EP0158891B1 - Pre-separator for a pipe transporting a biphase mixture - Google Patents

Description

The invention relates to a pre-separator according to the preamble of claim 1.

In saturated steam turbine systems, the steam that emerges wet from the high-pressure part of the turbine is dried before it re-enters the low-pressure turbine and then slightly overheated. This is done in water separator superheaters using wire mesh mats or baffle plates, as described in Brown Boveri Mitteilungen, January 1976, Volume 63, p. 66 ff.

The disadvantage of this circuit is that the underflow line between the high-pressure turbine and the water separator elements of the steam flow is exposed to a relatively high water content.

This inevitably increases the erosion / corrosion potential and the pressure losses.

Water gushes and high local moisture concentrations can also form, which can then no longer be separated by the separator with a clear degree of separation.

Furthermore, water separation using wire mesh mats and baffle plates is characterized in that their separation efficiency depends on the steam flow rate, the droplet size and the absolute amount of moisture treatment.

It is known to apply steam to the separator elements as evenly as possible by switching flow resistances upstream or downstream, in accordance with EP-A-0 005 225, or by special design of the flow paths, in accordance with CH-A-483 864.

Although this measure can partially equalize the wetness, water gushes and strands of water remain, and the absolute size of the average wetness cannot therefore be changed. In this context, it is known that at approx. 10% wetness, the pressure loss in the connecting lines between the high-pressure turbine and water separator is approx. 3 times greater than with dry steam.

From EP-A-0 096 916 it is further known to provide a water pre-separator in a high-speed water separator, upstream of the deflection vanes, which water separator essentially consists of a gap in the wall of the pipe elbow which extends from one into the flow channel protruding cover plate is overlapped. A separation of the water flowing in the vicinity of the pipe wall is achieved in this way, but the peeling of the wall wetness concentration can only be minimal if it is intended to record only stratified flow water.

In the case of a water separator known from FR-A-961 953, an inner tube, which has a cross section that is constant over its entire length, delimits an annular channel with the actual steam tube, in which the transport steam is separated from the water. In the front part of the inner tube there are two mutually entangled, oppositely inclined baffle plates, each covering half the flow cross-section and causing the incoming wet steam to rotate, whereby the water is to be centrifuged against the inner wall in order to create an annular gap at the downstream end of the inner tube is limited by this inner tube and an aperture-shaped insert to be peeled off and passed into said ring channel, where water and transport steam separate and are discharged separately from there. This device generates a considerable flow resistance at its upstream end, where the flow cross-section of the inner tube is abruptly reduced, and through the baffle plates. It is also doubtful whether the turbulence from the baffle plates can produce the desired strong and uniform centrifugal effect, which enables a high degree of separation.

The invention aims to remedy the disadvantages of the known solutions outlined above.

The invention, as characterized in the claims, is based on the task of proposing a pre-separator with which good water separation levels can be achieved and at the same time the transport vapor layer serving for the water to be separated out can be separated, with which irregular pipe wall water flows, such as slug flows, plug flows, wave flows etc., can be recorded. In addition, it is an object of the invention to design the pre-separator so that it can also be retrofitted into existing turbine systems with little effort.

This ensures that the steam-side pressure losses between the high-pressure turbine and superheater are minimized by reducing the wetness at an early stage.

The reduction in the moisture content induces a reduction in the erosion / corrosion potential in the connecting lines and a reduction in the heat consumption of the turbo group. The good water separation in the pre-separator reduces the potential of the water surge and water streaks in the downstream water separator elements according to the use of the pre-separator according to the invention, which consists in that it is arranged downstream of the high-pressure part of the turbine and upstream of a further water separator of any design upstream of an intermediate superheater. This reduces water penetration and increases, when viewed across all installed separator elements, the overall efficiency of water separation.

It turns out that the solution according to the invention brings advantages not only for newly designed, but also for existing plants, if it turns out after the start-up that the water separation is insufficient there.

Exemplary embodiments of the invention are shown schematically in the drawing.

• Fig. 1 eine Sattdampf-Turbinenschaltung mit eingebauten Wasserabscheidern,
• Fig. 2 einen Vorabscheider mit zwei Kammern,
• Fig. 3 einen Vorabscheider mit zwei Kammern, und
• Fig. 4 einen weiteren Vorabscheider mit drei Kammern.

It shows:

• 1 is a saturated steam turbine circuit with built-in water separators,
• 2 shows a pre-separator with two chambers,
• Fig. 3 shows a pre-separator with two chambers, and
• Fig. 4 shows another pre-separator with three chambers.

All elements not necessary for the immediate understanding of the invention have been omitted. The direction of flow of the media is indicated by arrows. In the figures, the same elements are provided with the same reference symbols.

1 shows a saturated steam turbine system with water separation, the pre-separator 3 according to the invention being integrated into this circuit. The steam emerging from the high-pressure turbine 1 initially flows through the pre-separator 3 located immediately downstream, then via the continuation of the pipeline 31 a further water separator - here, for example, a high-speed separator 4 - in order to then reach the reheater 5 via the line 8. Of course, the water separation, in addition to the aforementioned pre-separator 3, can consist of a series of downstream water separators of any type. This depends on the desired water trap, which must necessarily be large in order to improve the turbine efficiency and to reduce the blade erosion in the low-pressure turbine 2. It should also be noted that the introduction of the pre-separator 3, for example, means that the expensive and pressure-loss-prone water separator superheater can be dispensed with.

