FIELD OF THE INVENTION

[0002] This invention relates to an air-cooled steam condenser for turbines having improved efficiency. More specifically, this invention relates to turbine exhaust condensers having banks of aligned elongated tubes receiving steam from the turbine exhaust and an axial fan or fans directing ambient air over the tube banks.

BACKGROUND OF THE INVENTION

[0003] Steam turbines, as invented in 1884, extract thermal energy from pressurized steam and convert the thermal energy into rotary motion of the turbine shaft. Steam condensing systems are commonly used in electric power generating plants, solar collectors, fossil fuel and nuclear reactors generating steam and other steam generating processes where steam turbines are used.

[0004] The general configuration of an air-cooled steam condenser for a steam turbine as disclosed, for example, in U.S. Patent No. 5,305,945 has not changed much in 30 years. The steam condenser includes a horizontal steam delivery manifold delivering steam from the exhaust of the steam turbine, a first set of bundles of aligned elongated tubes having their inlets communicating with the delivery manifold along its length, a second set of bundles of aligned elongated tubes also having their inlets communicating with the delivery manifold along its length, wherein the first and second sets of bundles of aligned tubes extend downwardly and define a V-shaped structure with each bundle of tubes having a condensate collection manifold, and an axial fan located below the V-shaped structure formed by the bundles of tubes, directing ambient air upwardly over the first and second sets of bundles of aligned tubes. Each of the elongated tubes has opposed flat sidewalls and arcuate or rounded ends, wherein the external surface of the tubes is coated with aluminum or an aluminum alloy while the serpentine- shaped aluminum fins are bonded or brazed to the external surface of the tubes as disclosed in the above- referenced U.S. Patent No. 5,305,945.

[0005] As will be understood by a person skilled in this art, the efficiency of this embodiment of turbine exhaust condensers will depend primarily upon the "volume" of the condenser tubes, including the cross-sectional area and the length of the tubes, which is limited by the strength of the tubes. In a typical application where the tubes are formed from mild steel claded with aluminum or an aluminum alloy, the height of the tubes measured between the peaks of the rounded ends is typically 219 mm and the maximum length of the tube is between 10 and 11 meters (m). Further, the prior art turbine exhaust condensers often encounter imposing limits on the overall efficiency due to increased pressure drops experienced at low turbine back pressures. Air-cooled steam condensers tend to accumulate in the tubes some corrosive non-condensable gases, such as carbon dioxide and air. Such trapped gases can seriously corrode the inside of the conventional carbon steel elongated finned tubes. Thus, there has been a long felt need to improve the efficiency of turbine exhaust condensers, particularly air-cooled steam condensers comprising sets or bundles of finned tubes having a lower pressure drop inside the tubes, and thereby improve the overall efficiency of steam turbines and the turbine exhaust condenser of this invention. SUMMARY OF THE INVENTION

[0006] The air cooled steam condenser for condensing exhaust steam from a steam turbine of this invention may be similar in design to the prior art air cooled steam condensers described above. That is, the condenser includes a steam delivery manifold delivering steam from the steam turbine to the condenser, a first set of bundles of aligned elongated tubes extending downwardly at an acute angle relative to the axis of the steam delivery manifold, wherein each elongated tube has an inlet receiving steam from the steam delivery manifold, and a second set of bundles of aligned elongated tubes extending downwardly at an acute angle to the axis of the steam delivery manifold and at an angle to the first set of bundles of aligned elongated tubes, each tube having an inlet receiving steam from the steam delivery manifold, and wherein the first and second set of bundles of aligned elongated tubes form a downwardly opening V-shaped structure. Further, each of the elongated tubes has opposed generally parallel flat sidewalls and arcuate or rounded ends; wherein each of the elongated tubes has an external cladding of aluminum or an aluminum alloy with serpentine- shaped fins bonded to its sidewalls.

