Steam-liquid separator for boiler drums

Abstract

The boiler drum separator 1 for separating steam and water comprises a separation chamber 5 with a fluid inlet 2 at the bottom and a steam outlet 3 at the top, a spiral vane 9 is attached to the wall 6 of the separation chamber 5 between the fluid inlet 2 and the steam outlet 3 to achieve a circular motion of the incoming fluid, and a circular water outlet 4 surrounds the steam outlet 3. The upper end 8 of the wall 6 of the separation chamber 5 inside the water outlet 4 has a rounded upper profile and is preferably inwardly sloped to ensure a smooth flow and to keep a water trap 13 filled in the upper region of the water outlet 4. The slope at the upper end 8 of the wall 6 is preferably concave.

Description

Technical Field

[0001] The present invention relates to a steam-water separator, which comprises a separation chamber having a fluid inlet at the bottom and a steam outlet at the top.

Background Art

[0002] A boiler drum forms part of the boiler's circulation system. The drum performs two main functions. The first and primary function is to separate steam from the mixture of water and steam. Second, the drum houses equipment used for the purification of steam and water.

[0003] To perform the basic separation of water and steam, two different types of cyclones are used. The basic type has a tangential inlet, whereby the fluid rotates and the lighter steam separates from the water and exits from the top of the cyclone.

[0004] A vertical cyclone type separator has an inlet at the bottom and spiral blades that make the incoming fluid flow into a circulating motion. Thus, the water phase separates and flows horizontally to the side of the separation chamber of the separator, then flows upward along the inner wall of the separation chamber and exits into the space between the separation chamber and the outer wall of the separator. The steam exits from the top of the separator. The vertical separator is disclosed in the publications of U.S. Patent No. 3216182, EP2250437, JP-A-11-141802, U.S. Patent No. 3086343, GB664447, U.S. Patent No. 3329130, and U.S. Patent No. 5320652.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

[0006] As the demand for increased boiler operating efficiency continues to grow, the inflow into the boiler drum is also increasing, and the efficiency of steam separation must be optimized. Conventional solutions result in excessively high pressure differences and / or too much water escaping with the steam, leaving steam mixed in the wastewater. Water inside the steam cannot be allowed to enter the superheater, and even further into the steam turbine, where water can cause harmful consequences. Steam bubbles in the wastewater, when they burst, create small droplets of water inside the drum. The secondary demister captures most of these droplets. This increases the water load on the secondary demister, which can result in water flooding, and water may enter the superheater. If a large amount of water enters the superheater, it can destroy it, and in the worst case, impurities along with the water droplets can enter all the passages to the steam turbine. Furthermore, steam bubbles below the water surface can worsen water level control and, in the worst case, can be absorbed into the downpipe, thereby weakening the water head that drives the natural cooling water circulation.

[0007] Vertical separators, which are widely used and also publicly available, can effectively separate water and steam within a separation chamber. The main challenge is not the separation process itself, but the entry of steam into the water outlet. To keep the gas phase separated from the liquid phase, the water flow should be smooth and uniform within the water outlet. For example, the upper end design of the separation chamber of known separators has a sharp-edged water channel at the water outlet. U.S. Patent No. 3,216,182 acknowledges the challenge of steam entering the water outlet and returning from there. Such a return flow will be droplet-filled, as the sharp change in the flow path creates water droplets. The challenge was solved by directing the mixture to a separate water / steam outlet concentric with the water outlet. When steam enters the water outlet, it causes a backward flow of the water-steam mixture. This mixture should be separated again in a demister.

[0008] U.S. Patent No. 3,329,130 ​​discloses a rounded upper end of the upper edge of the wall of a separation chamber. Such a slightly rounded wall edge cannot prevent the induction of high levels of turbulence above the water outlet because its radius is too sharp to achieve a good flow guidance effect.

[0009] Uneven or turbulent flow within the water outlet will create a deeper entry point for steam to the water outlet. Similarly, steam entering the outlet may cause a backward jet of the water-steam mixture, leading to water entering the steam outlet. The present invention aims to prevent steam from entering the water outlet and mixing with the water outflow. Flow integrity is ensured by avoiding sharp changes in the flow path. Since the downward path of water will be completely filled, unevenness in the gravitational suction effect is avoided, and thus changes in the water flow are also avoided. The present invention enables a more perfect separation of the water phase from the steam phase without causing excessively high pressure drops across the separator. These and other objectives achieved by the separator according to the appended claims will be understood from the following summary of the invention and modes for carrying out the invention. [Means for solving the problem]

[0010] A boiler drum separator for separating steam and water comprises a separation chamber having a fluid inlet at the bottom and a steam outlet at the top center. Helical vanes for separating the water phase from the steam phase are mounted on the walls of the separation chamber between the fluid inlet and the steam outlet to achieve circular motion of the incoming fluid. A circular water outlet surrounds the steam outlet.

[0011] The rapid circular motion of the fluid directs a flat, upward flow of the water phase to the side of the separation chamber, where light steam bubbles move to the surface of the water flow and burst there. The steam flows upward through the separation chamber to the steam outlet at the top. If the separation chamber includes an upper shape with an increasing diameter upward, the upward flow of water will have a circular component and will rise best upward. The upward-flowing water will form a thinning layer, which improves the separation of the steam. The steam outlet may then also have a larger initial diameter to reduce the pressure drop. The pressure drop is further reduced if the steam outlet includes a bottom shape with a smoothly decreasing diameter upward.

[0012] The objective is to create a filled water trap with a uniform barrier surface, thereby preventing steam from further entering the water outlet. To achieve this objective, the water should flow smoothly inside the water outlet in a turbulence-suppressing manner, separating droplets or other flow irregularities. Otherwise, the steam would have entry points to the water outlet between droplets or separated flows. The water trap, though aligned in an inverted position, will function similarly to conventional traps, creating a stable barrier for the gas. The water trap will be filled by a continuous upward flow of separated water. Therefore, there must be a carefully designed channel for the water to prevent it from falling back down from the water trap. Since variations in operating conditions will result in the formation of water layers of different thicknesses, the dimensions should be designed to suit various operating conditions, i.e., flow velocity and flow rate. No active adjustments of any vanes or any other parts can be made during operation.

[0013] The most important novel feature for achieving the objective is the shape of the upper end of the separation chamber wall. The upper end of the separation chamber wall inside the water outlet has a rounded shape with a sufficiently large minimum radius. This cannot be achieved by simply grinding the cut upper end of the wall to a small radius. When the upper end has a radius sufficient for the flow velocity around it, the outflowing water will remain beside the upper end without splitting into droplets or causing other discontinuities in the flow. This is called the "teapot effect". Thus, the upper part is not merely a cylindrical or conical end, but a distinctive integral part of the separator. If the upper end of the separation chamber wall is formed from the wall of the separation chamber, the rounded shape should extend at least beyond the upper point, preferably at least 45 degrees beyond the upper point.

[0014] The water trap inside the water outlet is best kept filled and sealed from vapor by its upper end, which slopes inward into the separation chamber. The design ensures a stable, uniform water surface behind the water outlet opening for the incoming vapor phase. The sloped upper part of the separation chamber wall directs the inflow smoothly toward the wall opposite the water outlet. The inward slope is preferably concave, so as to best direct the inflow smoothly toward the wall opposite the water outlet. The surface opposite the outlet should have a low contact angle with the inflow surface to avoid droplet formation where the inflow contacts the opposite surface.

[0015] The outer wall opposite the water outlet, around the upper part of the separation chamber wall at the water outlet, should be smoothly curved to allow for a smooth and tight flow of water through the water trapping area. Sharp edges would create discontinuities in the flow through, thus creating potential paths for steam.

[0016] Behind the water trap inside the water outlet, when there are a plurality of guide vanes aligned downward at opposite pitch angles with respect to the spiral vanes between the wall of the separation chamber and the outer wall of the separator, it is additionally ensured that the water trap is kept in a filled state. The vanes deflect the passing flow in a more horizontal direction, thus creating a slight backpressure. In this way, the water outlet on the side of the separation chamber is full of only water, so that an effective gravitational suction effect can be created. It partially compensates for the pressure drop caused by the guide vanes. The cumulative circumferential effective range of the guide vanes is preferably at least 360 degrees. The pitch angle of the guide vanes is preferably between 45 and 75 degrees. The number of guide vanes is preferably 6 to 16, depending on the pitch angle and the targeted circumferential effective range.

[0017] The surface on the opposite side of the water outlet inside the water trap region should have a smoothly curved outer shape without edges, and this outer shape conforms to the rounded upper end of the wall of the separation chamber. The width of the water outlet should be substantially constant or preferably gradually narrow in the flow direction to ensure a smooth and uniform passing flow. The narrowing path ensures that the water trap remains perfectly filled, and the trapped steam can return backward from the wider mouth of the outlet.

[0018] It has been shown that, without increasing the pressure drop, the percentage of separation efficiency for both the water and vapor phases is better than that of the prior art vertical separators and worthy of attention. The demister also makes the residual water separated from the steam significantly less, thus increasing the efficiency of the demister and minimizing the pressure loss in the demister. With a carefully optimized design separator, higher steam power generation is ensured compared to boilers with conventional separators.

[0019] Here, referring to the accompanying drawings, examples of embodiments of the present invention will be described in more detail.

Brief Description of the Drawings

[0020] [Figure 1]The figure shows a boiler with a conventional steam drum configuration. [Figure 2] It is a cross-sectional view of a preferred embodiment of the present invention. [Figure 3] It is a figure showing the guide blade of the embodiment of FIG. 2.

Mode for Carrying Out the Invention

[0021] FIG. 1 shows a boiler with a conventional steam drum configuration for separating the fluid of steam and water entering from the cooling pipe of the boiler chamber. The vertical separator 1 first separates the incoming fluid. Depending on the capacity of the boiler, several separators 1 are installed inside the drum. The fluid is mainly steam bubbles inside water. At high levels of steam, the water can also be in the form of droplets

[0022] The primary demister at the upper part of the separator 1 prevents most of the residual droplets from entering the steam space of the drum. The secondary demister at the top of the drum removes the droplets so that they do not flow out to the superheater tubes. If the level of separation efficiency is too low, the demister can be filled with water, causing high pressure loss and incomplete separation.

[0023] The spiral blade 9 inside the separation chamber 5 directs the incoming fluid into circular motion, and the separated water phase rises up to the water outlet 4 along the wall 6 of the separation chamber 5. The separated water exits the separator 1 from the bottom end of the water outlet 4. The steam exits through the central steam outlet 3 at the upper part of the separation chamber 5.

[0024] The illustrated design has several defects, which cause pressure drop and incomplete separation inside the separator 1.The form of the water outlet 4 may cause resonance of the countercurrent where the unseparated steam can enter the water outlet 4, causing disturbance to the outflowing water. The sharp edge at the upper part of the wall 6 of the separation chamber 5 divides the flow of the separated water into droplets, and these droplets will mix with any jet where the trapped steam flows back from the water outlet 4. Then the droplets will exit the separator 1 through the steam outlet 3.

[0025] Figure 2 shows a cross-section of a preferred embodiment of the present invention. The separator 1 includes a separation chamber 5 having a fluid inlet 2 at its bottom. A helical vane 9 is mounted on the wall 6 of the separation chamber 5 between the fluid inlet 2 and the steam outlet 3. An annular water outlet 4 surrounds the steam outlet 3. The wall 6 of the separation chamber 5 has an upper section 7, which has an increasing diameter upwards at the top of the section of the separation chamber 5 beyond the helical vane 9. The steam outlet 3 has a bottom shape with an increasing diameter upwards. The curved shape at the top of the steam outlet 3 has an increasing diameter upwards.

[0026] The water outlet 4 first flows upward and then curves downward at the top of the water outlet 4 inside the inverted water trap 13. The upper end 8 of the wall 6 of the separation chamber 5 inside the water outlet 4 has a rounded shape, and its minimum radius R should be greater than 8 mm, preferably greater than 12 mm, and does not need to be constant. The wall opposite the water outlet 4 has a shape that conforms to the upper end 8 of the wall of the separation chamber 5. The width of the water outlet 4 is substantially constant or narrows in the outflow direction. The upper end 8 of the wall of the separation chamber 5 inside the water outlet 4 is inclined inward, i.e., has a diameter that decreases upward. The inclination angle β from the starting point to the point where the wall curves outward from the inclination line should be at least 15 degrees, and the length L of the inclination should be at least 25 mm. The shape of the inclination is preferably concave rather than straight, as shown in Figure 2. The inward inclination also causes the water inflow to uniformly bypass the outer wall 14 of the water outlet, thus closing the mouth area of ​​the water outlet 4 from free-flowing steam. The inward slope also locally reduces velocity and therefore increases the static pressure of the water. This enhances the removal of steam from the water.

[0027] Several guide vanes 12 are positioned inside the water outlet 4 between the upper region of the wall 6 of the separation chamber 5 and the outer wall 11 of the separator 1. The number of guide vanes 12 is preferably 6 to 16, more preferably 10 to 14. The cumulative effective circumferential range of the evenly spaced guide vanes 12 is at least 300 degrees, and most preferably more than 360 degrees, so that the guide vanes 12 cover at least a large portion of the entire circle.

[0028] The dashed surface 10 represents the surface of the water flow inside the separation 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 to prevent water from entering the steam outlet 3. A smooth and even flow will keep the water trap 13 in place at the highest point of the filled water outlet 4, and as a result, steam will not be able to enter beyond the opening of the water outlet 4. In practice, no backflow of steam in question occurs, but any return path of steam is indicated by a curved arrow. The guide vane 12 will restrict the inflow of water into the water outlet 4 to ensure that the water trap 13 remains filled. Similarly, or instead, if the width of the water outlet 4 is sufficiently reduced at or after the end of the water trap 13, it will be ensured that the water trap 13 remains filled.

[0029] Figure 3 shows a more detailed view of the guide vane 12 in the embodiment of Figure 2. The pitch angle α of the guide vane 12 is aligned in the opposite direction to the pitch angle of the helical vane 9. The pitch angle α of the guide vane 12 is preferably between 45 and 75 degrees. The arrows indicate the approximate direction of water flow. Increasing the angle of attack of the guide vane 12 relative to the direction of flow enhances the separation of steam from water, but also increases pressure loss. If the guide vane 12 were aligned in the same direction as the pitch angle of the helical vane 9, the guide vane 12 would draw in and strengthen the inflow of water. In this way, the water trap 13 is open to steam and may draw steam into it.

Claims

1. A separator (1) for a boiler drum for separating steam and water, comprising a separation chamber (5) having a fluid inlet (2) at the bottom and a steam outlet (3) at the top, with helical blades (9) attached to the wall (6) of the separation chamber (5) between the fluid inlet (2) and the steam outlet (3) to achieve circular motion of the incoming fluid, with a circular water outlet (4) surrounding the steam outlet (3), the water outlet (4) first passing upward and then curving downward, wherein the upper end (8) of the wall (6) of the separation chamber (5) located inside the water outlet (4) includes a rounded upper outer shape having a minimum radius (R) of 8 mm and is inclined inward, with a diameter decreasing upward, and the inclination at the upper end (8) of the wall (6) is concave inward.

2. The separator (1) according to claim 1, wherein the upper end (8) of the wall (6) of the separation chamber (5) is inclined inward, and as a result, the inclination angle (β) from the starting point of the inclination line to the point where the upper end (8) of the wall (6) curves outward from the inclination line is at least 15 degrees, and the length (L) of the upper end (8) of the wall (6) and the inclination is at least 25 mm.

3. The separator (1) according to claim 1 or 2, wherein the minimum radius (R) of the rounded upper outer shape is at least 12 mm.

4. The separator (1) according to any one of claims 1 to 3, wherein the outer wall (14) of the water outlet (4) around the upper end (8) of the wall (6) of the separation chamber (5) has a curved shape without edges.

5. The separator (1) according to any one of claims 1 to 4, wherein the separation chamber (5) includes an upper section (7) having an increasing diameter upward.

6. The separator (1) according to any one of claims 1 to 5, wherein, inside the water outlet (4), there is a plurality of guide vanes (12) between the upper region of the wall (6) of the separation chamber (5) and the outer wall (11) of the separator (1), which are aligned at a pitch angle (α) opposite to the pitch angle (α) of the helical vane (9).

7. The separator (1) according to claim 6, wherein the number of guide vanes (12) is 6 to 16 or 10 to 14.

8. The separator (1) according to claim 6 or 7, wherein the cumulative effective circumferential range of the guide vane (12) is at least 300 degrees or at least 360 degrees.

9. The separator (1) according to any one of claims 6 to 8, wherein the pitch angle (α) of the guide vane (12) is between 45 and 75 degrees.

10. The separator (1) according to any one of claims 1 to 9, wherein the outer wall (14) of the water outlet (4) around the upper end (8) of the wall (6) of the separation chamber (5) is curved, and as a result the width of the water outlet (4) is substantially constant or narrows in the direction of outflow.

11. The separator (1) according to any one of claims 1 to 10, wherein the steam outlet (3) includes a bottom shape having a diameter that decreases upward and / or an upper shape having a diameter that increases upward.

Images