Patent Publication Number: US-2016230700-A1

Title: Exhaust heat recovery apparatus of engine

Description:
TECHNICAL FIELD 
     The present invention relates to an exhaust heat recovery apparatus of an engine. 
     BACKGROUND ART 
     For example, there has been known a device that includes heat exchangers at respective passages for cooling water for an engine and for exhaust gas. After raising a temperature of a working fluid with the heat exchanger for cooling water, the temperature is further increased with the heat exchanger for exhaust gas to recover heat from the cooling water and the exhaust gas (for example, see Patent Document 1). The recovered heat is used as heat sources for a hot water supply facility and other power generation facilities. 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: Japanese Patent Application Laid-open Publication No. 10-141137 
     SUMMARY 
     However, when the temperature of the cooling water is lower than the temperature of the heat exchanger, the above-described recovery device of heat of the engine has the following features. 
     That is, at an engine start, the heat exchanger for cooling water does not recover the heat from the cooling water. On the contrary, the heat exchanger for cooling water possibly deprives the working fluid of heat, adversely affecting an effective use of exhaust heat from the engine. 
     During a steady operation of the engine, the heat exchanger for cooling water deprives the working fluid of heat, possibly resulting in providing the heat to the cooling water. This increases the temperature of the cooling water, an upper limit value of the temperature is exceeded, and the engine overheats. Consequently, this possibly damages the engine and its peripherals. 
     One or more embodiments of the present invention include an engine, a first cooler, a heat exchanger, and a first valve device. The first cooler contains a first cooling medium to cool a first mechanism to be cooled of the engine. The first cooler is configured to exchange heat between water at a first temperature output from a warm water utilization facility and the first cooling medium to output water at a second temperature. The second temperature is higher than the first temperature. The heat exchanger is configured to exchange heat between the water at the second temperature and exhaust gas from the engine to output water at a third temperature and supply the water at the third temperature to the warm water utilization facility. The third temperature is higher than the second temperature. The first valve device is configured to cause the water at the first temperature to be supplied to the heat exchanger when a temperature of the first cooling medium is lower than a temperature on a side of the first cooler to which the water at the first temperature is supplied. 
     Other features of one or more embodiments of the present invention will become apparent from descriptions of the accompanying drawings and of the present specification. 
     Advantages Effects of Invention 
     According to one or more embodiments of the present invention, exhaust heat from the engine is effectively used and the engine and its peripherals can be protected. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of an exhaust heat recovery apparatus of an engine according to one or more embodiments of the present invention. 
         FIG. 2  illustrates an example of a flow of water in the exhaust heat recovery apparatus during a steady operation of the engine. 
         FIG. 3  illustrates another example of a flow of water in the exhaust heat recovery apparatus during the steady operation of the engine. 
         FIG. 4  illustrates yet another example of a flow of water in the exhaust heat recovery apparatus during the steady operation of the engine. 
         FIG. 5  illustrates an example of a flow of water in the exhaust heat recovery apparatus at an engine start. 
         FIG. 6  illustrates another example of a flow of water in the exhaust heat recovery apparatus at the engine start. 
         FIG. 7  illustrates an example of a flow of water when the exhaust heat recovery apparatus is superheated. 
         FIG. 8  illustrates another example of a flow of water when the exhaust heat recovery apparatus is superheated. 
         FIG. 9  illustrates an example of a facility to which the exhaust heat recovery apparatus of the embodiment of this invention is coupled. 
     
    
    
     DETAILED DESCRIPTION 
     At least the following matters will become apparent from descriptions of the present specification and of the accompanying drawings. 
     With reference to  FIG. 1  to  FIG. 9 , the following describes an exhaust heat recovery apparatus according to one or more embodiments of the present invention. In this embodiment, water output from an exhaust gas heat exchanger  2  of an exhaust heat recovery apparatus  1  is used by a binary power generation device  8  and is recovered to a water tank  6  of the exhaust heat recovery apparatus  1 . An engine  71  of this embodiment is used as a power engine for an electric generator  72 . Cooling water of the engine  71  is cooled while the cooling water is circulated between the engine  71  and a cooling water cooler  3  with a pump P 3 . Lubricating oil for the engine  71  is cooled while the lubricating oil is circulated between the engine  71  and a lubricating oil cooler  4  with a pump P 4 . 
     Configuration 
       FIG. 1  is a schematic diagram of the exhaust heat recovery apparatus of this embodiment of this invention. As illustrated in  FIG. 1 , the exhaust heat recovery apparatus  1  includes the exhaust gas heat exchanger  2 , the cooling water cooler  3 , the lubricating oil cooler  4 , valves  51  to  55 , and the water tank  6 . With components of the exhaust heat recovery apparatus  1  each coupled to other components as described later, the components are mutually coupled via, for example, water pipes. 
