TANDEM STEAM-WATER SEPARATOR

Abstract: A steam-water separator in which a pair of risers (12, 24) are disposed in tandem within one or respective shell members (14, 44). The steam-water mixture to be separated is introduced into the lower riser (12) where it is discharged through spiral or tangential arms (20) onto the inner wall of the shell (12) to effect a first stage separation. The remaining portion of the mixture rises upwardly in the shell and passes through a second stage riser (24). The latter mixture portion discharges through an additional series of spiral or tangential arms (34) against the inner wall of the (14), or its shell (44) to effect a second stage separation. Prespin is imparted to the steam-water mixture by means of baffles (52, 54) in the riser of the first stage. The said spiral or tangential arms of one or both stages may be divided into separated passages one above the other by means of horizontal partitions (56A-56C) and the respective risers may be similarly divided into coaxial passages by nested coaxial cylinders (60A-60C) which are joined to respective ones of the arm partitions (56A-56C) to define a set of paths which start in the respective riser and branch into corresponding passages in the arms.

Description: This invention relates to a separator for receiving a mixture of steam and water, separating the steam from the water in two stages and discharging the steam and the water from separate outlets. Such a separator is known from GB-A-2 126 499. In natural circulation vapour generators, mixtures of water and steam rise in heated steam-generating tubes and discharge into a steam-water separator disposed in an elevated position above the tubes and usually in a steam drum. The separators operate to separate the water from the steam, with the latter being removed through openings of the upper portions of the drum and the former being recirculated through downcomers to the boiler and back to the steam generating tubes to complete the natural circulation loop. In these types of arrangements, it is essential that an efficient separation of the steam from the water be effected with minimal pressure loss in order to furnish steam of the required purity to the point of use, and steam-free water to the circulation system. Also, the separators must operate under high steam and water loading and must have sufficient flow area to minimize pressure loss and still achieve separation. Further, there must be low carryover over a wide range of steam and water flow conditions. Known steam separators are of the type in which a rising mixture of steam and water is guided into a swirling motion from which water is radially discharged by the centrifugal forces generated therein. Such separators can have one or two separator stages. Multi-stage steam separators are disclosed in GB-A-2,126,499 and DE-C-931,170. In these separators, a second separator stage is disposed directly over the first stage to receive steam-water mixture from which some water has already been removed. The present invention is directed at a steam water separator having lower and upper separator stages wherein the lower stage comprises a first riser for receiving a steam water mixture and for directing said mixture to an upper section thereof formed with a plurality of discharge slots, and discharge passages in registry with the slots and extending laterally therefrom to direct said mixture from the riser towards a shell surrounding the discharge passages, whereby water from said mixture collects on the shell and remaining mixture continues to rise therefrom, means being provided for directing said remaining mixture to the upper separator stage disposed over the first stage, the upper separator stage comprising a second riser for receiving said remaining mixture and directing same to an upper section thereof. A separator with this construction is disclosed in GB-A-2,126,499. According to the invention, the upper section of the second riser is formed with a plurality of discharge slots, and discharge passages in registry with the slots, which passages extend laterally from the slots to direct said mixture from the second riser towards a shell surrounding the discharge passages; and the discharge passages comprise a plurality of open-ended conduits uniformly angled relative to radii passing through the respective slots from which they extend. Further, in at least one of the separator stages the conduits comprising the discharge passages are divided internally with horizontal partitions to form in each conduit a plurality of steam-water mixture paths, one above the other, and the respective riser path is partitioned to form a plurality of vertical paths, corresponding in number with the number of paths in the conduits, with each path of the riser coupled only with the paths of the conduits which occupy the same relative vertical position. The two separator stages can thus operate in tandem. In a steam-water separator of the invention liquid can be separated from vapour at a relatively low pressure loss, but the separator can nevertheless operate under high steam and water loading. The separator permits a relatively low carryover over a wide range of steam and water flow conditions, yet is of a simple, efficient and inexpensive design. Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings wherein: Figure 1 is a vertical sectional view of a first embodiment of the steam-water separator of the present invention; Figure 2 is a cross-sectional view taken along the line 2-2 of Figure 1; Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2; Figure 4 shows schematically a second embodiment of the invention; Figure 5 is a cross-sectional view taken along the line 5-5 in Figure 4; Figure 6 shows a modified discharge member in plan view; Figure 7 shows a vertical section view of a portion of the riser and discharge device of Figure 6 taken along the line 7-7 thereof; and Figure 8 is a thumb-nail sketch of a fuller view of the riser of Figure 7. Referring to Figs. 1-3 of the drawings, the reference numeral 10 refers in general to the steam-water separator of the present invention. The separator 10 includes a first stage riser 12, which is adapted to receive a steam-water mixture from a riser or tube (not shown) or from a steam drum (not shown) which can be a part of a natural circulation steam generator, or the like. The riser 12 extends within an upright cylindrical shell 14 in a coaxially spaced relationship. A top plate 16 extends over the upper end of the riser 12 and a plurality of slots 18 are formed through the upper wall portion of the riser. A plurality of arcuate arms 20 are connected to the riser 12 in registry with the slots 18, respectively, with the free ends of the arms being open to permit the steam-water mixture to discharge therefrom in a substantially tangential direction relative to the inner wall of the shell 14. It is understood that a support structure (not shown) can be provided within the shell 14 for supporting the riser 12 within the shell in the coaxial position shown. A second stage riser 24 is provided in the upper portion of the shell 14 in a spaced relation to the riser 12. The riser 24 is supported relative to the shell 14 by a horizontally extending splash ring 26 having a drip ring 28 extending downwardly from the lower portion thereof and adapted to receive the mixture rising in the shell from the first stage separator formed by the riser 12 and the arms 20. A top plate 30 extends over the upper end of the riser 24 and a plurality of slots 32 are formed through the riser. A plurality of arcuate arms 34 are connected to, and extend outwardly from, the riser 24 in registry with the slots 32. The free ends of the arms 34 are open to permit the steam-water mixture to discharge therefrom in a substantially tangential direction relative to the inner wall of the shell 14. A plurality of water relief holes 36 extend through a portion of the shell 14 between the arms 20 and the splash ring 26. A series of drain openings 38 are provided around the shell 14 immediately above the splash ring 26. A series of spaced discharge slots 40 are provided in the upper end portion of the shell 14. In operation, the mixture of steam and water entering the lowers end portion of the riser 12 rises upwardly and then passes radially outwardly from the riser through the slots 18 and into arcuate arms 20 where it is directed tangentially against the inner wall of the shell 14. This creates a vortex, or swirling, stream of fluid with the resulting centrifugal forces causing a portion of the mixture, which is largely steam, to travel away from the inner wall of the shell 14 and towards the centre of the swirling steam and pass upwardly, by virtue of its buoyancy, into the upper portion of the shell 14. The water portion of the mixture collects on the inner wall of the shell 14 and a portion of this water flows down the wall by gravitational forces and is collected in the steam drum or in any other known manner. The remaining portion of the water collecting on the inner wall of the shell 14 rises upwardly slightly along the inner surface of the shell above the tops of the arms 20 due to the kinetic energy in the jet streams of the steam-water mixture discharging from the arms. This portion of water discharges from the water relief holes 36 and then falls by gravity downwardly into the steam drum, or the like. The remaining portion of the mixture, which is largely steam, rises upwardly in the shell 14 and is directed into the lower end portion of the riser 24 by the splash ring 26 and the drip ring 28. The mixture then passes radially outwardly from the riser 24 through the slots 32 and through the arcuate arms 34. This causes an additional separation of the steam from the