Patent Publication Number: US-9897103-B2

Title: Compressor

Description:
RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 12/828,774 filed Jul. 1, 2010, which claims the benefit of priority from Japanese Patent Application No. 2009-160228 filed on Jul. 6, 2009 entitled “Compressor,” the disclosures of which also entirely incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present subject matter relates to a compressor for compressing gas, and more particularly, to a compressor for recovering exhaust heat. 
     BACKGROUND 
     In compressors, a large amount of heat is generated, for example, at the time of air compression. This causes the temperature of compressed air to rise. Compressed air may be used at high temperature, however, generally it is cooled to close-to-ambient temperature and also dehumidified for its use. Also, in compressors, oil or water may be used for lubrication or cooling, and the oil or water heated to a high temperature is cooled. The heat generated in compressors in this manner is exhausted through compressed air, oil, water, or the like. As one of the devices for recovering such exhaust heat, a device with thermoelectric conversion elements installed in a compressor body and discharge piping has been proposed (for example, see Japanese Published Unexamined Patent Application No. 2006-125302). According to the related art disclosed in Japanese Published Unexamined Patent Application No. 2006-125302, heat from high-temperature portions such as the compressor body and the discharge piping is converted to electric power by the thermoelectric conversion elements, and the voltage is converted through a regulator so as to supply power to auxiliary devices such as a cooling fan and an oil pump. 
     SUMMARY 
     However, the related art described above has the following problem. That is, in the related art disclosed in Japanese Published Unexamined Patent Application No. 2006-125302, the thermoelectric conversion elements are installed in the compressor body and the discharge piping, however, since the surface area of the high-temperature portions such as the compressor body and the discharge piping is limited, a large area for the thermoelectric conversion elements cannot be provided. Therefore, there has been room for the improvement in exhaust heat recovery efficiency. 
     Accordingly, an object of the present subject matter is to provide a compressor capable of improving the exhaust heat recovery efficiency. In order to achieve the above-mentioned object, according to one example, a compressor, comprising: a compressor body for compressing gas; a heat exchanger for cooling a gas, coolant, water, or oil heated by the compressor during compressor operation by heat exchange with a working fluid, for circulating the working fluid; an expander for expanding the working fluid heated and vaporized by the heat exchanger to generate driving force; a condenser for cooling and liquefying the working fluid supplied from the expander to supply the liquefied working fluid to the heat exchanger; and a circulating pump for circulating the working fluid among the heat exchanger, the expander, and the condenser. The heat exchanger, the expander, the condenser, and the circulating pump implement a Rankine cycle. 
     In this manner, in the example, the Rankine cycle, composed of the heat exchanger, the expander, the condenser, and the circulating pump, is implemented as an exhaust heat recovery system, thereby allowing recovery of exhaust heat in the compressor and generation of driving force. It is therefore possible to improve the exhaust heat recovery efficiency. 
     In the example, preferably, the at least one heat exchanger includes a plurality of heat exchangers, and the plurality of heat exchangers are series-connected in such a manner that the working fluid circulates in increasing order of exchange heat quantity. With this configuration, the working fluid may be efficiently vaporized. It is therefore possible to improve the exhaust heat recovery efficiency. 
     According to the example, it is possible to improve the exhaust heat recovery efficiency. 
     Additional advantages and novel features will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of examples. The advantages of the present teachings may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed example discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawing figures depict one or more implementations in accord with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements. 
         FIG. 1  is a diagram showing the configuration of a compressor according to a first example; 
         FIG. 2  is a diagram showing the configuration of a compressor according to a second example; 
         FIG. 3  is a diagram showing the configuration of a compressor according to a third example; 
         FIG. 4  is a diagram showing the configuration of a compressor according to one modified example; 
         FIG. 5  is a diagram showing the configuration of a compressor according to a fourth example; 
         FIG. 6  is a diagram showing the configuration of a compressor according to another modified example; 
         FIG. 7  is a diagram showing the configuration of a compressor according to a fifth example; 
         FIG. 8  is a diagram showing the configuration of a compressor according to a sixth example; 
         FIG. 9  is a diagram showing the configuration of a compressor according to a seventh example; and 
         FIG. 10  is a diagram showing the configuration of a compressor according to an eighth example. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instance, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings. 
