AU1481400A

AU1481400A - Surface condenser

Info

Publication number: AU1481400A
Application number: AU14814/00A
Authority: AU
Inventors: Francisco Blangetti
Original assignee: ABB Alstom Power Switzerland Ltd
Current assignee: General Electric Switzerland GmbH
Priority date: 1999-02-04
Filing date: 2000-01-31
Publication date: 2000-08-10
Also published as: EP1025892A1

Description

o oeo, oe.• a **a 1..

0 *a at*** *L •o *ee •go.« *o *Q e

AUSTRALIA

Patents Act 1990 ABB ALSTOM POWER (Schweiz) AG

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Surface condenser The following statement is a full description of this invention including the best method of performing it known to us:- Technical field The invention relates to a surface condenser, as described in the preamble to claim 1, in which water to be treated is introduced into the condenser above the tubed zone and degassed in the process.

Prior art Such surface condensers are used, particularly in steam power stations, for the degassing and heating of condensate or make-up water. The water to be treated is sprayed over tube bundles inside the condenser. The basic philosophy for the injection over 15 bundles is based on the utilization of the tube assembly as an exchange apparatus. The contact period of the injected water with the steam, or the residence period in the steam space, is then extended so that the thermal and kinetic material exchange procedures have sufficient time to act. The time varies between 5 and S* 10 seconds, depending on the size of the tube bundles o* *and the steam velocity.

The strict requirements for a low oxygen content in the condensate demand special solutions, particularly when large quantities of water have to be treated. The manner described of spraying water over bundles can only be used where the total liquid loading, i.e. condensate and injected water, does not exceed a certain limit in terms of the exchange surface of the condenser. This limit lies at approximately to 20 g per m 2 and per s. The result of an excessive injection is that the water is indeed effectively degassed but the procedure then causes an increase in the pressure losses over bundles on the steam side and therefore a deterioration in the condenser vacuum. The pressure losses cause a reduction in the thermal performance of the condenser. The degassing is therefore obtained at the cost of a smaller k value.

It is known, from EP 0 561 012 B1 on which the 2 invention is based, to allow the water to be treated to slide down, as a film, on a vertically extending side wall of the surface condenser and to secure the degassing while it slides down the side wall. In this way, the side wall surface is used in order to form a water film. In many cases, however, the available condenser wall length is not sufficient to deal with the total mass flow at a maximum trickling mass flow of approximately 3.5 Furthermore, the walls in some condenser concepts are inaccessible, or only accessible with difficulty, or are just badly constructed so that they do not permit development of a descending film.

15 Sunummary of the invention The invention attempts to avoid these disadvantages. It is based on the object of creating a surface condenser which permits more effective degassing without large-scale technical outlay.

This is achieved, in accordance with the invention, by a surface condenser with the features of .claim 1.

In this surface condenser, an additional wall which extends at least approximately vertically is .25 arranged in the region of a central passage or in the region of a plurality of central passages, both wall surfaces of this wall being subjected to a water film by the appliance for introducing the water to be treated. The water, which is applied in-the form of two water films, slides downward along the additional wall and is degassed along the distance traveled by the film. This degassing takes place by the water in the water films coming into intimate contact with the steam flowing around the tube bundle adjacent to the wall.

The actual exchange of material and heat is achieved during this intimate contact.

Because of the introduction of the additional wall in the region of the central passage between two tube bundles, it is now possible to make additional -3 surfaces available for the formation of a water film and to provide both sides of it with a film so that the surface area of the water film available, in accordance with the invention, can be approximately doubled as compared with the known steam condenser.

It is expedient that the appliance for introducing the water to be treated should have a container configured in a longitudinal and box-shaped manner, the water to be treated being fed into the container. A continuous slot in the longitudinal direction, through which the additional wall is introduced, is present at the lower end of the container.

The slot is dimensioned in such a way that 15 narrow passage openings, which extend in the longitudinal direction, appear on both sides of the wall; the water can flow away in a controlled manner through the passage openings so that the water film is formed in an adhering and stable manner on both sides of the wall.

