Field

The present invention relates to the field of power plant components. More particularly, the invention relates to an air-cooled condenser for condensing vapor containing non-condensble gases (NCGs).

Background

Air cooled condensers are used in those geographical regions where cooling water for reducing the temperature of heat depleted vapor is not readily available. In air cooled condensers, heat is transferred from the hot fluid that flows inside the tubes to the ambient air by passive or forced air flow on the external side of the heat exchanger tubes. The condensers are configured by a plurality of heat exchanger tubes that are organized into vertically spaced banks of tubes, each of which is connected to an inlet header. The tubes are generally inclined so that the produced condensate flows downwardly to the inlet header and is collected. In many industrial applications, such as for a geothernial power plant, the inlet header receives a mixture of vapor and NCGs.

In the heat exchanger disclosed in US 4,815,296, the second end of each heat exchanger tube is connected to a separate header associated with each bank, through each of which the NCGs are vented to the atmosphere. Although the provision of separate headers for each bank of tubes is intended to prevent equalization of pressure between the banks and the resulting backflow of NCGs, a pressure drop of the NCGs within the lowermost, relatively high temperature tubes resulting from interaction with relatively cold temperature air is nevertheless noticeable. This pressure drop causes the NCGs to be separated from the vapor desired to be condensed and induces stagnation pockets of NCGs within the tubes that reduces the flow of fluid therewithin. The presence of the stagnation pockets reduces the effective heat transfer surface area of the tubes and also leads to corrosion of the tubes. The temperature of the condensate is therefore increased above its designed temperature due to the reduced cooling capability of the tubes, and the thermal efficiency of the industrial process is reduced.

It is an object of the present invention to provide to an air-cooled condenser for condensing vapor containing NCGs that avoids stagnation pockets of NCGs within the heat exchanger tubes, to increase thermal efficiency of the industrial process and to minimize corrosion within the tubes.

Other objects and advantages of the invention will become apparent as the description proceeds.

Summary

The present invention provides A multi-pass air-cooled condenser, comprising a first-pass bundle of heat exchanger tubes into which working fluid containing non-condensable gas (NCG) is introducible at such a velocity to ensure that a NCG portion of said working fluid will remain together with a non-NCG portion of said working fluid even after being air cooled and from which said working fluid is extractable to another bundle of heat exchanger tubes maintaining a temperature of said extracted working fluid close to the condensation temperature of said non-NCG portion, wherein said NCG portion is separable from said non-NCG portion in a final-pass bundle of heat exchanger tubes of said condenser such that the percentage of separated NCGs in said final-pass tubes is significantly greater than the percentage of NCGs in said first-pass bundle.

The present invention is also directed to a multi-pass air-cooled condenser, comprising: two spaced modules each of which includes first-pass bundles of heat exchanger tubes; a central module interposed between said two spaced modules and in fluid communication therewith, wherein said central module includes an upper second-pass bundle of heat exchanger tubes, a lower third-pass heat exchanger tube; a conduit through which NCG-containing working fluid is extractable from each of said first-pass bundles to said second-pass bundle to maintain a temperature of said extracted working fluid close to the condensation temperature of a non-NCG portion of said working fluid; a return header for directing NCG-containing working fluid from said second-pass bundle to said third-pass heat exchanger tube; a vent in fluid communication with said third- pass heat exchanger tube from which NCGs separated within said third-pass heat exchanger tube are dischargeable; and a collector disposed below said central module and said two spaced modules, for gravitationally receiving produced condensate.