     A first example will be described with reference to  FIG. 1 .  FIG. 1  is a schematic diagram showing the configuration of the primary parts of a compressor according to this example. 
     Referring to  FIG. 1 , an oil-free and non-water supply compressor includes: a screw compressor body  1 ; a motor (such as an electric motor  2  or an internal combustion engine) connected to the compressor body  1  through a gear system (speed increasing gear) not shown in the figure to drive the compressor body  1 ; and a suction filter  3  and a suction throttle valve  4  provided on a suction side of the compressor body  1 . When the compressor body  1  is driven by the electric motor  2 , air (atmosphere) is sucked through the suction filter  3  and the suction throttle valve  4  to be compressed to a predetermined pressure so as to discharge the compressed air. In addition, a controller (not shown) switches the suction throttle valve  4  from an open state to a closed state to thereby switch from load operation to no-load operation. 
     Here, the main feature of this example is that, on a discharge side of the compressor body  1 , there is provided a heat exchanger  5  for cooling compressed air, for example, to close-to-ambient temperature, and that there is also provided an exhaust heat recovery system for recovering exhaust heat from compressed air through the heat exchanger  5 . This exhaust heat recovery system includes: the heat exchanger  5  for heating and vaporizing a working fluid (water or a refrigerant) by means of heat exchange with compressed air; an expander  6  for expanding the working fluid vaporized by the heat exchanger  5  to generate driving force; a condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and a circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  5 , thereby constituting a Rankine cycle. 
     Furthermore, a generator  9  is connected to the expander  6  to convert the driving force generated by the expander  6  to electric power. The electric power generated by the generator  9  is returned, for example, to a power supply system, thereby making it possible to cover the power to be supplied to other apparatuses (in other words, the electric power can be sold to power companies). In that case, an inverter (not shown) for frequency control of electric power may be connected to the generator  9 . 
     The power generated by the generator  9  can cover the power to drive, for example, an auxiliary device (such as a cooling fan for ventilating the compressor) in the compressor. Also, for example, in a compressor mounted with an inverter (not shown) for controlling the rotational speed of the electric motor  2 , the generator  9  may be connected to the inverter. That is to say, not only the power from a commercial power supply (a main power supply) but also the power from the generator  9  may be supplied to the inverter. In that case, a rotational speed controller (not shown) calculates a rotational speed command value based on a deviation between a discharge pressure of the compressor body  1  and a preset pressure to output the calculated rotational speed command value to the inverter. The inverter controls a switching element based on the rotational speed command value to produce a voltage waveform of a desired frequency and supply it to the electric motor  2 . 
     In addition, a power supply control system (not shown) estimates power supply (that is, the power generation capacity of the generator  9 ) from the generator  9  to the inverter, and also adjusts power supply from the main power supply to the inverter so that the sum of the estimated power supply and the power supply from the main power supply to the inverter becomes a predetermined value. A more detailed explanation follows. The power generation capacity (that is, the recovered heat amount of the exhaust heat recovery system) of the generator  9  depends on the heating value of the compressor. Therefore, the power generation capacity is likely to increase as the heating value increases. The heating value of the compressor depends on the discharge pressure and the air quantity of the compressor body  1 , or the rotational speed and the torque of the electric motor  2 . Therefore, the power generation capacity of the generator  9  is estimated based on a detected value of the discharge pressure of the compressor body  1 , a detected value (or a rotational speed command value) of the rotational speed of the electric generator  2 , or a detected value of the torque current of the electric generator  2 . Further, the recovered heat amount depends on the temperature of the compressed air or ambient temperature. Therefore, by using a detected value thereof, estimate accuracy is improved. In addition, the power supply from the main power supply is reduced according to the power generation capacity of the generator  9 . It is therefore possible to apparently reduce the electric power required for the compressor and expect the energy-saving effect. 
     Next, the advantageous effect of this example will be described. 
