GB2489511A

GB2489511A - Moisture separator

Info

Publication number: GB2489511A
Application number: GB1105508.4A
Authority: GB
Inventors: Ca Dric Vessiller
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2011-03-31
Filing date: 2011-03-31
Publication date: 2012-10-03
Anticipated expiration: 2031-03-31
Also published as: CN102728145A; CN202605895U; GB201105508D0; CN102728145B; RU2012112491A; RU2552479C2; RU120192U1; GB2489511B

Abstract

A moisture separator comprising blocks of spaced-apart, mutually parallel corrugated plates wherein the undulations of the corrugated plates have a wavelength or period P in the range 6mm to 24mm and amplitude, A, which is about half the period P. Ideally, the gap G between adjacent corrugated plates in the moisture separator should be about the same as the amplitude A. The wavelength of the corrugations is preferably 9mm to 18mm. The separator may be used to separate liquid droplets entrained in gas or vapour and is ideally employed to remove droplets of water from steam that is used to drive turbines. Preferably, the width of the each corrugated plate, measured in the direction of the flow of the incident gas or vapour, is 10 times the wavelength.

Description

IMPROVED APPARATUS FOR SEPARATING OUT DROPLETS OF

LIQUID ENTRAINED IN A GAS OR A VAPOUR

Technical Field

The present disclosure relates to an improved apparatus capable of separating out liquid droplets entrained in a gas or a vapour flowing through the apparatus. For convenience, such an apparatus will hereafter be called a moisture separator.

Technical Background

Although the objective in a plant producing pressurised steam to drive turbines is to produce 100% dry steam for feeding to the turbines, and to keep the steam dry throughout the piping system, this is typically not possible, e.g., because heat loss in the pipes or in an upstream turbine will condense some steam to droplets of water.

Because steam turbines are vulnerable to erosion and/or corrosion caused by the droplets, moisture separators are required to remove water droplets from the steam before entry to the turbines. Moisture separators are particularly required before steam is input to intermediate pressure and low pressure turbines, because the steam will already have experienced substantial cooling due to expansion through a preceding higher pressure turbine.

A type of moisture separator known from United States patent no. 4,342,570 comprises adjacent blocks of spaced-apart, mutually parallel, corrugated plates that are bolted to support panels. A perforated plate placed upstream from the blocks spreads out the incident flow of wet steam in a uniform manner. The perforated plate is also bolted to the support panels. The corrugated plates are positioned so that the corrugations run transversly of the direction of flow of the steam. Hence, the steam is rapidly deflected alternately in different directions as it flows between adjacent plates over the corrugations, so that the water droplets, having more inertia than the surrounding steam, are intercepted by the corrugations instead of remaining entrained in the steam. The corrugated plates are tilted down at an angle relative to the horizontal, so that the intercepted droplets run down the corrugations to gutters that are placed to capture the water as it leaves each block of corrugated plates. The water is removed from the moisture separator through drain tubes connected to the gutters.

Due to the above-mentioned erosion and corrosion problem, there is a need to maximise the ability of the corrugated plates to effectively intercept and collect the water droplets that are entrained in the flow of steam through the moisture separator and to minimise the tendency of the intercepted and collected water to be re-entrained S in the steam flow before it can be drained away through the guters and drain tubes.

For this pupose we have found that certain geometric configurations of the corrugations are significantly more effective than others.

Summary of the Disclosure

According to the present disclosure, a moisture separator comprises corrugated plates having the following geometric characteristics: wavelength or period of the corrugations, P, is in the range 6mm to 24mm; and amplitude, A, is about P/2.

In preferred embodiments, P is in the range 9mm to 18mm.

Furthermore, we have found that good performance is obtained if the gap G between adjacent corrugated plates in the moisture separator is about the same as the amplitude A. We prefer that the width W of each corrugated plate, as measured in the direction of flow of the steam, should be about lop, whereas the height H of each corrugated plate, as measured in the planes of the plates transversely of the flow of the steam and at right angles to the width W, should be in the range of 0.75W to 1.5W.

Exact dimensions of the above corrugated plates will vary between the above limits according to the conditions encountered in particular steam supply systems in which the plates are used. Optimized values for particular systems will be arrived at by a combination of analysis using well-known commercial CFD (computational fluid dynamics) programs, and test rigs.

Further aspects of the disclosure will be apparent from the following description and claims.