The present invention is also directed to a method for condensing NCG- containing working fluid in an air-cooled condenser, comprising the steps of: injecting NCG-containing working fluid into an inlet header of a condenser at a saturation supporting velocity; introducing said working fluid to first-pass heat exchanger tubes; extracting said working fluid from said first-pass tubes so as to maintain a temperature of said extracted working fluid close to the condensation temperature of a non-NCG portion of said working fluid; introducing said extracted working fluid to a subsequent pass of heat exchanger tubes; and in a final-pass heat exchanger tube, causing NCGs to be separated from said working fluid and said non-NCG portion to be consequently completely condensed. Brief Description of the Drawings

In the drawings:

- Fig. 1 is a schematic side cross sectional view of an air-cooled condenser, according to one embodiment of the present invention;

- Fig. 2 is a schematic top view of the condenser of Fig. 1;

- Fig. 3 is a schematic side view of the condenser of Fig. 1;

- Fig. 4 is a schematic side cross sectional view of a module containing a first- pass bundle of heat exchanger tubes;

- Fig. 5 is a schematic side cross sectional view of a module containing second and third pass bundles of heat exchanger tubes; and

- Fig. 6 is a method for condensing NCG-containing working fluid in an air- cooled condenser, according to one embodiment of the present invention.

Detailed Description

The present invention is a multi-pass, air-cooled condenser for condensing hot vapor containing NCGs. While prior art air-cooled condensers are subject to stagnation pockets of NCGs due to the resulting pressure drop of the vapor flowing through the heat exchanger tubes, the condenser of the present invention reduces or just about avoids the occurrence of stagnation pockets by retaining the NCGs together with the non-NCG vapor and extracting the condensate produced in the stages and the vapor circulating in the condenser tubes so as to reduce sub-cooling losses.

The vapor desired to be condensed may be one used for any industrial process insofar as it contains NCGs. Typically but not exclusively, the vapor is heat depleted motive fluid such as an organic motive fluid that has been discharged from a turbine. Alternatively, the NCGs may be gases such as air and carbon dioxide that have been trapped in a working fluid as a result of an industrial process.

Power levels in a geothermal power plant or a waste heat power plant employing the condenser of the present invention generally range from 700 kW to 5 MW, and even as high as 20-100 MW.

Broadly speaking, the NCG-containing vapor is condensed by the method set forth in Fig. 6. The NCG-containing vapor is injected to an inlet header of an air- cooled condenser in step 18 at such a velocity to ensure that a large fraction of the NCG portion will flow together with the non-NCG portion even after being air cooled. After the NCG-containing vapor is introduced to first-pass tubes in step 22 and exposed to a stream of air for cooling the vapor, by forced or passive convection, e.g. in cross flow fashion, the condensate produced from the vapor (about 55% - 60% of the non-NCG vapor) is extracted from the first-pass tubes in step 24 in order to minimize sub-cooling thereof. That is, extraction of the liquid condensate serves to maintain its temperature close to the condensation temperature of the non-NCG portion. By maintaining a velocity of non-NCG vapor, the NCG portion stopped from separating therefrom and forming stagnation pockets as occurs in prior art air-cooled condensers, which would hinder heat transfer and passage of the vapor through the condenser. The NCG- containing vapor is then introduced to one or more subsequent passes of tubes in step 26. In the final-pass tubes, the NCG portion is caused to be separated in step 28 from the non-NCG portion such that the percentage of separated NCGs in the final-pass tubes is significantly greater than the percentage of NCGs in any other passes. The NCGs are then vented in step 30.

Fig. 1 schematically illustrates an air-cooled condenser, generally designated by numeral 1, according to one embodiment of the present invention. Condenser 1 comprises three heat exchanger modules: two spaced modules 3A and 3B each of which including first-pass bundles of heat exchanger tubes, and module 4 interposed between modules 3A and 3B and in fluid communication therewith. Module 4 includes an upper second-pass bundle 5 and a lower third-pass bundle 8. A divider 7 separates second-pass bundle 5 from third-pass bundle 8. Collector 9 disposed below modules 3A, 3B and 4 receives the produced condensate, which is generally recirculated, for example by a pump. After the NCG-containing working fluid desired to be condensed is introduced in parallel to the first-pass tubes, the latter are exposed to upwardly flowing unheated air, the flow of which is induced or forced by means of an air flow generator such as a fan. Due to the high temperature differential between the relatively hot working fluid and the relatively cool ambient air, a considerable amount of the working fluid would normally condense after being exposed to the cooling air, causing the NCGs to remain in the flow of the non-NCG vapor not condensed. Condensation is advantageously minimized by extracting the working fluid from modules 3A and 3B via conduits 6A and 6B, respectively, and is then introduced to central module 4.