     The oil-free and non-water supply compressor is operated in a state in which no oil or water is supplied to a compression chamber of the compressor body  1 . For this reason, compressed air is heated to high temperature. For example, the temperature of the compressed air, compressed from atmospheric pressure to a pressure of 0.7 MPa (gauge pressure), is in the range of approximately 300° C. to 400° C. For the purpose of using this compressed air, it is cooled, for example, to close-to-ambient temperature by the heat exchanger  5 . Also, in this example, the Rankine cycle, composed of the heat exchanger  5 , the expander  6 , the condenser  7 , and the circulating pump  8 , is implemented as the exhaust heat recovery system for recovering exhaust heat from compressed air, whereby the driving force generated by the expander  6  is converted to electric power by the generator  9 . It is therefore possible to improve the exhaust heat recovery efficiency, as compared with the case where thermoelectric elements are installed in the compressor body  1  and the discharge piping. 
     A second example will be described with reference to  FIG. 2 .  FIG. 2  is a diagram showing the configuration of a compressor according to this example. In  FIG. 2 , the same elements as those in the above-described first example are designated by the same reference signs as those described above, and the descriptions thereof will not be repeated when appropriate. 
     In this example, a coolant flow path (not shown) through which coolant circulates is formed in a casing of the compressor body  1 . Also, a coolant system for supplying coolant to the coolant flow path is provided. The coolant system includes: a heat exchanger  10  for cooling and supplying coolant to the coolant flow path of the compressor body  1 ; and a pump  11  for supplying to the heat exchanger  10  the coolant circulated through the coolant flow path of the compressor body  1  and heated. 
     Also, there is provided an exhaust heat recovery system for recovering exhaust heat from coolant through the heat exchanger  10  and recovering exhaust heat from compressed air through the heat exchanger  5 . The exhaust heat recovery system includes: the heat exchanger  10  for heating a working fluid by means of heat exchange with coolant; the heat exchanger  5  for heating and vaporizing the working fluid heated by the heat exchanger  10 , by means of heat exchange with compressed air; the expander  6  for expanding the working fluid vaporized by the heat exchanger  5  to generate driving force; the condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and the circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  10 , thereby constituting a Rankine cycle. 
     Also in this example configured in this manner, it is possible to improve the exhaust heat recovery efficiency. In addition, in this example, exhaust heat is recovered not only from compressed air but also from coolant. It is therefore possible to further improve the exhaust heat recovery efficiency, compared to the above-described first example. Furthermore, in this example, the heat exchange amount of the heat exchanger  10  is smaller than that of the heat exchanger  5 . Thus, the working fluid can be efficiently vaporized by allowing the working fluid to flow in order from the heat exchanger  10  to the heat exchanger  5 . It is therefore possible to improve the exhaust heat recovery efficiency. It should be noted that, for example, when the heat exchange amount of the heat exchanger  5  is smaller than that of the heat exchanger  10 , it is preferable to allow the working fluid to flow in order from the heat exchanger  5  to the heat exchanger  10 . 
     It is to be noted that, although in the above-described second example the exhaust heat recovery system for recovering exhaust heat from coolant through the heat exchanger  10  and recovering exhaust heat from compressed air through the heat exchanger  5  has been described, there may alternatively be provided, for example, an exhaust heat recovery system for recovering exhaust heat only from coolant through the heat exchanger  10 . More specifically, while not shown in the figure, the exhaust heat recovery system may include: the heat exchanger  10  for heating and vaporizing a working fluid by means of heat exchange with coolant; the expander  6  for expanding the working fluid vaporized by the heat exchanger  10  to generate driving force; the condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and the circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  10 , thereby constituting a Rankine cycle. 
     A third example will be described with reference to  FIG. 3 .  FIG. 3  is a diagram showing the configuration of a compressor according to this example. In  FIG. 3 , the same elements as those in the above-described second example are designated by the same reference signs as those described above, and the descriptions thereof will not be repeated when appropriate. 
     In this example, the compressor body  1  is connected to the electric motor  2  through a gear system  12 , and provided with a lubricating system for supplying lubricating oil to the gear system  12 . The lubricating system includes: a heat exchanger  13  for cooling lubricating oil for the gear system  12 ; and a pump  14  for supplying the lubricating oil lubricated and heated by the gear system  12  to the heat exchanger  13 . 