Brief Description of the Drawings

Preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is plan view of one of the corrugated plates, and Figure 2 is an edge view of two adjacent plates taken on section line 11-IT in Figure 1.

Detailed Description of the Preferred Embodiments

Figure 1 shows one embodiment of a corrugated plate 10 for use in a moisture separator. In plan view the plate is shaped as a parallelogram having a side of width W and a longer side H/sin a, where H is the height of the parallelogram when measured perpendicularly to the width W, and a is the acute included angle formed by the intersection of the sides of the parallelogram. The plate is made of stainless or other high alloy steel to withstand the effects of the hot steam S that flows across it.

As seen in Figure 2, the corrugations 12 in this particular embodiment arc shaped as a uniform series of sine waves across the width W of each plate 10. Although sine waves are shown, it is at the option of the designer to use other types of waves, such as parabolic, triangular or even square waves, though it would be expedient to radius the comers of the latter two types of waves to avoid overstraining that could lead to cracking and/or corrosion of the plates.

As shown by the arrows S in the embodiment of Figs. 1 and 2, the steam flows through the gap G between adjacent plates, transversely of the lengths of the corrugations, and this deflects the steam alternately in opposing directions as it flows between adjacent plates over the corrugations, so that the water droplets, having more inertia than the surrounding dry steam vapour, tend to be intercepted by the corrugations instead of remaining entrained in the steam flow.

We have found that for effective droplet removal, the wavelength or period of the corrugations, P, should be in the range 6mm to 24mm, preferably 9mm to 18mm, whereas the amplitude, A, should be about half the value of P. Performance is also improved if the gap 0, i.e., the separation distance between adjacent corrugated plates in the moisture separator, is set at about the same value as the amplitude A. To easily obtain and keep the dimension G constant throughout each block of corrugated plates, four lands 13 arc formed on each of the plates 10 during the pressing operation that forms the corrugations. A pair of the lands 13 are located near the leading edge of each plate and the other pair of lands are located near the trailing edge, the lands of each pair being spaced apart along the lateral extent of the corrugations. Each land 13 is arranged to bridge the trough between two peaks of the corrugations, so that a trough of the adjacent plate sits on the land, as shown in Figure 2.

It will be noticed that the steam S flows transversely of the lengths of the corrugations, but not at right angles to them. The intersection of the steam flow direction S with the lateral extent of the corrugations 12 makes an acute included angle 0, which in this preferred embodiment is the same as the acute included angle a formed by the intersection of the sides of the parallelogram. Although it would be possible to arrange the moisture separator so that the steam would flow over the corrugations at right angles to the corrugations, it is preferred that the steam flow meets the corrugations at an acute included angle 0, as shown, because this ensures that droplets intercepted by the corrugations are automatically given a component of flow velocity in the direction D along the lengths of the corrugations, which assists movement of the water droplets in the drainage direction. It is of course at the option of the designer to choose the angle of interception 0 between the steam flow and the longitudinal extent of the corrugations, but it simplifies construction of the moisture separator if 0 = a.

Drainage is also assisted by one end 14 of the corrugations being lower than the other end 15, so that the troughs of each block of corrugated plates empty into gutters arranged at their ends 14. For further information, see prior patent US 4,342,570, Fig. 1 and associated text.

It will be noted that the leading and trailing edges 16, 17, respectively of the corrugated plates are planar, i.e., without corrugations. They arc provided with holes 18 near each corner of the parallelogram shape for the insertion of round-section support rods (not shown), which help assembling the corrugated plates together and maintain them in the block.

The above description has been given purely by way of example, and modifications can be made within the scope of the appended claims.

Claims

CLAIMS: 1. A moisture separator comprising blocks of spaced-apart, mutually parallel, corrugated plates having the following geometric characteristics: wavelength or period of the corrugations, P, is in the range 6mm to 24mm; amplitude, A, is about P12.
2. A moisture separator according to claim 1, in which P is in the range 9mm to 18mm.
3. A moisture separator according to claim 1 or claim 2, in which the gap G between adjacent corrugated plates in the blocks is about the same as the amplitude A of the corrugations.
4. A moisture separator according to any preceding claim, in which the width W of each corrugated plate, as measured in the direction of flow of the steam, is about lop.
5. A moisture separator according to claim 4, in which the height H of each corrugated plate, as measured in the planes of the plates transversely the flow of the steam and at right angles to the width W, is in the range of 0.75W to 1.5W.