A WATER AND STEAM SEPARATOR OF A BOILER DRUM

Abstract

A separator (1) of a boiler drum for separating steam and water, which separator (1) has a separating chamber (5) having a fluid inlet (2) at the bottom of the separating chamber (5) and a steam outlet (3) at the top of the separating chamber (5) and spiral vanes (9) are attached to the wall (6) of the separating chamber (5) between the fluid inlet (2) and the steam outlet (3) for accomplishing circular motion of the incoming fluids and wherein a circular water outlet (4) surrounds the steam outlet (3). Top end (8) of the wall (6) of the separating chamber (5) within the water outlet (4) has a rounded top contour for ensuring smooth flow and keeping a water trap (13) filled up at the top art of the water outlet (4) and is inclined inwards. The inclination at the top end (8) of the wall (6) is concave.

Claims

1. A separator of a boiler drum for separating steam and water, wherein the separator includes: a separating chamber having a fluid inlet at a bottom of the separating chamber, a steam outlet at a top of the separating chamber, a water outlet around the steam outlet, and a wall from the bottom to the water outlet and extending around an interior of the separating chamber, and spiral vanes in the interior of the separating chamber and attached to the wall of the separating chamber, wherein the spiral vanes are between the fluid inlet and the steam outlet and are configured to impart a circular motion to fluids entering the separating chamber through the fluid inlet, wherein the water outlet leads first upwards and then turns downwards, and wherein a top end of the wall of the separating chamber includes an annular upper edge with a rounded top contour having a minimum radius of 8 mm and the annular upper edge defines a surface of the water outlet.

2. The separator of claim 1, wherein the top end of the wall of the separating chamber is inclined radially inward by an inclination angle relative to vertical of at least 15 degrees from a start of an inclination line to a point where the top end of the wall curves outwards from the inclination line, and the top end of the wall and the length of the inclination is at least 25 mm.

3. The separator of claim 1, wherein the minimum radius of the rounded top contour is at least 12 mm.

4. The separator of claim 1, wherein the rounded top contour of the top end is concave.

5. The separator of claim 1, further comprising an opposite wall which is opposite to the water outlet and is around the top end of the wall of the separating chamber, wherein the opposite wall is curved and is without edges.

6. The separator of claim 1, wherein the separating chamber has a top section and the top section increases in diameter in an upward direction.

7. The separator of claim 1, wherein within the water outlet, between the upper wall of the separating chamber and an outer wall of the separator is a plurality of guiding vanes are aligned to an opposite direction of a pitch angle related to a pitch angle of the spiral vanes.

8. The separator of claim 7, wherein the guiding vanes number in a range of 6 to 16.

9. The separator of claim 7, wherein a cumulative circumferential coverage of the guiding vanes is at least 300 degrees.

10. The separator of any of claim 7, wherein the pitch angle of the guiding vanes is in a range of 45 to 75 degrees.

11. The separator of claim 5, wherein the opposite wall of the top end of the wall of the separating chamber the water outlet is curved and a width of the water outlet is substantially constant or narrows in an outflow direction.

12. The separator of claim 1, wherein the steam outlet has a bottom which has an upwards decreasing diameter and/or a top shape having an upwards increasing diameter.

13. A separator of a boiler drum comprising: a separating chamber including an annular first wall having a lower fluid inlet configured to receive fluid from the boiler drum, wherein a flow passage extends up through the annular first wall from the lower fluid inlet towards a steam outlet and an inlet to an annular water outlet which extends around the steam outlet, an annular top region of the annular first wall, wherein the annular top region includes an upper edge having a cross section with a radius of curvature of at least 8 mm and the annular top region is an inner wall of the annular water outlet; an annular outer wall of the annular water outlet positioned over and at least partially enclosing the annular top region, wherein the annular outer wall includes a concave surface opposite to the annular top region and the annular outer wall extends around the steam outlet, and vanes within the separating chamber and below the annular top region, wherein the vanes are configured to impart a rotational flow to the fluid flowing from the boiler up through the separating chamber, wherein a water flow passage through the annular water outlet extends from the inlet, upwards towards the upper edge between an annular inner surface of the annular top region and the concave surface of the outer wall, and downward from the upper edge past an outer surface of the annular top region.

14. The separator of claim 13, wherein The separator of claim 1, wherein the annular inner surface of the annular top region extends increasingly radially inward in an upward direction from a lower portion of the top portion to a radially inward-most portion of the inner surface of the top portion, and a line extending in a vertical plane from the lower portion to the radially inward-most portion has a length of at least 25 mm and forms an angle with respect to vertical of at least 15 degrees.

15. The separator of claim 13, wherein the annular water outlet includes an outer wall defining a radially outward surface of the water outlet and extending around the first wall.

16. The separator of claim 13, wherein the annular first wall includes a frustoconical section above the vanes and below the annular top region, wherein the frustoconical section increases in diameter in an upward direction.

17. The separator of claim 13, wherein the annular top region has a shape in cross section which is bulbous with a narrow tapered lower end and a rounded upper surface, and the rounded upper shape includes the upper edge.

18. The separator of claim 13, wherein the annular water outlet includes guide vanes having a pitch angle opposite to a pitch angle of the vanes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Examples of embodiments of the invention will now be described in more detail with reference to the appended drawings in which:

[0019] FIG. 1 Illustrates a prior art steam drum arrangement of a boiler.

