Patent Publication Number: US-7908861-B2

Title: Heat energy supply system and method, and reconstruction method of the system

Description:
CROSS-REFERENCE 
     This is a continuation application of U.S. Ser. No. 11/304,626, filed Dec. 16, 2005 now U.S. Pat. No. 7,669,418. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat energy supply system and method for supplying heat energy to a heat utilization facility, and also relates to a method of reconstructing the heat energy supply system by utilizing the existing equipment. 
     2. Description of the Related Art 
     As one proposal aiming to improve energy efficiency of a heat energy supply system, there is known a combination of a cogeneration system and a heat pump (see, e.g., Patent Document 1: JP, B 7-4212). The heat pump is to take in atmospheric heat, waste heat, etc. In that related art, hot water and cold water produced by the heat pump are utilized as washing water, cooling water, etc. in a facility. 
     Also, in a system using a heat pump alone without generation of electric power, it is proposed to utilize, as a medium, water instead of Freon that has hitherto been used (see Patent Document 2: JP, A 2001-147055). 
     SUMMARY OF THE INVENTION 
     In the case of supplying heat energy to a heat utilization facility, however, it is difficult to maintain an amount of energy transferable per unit medium weight at a sufficient level even with hot water and cooling water used as heat mediums. For that reason, even when the hot water and the cooling water produced by using the heat pump are supplied to the heat utilization facility according to the above-mentioned related art, the installation place of a heat energy supply system is limited to an area near the heat utilization facility. 
     Further, it is known that, by utilizing water as a heat medium in the heat pump, steam (water vapor) having high energy density can be used as a heat medium. However, large motive power is required to compress the steam having low density, and practical use of such a system is limited. 
     In view of the state of the art described above, an object of the present invention is to provide a heat energy supply system and method capable of drastically increasing energy efficiency and energy supply efficiency, as well as a reconstruction method of the heat energy supply system. 
     To achieve the above object, the heat energy supply system of the present invention comprises a boiler for heating a heat medium and producing steam including water and other vapors, a heat pump including a steam turbine driven by the steam supplied from the boiler and a heat exchanger for heating the heat medium by employing external, thereby producing the steam at a setting temperature, and a steam supply line for supplying the steam discharged from the steam turbine and the steam heated by the heat exchanger to a heat utilization facility. 
     According to the present invention, energy efficiency and energy supply efficiency can be drastically increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system flowchart showing the overall arrangement of a heat energy supply system according to a first embodiment of the present invention; 
         FIG. 2  is a system flowchart showing the overall arrangement of a heat energy supply system according to a second embodiment of the present invention; 
         FIG. 3  is a system flowchart showing the overall arrangement of a heat energy supply system according to a third embodiment of the present invention; 
         FIG. 4  is a system flowchart showing the overall arrangement of a heat energy supply system according to a fourth embodiment of the present invention; 
         FIG. 5  is a system flowchart showing the overall arrangement of a heat energy supply system according to a fifth embodiment of the present invention; and 
         FIG. 6  is a system flowchart showing the overall arrangement of a heat energy supply system utilizing water as a heat medium, the system including a known heat pump. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Cogeneration systems according to embodiments of the present invention will be described below with reference to the drawings. 
     (1) First Embodiment 
       FIG. 1  is a system flowchart showing the overall arrangement of a heat energy supply system according to a first embodiment of the present invention. 
     As shown in  FIG. 1 , the heat energy supply system of this embodiment comprises a gas turbine  10  serving as an engine for converting combustion energy to a driving force, a boiler (waste heat recovery boiler)  30  operated using, as a heating source, exhaust gas from the gas turbine  10 , a heat pump  50  driven by steam from the boiler  30 , and a steam supply line  70  for supplying steam produced by the heat pump  50  to a heat utilization facility  1 . 
     (1-1, 1) Arrangement of Gas Turbine  10   
     The gas turbine  10  comprises a compressor  11  for sucking and compressing the atmosphere (air) A, a combustor  12  for burning fuel B together with the compressed air from the compressor  11  and producing high-temperature, high-pressure exhaust gas, and a turbine  13  for obtaining rotatory power through expansion work of the exhaust gas from the combustor  12 . The fuel used in the combustor  12  may be, for example, natural gas, town gas containing natural gas as a main component, lamp oil, light oil, or diesel fuel. In this embodiment, a generator  14  is coaxially coupled to the compressor  11 . The rotatory power obtained from the turbine  13  is transmitted to the generator  14  for conversion to electrical energy. Note that, instead of the generator, other suitable load equipment, such as a pump, may be coupled to the gas turbine  10 . 
     (1-1, 2) Arrangement of Boiler  30   
     The boiler  30  heats a heat medium to produce steam by using the exhaust gas from the gas turbine  10 . An outlet for the exhaust gas passing through the boiler  30  is connected to a stack  43 . When it is required to reduce the nitrogen concentration in exhaust gas C released to the atmosphere through the stack  43 , denitration equipment (not shown) filled with a catalyst is preferably installed in the boiler  30  so that most of nitrogen oxides contained in the exhaust gas C is decomposed to oxygen and nitrogen which are harmless. 
     The boiler  30  comprises four heat exchangers, i.e., a low pressure economizer  31 , a high pressure economizer  32 , a high pressure evaporator  33 , and a high pressure super-heater  34 , which are installed in this order from the downstream side in the direction of flow of the exhaust gas. In the boiler  30 , heat energy contained in the exhaust gas is recovered by those four heat exchangers  31 - 34 , thereby heating a heat medium supplied by a circulation pump  35 . The circulation pump  35  has the function of supplying, to the boiler  30  in a circulating manner, the heat medium that has been supplied from the heat pump  50  to the heat utilization facility  1  and then condensed after being utilized as a heat source in the heat utilization facility  1 . When the heat medium requires to be cleaned depending on the conditions in use of steam inside the heat utilization facility  1  or corrosion of piping, desalination equipment (not shown) filled with an ion exchange resin, for example, is preferably installed upstream of the circulation pump  35 . 
