Patent Publication Number: US-2022228809-A1

Title: Heat exchanger, method for producing a heat exchanger and power plant comprising such a heat exchanger

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2020/063124 filed 12 May 2020, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 10 2019 208 619.5 filed 13 Jun. 2019. All of the applications are incorporated by reference herein in their entirety. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a heat exchanger through which a medium to be cooled flows in a flow direction during operation thereof. The present invention further relates to a process for producing such a heat exchanger. The invention additionally relates to a power plant having a generator cooled by means of a generator cooling gas and a heat exchanger that cools the generator cooling gas. 
     BACKGROUND OF INVENTION 
     Power plants, for example gas turbine power plants, steam turbine power plants, combined gas and steam turbine power plants, solar power plants or the like, comprise a multitude of components that require cooling, in order firstly to remove the waste heat that arises and secondly to increase the output of the power plant. This is also true of the generator used for power generation, which is generally cooled with generator cooling gas recooled by means of a heat exchanger. The heat exchanger is usually connected to a closed cooling water system of the power plant, via which further heat exchangers are also supplied with cooling water for example those for lubricant oil and/or sealing oil cooling, for cooling of pumps or the like. The cooling water of the cooling water circuit can be re-cooled in various ways, for example by means of fresh water flow cooling, circulation cooling using a cooling tower or air-cooled coolers, etc. 
     A possible achievable electrical power in the generator depends on the cold gas temperature of the generator cooling gas defined for cooling of the generator windings, i.e. the generator cooling gas temperature on entry into the generator. The lower the cold gas temperature, the more mechanical energy can be converted to electrical energy in the generator. The generator cooling gas is recooled as described above within a heat exchanger, through which cooling water from the cooling system of the power plant flows. Thus, the cold gas temperature of the generator cooling gas is coupled to the cooling water temperature of the cooling water flowing through the heat exchanger. The cooling water temperature in turn is dependent on the recooling of the cooling water and consequently cannot be lowered at will. There are thus limits to the electrical power achievable in the generator. 
     If power-increasing measures on the turbine of the power plant result in a rise in mechanical power at the generator shaft, it would be desirable to provide improved cooling for the generator in order to be able to convert more power to electrical energy therewith. 
     SUMMARY OF INVENTION 
     Proceeding from this prior art, it is an object of the present invention to provide improved cooling, especially improved generator cooling. 
     This object is achieved by the present invention by providing a heat exchanger comprising a first stack of fins having a multitude of first fins stacked in a stacking direction that extends transverse to the flow direction, wherein the first fins are each provided with a multitude of first passage holes that are flush with one another in stacking direction, at least one further stack of fins arranged adjacent to the first stack of fins in flow direction, and having a multitude of second fins stacked in the stacking direction, wherein the second fins are each provided with a multitude of second passage holes that are flush with one another in stacking direction, first pipe conduits that extend through the first passage holes of the first fins of the first stack of fins and are press-fitted with the first fins, second pipe conduits that extend through the second passage holes of the second fins of the at least one further stack of fins and are press-fitted with the second fins, wherein the first pipe conduits and the second pipe conduits are not connected to one another for flow purposes and are provided for passage of a first cooling medium and a second cooling medium, wherein the cooling media are different from one another, and at least one cover that connects the first stack of fins and the at least one further stack of fins to one another, which is placed atop an outer first fin of the first stack of fins and atop the adjacent outer second fin of the at least one further stack of fins and covers these fins, wherein the at least one cover has been provided with first passage holes arranged and formed so as to correspond to the first passage holes of the first fins of the first stack of fins, through which the first pipe conduits are guided, and has been provided with second passage holes arranged and formed so as to correspond to the second passage holes of the second fins of the at least one further stack of fins, through which the second pipe conduits are guided. 
     Such a heat exchanger is advantageous in that it can be operated with two different cooling media. The first cooling medium may be cooling water, for example. The second cooling medium used may, for example, be a coolant which is recooled in a cooling unit. If the medium to be cooled is generator cooling gas, the cold gas temperature thereof on entry into the generator is not limited by the degree of recooling of the cooling water of the cooling water system of the power plant. Instead, the cold gas temperature of the generator cooling gas can be lowered further via heat exchange with the coolant that flows through the heat exchanger, such that it can be adapted flexibly to the cooling demand of the generator if, for example, power-increasing measures are undertaken on the turbine. A further advantage of the heat exchanger of the invention is that the mechanical coupling of the stacks of fins through which the different cooling media flow via the at least one cover imparts very good mechanical stiffness to both stacks of fins with a simultaneously very inexpensive construction of low volume, even if one of the stacks of fins in itself should have only very low intrinsic stiffness, for example, on account of low construction depth. This is important especially when an existing heat exchanger in which the generator cooling gas has to date been recooled by means of cooling water only is to be replaced by a heat exchanger of the invention in order to lower the cold gas temperature of the generator cooling gas by additional cooling by means of a coolant. In such cases, the construction space available is defined by the dimensions of the old heat exchanger and is very limited. Correspondingly, barely any space is available for a stack of fins through which a second cooling medium flows, and therefore this second stack of fins can frequently be executed only with a very low construction depth, which leads to low intrinsic stiffness. 