[0007] However, the elongated tubes of the air cooled steam condenser of this invention further includes an internal coating or cladding of stainless steel material having a thickness of between 50 and 150 microns and the tubes have a length of greater than 11 m and able to withstand an internal pressure of 0.1 mm of mercury. Further, as set forth above, the air cooled steam condenser of this invention includes an axial fan located below the first and second set of bundles of aligned elongated tubes, directing ambient air upwardly onto the first and second set of bundles of aligned tubes, thereby condensing the steam in the tubes. [0008] The increase in the strength of the condenser tube resulting from the thin internal cladding of stainless steel permits the use of tubes of greater height and length resulting in a significant increase in capacity and cost savings. For example, the height measured between the rounded or arcuate ends of the tubes may be increased about 23% from 219 mm to 270 mm and the length of the tubes may be increased by about 25% from typically 10 to 11 m with the prior art to greater than 12 m with the present invention. Thus, the number of tubes may be reduced by as much as 20% for the same capacity. Further, as will be understood by those skilled in this art, the lower the back pressure, the greater the efficiency of the steam turbine. The increased internal cross sectional area of the tubes allows a lower back pressure of the steam turbine. In one preferred embodiment, the length of the condenser tubes is between 12 and 14 m or up to 16 m or greater. The thickness of the internal cladding of stainless steel in one preferred embodiment is between 45 and 125 microns or about 100 microns. Further, in one preferred embodiment, the height of the elongated tubes measured between the arcuate ends is greater than 220 mm. In another preferred embodiment, the height of the elongated tubes is between 220 and 280 mm or about 270 mm.

[0009] As will be understood by those skilled in this art, various modifications may be made to the disclosed embodiment of the air cooled condenser for condensing exhaust steam from a steam turbine of this invention within the purview of the appended claims and the disclosed embodiment is for illustrative purposes only and does not limit the claims in any way.

BRIEF DESCRIPTION OF THE DRAWINGS [00010] Figure 1 is a side elevation partially broken away of one embodiment of an air cooled condenser for condensing exhaust steam from a steam turbine of this invention;

[00011] Figure 2 is a perspective view of a bundle of aligned elongated condenser tubes as may be used with a condenser of this invention; and

[00012] Figure 3 is a cross-sectional view of the elongated tubes shown in Figure 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT [00013] As set forth above, the air cooled steam condenser of this invention is particularly, but not exclusively adapted to condense steam from the exhaust of a steam turbine. A steam turbine is a mechanical device that extracts thermal energy from pressurized steam and converts it to rotary shaft motion. Steam turbines have been used commercially for over 100 years and are particularly suited to be used to drive an electric power generator. About 80 % of all electricity generated in the world is by use of steam turbines. Air cooled steam condenser systems are commonly used in various industries as set forth above. However, there are limits in the overall efficiency of current turbine exhaust steam condensers due to the higher pressure drops experienced at low turbine back pressure. Further, air-cooled steam condensers for condensing steam from a steam turbine also accumulate corrosive non- condensable gases, such as carbon dioxide and air. Such trapped gases can corrode the inside surface of conventional carbon steel finned tubes as disclosed in the above- referenced patent.

[00014] The embodiment of the condenser 20 as shown in Figure 1 for condensing steam from a steam turbine includes a steam delivery manifold 22, a first set of bundles of aligned elongated condenser tubes 24 extending downwardly at an acute angle relative to the axis "a" of the steam inlet manifold 22 and a second set of bundles of aligned elongated condenser tubes 26 extending at an acute angle to the axis "a" of the steam inlet manifold 22 and, in this embodiment, at an acute angle relative to the first set of bundles of aligned elongated tubes 24. The first and second sets of bundles of condenser tubes are supported on a tent-shaped or V-shaped frame structure 28 as shown in Figure 1. The condenser assembly 20 further includes a axial fan 30 directing ambient air upwardly onto or through the first and second sets of bundles of elongated condenser tubes 24 and 26 as shown by arrows 56. The fan is driven by an electric motor 34 connected to a motor speed reducer 36, rotating the blades of the fan 30. The fan blades are partially enclosed within a fan deck or housing 32 directing ambient air upwardly into the first and second sets of bundles of elongated condenser tubes 24 and 26 as shown in Figure 1. The condenser assembly further includes condensate collection manifolds 38 which receive the condensed water from the steam received through the delivery manifold 22. As will be understood by those skilled in this art, the inlet steam delivery manifold 22 has a plurality of openings which receive the elongated condenser tubes, ambient air is blown upwardly onto or through the tubes, condensing the steam in the tubes and the condensate then flows down the tubes into the condensate collection manifolds 38 and the condensate is then recycled through the condensate return manifolds 38 to a boiler (not shown).

[00015] Figures 2 and 3 illustrate one embodiment of the condenser tubes of the air cooled steam condenser of this invention. Figure 2 illustrates a portion of a bundle of aligned elongated finned tubes 27. As shown, the bundle of tubes include elongated tubes 40 each having generally parallel and generally flat sidewalls 42 and arcuate or rounded end walls 44. In the disclosed embodiment, the flat sidewalls 42 include "serpentine" shaped fins 46 as shown in Figure 2. However, as will be understood by those skilled in the art, the fins 46 may take other shapes.

[00016] Figure 3 illustrates one preferred embodiment of a partial cross- section of the elongated tubes 40, wherein the tubes 40 may be formed of mild steel, for example, as shown at 48 having a thin exterior coating of aluminum or an aluminum alloy 50, particularly where the serpentine-shaped fins 46 are formed of aluminum when brazed or bonded to the base carbon steel core 48 as described in the above-referenced patent. [00017] In the preferred embodiment of the condenser 20 for condensing steam from the exhaust of a steam turbine of this invention, the interior surface of the elongated tubes is clad with a layer of stainless steel as shown at 52 which has several important and unexpected advantages, including providing increased strength, permitting a greater cross-sectional area and length of the tubes, significantly improving the efficiency of the steam condenser and the steam turbine.

[00018] First, as set forth above, the stainless steel interior cladding or coating 52 of the tubes 40 significantly increases the strength of the condenser tubes 40, permitting the use of tubes having a greater height and internal cross-sectional area, thereby improving the efficiency of the condenser 20. For example, in a conventional air cooled steam condenser of this type, the typical height of the tubes measured between the rounded ends is about 220 mm. However, where the tubes have an interior cladding of stainless steel, the tubes may have a height of 270 mm or greater. Further, for an equivalent pressure drop, the length of the tubes may be increased from typically 10 to 11 m to 12 to 14 meters and up to 14 to 17 m or greater where a larger capacity fan is utilized. The interior cladding of stainless steel may be relatively thin, ranging from about 45 to 125 microns or more preferably about 100 microns. As will be understood by those skilled in this art, an internal cladding of about 100 microns of stainless steel does not significantly increase the cost of the elongated tubes 40, but as discovered by the applicant, this internal cladding of stainless steel results in a significant improvement in the overall strength of the elongated tubes, resulting in an increase in the internal cross-section and length of the tubes and thus an increase in efficiency of the condenser and reduced cost. Further, as set forth above, the improved air cooled steam condenser for condensing steam from the exhaust of a steam turbine of this invention also results in improved efficiency of the steam turbine. As will be understood by those skilled in this art, the lower the back pressure of the steam turbine, the greater the efficiency. Thus, because the condenser tubes have a greater internal cross-section and length, the turbine exhaust condenser of this invention can condense steam at a lower back pressure, resulting in an improved efficiency of the steam turbine. [00019] As will be understood by those skilled in this art, various modifications may be made to the air cooled condenser for condensing steam from a steam turbine of this invention within the purview of appended claims. The stainless steel internal cladding 52 of the elongated tubes 40 may be any conventional stainless steel, which also has the advantage of reducing corrosion. Stainless steel differs from carbon steel by the amount of chromium present in the alloy. Carbon steel rusts when exposed to air and moisture. The internal cladding of stainless steel also provides improved corrosion resistance against the presence of non condensable corrosive gasses, such as carbon dioxide and air in water vapor. The exterior aluminum alloy coating 50 may be about 50 microns thick. The width of the tubes measured between the sidewalls may be about 16 to 20 mm. [00020] Having described the invention, it is now claimed as follows.