     The heat medium introduced to the boiler  30  by the circulation pump  35  passes through the low pressure economizer  31 , the high pressure economizer  32 , the high pressure evaporator  33 , and the high pressure super-heater  34  in this order. Pipes  37 ,  38  branched at a branch point  36  are connected to the low pressure economizer  31  at its downstream side in the direction of flow of the heat medium. The pipe  37  is connected to the high pressure economizer  32  through a high pressure pump  39 , and the pipe  38  is connected to the heat pump  50  through a control valve  40 . The high pressure economizer  32  and the high pressure evaporator  33  are connected to each other through a steam drum  41 . The steam drum  41  is connected to the high pressure super-heater  34  positioned at the most downstream side in the direction of flow of the heat medium. Further, the high pressure super-heater  34  and the heat pump  50  are connected to each other through a pipe  42 . 
     When the temperature of the exhaust gas lowers through the heat exchange with the heat medium in the heat exchangers  34 ,  33 ,  32  and  31 , there arises a possibility that water vapor contained in the exhaust gas is condensed on a heat surface of the low pressure economizer  31 , etc. and causes piping corrosion. Therefore, piping materials of the low pressure economizer  31 , etc. are preferably made of stainless steel or plastic having superior corrosion resistance. Depending on cases, the low pressure economizer  31 , etc. may be divided into an upstream part and a downstream part in the direction of flow of the exhaust gas, and only the downstream part subjected to lower temperatures may be made of stainless steel. Further, an exhaust gas outlet portion of the boiler  30  and an inner wall surface of the stack  43  may be lined with stainless steel or plastic. 
     (1-1, 3) Arrangement of Heat Pump  50   
     The heat pump  50  comprises a steam turbine  51  driven by the heat medium (steam) supplied from the boiler  30  through the pipe  42 , a two-phase flow expansion turbine  52  and a compressor  53  which are coaxially coupled to the steam turbine  51 , and a heat exchanger (evaporator)  54  for heating the heat medium (for example, high temperature water), which has been preheated by the low pressure evaporator  31  in the boiler  30  and branched into the pipe  38  through the branch point  36 , by utilizing external heat (such as waste heat from the heat utilization facility  1  or heat obtained from environment). The high pressure super-heater  34  is connected to the steam turbine  51  through the pipe  42 , and the low pressure economizer  31  is connected to the heat exchanger  54  through the pipe  38 . 
     A pipe  55  through which a heating medium for heating the heat medium supplied to the heat utilization facility  1  flows is disposed inside the heat exchanger  54 . The pipe  55  is connected to the two-phase flow expansion turbine  52  at its downstream side in the direction of flow of the heating medium and to the compressor  53  at its upstream side. Also, the two-phase flow expansion turbine  52  is connected to an evaporator  57  through a pipe  56 , and the evaporator  57  is connected to the compressor  53  through a pipe  58  so that the heating medium is circulated in a closed system. In this embodiment, trifluoroethanol (TFE), for example, is preferably used as the heating medium. As an alternative, the atmosphere or water (e.g., river water) may also be used if the temperature of the atmosphere or water can be increased to a level sufficient to heat the heat medium supplied to the heat utilization facility  1  to a setting temperature with pressure adjustment in the two-phase flow expansion turbine  52  and the compressor  53 . 
     The evaporator  57  has the function of taking in external heat for application to the heating medium introduced to the heat exchanger  54 . Thus, the heat exchanger  54  heats the heat medium (for example, high temperature water) from the boiler  30  through heat exchange of the external heat with the recovered heating medium. When the heat source has a low heat transfer rate such as the case of using, e.g., the atmosphere as the heat source, a fan  59  may be installed, as shown, to increase the heat exchanger efficiency between the environment and the heating medium. 
     (1-1, 4) Arrangement of Steam Supply Line  70   
     The steam supply line  70  is a piping line for supplying the steam from the heat pump  50  to the heat utilization facility  1  as required. In this embodiment, the steam supply line  70  comprises a pipe  71  connected at its upstream end to an outlet (or an extraction port) of the steam turbine  51 , a pipe  72  connected at its upstream end to the pipe  38  through the heat exchanger  54 , a joining unit  73  connected to respective downstream ends of the pipes  71 ,  72 , and a pipe  74  connecting the joining unit  73  and the heat utilization facility  1 . In this embodiment, the steam discharged from the steam turbine  51  and the steam heated by the heat exchanger  54  are joined and mixed together in the joining unit  73  after passing through the pipes  71 ,  72 , respectively, and are then supplied to the heat utilization facility  1 . 
     (1-1, 5) Construction of Heat Energy Supply System 
     When constructing the heat energy supply system of this embodiment, the entire system can be of course newly constructed, but if there is existing equipment such as an engine and a boiler, it is also possible to reconstruct the system by employing the existing equipment. 
     For example, if the gas turbine  10  already exists, the heat energy supply system is constructed as follows. The boiler  30  is connected to the gas turbine  10  so as to heat the heat medium by the exhaust gas from the gas turbine  10 , thereby generating steam. The heat pump  50  is additionally installed and connected to the boiler  30  such that the steam turbine  51  is driven by the steam from the boiler  30  and the heat medium preheated by the boiler  30  is heated by the heat exchanger  54  to generate steam. Then, the heat pump  50  and the heat utilization facility  1  are connected to each other through the steam supply line  70  such that the steam discharged from the steam turbine  51  and the steam heated by the heat exchanger  54  are supplied to the heat utilization facility  1 . The heat medium condensed after being utilized as a heat source in the heat utilization facility  1  is circulated to the boiler  30  by the circulation pump  35 . 
     As another example, if the boiler  30  (or any other boiler) already exists, the heat energy supply system can be constructed by modifying the existing boiler to be supplied with the heat medium from the gas turbine  10 , and then by installing the heat pump  50 , the steam supply line  70 , and the circulation pump  35  in a similar manner to that described above. While the heat medium branched from the heat medium for driving the steam turbine  51  is used as the heat medium supplied to the heat exchanger  54  of the heat pump  50  in this embodiment, different heat mediums from separate supply sources may be used for the steam turbine  51  and the heat exchanger  54  if there is another heat-medium supply source. 
     The operation of the heat energy supply system according to the present invention will be described below. 
     (1-2, 1) Operation of Gas Turbine  10   
     When the atmosphere (air) A having been deprived of foreign matters through a filter (not shown) is sucked into the compressor  11 , the air is compressed by the compressor  11  and pressurized to a setting pressure (e.g., about 8 atm). Simultaneously, the air sucked into the compressor  11  is heated under pressurization to a setting temperature (e.g., about 250° C.). The compressed air from the compressor  11  is burnt in the combustor  12  together with the fuel B, to thereby produce the high-temperature, high-pressure exhaust gas. When the exhaust gas is supplied to the turbine  13 , the turbine  13  is given with rotatory power through expansion work of the exhaust gas, and the rotary power is transmitted to the generator  14  for conversion to electrical energy. 