     In the exhaust heat recovery apparatus  1 , water, which is a working medium, is preheated by a preheating system, which will be described later. After that, the water is heated by the exhaust gas heat exchanger  2  and then is sent to the binary power generation device  8 . The exhaust heat recovery apparatus  1  includes a main preheating system and a sub preheating system. The main preheating system includes from the water tank  6 , through the valves  51  and  52  and the cooling water cooler  3 , and to the exhaust gas heat exchanger  2 . The sub preheating system includes from the water tank  6 , through the valve  51 , the lubricating oil cooler  4 , and the valve  54 , and to the exhaust gas heat exchanger  2 . The exhaust heat recovery apparatus  1  includes a cooling water supply system. The cooling water supply system supplies cooling water to the cooling water cooler  3 , the lubricating oil cooler  4 , and the water tank  6  via the valves  53  and  55 . 
     &lt;Main Preheating System&gt; 
     As described above, the main preheating system includes from the water tank  6 , through the valves  51  and  52  and the cooling water cooler  3 , and to the exhaust gas heat exchanger  2 . 
     To describe specifically, the water tank  6  is a device that accumulates the water output from the binary power generation device  8 . The water tank  6  is coupled to an outlet for water in the binary power generation device  8  via the water pipe. The water tank  6  recovers the water returned from the cooling water cooler  3  and the lubricating oil cooler  4  and receives the cooling water replenished from the valve  55 . After accumulating the water as described above, the water tank  6  outputs the accumulated water to the valve  51 . 
     The water tank  6  includes a water level sensor  61 , which measures the water level of the water tank  6 . When the measured value falls below a predetermined lower limit, the water level sensor  61  outputs a measurement signal to a control unit  59  such that the cooling water is replenished via the valve  55 . 
     A temperature sensor  62  is disposed to the outlet for water at the water tank  6 . The temperature sensor  62  measures a temperature T 1  of water output from the water tank  6  and outputs the measurement signal to the control unit  59 . The temperature of water flowing from the binary power generation device  8  into the water tank  6  is, for example, around 80 Celsius degrees. 
     The water output from the water tank  6  is sent to the cooling water cooler  3  through the valves  51  and  52  with the pump P 1 . The valves  51  and  52  will be described later. 
     The cooling water cooler  3  is a device that contains cooling water as a cooling medium to cool a peripheral area of a combustion chamber of the engine  71 . The cooling water cooler  3  exchanges heat between the cooling water of the engine  71  and the water output from the water tank  6 . Thus, the cooling water cooler  3  cools the cooling water of the engine  71 , preheats the water from the water tank  6 , and outputs the water to the exhaust gas heat exchanger  2 . An inlet for water in the cooling water cooler  3  is coupled to the outlet for water in the valve  52 . The outlet for water in the cooling water cooler  3  is coupled to the inlet for water in the exhaust gas heat exchanger  2 . 
     The cooling water cooler  3  includes a cooling water inlet and a cooling water outlet. The cooling water is supplied to the cooling water inlet via the valve  53 . The cooling water whose temperature has increased by the cooling water cooler  3  is output to the water tank  6  with the cooling water outlet. 
     The cooling water cooler  3  includes two temperature sensors  31  and  32 . The temperature sensor  31  measures a temperature T 2  of the cooling water cooler  3  and outputs a measurement signal to the control unit  59 . The temperature sensor  32  is disposed to the outlet for water at the cooling water cooler  3 . The temperature sensor  32  measures a temperature T 3  of water output from the cooling water cooler  3  and outputs the measurement signal to the control unit  59 . The cooling water cooler  3  includes a flowmeter  33 . The flowmeter  33  measures a flow rate of the water flowing into the cooling water cooler  3 . When the measured value falls below a predetermined lower limit, the flowmeter  33  outputs the measurement signal to the control unit  59  to receive replenishment of cooling water from the valve  53 . 
     The water preheated in the cooling water cooler  3  is output to the exhaust gas heat exchanger  2 . For example, in the case where the water output from the binary power generation device  8  has a temperature of around 80 Celsius degrees, heat of the water is slightly dissipated in the water tank  6  and is output from the water tank  6  at a temperature around 70 Celsius degrees. The water at such temperature is preheated by the cooling water cooler  3  at a temperature up to 90 Celsius degrees as a limit and then is output. 
