Patent Publication Number: US-2018033941-A1

Title: Power generation system

Description:
TECHNICAL FIELD 
     The present invention relates to a power generation system for generating electric power with a thermoelectric element utilizing a temperature difference between supplied high- and low-temperature fluids and for adjusting at least one of the high- and low-temperature fluids to a prescribed temperature before discharging it out of the system. 
     BACKGROUND ART 
     Known power generation systems include a system using thermoelectric elements to convert thermal energy into electric energy by the Seebeck effect (as shown in Patent Document 1, for example). Patent Document 1 discloses that a system includes thermoelectric elements interposed between a pair of thermally conductive plates to thereby form plate-like power generating units, and that a plurality of the plate-like power generating units are laminated to form high- and low-temperature passages between adjoining pairs of the plate-like power generating units which passages allow high- and low-temperature fluids to flow, respectively. The power generation system is incorporated into a power generating plant and utilizes water vapor that has passed through a steam turbine as the high-temperature fluid. This type of power generation system utilizes waste heat in the plant in generating power, and thus can help improve energy efficiency of the whole plant. 
     PRIOR ART DOCUMENT(S) 
     Patent Document(s) 
     Patent Document 1: JP2009-081970A 
     SUMMARY OF THE INVENTION 
     Task to be Accomplished by the Invention 
     Since each thermoelectric element generates only a low electromotive force, a large number of thermoelectric elements are generally used in series connection. However, the larger the number of thermoelectric elements is, the larger the amount of heat exchange between the high-temperature fluid and the low-temperature fluid flowing in the power generation system, which results in decreased temperature differences between both sides of some thermoelectric elements. The electromotive force generated by a thermoelectric element changes depending on a temperature difference between both sides of the thermoelectric element. Thus, when a power generation system operates in a state where temperature differences between both sides of the thermoelectric elements are relatively small, the power generation efficiency per element decreases, resulting in an increase in the cost of the power generation system in terms of a power generation amount. Thus, from a perspective of efficiency of electric power generation, it is preferable to configure a power generation system to include a decreased number of thermoelectric elements, thereby reducing the amount of heat exchange between the high- and low-temperature fluids to maintain higher temperature differences between both sides of the respective thermoelectric elements. However, in this case, only a small amount of heat is exchanged between the high- and low-temperature fluids when the fluids flow between thermoelectric elements. Thus, it becomes difficult to cool the discharged high-temperature fluid or to heat the discharged low-temperature fluid; that is, it becomes difficult to adequately adjust the temperatures of the discharged fluids. 
     The present invention has been made in view of the aforementioned problems of the prior art, and a primary object of the present invention is to provide a power generation system having an increased power generation efficiency per each thermoelectric element and capable of adjusting the temperature of high- or low-temperature fluid to be discharged out of the system. 
     Means to Accomplish the Task 
     In order to attain the above object, one aspect of the present invention provides a power generation system ( 1 ) comprising a power generation module ( 2 ) provided with one or more thermoelectric elements ( 7 A,  7 B); a heat exchanger ( 3 ); a high-temperature fluid passage ( 4 ) including a high-temperature fluid inlet ( 4 A) and a high-temperature fluid outlet ( 4 B), the high-temperature fluid passage being connected to the power generation module and the heat exchanger both located between the high-temperature fluid inlet and the high-temperature fluid outlet; and a low-temperature fluid passage ( 5 ) including a low-temperature fluid inlet ( 5 A) and a low-temperature fluid outlet ( 5 B), the low-temperature fluid passage being connected to the power generation module and the heat exchanger both located between the low-temperature fluid inlet and the low-temperature fluid outlet, wherein the low-temperature fluid passage includes a low-temperature-side bypass passage ( 5 F) for bypassing the power generation module, and a low-temperature-side flow rate adjusting valve ( 50 ) for adjusting a flow rate of the low-temperature fluid flowing into the power generation module, and a degree of opening of the low-temperature-side flow rate adjusting valve is controlled based on a temperature difference between the high-temperature fluid and the low-temperature fluid immediate after flowing out of the high-temperature fluid outlet and the low-temperature fluid outlet. 
     According to this aspect of the present invention, even when the system is used under the condition that less heat is exchanged in order to maintain the temperature difference between the high-temperature fluid and the low-temperature fluid in the power generation modules, the system is allowed to use the heat exchanger provided downstream of the power generation module to cool the high-temperature fluid or to heat the low-temperature fluid before discharging it out of the system. This means that even when the system is used under the condition that the temperature difference between the high-temperature fluid and the low-temperature fluid in the power generation modules is maintained rather high so as to improve the power generation efficiency per element, the system is allowed to adjust the temperature of the high-temperature fluid or heat the low-temperature fluid by the heat exchanger before discharging it out of the system. Accordingly, the power generation system can be applied to a part of various plants where cooling or heating fluid is required, and thus can be substituted for a conventional heat exchanging system. Also, the power generation system of the present invention can be constructed by adding the power generation module at a location upstream of a conventional heat exchanging system. This means that the system of the present invention can be easily applied to an existing facility. In addition, in the power generation system, the power generation module and the heat exchanger use the common high- and low-temperature fluids, thereby enabling the system to be simple. Moreover, since the high- and low-temperature fluids are supplied to the power generation module before being supplied to the heat exchanger, the system is allowed to increase the temperature difference between the high- and low-temperature fluids in the power generation module. Furthermore, even when changes occur in the temperatures and flow rates of the high-temperature fluid and the low-temperature fluid, the system is allowed to adjust the flow rate of the low-temperature fluid supplied to the power generation module to maintain the temperature difference between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module to a prescribed level or more. 
     The above-described system of the present invention may further include a high-temperature-side bypass passage ( 4 F) for bypassing the power generation module, and a high-temperature-side flow rate adjusting valve ( 55 ) for adjusting a flow rate of the high-temperature fluid flowing into the power generation module, wherein a degree of opening of the high-temperature-side flow rate adjusting valve is controlled based on the temperature difference between the high-temperature fluid and the low-temperature fluid immediate after flowing out of the power generation module. 
     In this case, even when changes occur in the temperatures and flow rates of the high- and low-temperature fluids, the system is allowed to adjust the flow rate of the high-temperature fluid supplied to the power generation module to maintain the temperature difference between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module to a prescribed level or more. 