     (1-2, 2) Operation of Boiler  30   
     The boiler  30  is supplied with, as a heat source, the exhaust gas discharged from the turbine  13  after making the expansion work therein. The exhaust gas supplied to the boiler  30  has a high temperature (e.g., about 560° C.) near an outlet of the turbine  13 , but the exhaust gas temperature gradually lowers through the successive heat exchanges with the heat medium supplied by the circulation pump  35  while passing through the heat exchangers  34 ,  33 ,  32  and  31  until the exhaust gas is discharged from the stack  43 . 
     The heat medium at a predetermined temperature (e.g., about 30° C.), which has been condensed after being used as a heat source in the heat utilization facility  1 , is first pressurized by the circulation pump  35  to a setting pressure (e.g., about 0.6 MPa). Then, the heat medium is supplied to the low pressure economizer  31  and is heated to a setting temperature (e.g., about 100° C.). Simultaneously, the pressure of the heat medium in the state of high temperature water is reduced to a predetermined pressure (e.g., about 0.5 MPa) due to pressure loss in the low pressure economizer  31 . The heat medium is then distributed to the pipes  37 ,  38  through the branch point  36 . A flow rate ratio at which the heat medium is distributed to the pipes  37 ,  38  at that time is adjusted depending on the opening degree of the control valve  40 . 
     The heat medium introduced to the pipe  37  is pressurized to a setting pressure (e.g., about 5.4 MPa) by the high pressure pump  39 , and is then heated to near a saturation temperature (269° C.) by the high pressure economizer  32 . When the heat medium in the state of saturated water is supplied to the steam drum  41 , it is heated by heat energy of the exhaust gas in the high pressure evaporator  33  in a naturally circulating manner for phase change into steam. Inside the steam drum  41 , the saturated water and the saturated steam are separated from each other depending on density difference between them, and the saturated steam is transferred from an upper gas-phase region to the high pressure super-heater  34 . The heat medium is heated and pressurized in the high pressure super-heater  34  to become super heat steam having a setting temperature and pressure (e.g., about 450° C. and about 5.0 MPa), and the heat medium in the form of super heat steam is supplied to the steam turbine  51  serving as a motive power source of the heat pump  50 . 
     (1-2, 3) Operation of Heat Pump  50   
     The heat medium (super heat steam) exiting the high pressure super-heater  34  at a setting pressure (e.g., about 5.0 MPa) performs expansion work in the steam turbine  51  and is discharged from the steam turbine  51  after being depressurized to a setting pressure (e.g., about 0.4 MPa) suitable for use as a heat source in the heat utilization facility  1 . The rotatory power obtained by the steam turbine  51  is transmitted to the two-phase flow expansion turbine  52  and the compressor  53  for driving them. 
     The heating medium (e.g., TFE) flowing through the pipe  58  at a predetermined pressure (e.g., about 0.03 MPa) is compressed and pressurized to a setting pressure (e.g., about 1.1 MPa) by the compressor  53 . The heating medium heated with the compression is supplied to the heat exchanger  54  for heat exchange with the heat medium that is supplied from the boiler  30  through the pipe  38  and has the predetermined temperature (e.g., about 100° C.). The heat medium is thereby evaporated to become saturated steam having a setting temperature and pressure (e.g., about 140° C. and about 0.4 MPa). 
     The heating medium having been subjected to the heat exchange in the heat exchanger  54  is condensed into a liquid, and when the liquid undergoes adiabatic expansion and is depressurized to a setting pressure (e.g., about 0.03 MPa) in the two-phase flow expansion turbine  52 , a part of the liquid is evaporated and a two-phase flow is obtained at a lowered setting temperature (e.g., about 45° C.). Thus, because of such adiabatic expansion causing depressurization to the low pressure and the temperature drop, the heating medium in the heat pump  50  is able to absorb the external heat with very high efficiency. The heating medium in the state of the two-phase flow is heated by the evaporator  57  by, e.g., waste heat obtained from the heat utilization facility  1  at a predetermined temperature (e.g., about 50° C.) for phase change into vapor. If there is no suitable factory waste heat from the heat utilization facility  1 , the pressure of the heat medium may be further reduced to be evaporated by heat of the atmosphere as described above. In that case, since the heat transfer efficiency of gas, such as the atmosphere, is relatively low, the heat exchange efficiency in the evaporator  57  can be increased by providing the fan  59 , as shown, so that heat transfer is promoted. 
     (1-2, 4) Operation of Steam Supply Line  70   
     The steam discharged from the steam turbine  51  and the steam obtained from the heat exchanger  54  are joined and mixed together in the joining unit  73  after passing through the pipes  71 ,  72 , respectively, and are then supplied to the heat utilization facility  1  through the pipe  74  for use as a heat source therein. After being condensed upon release of the heat in the heat utilization facility  1 , the heat medium is discharged from the heat utilization facility  1  and is returned to the circulation pump  35  through a proper cleaning process, as required. Then, the heat medium is supplied again to the boiler  30  by the circulation pump  35  in a circulating manner. 
     (1-3) Operating Advantages 
     With this embodiment, since the heat medium in a vapor (steam) state is supplied to the heat utilization facility  1 , an energy amount transferable per unit medium weight can be drastically increased in comparison with the case of supplying the heat medium in a liquid state. Accordingly, power required for transporting heat can be reduced, thus resulting in that the installation place of the heat energy supply system is not limited to an area near the corresponding heat utilization facility  1  and a wide variety of applications can be realized. Further, since the heat pump  50  is employed to produce the steam supplied to the heat utilization facility  1 , it is possible to take, into the system, not only the heat energy of the boiler  30 , i.e., the fuel energy applied to the gas turbine  10 , but also the waste heat of the heat utilization facility  1 , which is released without being utilized, or heat energy infinitely present in environment, and to drastically increase the energy efficiency. 