It is, furthermore, advantageous for the container configured in a longitudinal manner to be configured so that it contracts in cross section, for example in V-shape, at least in the region of the slot.

25 This leads, in a construction of simple design, to a uniform passage of the water to be treated through the opening fixed by the slot and the wall and this ensures the uniform nature of the water films and, in consequence, uniform degassing of the water.

Finally, the fact that the length of the container corresponds to the length of the additional wall, and that the slot in the container accommodates the complete length of the wall, has the effect that the additional wall is completely covered by a water film on both wall surfaces and, in consequence, the maximum surface area of the water is utilized on the additional wall and particularly efficient degassing is achieved.

It is particularly expedient to provide the 4 container configured in a longitudinal manner with a tube for supplying the water to be treated, which tube extends in the longitudinal direction and is provided with a plurality of openings through which the water to be treated emerges. These openings are uniformly distributed over the length of the tube. This ensures that the water is fed in so that it is uniformly distributed over the total length and therefore within the total region of the container and so that balancing flows in the longitudinal direction, which could impair the formation of optimum trickling films, are avoided.

It has, eventually, proved particularly advantageous to provide a level indicator in the container for the reservoir of water to be treated.

Because the quantity and the velocity of the water to be treated, which emerges through the slot, depend on 0 0.

the water level in the container, and because this directly affects the flow resistance of the water film and the quality of the degassing, it is expedient to influence the water level in a deliberate manner, i.e.

to increase or, if required, reduce the quantity of the water to be treated which is supplied by using the level indicator. A supply, appropriate to the current demand, of water to be treated is consequently provided S 25 and optimized process control and degassing are achieved.

It has, eventually, proved advantageous to configure the container configured in a longitudinal manner so that it can be vented. This ensures that the water in the container, which is to be treated and degassed, can no longer come in contact with air after venting because it is located in the condensation space and, therefore, cannot take up any additional oxygen or similar gases which would have to be withdrawn subsequently from the water by degassing according to the invention.

The air desorbed from the water, by expansion degassing of the water when it is subjected to the condenser pressure, is led through a gap in the 5 condensation space, from which this air is led through an air cooler present in the bundles and is finally removed from the condenser by vacuum pumps. The kinetic material degassing therefore takes place exclusively in the descending film.

It is, furthermore, advantageous to provide the additional wall with a plurality of balance openings in the region above the slot and, in particular, to distribute these over the length of the container.

These balance openings prevent or reduce balancing flows, of the water to be treated, in the container near the slot. This achieves the effect that the water to be treated is, as far as possible, undisturbed by balancing flows when passing through the passage 15 openings. This markedly improves the formation of trickle films.

The height of the descending film hF[m] (and therefore of the vertical wall) depends on the degassing necessary. As a general rule, the following relationship applies: hF 0.95*ln (xO2,E/xO2,A) where xO2,E is the mass proportion of the dissolved oxygen at inlet *0 00 25 xO2,A is the mass proportion of the dissolved oxygen at outlet S"Brief description of the drawing An embodiment example of the inv-ention, with a plurality of tube bundles, is represented diagrammatically in the drawing. In this: Fig. 1 shows a section through the surface condenser and Fig. 2 shows an excerpt from Fig. i, with the appliance for introducing the water to be treated.

Only the elements essential to understanding 6 the invention are shown. Not shown are further subassemblies of the installation, for example the steam supply and the water supply, the fastening of the condenser casing onto the turbine casing, the support plates for the condenser tubes and the like.

Method of implementing the invention Surface condensers are known with a part-bundle type arrangement of cooling tubes through which water flows and which are decisive for the box-type basic shape of the casing, which has a rectangular plan view in the present case. The casing forms the outer boundary of the steam space of the condenser and is composed of the side walls 1 and the tube plates 2, the 15 side walls comprising a condenser floor 12 and a condenser cover 13.