     In one configuration of the heat exchanger of the invention, the first fins have a greater area than the second fins. In other words, the dimensions of the fins of the respective stacks of fins are matched to the respective cooling medium. 
     The design of the surface of the first fins is advantageously different than the design of the surface of the second fins. In this way too, it is possible to achieve adaptation of the stacks of fins to the respective cooling medium. 
     Advantageously, the first fins and the second fins have been produced from a sheet material, for example from aluminum, in order to achieve good thermal conductivity. 
     In one configuration of the heat exchanger of the invention, a distance between the first fins in stacking direction is different than the distance between the second fins in stacking direction, advantageously greater. 
     According to the invention, the first fins and the second fins may have been produced from a sheet material having a coating on one or both sides. 
     The first pipe conduits are each connected to one another via U-shaped connecting conduits, and the first cooling medium flows through them successively, and/or the second pipe conduits are each connected to one another by U-shaped connecting conduits, and the second cooling medium flows through them successively. 
     The flow cross section of the first pipe conduits is advantageously different than the flow cross section of the second pipe conduits, advantageously greater. 
     In one configuration of the present invention, the first pipe conduits and the second pipe conduits have been produced from a metallic material, advantageously from copper, which achieves good thermal conductivity. 
     Advantageously, the inner faces of the first pipe conduits and/or the inner faces of the second pipe conduits are structured in order to increase their size, which is conducive to better heat transfer. 
     An arrangement pattern of the first passage holes advantageously differs from the arrangement pattern of the second passage holes. 
     The at least one cover has advantageously been produced from a metallic material, advantageously from a metal sheet. This leads to a simple and inexpensive construction of the at least one cover. 
     Advantageously, the at least one cover encompasses the first stack of fins and the at least one further stack of fins on opposite sides, which further increases the mechanical stiffness of the construction. 
     In one configuration of the present invention, the first stack of fins and the at least one further stack of fins are joined to one another via at least one side section. Such a side section is also very conducive to the mechanical stiffness of the construction. 
     The present invention further provides a process for producing a heat exchanger designed in accordance with the invention, in which the first fins and the second fins are produced simultaneously in a single fin compression device, for example using a fin compression mold that defines both features of the first fins and features of the second fins. In this way, very effective manufacture of the heat exchanger of the invention is achieved. 
     The first pipe conduits and the second pipe conduits are advantageously expanded simultaneously in a pipe conduit expansion machine. Such simultaneous expansion is also very conducive to effective manufacture of the heat exchanger of the invention. 
     The present invention additionally provides a power plant having a generator cooled by means of a generator cooling gas and a heat exchanger of the invention that cools the generator cooling gas. 
     Advantageously, the first cooling medium that flows through the heat exchanger is cooling water, and the second cooling medium that flows through the heat exchanger is a coolant, for example tetrafluoromethane (R-134a) or carbon dioxide. 
     Further features and advantages of the present invention become clear from the description that follows with reference to the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures show: 
         FIG. 1  a schematic view of a power plant in one embodiment of the present invention; 
         FIG. 2  a schematic view of one embodiment of a heat exchanger of the invention in the power plant shown in  FIG. 1 ; 
         FIG. 3  a schematic side view in the direction of the arrow III in  FIG. 2 , showing a first stack of fins and a second stack of fins of the heat exchanger, omitting struts and an upper and lower cover for illustration purposes; 
         FIG. 4  a top view of a first fin of a first stack of fins of the heat exchanger shown in  FIG. 2 ; 
         FIG. 5  a top view of a second fin of a further stack of fins of the heat exchanger shown in  FIG. 2 ; 
         FIG. 6  a schematic view of a fin production machine for production of the fins shown in  FIGS. 4 and 5 ; 
         FIG. 7  a schematic perspective view of a fin compression mold of the fin production machine shown in  FIG. 6 ; and 
         FIG. 8  a schematic view of pipe conduit expansion tools of a pipe conduit expansion machine. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows a power plant  1  in one embodiment of the present invention. The power plant  1  in the present case is a gas turbine power plant, which may in principle likewise be any type of power plant. The power plant  1  comprises an air compressor  2 , a gas turbine  3 , a generator  4  and a transformer  5 . During the operation of the power plant  1 , air compressed by the air compressor  2  is mixed with fuel in a known manner, and the air-fuel mixture is ignited. The resultant combustion gas is supplied to the gas turbine  3 , where it is expanded to drive a gas turbine rotor  6 . The gas turbine rotor  6  drives the rotor  46  of the generator  4 , which converts the kinetic energy to electrical energy. The transformer  5  transforms the electrical energy in such a way that it can be fed to a power supply grid. The generator  4  is supplied by DC power in operation via contact rings or a brushless exciter  47 . 