water, with the steam discharging through the slots 40 whereby it leaves the separator for further treatment. The water portion of the mixture collects on the upper inner wall of the shell 14 and passes downwardly through the drain openings 38 where it is collected in the steam drum, or the like. As a result of the tandem separation achieved by the first and second separator stages thus described, several advantages result. For example, the steam-water separator is achieved at relatively low pressure loss and low carryover over a wide range of steam and water flow conditions. Also, the separator 10 can operate under high steam and water loading while maintaining the low pressure loss. Finally, the separator of the present invention is of a simple, efficient design and is relatively inexpensive to fabricate. In a second embodiment of the invention shown in Figs. 4 and 5 the shell 14 is terminated a short way above the discharge member 20 in an open end and the water relief holes of the previous embodiment are omitted. Furthermore, the splash ring 26 extends radially to a depending skirt 42 which surrounds the top end of the shell 14. A further cylindrical member 44 of greater diameter than the skirt 42 surrounds the discharge member 34 and extends downwards to overlap the said skirt 42. Members 44 and 42 comprise shrouds which trap any water which is separated from the steam-water mixture as a consequence of its centrifugal motion when it emerges from the discharge means 20, 34. The swirl kinetic energy is absorbed on the inner walls of members 42, 44 and the water drops under gravitational force to the base of the steam drum. As is best seen from Figure 5, within and at the base of the shell 14 there is disposed a plurality of radial fins or plates 46. These plates extend for a short way up the shell from the base thereof and serve to remove any swirl kinetic energy from the water which drains downwards from the inner walls of the shell and from the discharge device 20. The fins or plates 46 are uniformly perforated (47) to assist in the removal of the said swirl kinetic energy. Shell 14 has a bottom axial end wall formed by an inverted dish-shaped member 48 on which the fins 46 are mounted. The member 48 is also perforated over its whole surface with perforations 50 to allow drainage of water from the separator. Riser 12 is fitted internally along its axial length with a pair of helical ribs 52, 54. These ribs act as baffles and provide the steam-water mixture with pre-spin before it enters the first stage discharge member 20. In a further modification shown in Figure 6 the individual arms 20, 34 of the discharge members, or of at least one of the discharge members, are straight along a substantial part of their length instead of being curved or spiral-shaped as in Figures 2 and 3. These arms are disposed substantially tangentially to their root diameter. The ends of the arms are curved all in the same direction so as to discharge the steam-water mixture in a direction substantially tangential to the inner wall of the shell 14 or shroud 44, as the case may be. The respective riser and discharge devices 20, 34 also have the features shown in Figures 7 and 8, wherein Figure 8 is a purely schematic illustration of the structure shown in detail in Figure 7. Each arm of the respective discharge device is fitted with a plurality of horizontal separators 56A-56C spaced apart in the vertical direction so as to divide the hollow interior into a series of substantially equally dimensioned passages 58A-58D arranged one above the other. The separators 56A-56C are each joined to a respective one of a number of nested vertically disposed cylindrical coaxial separators 60A-60C mounted in the respective riser 12, 28. Thus the inner coaxial separator 60C defines a cylindrical passage 62D which communicates with the top compartment in each of the arms of the discharge device 20, 34 and the other two coaxial separators 60A, 60B define annular passages 62A-62C each of which communicates with respective corresponding passages in the said arms, each passage thereby defining a path which is isolated from the paths defined by the other passages. As the mixture rises in the riser, the kinetic energy contained by the separated water droplets carries the latter upwards to the upper surfaces of the discharge device. In the absence of the above-described modification, the water has a tendency to mainly collect at the top of the device and be discharged at a higher level than the separated steam and so become re-entrained with the steam as the latter rises. By dividing the separator into a plurality of separate paths, the separated water remains in each path, collecting at the ends of the passages as shown at 64A-64D. The consequent discharge of water from the discharge devices at lower levels improves the overall performance characteristic of the separator.

