TECHNICAL FIELD

The invention relates to a mixing condenser designed to condensate spent steam in condensation power plants.

BACKGROUND ART

The mixing condensers well-known in the power plant industry have been developed primarily as condensers used in the so-called Heller cooling systems. They work in a way that cooling water chilled in the closed circuit water to air heat exchangers of cooling towers is fed via so-called water film nozzles into one or more vacuum sealed vessels attached to the steam turbine. The steam is condensed on this water film. In the meantime, the water is heated by the latent heat of the steam, and then fed into the water to air heat exchangers again where it is re-chilled. The circulation of water is made by circulating pumps. A water volume corresponding to the steam volume under condensation is returned from the cooling water system to the feeding system and then to the boiler. Since the steam is directly exposed to the cooling water, the quality of water is identical with that of steam. The embodiments of conventional mixing condensers are shown in Figs. 1A, 1 B, and 2A, 2B.

The steam 1 flowing out from the low pressure housing of a steam turbine is passed through a turbine stub and in the case of differing cross sections via a diffusor or confusor to the condenser member shown in a schematic lateral sectional view in Figs. 1A and 2A and in a schematic longitudinal sectional view according to the planes A-A in Figs. 1 B and 2B. In the steam chamber 24 of the condenser members, the steam 1 flows from top to bottom. There is one or there are many parallel water chambers 3 with centre planes perpendicular to the flow direction of steam 1. These water chambers 3 distribute the cooling water 2 returning from the cooling tower. The steam turbine, the condenser body and the steam tube are not shown in the figures. Water is fed into the condenser members via transfer ducts connected to the side wall or bottom thereof. On the two sides of the water chamber 3 water film nozzles 4 spreading water essentially in a vertical plane are arranged in rows of nozzles 25. The cooling water 2 is introduced through these components to the steam chamber 24, where the steam is condensed. The warmed up water film 13 is transferred onto the catch plates 5 located in parallel with the water chambers 3, where it flows into the water chamber 23 of the condenser in the form of a water curtain. From here, it is fed via the water outlet 28 (see Fig. 7A) to the cooling water pumps (not shown) and then again to the water to air heat exchangers of the cooling tower. Conventionally, the so-called aftercoolers 6 condensing the remaining 5 to 10 % of the steam are formed in the bottom part of the water chambers 3. The aftercoolers 6 receive the cooling water representing again 5 to 10 % of the full transferred water volume from the water space of the water chambers 3 above them, generally via nozzles or so-called transfer pipes. Contrary to the condensation section 40 in which the water flows crosswise to the steam, the aftercooler 6 has a counter cross flow design. The remaining 5 to 10% steam flows into the aftercooler 6 horizontally via the discharge duct 34 above the water surface 11 of the water space 23, and then turning upwards, it proceeds in a counter cross flow towards the air discharge 8 via the waterdrop curtains 9 generated on the perforated trays 7. Most of the steam is condensed, and the remaining approx. 0.015% steam volume is fed with the air to the vacuum pumps through the air discharge 8. The structure of well-known mixing condensers is designed so that the aftercooler 6 is always integrated with the water chamber 3. In the technical field, an aftercooler is always required. This is because in case in the condensation phase the intention is to condensate the whole steam volume, the partial pressure of non-condensing air inevitably entering the machine units under vacuum would increase continuously, which would lead to the ceasing of the vacuum with time. This is why it is necessary to discharge the air continuously, which may not take place without discharging the vapour as well. The aftercooler serves for condensing this remaining vapour. The mixing condenser shown in Figs. 2A and 2B differs only from the one depicted in Figs. 1A and 1 B in that there the cooling water 2 does not flow to the water chambers 3 from the side, but it flows from the bottom to the top through the bottom plate 17 and the water space 23 of the condenser. Accordingly, the aftercooler 6 is arranged on the two sides of the water chamber 3. The advantage of this arrangement is that the water chambers have a lower resistance than in the case of water chambers fed from the side. The other benefit is that the height difference between the water surface 11 and the water film nozzles 4 can be smaller.

In practice, the space below the turbines is very much limited, but an appropriate height is required for using mixing condensers. For example, in the embodiment according to Figs. 1A and 1 B, the height of the aftercooler 6 is 60 to 80 cm, and the distance between the aftercooler and the water surface 11 is added to this, which distance may not be shorter than 20 to 30 cm. However, it is desirable to reduce the height of mixing condensers, because even with a small reduction in height, the saving in weight and pump power is substantial, and hence a large cost saving is achievable. The disadvantage of prior art mixing condensers is that they have a relatively large height, to which the aftercooler below the water chamber greatly contributes. In addition, an aftercooler linked to a water chamber requires a substantial planning and geometrical effort, and in prior art solutions it is not possible to independently control the capacity of the aftercooler. Prior art mixing condensers have also further disadvantages, such as a complicated structure, a considerable flow resistance and a lack of ability of separation and circulation of gas-free water in independent water circuits.