[0020] FIG. 2 illustrates a cross section of a preferred embodiment of the invention and

[0021] FIG. 3 illustrates a view of guiding vanes of the embodiment of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0022] FIG. 1 illustrates a prior art steam drum arrangement of a boiler for separating steam and water fluids coming in from cooling tubes of boiler chamber. A vertical separator 1 initially separates the incoming fluids. Several separators 1 are installed within the drum according to the capacity of the boiler. The fluid is mainly steam bubbles within water. At high levels of steam, water can also be in a form of droplets.

[0023] Primary demisters on top of the separator 1 prevent most of residual droplets entering steam space of the drum. Secondary demisters atop of the drum remove the droplets so that they do not flow out to superheater tubes. If separation efficiency is at a too low level, the demisters can be filled with water causing high pressure loss and incomplete separation.

[0024] Spiral vanes 9 within a separating chamber 5 direct incoming fluids to circular motion and separated water phase rises aside the wall 6 of the separating chamber 5 to water outlet 4. Separated water exits the separator 1 from bottom end of the water outlet 4. Steam exists through a central steam outlet 3 at the top of the separating chamber 5.

[0025] The illustrated design has several deficiencies, which cause pressure drops and incomplete separation within the separator 1. The form of water outlet 4 causes disturbances to outflowing water as incompletely separated steam can enter the water outlet 4 and may cause resonating backflow. A sharp edge at top of the wall 6 of the separating chamber 5 breaks separated flow of water to droplets, which will mix with any bursts of trapped steam flowing back from the water outlet 4. Then the droplets will exit the separator 1 via the steam outlet 3.

[0026] FIG. 2 illustrates a cross section of a preferred embodiment of the invention. The separator 1 has a separating chamber 5 having a fluid inlet 2 at bottom of the separating chamber 5. Spiral vanes 9 are attached to the wall 6 of the separating chamber 5 between the fluid inlet 2 and a steam outlet 3. An annular water outlet 4 surrounds the steam outlet 3. The wall 6 of the separating chamber 5 has a top section 7, which has an upwards increasing diameter on top of the section of the separating chamber 5 over the spiral vanes 9. The steam outlet 3 has bottom shape, which has upwards decreasing diameter. Top curved shape of the steam outlet 3 has upwards increasing diameter.

[0027] The water outlet 4 leads first upwards and then turns downwards atop of the water outlet 4 within an upside-down water trap 13. The top end 8 of the wall 6 of the separating chamber 5 within the water outlet 4 has a rounded contour. The minimum radius R should be more than 8 mm and preferably over 12 mm and it doesn't need to be constant. The opposite wall of the water outlet 4 has a contour which conforms with the top end 8 of the wall of the separating chamber 5. The width of the water outlet 4 is substantially constant or narrows in the outflow direction. The top end 8 of the wall of the separating chamber 5 within the water outlet 4 is inclined inwards i.e. it has an upwards decreasing diameter. An inclination angle ? from start to a point, where the wall curves outwards from an inclination line should be at least 15 degrees and the length L of the inclination should be at least 25 mm. Preferably, the form of the inclination is not straight but concave as illustrated in FIG. 2. Inward inclination also diverts inflow of water uniformly against the outer wall 14 of the water outlet and thus closes the mouth area of the water outlet 4 from free flow of steam. The inward inclination also reduces velocity locally and therefore increases static pressure of water. This enhances removal of steam out of water.

[0028] Several guiding vanes 12 are located within the water outlet 4, between the top area of the wall 6 of the separating chamber 5 and an outer wall 11 of the separator 1. The number of the guiding vanes 12 is preferably 6 to 16, more preferably 10 to 14. The cumulative circumferential coverage of the equally spaced guiding vanes 12 is preferably at least 300 degrees and most preferably over 360 degrees, so that they cover at least most of full circle.

[0029] Dashed line of surface 10 illustrates surface of water flow within the separating chamber 5 and into the water outlet 4. There should be a gap between the wall of the steam outlet 3 and the surface 10 of the water flow for avoiding water entering the steam outlet 3. The smooth and consistent flow will keep a water trap 13 at the highest area of the water outlet 4 filled, so that steam cannot enter further than the mouth of the water outlet 4. There will not actually happen relevant backflow of steam, but the path of any returning steam is illustrated by a curved arrow. The guiding vanes 12 will constrict inflow of water within the water outlet 4 so that they ensure that the water trap 13 will stay filled up. Keeping the water trap 13 filled up may also or instead be ensured, if the width of the water outlet 4 decreases enough at or after the end of the water trap 13.

[0030] FIG. 3 illustrates a more detailed view of the guiding vanes 12 of the embodiment of FIG. 2. The pitch angle ? of the guiding vanes 12 is aligned to an opposite direction than pitch angles of the spiral vanes 9. The pitch angle ? of the guiding vanes 12 is preferably between 45 to 75 degrees. The arrow illustrates an approximate direction of flow of water. Increasing angle of attack of the guiding vanes 12 against the direction of flow will enhance separation of steam from water but will also increase pressure loss. If the guiding vanes 12 would be aligned to the same direction than the pitch angles of the spiral vanes 9, they would suck and intensify the inflow of water. The water trap 13 could thus be open for steam and suck it in.