After flowing through the reheater 5, the now optimally dry steam 9 acts on the low-pressure turbine 2. The steam 9 is then considered to be optimally prepared when it expands in the low-pressure turbine 2 to "conventional" final wetting. A water / transport steam / working steam phase separation takes place in the pre-separator 3. In this case, the separated water 37 and the separated transport steam 36 are fed to a pressure sink 6. Of course, the transport steam 36 separated in the pre-separator 3 can be fed individually to another pressure sink, for example a preheater. The water 7 still separated in the high-speed separator 4 flows off together with water 36.

On the basis of the circuit described, the high-speed separator 4 does not need to be trimmed to the required water separation efficiencies of greater than 95% by applying internal measures. Rather, high separator types and efficiencies can be achieved by connecting a plurality of simple high-speed separators 4 in series with the addition of an upstream pre-separator 3. With this circuit, a residual moisture of low pressure turbine of 1-2% is achieved. Due to the present reduction in pressure losses and residual moisture, 7.5 MWe more electrical energy is generated in a 1000 MWe plant.

The connection of the water separators to one another does not necessarily have to be parallel.

FIG. 2 shows an embodiment of the pre-separator 3 according to the invention.

The steam-carrying pipe 31 has a concentric inner pipe, which preferably has the shape of a Laval nozzle 33a. An annular gap opening 32 is present between the pipe 31 and the inlet opening of the inner pipe 33. Further downstream of the annular gap opening 32, the pipeline 31 bulges out into an intermediate space 35 in which a second concentric intermediate pipe 34 is arranged, which on the pipeline side reproduces the fully guided contour of the pipeline 31. This creates a chamber 35b that remains constant in the flow direction between the pipeline 31 and the intermediate pipe 34.

Where the flow conditions require it, the chamber 35b is expanded in the flow direction, for example at a rate of 5%. The inner tube 34 has a bottom closure downstream of the opening 36 and upstream of the other opening 37, with the result that the other chamber 35a is formed, from which the opening 36 designed as a line emerges. Downstream of the bottom end of the inner tube 34 and upstream of the vapor-tight connection between the pipeline 1 and the inner tube 33, the chamber 35b also has an opening 37 in the form of a line.

In the pipeline 31, which according to FIG. 1 is the underflow line carrying steam between the high-pressure turbine 1 and the pre-separator 3, the water flows in large part in the vicinity of the pipe wall. This already existing phase separation in the flow is separated in the annular gap opening 32, the dimensions of which are selected such that the flow through the annular gap 32 remains isokinetic.

Because the inner tube 33 is in the form of a Laval nozzle 33a, the speed of the annular gap 32 is reduced downstream Separated water / transport steam mixture This has the consequence that, for example, a wave flow calms down into a stratified flow, so that an internal phase separation of this mixture can easily be carried out in the space 35 through the gap-forming inlet opening of the inner tube 34. While the transport steam is drawn off through the opening 36, the water flows out through the opening 37.

FIG. 3 shows a further pre-separator 3. Compared to the pre-separator from FIG. 2, the pipeline 31 is not bulged here. The intermediate space 35 is therefore naturally smaller and downstream of the annular gap opening 32, the internal phase separation between water and transport steam does not occur due to peeling by attaching a further gap-forming inner tube. The inner tube 38 provided here is open at the bottom and it divides the intermediate space 35 only into two chambers 35a, 35b communicating with one another. The inner tube 38 is connected in a vapor-tight manner upstream of the opening 36 to the pipeline 1. The water / transport steam mixture which relaxes downstream of the annular gap opening 32 flows through the chamber 35a, the phase separation of the mixture having been created after it has passed so far that the transport steam can now flow through the chamber 35b in the counterflow direction to the opening 36. The water, however, flows out through the opening 37.

As shown in Fig. 4, this pre-separator has three chambers 35a, 35b, 35c. The inner tube 39 forms the continuation of the pipeline 31 from the beginning of the bulge. This extends up to the outlet of the laval nozzle-shaped section of the inner tube 33 and there it is provided with openings 41 arranged in the circumferential direction. These openings 41 are in turn encased in a further inner tube 40, which fills the function of a baffle.

If the separated water / transport steam mixture now flows out of the openings 31 via the chamber 35a, it bounces off against the inner wall of the inner tube 40, with the effect that the phase separation is now largely mechanical. While the water can flow out through the opening 37, the transport steam flows out through the opening 36.

The subsequent installation of the pre-separator according to the invention on existing systems can easily be accomplished by cutting out a piece of pipeline 31 and using the desired pre-separator variant in its place.

The pre-separators should preferably be installed vertically.

Claims (3)

1. Preseparator for pipework carrying a two- phase mixture, in particular for separating water from the working steam, which is led from one turbine part via a pipework to another turbine part, into a consumption unit or into a heat sink, the pipework (31) having at least one inner pipe (33) narrowing the cross-section, characterized in that an isokinetically dimensioned annular gap opening (32) is present between the inlet flow end of the inner pipe (33) and the pipework (31), that at least one further inner pipe (34, 38, 39, 40) downstream of the annular gap opening (32) between the inner pipe (33) and the pipework (31) divides the intermediate space (35) into at least two chambers (35a, 35b, 35c), that one opening (36, 37) for the removal of transport steam or water is available from each of at least two of the chambers (35a, 35b), and that the pipework (31) is closed in a steam-tight manner downstream of the last opening (37) relative to the chambers mentioned for the removal of water.

2. Preseparator according to Claim 1, characterized in that the inner pipe (33) narrowing the cross-section has the shape of a Laval nozzle (33a).

3. Use of the preseparator (3) according to Claim 1 in a saturated steam turbine installation, the preseparator (3) being located downstream of the high pressure turbine (1) and upstream of at least one further water separator (4) of arbitrary design installed upstream of a reheat superheater (5).

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