DESCRIPTION OF INVENTION

It is a main object of the invention to eliminate the disadvantages of prior art mixing condensers. It is another object of the invention to create a mixing condenser with a reduced height. A further object of the invention is to provide a solution which has a low flow resistance, simple structure and efficient exhaustion. It is also an object of the invention to provide an apparatus appropriate for separating the gas-free water.

The objects of the invention have been achieved by the mixing condenser according in claim 1. Preferred embodiments of the invention are defined in the dependent claims.

BRIEF DESCRIPTION OF DRAWINGS

The preferred embodiments of the invention will be described by examples with reference to the drawings, in which

Figs. 1A, 1 B and 2A, 2B show schematic lateral sectional views and longitudinal sectional part-views of two prior art solutions,

Fig. 3 shows a schematic lateral sectional view of a preferred embodiment of the invention,

Figs. 4A and 4B show a schematic lateral sectional view and a longitudinal sectional part-view of another preferred embodiment of the invention,

Figs. 5A and 5B show a schematic lateral sectional view and a longitudinal sectional part-view of a further preferred embodiment of the invention,

Fig. 6 shows a schematic structural view of a mixing condenser consisting of three condenser members,

Fig. 7 shows a schematic view of a low pressure unit fitted with a mixing condenser according to Fig. 6,

Fig. 8 shows a schematic lateral sectional view of a further preferred embodiment of the invention, and

Fig. 9 shows a schematic lateral sectional view of a preferred embodiment of the invention fitted with an internal aftercooler.

MODES FOR CARRYING OUT THE INVENTION

In accordance with Fig. 3 and other figures, the invention is a mixing condenser which has at least one condenser member 39 comprising a steam space 24, and a water chamber 3 which provides cooling water 2 for condensing the steam 1 flowing downwards in the steam space 24, with nozzles 4 arranged on the water chamber 3 and ejecting cooling water 2 essentially crosswise to the flowing direction of the steam 1. Opposite to the nozzles 4, a catch plate 5 receiving the cooling water heated up by the steam 1 and ejected by the said nozzles is arranged. Furthermore, the mixing condenser comprises a mixture chamber 15 which is designed to collect the air enriched air and steam mixture and has its opening in the vicinity of the water surface 11 of the water collected in the bottom of the condenser member 39. The separate aftercooler designed for condensing the steam content of the steam and air mixture discharged from the mixture chamber is not depicted here. In one condenser member 39 there can be one or more water chambers 3 surrounded by the catch plates 5. In the mixing condenser according to the invention the aftercooler 6 is formed separately from the water chamber 3 which provides the cooling water 2 for condensing the steam 1 flowing downwards. The separated design implies that the aftercooler 6 is not below the water chamber 3 in a direct communication therewith, but it is located within or outside the condenser member 39 in such an arrangement that discharging the steam and air mixture from the vicinity of the water surface 11 does not increase the height of the mixing condenser. Fig. 3 shows such an arrangement where in order to reduce the height of the condenser, the aftercooler 6 is not located below the water chamber 3, but the steam and air mixture remaining after the cross flow condensation section 40 is discharged via the mixture chamber 15, and the condensation is continued in the separate aftercooler 6. Here so the mixture chamber 15 designed for collecting the air enriched air and steam mixture is formed below the water chamber 3 which provides the cooling water 2 for condensing the steam 1 flowing downwards. The aftercooler 6 can be another condenser member 39, a conventional aftercooler 6 in another condenser member 39, a surface condenser or even a direct-contact condenser.

Figs. 4A and 4B show such a particularly preferred embodiment of the invention, where the discharging mixture chamber 15 designed for collecting the air enriched air and steam mixture is located opposite to the water chamber 3, below the catch plate 5. In this case, the cooling water 2 does not enter the water chambers 3 from the side, but it flows from the bottom to the top through the bottom plate 17 and the water space 23 of the condenser. The inlets and outlets of the cooling water 2 are provided by the water transfer ducts 21.

It is a great advantage of this embodiment that through its application the height difference between the lowest row of nozzles 25 and the water surface 11 may be reduced to one half of the largest width of the vertical water film ejected by the nozzle 4.

In order that the waterdrop curtain pouring down from the catch plate 5 should not make for the steam 1 to escape through the discharge duct 34 difficult, the baffle plates 10 preferably converging downwards in pairs on the catch plate 5 may be applied, to guide and collect the waterflow curtain flowing down on the plate into water jets 14. As shown in Fig. 5B, draining ducts 26 may be applied to conduct the water jets 14 collected by the baffle plates 10 from the bottom edge of the catch plates 5 below the water level of the condenser.

The particularly preferred embodiment shown in Figs. 5A and 5B comprises an actuator, preferably a floating element or a water level sensor controlled mechanism 20 which keeps a constant distance between the mixture chamber 15 below the catch plates 5 and the water surface 11 of the water collected in the bottom of the condenser member 39. The mixing condenser consisting of the three condenser members 39 and shown in Fig. 6 also includes such an embodiment.