Working fluid extraction is carried out by fluid bleeding, gravitation, or by any other means well known to those skilled in the art.

This process is repeated within the second-pass bundle 5 whereby the working fluid exposed to cooling air is extracted to the third-pass bundle or tube 8. The working fluid in the third-pass module 8 is exposed to the cooling air for a significantly greater period of time than the exposure time of the working fluid within the first or second pass bundles, to enable separation of the NCGs.

Condensate, if produced within modules 3A and 3B, flows by gravitation via discharge conduits 10A and 10B, respectively, to collector 9. Likewise, condensate produced in the second-pass bundle 5 is discharged via conduit 11 to collector 9. As the NCGs are caused to separate from the working fluid in the third-pass bundle 8 and then be vented, a large amount of condensate as represented by delta h is allowed to be produced in the third-pass bundle 8 and discharged to collector 9 via conduit 12 as opposed to the condensate discharged from the first- pass bundles.

The tubes within each module may be disposed at an incline with respect to the horizontal, so that if condensate is produced, it will be collected at the bottom of the module. Condensate produced in the second-pass bundle 5 will collected on top of divider 7.

An important aspect of the invention is the presence of two first-pass bundles. When condenser 1 receives turbine exhaust, which is characterized many times by superheated fluid and a large volumetric flow rate, two first-pass bundles are needed to handle the flow. However, when the fluid becomes desuperheated, the volumetric flow rate decreases until condensation occurs, so that a single second- pass bundle and a single third-pass bundle or tube suffice.

Additionally, the use of two first-pass bundles, as opposed to three first-pass bundles used in prior art air-cooled condensers even though they do not provide extraction means, advantageously ensures that the fluid velocity will be increased. That is, a reduced cross sectional area to handle substantially the same volumetric flow rate will induce an increase in the fluid velocity.

It will be appreciated, however, the invention is also applicable when there is only one first-pass bundle.

Fig. 2 illustrates a top view of condenser 1. Vapor is introduced into modules 3A and 3B via inlets 14. The extracted fluid then flows to module 4 by conduits 6A and 6B.

Fig. 3 illustrates the drains from the various modules, by which the condensate is directed to the collector.

Fig. 4 illustrates a partial cross sectional view of module 3A, which is symmetrical to module 3B and may be rectangular. The NCG-containing vapor is introduced into inlet header 15, which may be rectangular. Three vertically spaced tubes 9a-c extend from inlet header 15 to outlet header 16, from which the circulating vapor is able to be extracted. There may also be a plurality of tubes that are laterally spaced from each of tubes 9a-c.

Fig. 5 illustrates a partial cross sectional view of central module 4, which may be rectangular. Module 4 comprises inlet/outlet header 17, return header 19, and four vertically spaced tubes 23a-d, as well as a plurality of laterally spaced tubes, extending from header 17 to header 19. Second-pass tubes 23a-d may be parallel to first-pass tubes 9a-c.

The vapor extracted from the first-pass tubes is introduced into header 17, from which the extracted vapor is transferred in parallel to all of the second-pass tubes. The NCG-containing vapor flowing within the second-pass tubes may also be maintained at a saturation supporting velocity.

Return head 19 is configured to direct, by any means well known to those skilled in the art such as a labyrinth, the vapor extracted from the second-pass tubes at a temperature close the condensation temperature to the single-level third-pass tubes 27, which extend from return header 19 to inlet/outlet header 17, but in an opposite direction as the flow direction of tubes 23a-d. The NCGs are allowed to separate from the non-NCG portion within tubes 27 and are discharged via vent 29.

Headers 17 and 19 may be contiguous to a header of a neighboring module, or may be common therewith. This arrangement therefore facilitates a compact configuration for reliably maintaining a designed condensation temperature with minimum sub-cooling losses by advantageously draining the condensate produced of each stage or pass and extracting the NCG-containing vapor from one heat exchanger module to another.

While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried out with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without exceeding the scope of the claims.