     Another aspect of the present invention provides a power generation system ( 1 ) comprising a power generation module ( 2 ) provided with one or more thermoelectric elements ( 7 A,  7 B); a heat exchanger ( 3 ); a high-temperature fluid passage ( 4 ) including a high-temperature fluid inlet ( 4 A) and a high-temperature fluid outlet ( 4 B), the high-temperature fluid passage being connected to the power generation module and the heat exchanger both located between the high-temperature fluid inlet and the high-temperature fluid outlet; and a low-temperature fluid passage ( 5 ) including a low-temperature fluid inlet ( 5 A) and a low-temperature fluid outlet ( 5 B), the low-temperature fluid passage being connected to the power generation module and the heat exchanger both located between the low-temperature fluid inlet and the low-temperature fluid outlet, wherein the high-temperature fluid passage includes a high-temperature-side bypass passage ( 4 F) for bypassing the power generation module, and a high-temperature-side flow rate adjusting valve ( 55 ) for adjusting a flow rate of the high-temperature fluid flowing into the power generation module, and a degree of opening of the high-temperature-side flow rate adjusting valve is controlled based on a temperature difference between the high-temperature fluid and the low-temperature fluid immediate after flowing out of the high-temperature fluid outlet and the low-temperature fluid outlet. 
     In this aspect of the present invention, the high-temperature-side bypass passage ( 4 G) may bypass the power generation module and the heat exchanger. 
     In this case, when the temperature of the high-temperature fluid is low, the system is allowed to discharge the high-temperature fluid out of the system without causing the fluid to flow through the power generation module and the heat exchanger. 
     In the above-described aspect, the system preferably comprise a temperature controller ( 141 ,  151 ) provided between the high-temperature fluid inlet and the power generation module for controlling a temperature of the high-temperature fluid. 
     In this case, the system is allowed to adjust the temperature of the high-temperature fluid to be supplied to the power generation module. This means that the system can prevent the high-temperature fluid having an excessively high temperature from being supplied to the power generation module, thereby preventing heat damage to the thermoelectric elements. 
     Preferably, the above-described system of the present invention includes the temperature controller ( 151 ) which is connected to a branch passage branched from the low-temperature fluid passage and controls the temperature of the high-temperature fluid by mixing the low-temperature fluid supplied from the branch passage and the high-temperature fluid. 
     In this case, the system can decrease the temperature of the high-temperature fluid in an efficient manner. For example, the system so configured is suitable for cases where the high-temperature fluid and the low-temperature fluid can be mixed, for example cases where the high-temperature fluid and the low -temperature fluid are the same fluid (e.g. an aqueous solution such as water). 
     The above-described system of the present invention preferably includes the temperature controller ( 141 ) which is connected to a branch passage branched from the low-temperature fluid passage and controls the temperature of the high-temperature fluid by exchanging heat between the low-temperature fluid supplied from the branch passage and the high-temperature fluid without mixing the low-temperature fluid and the high-temperature fluid. 
     In this case, the system can decrease the temperature of the high-temperature fluid while avoiding mixing of the high-temperature fluid and the low-temperature fluid. For example, the system so configured is suitable for cases where the high-temperature fluid is an organic solution such as hydrocarbon and the low-temperature fluid is an aqueous solution such as water. 
     Preferably, in the above-described system of the present invention, the temperature of the low-temperature fluid is  60 -degrees Celsius or lower at the low-temperature fluid outlet. 
     In this case, the system can prevent an undesirable rise in the temperature of the fluid in the low-temperature fluid passage, thereby minimizing clogging of the low-temperature fluid passage due to the growth of algae or the like. 
     Preferably, in the above-described system of the present invention, the power generation module is configured such that the high-temperature fluid and the low-temperature fluid flow in opposite directions along opposite sides of each thermoelectric element. 
     In this case, the system is allowed to unify the distribution of the temperature differences between the high-temperature fluid and the low-temperature fluid over the power generation module, thereby improving the efficiency of power generation by the thermoelectric elements. 
     Effect of the Invention 
     As can be appreciated from the foregoing, the present invention can provide a power generation system which can realize increased power generation efficiency and can be substituted for a conventional heat exchanging system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a power generation system in accordance with a first embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of the power generation system of the first embodiment of the present invention; 
         FIG. 3  is an exploded perspective view of a plate unit of the system of the first embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of the power generation system of the first embodiment of the present invention; 
         FIG. 5(A)  is a block diagram and  FIG. 5(B)  is a graphic representation showing temperature changes in the power generation system of the first embodiment of the present invention; 
         FIG. 6(A)  is a block diagram and  FIG. 6(B)  is a graphic representation showing temperature changes in a power generation system of a comparative embodiment; 
         FIG. 7  is a block diagram showing a power generation system in accordance with a second embodiment of the present invention; 
         FIG. 8  is a block diagram showing a power generation system in accordance with a third embodiment of the present invention; 
         FIG. 9  is a block diagram showing a power generation system in accordance with a fourth embodiment of the present invention; 
         FIG. 10  is a block diagram showing a power generation system in accordance with a fifth embodiment of the present invention; 
         FIG. 11  is a block diagram showing a power generation system in accordance with a sixth embodiment of the present invention; 
         FIG. 12  is a block diagram showing a power generation system in accordance with a seventh embodiment of the present invention; 
         FIG. 13  is a block diagram showing an example in which a power generation system of one embodiment of the present invention is applied to a petroleum refining plant; 
         FIG. 14  is a block diagram showing an example in which a power generation system of one embodiment of the present invention is applied to a power generating plant; 
         FIG. 15  is a block diagram showing an example in which a power generation system of one embodiment of the present invention is applied to an LNG regasification facility; 
         FIG. 16  is a block diagram showing an example in which a power generation system of one embodiment of the present invention is applied to a reaction facility; and 
         FIG. 17  is a block diagram showing an example in which a power generation system of one embodiment of the present invention is applied to a dehydrogenation reaction facility for hydrogenated aromatic compound. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Power generation systems in accordance with preferred embodiments of the present invention are described in the following with reference to the appended drawings. 
     First Embodiment 
     As shown in  Figure. 1 , the power generation system  1  includes a power generation module  2 , a heat exchanger  3 , a high-temperature fluid passage  4 , and a low-temperature fluid passage  5  connected to the power generation module  2  and to the heat exchanger  3 . The high-temperature fluid passage  4  includes a high-temperature fluid inlet  4 A serving as an inlet for a high-temperature fluid to the power generation system  1  and a high-temperature fluid outlet  4 B serving as a high-temperature fluid outlet from the power generation system  1 , and is connected to the power generation module  2  and the heat exchanger  3  both located between the high-temperature fluid inlet  4 A and the high-temperature fluid outlet  4 B. The low-temperature fluid passage  5  includes a low-temperature fluid inlet  5 A serving as an inlet for low-temperature fluid to the power generation system  1  and a low-temperature fluid outlet  5 B serving as an outlet of low-temperature fluid from the power generation system  1 , and is connected to the power generation module  2  and the heat exchanger  3  both located between the low-temperature fluid inlet  5 A and the low-temperature fluid outlets  5 B. 