     Also, there is provided an exhaust heat recovery system for recovering exhaust heat from lubricating oil through the heat exchanger  13 , recovering exhaust heat from coolant through the heat exchanger  10 , and recovering exhaust heat from compressed air through the heat exchanger  5 . The exhaust heat recovery system includes: the heat exchanger  13  for heating a working fluid by means of heat exchange with lubricating oil; the heat exchanger  10  for heating the working fluid heated by the heat exchanger  13 , by means of heat exchange with coolant; the heat exchanger  5  for heating and vaporizing the working fluid heated by the heat exchanger  10 , by means of heat exchange with compressed air; the expander  6  for expanding the working fluid vaporized by the heat exchanger  5  to generate driving force; the condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and the circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  13 , thereby constituting a Rankine cycle. 
     Also in this example configured in this manner, it is possible to improve the exhaust heat recovery efficiency. In addition, in this example, exhaust heat is recovered not only from compressed air and coolant but also from lubricating oil. It is therefore possible to further improve the exhaust heat recovery efficiency, compared to the above-described second example. Furthermore, in this example, the heat exchange amount becomes larger in the order of the heat exchanger  13 , the heat exchanger  10 , and the heat exchanger  5 . Thus, the working fluid can be efficiently vaporized by allowing the working fluid to flow in that order. It is therefore possible to improve the exhaust heat recovery efficiency. It should be noted that, for example, when the order of the heat exchange amount of the heat exchangers  5 ,  10 , and  13  is different from that described in this example, it is preferable to allow the working fluid to flow in the corresponding order. 
     It is to be noted that, although in the above-described third example the exhaust heat recovery system for recovering exhaust heat from lubricating oil through the heat exchanger  13 , recovering exhaust heat from coolant through the heat exchanger  10 , and recovering exhaust heat from compressed air through the heat exchanger  5  has been described, there may alternatively be provided, for example, an exhaust heat recovery system for recovering exhaust heat from lubricating oil through the heat exchanger  13  and recovering exhaust heat from compressed air through the heat exchanger  5 . More specifically, while not shown in the figure, the exhaust heat recovery system may include: the heat exchanger  13  for heating a working fluid by means of heat exchange with lubricating oil; the heat exchanger  5  for heating and vaporizing the working fluid heated by the heat exchanger  13 , by means of heat exchange with compressed air; the expander  6  for expanding the working fluid vaporized by the heat exchanger  5  to generate driving force; the condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and the circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  13 , thereby constituting a Rankine cycle. 
     Note that the first to third examples have been described by using an example of the case where the present subject matter is applied to the structure including the single-stage compressor body  1 . However, the present subject matter is not limited thereto, but also can be applied to, for example, a structure including a second-stage compressor body. One of such modifications will be described with reference to  FIG. 4 . 
       FIG. 4  is a schematic diagram showing the configuration of a compressor according to this modification. In  FIG. 4 , the same elements as those in the above-described first example are designated by the same reference signs as those described above, and the descriptions thereof will not be repeated when appropriate. 
     According to this modification, the compressor includes: a low-pressure stage compressor body  1 A; a heat exchanger  5 A for cooling the air compressed by the compressor body  1 A; a high-pressure compressor body  1 B for further compressing the compressed air cooled by the heat exchanger  5 A; and a heat exchanger  5 B for cooling the air compressed by the compressor body  1 B, for example, to close-to-ambient temperature. The compressor bodies  1 A and  1 B are connected to the electric motor  2  through a gear system  12 A. 
     Also, there is provided an exhaust heat recovery system for recovering exhaust heat from compressed air through the heat exchangers  5 A and  5 B. The exhaust heat recovery system includes: the heat exchanger  5 A for heating a working fluid by means of heat exchange with the compressed air generated by the low-pressure stage compressor body  1 A; the heat exchanger  5 B for heating and vaporizing the working fluid heated by the heat exchanger  5 A, by means of heat exchange with the compressed air generated by the high-pressure compressor body  1 B; the expander  6  for expanding the working fluid vaporized by the heat exchanger  5 B to generate driving force; the condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and the circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  5 A, thereby constituting a Rankine cycle. 
