CN1088144C - Steam filter for steam turbine - Google Patents

Abstract

A steam filter is provided in the steam turbine inlet system to prevent large metal particles in the steam from entering the turbine. A plurality of through holes of different diameters arranged at a certain interval in a majority of the circumference of the filter, the holes of the same diameter being located in the same longitudinally extending circumferential region, the holes of the largest diameter being arranged in the region where there is little possibility of entry of metal particles, the holes of smaller diameter being arranged in the region where there is most possibility of entry of metal particles; and there is a longitudinally extending circumferential region of the filter which is free of holes; each of the through holes has an inlet end Y on the outer wall of the filter cylinder and an outlet end on the inner wall of the filter cylinder, the diameter of the outlet end is larger than that of the middle part, and the outlet end is used for reversely slowing down the flow rate of the steam and reducing the pressure drop of the steam.

Description

Turbine steam filter

Technical field

This application is a continuation-in-part of pending application Serial No. 08/344862 filed November 25,1994.

This invention relates to steam turbines and apparatus for preventing large particulate matter entrained in steam from entering the steam turbine.

Background technique

All steam turbines have steam filters to capture particulate matter carried in the steam supplied by the boiler and prevent it from entering the turbine and causing serious damage to the turbine.

Existing steam turbines typically use one of two types of steam filters.

The first type is a cylinder with large holes arranged such that a screen with small holes is arranged around the cylinder. This type of filter can filter out particles larger than about 1/8 inch in size from the steam. Such systems can also be temporarily retrofitted with a finer screen for short-term use in situations where the boiler is known to generate significant particulate matter. A minor drawback with this type of filter is that the screen itself will fail over time with operation and use, causing serious damage to the interior of the steam turbine. At the same time, when the steam passes through the holes of the filter screen and the filter, the pressure drop of the steam is increased.

The second type of filter is a simple cylinder with many small holes. These pores allow the passage of steam but prevent the passage of particles larger than the pores. The choice of holes varies with the design of the steam turbine. Some designs use approximately 1/4" holes, while others use approximately 3/32" holes. The hole of this type of filter adopts a square direct-cut guide port, so that the flow coefficient is relatively small, resulting in a large inlet steam pressure drop. These holes are easily damaged by high-speed moving particles, reducing the effective flow area for airflow and increasing unnecessary pressure drop.

It is an object of the present invention to eliminate the problem of screen failure occurring in the above-mentioned first type of filter; a further object is to reduce the maximum size of particles passing through the filter; a further object is to reduce the The resulting operating pressure drop. In addition, the use and maintenance of the filter is simplified.

In order to achieve the above-mentioned purpose of the invention, the present invention provides a steam filter, which is fixedly installed in the steam inlet system of the steam turbine to prevent large metal particles in the steam from entering the steam turbine, and is characterized in that: most of the circumference of the filter There are a plurality of through-holes arranged at certain intervals. The diameters of the through-holes are different. The holes of the same diameter are located in the same longitudinally extending circumferential area. The largest-diameter holes are arranged in the area where metal particles are rarely likely to enter. The holes are arranged in the area where the metal particles are most likely to enter; and there is a longitudinally extending circumferential area without holes in the filter; each through hole has an introduction end Y on the outer wall of the filter cylinder, and a Y on the inner wall of the filter cylinder. A lead-out end, and there is a middle part between the lead-in end and the lead-out end, and the diameter of the lead-out end is larger than the middle part.

Description of drawings

Figure 1 is a partial cross-sectional view of a filter installed in a turbine stop valve housing embodying the present invention;

Fig. 2 is a perspective view of the filter in Fig. 1;

Fig. 3 is a plan view of the filter of Fig. 2 shown in an unrolled or unrolled state;

Figure 4 is a partially enlarged view of a cutaway cross-section taken transversely through the filter in Figure 2;

Figure 5 is a partially enlarged cross-sectional view taken transversely through a modified form of the filter;

Figure 6 is a partial cross-sectional view of the improved filter of Figure 5 installed in the turbine stop valve housing; and

Figure 7 is a perspective view of the modified filter of Figure 5 with the screen removed for clarity.