     For example, if high temperature water of 100° C. is produced taking into account a temperature drop occurred during transport of the heat medium from the heat pump  50  to the heat utilization facility  1  on condition that the heat medium temperature required by the heat utilization facility  1  is 50° C., the amount of heat energy per unit weight of the heat medium transported is 0.21 MJ/kg by calculation. On the other hand, when steam of 100° C. is produced, the amount of heat energy per unit medium weight is 2.7 MJ/kg by calculation because of large latent energy. Stated another way, by supplying the heat medium in a steam state to the heat utilization facility  1 , the amount of transported heat energy per unit medium weight is increased 13 times that resulting when the high temperature water is used. 
     Let here suppose, for example, the case where the heat medium is completely evaporated in the high pressure super-heater  34  to produce steam at a setting temperature and pressure (e.g., about 450° C. and about 5.0 MPa) in the boiler  30 . In this case, assuming that the temperature of the heat medium supplied to the low pressure economizer  31  is 30° C., the enthalpy of that heat medium is 125 kJ/kg. On the other hand, because the enthalpy of super heat steam at 450° C. is 3315 kJ/kg, calorie of 3190 kJ/kg has to be added to the heat medium in the boiler  30  in order to raise the temperature of the heat medium to 450° C. Assuming the heat medium to be saturated water at 269° C. at the time when the heat medium flows into the high pressure evaporator  33 , calorie required for heating the heat medium from such a state to become the super heat steam at 450° C. through phase change is 2137 kJ/kg that is 67% of total exchanged calorie (3190 kJ/kg) required in the entire boiler  30 . 
     On that occasion, to enable heat to be transferred from the exhaust gas to the heat medium (saturated water) in the high pressure evaporator  33 , the temperature of the exhaust gas near the high pressure evaporator  33  must be 10° C. or more higher than the saturation temperature (269° C.), and therefore that exhaust gas is required to have at least a temperature of 279° C. In this case, assuming that the temperature of the exhaust gas immediately after being discharged from the turbine  13  is 560° C., it lowers by 281° C. until reaching 279° C. near the high pressure evaporator  33 . 
     On the other hand, calorie required for heating the heat medium supplied to the boiler  30  at 30° C. to 269° C. until the heat medium flows into the high pressure evaporator  33  is 1178 kJ/kg. This calorie is as small as about 50% of the calorie (2137 kJ/kg) required for raising the temperature of the heat medium from 269° C. to 450° C., and the temperature of the exhaust gas is lowered just to about 140° C. at the exhaust gas outlet of the boiler  30 . In this case, therefore, heat energy corresponding to the difference between the temperature (140° C.) of the exhaust gas at the outlet of the boiler  30  and the atmospheric temperature is released to the atmosphere without being utilized, thus resulting in energy loss. 
     In this embodiment, to eliminate such energy loss and to effectively utilize the calorie of the exhaust gas C which is released to the atmosphere without being utilized, 45% of the heat medium (at, e.g., about 100° C.) obtained as the high temperature water in the low pressure economizer  31  is branched and supplied to the heat exchanger  54  in the heat pump  50 . As a result, the heat medium to be heated by the heat pump  50  can be preheated by utilizing the calorie of the exhaust gas C released to the atmosphere without being utilized, and the energy efficiency of the heat pump  50  can be further increased. Also, the temperature of the exhaust gas C released to the atmosphere can be lowered and hence heat energy loss can be reduced. For example, when the heat medium supplied to the boiler  30  at 30° C. is heated to about 100° C. by the low pressure economizer  31 , the temperature of the exhaust gas C released to the atmosphere is lowered from 140° C. to a level nearer to the atmospheric temperature (e.g., about 60° C. or below), and the fuel energy applied to the combustor  12  is substantially all recovered. 
     Energy consumption efficiency, i.e., coefficient of performance (COP), indicating the performance of the heat pump  50  is defined as a ratio of the motive power applied to the heat pump  50  by the compressor  53  to the calorie applied to the steam produced by the heat exchanger  54 . Calorie used for heating the heat medium in the heat exchanger  54  is expressed by a total of the calorie recovered into the heat medium from the exterior by the evaporator  57  and the motive power used by the compressor  53  for pressurizing the heating medium. When overall system efficiency is calculated by setting the fuel energy applied to the combustor  12  as a denominator and a total of the amount of electric power generated by the generator  14  and the calorie supplied to the heat utilization facility  1  as a numerator with the COP value being a parameter, the overall system efficiency exceeds 100% if the COP value exceeds 1.7, and becomes 128% if the COP value is increased to 5. This is resulted from the effect obtained by taking in the heat energy by the evaporator  57  from the exterior in addition to the fuel energy applied to the combustor  12 . Further, the motive power used by the circulation pump  35  and the high pressure pump  39  in the boiler  30  also contributes to heating the heat medium. 
     Thus, while the overall efficiency of a general cogeneration system is about 80%, the overall efficiency of the heat energy supply system of this embodiment is notably higher than 80%. By calculation, the heat energy supply system of this embodiment is able to cut the amount of CO 2 , which is generated from the system and adversely affects the global warming, about 37% as compared with the general cogeneration system having the overall efficiency of 80%. The heat loss in the heat energy supply system of this embodiment is expressed by calorie corresponding to the temperature difference between the exhaust gas C released to the atmosphere from the boiler  30  and the atmosphere A sucked into the compressor  11 . Accordingly, the overall efficiency of the heat energy supply system of this embodiment exceeds 100% by taking in larger calorie by the evaporator  57  from the exterior than that heat loss. 
     Further, in this embodiment, the motive power obtained by the steam turbine  51  is all used as forces for driving the compressor  53  and the two-phase flow expansion turbine  52  in the heat pump  50  without converting the motive power obtained by the steam turbine  51  to electric power. There is hence no loss attributable to conversion to electric power in the heat pump  50 . In addition, since the steam discharged from the steam turbine  51  and the steam produced by the heat pump  50  are mixed and transported to the heat utilization facility  1  through the common steam pipe  74 , a larger amount of heat medium can be supplied to the heat utilization facility  1  without causing loss. Those points are also major advantages with the heat energy supply system of this embodiment. 
     Another major advantage is that, when there is existing equipment releasing unused waste heat to the atmosphere, such as an engine and a boiler, the heat energy supply system of this embodiment can be constructed with ease by employing such existing equipment. 
     (2) Second Embodiment 
       FIG. 2  is a system flowchart showing the overall arrangement of a heat energy supply system according to a second embodiment of the present invention. Note that, in  FIG. 2 , similar components to those in  FIG. 1  are denoted by the same reference numerals, and a duplicate description of those components is omitted here. 