     Also in this modification configured in this manner, it is possible to improve the exhaust heat recovery efficiency, in the same manner as the above-described first example. Furthermore, in this modification, the heat exchange amount of the heat exchanger  5 A is smaller than that of the heat exchanger  5 B. Thus, the working fluid can be efficiently vaporized by allowing the working fluid to flow in order from the heat exchanger  5 A to the heat exchanger  5 B. It is therefore possible to improve the exhaust heat recovery efficiency. It should be noted that, for example, when the heat exchange amount of the heat exchanger  5 B is smaller than that of the heat exchanger  5 A, it is preferable to allow the working fluid to flow in order from the heat exchanger  5 B to the heat exchanger  5 A. 
     A fourth example will be described with reference to  FIG. 5 .  FIG. 5  is a diagram showing the configuration of a compressor according to this example. In  FIG. 5 , the same elements as those in the above-described third example are designated by the same reference signs as those described above, and the descriptions thereof will not be repeated when appropriate. 
     In this example, a temperature sensor  15  for detecting the temperature of the compressed air is provided, for example, downstream of the heat exchanger  5 , and a detection signal of the temperature sensor  15  is outputted to a controller  16 . The controller  16  prestores a preset temperature of the compressed air in memory (memory means) to control the discharge rate (that is, the circulating volume of the Rankine cycle) of the circulating pump  8  so that the detected temperature of the compressed air, detected by the temperature sensor  15 , becomes equal to the preset temperature. In concrete terms, for example, when the detected temperature of the compressed air is higher than the preset temperature, the discharge rate of the circulating pump  8  is increased depending on differences between the detected temperature of the compressed air and the preset temperature. On the other hand, for example, when the detected temperature of the compressed air is lower than the preset temperature, the discharge rate of the circulating pump  8  is reduced depending on differences between the detected temperature of the compressed air and the preset temperature. Thus, the temperature of the compressed air can be stabilized, regardless of load changes of the compressor. 
     Also in this example configured in this manner, it is possible to improve the exhaust heat recovery efficiency, in the same manner as the foregoing examples. 
     Note that the fourth example has been described by using an example of the case where, in the structure including the exhaust heat recovery system for recovering exhaust heat through the heat exchangers  5 ,  10 , and  13  in the same manner as the above-described third example, there are further provided the temperature sensor  15  and the controller  16 . However, the present subject matter is not limited thereto, but also, for example, in the structure including the exhaust heat recovery system for recovering exhaust heat through the heat exchanges  5  and  10  in the same manner as the above-described second example, or in the structure including the exhaust heat recovery system for recovering exhaust heat through the heat exchanger  5  in the same manner as the above-described first example, there may be provided the temperature sensor  15  and the controller  16 . Alternatively, in the structure including the exhaust heat recovery system for recovering exhaust heat through the heat exchangers  5 A and  5 B in the same manner as the above-described one modification, there may be provided with the temperature sensor  15  and the controller  16 . In this case, for example, the temperature sensor  15  may be provided between the low-pressure stage compressor body  1 A and the high-pressure stage compressor body  1 B, as shown in  FIG. 6 . In those cases, the same effect as above can be also obtained. 
     A fifth example will be described with reference to  FIG. 7 .  FIG. 7  is a schematic diagram showing the configuration of a compressor according to this example. In  FIG. 7 , the same elements as those in the foregoing examples are designated by the same reference signs as those described above, and the descriptions thereof will not be repeated when appropriate. 
     In this example, the compressor is of the oil-lubricated type. An oil separator  17  for separating oil included in compressed air is provided on the discharge side of the compressor body  1 . Also, there is provided an oiling system for supplying the oil separated by the oil separator  17  into the compression chamber of the compressor body  1 . The oiling system includes a heat exchanger  18  for cooling oil to supply oil from the oil separator  17  to the heat exchanger  18  with the inner pressure of the oil separator  17 . Further, while not shown in the figure, the oiling system is branched downstream of the heat exchanger  18  so as to supply oil into both the compression chamber of the compressor body  1  and the gear system. 
     Also, there is provided an exhaust heat recovery system for recovering exhaust heat from oil through the heat exchanger  18 . The exhaust heat recovery system includes: the heat exchanger  18  for heating and vaporizing a working fluid by means of heat exchange with oil; the expander  6  for expanding the working fluid vaporized by the heat exchanger  18  to generate driving force; the condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and the circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  18 , thereby constituting a Rankine cycle. 