Specific implementation description

FIG. 1 is a partial cross-sectional view of a turbine stop valve housing 11. Referring to FIG. The steam enters the valve casing through the steam inlet channel 14, and the arrow S indicates the steam flow direction.

Contained within the valve housing 11 is a cylindrical steam filter 13 which embodies the preferred form of the invention. The steam filter 13 has rows of spaced parallel holes, generally indicated at 17, extending horizontally through the wall of the filter cartridge.

All steam must pass through holes 17 in the filter cartridge wall, which are provided to prevent large metal particles (not shown) from the boiler from entering the turbine (not shown).

After the steam passes through the holes 17 in the filter 13, it flows through the valve discharge pipe 12, and then enters the steam turbine (not shown). The upper end of the filter is in contact with the cover of the valve housing, and the lower end is in contact with the inner surface of the valve housing. This metal-to-metal contact at both ends prevents steam flow from bypassing.

In the valve housing 11 an annular channel 26 surrounds the filter 13 . This channel allows steam to pass between the valve housing and the filter, allowing steam to pass through all the holes 17 in the filter. By arranging a boss 27 in the annular passage 26 facing the steam inlet 14, a local blockage is formed to minimize the circulation of steam or particles.

As shown in Figure 4, each hole 17 has an outer mouth or lead-in end X on the outer wall of the filter cylinder, and an inner mouth or lead-out end Y is arranged on the inner wall of the filter cylinder, between the lead-in end X and the lead-in end Y. Between the outlet Y is the middle part W.

The diameter of each hole 17 is substantially constant from the lead-in end X to about the center of the length of the middle portion W, and from this center to the inner end of the hole there is a uniform taper Z, providing a The inner end or the leading end Y of the shape. Therefore, the aperture at the outlet end Y is larger than that at the middle part W.

This configuration of the holes 17 reduces the pressure drop when steam passes through the filter 13, since the taper Z leading to the outlet Y forms a radial passage.

The purpose of the radial channels is to reversely slow the steam flow rate at the outlet end of the hole to increase the steam pressure. This reduces the pressure drop at orifice 17 and also reduces the pressure drop caused by turning the steam flow 90 degrees so that the steam flow is directed to the turbine stop valve (not shown), thereby improving turbine performance.

The taper and angle of the hole 17 can be changed to suit different application needs. It was suggested that the half angle of the taper be 3.5 degrees, and the taper length should be enough to double the flow area of the hole.

FIG. 2 is a perspective view of a cylindrical steam filter 13 . The holes 17 are distributed over most of the circumference of the filter cartridge wall. However, for the portion 16 of the filter which is impacted by the high-speed steam flow entered by the steam inlet channel 14, no holes are arranged in the longitudinally extending circumferential region. This area is denoted by a-a' in the circumferential direction.

In the spaced apart longitudinally extending circumferential regions b-d, holes 17b-17d of different diameters are provided. Holes 17b'-17d' of different diameters are provided in the remaining spaced apart longitudinally extending circumferential regions b'-d' of the filter circumference.

In regions b and b', which flank portion 16 and regions a and a', respectively, apertures 17b and 17b' are relatively large in diameter, on the order of 1/4 inch.

In regions c and c' on either side of regions b and b', respectively, holes 17c and 17c' are slightly smaller, being a modest 1/8 inch in diameter.

In regions d and d' on either side of regions c and c', respectively, the apertures 17d and 17d' have the smallest diameter on the order of 3/22 inch.

The variation diagram from each area a-d and a'-d' is shown in Fig. 3, where the wall of the filter is unfolded.