It is well known that if the steam turbine has several outlets, then the total cost of the cooling system may be reduced even by 20 to 25%, if separate condenser members 39 are built for these outlets, which are connected in parallel on the steam side and in series on the water side. This method is called the series connection of condensers. Figs. 6 and 7 illustrate a three-stage series connection. It can be seen that in this solution in addition to the above mentioned weight reduction and energy saving, the biggest advantage of the approach according to the invention is that it is easier to dispose below the turbine table the condenser members which would require a greater height in a parallel connection. In this solution, the cooling water 2 enters via the water inlet 27 the highest located condenser member 39 which has the lowest temperature and hence the lowest pressure, and then from here it is passed through the water transfer ducts 21 to each of the higher pressure condenser members 39. In such an approach it is not necessary to have an aftercooler 6 in each condenser member 39. Instead, it is a satisfactory solution to guide via the steam transfer ducts 16 the steam and air mixture remaining in the condenser members 39 opposite to the flow direction of cooling water, from the highest pressure lower located condenser member to the steam space 24 of each of the lower pressure condenser members 39. This is enabled by the fact that the remaining 5 to 10% steam and air mixture fed into the conventional aftercooler, values evolved in the practice, can be reduced to even 1 %. Fig. 6 is rather a circuit diagram, which depicts the mixture chambers 15 designed to collect the remaining steam and located in each condenser member 39, as well as the steam transfer ducts 16 which ensure steam transfer among the condenser members 39. The steam and air mixture remaining at the very end is removed through the air discharge 8. Of course, the aftercooler 6 can be disposed in any of the condenser members 39, preferably in the last one, and by means of this aftercooler, the volume of steam escaping through the discharge can be decreased to the minimum, that is to approx. 0.015%.

In a series connection, the pressures of cascaded condenser members 39 are not identical. This means that since the water is introduced gravitationally to a lower member from an upper one, the water level of the upper member with a given moved volume of water depends on the pressure difference. Since the pressure difference also depends on the temperature and the turbine load, a different water level belongs to each operating condition. This variation in the water level can be handled by the solution shown in Fig. 5A, where the catch plate 5 and all components assembled therewith are moved up and down following the water level. Hence, the catch plate 5, the associated mixture chamber 15 and other structural elements like the baffle plates 10 and the draining ducts 26 can be moved up and down following the water level by means of a passive floating element or a floating element controlled active actuating mechanism 20. Fig. 7 clearly shows the conduits 29 of the steam entering the low pressure housing, the turbine stubs 32 connected to the turbines 33 in the low pressure housing and the condenser members 39 connected to the turbine stubs 32, with their inlets and outlets.

A further preferred embodiment is shown in Fig. 8, where the water of the topmost row of nozzles is fully or partially collected in a separate upper water collecting duct 37. This has its significance, because the degassing effect of the condenser is most effective on this row of nozzles. The water collected here has the lowest concentration of the gases forming the air, each of them having an unfavourable effect on the corrosion life of the steam boiler. This degassing method works especially well when the water of the upper water collecting ducts is separated from the other cooling waters, passed through the condenser members 39 in serial connection. Of course, this can only be implemented if the upper row of nozzles has a separate water chamber illustrated by a separating plate 30 in the drawing. In this case, using three-stage cascading, a three-stage degassing process can be realized. Another benefit of the approach shown in Fig. 8 is that if, for example, the water of the first row of nozzles is collected in a separate upper water collecting duct 37, one level difference of condensers, and when the water of two or more rows is collected, two or more height differences of row of nozzles can be saved.

Fig. 9 shows such an embodiment where the aftercooler 6 is formed below the catch plate 5 and comprises

- an aftercooler water chamber 41 arranged above the discharge mixture chamber 15, and

- nozzles 4 arranged on the bottom surface of the aftercooler water chamber 41. Consequently, in this solution the aftercooler 6 receives the cooling water via the separate aftercooler water chamber 41. Although the aftercooler 6 is within the condenser member 39, due to its special location it does not increase the height of the condenser member 39. On the bottom surface of the aftercooler water chamber 41 , nozzles 4, transfer pipes or transfer ducts are arranged, which ensure the condensation of the remaining steam by a counter flow waterflow curtain 9 or by a conventional perforated tray counter cross flow waterdrop curtain 7.

The mixing condenser according to the invention may of course be designed not only in accordance with the preferred embodiments shown by way of example, but also in other ways. The mixing condenser may consist of the necessary number of members, and one member may include the necessary number of water chambers. The air enriched remaining steam and air mixture can be guided into aftercoolers separated from the water chambers, into a separate mixing condenser, a surface condenser or a direct-contact air condenser, which is then switched to a steam and air mixture discharge. Therefore, the remaining steam is flows into a space separated from the water chambers, and this said space may also be the steam space of another condenser member providing for full condensation, where under the impact of the water ejected by the water film nozzles, the steam condensation is interrupted when reaching the discharge duct.

It can be seen that the mixing condenser according to the invention has a relatively simple structure, does not cause significant flow resistance and certain embodiments may even be suitable for separating degassed water, or for circulating it in separate water circuits.

Consequently, the invention is not limited to the embodiments described in details, but further modifications and variants are possible within the scope of protection defined by the claims.