     In the present embodiment, the high-temperature fluid passage  4  includes a passage  4 C connecting the high-temperature fluid inlet  4 A and the power generation module  2 , a passage  4 D connecting the power generation module  2  and the heat exchanger  3 , and a passage  4 E connecting the heat exchanger  3  and the high-temperature fluid outlet  4 B. Thus, the high-temperature fluid passage  4  connects the power generation module  2  and the heat exchanger  3  in series, and the high-temperature fluid flows in the order of the power generation module  2  and the heat exchanger  3 . 
     In the present embodiment, the low-temperature fluid passage  5  includes a passage  5 C connecting the low-temperature fluid inlet  5 A and the power generation module  2 , a passage  5 D connecting the power generation module  2  and the heat exchanger  3 , and a passage  5 E connecting the heat exchanger  3  and the low-temperature fluid outlet  5 B. Thus, the low-temperature fluid passage  5  connects the power generation module  2  and the heat exchanger  3  in series, and the low-temperature fluid flows in the order of the power generation module  2  and the heat exchanger  3 . In addition, the low-temperature fluid passage  5  includes a bypass passage  5 F connected to the passages  5 C and  5 D to bypass the power generation module  2 . 
     As shown in  FIGS. 3 and 4 , the power generation module  2  includes thermoelectric elements  7 A,  7 B, which convert thermal energy into electric energy by the Seebeck effect. In the present embodiment, each thermoelectric element  7 A is formed of a p-type semiconductor and each thermoelectric element  7 B is formed of an n-type semiconductor. In other embodiments, the thermoelectric elements  7 A,  7 B may be formed of metal. 
     Multiple sets of the elements  7 A and  7 B are combined with each other to form a subunit  8 . The subunit  8  includes two plates  9 A,  9 B. The thermoelectric elements  7 A,  7 B are arranged between the two plates  9 A,  9 B. The plates  9 A and  9 B are preferably made of a material having high thermal conductivity. The multiple sets of the thermoelectric elements  7 A and  7 B are arranged in a planar fashion along and between the two plates  9 A and  9 B. One end on the side of the plate  9 A of a thermoelectric element  7 A is electrically connected to one end of the same side of an adjoining thermoelectric element  7 B via an electrode  13 , and the other end on the side of the plate  9 B of the thermoelectric element  7 B is in turn electrically connected to one end of the same side of another adjoining thermoelectric element  7 A via another electrode  13 . As a result, the multiple sets of the thermoelectric elements  7 A and  7 B form a series of electric circuits. The thermoelectric elements  7 A and  7 B may be connected to one another in any fashion, such as in series, in parallel or the combination thereof. In the present embodiment, a single plate unit  12  includes the multiple sets of the thermoelectric elements  7 A and  7 B, which are connected in series to one another to form an electric circuit having two electrodes  13  at either end of the circuit. Each electrode  13  is connected to a lead  15 . 
     An insulator  16  is provided such that it extends between each electrode  13  and either of the two plates  9 A and  9 B, between the two electrodes  13 , and between the thermoelectric elements  7 A and  7 B. Respective edges of the plates  9 A,  9 B are bonded to each other at either end except for where the leads  15  are drawn out. The plates  9 A and  9 B may be bonded by pressing bonding or any other bonding method. 
     The plurality of subunits  8  formed as described above are disposed between two plates  11 A and  11 B so that the subunits  8  and the plates  11 A and  11 B form a plate unit  12 . Each subunit  8  is arranged such that the plates  9 A,  9 B are in contact with the plate  11 A,  11 B, respectively. The subunits  8  are connected one another by the leads  15  to form a series of electric circuits. The subunits  8  may be connected to one another in any fashion such as in series, in parallel or the combination thereof. In the present embodiment, the subunits  8  are connected in series to one another. Respective edges of the plates  11 A,  11 B are bonded to each other at either end except for where the leads  15  are drawn out from the subunits  8  at the ends of the circuits. The plates  11 A and  11 B may be bonded by pressing bonding or any other bonding method. 
     In the present embodiment, the thermoelectric elements  7 A and  7 B are combined to form each of the subunits  8 , and the subunits  8  are disposed between the two plates  11 A and  11 B. In other embodiments, the plates  9 A and  9 B may be omitted and the thermoelectric elements  7 A and  7 B may be disposed between the plates  11 A and  11 B with the insulator  16  being disposed therebetween. 
     As shown in  FIG. 2 , the bonded upper edges of the two plates  11 A and  11 B define a first hole  21  and a second hole  22  extending through both the plates  11 A and  11 B in their thickness direction Similarly, the bonded lower edges of the two plates  11 A and  11 B define a third hole  23  and a fourth hole  24  extending through both the plates  11 A and  11 B in their thickness direction. Since the first to fourth holes  21 - 24  are formed in the portions where the plates  11 A and  11 B are bonded to each other, the first to fourth holes  21 - 24  are separated from the space where the thermoelectric elements  7 A and  7 B are arranged between the two plates  11 A and  11 B. In another embodiment, a gasket may be interposed between the plates  11 A and  11 B so that the space in which the thermoelectric elements  7 A and  7 B are disposed is liquid-tightly partitioned from the first to fourth holes  21 - 24 . 
     The power generation module  2  includes a plurality of plate units  12  laminated in a front-to-rear direction, a front end plate  26  disposed on the front side of the frontmost plate unit  12 , a rear end plate  27  disposed on the rear side of the rearmost plate unit  12 , and gaskets  30 A,  30 B,  30 C disposed between respective adjoining plate units  12  which are arranged between the frontmost plate unit  12  and the front end plate  26 , and disposed between the rearmost plate unit  12  and the rear end plate  27 . A front outer plate  31  is disposed on the front side of the front end plate  26  and a rear outer plate  32  is disposed on the rear side of the rear end plate  27 . The front outer plate  31  and the rear outer plate  32  are connected by a plurality of tie rods (not shown) extending in the front-to-rear direction, and thus the front end plate  26 , the plurality of plate units  12 , the rear end plate  27 , and the gaskets  30 A,  30 B,  30 C are laminated in the front-to-rear direction and sandwiched between the front outer plate  31  and the rear outer plate  32 . 
