AU655537B2

AU655537B2 - Method and device for treating water in a surface condenser

Info

Publication number: AU655537B2
Application number: AU35169/93A
Authority: AU
Inventors: Francisco Dr. Blangetti; Cecilia Dr. Smoglie; Gerry Timoney
Original assignee: ABB Asea Brown Boveri Ltd; Asea Brown Boveri AB
Current assignee: Alstom SA
Priority date: 1992-03-16
Filing date: 1993-03-12
Publication date: 1994-12-22
Anticipated expiration: 2013-03-12
Also published as: DK0561012T3; AU3516993A; EP0561012B1; DE59206426D1; ES2089268T3; EP0561012A1

Description

.LL

655537

AUSTRALIA

Patents Act 1990 ASEA BROWN BOVERI LTD

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT ©o r o o 1 t e •r *u Invention Title: "Method and device for treating water in a surface condenser" The following statement is a full description of this invention including the best method of performing it known to us:x i. Technical field The invention concerns a method for treating water in a surface condenser in which the water is introduced into the condenser above the tubed zone. It also concerns a device for carrying out the method.

State of the art Such methods are employed, particularly in steam power stations, for degassing and heating condensate or make-up water. The water to be treated is then sprayed over the tube bundles within the condenser. The basic philosophy for the injection over bundles is based on the utilisation of the tube composite as an exchange apparatus. The contact period between the injected water and the steam, or the residence time in the steam space, is lengthened by this means so that the kinetic thermal and material exchange procedures have sufficient time to act. This time varies between 5 and seconds depending on the size of the tube bundles and the velocity of the steam.

The stringent requirements for a low oxygen content in the condensate demand special solutions where there are large quantities of water to be treated.

This is because the prccedure described above spraying water over bundles can only be employed where the total liquid load, i.e. the condensate and the injected water, referred to the exchange sur1ej of the condenser, does not exceed a certain limit. This limit is approximately 15 The consequences of excessive injection are that although the water is effectively degassed, the procedure causes an increasi in the steam-side pressure losses over the bundles and, therefore, a deterioration in the condenser vacuum.

These pressure losses cause a reduction in the thermal output of the condenser. The degassing is therefore obtained at the cost of a small k value.

2 Summary of the invention It is on this point that the invention is intended to provide help. It is based on the objective of creating a method in which the water to be treated within the condenser is subjected to effective degassing without the condenser vacuum being impaired in the process.

In a first broad aspect, the present invention provides a method for treating water in a surface condenser comprising a plurality of tube bundles, in which method iO water is introduced into a zone of the condenser above the tube bundles, wherein water flows down into a condensate ereceiver in the form of an adhering water film on inner walls of the condenser which extend at least approximately vertically such that the water comes into intimate contact 15 with steam flowing around the tube bundles nearest to the wall during a residence time of several seconds.

In another aspect, the present invention provides a device to carry out the inventive method, said device eo• comprising a distributor tube for the water to be treated extends within the condenser above the tube bundles and along the inner wall of the condenser, which distributor tube is p:ovided with a plurality of holes directed towards the wall.

By means of this measure, an actual material exchanger and heat exchanger is created in the form of a falling film or trickle film when adhered to the condenser wall.

It is expedient for the bottom of the tube to be connected, over the complete longitudinal extension of the tube, in a steam-tight manner to a trough, which has an outlet flow opening adjacent to the inner wall.

Brief description of the drawing An embodiment example of the invention is shown diagrammatically in the drawing using a partial bundle coc'enser. In this: _r 0~i~ i i 2a Fig 1 shows a partial longitudinal section of a surface condenser; Fig 2 shows a section through the condenser along line 2-2 in Fig i.

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rr or r I I I I- Only the elements essential for understanding the invention are shown. Parts of the installation which are not shown are, for example, the steam supply and the water supply, the fastening of the condenser shell to the turbine casing, the support plates for the condenser tubes and the like. The flow direction of the working media is indicated by arrows.

Way of carrying out the invention The partial bundle type of cooling tube arrangement with water flowing through the tubes, known for example from DE 1 501 337, determines the box-type basic shape of the condenser shell, in this case having a rectangular horizontal projection. This shell forms the outer boundary of the steam space of the condenser and is composed of the outer cover, which is formed by the two side walls 1 and the two tube plates 2, together with the condenser bottom 3.

The individual partial bundles 4, which consist of 20 up to 2000 cooling tubes each and which can reach a height of 5 m, are guided in the tube longitudinal direction in support plates (not shown). The cooling tubes themselves are welded and/or rolled at both ends into the tube plates 2. The water chambers 6 are indicated on the sides of the tube plates 2 facing away St €from the steam space The steam flows into the elongated condenser throat via an exhaust steam connection (not shown) by eC means of which the condenser is suspended on the tur- 30 bine. A homogeneous flow field which is as good as possible is generated in this condenser throat in order to undertake effective steam flushing of the downstream bundles over their complete length. The steam is distributed in the steam space by means of flow passages.

These contract in the general direction of the flow in such a way that the flow velocity of the steam in these passages remains at least approximately constant or even accelerates. The free flow of the steam to the external tubes of the partial bundle is ensured. The

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4 steam subsequently flows through the bundles with low resistance due to the small depth of the tube rows. In order to satisfy the condition that the steam velocity in the flow passages should be kept constant or increased, the partial bundles are arranged adjacent to one another in the condenser in such a way that the flow passages occurring between them appear, in the sectional diagram, to have a similar order of size as the partial bundles themselves. Furthermore, the tubes in the rows following one another in series form an intrinsically closed wall which is preferably of the same thickness throughout.