The individual tube bundles, which consist of up to 4,000 cooling tubes each and which can reach a height of 5 m, are guided, in the longitudinal direction of the tubes, in support plates (not shown) o These cooling tubes are themselves welded and/or rolled into the tube plates 2 at both their ends. Water chambers, which collect the cooling water and guide it into the other water boxes via the tube bundles 4 through the steam space 3, abut the tube plates 2.

The steam flows into an elongated condenser throat via an exhaust steam connection (not shown) by means of which the condenser is supported on the turbine. The best homogeneous flow field possible is generated in the condenser throat so that a clean flushing with steam around the bundles 4 arranged downstream can be undertaken over the complete length of said bundles. In the steam space 3, the steam is distributed by flow ducts. These contract in the flow direction in such a way that the flow velocity of the steam in these ducts is approximately constant and/or is even accelerated. The steam flows through the bundles with little resistance due to the small row depth. In order to keep the conditions in the flow 7 ducts constant or to achieve increasing steam velocity, the tube bundles 4 in the condenser are arranged adjacent to one another in such a way that flow ducts occur between them which, in section, appear to have a similar order of magnitude as the tube bundles 4 themselves. These flow ducts between the tube bundles 4 are referred to as central passages Such a condenser has the advantage that, due to the open arrangement of the tube bundles 4, all the tubes of a tube bundle 4 are subjected to steam without any noticeable loss of pressure. On the other hand, the requirement for an at least approximately uniform thickness of the total tube bundle 4 requires a relatively high installation height of the tube bundle 4. The outstanding suitability of this tube bundle concept for large condensers in which a plurality of tube bundles 4 are arranged adjacent to one another so as to form central passages 5 is a result of this.

After achieving the maximum specified velocity in the steam space 3, the steam is retarded down to zero velocity in the central passage 5, with a simultaneous recovery of pressure. This is achieved by configuring the lower part of the central passage 5 so that it is divergent. At this point, it should be 25 noted that the widening of the central passage 5 does not necessarily have to be optically recognizable because of the increasing reduction in the mass flow.

The essential feature is that the residual steam flowing to the condenser floor 12- generates a stagnation pressure there. By this means, the steam is deflected and therefore also supplies the lower parts of the tube bundles 4 completely. The increase in temperature caused by the stagnation pressure is to the benefit of the condensate flowing down from tube to tube because, if it has been cooled to less than saturation temperature, it is reheated. This secures two advantages: there are no thermodynamic losses due to undercooling of the condensate and 8 the oxygen content of the condensate is reduced to a small amount.

In operation, the steam condenses on the tubes and the condensate drips down toward the condenser floor 12 and, in fact, into a condensate collection vessel arranged on the condenser floor 12. From there, it passes into a 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 occurs in particular during the drainage of preheaters, is now fed into an appliance 6 for introducing the water to be treated above the tube bundles 4. The appliance 6 is associated with an additional wall 8 in the region of 15 the central passage 5 and generates a water film 7 on both wall surfaces of the additional wall 8, so that .0.very efficient degassing of the water to be treated is achieved by the steam flowing along the central passage The additional wall 8 extends essentially from the condenser cover 13 through the steam space 3 in the region of the central passage 5 as far as the condenser floor 12. The appliance 6 is arranged at the top end of the additional wall 8 in a recess in the condenser S 25 cover 13 and closes the latter in a gas-tight manner.

At its lower end, the appliance 6 has a slot 10 through which the additional wall 8 is introduced. The dimensions of the slot 10 are selected in such a way that there are narrow through-openings- 10a, 10b which extend in the longitudinal direction on both sides of the wall 8 and through which the water can flow down in a controlled manner and in such a way that a water film 7 occurs on both sides of the wall 8. A turbulent flow condition is reached after the film has traveled for a short distance, with the water film 7 adhering to the wall 8.

While it flows down over the wall 8, this film 7 is in intimate contact with the steam which is located in the region of the central passage 5 and is 9 degassed by this steam. The appliance 6 and the wall 8 are configured in such a way that a preferred trickling flow of between 1.5 and 3.5 kg/(ms), ideally occurs.

