles from said outflow within the main separating chamber, said plate having its lower edge projecting slightly below the liquid surface and being i'rrebverlapping spaced relationship with the submerged baffle at approximately the height of the liquid level to form a longitudinally extending opening through which the higher density portions of the liquid-vapor mixture pass directly from the receiving chamber into the liquid space, and means defining a vapor outlet communicating with said main separating chamber and disposed near the top of and on the side of said drum opposite said receiving chamber, said outlet cooperating with said plate to effect a sweeping U-shaped path of all of the outflow from the perforations in said plate whereby entrained liquid is separated from the outflow within said main separating chamber.

References Cited by the Examiner UNITED STATES PATENTS KENNETH W. SPRAGUE, Primary Examiner.

JAMES W. WESTHAVER, Examiner.

Claims

1. IN A NATURAL CIRCULATION VAPOR GENERATOR, A CYLINDRICAL ELONGATED VAPOR-LIQUID SEPARATING DRUM HAVING THEREIN A LIQUID LEVEL DEFINING THE BOUNDARY BETWEEN A LIQUID SPACE AND A VAPOR SPACE, GENERATING TUBES OPENING INTO SAID DRUM FOR DISCHARGING A LIQUID-VAPOR MIXTURE THEREINTO, AND A PARTITION LONGITUDINALLY DIVIDING SAID DRUM INTO A RECEIVING CHAMBER WHEREIN SAID LIQUID-VAPOR MIXTURE IS DISCHARGED AND A MAIN SEPARATING CHAMBER INCLUDING A SUBSTANTIALLY UNOBSTRUCTED MAJOR PORTION OF SAID VAPOR SPACE WHEREIN A SIGNIFICANT PORTION OF THE VAPOR/LIQUID SEPARATION TAKES PLACE, SAID PARTITION INCLUDING A SUBMERGED BAFFLE ENCLOSING THE DISCHARGE ENDS OF SAID GENERATING TUBES, AND AN UPWARDLY EXTENDING SUBSTANTIALLY PLANAR PLATE CONNECTED WITH SAID BAFFLE AND FORMED WITH PERFORATIONS ALONG ITS LENGTH AND SO ARRANGED RELATIVE TO THE REMAINING PORTIONS OF SAID PARTITION THAT THE VAPOR AND LOWER DENSITY PORTIONS OF THE LIQUID-VAPOR MIXTURE ARE CONSTRAINED TO FLOW THROUGH THE PERFORATIONS IN PASSING FROM THE RECEIVING CHAMBER DIRECTLY INTO THE MAIN SEPARATING CHAMBER, THE PERFORATIONS OF SAID PLATE HAVING A CUMULATIVE CROSS-SECTIONAL FLOW AREA SUFFICIENT TO PROVIDE AN EVENLY DISPERSED SLOW MOVING FLUID OUTFLOW FROM THE PERFORATIONS ALONG SUBSTANTIALLY THE ENTIRE LENGTH OF THE DRUM TO ENHANCE GRAVITY SEPARATION OF THE LIQUID PARTICLES FROM SAID OUTFLOW WITHIN SAID MAIN SEPARATING CHAMBER, SAID PARTITION BEING FROMED AT APPROXIMATELY THE HEIGHT OF THE LIQUID LEVEL WITH OPEING MEANS THROUGH WHICH LIQUID PASSES DIRECTLY FROM SAID RECEIVING CHAMBER TO SAID LIQUID SPACE, SAID OPENING MEANS EXTENDING SUBSTANTIALLY THE ENTIRE LENGTH OF THE PARTITION.