Such a condenser has the advantage that because of the loose arrangement of the partial bundles, all the peripheral tubes of a partial bundle are satisfactorily subjected to steam without any noticeable pressure loss. On the other hand, the requirement for an at least approximately equal "wall thickness" of the tubed partial bundles requires a relatively large 20 installation height of the partial bundle. The result is that this partial bundle concept is outstandingly ruitable for large condensers, in which a plurality of partial bundles 4 are arranged upright adjacent to one another.

After reaching the maximum specified velocity in steam is retarded down to zero velocity with simulj the steam space between each two partial bundles, the taneous pressure recovery. This is achieved in that the lower part of the steam lane has a divergent con- 30 figuration. On this point, it should be noted that the passage widening does not have to be optically recoge nisable because of the continuous decrease in the mass rtri flow. The decisive point is that the residual steam flowing to the bottom of the condenser generates a build-up of pressure there. This deflects the steam and therefore also supplies the lower parts of the bundles. The increase in temperature caused by the build-up of pressure benefits the condensate flowing down from tube to tube in that it heats it again if it I should have cooled down below the saturation temperature. This ensures two advantages: there are no thermodynamic losses due to undercooled condensate and the oxygen content of the condensate is reduced to a minimum.

In operation, the steam condenses on the tubes and the condensate drips down towards the condenser bottom 3 and, specifically, into the condensate receiver 7 arranged under the partial bundles. From there, it passes to the water/steam cycle (not shown).

In accordance with the invention, the water to be treated in the steam space, which can for example be make-up water or condensate which becomes available during the removal of water from preheaters, is introduced into a distributor tube 8. In the case shown, this distributor tube 8 extends along the free side walls 1 and above the partial bundles 4. It has a plurality of spaced-out holes 9 which are directed 4#*t towards the respective wall. The number, distance 20 apart and size of the holes are selected in such a way that the water sprayed towards the wall forms a closed iwater film. As a guideline, it can be stated here that the delivery velocity, referred to the hole diameter, is approximately 2 ni/s. For a water delivery of a maximum of 5 kg/s and per m of wall, the film 12 will S; remain substantially adhering to the wall. It will a"flow down at an average velocity of between 0.7 and 0.9 m/s. This turbulent film, which has a film c •thickness of approximately 1 mm, moves over a drop of a. 30 approximately 5 m because of the high location of the distributor tube. This means that the residence time of the water to be treated corresponds approximately to that which was achieved in the case of the previously usual spraying onto the partial bundles.

In the example shown in Fig. i, the water from the holes 9 first passes into a trough 10. This is a sheet-metal construction which is connected in a steamtight manner to the bottom of the distributor tube and forms an actual film delivery device 11 towards the 6 side wall 1. This delivery device consists of a number of spaced-out holes. Within the trough, the water builds up to a liquid level. This can be selected in such a way that the hydrostatic head occurs which is necessary for the delivery device.

The water flowing down from the film delivery device forms; after a certain starting distance x which is approximately 0.5 m, a fully developed turbulent film 12 which adheres to the wall. While it is flowing down, this film is in intimate contact with the steam flowing between the side wall and the partial bundle nearest to the wall.

As a departure from the arrangement shown, the distributor tube does not need to extend only along the side wall 1; it can, of course, additionally extend along the tube plate 2 so that the free wall parts between the tube bundles can also be used for exchange purposes.

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7 List of reference signs 1 Side wall 2 Tube plate 3 Condenser bottom 4 Partial bundle Steam space 6 Water chamber 7 Condensate receiver 8 Distributor tube 9 Hole Trough 11 Film delivery device 12 Water film x Film starting distance 4 i t tI 156

Claims

1. A method for treating water in a surface condenser comprising a plurality of tube bundles, in which method water is introduced into a zone of the condenser above the tube bundles, wherein water flows down into a condensate receiver in the form of an adhering water film on inner walls of the condenser which extend at least approximately vertically such that the water comes into intimate contact with steam flowing around the tube bundles nearest to the wall during a residence time of several seconds. a2. Device for carrying out the method according to °claim 1, said device comprising a distributor tube for the O water to be treated which extends within the condenser above the tube bundles and along the inner wall of the condenser, said distributor tube being provided with a o plurality of holes directed towards the wall.

3. Device according to claim 2, wherein the bottom of the tube is connected, over the complete longitudinal extension of the tube, in a steam-tight manner to a trough which has a film delivery appliance adjacent to the inner wall. r.

4. Method for treating water substantially as 0 tI r hereinbefore described with reference to the accompanying drawings.

5. A device for treating water substantially as hereinbefore described with reference to the accompanying drawings. DATED this 14th day of October 1994 ASEA BROWN BOVERI LTD Patent Attorneys for the Applicant: F.B. RICE CO. Ik a -7 __I I Abstract In a method for treating water in a surface con- denser, the water is introduced into the condenser above thz tubed zone. The water flows down into the condensate receiver in the form of an adhering water film (12) on the condenser inner walls which extend at least approximately vertically, and, in the process, the water comes into intimate contact with the steam flowing around the tube bundles nearest to the wall during a residence time of several seconds. A distributor tube for the water to be treated extends within the condenser above the tube bundles (4) and along the inner wall The distributor tube is provided with a plurality of holes directed towards the wall. (Pig. 1) t to i S.. Ct C j c C C CCC: "C C