     The exhaust gas heat exchanger  2  is a device that heats the water preheated by the cooling water cooler  3  by heat exchange with the exhaust gas from the engine  71 . The outlet for water at the exhaust gas heat exchanger  2  is coupled to the inlet for water at the binary power generation device  8 . The water heated by the exhaust gas heat exchanger  2  is output to the binary power generation device  8 . For example, the exhaust gas from the engine  71  in the embodiment is around 500 Celsius degrees. The temperature of water after the heat exchange fully exceeds 95 Celsius degrees, which is a temperature required in the binary power generation device  8 . The heat exchange by the exhaust gas heat exchanger  2  reduces the temperature of the exhaust gas from the engine  71  to 200 to 300 Celsius degrees and then the exhaust gas is emitted to the atmosphere. 
     &lt;Sub Preheating System&gt; 
     As described above, the sub preheating system includes from the water tank  6 , through the valve  51 , the lubricating oil cooler  4 , and the valve  54 , and to the exhaust gas heat exchanger  2 . 
     Specifically, the lubricating oil cooler  4  is a device that contains lubricating oil as a cooling medium to cool the inside of the engine  71 . The lubricating oil cooler  4  exchanges heat between the lubricating oil of the engine  71  and the water output from the water tank  6 . Thus, the lubricating oil cooler  4  cools the lubricating oil of the engine  71 , preheats the water from the water tank  6 , and outputs the water. An inlet for water in the lubricating oil cooler  4  is coupled to one outlet for water in the valve  51 . The outlet for water in the lubricating oil cooler  4  is coupled to the inlet for water in the valve  54 . One outlet for water in the valve  54  is coupled to the exhaust gas heat exchanger  2 . Accordingly, the lubricating oil cooler  4  preheats the water supplied from the water tank  6  to the lubricating oil cooler  4  via the valve  51 . After that, the water is output to the exhaust gas heat exchanger  2  for heating or, as described later, is recovered to the water tank  6  for additional preheating. 
     The lubricating oil cooler  4  includes two temperature sensors  41  and  42 . The temperature sensor  41  measures a temperature T 4  of the lubricating oil cooler  4  and outputs the measurement signal to the control unit  59 . The temperature sensor  42  is disposed to the outlet for water of the lubricating oil cooler  4 . The temperature sensor  42  measures a temperature T 5  of water output from the lubricating oil cooler  4  and outputs the measurement signal to the control unit  59 . The lubricating oil cooler  4  includes a flowmeter  43 . The flowmeter  43  measures a flow rate of the water flowing into the lubricating oil cooler  4 . When the measured value falls below a predetermined lower limit, the flowmeter  43  outputs the measurement signal to the control unit  59  to receive replenishment of cooling water from the valve  53 . 
     &lt;Cooling Water Supply System&gt; 
     As described above, the cooling water supply system supplies the cooling water to the cooling water cooler  3 , the lubricating oil cooler  4 , and the water tank  6  via the valves  53  and  55 . The cooling water is supplied from a facility different from the binary power generation device  8 , for example, waterworks. From an aspect of preventing a scale, fresh water is used as the cooling water. 
     Specifically, the cooling water inlet of the valve  55  is coupled to, for example, the waterworks via a pump P 2 . The one cooling water outlet for the valve  55  is coupled to the cooling water inlet for the water tank  6 , and another cooling water outlet is coupled to the cooling water inlet for the valve  53 . The one cooling water outlet for the valve  53  is coupled to the cooling water inlet for the cooling water cooler  3 , and the other coolingwater outlet is coupled to the coolingwater inlet for the lubricating oil cooler  4 . 
     Accordingly, under conditions described later, the cooling water is supplied to the cooling water cooler  3  and the lubricating oil cooler  4  via the valve  53  and also is supplied to the water tank  6  via the valve  55 . 
     &lt;Valve&gt; 
     The valves  51 ,  52 , and  54  are devices to adjust a flow of water in the main and sub preheating systems. The valves  53  and  55  are devices to adjust a flow of cooling water in the cooling water supply system. The valves  51  to  55  operate based on the output from the control unit  59 . 
     Specifically, the valve  51  is a device that distributes and outputs the water supplied from the water tank  6  to the valve  52  and the lubricating oil cooler  4 . Accordingly, the valve  51  includes the one inlet and the two outlets. The water from the water tank  6  flows into the inlet. The water is output from the outlets to each of the valve  52  side and the lubricating oil cooler  4  side. 
     The distribution of water output from the valve  51  is changed according to the situation. For example, the water may be all output to the valve  52  side or may be all output to the lubricating oil cooler  4  side. The water may be half output to the valve  52  side and half output to the lubricating oil cooler  4  side. Alternatively, one-third of the water may be output to the valve  52  side, and two-third of the water may be output to the lubricating oil cooler  4  side. During a usual operation of the exhaust heat recovery apparatus  1 , the valve  51  is controlled such that the water is output to both the valve  52  side and the lubricating oil cooler  4  side. 