     The generator  4  is cooled using generator cooling gas, which is circulated through a generator cooling circuit  7  by means that are not shown in detail. The generator cooling gas is recooled by provision of a heat exchanger  8  in one embodiment of the present invention. In the heat exchanger  8 , the generator cooling gas is cooled firstly using cooling water that circulates in a cooling water circuit  9 , and secondly by means of a coolant that circulates in a coolant circuit  10 . The cooling water circuit  9  in the present case is what is called the intermediate cooling water circuit of the power plant  1 , to which further heat exchangers are also connected, by means of which lubricant oil, sealing oil, pumps and/or other components of the power plant  1 , for example, are cooled. The coolant circuit  10  through which the coolant flows comprises a cooling unit for recooling of the coolant. The coolant used in the present context is tetrafluoroethane (R-134a). Alternatively, it is also possible to use another coolant such as carbon dioxide, to give just one example. 
     During the operation of the power plant  1 , the generator cooling gas removes heat from the generator  4 , is recooled in the heat exchanger  8  and then is guided back into the generator  4 . In the heat exchanger  8 , the heat withdrawn from the generator cooling gas is transferred firstly to the cooling water that flows through the cooling water circuit  9  and secondly to the coolant that flows through the coolant circuit  10 . 
     A significant advantage of the power plant  1  shown in  FIG. 1  is that the generator cooling gas that flows through the generator cooling gas circuit  7  is recooled not solely by means of cooling water but additionally by means of a coolant. In this way, the cold gas temperature of the generator cooling gas on entry into the generator  4  is adjustable or controllable very flexibly and as required. A further advantage is that the generator cooling gas is recooled by the cooling water and by the coolant in a single heat exchanger  8 , since the use of a single heat exchanger  8  saves construction space. This is of particular importance especially when an existing heat exchanger of a power plant in which the recooling is effected solely using cooling water is to be replaced by a heat exchanger of the invention, since the construction space that is then available is defined by the dimensions of the old heat exchanger and is correspondingly limited. 
       FIG. 2  shows one possible design of a heat exchanger  8  of the invention. The heat exchanger  8  through which a generator cooling gas flows in a flow direction indicated by the arrows  11  comprises a first stack of fins  12  having a multitude of first fins  14  stacked in a stacking direction that extends transverse to the flow direction indicated by the arrow  13 . The first fins  14 , as shown in  FIG. 4 , are each provided with a multitude of first passage holes  15  that are flush with one another in stacking direction. The heat exchanger  8  further comprises at least one further stack of fins  16  arranged adjacent to the first stack of fins  12  in flow direction and having a multitude of second fins  17  stacked in the stacking direction, wherein the second fins  17  are each provided with a multitude of second passage holes  18  that are flush with one another in stacking direction. 
     The first fins  14  and the second fins  17  are each produced from sheet material, in the present case from aluminum, wherein the first fins  14  and/or the second fins  17  may be provided with a coating on one or both sides. The first fins  14  differ from the second fins  17  firstly in that they have a greater area. Secondly, the surfaces of the first fins  14 , apart from the first passage holes  15 , in the present case are smooth, whereas the surfaces of the second fins  17  are structured. The structuring in the working example presented is defined by elevated regions  19  that are slotted at the side and are provided in the upward direction, which increases the surface areas of the second fins  17  and influences the flow of the generator cooling gas through the further stack of fins  16 . However, it should be pointed out that the design of the surfaces both of the first fins  14  and of the second fins  17  may in principle vary as required. A further difference is that a distance a 1  between the first fins  14  in stacking direction is greater than a distance a 2  between the second fins  17  in stacking direction. Furthermore, the arrangement patterns of the first passage holes  15  differ from the arrangement patterns of the second passage holes  18 , as apparent from  FIGS. 3 and 4 . 
     The heat exchanger  8  further comprises first pipe conduits  20  that extend through the first passage holes  15  of the first fins  14  of the first stack of fins  12  and are press-fitted with the first fins  14 , and second passage holes  21  that extend through the second passage holes  18  of the second fins of the at least one further stack of fins  16  and are press-fitted with the second fins  17 . The first pipe conduits are each connected to one another via U-shaped connecting conduits  22 , and the cooling water flows through them successively, entering the first stack of fins  12  in the direction of the arrow  23  and exiting therefrom in the direction of the arrow  24 . The second pipe conduits  21  are each connected to one another by U-shaped connecting conduits  25 , and the coolant flows through them successively, entering the further stack of fins  16  in the direction of the arrow  26  and exiting therefrom in the direction of the arrow  27 . The first pipe conduits  20  and the second pipe conduits  21  have each been produced from a metallic material, from copper in the present case, where the flow cross section of the first pipe conduits  20  is greater than the flow cross section of the second pipe conduits  21 . The inner faces of the first pipe conduits  20  and/or the inner faces of the second pipe conduits  21  may be structured in order to increase their surface area. 
     The heat exchanger  8  additionally comprises an upper cover and lower cover  28 , each of which connect the first stack of fins  12  and the further stack of fins  16  to one another. The covers  28  are respectively placed onto the outer first fins  14  of the first stack of fins  12  and onto the adjacent outer second fins  17  of the further stack of fins  16  in stacking direction from the bottom and from the top, and cover these fins  14  and  17 . The covers  28  have been provided with first passage openings  29  that are arranged and formed so as to correspond to the first passage holes  15  of the first fins  14  of the first stack of fins  12 , through which the first pipe conduits  20  are conducted, and with second passage openings  30  that are arranged and formed so as to correspond to the second passage holes  18  of the second fins  17  of the further stack of fins  16 , through which the second pipe conduits  21  are conducted. The covers  28  have been produced from a metallic material, in the present case each from a metal sheet of aluminum. They firstly have chamfers  31  that point in the direction of the stacks of fins  12  and  16 , which encompass these opposite sides, and secondly chamfers  32  that point outward, which serve to protect the pipe conduits  20 ,  21  or the connecting conduits  22 ,  25  that connect these to one another. The covers  28  are connected to one another via struts  33  in the present case, which impart good mechanical stiffness to the heat exchanger. 
       FIG. 6  shows a schematic of a fin production machine  34  with a sheet metal roll accommodation device  36  that accommodates a roll of sheet metal  35 , a sheet metal conveying device  37 , a fin pressing device  38  having an upper fin press mold  39  and a lower fin press mold  40 , a fin transport device  41  and a fin stacking device  42 . 
     During the operation of the fin production machine  34 , sheet metal from which the first fins  14  and the second fins  17  are to be manufactured is unwound by means of the sheet metal conveying device  37  from the roll of sheet metal  35  that is held by the sheet metal roll accommodation device  36  and fed to the fin pressing device  38 . Both the first fins  14  and the second fins  17  are formed therein by movement of the fin press molds  39  and  40  together and movement thereof away from one another. As shown in  FIG. 7 , the fin press molds  39  and  40  have different regions A 1 , A 2 , A 3 , A 4 , B 1 , B 2 , B 3  and B 4 , which form features of the fins  14  and  17 . The regions identified by A form features of the first fin  14 , and the regions identified by B form features of the second fin  17 . The regions identified by number  1  form slots in the sheet metal; the regions identified by number  2  expand slotted regions; the regions identified by number  3  perform deep drawing of the sheet metal. The first fins  14  and second fins  17  manufactured in this way in the fin pressing device  38  are then moved using the fin transport device  41  to the fin stacking device  42 , where the first fins  14  and the second fins  17  are respectively stacked one on top of another. 
     The stacked fins  14  and  17  are then moved to a pipe conduit expansion machine  43 . The pipe conduits  20  and  21  that have been introduced in the meantime into the corresponding passage holes  15 ,  18  of the stacked fins  14 ,  17  are expanded simultaneously therein using suitably shaped pipe conduit expansion tools  44  by pushing the pipe conduit expansion tools  44  through the pipe conduits  20 ,  21  from the top in the direction of the arrows  45 . 
     In further steps, the covers  28 , the struts  33  and the connecting conduits  22 ,  25  are mounted. 
     Even though the invention has been further illustrated and described in detail by the working example, the invention is not limited by the examples disclosed, and other variations may be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.