     As shown in  FIG. 2 , this second embodiment differs from the first embodiment in the arrangement of a heat pump  50 A, namely in that the heat medium from the boiler  30  is supplied to a heat medium cycle for the heat pump  50 A without using the above-mentioned different heating medium, such as TFE, and steam obtained in the heat medium cycle is supplied to the heat utilization facility  1 . As a result, a heat exchanger for making heat exchange between the heat medium supplied to the heat utilization facility  1  and the heating medium for heating the former (i.e., the heat exchanger  54  in  FIG. 1 ) is omitted. 
     The heat pump  50 A comprises the steam turbine  51  driven by the heat medium (steam) supplied from the boiler  30  through the pipe  42 , a two-phase flow expansion turbine  52 A and compressors  53 A,  53 B which are coaxially coupled to the steam turbine  51 , and a heat exchanger (evaporator)  54 A for heating the heat medium (high temperature water), which is supplied from the boiler  30  through the pipe  38 , by utilizing external heat (such as waste heat from the heat utilization facility  1  or heat obtained from environment). 
     In this embodiment, the pipe  38  extending from the low pressure economizer  31  is connected to the two-phase flow expansion turbine  52 A. The two-phase flow expansion turbine  52 A is connected to the compressor  53 A in the upstream stage through the heat exchanger  54 A, and the compressor  53 A is connected to the compressor  53 B in the downstream stage through a pipe  60 , a mixer  61 , and a pipe  62 . Further, a branch point  80  is provided in the pipe  38  connecting the low pressure economizer  31  and the two-phase flow expansion turbine  52 A to each other, and a pipe  81  branched from the pipe  38  at the branch point  80  is connected to the mixer  61 . A control valve  82  is disposed in the pipe  81 , and a flow rate ratio at which the heat medium is distributed to the pipes  38 ,  81  is adjusted depending on the opening degree of the control valve  82 . 
     The heat exchanger  54 A includes a pipe  83  disposed therein for passage of, e.g., the wastewater of the heat utilization facility  1  or the atmosphere. A partition  84  is disposed inside the heat exchanger  54 A such that an upper space in the heat exchanger  54 A is divided into two parts on the side closer to the two-phase flow expansion turbine  52 A and on the side closer to the compressor  53 A. 
     The remaining arrangement is the same as that of the above-described first embodiment, and this second embodiment can also provide the same advantages as those obtained with the first embodiment. Further, the heat energy supply system of this second embodiment can be constructed by utilizing the existing engine and boiler in a similar way. In addition, this second embodiment can provide the operating advantages as follows. 
     Since the heat medium supplied from the boiler  30  is used as the medium in the heat pump  50 A in this embodiment, the two-phase flow expansion turbine  52 A can produce a larger motive force, for example, by designing the system in which the heat medium heated to a state substantially under the saturation conditions flows into the two-phase flow expansion turbine  52 A. 
     For example, when the heat medium is prepared at the outlet of the low pressure economizer  31  in the boiler  30  as high temperature water at about 130° C. and 0.5 MPa, i.e., a state near the saturation conditions, the opening degree of the control valve  82  is adjusted such that the heat medium is supplied to the two-phase flow expansion turbine  52 A through the branch point  80  at a proportion of 80% and the supplied heat medium is depressurized to about 0.01 MPa at 46° C. by the two-phase flow expansion turbine  52 A. The heat medium supplied to the heat exchanger  54 A is evaporated at a predetermined proportion (e.g., about 14%) during the expansion process in the two-phase flow expansion turbine  52 A so as to form a two-phase flow, and the liquid phase separated from the steam phase is accumulated in a lower portion of the heat exchanger  54 A. In this case, the liquid phase is heated and evaporated by utilizing factory waste heat or town waste heat at about 50-60° C. When the outlet pressure of the two-phase flow expansion turbine  52 A is further reduced (for example, to about 0.002 MPa), the temperature in the heat exchanger  54 A is correspondingly further lowered (for example, to about 18° C.). In such a case, the heat medium can be evaporated by utilizing heat of the infinitely existing atmosphere. 
     The steam present in the upper space of the heat exchanger  54 A at a predetermined pressure (e.g., about 0.01 MPa) is pressurized (for example, to about 0.4 MPa) by the compressors  53 A,  53 B and is supplied as a heat source to the heat utilization facility  1 . In the mixer  61  disposed between the compressor  53 A in the upstream stage and the compressor  53 B in the downstream stage, the heat medium in the state of high temperature water is sprayed through the pipe  81  branched from the branch point  80  to lower the temperature of the heat medium supplied from the compressor  53 A to the compressor  53 B. 
     The reason is that when compressing steam of 0.01 MPa to 0.4 MPa, for example, unless the steam is cooled midway, the steam temperature reaches about 490° C. even if the compression efficiency is 100%, and reaches about 550° C. if the compression efficiency is 85%. In the latter case, energy corresponding to the temperature difference between the saturation temperature, i.e., 46° C., of the heat medium (water) at 0.01 MPa and 550° C. is required as motive power for driving the compressors  53 A,  53 B. In compression of gas, the lower gas density, the larger is motive power required for the compression. In view of the above, the flow rate of the heat medium is adjusted by the control valve  82  so that the high temperature water of 0.5 MPa is branched from the branch point  80  and poured into the mixer  61  for spray to the steam during the compression process, thereby lowering the steam temperature. 
     In this embodiment, the two compressors  53 A,  53 B are installed and the mixer  61  is disposed between them. For the purpose of reducing the motive power required for driving the compressors, however, it is also conceivable to install three or more compressors and to dispose a mixer between every two adjacent compressors. 
     With this embodiment, as described above, by spraying the steam to the heat medium in the state of super heat steam flowing out of the compressor  53 A, the temperature of the super heat steam can be easily lowered to the saturation temperature. Alternatively, in the step of spraying the heat medium, the heat steam may be sprayed until the steam is slightly humidified. In this case, the heat medium is in the state of humid steam at the inlet of the compressor  53 B in the downstream stage, but water droplets are evaporated inside the compressor  53 B. Thus, a temperature rise in the compressor  53 B can be suppressed and the motive power required for driving the compressors can be reduced as a whole. From the viewpoint of obtaining higher efficiency, an amount of the heat medium sprayed in the mixer  61  is preferably adjusted such that the steam temperature at the outlet of the compressor  53 B is held at the temperature (e.g., about 140° C.) utilized by the heat utilization facility  1 . 