     The front end plate  26  defines connection hole  35  extending through in the thickness direction and substantially aligned with the first to fourth holes  21 - 24 . The front outer plate  31  defines a high-temperature fluid inlet hole  36 , a low-temperature fluid outlet hole  37 , a high-temperature fluid outlet hole  38 , and a low-temperature fluid inlet hole  39  which are substantially aligned with the first hole  21 , the second hole  22 , the third hole  23 , and the fourth hole  24 , respectively. The high-temperature fluid inlet hole  36 , the low-temperature fluid outlet hole  37 , the high-temperature fluid outlet hole  38 , and the low-temperature fluid inlet hole  39  extend through the front outer plate  31  in its thickness direction. 
     The gaskets  30 A,  30 B,  30 C include three types of gaskets; that is, a first, gasket  30 A, a second gasket  30 B, and a third gasket  30 C. The plate units  12  are numbered as first, second, . . . n-th in ascending order from the front side (n is an odd number in the present embodiment). Each first gasket  30 A is interposed between the front surface of an odd-numbered plate unit  12  and the rear surface of a corresponding even-numbered plate unit  12  or the rear surface of the front end plate  26 . Each second gasket  30 B is interposed between the rear surface of an odd-numbered plate unit  12  and the front surface of a corresponding even-numbered plate unit  12  or the front surface of the rear end plate  27 . The third gaskets  30 C are interposed between the rear surface of the front outer plate  31  and the front surface of the front end plate  26 , respectively. 
     Each first gasket  30 A, the rear surface of a corresponding even-numbered plate unit  12 , and the front surface of an corresponding odd-numbered plate unit  12  form low-temperature continuous passages  41 B connecting the second holes  22  of both the plate units  12  and connecting the fourth holes  24  of both the plate units  12 , respectively, and also form high-temperature main passages  42 A connecting the first holes  21  of both the plate units  12  and connecting the third holes  23  of both the plate units  12 , respectively Similarly, the first gasket  30 A, the rear surface of the front end plate  26 , and the front surface of the odd-numbered plate unit  12  form the low-temperature continuous passages  41 B connecting the second hole  22  and the connection hole  35  substantially aligned with the second hole  22  and connecting the fourth hole  24  and the connection hole  35  substantially aligned with the fourth hole  24 , respectively, and also form the high-temperature main passage  42 A connecting all the four holes including the first hole  21 , the third hole  23 , and the two connections holes  30  substantially aligned with the first hole  21  and the third hole  23 , respectively. The high-temperature main passages  42 A are formed so as to cover most part of the main surfaces of the plate units  12 . 
     Each second gasket  30 B, the rear surface of a corresponding odd-numbered plate unit  12 , and the front surfaces of an corresponding even-numbered plate unit  12  form high-temperature connection passages  42 B which are one connecting the first holes  21  of the plate units  12  and the other connecting the third holes  23  of both the plate units  12 , and also form low-temperature main passages  41 A which are one connecting the second holes  22  of both the plate units  12  and the other connecting the fourth holes  24  of both the plate units  12 . Also, the second gasket  30 B, the rear surface of the odd-numbered plate unit  12 , and the front surface of the rear end plate  27  form the low-temperature main passage  41 A connecting the second hole  22  and the fourth hole  24 , and closes the first hole  21  and the third hole  23 . The low-temperature main passages  41 A are formed so as to cover most part of the main surfaces of the plate units  12 . 
     The third gasket  30 C, the rear surface of the front outer plate  31 , and the front end plate  26  form the high-temperature connection passages  42 B which are one connecting the high-temperature fluid inlet hole  36  and the connection hole  35  substantially aligned with the hole  36  and the other connecting the high-temperature fluid outlet hole  38  and the connection hole  35  substantially aligned with the hole  38 , and also form the low-temperature continuous passages  41 B which are one connecting the low-temperature fluid inlet hole  39  and the connection hole  35  substantially aligned with the hole  39  and the other connecting the low-temperature fluid outlet hole  37  and the connection hole  35  substantially aligned with the hole  37 . 
     With the above-described configuration, the high-temperature fluid inlet hole  36  and the high-temperature fluid outlet hole  38  are connected to each other via the high-temperature connection passage  42 B, the first hole  21 , the high-temperature main passage  42 A, and the third hole  23  to form part of the high-temperature fluid passage  4 . Likewise, the low-temperature fluid inlet hole  39  and the low-temperature fluid outlet hole  37  are connected to each other via the low-temperature connection passage  41 B, the fourth hole  24 , the low-temperature main passage  41 A, and the second hole  22  to form part of the low-temperature fluid passage  5 . The high-temperature fluid passage  4  and the low-temperature fluid passage  5  are disposed on either of the front and rear surfaces of each plate unit  12 . The high-temperature fluid flowing through the high-temperature fluid passage  4  flows downward on one surface of the plate unit  12  (see voided arrows in  FIG. 2 ), and the low-temperature fluid flowing through the low-temperature fluid passage  5  flows upward on the other surface of the plate unit  12  (see black arrows in  FIG. 2 ). Thus, the high-temperature fluid and the low-temperature fluid flow in opposite directions along opposite sides of the plate unit  12 . 
     The heat exchanger  3  has a passage through which the high-temperature fluid flows and another passage through which the low-temperature fluid flows, and exchanges heat between the high-temperature fluid and the low-temperature fluid. The heat exchanger  3  may be a known heat exchanger  3  such as a plate-type heat exchanger or a spiral-type heat exchanger. The passage for the high-temperature fluid and the passage for the low-temperature fluid are arranged such that the high-temperature fluid and the low-temperature fluid flow in opposite directions. 
     In the power generation module  2 , the high-temperature fluid inlet hole  36 , the high-temperature fluid outlet hole  38 , the low-temperature fluid inlet hole  39 , and the low-temperature fluid outlet hole  37  are connected to the passage  4 C, the passage  4 D, the passage  5 C, and the passage  5 D, respectively. 
     A flow rate adjusting valve  50  is provided in the bypass passage  5 F. By opening and closing the flow rate adjusting valve  50 , the flow rate of the low-temperature fluid flowing through the bypass passage  5 F is adjusted. Thus, by opening and closing the flow rate adjusting valve  50 , the flow rate of the low-temperature fluid flowing into the power generation module  2  is adjusted. 