     Also in this example configured in this manner, it is possible to improve the exhaust heat recovery efficiency, as compared with the case where thermoelectric elements are installed in the compressor body  1  and the discharge piping. 
     A sixth example will be described with reference to  FIG. 8 .  FIG. 8  is a schematic diagram showing the configuration of a compressor according to this example. In  FIG. 8 , the same elements as those in the above-described fifth example are designated by the same reference signs as those described above, and the descriptions thereof will not be repeated when appropriate. 
     In this example, there is provided a heat exchanger  19  for cooling the compressed air separated by the oil separator  17 . 
     Also, there is provided an exhaust heat recovery system for recovering exhaust heat from compressed air through the heat exchanger  19  and recovering exhaust heat from oil through the heat exchanger  18 . The exhaust heat recovery system includes: the heat exchanger  19  for heating a working fluid by means of heat exchange with compressed air; the heat exchanger  18  for heating and vaporizing the working fluid heated by the heat exchanger  19 , by means of heat exchange with oil; the expander  6  for expanding the working fluid vaporized by the heat exchanger  18  to generate driving force; the condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and the circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  19 , thereby constituting a Rankine cycle. 
     Also in this example configured in this manner, it is possible to improve the exhaust heat recovery efficiency. In addition, in this example, exhaust heat is recovered not only from oil but also from compressed air. It is therefore possible to further improve the exhaust heat recovery efficiency compared to the above-described fifth example. Furthermore, in this example, the heat exchange amount of the heat exchanger  19  is smaller than that of the heat exchanger  18 . Thus, the working fluid can be efficiently vaporized by allowing the working fluid to flow in order from the heat exchanger  19  to the heat exchanger  18 . It is therefore possible to improve the exhaust heat recovery efficiency. It should be noted that, for example, when the heat exchange amount of the heat exchanger  18  is smaller than that of the heat exchanger  19 , it is preferable to allow the working fluid to flow in order from the heat exchanger  18  to the heat exchanger  19 . 
     Note that the fifth and sixth examples have been described by using an example of the case where the present subject matter is applied to the oil-lubricated compressor, but also can be applied to a water-supply compressor. More specifically, while not shown in the figure, the compressor may include, for example, a water separator provided on the discharge side of the compressor body for separating water included in compressed air, and a water heat exchanger for cooling and supplying the water separated by the water separator into the compression chamber of the compressor body  1 , and there may be provided an exhaust heat recovery system for recovering exhaust heat from water through the water heat exchanger. Alternatively, the compressor may further include, for example, a compressed air heat exchanger for cooling the compressed air separated by the water separator, and there may be provided an exhaust heat recovery system for recovering exhaust heat from compressed air through the compressed air heat exchanger and recovering exhaust heat from water through the water heat exchanger. In those cases, the same effect as above can be also obtained. 
     A seventh example will be described with reference to  FIG. 9 .  FIG. 9  is a schematic diagram showing the configuration of a compressor according to this example. In  FIG. 9 , the same elements as those in the foregoing examples are designated by the same reference signs as those described above, and the descriptions thereof will not be repeated when appropriate. 
     In this example, the compressor is of the water-supply type. A water separator  20  for separating water included in compressed air is provided on the discharge side of the compressor body  1 . Also, there is provided a water system for supplying the water separated by the water separator  20  into the compression chamber of the compressor body  1 . The water system includes a heat exchanger  21  for cooling water to supply water from the water separator  20  to the heat exchanger  21  with the inner pressure of the water separator  20 . Also, the heat exchanger  19  for cooling the compressed air separated by the water separator  20  is provided. 
     The compressor body  1  is connected to the electric motor  2  through the gear system  12 , and provided with a lubricating system for supplying lubricating oil to the gear system  12 . The lubricating system includes: the heat exchanger  13  for cooling lubricating oil for the gear system  12 ; and the pump  14  for supplying the lubricating oil lubricated and heated by the gear system  12  to the heat exchanger  13 . 