Claims: A steam water separator (10) having lower and upper separator stages wherein the lower stage comprises a first riser (12) for receiving a steam water mixture and for directing said mixture to an upper section thereof formed with a plurality of discharge slots (18), and discharge passages (20) in registry with the slots and extending laterally therefrom to direct said mixture from the riser towards a shell (14) surrounding the discharge passages, whereby water from said mixture collects on the shell and remaining mixture continues to rise therefrom, means being provided for directing said remaining mixture to the upper separator stage disposed over the first stage, the upper separator stage comprising a second riser (24) for receiving said remaining mixture and directing same to an upper section thereof, CHARACTERISED IN THAT the upper section of the second riser is formed with a plurality of discharge slots (32), and discharge passages (34) in registry with the slots, which passages extend laterally from the slots (32) to direct said mixture from the second riser towards a shell (44) surrounding the discharge passages (34), IN THAT the discharge passages (20,34) comprise a plurality of open-ended conduits uniformly angled relative to radii passing through the respective slots (18,32) from which they extend, AND IN THAT in at least one of the separator stages the conduits comprising the discharge passages (20,34) are divided internally with horizontal partitions (56) to form in each conduit a plurality of steam-water mixture paths (58), one above the other, and the respective riser path is partitioned to form a plurality of vertical paths (62), corresponding in number with the number of paths (58) in the conduits, with each path (62) of the riser (12,24) coupled only with the paths (58) of the conduits which occupy the same relative vertical position. A separator according to Claim 1 CHARACTERISED IN THAT the same shell (14) extends around the first and second separator stage risers. A separator according to Claim 2 CHARACTERISED IN THAT a plurality of openings (36) are formed in said shell to permit radial discharge of water between the separator stages. A separator according to Claim 3 CHARACTERISED IN THAT at least a portion of the openings (36) in the shell (14) are located above the level of the discharge passages (20) of the first separator stage. A separator according to Claim 3 or Claim 4 CHARACTERISED IN THAT one or more shrouds surround the openings (36) for intercepting the radial discharges of water, whereby the trapped water flows vertically downwards so as to fall from the shroud with little or no radial or swirl velocity. A separator according to any preceding Claim CHARACTERISED IN THAT the directing means comprises a coaxial drip ring (28) depending from the second stage riser (24) towards said discharge passages (20) associated with the first stage riser, and a splash plate (26) isolating the discharge passages (34) of the second separator stage from the discharge passages (20) of the first separator stage. A separator according to any preceding Claim CHARACTERISED IN THAT the discharge passages (20,34) of at least one of the separator stages comprises a plurality of spiral conduits. A separator according to any of Claims 1 to 6 CHARACTERISED IN THAT the discharge passages (20,34) of at least one of the separator stages comprises a plurality of substantially linear tangential conduits. A separator according to Claim 8 CHARACTERISED IN THAT the tangential arms are incursive at their open-ends. A separator according to any preceding Claim CHARACTERISED IN THAT at least said first riser (12) comprises a cylindrical tube fitted internally with helical baffle means (52,54) to rotate the steam-water mixture as it passes up the riser and before it enters the respective discharge passages (20). A separator according to any preceding Claim CHARACTERISED IN THAT water anti-vortex means are provided at the base of the separator whereby the velocity of discharged water has components only in the vertical plane. A separator according to Claim 11 CHARACTERISED IN THAT the anti-vortex means comprises a flow diffuser at the bottom end of the shell and/or vertical radial plates. A separator according to Claim 12 CHARACTERISED IN THAT the anti-vortex means comprises a flow diffuser in the form of a dish-shaped perforated annular member, and radial plates perforated so as to facilitate the removal of the kinetic energy in the water exiting from the separator due to the swirl imparted to the mixture as the latter passes through the risers and discharge means. A separator according to any preceding Claim CHARACTERISED IN THAT the partitions in the respective riser (12,24) comprise concentric tubes (60); and the partitions in the respective discharge passages (20,34) comprise horizontal plates (56).

Inventors: HOLDEN, WILLIAM, HOUGHTON, FRED, IDVORDIAN, NICK, RENSHAW, ROBERT
Applicants: FOSTER WHEELER ENERGY LIMITED
Application year: 1987
Main classification: F22B37
IPC codes: B04C5, B04C3, F22B37