     The motive power used by the compressors  53 A,  53 B is supplied from the steam turbine  51  and the two-phase flow expansion turbine  52 A. Since the heat medium supplied to the heat utilization facility  1  is used as the medium in the heat pump  50 A, it is possible to cool the heat medium by directly spraying the branched heat medium at the midpoint between the compressors  53 A,  53 B, and to omit a large-sized heat exchanger (i.e., the heat exchanger  54  in the embodiment of  FIG. 1 ) which is required when the heat medium is indirectly cooled by using the dedicated heating medium, such as TFE. Because the weight of the two evaporators  54 ,  57  occupies half or more of the total weight of the heat pump  50  shown in  FIG. 1 , the omission of one of those two evaporators like this embodiment greatly contributes to simplifying the equipment arrangement. Further, when the heat medium is heated through the heat exchange with another heating medium, such as TFE, the temperature difference is required between the heat medium to be heated and the heating medium for heating the former. However, that temperature difference is no longer required and higher efficiency can be obtained correspondingly. 
     Moreover, in this embodiment, the pressure in the heat exchanger  54 A is low (e.g., about 0.01 MPa) and the fluid density at each of the outlet of the two-phase flow expansion turbine  52 A and the inlet of the compressor  53 A is relatively small. Accordingly, by connecting the outlet of the two-phase flow expansion turbine  52 A and the inlet of the compressor  53 A to the upper space in the heat exchanger  54 A as shown  FIG. 2 , the need of arranging a pipe to increase the fluid speed midway can be eliminated. In addition, since the interior of the heat exchanger  54 A is divided by the partition  84  into two parts, water droplets at the outlet of the two-phase flow expansion turbine  52 A can be prevented from directly flowing into the compressor  53 A. The liquid phase remains at a standstill inside the heat exchanger  54 A. If the heat exchange efficiency between the liquid phase and the pipe  83  is poor, it is more preferable to install a stirrer (not shown) for causing the liquid phase to flow in a forcible manner and to provide an internal partition (not shown) so that a uniform flow is formed and heat conduction is promoted. 
     (3) Third Embodiment 
       FIG. 3  is a system flowchart showing the overall arrangement of a heat energy supply system according to a third embodiment of the present invention. Note that, in  FIG. 3 , similar components to those in the above-referenced drawings are denoted by the same reference numerals, and a duplicate description of those components is omitted here. 
     As shown in  FIG. 3 , this third embodiment differs from the foregoing embodiments in that a ratio of generated power output to thermal output is made variable, i.e., that respective drive shafts of the steam turbine  51  and the compressor  53 B are coupled to each other through a variable speed reducer  85 . 
     Also, a condenser  86  for condensing the steam discharged from the steam turbine  51  after performing expansion work therein is connected to the outlet of the steam turbine  51  through a pipe  87 . The condenser  86  is connected through a pipe  90  to a joining unit  89  disposed in a pipe  88  interconnecting the heat utilization facility  1  and the circulation pump  35 . Control valves  91 ,  92  are disposed respectively in the pipes  88 ,  90 . Further, a control valve  93  is disposed in a pipe  71  interconnecting the extraction port of the steam turbine  51  and the joining unit  73 . 
     The remaining arrangement is the same as that of the above-described second embodiment, and this third embodiment can also provide the same advantages as those obtained with the second embodiment. Further, the heat energy supply system of this third embodiment can be constructed by utilizing the existing engine and boiler in a similar way. In addition, this third embodiment can provide the operating advantages as follows. 
     The compressors  53 A,  53 B are coaxially coupled to not only the two-phase flow expansion turbine  52 A and the steam turbine  51 , but also to the gas turbine  10 . Therefore, the rotatory power produced from the turbine  13  can be utilized as the motive power for driving the compressors  53 A,  53 B. The motive power remained after driving the compressors  53 A,  53 B is converted to electrical energy by the generator  14 . 
     A ratio of heat to electric power required in the heat utilization facility  1 , etc. varies. Corresponding to such a variation, the system of this embodiment is able to continuously change a proportion of heat supply with respect to the total amount of supplied energy from 0% (supply of electric power: 100%) to 100% (supply of electric power: 0%). 
     When only electric power is supplied, the control valve  40  is closed to make 0 (zero) the flow rate of steam produced by the heat pump  50 A (heat exchanger  54 A). In this state, the rotation speed of the circulation pump  35  is controlled to be matched with the conditions of super heat steam that is finally produced by the high pressure super-heater  34  in the boiler  30 , thereby adjusting the amount of the heat medium supplied to the boiler  30 . When the control valve  40  is closed and no heat medium is introduced to the pipe  38  like this case, the temperature of the exhaust gas C discharged from the boiler  30  rises. 
     Here, the amount of the heat medium supplied by the circulation pump  35  can be decided by dividing the calorie given to the heat medium in the boiler  30  by the calorie required per unit flow rate. The calorie given to the heat medium in the boiler  30  can be calculated from both the temperature difference of the exhaust gas between the outlet of the turbine  13  and the outlet of the boiler  30  and the flow rate of the exhaust gas discharged from the turbine  13 . The calorie required per unit flow rate can be obtained from the difference between the enthalpy of the heat medium at the outlet of the circulation pump  35  and the enthalpy of the heat medium at the outlet of the high pressure super-heater  34 . 
     By closing the control valve  93  to cut off the supply of the heat medium extracted from the steam turbine  51  to the heat utilization facility  1  and opening the control valve  92 , the heat medium used for driving the steam turbine  51  is all supplied to the condenser  86  and condensed for return to water. Because no heat medium flows into the two-phase flow expansion turbine  52 A and the compressors  53 A,  53 B, the energy loss can be reduced by disconnecting the variable speed reducer  85  such that it is released from the state coupled to the steam turbine  51 . 
     On the other hand, when electric power and heat are supplied to the heat utilization facility  1  at the same time, proportions of the flow rate of the heat medium supplied to the heat pump  50  and the high pressure economizer  32  through the branch point  36  are adjusted by controlling the opening degree of the control valve  40  and the rotation speed of the circulation pump  35 . The flow rate of the heat medium sprayed to the heat medium in the state of super heat steam at the midpoint between the compressors  53 A,  53 B is adjusted by controlling the opening degree of the control valve  82  so that the heat medium is sprayed at a constant ratio with respect to the flow rate of the heat medium flowing into the compressor  53 B. 
     Because the performance of the heat pump  50 A is decided depending on the pressure in the evaporator  54 A, the rotation speeds of the compressors  53 A,  53 B are controlled by the variable speed reducer  85  so as to hold the pressure in the evaporator  54 A at a predetermined value. During a period in which a heat demand is small, the control valve  93  is closed to maximize the output of the steam turbine  51 . If there is a demand requiring a further increase of the thermal output after the flow rate of the heat medium flowing through the two-phase flow expansion turbine  52 A has increased to a level at which the evaporator  54 A can sufficiently develop its capability of evaporating the heat medium, the opening degree of the control valve  93  is enlarged to increase the flow rate of the heat medium introduced to the joining unit  73 . By enlarging the opening degree of the control valve  93 , the flow rate of the heat medium introduced to the joining unit  73  is increased correspondingly, while the output of the steam turbine  51  is reduced and so is the amount of electric power generated by the generator  14  in a reverse proportional relation. At the time when the amount of generated electric power becomes 0 (zero), the thermal output in the entire system is maximized. 
     When the steam discharged from the steam turbine  51  is introduced to the condenser  86  and condensed therein, the resulting condensation heat is recovered by cooling water and released to the exterior. Accordingly, the heat loss of the system is given by the calorie of the exhaust gas C discharged through the stack  43  and such condensation heat. In the state where the control valve  92  is closed and no heat medium flows into the condenser  86  under the conditions of maximizing heat energy, the overall energy efficiency of the system shows a maximum value. 
     In the case of supplying energy only as thermal output, a percentage of energy of the heat medium capable of being supplied to the heat utilization facility  1  with respect to fuel energy supplied to the combustor  12  is in the range of 180-220% depending on the temperature of waste heat available by the evaporator  54 A and the efficiencies of the compressors  53 A,  53 B. Steam energy available in a general boiler is about 90% of input fuel energy and never exceeds 100%. In the system of this embodiment, since the motive power produced by the gas turbine  10  is also used as a driving force for the heat pump  50 A, the total energy amount capable of being supplied to the heat utilization facility  1  is able to exceed 200% depending on the conditions by employing not only the fuel energy supplied to the combustor  12 , but also energy of the atmosphere or waste heat utilized by the evaporator  54 A. 
     (4) Fourth Embodiment 
       FIG. 4  is a system flowchart showing the overall arrangement of a heat energy supply system according to a fourth embodiment of the present invention. Note that, in  FIG. 4 , similar components to those in the above-referenced drawings are denoted by the same reference numerals, and a duplicate description of those components is omitted here. 
     As shown in  FIG. 4 , this fourth embodiment differs from the foregoing embodiments in that the steam discharged from the steam turbine  51  after performing expansion work therein and the steam heated by the heat exchanger  54 A are supplied to corresponding different heat utilization facilities  1 A,  1 B, respectively. 
     In this fourth embodiment, the steam supply line  70  includes a pipe  75  interconnecting the steam turbine  51  and a heat utilization facility  1 A, e.g., a factory, and a pipe  76  interconnecting the compressor  53 B and another heat utilization facility  1 B, e.g., a heated swimming pool. The heat medium used for driving the steam turbine  51  and the heat medium heated by the heat exchanger  54 A are supplied respectively to the heat utilization facilities  1 A,  1 B through the pipes  75 ,  76 . The heat mediums having been utilized as heat sources in the heat utilization facilities  1 A,  1 B and condensed are discharged from the heat utilization facilities  1 A,  1 B and then joined with each other by a joining unit  94  for return to the circulation pump  35 . 
     The remaining arrangement is the same as that of the above-described second embodiment, and this fourth embodiment can not only provide the same advantages as those obtained with the second embodiment, but also supply the heat mediums to a plurality of heat utilization facilities as required. Further, the heat energy supply system of this fourth embodiment can be constructed in a similar way. While this fourth embodiment has been described in connection with the case of supplying energy to a plurality of heat utilization facilities in the system according to the second embodiment, the arrangement of this fourth embodiment is also applicable to the case of supplying energy to a plurality of heat utilization facilities in the systems according to the other above-described embodiments. 
     (5) Fifth Embodiment 
       FIG. 5  is a system flowchart showing the overall arrangement of a heat energy supply system according to a fifth embodiment of the present invention. Note that, in  FIG. 5 , similar components to those in the above-referenced drawings are denoted by the same reference numerals, and a duplicate description of those components is omitted here. 
     As shown in  FIG. 5 , this fifth embodiment differs from the foregoing embodiments in that, instead of waste heat of an engine (such as the gas turbine  10 ), a boiler  30 A installed in any of various facilities, e.g., a sanitation factory, is employed as a heat source for generating the steam (heat medium) to drive a heat pump  50 A. While one example of the boiler  30 A is an incinerator boiler in the sanitation factory, the boiler  30 A is not limited to such an example and may be any other boiler so long as it is able to heat a heat medium for conversion to steam, e.g., a boiler using heavy oil or tires as fuel. In this embodiment, water pumped up from a river  96  by a pump  95  is introduced to the heat exchanger  54 A as a heating medium used in the heat pump  50 A to heat the heat medium. In the thus-arranged system of this embodiment, heat energy is supplied to the heat utilization facility  1 , such as a heated swimming pool, with high efficiency by adding calorie obtained from the river water to calorie obtained from a heat exchanger  30 Aa which is disposed in the boiler  30 A. 
     The heat medium returned from the heat utilization facility  1  is pressurized to a setting pressure (e.g., about 7 MPa) by the circulation pump  35  and then supplied to the boiler  30 A for heating in the heat exchanger  30 Aa. The heat medium coming into the state of high-temperature, high-pressure water is supplied to an expansion turbine  52 A through a pipe  38 , and the heat medium coming into the state of high-pressure super heat steam is supplied through a pipe  42  to the steam turbine  51  for driving the heat pump  50 A. In the case of the heat medium being water, when the water is expanded to about 0.002 MPa by the expansion turbine  52 A, it can be evaporated by heat infinitely obtained from the river  96  because the saturation temperature lowers to 17.5° C. The water of the river  96  is supplied to the heat exchanger  54 A through a pipe  83  by the pump  95 . If the river water is highly contaminated, a filter is disposed in the pipe  83  to remove insoluble materials. 