     Also, there is provided an exhaust heat recovery system for recovering exhaust heat from lubricating oil through the heat exchanger  13 , recovering exhaust heat from compressed air through the heat exchanger  19 , and recovering exhaust heat from water through the heat exchanger  21 . The exhaust heat recovery system includes: the heat exchanger  13  for heating a working fluid by means of heat exchange with lubricating oil; the heat exchanger  19  for heating the working fluid heated by the heat exchanger  13 , by means of heat exchange with compressed air; the heat exchanger  21  for heating and vaporizing the working fluid heated by the heat exchanger  19 , by means of heat exchange with water; the expander  6  for expanding the working fluid vaporized by the heat exchanger  21  to generate driving force; the condenser  7  for cooling and liquefying the working fluid from the expander  6 ; and the circulating pump  8  for supplying the working fluid liquefied by the condenser  7  to the heat exchanger  13 , thereby constituting a Rankine cycle. 
     Also in this example configured in this manner, it is possible to improve the exhaust heat recovery efficiency. In addition, in this example, exhaust heat is recovered not only from water and compressed air but also from lubricating oil. It is therefore possible to improve the exhaust heat recovery efficiency. Furthermore, in this example, the heat exchange amount becomes larger in the order of the heat exchanger  13 , the heat exchanger  19 , and the heat exchanger  21 . Thus, the working fluid can be efficiently vaporized by allowing the working fluid to flow in this order. It is therefore possible to improve the exhaust heat recovery efficiency. It should be noted that, when the order of the heat exchange amount of the heat exchangers  13 ,  19 , and  21  is different from that described in this example, it is preferable to allow the working fluid to flow in the corresponding order. 
     An eighth example will be described with reference to  FIG. 10 .  FIG. 10  is a diagram showing the configuration of a compressor according to this example. In  FIG. 10 , the same elements as those in the above-described sixth example are designated by the same reference signs as those described above, and the descriptions thereof will not be repeated when appropriate. 
     In this example, there is provided a temperature sensor  22  for detecting, upstream of the oil separator  17 , the temperature of compressed air, and a detection signal of the temperature sensor  22  is outputted to a controller  23 . The controller  23  prestores a preset temperature of the compressed air in internal memory to control the discharge rate (that is, the circulating volume of the Rankine cycle) of the circulating pump  8  so that the detected temperature of the compressed air, detected by the temperature sensor  22 , becomes equal to the preset temperature. In concrete terms, for example, when the detected temperature of the compressed air is higher than the preset temperature, the discharge rate of the circulating pump  8  is increased depending on differences between the detected temperature of the compressed air and the preset temperature. On the other hand, for example, when the detected temperature of the compressed air is lower than the preset temperature, the discharge rate of the circulating pump  8  is reduced depending on differences between the detected temperature of the compressed air and the preset temperature. Thus, regardless of load changes of the compressor, the temperature of the compressed air can be stabilized, and the precipitation of drain in oil can be suppressed. 
     Also in this example configured in this manner, it is possible to improve the exhaust heat recovery efficiency, in the same manner as the foregoing examples. 
     Note that the eighth example has been described by using an example of the case where, in the structure including the exhaust heat recovery system for recovering exhaust heat through the heat exchangers  18  and  19  in the same manner as the above-described sixth example, there are further provided the temperature sensor  22  and the controller  23 . However, the present subject matter is not limited thereto, but also, for example, in the structure including the exhaust heat recovery system for recovering exhaust heat through the heat exchanger  18  in the same manner as the above-described fifth example, there may be provided the temperature sensor  22  and the controller  23 . Alternatively, in the case, including the above-described seventh example, where the present subject matter is applied to the water-supply compressor, there may be provided the temperature sensor  22  and the controller  23 . In those cases, the same effect as above can be also obtained. 
     While the present subject matter has been described by using an example of the compressor body for compressing air, the subject matter is not limited thereto, and the compressor body may compress other gases (such as a refrigerant). Also, while the present subject matter has been described by using an example of the compressor body of the screw type, the subject matter is not limited thereto, and other types of compressors (such as a reciprocating compressor) may be used. Further, while the present example has been described as using an electric motor for generating power of the compressor body, the subject matter is not limited thereto, and the other motors (such as an engine) may be provided. In addition, while the present subject matter has been described by using an example of the case where the driving force generated by the expander is converted to electric power by the generator, the subject matter is not limited thereto, and the driving force generated by the expander may drive other devices (such as an auxiliary device in the compressor). In those cases, the same effect as above can be also obtained. 
     While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings.