Patent Publication Number: US-2012023940-A1

Title: High performance orc power plant air cooled condenser system

Description:
The present application claims priority to U.S. provisional application Ser. No. 61/369,489, filed on Jul. 30, 2010, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to industrial, flat-coil, air-cooled heat exchanger systems, and more particularly as an air-cooled condenser system for an Organic Rankine Cycle (ORC) power plant. 
     Thermal power plants traditionally utilize the Rankine steam cycle to generate electric power. While a variety of modifications have been used in practical applications for improvement of system performance, the basic Rankine cycle  100 , illustrated in  FIG. 1   a , is a closed thermodynamic cycle of which the working fluid experiences at least four stages: evaporation in an evaporator  102  by absorbing heat  104 , expansion in an expander  106 , such as a turbine, to drive a generator  108  in order to create power, heat exchange in a condenser heat exchanger  110  to release heat and condense the working fluid from a vapor to a liquid, and pump  112  to increase the pressure of the liquid from the condensing pressure (lower pressure) to the evaporator pressure (higher pressure). The working fluid in a Rankine steam cycle is water. An ORC system employs the same principle as a Rankine steam cycle. The difference between these two systems is that an ORC system, which is generally used with a low-temperature heat source, uses an organic working fluid as opposed to water. Selection of the working fluid depends on heat source property, working fluid thermodynamic properties, and operating conditions. 
     Heat  104  may arise from a number of sources. In traditional power plants, heat  104  is supplied from burning of coal or other fuels. Alternatively, heat may be generated from a nuclear reaction. More recently, heat may be supplied from super heated fluid, such as steam or brine, captured from a geothermal reservoir. 
     Traditional air cooled heat exchangers, such as air cooled condensers, have been manufactured for many years for use in steam power plants. Such air-cooled heat exchangers typically employ an A-Frame style of construction where a series of fans force air up through two bundles of condenser coils mounted in an A arrangement (as shown in  FIG. 1   f ). For air-cooled condensers used in ORC plants, the prior art has utilized flat condenser coils bundles with multiple, close-coupled fans dedicated to each condenser coil bundle, as illustrated in  FIGS. 1   b ,  1   c ,  1   d  and  1   e . These ORC air-cooled condensers utilize single-unit, factory-built modules that include a frame  10  supporting a single heat exchanger coil bundle  12  and one or more fans  14  fluidly connected to the coil bundle by a plenum  16 . As shown, the fan deck is typically supported below the condenser coil bundle and pushes air through the bundle using forced draft air flow. The fans may also be above the heat exchange coil bundle and draw air through the coils of the bundle in an induced draft configuration. In either configuration, forced or induced draft, these single-unit modules are very heavy since the frame is typically structural steel, the condenser coils, including metal finned tubing, and the plenum are typically constructed of heavy gauge steel. The design and fabrication materials are selected in part to withstand shipping vibration forces for these factory built fan/coil modules. Furthermore, as shown specifically in  FIG. 1   b , the diameter of the fan/fans is limited to no more than the width of a condenser coil bundle so that the fan/fans and the condenser coil bundle may be shipped as an assembled unit. Moreover the fan/fans are positioned in close proximity to the condenser coil bundle so as to minimize height and weight of the assembly for shipping, and the fan stacks are typically square edged and short such that they provide little aerodynamic efficiency. In addition, the amount of air per square foot of coil face area (coil face velocity) is typically comparatively high so as to minimize the coil surface area required for cooling and thus the number of fans required. While these high velocities reduce cost and improve the “throw” of the hot air exhausted so as to reduce the amount of recirculated air, this high velocity also imposes a high fan power cost. Typically, a plurality of these essentially independent modules are coupled together and supported above the ground by heavy I-beam steel structures in order to allow sufficient airflow circulation. Significantly, this results in the need for many fans, as shown in  FIG. 1   d , particularly since each fan is typically close-coupled to the condenser coil bundle it serves. More specifically,  FIG. 1   d  illustrates thirty side-by-side coil bundles of the prior art, each bundle having only a single fan across its width and three fans across its length. This particular example may have a bundle width of approximately 14 feet and a length of 60 feet with 3 fans for each bundle. This example shows a total of 30 bundles for an overall plot dimension of approximately 60 feet by 420 feet. In any event, such fans are typically driven by belts  18 , which those skilled in the art will appreciate, require significant maintenance to keep correctly tensioned under different operating conditions and which must be replaced at regular intervals. In induced draft configurations, the motor  20  is typically mounted below the coil with two intermediate bearings between the belt  18  and the fan  14 . These bearings are another source of maintenance cost to meet recommended lubrication schedules. Furthermore, the close proximity of the fan/fans and condenser coils via a short plenum, results in inefficiencies when hot outlet air from the system is readily drawn back in and recirculates, as illustrated in  FIG. 1   e , where a front view of a modeled exhaust plenum from the prior art cooler array at 20 mph cross-wind is shown. Such a system reduces the heat exchange capacity of the coils even when considering the rather high face velocities (mentioned above) typically used in the close-coupled design. 
     More recently, these traditional air-cooled condensers have been utilized in ORC power plants as well. However, those skilled in the art will understand that ORC power plants typically have even larger heat management requirements than traditional steam power plants, thus requiring larger air-cooled heat exchange systems. Thus, as the heat management requirements for these industrial systems continues to grow, drawbacks of the prior art become even more significant and magnified. As an example, geothermal power plants have even larger heat management requirements, given the superheated nature of the geothermal fluids withdrawn from a geothermal reservoir. In such plants, the working fluid may be geothermal steam and/or brine extracted from the geothermal reservoir. An air-cooled condenser system for a geothermal power plant may require 10,000 to over 50,000 sq ft of condenser bundles to meet the cooling needs of the plant. Shipping, constructing and maintaining such an immense system utilizing the bulky, maintenance intensive systems of the prior art is not an optimal solution. 
     Accordingly, it would be desirable to provide an improved air-cooled heat exchanger system for removal of large amounts of heat in industrial applications, which system reduces air recirculation potential, at the same time reducing capital cost and fan power required for the system. It would also be desirable to reduce the face velocity of the air passing across the coils of such a system while at the same time improving the overall efficiency of the system. 
     SUMMARY 
     These and other objectives are achieved by the system of the invention, wherein an air-cooled condenser system for industrial waste heat management is provided that includes a support structure disposed to horizontally support a fan and at least two side-by-side condenser bundles above the ground. Each fan of the system is mounted above at least two condenser bundles and disposed to induce draft air flow across the two condenser bundles. Preferably, a plenum structure is disposed between each fan and its corresponding at least two condenser coils. The plenum structure is formed of a light weight skin to prevent air ingress except through the coils of the condenser bundles. The height of the plenum is selected to decouple external air flow of the fan from the condenser bundles, maintaining a separation between the air inlet for the condenser bundle and the air outlet of the fan, thereby minimizing recirculation. The support structure is preferably substantially comprised of truss members forming beams, columns, and diagonal components to horizontally support the condenser bundles in a side-by-side relationship, and likewise provide support for the fan unit and the plenum. The support structure as described, as well as the plenum, is lightweight and thus, permits assembly on the system on site at the industrial complex. The plenum and fan design allows much greater spatial separation between the fans and the coils of the condenser bundles than is realized in the prior art. Moreover, this separation permits fewer fans (relative to the prior art) of a larger fan diameter to be fluidly coupled, with internal air flow, with multiple heat exchanger coil bundles. 
     In one embodiment, an air-cooled condenser system as described above is utilized in conjunction with an Organic Rankin Cycle (ORC) power plant. The overall ORC system includes a pump that is operable to increase the pressure in a liquid organic working fluid, an evaporator that is fluidly coupled to the pump and operable to supply heat to the organic working fluid, an expander system, such as a turbine and generator, that is coupled to the evaporator and operable to expand the organic working fluid and produce useful electrical power or mechanical work, and a heat exchanger that is coupled to the expander and operable to release heat from the organic working fluid, wherein the heat exchanger includes an air-cooled condenser system having a support structure disposed to horizontally support a fan and at least two side-by-side condenser bundles above the ground. Each fan of the system is mounted above at least two condenser bundles and disposed to induce draft air flow across the two condenser bundles. A plenum structure is disposed between each fan and its corresponding at least two condenser bundles to maintain a predetermined separation between the fan and condenser bundles. 
     In another embodiment, an air-cooled condenser system for an ORC system as described above is utilized in conjunction with a geothermal power plant. The overall geothermal power plant utilizes the geothermal brine to directly release heat from the geothermal brine. The ORC system includes an air-cooled condenser system having a support structure disposed to horizontally support a fan and at least two side-by-side condenser bundles above the ground. Each fan of the system is mounted above at least two condenser bundles and disposed to induce draft air flow across the two condenser bundles. A plenum structure is disposed between each fan and its corresponding at least two condenser coils to maintain a predetermined separation between the fan and condenser bundles. 
     In another embodiment, an air-cooled condenser system for an ORC system as described above is utilized in conjunction with a geothermal power plant. The overall geothermal power plant includes a separator to separate geothermal steam from geothermal liquid, such as brine, a steam turbine across which the geothermal steam is directed, and an ORC system or systems that is coupled to the steam turbine exhaust and/or the geothermal brine and operable to release heat from the geothermal steam and/or geothermal brine. The ORC system includes an air-cooled condenser system having a support structure disposed to horizontally support a fan and at least two side-by-side condenser bundles above the ground. Each fan of the system is mounted above at least two condenser bundles and disposed to induce draft air flow across the two condenser bundles. A plenum structure is disposed between each fan and its corresponding at least two condenser coils to maintain a predetermined separation between the fan and condenser bundles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a schematic view illustrating an embodiment of a Rankine Cycle power system. 
         FIG. 1   b  is a top view of a condenser bundle and fan configuration of a prior art air-cooled condenser system. 
         FIG. 1   c  is a side view of side view of the prior art air-cooled condenser system of  FIG. 1   b.    
         FIG. 1   d  illustrates thirty side-by-side coil bundles of the prior art, each bundle having only a single fan across its width and three fans across its length. 
         FIG. 1   e  illustrates the circulation pattern for a prior art air-cooled system, operating at 20 mph cross-wind. 
         FIG. 1   f  illustrates a prior art air cooled condenser for a steam power plant. 
         FIG. 2   a  is a perspective view illustrating an embodiment of a support structure for the air cooled condenser system of the invention. 
         FIG. 2   b  is a front view illustrating an embodiment of the support structure of  FIG. 2   a.    
         FIG. 2   c  is a side view illustrating an embodiment of the support structure of  FIG. 2   a.    
         FIG. 2   d  is a top view illustrating an embodiment of the support structure of  FIG. 2   a.    
         FIG. 3   a  is a side view illustrating an embodiment of a fan and fan shroud used with the support structure of  FIGS. 2   a ,  2   b ,  2   c , and  2   d.    
         FIG. 3   b  is a top view illustrating an embodiment of the fan and fan shroud of  FIG. 3   a.    
         FIG. 3   c  is a cut-away side view illustrating an embodiment of the fan and fan shroud of  FIG. 3   a.    
         FIG. 4   a  is a perspective view illustrating an embodiment of a condenser bundle used with the support member of  FIGS. 2   a ,  2   b ,  2   c , and  2   d  and the fan of  FIGS. 3   a ,  3   b , and  3   c.    
         FIG. 4   b  is a side view illustrating an embodiment of a condenser bundle of  FIG. 4   a.    
         FIG. 4   c  is a front view illustrating an embodiment of a condenser bundle of  FIG. 4   a.    
         FIG. 5   a  is a flow chart illustrating an embodiment of a method for operating an air-cooled condenser system. 
         FIG. 5   b  is a perspective view illustrating an embodiment of the condenser bundle of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c.    
         FIG. 5   c  is a front view illustrating an embodiment of the condenser bundle of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c.    
         FIG. 5   d  is a side view illustrating an embodiment of a plurality of the condenser bundles of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c.    
         FIG. 5   e  is a perspective view illustrating an embodiment of the condenser bundle of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c  with a skin coupled to the support structure (but with end skin left off for clarity). 
         FIG. 5   f  is a perspective view illustrating an embodiment of the condenser bundle of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c  with a skin coupled to the support structure. 
         FIG. 5   g  is a perspective view illustrating an embodiment of a plurality of the fans of  FIGS. 3   a ,  3   b , and  3   c  and a plurality of the condenser bundles of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c  with a skin coupled to the support structure. 
         FIG. 5   h  is a cut-away side view illustrating an embodiment of a plurality of the fans of  FIGS. 3   a ,  3   b , and  3   c  and a plurality of the condenser bundles of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c  with a skin coupled to the support structure. 
         FIG. 5   i  is a front view illustrating an embodiment of a plurality of the fans of  FIGS. 3   a ,  3   b , and  3   c  and a plurality of the condenser bundles of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c  with a skin coupled to the support structure. 
         FIG. 5   j  is a cut-away top view illustrating an embodiment of a plurality of the fans of  FIGS. 3   a ,  3   b , and  3   c  and a plurality of the condenser bundles of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c  with a skin coupled to the support structure. 
         FIG. 5   k  is a cut-away top view illustrating an embodiment of a plurality of the fans of  FIGS. 3   a ,  3   b , and  3   c  and a plurality of the condenser bundles of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c  with a skin coupled to the support structure and a support frame coupled to one of the fans. 
         FIG. 5   l  is a side view illustrating an embodiment of a plurality of the condenser bundles of  FIGS. 4   a ,  4   b , and  4   c  supported by the support structure of  FIGS. 2   a ,  2   b , and  2   c , where three condenser bundles are fluidly coupled to one fan. 
         FIG. 6   a  is a perspective view of an air-cooled condenser system of the invention. 
         FIG. 6   b  is an end view of a modeled air recirculation pattern for an air-cooled system of the invention. 
         FIG. 6   c  is a perspective view of a modeled air recirculation pattern for an air-cooled system of the invention. 
         FIG. 7   a  illustrates an ORC power plant integrating the air-cooled condenser system of the invention. 
         FIG. 7   b  illustrates a geothermal ORC power plant integrating the air-cooled condenser system of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     One aspect of the invention is the lightweight structure utilized to support fans and condenser bundles of the air-cooled condenser system. As used herein, bundle is used to refer to a collection or panel of one or more coils arranged to carry a working fluid to be cooled. Referring initially to  FIGS. 2   a ,  2   b ,  2   c , and  2   d , such a support structure  200  is illustrated. The support structure  200  includes a plurality of truss members  202 . As used herein, a truss is a structure comprising one or more triangulated units constructed with straight and/or curved members whose ends are connected at joints or nodes. Although any type of truss is contemplated by the invention, including planar trusses and three dimensional or space frame trusses, in the illustrated embodiment, each truss member  202  is a planar truss. Support structure  200  is illustrated in  FIG. 2   b  as having side or leg trusses  204 , upper trusses  206  and lower or intermediate trusses  208 . As best seen in  FIGS. 2   a  and  2   b , the plurality of leg trusses  204 , upper trusses  206  and lower trusses  208  of the support structure  200  are joined together by a plurality of beams  210 . 
     More particularly, side (or leg) trusses  204  each having a distal end  204   a  and a straight portion  204   b  that extends from the distal end  204   a . Although not necessary, side trusses  204  may also include an arcuate section  204   c  that extends from the straight portion  204   b . Those skilled in the art will appreciate that arcuate section  204   c  is simply one preferred embodiment and side trusses  204  could simply comprise straight portion  204   b . In any event, respective upper ends of leg trusses  204  are joined by an upper truss  206  that extends between the ends of the arcuate sections  204   c . Intermediate truss  208  is disposed to extend between the leg trusses  204  from sections on the leg trusses  204  that are preferably between the distal ends  204   a  and the ends of the arcuate sections  204   c , as illustrated in  FIG. 2   b , but in any event upper trusses  206  are spaced apart from intermediate trusses  208  a select distance (so as to permit formation of an air plenum as described below). The plurality of intermediate truss members  208  are coupled together by a plurality of beams  210  and held in a spaced apart orientation from each other such that a condenser bundle support structure  212  is defined between any two intermediate truss members  208 . Likewise, the plurality of upper trusses  206  and the plurality of beams  210  that extend between the upper trusses  206  form a fan support frame  214 . While the truss members  202  have been described and illustrated having specific structures, one of skill in the art will recognize that the truss members  202  may have different structure (e.g., space frame trusses as opposed to planar trusses) and may be coupled together in different manners without departing from the scope of the present disclosure. 
     Likewise, while a particular shape for lightweight support structure  200  is described, those skilled in the art will appreciate that the particular orientation of components is not intended to be a limitation. For example, support structure  200  need not have an arcuate section  204   c . Rather, it is the construction of a support system utilizing a plurality of substantially similar, lightweight truss members for an industrial air cooled condenser and the particular arrangement of condenser bundles and fans that represents one novel aspect of the invention. The support structure as described herein permits comparatively simple, cost-effective, on-site fabrication of an air cooled condenser system, thereby minimizing capital expenditures. This is particularly significant given the size requirements of geothermal power plants, which may require acres of condenser bundles to meet the needs of the power plant. 
     Referring now to  FIGS. 3   a ,  3   b , and  3   c , a fan  300  is illustrated. The fan  300  includes a fan housing (also called a fan shroud or fan ring)  302  having a top edge  302   a , a bottom edge  302   b  located opposite the fan housing  302  from the top edge  302   a , and a side wall  302   c  that extends between the top edge  302   a  and the bottom edge  302   b . The fan  300  has a diameter D, which is preferably the diameter of the fan housing  302 . In an embodiment, the diameter D is at least 12 feet. In another embodiment, the diameter D is at least 20 feet. A fan member cavity  304  is defined by the side wall  302   c  and located between the top edge  302   a , the bottom edge  302   b , and the side wall  302   c . In the illustrated embodiment, side wall  302   c  is contoured in order to provide aerodynamic airflow through fan housing  302 , and one of skill in the art will recognize that a variety of different contours and overall housing shapes, may be used without departing from the scope of the present disclosure. A fan member  308  is at least partially disposed within the fan member cavity  304 . The fan member  308  has a diameter that is approximately the same as the diameter of the fan housing  302  (and therefore the fan  300 ). Fan member  308  includes one or more fan blades  305  mounted on a hub  307  which is coupled to a spindle  309  driven by a motor  306 . Preferably, the fan is a direct drive fan so that the motor  306  is directly linked to the spindle  309 , and thus requires less maintenance than belt driven fans. In an alternative embodiment, a gearbox (not shown) may be disposed between the motor and the spindle, so that the spindle  309  is linked via a gear box to the output shaft of the motor  306 . In an embodiment, the motor  306  is a variable frequency drive motor that is operable to vary the speed of the fan member  308 . The top edge  302   a  of fan  300  corresponds with the air outlet for the fan (and for the overall air-cooled system), while the bottom edge  302   b  of fan  300  corresponds with the air inlet for the fan. Preferably the distance between the top edge  302   a  and the bottom edge  302   b  is at least three feet. The large fan results in a tall shroud that is centered in over the length of the tubes. This geometry creates the double benefit of increasing vertical separation and horizontal separation from the edge of the top of the shroud to the closest point of intake into the air cooled condenser system. Moreover, it is believed that a velocity recovery cylinder such as fan housing  302  decreases required fan horsepower. 
     In one preferred embodiment, each fan operates at less than 250 RPMs and has a power output of greater than 25 horsepower and a diameter greater than 15 ft., such operational parameters determined based on the preferred volume of air movement for a fan spanning more than one condenser bundle. In another preferred embodiment, each fan operates at approximately 110 RPMs and has a power consumption of approximately 90 horsepower and a diameter D of approximately 30 ft. 
     Referring now to  FIGS. 4   a ,  4   b , and  4   c , a condenser bundle, also referred to as a condenser panel or condenser tube bundle or panel,  400  is illustrated. The condenser bundle  400  includes one or more coils or tubes  401  extending from a header  402 . Condenser bundle  400  has a top surface  402   a , a bottom surface  402   b , a proximal end  402   c , a distal end  402   d , and a pair of sides  402   e  and  402   f , the surfaces  402   a, b ; the ends  402  c, d; and the sides  402   e, f  thereby defining a spread or boundary for coil  401 . In an embodiment, the condenser bundle  400  is characterized by a width W that is the shortest distance between the side surfaces  402   e  and  402   f  and a length L that is the shortest distance between the ends  402   c, d . In one preferred embodiment, the width W is at least approximately 8 feet. In one preferred embodiment, the width W is at least approximately 10 feet. In one preferred embodiment, the length L is at least approximately 40 feet. In one preferred embodiment, the length L is at least approximately 60 feet. In another preferred embodiment, the bundle length L is greater than 40 feet and the bundle width W is greater than 8 feet. Those skilled in the art will appreciate that condenser bundles of the foregoing dimensions are necessary for the industrial waste heat removal contemplated by the invention. In this regard condenser bundles of such a size must be readily and easily supported, which is why the truss system described herein is one aspect of the invention. 
     Header  402  may include a plurality of inlets and outlets  404  in fluid communication with tube or coil  401 . In an embodiment, a plurality of other feature known in the art of condenser bundles may be included on or otherwise form part of condenser bundle  400  but have been omitted for clarity of discussion. In one embodiment, for example, the bundle  400  comprises a multiplicity of coils or tubes  401 , preferably substantially extending longitudinally along the length of the condenser bundle  400 . In another embodiment, coils  401  may be provided with fins externally mounted thereon. In yet another embodiment, a second header with fluid flow ports may be provided at the distal end  402   d  of bundle  400  and attached to the coil to permit fluid communication therebetween. The bottom surface  402   b  of condenser bundle  400  corresponds with the air inlet for the bundle (and for the overall air-cooled system), while the top surface  402   a  of condenser bundle  400  corresponds to the air outlet for the bundle. 
     Those skilled in the art will appreciate that the other than orientation of the bundles, the invention is not limited to a particular bundle configuration of coils or tubes, and that the foregoing is only for illustrative purposes in further describing the invention. 
     As described above, in the preferred embodiment, the fan  300  is disposed to draw air across at least two side-by-side, substantially horizontal condenser bundles  400 , and as such, the diameter D of fan  300  is greater than the width W of a bundle  400  such that fan  300  extends across a portion of at least two bundles  400 . Preferably the diameter D of fan  300  is at least equivalent to twice the width W of bundles  400 . Put another way, diameter D of fan  300  is equal to or greater than twice the width W of bundle  400 . In another preferred embodiment, diameter D is equal to or greater than three times the width W, such that fan  300  extends across, and operates to draw air across at least three side-by-side condenser bundles  400 . In another embodiment, the diameter D of the fan is greater than 150% of the width W of bundles  400 . For the overall system, which may consist of tens or hundreds of fans and an even greater number of condenser bundles, in one preferred embodiment, it is desirable to have a ratio of at least two condenser bundles to each fan, and preferably three condenser bundles to each fan in the system. 
     With respect to the spacing between the fan  300  and its respective bundles  400 , in order to ensure that one fan can draw air across at least two condenser bundles  400 , fan  300  is spaced apart from the top surface  402   a  of condenser bundles  400  by at least 5 feet. 
     Moreover, in order to minimize recirculation of heated exhaust air into the system, the air outlet for the system at or above top edge  302   a  of fan  300  is separated from the air inlet for the system at or below bottom surface  402   b  of condenser bundle  400  by at least 10 feet. In another embodiment, the separation is at least 15 feet, while in another embodiment, the separation is at least 20 feet. Preferably the air inlet and the air outlet are each substantially horizontal to further minimize the likelihood of recirculation. 
     With the air cooled condenser system of the invention, and its respective components, now generally described, certain components and their functional relationships will be more specifically described. Support structure  200  is provided and engaged with a support surface. In one embodiment, the support structure  200 , described above with reference to  FIGS. 2   a ,  2   b ,  2   c , and  2   d , has leg trusses  204  that are engaged with a support surface  504   a  (such as the ground or a foundation or footings), as illustrated in  FIG. 2   a . The support structure  200  may be secured to the support surface  504   a  using securing methods known in the art. The truss members  202  are preferably prefabricated and substantially similar to each other. Likewise, beams  210  are preferably prefabricated and substantially similar to each other. Prefabrication may provide for couplings on the truss members  202  and beams  210  that allow them to be coupled to each other quickly and easily. Prefabrication also allows the truss members  202  and the beams  210  to be shipped before they are coupled to each other, which lowers shipping costs as they may be stacked and their shipping volume minimized. The truss members  202  and the beams  210  may be shipped to an industrial site before they are coupled together. In one embodiment, the industrial site is a location that includes a power system such as, for example, a power plant. In one embodiment, the power system or power plant may employ a Rankine Cycle or an Organic Rankine Cycle similar to the basic Rankine Cycle  100  described above with reference to  FIG. 1  (e.g., the power plant may be an Organic Rankine Cycle geothermal power plant). In the event, the truss members  202  and beams  210  are preferably coupled together “on site” at the power plant to form the features of the support structure  200  described above. 
     An additional benefit to the support structure  200  format of the truss member  201  is that it minimizes interface with air flow into the system. Given the “open” nature of a truss member, air can readily flow through the member to the air intake. 
     A plurality of condenser bundles (also called tube bundles or coil panels) are supported with the support structure  200 . More specifically, a condenser bundle  400 , described above with reference to  FIGS. 4   a ,  4   b , and  4   c , is positioned on a condenser support structure  212  defined by the support structure  200  and oriented so that the bottom surface  402   b  condenser bundle  400  faces downward and is substantially parallel with and in a spaced apart orientation from the support surface  504   a , as illustrated in  FIGS. 5   b  and  5   c , thereby forming an air intake for the air-cooled condenser system of the invention. A plurality of condenser bundles  400  may be supported side-by-side in this orientation by the support structure  200  in the same manner by positioning those condenser bundles  400  on respective condenser support structures  212  located between any two truss members  202 , as illustrated in  FIG. 5   d . The condenser bundles  400  may then be fluidly coupled (e.g., through the inlets and outlets  404 ) to each other and/or to an evaporator, an expander, and a pump (e.g., the evaporator  102 , the expander  104 , and the pump  112  described above with reference to  FIG. 1 ) in order to allow a working fluid to be cooled through the condensers  400 , as described in further detail below. The fluid couplings between the condenser bundles  400  and other components of the power system have not been illustrated for clarity of discussion. In an embodiment, the condenser bundles  400  may be secured to the support structure  200  using securing methods known in the art. 
     In one preferred embodiment, an air plenum  502  between fan  300  and condenser bundle  400  may be formed. Preferably, plenum  502  is disposed between each fan  300  and its corresponding at least two condenser bundles  400  and forms a barrier to prevent air ingress into the system except through the air inlet of the condenser bundles. As shown in  FIG. 5   e , air plenum  502  may be constructed by securing a skin to the portion of truss members  202  extending between fan  300  and condenser bundle  400 , both on the sides between adjacent leg truss member  204   c  as well as on the ends of the support structure. More specifically, a skin  508   a  is coupled to the support structure  200  such that the skin  508   a  extends between the opposing ends of the support structure  200 , with a first section  508   b  located immediately adjacent the upper support frame  214 , and two second sections  508   c  located immediately adjacent the arcuate sections  204   c  on the leg trusses  204 , as illustrated in  FIG. 5   e . In an embodiment, the skin  508   a  may be secured to the support structure  200  using securing methods known in the art. In an embodiment, the first section  508   b  of the skin  508   a  defines a plurality of fan openings  508   d  that are located in a spaced apart orientation on the first section  508   b  of the skin  508   a . In one embodiment, the skin  508   a  is a fabric material. In another embodiment, the skin  508   a  is flexible polymer membrane. In another embodiment, the skin  508   a  is a reinforced polymer covering. In another embodiment, skin  508   a  is lightweight sheet metal or other lightweight flexible material. While  FIG. 5   e  illustrates only one condenser  400  being supported by the support structure  200 , a plurality of condensers  400  may be supported by the support structure  200 , as illustrated and described above with reference to  FIG. 5   d . In an embodiment, the skin  508   a  may include two third sections  508   e  that are coupled to the opposing ends of the support structure  200  and extend between the ends of the first section  508   b  and second sections  508   c , as illustrated in  FIG. 5   e . In an embodiment, skin  508   a  may also be disposed internally on support structure  200  to form a barrier between adjacent fans. In other words, a section similar to section  508   e  may be disposed internally in structure  200  so that air flow between adjacent fans is not comingled, thereby reducing turbulence in the path of air flow through the system. In any event, as with the support structure  200 , skin  508   a  is lightweight and easily installed on site during construction of the air-cooled condenser system of the invention. In this regard, skin  508   a  of plenum  502  may be installed before or after installation of fans  300  on support structure  200 . 
     In order to minimize recirculation of warm air into the system, in one preferred embodiment, plenum  502  has a first end adjacent condenser bundles  400  and a second end adjacent fans  300 . The first end of plenum  502  is characterized by a first perimeter length and the second end of plenum  502  is characterized by a second perimeter length. The second perimeter length is less than the first perimeter length so that plenum  502  narrows or necks down, as can be seen in  FIG. 5   i . In the embodiment, the first perimeter length is the perimeter around the side-by-side bundles served by a fan and the second perimeter is the perimeter of the fan housing those skilled in the art will appreciate that this corresponds to an air inlet for fan  300  that is smaller than the air outlet of bundle  400 . In one preferred embodiment, the air outlet of the plenum is at least 10% smaller than the air inlet for the plenum. 
     A plurality of the fans  300 , described above with reference to  FIGS. 3   a ,  3   b , and  3   c , are positioned on the support structure  200  and, more specifically, supported by fan support frame  214 , such that the bottom edges  302   b  of the fans  300  are located adjacent the fan openings  508   d , as illustrated in  FIGS. 5   g ,  5   h , and  5   i . In an embodiment, the fans  300  may be secured to the support structure  200  using securing methods known in the art. In an embodiment, each fan is located a distance X above the top surface  402   a  of the condenser bundles  400 , as illustrated in  FIG. 5   i . In an embodiment, the distance X is at least 5 feet. In another embodiment, distance X is at least 10 feet and preferably 15-20 feet or more. In another embodiment, distance X is at least 8 feet and no more than 20 feet. Distance X is selected to permit a fan  300  to draw air across its associated at least two condenser bundles  400 . Moreover, distance X corresponds with the height of the plenum  502 . With the support structure  200 , the condensers  300 , and the fans  300  coupled together as illustrated in  FIG. 5   g , an air-cooled condenser system  510   a  is provided.  FIGS. 5   h  and  5   j  illustrate the air-cooled condenser system  510   a  with a portion of the skin  508   a  removed to show that the fan diameter D is such that each fan  300  is located above at least a portion of two or more condenser bundles  400 . In other words, the diameter D of the fan is selected to extend over a plurality of condenser bundles. In the illustrated embodiment, each fan  300  is located above more than at least half the width W of each of the three condenser bundles  400 . In an embodiment illustrated in  FIG. 5   k , a fan support frame  510   b  is coupled to and/or secured to the fans  300  and/or the support structure  200  in order to provide additional support for the fans  300 . The fan support frame  510   b  is only illustrated for one fan  300  for clarity of discussion, but may be used with both fans  300 . 
     It has been found that the air cooled condenser system of the invention is particularly suitable for the large heat management requirements of ORC power plants to permit airflow to cool the organic working fluid of the power plant. As described above with reference to  FIG. 1 , a working fluid in the power system that is coupled to the air-cooled condenser system  510   a  may be pumped, heated, and expanded prior to being introduced to the air-cooled condenser system  510   a . When introduced to the air-cooled condenser system  510   a , the heated working fluid enters the condenser bundles  400 . As shown in  FIG. 51 , the motors  306  in the fans  300  activate the fan members  308  which draw air into the system, shown as an airflow A, from outside the support structure  200 . As mentioned above, the open cell nature of the leg trusses supporting the system promotes air flow into the system. Once in the system, the path of airflow through the system is substantially linear, truly promoting faster and more efficient cooling by minimizing turbulence. Specifically an airflow B is drawn through the condensers  400  to cool the working fluid in the condensers  400 , becoming an airflow C that is linearly directed towards the fans  300 , which then travels through the fans  300  and becomes an airflow D that is discharged from the system. The skin  508   a  forms a plenum that helps to direct the airflow discussed above. The shape of the fan housing  302  may be chosen to ensure that the maximum amount of airflow is directed through each condenser bundle  400 . Furthermore, the spacing between the fans  300  and the inlet airflow B helps to prevent inefficiencies in the system that can result when hot outlet air recirculates back into the system. In essence, the comparatively large height X of the plenum permits exhaust air flow from the fans to be decoupled from the cooling air flow across the condenser bundles so as to minimizes the recirculation problems of the prior art. In an embodiment, the motors  306  are direct drive motors that eliminate the need for conventional belt drives, thus reducing the need for maintenance and replacement of belts. 
       FIG. 7   a  illustrates the air cooled condenser system of the invention integrated with an ORC power plant. As shown, an ORC power plant  700  is comprised of a pump  702  that is operable to increase the pressure in an organic working fluid  713 . A first heat exchanger system  704  is coupled to the pump and operable to supply heat to the organic working fluid. Preferably, the organic working fluid is selected from a group consisting of hydrocarbons (for example pentane and its isomers, butane and its isomers), halocarbons (for example R-134a, R-245fa, R1234yf), siloxanes, mixtures comprised of or incorporating one or more of the foregoing, ammonia water mixtures, ammonia or carbon dioxide. In any event, power plant  700  employs a source of heat  706  that may be derived from any waste heat, any renewable resource, or by the direct combustion of a fuel to provide heat to the first heat exchange system  704 . An expander  708  is coupled to the first heat exchanger system  704  and is operable to expand the organic working fluid. Those skilled in the art will appreciate that expander  708  is in turn coupled to a generator  710  to produce electrical power. A second air-cooled heat exchanger system  510   a  is coupled to the expander  708  and operable to release heat from the organic working fluid and transfer the heat to the air flowing through heat exchanger  510   a . In one embodiment, ORC power plant  700  may form a bottoming system which may be combined with a steam topping system having a steam turbine  712 . 
       FIG. 7   b  illustrates the air cooled condenser system of the invention integrated with a geothermal ORC power plant. As shown, an ORC power plant  700  is comprised of a pump  702  that is operable to increase the pressure in an organic working fluid  703 . A first heat exchanger system  704  is coupled to the pump  702  and operable to supply heat to the high pressure organic working fluid  703 , thereby producing a high pressure organic working fluid vapor  705 . The power plant  700  draws upon a heat source  706 , which in this case is heated geothermal fluid  701 , such as steam and/or brine, pumped from a geothermal reservoir which provides heat to the first heat exchange system  704 . An expander  708  is coupled to the first heat exchanger system  704  and is operable to expand the high pressure organic working fluid vapor  705 , thereby resulting in a low pressure organic working fluid vapor  707  exiting the expander  708 . Those skilled in the art will appreciate that expander  708  is in turn coupled to a generator  710  to produce electrical power. A second air-cooled heat exchanger system  510   a  is coupled to the expander  708  and operable to release heat from the low pressure organic working vapor  707  and transfer the heat to the air  709  flowing through heat exchanger  510   a . The heat depleted geothermal fluid  711  is them pumped back into the geothermal reservoir via an injection well(s). 
     Referring now to  FIG. 5   a , a method  500  for providing an air-cooled condenser system is illustrated. The method  500  begins at blocks  502  and  504 , where a lightweight support structure is provided and engaged with a support surface. In an embodiment, the support structure is similar to support structure  200 , described above with reference to  FIGS. 2   a ,  2   b ,  2   c , and  2   d . The method  500  then proceeds to block  506  where a plurality of condensers bundles are supported with the support structure. The condenser bundles are arranged and positioned as described above with respect to condenser bundles  400 . The condenser bundles  400  may then be fluidly coupled (e.g., through the inlets and outlets  404 ) to each other and to an evaporator, an expander, and a pump in order to allow a working fluid to be cooled through the condensers  400 , as described above. The method  500  then proceeds to block  508  where a skin is extended between a plurality of the support structure truss members. The skin may be similar so skin  508   a  described above. The method  500  then proceeds to block  510  where a fan is supported with the support structure. The fan is supported so that it extends over at least two condenser bundles so as to be fluidly coupled to the at least two condenser bundles. The fan may be fan  300  as described above. The method  500  then proceeds to block  512  where airflow is provided to the condensers to cool a power system working fluid. As described above with reference to  FIG. 1 , a working fluid in the power system that is coupled to the air-cooled condenser system, such as system  510   a , may be pumped, heated, and expanded prior to being introduced to the air-cooled condenser system. When introduced to the air-cooled condenser system  510   a , the heated working fluid enters the condenser bundles  400  where air flow across the bundles from induced draft fans  300  cools the working fluid. The air travels through the system in a substantially linear travel path once entering the system. 
     While the above described system is preferably utilized with ORC power plants, it is equally suitable for other types of power plants where large banks of air cooled heat exchanges are required. This is particularly true of geothermal power plants. 
     As described above, the heat exchanger system of the invention is readily constructed on site at the industrial facility by delivering at least three heat exchanger bundles to a construction site at which a heat exchanger system is to be installed. None of the heat exchanger bundles are delivered with fans attached thereto, making transport and delivery of the individual components much simpler. Rather, the fans are delivered as separate, detached components. Once delivered, the trusses are arranged and secured for form a support structure. The heat exchanger bundles, i.e., the condenser bundles, are then arranged in substantially horizontal, side-by-side relationship above the ground on the truss structure. Fans are mounted above the heat exchanger bundles so that each fan extends over a portion of at least two and preferably at least three of the bundles. Finally, to enhance air flow and minimize recirculation effects, a substantially enclosed, elongated air plenum is formed between the fan and the bundles over which the fan extends. 
     Thus, an air-cooled condenser system has been described that includes an option for a prefabricated lightweight structural support components, but in all cases uses fewer and larger fans that are spaced further away from the condenser bundles than conventional systems. As an example, prior art air-cooled condensers for ORC plants would have a height from inlet of the condenser coil to the outlet of the fan plenum of approximately 4 to 9 feet in the direction of airflow (composed of approximately 2-3 feet of coil, 1-2 feet of plenum and 1-4 foot fan ring). The design of the invention greatly increase this separation between the inlet of the condenser bundle to the outlet of the fan plenum by often more than double the prior art designs. For example in one embodiment of the invention, the condenser bundle inlet to fan outlet separation is approximately 26 feet (composed of 2-3 feet of coil, 10 feet of plenum, and 14 feet of fan ring). The prefabricated lightweight components such as the truss members, beam members, and skin decrease the cost of shipping and assembly of the air-cooled condenser. The use of fewer larger fans fluidly coupled to more than one condenser bundle, along with the option of direct driving of those fans, provided for reduced fan-related maintenance costs. The larger fans and plenum, as well their orientation relative to the condenser bundles, provide improved airflow across the condenser bundles. The significant separation of the fans and the condenser bundles prevents hot exhaust from recirculating into the system. The optional prefabricated truss member allows the system to be quickly and easily fabricated onsite. 
     Another advantage of the invention is that it results in much fewer footings and less civil work on site when compared to the prefabricated units of the prior art. For a typical project, the system of the invention might have less than 25% of the footings as the typical prior art air-cooled condenser. 
     Modeling of the invention has confirmed that the air recirculation rate can be greatly reduced, and therefore the capacity of the ORC plant can be better maintained, regardless of wind speed and direction. As mentioned above,  FIG. 1   d . illustrates an air cooled condenser system of the prior art.  FIG. 1   e  illustrates a front view of a modeled exhaust plenum from the  FIG. 1  prior art cooler array, wherein the cross wind is blowing at 20 mph. This prior art array was modeled using a conventional arrangement array of thirty bundles with each bundle having 3 fans totaling  90  fans. Hot fluid that needs cooling is passed through the tube side of a heat exchanger. At the same time, ambient air enters the tube bank from below, passes over the outside of the tube bank, then exits the cooler through the three fans located on the top of the unit. Table 1 summarizes the results for the conventional array modeling. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Summary of results for conventional cooler array. 
               
            
           
           
               
               
               
            
               
                   
                 6 mph Wind Speed 
                 20 mph Wind Speed 
               
            
           
           
               
               
               
               
               
            
               
                 Wind 
                 Temperature 
                 Recirculation 
                 Temperature 
                 Recirculation 
               
               
                 Direction 
                 (° F.) 
                 (%) 
                 (° F.) 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 North 
                 52.8 
                 4.7 
                 58.2 
                 35.7 
               
               
                 Northeast 
                 54.3 
                 13.0 
                 52.4 
                 2.3 
               
               
                 East 
                 53.0 
                 5.8 
                 52.1 
                 0.7 
               
               
                   
               
            
           
         
       
     
     The conventional cooler array experienced varying levels for recirculation for all three wind directions. Significant recirculation took place when the wind was aligned with the long axis of the array. As the wind speed increased, the amount of recirculation increased. This appears to be the result of the plume remaining closer to the ground as the wind speed increase. When the wind was at 45° and 90° to the long axis of the array, the amount of recirculation was higher with the 6 mph wind speed than with the 20 mph wind speed. This appears to be the result of the higher wind speed blowing the plume away from the array and that the higher wind speed forces cooler ambient air into the area below the intake of the cooler array, reducing the amount of exhaust recirculation. 
       FIG. 6   a , illustrates an air cooled condenser system of the invention as described above, and in particular, illustrates the geometry when compared to the prior art air cooled condenser of  FIG. 1   d . In  FIGS. 6   b  and  6   c , modeling of airflow of an air-cooled condenser system of the invention is shown, where the same array of thirty bundles as the example of prior art is shown. This example of the invention uses a single fan for every 3 bundles giving a total of just 10 fans. Table 2 summarizes the results for the modeling of the cooler array of the invention. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Summary of results for TAS cooler array. 
               
            
           
           
               
               
               
            
               
                   
                 6 mph Wind Speed 
                 20 mph Wind Speed 
               
            
           
           
               
               
               
               
               
            
               
                 Wind 
                 Temperature 
                 Recirculation 
                 Temperature 
                 Recirculation 
               
               
                 Direction 
                 (° F.) 
                 (%) 
                 (° F.) 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 North 
                 52.0 
                 0.0 
                 52.2 
                 1.2 
               
               
                 Northeast 
                 52.0 
                 0.0 
                 52.0 
                 0.0 
               
               
                 East 
                 52.0 
                 0.0 
                 52.0 
                 0.0 
               
               
                   
               
            
           
         
       
     
     The cooler array of the invention experienced some recirculation when the wind was aligned with the long axis of the array when the wind speed was 20 mph, but no recirculation when the wind speed was 6 mph. There was no recirculation when the wind was at either 45° or 90° from the long axis of the array for either wind speed. 
     Thus, in one embodiment of the invention, a heat exchange system for industrial cooling comprises at least three elongated, heat exchange bundles, each elongated bundle disposed along a longitudinal axis and characterized by a length L and a width W; a support structure on which the heat exchanger bundles are mounted, said bundles mounted so that the longitudinal axis of the bundles are substantially parallel to one another and substantially horizontal; a substantially horizontal induced draft fan characterized by a diameter D and comprising a fan blade and a motor, the fan mounted above the heat exchanger bundles, wherein the diameter D of the fan is greater than the heat exchanger width W. 
     In another embodiment of the invention, a heat exchange system for industrial cooling comprises at least three elongated, flat bundles of heat exchange tubes, each elongated bundle disposed along a longitudinal axis and characterized by a length L and a width W; a support structure on which the heat exchanger bundles are mounted, said bundles mounted so that the longitudinal axis of the bundles are substantially parallel to one another and substantially horizontal; a substantially horizontal induced draft fan characterized by a diameter D, the fan mounted above the heat exchanger bundles and configured to draw air over said tubes, wherein the diameter D of the fan is greater than the heat exchanger width W. 
     In another embodiment of the invention, a heat exchange system for industrial cooling comprises at least three elongated, flat bundles of heat exchange tubes, each elongated bundle disposed along a longitudinal axis and characterized by a length L and a width W; a support structure on which the heat exchanger bundles are mounted, said bundles mounted so that the longitudinal axis of the bundles are substantially parallel to one another and substantially horizontal; at least two substantially horizontal induced draft fans each characterized by a diameter D, each fan mounted above at least two heat exchanger bundles and configured to draw air over said tubes, wherein the diameter D of each fan is greater than the heat exchanger width W. 
     In another embodiment of the invention, a heat exchanger for the transfer of heat from one fluid to another fluid comprises a plurality of heat exchanger bundles, horizontally disposed in a side-by-side relationship to one another; a plurality of induced draft fans disposed in a spaced apart relationship above the bundles, wherein there is less than one fan per heat exchanger bundle. 
     In a method for cooling a process fluid in a heat exchanger system, the following steps are provided for: driving at least one induced draft fan; delivering a heated process fluid through at least three side-by-side, substantially horizontally disposed heat exchanger bundles; and utilizing the induced draft fan to draw air across the at least three side-by-side, horizontally disposed heat exchanger bundles, thereby cooling the process fluid disposed within the bundles. 
     Other industrial processes that might be suitable for the air-cooled condenser system of the invention include refrigeration cycles were the process fluid is the discharge from a refrigeration compressor; a refinery, where the process fluid is a liquid or gas being manufactured at the refinery; a liquefied natural gas processing plant as part of either the liquefaction or gasification processes. Moreover, it is contemplated that the heat exchanger described for use with the system may be used to cool, among other things, the discharge from a gas compressor; a water based liquid; steam from the discharge from a steam turbine; or discharge from a turbine used in an organic Rankine cycle power plant. 
     Although illustrative embodiments have been shown and described, a wide range of modification, change and substitution is contemplated in the foregoing disclosure and in some instances, some features of the embodiments may be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the embodiments disclosed herein.