     A high-temperature-side temperature sensor  51  is provided in the passage  4 D of the high-temperature fluid passage  4  at the outlet of the power generation module  2 , and a low-temperature-side temperature sensor  52  is provided in the passage  5 D of the low-temperature fluid passage  5  at the outlet of the power generation module  2 . The low-temperature-side temperature sensor  52  is provided in the passage  5 D upstream from where the downstream end of the bypass passage  5 F is connected to the passage  5 D. Furthermore, the power generation system  1  has a control device (not shown) for controlling the flow rate adjusting valve  50 . The control device receives detection signals from the high-temperature-side temperature sensor  51  and the low-temperature-side temperature sensor  52  and calculates, on the basis of these detection signals, a temperature difference AT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2 . Then, the control device sets the target opening degree of the flow rate adjusting valve  50  based on the calculated temperature difference AT, and controls the degree of opening/closing of the flow rate adjusting valve  50 . For example, when the temperature difference AT is equal to or greater than the prescribed threshold value, the control device  53  closes the flow rate adjusting valve  50 , and when the temperature difference AT is less than the threshold value, the control device  53  controls the low-rate-adjusting valve  50  so that the degree of opening increases as the temperature difference AT decreases. 
     In the power generation module  2 , when the high-temperature fluid flows on one surface of the plate unit  12  and the low-temperature fluid flows on the other surface of the plate unit  12 , the temperatures of one ends of the thermoelectric elements  7 A and  7 B on the side of the one surface of the plate unit  12  become higher than those of the other ends of the thermoelectric elements  7 A and  7 B on the other side, by which temperature differences occur between the respective ends of the thermoelectric elements  7 A and  7 B. As a result, an electromotive force is generated in each of the thermoelectric elements  7 A and  7 B due to the Seebeck effect. The electromotive forces generated in the thermoelectric elements  7 A and  7 B are proportional to the temperature differences occurring in the thermoelectric elements  7 A and  7 B, respectively. 
     In the power generation system  1  shown in  FIG. 5 , T 1   in  denotes a temperature of the high-temperature fluid measured at the inlet of the system  1  (or the high-temperature fluid inlet hole  36 ), T 1   x  denotes a temperature of the high-temperature fluid measured at the outlet of the power generation module  2  (or the high-temperature fluid outlet hole  38 , the inlet of the heat exchanger  3 ), Tlout denotes a temperature of the high-temperature fluid measured at the outlet of the system  1  (or the outlet of the heat exchanger  3 ), T 2 in denotes a temperature of the low-temperature fluid measured at the inlet (or the low-temperature fluid inlet hole  39 ) of the power generation system  1 , T 2 x denotes a temperature of the low-temperature fluid measured at the outlet of the power generation module  2  (or the low-temperature fluid outlet hole  37 , the inlet of the heat exchanger  3 ), and T 2  denotes a temperature of the low-temperature fluid measured at the outlet of the system  1  (or the outlet of the heat exchanger  3 ). 
     The temperature difference ΔT (ΔT=T 1   x −T 2   x ) between the high-temperature fluid and the low-temperature fluid at the outlet of the power generation module  2  is set to be not less than a prescribed level. The temperature difference ΔT is set to 30-degrees Celsius or more, preferably 50-degrees Celsius or more. The temperature difference ΔT can be varied by changing the temperatures and/or flow rates of the high-temperature fluid and the low-temperature fluid. 
     In the power generation system  1 , the amount of heat loss from the high-temperature fluid occurring during flow of the fluid in the power generation module  2  is indicated by Qg, the amount of heat loss from the high-temperature fluid occurring during flow of the fluid in the heat exchanger  3  is indicated by Qc, and the amount of heat loss from the high-temperature fluid occurring during flow of the fluid in the entire system is represented by Q 0  (=Qg+Qc). The amount of heat loss (Qg) from the high-temperature fluid occurring in the power generation module  2  is the total sum of the amount of heat received by the low-temperature fluid by heat transfer (Q 1 ), the amount of heat applied to the thermoelectric elements  7 A,  7 B by thermal conduction and converted to electricity (Q 2 ), Joule heat generated by current flowing through the thermoelectric elements  7 A and  7 B (Q 3 ), and the amount of heat dissipated from the power generation module  2  (Q 4 ). The amount of heat (Q 5 ) which causes the temperature rise of the low-temperature fluid is the total sum of the amount of heat transferred to the low-temperature fluid by heat conduction (Q 1 ) and the Joule heat (Q 3 ). The amount of heat Q 5  (=Q 1 +Q 3 ) received by the low-temperature fluid can be obtained by measuring the inlet temperature T 2 in and the outlet temperature T 2   x  of the low-temperature fluid of the power generation module  2 . In the present embodiment, the power generation efficiency η (%) in the power generation module  2  is defined as η=Q 2 /(Q 5 +Q 2 ) with reference to the amount of heat Q 5  received by the low-temperature fluid. 
       FIG. 6  shows a power generation system  1 , in which the heat exchanger  3  is omitted and only the power generation module  2  is used, as a comparative embodiment to be compared with the power generation system  1  according to the present embodiment. In the power generation system  1  of the comparative embodiment, the temperatures of the high- and the low-temperature fluids measured at their inlets and the temperatures of the high- and the low-temperature fluids measured at their outlets are set to the same values as the temperatures T 1   in,  T 2   in,  T 1   out,  T 2   out  of the power generation system  1  of the present embodiment. In the power generation system  1  of the comparative embodiment, the temperature difference ΔT 2  (T 1   out −T 2   out ) between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2  is obtained. Since the temperature difference ΔT at the outlets of the power generation module  2  in the power generation system  1  according to the present embodiment is larger than the temperature difference ΔT 2  at the outlet of the power generation module  2  according to the comparative embodiment, the amount of power generation per one thermoelectric element  7 A,  7 B increases. In addition, the temperature T 2   x  of the low-temperature fluid at the outlet of the power generation module  2  of the present embodiment is lower than the temperature T 2   out  of the low-temperature fluid at the outlet of the power generation module  2  of the comparative embodiment and the amount of heat Q 5  received by the low-temperature fluid in the present embodiment is smaller than that in the comparative embodiment, which means that the power generation efficiency of the power generation system  1  according to the present embodiment is improved as compared with the comparative embodiment. 
     Since the power generation system  1  according to the first embodiment includes the heat exchanger  3  located downstream of the power generation module  2 , the system is allowed to lower the temperature of the high-temperature fluid at the outlet of the power generation system  1  to a prescribed level or less while maintaining a large temperature difference between the high-temperature fluid and the low-temperature fluid in the power generation module  2 . As a result, the power generation system  1  of the present embodiment can be substituted for a heat exchanger  3  located in a place where otherwise only the heat exchanger  3  is used in a plant or other facilities of the prior art. Also, the power generation system  1  of the present embodiment can be formed by adding a thermoelectric module to a location upstream from where only the heat exchanger  3  is used in a plant or other facilities of the prior art. 
     Since the system controls the flow rate adjusting valve  50  based on the temperature difference ΔT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2  to thereby control the flow rate of the low-temperature fluid passing through the power generation module  2 , the temperature difference ΔT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2  is maintained at a prescribed threshold level or more, which enables the thermoelectric elements  7 A and  7 B to generate power with high efficiency. As a result, even when changes occur in the temperatures and flow rates of the high-temperature fluid and the low-temperature fluid flowing into the power generation system  1 , the power generation module  2  can generate power with high efficiency. 
     Power generation systems according to the second to seventh embodiments of the present invention will be described below. The power generation systems of the second to seventh embodiments are different from the power generation system  1  of the first embodiment in configurations of the high-temperature fluid passage and the low-temperature fluid passage. In the power generation systems of the second to seventh embodiments, the same or similar parts as in the first embodiment are designated by the same or similar references and the descriptions of those parts will not be repeated. 
     Second Embodiment 
     As shown in  FIG. 7 , a power generation system  100  according to the second embodiment is different from the power generation system  1  according to the first embodiment in that, in the system  100 , the high-temperature fluid passage  4  has a bypass passage  4 F connected to the passage  4 C and to the passage  4 D to bypass the power generation module  2 . The power generation system  100  is also different from the power generation system  1  in that, in the system  100 , the low-temperature fluid passage  5  of the power generation system  100  is not provided with the bypass passage  5 F and the flow rate adjusting valve  50 . 
     A flow rate adjusting valve  55  is provided in the bypass passage  4 F. By opening and closing the flow rate adjusting valve  55 , the flow rate of the high-temperature fluid flowing through the bypass passage  4 F is adjusted. Thus, by opening and closing the flow rate adjusting valve  55 , the flow rate of the high-temperature fluid flowing into the power generation module  2  is adjusted. The control device controls the flow rate adjusting valve  55  based on the temperature difference ΔT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2 . 
     In the power generation system  100 , even when changes occur in the temperatures and the flow rates of the high-temperature fluid and the low-temperature fluid flowing into the power generation system  100 , the flow rate of the high-temperature fluid supplied to the power generation module  2  can be controlled by the flow rate adjusting valve  55 . As a result, the temperature difference ΔT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2  is maintained at around a prescribed level, thereby enabling the power generation module  2  to generate power with high efficiency. 
     Third Embodiment 
     As shown in  FIG. 8 , a power generation system  110  according to the third embodiment is different from the power generation system  1  according to the first embodiment in that, in the system  110 , the high-temperature fluid passage  4  has a bypass passage  4 F connected to the passage  4 C and to the passage  4 D to bypass the power generation module  2 . A flow rate adjusting valve  55  is provided in the bypass passage  4 F. The control device controls the flow rate adjusting valve  50  based on the temperature difference ΔT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2 . 
     In power generation system  110 , even when changes occur in the temperatures and the flow rates of the high-temperature fluid and the low-temperature fluid flowing into the power generation system  110 , the flow rates of the high-temperature fluid and the low-temperature fluid supplied to the power generation module  2  can be controlled by the flow rate adjusting valves  50 ,  55 . 
     Fourth Embodiment 
     As shown in  FIG. 9 , a power generation system  120  according to the fourth embodiment is different from the power generation system  1  according to the first embodiment in that, in the system  120 , the high-temperature fluid passage  4  has a bypass passage  4 G connected to the passage  4 C and to the passage  4 D to bypass the power generation module  2  and the heat exchanger  3 . A flow rate adjusting valve  55  is provided in the bypass passage  4 G. By opening and closing the flow rate adjusting valve  55 , the flow rate of the high-temperature fluid flowing through the bypass passage  4 F is adjusted. The control device controls the flow rate adjusting valve  55  based on the temperature difference ΔT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2 . 
     Fifth Embodiment 
     As shown in  FIG. 10 , a power generation system  130  according to the fifth embodiment is different from the power generation system  1  according to the first embodiment in that, in the system  130 , each of the high-temperature fluid passage  4  and the low-temperature fluid passage  5  connects the power generation module  2  and the heat exchanger  3  in parallel. The high-temperature fluid passage  4  includes a passage  4 H connecting the high-temperature fluid inlet  4 A and the power generation module  2 , a passage  4 J connecting the power generation module  2  and the high-temperature fluid outlet  4 B, a passage  4 K connecting the passage  4 H and the heat exchanger  3 , and a passage  4 L connecting the heat exchanger  3  and the passage  4 J. The passage  4 K, the heat exchanger  3 , and the passage  4 L form a series of bypass passages to bypass the power generation module  2 . A flow rate adjusting valve  131  is provided in the passage  4 H downstream (on the side of the power generation module  2 ) from where the passage  4 K is connected to the passage H. A high-temperature-side temperature sensor  51  is provided in the passage  4 J upstream (on the side of the power generation module  2 ) from where the passage  4 L is connected to the passage  4 J. 
     The low-temperature fluid passage  5  includes a passage  5 H connecting the low-temperature fluid inlet  5 A and the power generation module  2 , a passage  5 J connecting the power generation module  2  and the low-temperature fluid outlet  5 B, a passage  5 K connecting the passage  5 H and the heat exchanger  3 , and a passage  5 L connecting the heat exchanger  3  and the passage  5 J. The passage  5 K, the heat exchanger  3 , and the passage  5 L form a series of bypass passages to bypass the power generation module  2 . A flow rate adjusting valve  132  is provided in the passage  5 K. A low-temperature-side temperature sensor  51  is provided in the passage  5 J upstream (on the side of the power generation module  2 ) from where the passage  5 L is connected to the passage  5 J. The control device controls the flow rate adjusting valves  131  and  132  based on the temperature difference AT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2 . 
     Sixth Embodiment 
     As shown in  FIG. 11 , a power generation system  140  according to the sixth embodiment is different from the power generation system  1  according to the first embodiment in that, in the system  140 , the high-temperature fluid passage  4  has the passage  4 C in which a temperature controller  141  is provided. The temperature controller  141  is an apparatus for adjusting the high-temperature fluid supplied to the power generation system  140  to a temperature suitable for the power generation module  2 . In the sixth embodiment, the temperature controller  141  is a known countercurrent type heat exchanger, which exchanges heat between the high-temperature fluid supplied to the high-temperature fluid inlet  4 A and the low-temperature fluid supplied to the low-temperature fluid inlet  5 A without mixing the high-temperature fluid and the low-temperature fluid. 
     The temperature controller  141  is connected to the high-temperature fluid inlet  4 A via a passage  4 C 1 , a part of the passage  4 C on the upstream side of the controller  141 , and connected to the power generation module  2  via a passage  4 C 2 , a part of the passage  4 C on the downstream side of the controller  141 . Moreover, the temperature controller  141  is connected to the power generation module  2  via a passage  5 D 1 , a part of the passage  5 D on the upstream side of the controller  141 , and connected to the heat exchanger  3  via a passage  5 D 2 , a part of the passage  5 D on the downstream side of the controller  141 . The passage  5 C and the passage  5 D 1  are connected to each other via a bypass passage  5 D 3  for bypassing the power generation module  2 . A flow rate adjusting valve  142  is provided in the bypass passage  5 D 3  for changing the flow rate of the low-temperature fluid flowing into the power generation module  2 . 
     An inlet temperature sensor  143  is provided in the passage  4 C 2  at the inlet of the power generation module  2  for detecting the temperature of the high-temperature fluid flowing into the power generation module  2 . The control device of the power generation system  140  controls the flow rate adjusting valve  142  based on the detected signal from the inlet temperature sensor  143 . For example, when the temperature of the high-temperature fluid flowing into the power generation module  2  is equal to or higher than a prescribed level, the control device opens the flow rate adjusting valve  142 , and increases the opening degree as the temperature rises. 
     The thermoelectric elements  7 A and  7 B of the power generation module  2  may be deformed or damaged when exposed to an excessively high temperature exceeding their use temperature range. However, in the power generation system  140 , the temperature controller  141  controls the temperature of the high-temperature fluid flowing into the power generation module  2  to ensure that damage to the thermoelectric elements  7 A,  7 B is prevented. The temperature controller  141  for cooling the high-temperature fluid is applied to cases where the high-temperature fluid is steam or high temperature steam of thermal oil, hydrocarbon, or the like. 
     Seventh Embodiment 
     As shown in  FIG. 12 , a power generation system  150  according to the seventh embodiment is different from the power generation system  140  according to the sixth embodiment in the configurations of a temperature controller  151  and a passage  5 C. The passage  5 C includes a passage  5 C 1  connecting the low-temperature fluid inlet  5 A and the power generation module  2  and a passage  5 C 2  connecting the passage  5 C 1  and the temperature controller  151 . A flow rate adjusting valve  152  is provided in the passage  5 C 2  for changing the flow rate of the low-temperature fluid flowing into the temperature controller  151 . The temperature controller  151  cools the high-temperature fluid by mixing the low-temperature fluid supplied from the passage  5 C 2  and the high-temperature fluid flowing from the passage  4 C 1  to the passage  4 C 2 . The control device of the power generation system  150  controls the flow rate adjusting valve  152  based on the detection signal from the inlet temperature sensor  143 . The seventh embodiment can be applied to cases where a high-temperature fluid and a low-temperature fluid can be mixed, e.g. when the high-temperature fluid is steam and the low-temperature fluid is water. 
     Example applications of the power generation systems of the first to seventh embodiments to various types of plants will be described below. Although the power generation system  1  according to the first embodiment is used in the following examples, the power generation systems  100 ,  110 ,  120 ,  130 ,  140 , and  150  according to the second to seventh embodiments can be used in a similar manner. 
     (Example Application to Petroleum Refining Plant) 
     As shown in  FIG. 13 , a petroleum refining plant  200  includes a heating furnace  201  for heating crude oil and a distillation unit  202  (distillation column) for distilling the crude oil heated in the heating furnace  201 . The power generation system  1  is provided downstream of the distillation unit  202  and is used as a heat exchanger for cooling any component of crude oil (e.g. heavy oil, light oil, kerosene, gasoline, or other component) separated in the distillation unit  202 . The high-temperature fluid inlet  4 A of the power generation system  1  is connected to a passage in which the component distilled in the distillation unit  202  flows, and the low-temperature fluid inlet  5 A of the power generation system  1  is connected to a cooling water passage. The component separated from crude oil in the distillation unit  202  is cooled during passing through the power generation system  1 , and the power generation system  1  utilizes part of heat of the component to generate power. 
     The low-temperature fluid inlet  5 A of the power generation system  1  may be connected to a passage in which crude oil flows before being fed to the heating furnace  201 , instead of being connected to the cooling water passage. In this case, crude oil is heated using heat obtained from a component which has flown through the distillation unit  202  in the power generation system  1 , which improves the energy efficiency in the petroleum refining plant  200 . 
     A heating unit  203  for providing heat by using electric power is provided in the heating furnace  201  or passage in which crude oil flows, and electric power generated by the power generation system  1  is supplied to the heating unit  203 . The heating unit  203  may be, for example, a heating device utilizing resistive heating. In this case, energy efficiency in the petroleum refining plant  200  is improved. In another embodiment, the heating unit  203  may be a heat exchanger, a heater for providing heat by fuel burning or the like, instead of using the heating device for providing heat by using electric power. 
     (Example Application to Power Generating Plant) 
     As shown in  FIG. 14 , a power generating plant  300  includes a boiler  301  for heating water to generate steam, a steam turbine  302  driven by steam generated by the boiler  301 , a generator  303  driven by the steam turbine  302 , and a condenser  304  for cooling and condensing the steam which has passed through the steam turbine  302 . The power generation system  1  of the present embodiment is provided between the steam turbine  302  and the condenser  304  and is used as a heat exchanger for cooling steam. The high-temperature fluid inlet  4 A of the power generation system  1  is connected to a passage in which the steam having passed through the steam turbine  302  flows and the low-temperature fluid inlet  5 A of the power generation system  1  is connected to a cooling water passage common to the condenser  304 . This means that the steam that has passed through the steam turbine  302  is used as the high-temperature fluid, and the cooling water used for the condenser  304  is used as the low-temperature fluid. The cooling water may be seawater, for example. The steam that has passed through the steam turbine  302  is cooled during passing through the power generation system  1 , and the power generation system  1  utilizes part of the heat of the steam to generate electric power. The power generation system generates power using the heat of steam otherwise discarded in the condenser  304 , which improves the energy efficiency of the power generating plant  300 . 
     (Example Application to LNG Regasification Facility) 
     As shown in  FIG. 14 , an LNG regasification facility  400  includes an LNG tank  401  for storing LNG and a seawater type vaporizer  402  for vaporizing LNG. The seawater type vaporizer  402  exchanges heat between seawater and LNG to vaporize the LNG by using the heat of the seawater. The power generation system  1  according to the present embodiment is provided between the LNG tank  401  and the seawater type vaporizer  402  and is used as the heat exchanger  3  that increases the temperature of the LNG. The high-temperature fluid inlet  4 A of the power generation system  1  is connected to a seawater passage, which is also connected to the seawater type vaporizer  402 , and the low-temperature fluid inlet  5 A of the power generation system  1  is connected to a passage in which the LNG from the LNG tank  401  flows. This means that the seawater is used as the high-temperature fluid, and the LNG is used as the low-temperature fluid. The LNG is heated during passing through the power generation system  1 , and the power generation system  1  utilizes a temperature difference between the seawater and the LNG to generate electric power. 
     (Example Application to Reaction Facility) 
     As shown in  FIG. 16 , a reaction facility  500  is a facility for reacting various materials to produce a product. The reaction facility  500  includes a raw material tank  501 , a heater  502 , and a reactor  503 . The power generation system  1  can be applied to various chemical industrial plants utilizing such a reaction facility  500  including plants for the petrochemical industry, the natural gas chemical industry, the coal chemical industry, the polymer chemical industry and other industries. 
     The raw material tank  501  is a tank for storing a raw material. The heater  502  heats the raw materials fed from the raw material tank  501  to the reactor  503 . The heater  502  is an electric heater, a heat exchanger, or any other type of heater. The reactor  503  is a vessel for causing an exothermic reaction or an endothermic reaction. 
     The power generation system  1  according to the present embodiment is provided downstream of the reactor  503  and is used as a heat exchanger for cooling the product generated in the reactor  503 . The high-temperature fluid inlet  4 A and the low-temperature fluid inlet  5 A of the power generation system  1  are connected to an outlet of the reactor  503  and a cooling water passage, respectively. The product is cooled during passing through the power generation system  1 . The power generation system  1  utilizes a temperature difference between the product and the cooling water to generate power. For example, when the heater  502  is an electric heater, the electric power generated by the power generation system  1  is supplied to the heater  502  and used to heat the raw material. 
     (Example Application to Dehydrogenation Reaction Facility) 
     As shown in  FIG. 17 , a dehydrogenation reaction facility  600  is a facility for producing hydrogen and an aromatic compound from a hydrogenated aromatic compound. Non-limiting examples of the hydrogenated aromatic compounds include benzene, toluene, and naphthalene, and non-limiting examples of the aromatic compounds include cyclohexane, methylcyclohexane, and tetralin. The dehydrogenation reaction facility  600  includes a hydrogenated aromatic compound tank  601 , a heater  602 , a dehydrogenation reaction unit  603 , a gas-liquid separation apparatus  604 , a hydrogen tank  605 , and an aromatic compound tank  606 . 
     The hydrogenated aromatic compound tank  601  is a tank for storing a hydrogenated aromatic compound as a raw material. The heater  602  heats the hydrogenated aromatic compound fed from the hydrogenated aromatic compound tank  601  to the dehydrogenation reaction unit  603 . The heater  602  is an electric heater, a heat exchanger, or any other type of heater. The dehydrogenation reaction unit  603  is a reaction vessel filled with a dehydrogenation catalyst for separating the hydrogenated aromatic compound into hydrogen and an aromatic compound. The hydrogenated aromatic compound heated by the heater  602  is decomposed in the dehydrogenation reaction unit  603  and fed to a gas-liquid separation apparatus  604  as a mixture of the hydrogen and the aromatic compound. The gas-liquid separation apparatus  604  separates the mixture to the hydrogen in the gaseous form and the aromatic compound in the liquid form. The hydrogen separated by the gas-liquid separation apparatus  604  is stored in a hydrogen tank  605 , and the aromatic compound is stored in an aromatic compound tank  606 . 
     The power generation system  1  according to the present embodiment is provided between the dehydrogenation reaction unit  603  and the gas-liquid separation apparatus  604  and used as a heat exchanger for cooling the hydrogen and the aromatic compound generated in the dehydrogenation reaction unit  603 . The high-temperature fluid inlet  4 A and the low-temperature fluid inlet  5 A of the power generation system  1  are connected to an outlet of the dehydrogenation reaction unit  603  and a cooling water passage, respectively. The hydrogen and the aromatic compound are cooled during passing through the power generation system  1 , and the gaseous aromatic compound is condensed. The power generation system  1  utilizes a temperature difference between the mixture of the hydrogen and the aromatic compound and cooling water to generate electric power. For example, when the heater  602  is an electric heater, the electric power generated by the power generation system  1  is supplied to the heater  602  and used to heat the hydrogenated aromatic compound. 
     Although the specific embodiments have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways. For example, although in the above-described embodiments, the control device controls the flow rate adjusting valves ( 50 ,  60 , etc.) based on the temperature difference AT between the high-temperature fluid and the low-temperature fluid at the outlets of the power generation module  2 , the temperature of the low-temperature fluid at the outlet of the power generation module  2  may be further controlled to be  60 -degrees Celsius or less. In this case, the system can prevent an undesirable rise in the temperature of the fluid in the low-temperature fluid passage  5 , thereby minimizing the growth of algae. 
     GLOSSARY 
     
         
           1 ,  100 ,  110 ,  120 ,  130 ,  140 ,  150  power generation system 
           2  power generation module 
           3  heat exchanger 
           4  high-temperature fluid passage 
           4 A high-temperature fluid inlet 
           4 B high-temperature fluid outlet 
           4 F,  4 G bypass passage 
           5  low-temperature fluid passage 
           5 A low-temperature fluid inlet 
           5 B low-temperature fluid outlet 
           5 F bypass passage 
           7 A thermoelectric element 
           7 B thermoelectric element 
           11  plate 
           12  plate unit 
           13  electrode 
           15  lead 
           16  insulator 
           30  gasket 
           50 ,  55 ,  142 ,  152  flow rate adjusting valve 
           51  high-temperature-side temperature sensor 
           52  low-temperature-side temperature sensor 
           141 ,  151  temperature controller 
           143  inlet temperature sensor 
           200  petroleum refining plant 
           201  heating furnace 
           202  distilling unit 
           203  heating unit 
           300  power generating plant 
           301  boiler 
           302  steam turbine 
           303  power generator 
           304  condenser 
           400  regasification facility 
           401  LNG tank 
           402  seawater type vaporizer 
           501  raw material tank 
           502  heater 
           503  reactor 
           600  dehydrogenation reaction facility 
           601  hydrogenated aromatic compound tank 
           602  heater 
           603  dehydrogenation reaction unit 
           604  gas-liquid separation apparatus 
           605  hydrogen tank 
           606  aromatic compound tank