     The evaporated saturated steam is compressed to a setting pressure (e.g., about 0.4 MPa) by the compressors  53 A,  53 B. In order to reduce compression motive forces to be applied from the compressors  53 A,  53 B, the heat medium in the state of high temperature water is sprayed to cool the steam at the midpoint between the compressors  53 A,  53 B. The motive power for driving the compressors  53 A,  53 B is provided by energy produced when the heat medium in the state of super heat steam at the setting pressure (e.g., about 7 MPa) is depressurized by the steam turbine  51  to a pressure (e.g., about 0.4 MPa) suitable for use in the heat utilization facility  1 . The steam exiting the steam turbine  51  and the steam exiting the compressor  53 B are mixed with each other in the joining unit  73  and supplied as a heat source to the heat utilization facility  1 . 
     This fifth embodiment can also provide the same advantages as those obtained with the foregoing embodiments, and the heat energy supply system of this fifth embodiment can be constructed in a similar way by using the existing boiler. By utilizing the heat of the river  96  as well, the calorie capable of being supplied from the same boiler  30 A can be increased about 1.8 times depending on the conditions as compared with the system in which only the steam generated by the existing boiler  30 A is supplied to the heat utilization facility  1 . 
     While the foregoing embodiments have been described in connection with the case of using water as the heat medium supplied to the heat utilization facility, other suitable medium, such as carbon dioxide, ammonia or trifluoroethanol (TFE), may also be used as the heat medium because the heat medium is circulated in a closed system and will not flow out to the exterior. As a matter of course, although those other mediums may be each used alone, they may also be used in mixed form of several kinds of mediums or mixed with water. Further, when a harmless and mixable medium is used as the heat medium, the closed system is not essential. In such a case, the heat medium for driving the steam turbine  51  and the heat medium heated by the heat pump  50  or  50 A may be supplied from different supply sources. In the case of using plural kinds of heat mediums, when the heat medium for driving the steam turbine  51  and the heat medium heated by the heat pump  50  or  50 A are supplied to different heat utilization facilities and circulated in respective closed systems, both the heat mediums are not necessarily required to be mixable. 
     (6) Sixth Embodiment 
     In the system of  FIG. 1 , the heat medium having been utilized in the heat utilization facility  1  is condensed and returned to the circulation pump  35 . On the other hand, this sixth embodiment is featured in omitting the pipe through which the heat medium having been utilized as a heat source in the heat utilization facility  1  and condensed is supplied to the boiler  30  in a circulating manner, and in supplying the heat medium to the circulation pump  35  from other supply source than the heat utilization facility  1 . 
     It is supposed that, instead of utilizing only the steam (heat medium) supplied from the steam supply line  70 , the heat utilization facility  1  employs the steam in a reaction process. The steam having been used in the reaction process has a difficulty in directly circulating it to the heat pump for reuse. In this embodiment, therefore, the pipe through which the heat medium having been utilized as a heat source in the heat utilization facility  1  and condensed is supplied to the boiler  30  in a circulating manner is not disposed, and water from other supply source, e.g., a river or the underground, than the heat utilization facility  1  is cleaned and supplied to the circulation pump  35 . With such a system arrangement, because of no need of installing the return pipe from the heat utilization facility  1  to the circulation pump  35 , an effect of cutting the installation cost is increased as the distance between the heat pump  50  and the heat utilization facility  1  increases. 
     (7) Seventh Embodiment 
     In the second embodiment shown in  FIG. 2 , the heat medium supplied to the heat utilization facility  1  is also employed as the heat medium for use in the heat pump  50 . This seventh embodiment uses water as the common heat medium. 
     The following description is made in comparison with a system arrangement in which the heat pump has the same arrangement as that of a known heat pump and the heat medium is just replaced with water.  FIG. 6  is a system flowchart showing the overall arrangement of a heat energy supply system utilizing water as the heat medium, the system including the known heat pump. Comparing with  FIG. 2  described above, the heat pump  50 A includes one compressor  53 , and does not include the mixer  61  connected to the pipe branched from the pipe  38  interconnecting the low pressure economizer  31  and the two-phase flow expansion turbine  52 A. In the system of  FIG. 6 , when gas is compressed by the compressor  53  of the heat pump  50 A, a larger temperature rise is caused as the gas has lower density. For example, the density of steam at 0.01 MPa and 46° C. is 0.068 kg/m 3  that is just 13% of 0.52 kg/m 3 , i.e., the density of R-11 as one of coolants. In the case of using R-11, therefore, even when it is compressed to 0.4 MPa, the temperature rises up to just 185° C. On the other hand, when the steam is compressed to the same level, the temperature rises up to 490° C. Because the saturation temperature of water at 0.4 MPa is 144° C., the motive power required for raising the temperature from 144° C. to 490° C. is merely converted to heat, thus resulting in a significant reduction of the system efficiency. Thus, the system having the same arrangement as that of the known heat pump and simply employing water as the heat medium accompanies a large efficiency reduction and hence has a difficulty in putting it into practical use. 
     To avoid that problem, in this embodiment using water as the heat medium in the heat pump, the system has to be modified as shown in  FIG. 2 . More specifically, the compressor  53  of the heat pump  50 A is divided into plural stages, and the steam is cooled to increase density at the intermediate between the divided compressor stages, thereby reducing the compression motive power required. 
     A manner of cooling the steam at the intermediate between the divided two compressor stages can be realized by not only spraying water to the steam as described above, but also installing a heat exchanger. In the latter case, although the heat exchanger is installed outside containers for the compressors  53 A,  53 B and hence the equipment size is enlarged, the steam temperature can be adjusted with higher accuracy. 
     In addition to simple condensation of the steam to be utilized as heat, the heat utilization facility  1  can also utilize the steam in other ways as follows. First, an absorption freezer using lithium bromide as a coolant is installed in the heat utilization facility, and high temperature steam is utilized to evaporate the coolant, thereby cooling the heat utilization facility. Secondly, the steam is directly injected or sprayed to products in a chemical process or a drying process. In this case, the heat utilization facility  1  is not required to include the condenser for condensing the steam.