     To the outlet on the valve  52  side in the valve  51 , a temperature sensor  511  is disposed. The temperature sensor  511  measures a temperature T 6  of water output from the valve  51  to the valve  52  side and outputs the measurement signal to the control unit  59 . 
     The valve  52  is disposed at a flow passage coupling the valve  51  and the cooling water cooler  3 . When the temperature T 2  of the cooling water cooler  3  is lower than the temperature T 6  of water, which is output from the valve  51  to the valve  52  side, the valve  52  is a device that supplies the water at the temperature T 6  to the exhaust gas heat exchanger  2 . That is, the valve  52  forms the flow passage with which the water from the water tank  6  is supplied to the exhaust gas heat exchanger  2  without passing through the cooling water cooler  3  in the above-described case. In the case other than that, the valve  52  causes the water at the temperature T 6  to be supplied to the cooling water cooler  3 . 
     The valve  53  is a device that supplies the cooling water to the cooling water cooler  3  and the lubricating oil cooler  4  when the main and the sub preheating systems are superheated. Specifically, the valve  53  operates in the case where the temperature T 2  of the cooling water cooler  3  exceeds a predetermined allowable temperature and in the case where the temperature T 4  of the lubricating oil cooler  4  exceeds a predetermined allowable temperature. The valve  53  causes the cooling water to be supplied to the cooling water cooler  3  and the lubricating oil cooler  4  also in the case where the flow rate of the water supplied to each of the cooling water cooler  3  and lubricating oil cooler  4  falls below the respective predetermined lower limits. In the case other than these two cases, the valve  53  is set such that the operation is disabled, however, the valve  53  may be configured to operate according to the situation. 
     The valve  54  is a device that supplies the water output from the lubricating oil cooler  4  to any of the exhaust gas heat exchanger  2  and the water tank  6 . That is, in the case where the temperature T 5  of water output from the lubricating oil cooler  4  is lower than the temperature T 3  of water output from the cooling water cooler  3 , the valve  54  causes the water tank  6  to recover the water output from the lubricating oil cooler  4 . In cases except for the above, the valve  54  causes the water to be supplied to the exhaust gas heat exchanger  2 . 
     The valve  55  is a device that causes the cooling water to be supplied to the water tank  6  when the water level of the water tank  6  falls below the predetermined lower limit. 
     &lt;Control Unit&gt; 
     The control unit  59  is a device that controls the valves  51  to  55  based on the measurement signals output from the temperature sensors  31 ,  32 ,  41 ,  42 ,  62 , and  511 , the flowmeters  33  and  43 , and the water level sensor  61 . 
     Specifically, the control unit  59  compares the temperature T 4  of the lubricating oil cooler  4 , which has been measured with the temperature sensor  41 , with the temperature T 1  of water, which is output from the water tank  6  and has been measured with the temperature sensor  62 . When the temperature T 4  is higher than the temperature T 1 , the control unit  59  controls the valve  51  such that the water output from the water tank  6  is supplied to the lubricating oil cooler  4  for heat exchange. On the other hand, when the temperature T 4  is lower than the temperature T 1 , the control unit  59  controls the valve  51  such that the water from the water tank  6  is supplied to the valve  52 . 
     The control unit  59  compares the temperature T 2  of the cooling water cooler  3 , which has been measured with the temperature sensor  31 , with the temperature T 6  of water, which is output from the valve  51  to the valve  52  side and has been measured with the temperature sensor  511 . When the temperature T 2  is lower than the temperature T 6 , the control unit  59  controls the valve  52  such that the water supplied from the valve  51  is supplied to the exhaust gas heat exchanger  2  without passing through the cooling water cooler  3 . On the other hand, when the temperature T 2  is higher than the temperature T 6 , the control unit  59  controls the valve  52  such that the water supplied from the valve  51  is supplied to the cooling water cooler  3 . 