The appliance 6 is provided with a container 9 into which the water to be treated is fed via a tube 11. A hydrostatic pressure of defined magnitude is set by the quantity of water in intermediate storage. The trickling flow can be increased or reduced as a function of the hydrostatic pressure. The level in the container 9 is used as a measure of the hydrostatic pressure, this level being measured by a level indicator (not shown here) The level of the water to be treated is 15 indicated in Fig. 2 as a wavy line or as a broken wavy fee* line.

0 Because of the additional wall 8 which passes through it, the slot 10 forms two through-openings o10b, through which the water to be treated passes from 0 the container 9 and forms the two water films 7.

Balance openings 14 are arranged in the wall 8 of the e g.

container 9 in the region above the slot 10, or above the through-openings 10a, 10b. In addition, openings 15 are present along the tube 11 so that the water 25 supplied can flow down in an optimally uniform manner.

The container 9 is provided with a removable :container cover 9a by means of which, in a simple manner, maintenance, repair and cleaning of the container 9 is provided.

An open edge-gap occurs between the container cover 9a and the container 9. It is used to balance the pressure with that in the condenser and, at the same time, permits the escape of the desorbed air which, in the case of saturated air, can occur due to the expansion degassing.

The container 9 of the appliance 6 is configured so that it contracts in V-shape in its lower region, in the direction of the slot In contrast to a realization of water films for 10 degassing on the side walls, the configuration in accordance with the invention of the additional wall 8 in the region of the central passage 5 displays an increased degassing efficiency. This is because the steam does not have to initially penetrate through the tube bundles 4 as far as the side walls 1 and only there is it possible for it to be used for the final degassing.

In addition, the concept according to the invention permits the low-cost retrofitting of existing surface condensers, whose degassing efficiency can be increased substantially.

*aa.

11 List of designations 1 Side wall 2 Tube plate 3 Steam space 4 Tube bundle Central passage 6 Appliance for introducing the water to be treated 7 Water film 8 Additional wall 9 Container 9a Container cover Slot Through-opening Through-opening 11 Tube 12 Condenser floor 13 Condenser cover 14 Balance opening Opening *o* *oo o* *o ooo

Claims

1. As surface condenser having a casing, which consists essentially of side walls and tube plates whose inner walls bound a steam space having tube bundles which extend in the steam space between the tube plates and which are separated from one another by one or a plurality of central passages having an appliance for introducing the water to be treated above the tube bundles which appliance generates a water film which flows down along a wall and, in the process, enters into intimate contact with the steam flowing around the adjacent tube bundles and is degassed in the process, characterized in that, in the region of at 15 least one central passage an additional wall is arranged which extends at least approximately vertically and with which the appliance for introducing the water to be treated is associated in such a way that both wall surfaces of the additional 20 wall are subjected to a water film and degassing of the water can take place on both wall surfaces The surface condenser as claimed in claim 1, characterized in that the appliance for introducing 25 the water to be treated has a container configured in a longitudinal manner, which accommodates the water to be treated and which, at its lower end, exhibits a slot through which the additional wall is introduced with the formation of side through-openings.

3. The surface condenser as claimed in claim 2, characterized in that the container is configured so that it contracts in cross section, preferably in V-shape, at least in the region of the slot

4. The surface condenser as claimed in claim 2 or 3, characterized in that the length of the container corresponds to the length of the additional wall and the wall passes through the complete length of the slot The surface condenser as claimed in one of 13 99/016 claims 2 to 4, characterized in that the container is configured so that it can be vented.

6. The surface condenser as claimed in one of claims 2 to 5, characterized in that the container configured in a longitudinal manner has a tube for supplying the water to be treated, which tube extends longitudinally in the container and is provided with a plurality of openings over its length.

7. The surface condenser as claimed in one of claims 2 to 6, characterized in that the container configured in a longitudinal manner has a level indicator.

8. The surface condenser as claimed in one of claims 2 to 7, characterized in that the wall has a 15 plurality of balance openings in the region above the slot DATED THIS 31 DAY OF JANUARY 2000 ABB ALSTOM POWER (Schweiz) AG Patent Attorneys for the Applicant:- F.B.RICE CO *m o