Based on this partition arrangement, relatively large holes 17b and 17b' are used in areas b and b', and particles have little chance to enter this area. And aperture 17d and 17d ' are used in area d and d' this district particle is active, enters hole easily. Particles adjacent to regions b and b' enter the bore 17 via the annular channel 26 in a direction generally parallel to the axis of the bore 17. Particles in the adjacent regions d and d' jump and are stirred by the gas flow to move in random directions, therefore, these particles are more likely to enter the holes 17 in these regions, especially if these holes are larger.

Figures 5-7 illustrate an improved form of filter 113 embodying the present invention.

In this embodiment, a fine screen 122 is mounted outside the filter 113, its inlet welded at 123, and/or rivets or gongs (not shown); and the filter 113 replaces the valve housing 11 Central filter 13 .

A filter 113 with a fine mesh 112 can be temporarily used in the case of particles most likely from the boiler. The shoulder 128 in the figure is used to protect the fine filter.

As with the filter 13 of FIGS. 1-4, the filter 113 is provided with holes 117 over most of the circumference of the cylinder wall. And a longitudinally extending circumferential portion or region 116 where the filter is subjected to the impact of the high-speed steam flow entering from the steam inlet channel 14 is not perforated.

On the filter 113, there are holes 117b-117d and holes 117b'-117d' of different diameters which are arranged at intervals throughout the remainder of the filter wall in the circumferential region in the direction of longitudinal extension.

As shown most clearly in Figure 5, the holes 117 are circular, as are the outer inlet ports X', and the filter wall is also rounded at 124 to reduce vapor pressure drop and impact on the holes due to particle impingement. damage.

In addition, each hole 117 has an inner or outlet end Y' on the inner wall of the filter cylinder, and an intermediate portion W' between the inlet end X' and the outlet end Y'.

The diameter of each hole 117 is substantially constant from the circular lead-in end X' to the approximate center of the length of the middle portion W'. From the approximate center position to the inner end of the hole there is a gradually increasing taper Z to form a bell-shaped inner or lead-out end Y'. Therefore, the aperture at the outlet end Y' is larger than that at the middle part W'.

As with the embodiment of Figs. 1-4, this configuration of holes 117 reduces the pressure drop that occurs when steam passes through filter 113. The taper Z' leading to the outlet end Y' forms a radial channel, the purpose is to reversely slow down the steam flow rate and increase the steam pressure at the outlet end of the hole. It also reduces the pressure drop created at the orifice 117 and the pressure drop required to turn the flow through 90 degrees in order to direct the flow to the stop valve (not shown) of the turbine. Thereby improving the working performance of the steam turbine.

It should be pointed out that the steam filter of the present invention is suitable for high-pressure steam turbines, and is also suitable for the steam inlet system of reheating steam turbines.

Claims (5)

1. A steam filter, which is fixedly installed in the steam inlet system of the steam turbine, is used to prevent large metal particles in the steam from entering the steam turbine, and is characterized in that: A plurality of through-holes with certain intervals are arranged on most of the circumference of the filter, and the diameters of the through-holes are different. The holes of the same diameter are located in the same longitudinally extending circumferential area, and the largest diameter holes are arranged in the area where there are few metal particles. The area that may enter, the small-diameter holes are arranged in the area where the metal particles are most likely to enter; and there is a longitudinally extending circumferential area without holes in the filter; each through hole has an introduction end Y on the outer wall of the filter cylinder, There is a lead-out end on the inner wall of the filter cylinder, and there is a middle part between the lead-in end and the lead-out end, and the diameter of the lead-out end is larger than the middle part. 2. An improved filter as claimed in claim 1, wherein the central portion of each through hole is tapered for a portion of its length, the taper terminating at the outlet end. 3. An improved filter as claimed in claim 2, characterized in that the half angle of the taper is 3.5 degrees and the length of the taper is sufficient to double the flow area of the holes. 4. An improved filter according to claim 1, characterized in that the fine screen is located on the outside and serves to protect the holes in the various regions of the filter. 5. An improved filter according to claim 1, wherein the holes have circular inlet ends.

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