     When the temperature T 2  of the cooling water cooler  3 , which has been measured with the temperature sensor  31 , exceeds the allowable temperature of the cooling water cooler  3  and the temperature T 4  of the lubricating oil cooler  4 , which has been measured with the temperature sensor  41 , exceeds the allowable temperature of the lubricating oil cooler  4 , the control unit  59  controls the valve  53  such that the cooling water is supplied from the valve  53  to the cooling water cooler  3  and the lubricating oil cooler  4 . Additionally, when the flow rate of the water flowing through the cooling water cooler  3 , which has been measured by the flowmeter  33 , falls below the predetermined lower limit and also when the flow rate of the water flowing through the lubricating oil cooler  4 , which has been measured by the flowmeter  43 , falls below the predetermined lower limit, the control unit  59  controls the valve  53  such that the cooling water is supplied to the cooling water cooler  3  and the lubricating oil cooler  4 . In the case other than these two cases, the control unit  59  controls the valve  53  such that the cooling water is supplied to neither the cooling water cooler  3  nor the lubricating oil cooler  4 . For example, in the case of an engine for generating electricity, the cooling water and the lubricating oil of the engine  71  reaches a temperature around 200 to 300 Celsius degrees. However, the allowable temperatures of the respective cooling water cooler  3  and lubricating oil cooler  4  are around 95 Celsius degrees. 
     Furthermore, the control unit  59  compares the temperature T 3  of water, which is output from the cooling water cooler  3  and that has been measured with the temperature sensor  32 , with the temperature T 5  of water, which is output from the lubricating oil cooler  4  and that has been measured with the temperature sensor  42 . When the temperature T 3  is higher than the temperature T 5 , the control unit  59  controls the valve  54  such that the water at the temperature T 5  output from the lubricating oil cooler  4  is recovered to the water tank  6 . On the other hand, when the temperature T 3  is lower than the temperature T 5 , the control unit  59  controls the valve  54  such that the water at the temperature T 5  output from the lubricating oil cooler  4  is supplied to the exhaust gas heat exchanger  2 . 
     When the water level of the water tank  6  that has been measured by the water level sensor  61  falls below the predetermined lower limit, the control unit  59  controls the valve  55  such that the cooling water is replenished to the water tank  6 . 
     &lt;Binary Power Generation Device&gt; 
     In this embodiment, the binary power generation device  8  uses the water that has been heated in the exhaust heat recovery apparatus  1 . That is, this embodiment is configured as a multistage power generation system that further generates electricity using the exhaust heat from the engine  71  simultaneously with the electric generation using the engine  71  as a power engine. 
     As illustrated in  FIG. 9 , the binary power generation device  8  includes an evaporator  81 , aturbine  82 , acondenser  83 , anelectricgenerator  84 , an inverter  85 , a converter  86 , and a cooling tower  87 . An appropriate temperature of water input to the binary power generation device  8  is, for example, around 95 Celsius degrees. A temperature of warm water output from the binary power generation device  8  is, for example, around 83 Celsius degrees. 
     The water output from the exhaust gas heat exchanger  2  of the exhaust heat recovery apparatus  1  is guided to the evaporator  81  of the binary power generation device  8 . After the evaporator  81  provides heat to the working medium of the binary power generation device  8 , the working medium is returned to the water tank  6  in the exhaust heat recovery apparatus  1 . 
     The evaporator  81  heats and evaporates the working medium of the binary power generation device  8 . The evaporated working medium is guided to the turbine  82 . After the turbine  82  has been rotated, the condenser  83  liquefies the working medium. The liquefied working medium is sent to the evaporator  81  again with a pump P 6 . 
     The turbine  82  is a power engine for the electric generator  84 , thus the rotation of the turbine  82  causes the electric generator  84  to generate electricity. The electric power, which is generated by the electric generator  84 , passes through the inverter  85  and the converter  86  and is sent to a power transmission system. 
     Operation 
     The following describes operations of the exhaust heat recovery apparatus according to one or more embodiments of the present invention with reference to  FIG. 2  to  FIG. 8 . 
     &lt;During Steady Operation of Engine&gt; 
       FIG. 2  to  FIG. 4  indicate by bold lines flow of water for the preheating system and of cooling water for the cooling water supply system during the steady operation of the engine. 
       FIG. 2  illustrates a basic flow of water during the steady operation of the engine. In this case, the temperature T 2  of the cooling water cooler  3  and the temperatureT 4  of the lubricating oil cooler  4  are lower than the allowable temperatures and are higher than the temperatures T 1  and T 6  of water output from the water tank  6  and the valve  51 . The temperature T 3  of water output from the cooling water cooler  3  is lower than the temperature T 5  of water output from the lubricating oil cooler  4 . The water level of the water tank  6  exceeds the lower limit and the flow rates of water flowing into the respective cooling water cooler  3  and lubricating oil cooler  4  exceed the lower limits. 
     At this time, the control unit  59  compares the measurement signals from the temperature sensors  62  and  41  and determines that the temperature T 1  is lower than the temperature T 4 . The control unit  59  controls the valve  51  such that the water supplied to the valve  51  flows through both the cooling water cooler  3  and the lubricating oil cooler  4 . 
     The control unit  59  compares the measurement signals from the temperature sensors  511  and  31  and determines that that temperature T 6  is lower than the temperature T 2 . The control unit  59  controls the valve  52  such that the water supplied to the valve  52  flows through the cooling water cooler  3 . 
     The control unit  59  compares the measurement signals from the temperature sensors  32  and  42  and determines that the temperature T 3  is lower than the temperature T 5 . The control unit  59  controls the valve  54  such that the water supplied to the valve  54  flows through the exhaust gas heat exchanger  2 . 
     The control unit  59  determines that the water level of the water tank  6  exceeds the lower limit by the measurement signal from the water level sensor  61  and controls the valve  55  such that the cooling water is not supplied to the water tank  6 . The control unit  59  determines that the flow rates of the water flowing into the respective cooling water cooler  3  and lubricating oil cooler  4  exceed the lower limits by the measurement signals from the flowmeters  33  and  43 . The control unit  59  controls the valve  53  such that the cooling water is not supplied to either the cooling water cooler  3  or the lubricating oil cooler  4 . 
     Consequently, after flowing through both the main preheating system and the sub preheating system, the water is heated with the exhaust gas heat exchanger  2 . The cooling water does not flow through the cooling water supply system. 
       FIG. 3  illustrates a flow of water during the steady operation of the engine in the case where the temperature T 3  of water output from the cooling water cooler  3  is higher than the temperature T 5  of water output from the lubricating oil cooler  4 . The control unit  59  compares the measurement signals of the temperature sensor  32  with the temperature sensor  42  and determines that the temperature T 3  is higher than the temperature T 5 . The control unit  59  then controls the valve  54  such that the water output from the lubricating oil cooler  4  flows through the water tank  6 . 
     Consequently, the exhaust gas heat exchanger  2  heats the water flowing through the main preheating system. The water flowing through the sub preheating system, however, is recovered to the water tank  6  for preheating again. This ensures avoiding a reduction in the temperature of water from the cooling water cooler  3  due to confluence of the water preheated by the cooling water cooler  3  and the water from the lubricating oil cooler  4 , which has a temperature lower than a temperature of the preheated water, namely, for effective use of heat. 
       FIG. 4  illustrates flow of the water and the cooling water during the steady operation of the engine in the case where the water level of the water tank  6  falls below the predetermined lower limit. Based on the measurement signal from the water level sensor  31 , the control unit  59  determines that the water level of the water tank  6  falls below the lower limit. The control unit  59  controls the valve  55  such that the cooling water is supplied to the water tank  6 . Consequently, until the water level of the water tank  6  exceeds the lower limit, the cooling water is replenished via the valve  55 . 
     &lt;At Engine Start&gt; 
       FIG. 5  and  FIG. 6  indicate by bold lines flow of water for the preheating system and of cooling water for the cooling water supply system at the engine  71  start. 
       FIG. 5  illustrates a basic flow of water at the engine  71  start. In this case, the temperature T 2  of the cooling water cooler  3  is lower than the temperature T 6  of water output from the valve  51  to the valve  52  side. The control unit  59  compares the measurement signals from the temperature sensors  31  and  511  and determines that the temperature T 2  is lower than the temperature T 6 . The control unit  59  controls the valve  52  such that the water that has flowed from the valve  51  is supplied to the exhaust gas heat exchanger  2 . 
     The temperature T 4  of the lubricating oil cooler  4  is lower than the temperature T 1  of water output from the water tank  6 . The control unit  59  compares the measurement signals from the temperature sensors  41  and  62  and determines that the temperature T 4  is lower than the temperature T 1 . The control unit  59  controls the valve  51  such that the water that has flowed from the water tank  6  is supplied to the valve  52 . 
     Consequently, the water output from the water tank passes through the valves  51  and  52  and is supplied to the exhaust gas heat exchanger  2 . This ensures avoiding a situation of providing heat to the cooling water of the engine  71  that should be cooled. This also ensures avoiding the case where the cooling water cooler  3  deprives the heat of the water from the water tank  6  that should be preheated, and effective use of heat may be achieved. 
       FIG. 6  illustrates flow of water and cooling water at the engine  71  start in the case where the water level of the water tank  6  does not reach the lower limit. Based on the measurement signal from the water level sensor  31 , the control unit  59  determines that the water level of the water tank  6  does not reach the lower limit. The control unit  59  controls the valve  55  such that the cooling water is supplied to the water tank  6 . Consequently, until the water level of the water tank  6  exceeds the lower limit, the cooling water is replenished via the valve  55 . 
     &lt;While Main and Sub Preheating Systems in Exhaust Heat Recovery Apparatus are Superheated&gt; 
       FIG. 7  and  FIG. 8  indicate by bold lines flow of water for the preheating system and of cooling water for the cooling water supply system when the main and the sub preheating systems of the exhaust heat recovery apparatus  1  are superheated. 
       FIG. 7  illustrates a basic flow of water when the main and the sub preheating systems of the exhaust heat recovery apparatus  1  are superheated. In this case, the temperatures T 2  and T 4  of the cooler  3  and the lubricating oil cooler  4  exceed the allowable temperatures of each of the cooler  3  and the lubricating oil cooler  4 . The control unit  59  compares the measurement signals from the temperature sensors  31  and  41  and determines that the temperatures T 2  and T 4  exceed the respective allowable temperatures. The control unit  59  controls the valve  55  such that the cooling water is supplied to the valve  53  and controls the valve  53  such that the cooling water is supplied to the cooling water cooler  3  and the lubricating oil cooler  4 . 
     The Temperature T 1  of water output from the water tank  6  is higher than the temperature T 4  of the lubricating oil cooler  4 . The control unit  59  compares measurement results of the temperature sensors  62  and  41  and determines that the temperature T 1  is higher than the temperature T 4 . The control unit  59  controls the valve  51  such that the water output from the water tank  6  is supplied to the valve  52 . 
     Furthermore, the temperature T 6  of water output from the valve  51  is higher than temperature T 2  of the cooling water cooler  3 . The control unit  59  compares the measurement signals from the temperature sensors  511  and  31  and determines that the temperature T 6  is higher than the temperature T 2 . The control unit  59  controls the valve  52  such that the water output from the valve  51  is supplied to the exhaust gas heat exchanger  2 . 
     Consequently, the water output from the water tank passes through the valves  51  and  52  and is supplied to the exhaust gas heat exchanger  2 . The cooling water is supplied to the cooling water cooler  3  and the lubricating oil cooler  4  to cool these devices. The cooling water thus supplied is recovered from the cooling water cooler  3  and the lubricating oil cooler  4  to the water tank  6 . 
     Superheating the cooling water cooler  3  and the lubricating oil cooler  4  overheats the engine  71 , possibly resulting in damages of the engine  71  and its peripherals. Accordingly, by preventing the cooling water cooler  3  and the lubricating oil cooler  4  from being superheated, protection of the various devices is achieved. 
       FIG. 8  illustrates a flow of water when the water level of the water tank  6  falls below the lower limit in addition to superheat of the main and the sub preheating systems in the exhaust heat recovery apparatus  1 . Since the control unit  59  controls the valve  55  so as to be open based on the measurement signal from the water level sensor  61 , the cooling water is supplied to the water tank  6 . This cools the entire superheated main and the sub preheating systems. 
     As described above, the cooling water cooler  3  contains the cooling water as the cooling medium to cool the peripheral area of the combustion chamber of the engine  71 . The cooling water cooler  3  exchanges the heat between the water at a first temperature output from the warm water utilization facility and the cooling water of the engine  71 . Thus, the cooling water cooler  3  outputs the water at a second temperature higher than the first temperature. By heat exchange between the water at the second temperature and the exhaust gas from the engine  71 , the exhaust gas heat exchanger  2  outputs water at a third temperature, which is higher than the second temperature, and supplies the water to the binary power generation device  8 . When the temperature of the cooling water of the engine  71  is lower than the temperature on a side of the cooling water cooler  3  to which the water at the first temperature is supplied, the valve  52  causes the water at the first temperature to be supplied to the exhaust gas heat exchanger  2 . Accordingly, the water supplied from the warm water utilization facility side passes through the valve  52  and is supplied to the exhaust gas heat exchanger  2 . That is, the water does not pass through the cooling water cooler  3 . This ensures avoiding the situation of providing heat to the cooling water of the engine  71  that should be cooled. This also leads to prevention of the overheating of the engine  71  and the damages of the engine  71  and its peripherals in association with the overheating, in the case where the preheating system in the exhaust heat recovery apparatus  1  is superheated. This ensures avoiding the cooling water cooler  3  to deprive the heat of the water from the warmwaterutilization facility side that shouldbepreheated, achieving effective use of heat. 
     The lubricating oil cooler  4  contains the lubricating oil as the cooling medium to cool the inside of the engine  71 . The lubricating oil cooler  4  exchanges the heat between the water at the first temperature output from the warm water utilization facility and the lubricating oil. This outputs the water at a fourth temperature higher than the first temperature and supplies the water to the exhaust gas heat exchanger  2 . Accordingly, the exhaust heat recovery apparatus  1  includes two preheating providing means, the cooling water cooler  3  and the lubricating oil cooler  4 , achieving effective use of heat. 
     The valve  51  is disposed on a side of the valve  52  into which the water at the first temperature flows. When the temperature of the lubricating oil is lower than the temperature on the side of the lubricating oil cooler  4  to which the water at the first temperature is supplied, the water at the first temperature to be supplied to the lubricating oil cooler  4  is supplied to the valve  52 . This ensures avoiding the situation of providing heat to the lubricating oil of the engine  71  that should be cooled. This leads to prevention of overheating of the engine  71  and the damages of various devices in association with the overheating, in the case where the preheating system in the exhaust heat recovery apparatus  1  is superheated. This ensures avoiding the lubricating oil cooler  4  to deprive the heat of the water from the warm water utilization facility side that should be preheated, achieving effective use of heat. 
     The water tank  6  is disposed on a side of the valve  51  into which the water at the first temperature flows. The water tank  6  accumulates the water at the first temperature output from the warm water utilization facility and then the water is output to the valve  51 . This ensures adjusting the amount of water flowing through the preheating system in the exhaust heat recovery apparatus  1  and ensures stably operating the exhaust heat recovery apparatus  1 . 
     When the temperature on the side of the lubricating oil cooler  4  from which the water at the fourth temperature is output is lower than the temperature on the side of the cooling water cooler  3  from which the water at the second temperature is output, the valve  54  causes the water at the fourth temperature to be supplied to the water tank  6 . Accordingly, the exhaust gas heat exchanger  2  heats the water output from the cooling water cooler  3 . Meanwhile, the water output from the lubricating oil cooler  4  is recovered to the water tank  6  for preheating again. This ensures avoiding the reduction in the temperature of water from the cooling water cooler  3  due to the confluence of the water preheated by the cooling water cooler  3  and the water from the lubricating oil cooler  4 , which has the temperature lower than the temperature of the preheated water, and the above is useful for effective use of heat. 
     The valve  53  causes water at a fifth temperature output from a facility different from the warm water utilization facility, such as waterworks, and lower than the temperatures of the cooling water and the lubricating oil of the engine  71  to be supplied to at least one of the cooling water cooler  3  and the lubricating oil cooler  4 . This ensures securing the water flowing into the cooling water cooler  3  and the lubricating oil cooler  4 , and the above is useful for stable operation of the exhaust heat recovery apparatus  1 . 
     When the temperature on a side of the cooling water cooler  3  to which the water at the first temperature is supplied is higher than the allowable temperature of the cooling water of the engine  71  and when the temperature on a side of the lubricating oil cooler  4  to which the water at the first temperature is supplied is higher than the allowable temperature of the lubricating oil, the valve  53  supplies the water at the fifth temperature to the cooling water cooler  3  and the lubricating oil cooler  4 . This ensures preventing the cooling water cooler  3  and the lubricating oil cooler  4  from being superheated, avoiding the overheating of the engine  71  and the damages of the engine  71  and its peripherals in association with the overheating. 
     When the flow rates of the water at the first temperature supplied to the cooling water cooler  3  and the lubricating oil cooler  4  become the predetermined flow rates or less, the valve  53  supplies the water at the fifth temperature to the cooling water cooler  3  and the lubricating oil cooler  4 . This ensures securing constant flow rates of water flowing into the cooling water cooler  3  and the lubricating oil cooler  4 , and the above is useful for the stable operation of the exhaust heat recovery apparatus  1 . 
     When the amount of water accumulated in the water tank  6  becomes a predetermined amount or less, the valve  55  causes the water at the fifth temperature to be supplied to the water tank  6 . Thus, this secures the accumulation of the water by the predetermined amount in the water tank  6 . This means the stable supply of water from the water tank  6  to the cooling water cooler  3  and the lubricating oil cooler  4 , and leads to the stable operation of the exhaust heat recovery apparatus  1 . 
     The warm water utilization facility is the binary power generation device. This ensures additional electric generation using the exhaust heat from the engine  71 , achieving the effective use of the exhaust heat from the engine  71 . 
     The embodiments are intended for easy understanding of the present invention and are not in any way to be construed as limiting the present invention. The present invention may be modified and improved without departing from the scope of the invention, and equivalents thereof are also encompassed by the invention. 
     For example, the first cooler and the second cooler are described corresponding to the cooling water cooler  3  and the lubricating oil cooler  4 , however, the cooling water cooler  3  and the lubricating oil cooler  4  may be exchanged. 
     As another example of the warm water utilization facility, a heated pool is included. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
           1  exhaust heat recovery apparatus 
           2  exhaust gas heat exchanger 
           3  cooling water cooler 
           4  lubricating oil cooler 
           51  to  55  valve 
           6  water tank 
       
    
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.