Abstract:
According to one embodiment, a power recovery device is used in an apparatus in which firstly pressurized raw water (FPRW) is supplied to a reverse osmosis membrane unit to extract fresh water and condensed and depressurized raw water (HPB) remains. The device recovers the energy of HPB, rises a pressure of raw water (LPF) by using the recovered energy, and adds such secondly pressurized raw water (HPF) to the FPRW. The device accommodates a fixed center shaft and a rotary member on the shaft in a housing. LPF flows into one paired chambers of the housing and radial channels of the member to push and rotate the member, and HPB is introduced into the channels through paired openings of the shaft to push out LPF as HPF from the channels and another paired chambers of the housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation Application of PCT Application No. PCT/JP2010/059220, filed May 31, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    Embodiments described herein relate generally to a power recovery device of a liquid processing apparatus. 
       BACKGROUND 
       [0003]    A liquid processing apparatus which processes water containing a plurality of components (to be referred to as raw water hereinafter) by using a reverse osmosis membrane called, e.g., an RO membrane is known. 
         [0004]    The raw water is supplied to the reverse osmosis membrane at a high pressure, and fresh water is extracted from the raw water by the reverse osmosis membrane. In this process, a ratio of fresh water extracted by the reverse osmosis membrane rises as a value of the pressure of the raw water supplied to the reverse osmosis membrane rises. To raise the pressure value of the raw water, however, it is necessary to increase a strength of a raw water pressure raising device which is necessary to raise the pressure value of the raw water, and an amount of energy required to increase the pressure of the raw water also increases. In addition, a structure of the raw water pressure raising device is normally complicated. 
         [0005]    Raw water from which the fresh water is extracted at a given ratio by the reverse osmosis membrane (to be referred to as high-concentration raw water hereinafter) loses its pressure more or less because the fresh water is extracted by the reverse osmosis membrane. However, the high-concentration raw water maintains most of the high pressure loaded on the raw water when supplied to the reverse osmosis membrane. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a view schematically showing the whole of one example of a liquid processing apparatus in which a power recovery device according to a first embodiment. 
           [0007]      FIG. 2  is a perspective view schematically showing an outer appearance of the power recovery device according to the first embodiment. 
           [0008]      FIG. 3  is a schematic exploded perspective view of the power recovery device of  FIG. 2 . 
           [0009]      FIG. 4  is a schematic perspective view showing, from below, a case including a center shaft of the power recovery device of  FIG. 3 . 
           [0010]      FIG. 5  is a schematic perspective view showing a horizontal section of a rotary member of the power recovery device of  FIG. 3 . 
           [0011]      FIG. 6  is a schematic perspective view of the center shaft of the power recovery device of  FIG. 3 . 
           [0012]      FIG. 7  is a schematic perspective view of a lower portion of the center shaft of  FIG. 6 , after the center shaft is cut along a line IIV-IIV. 
           [0013]      FIG. 8  is an exploded perspective view similar to  FIG. 3 , for explaining an operation of the power recovery device of  FIG. 2 . 
           [0014]      FIG. 9  is a schematic plan view of a combination of the case, center shaft, and rotary member of  FIG. 8 , for explaining the operation of the power recovery device of  FIG. 2 . 
           [0015]      FIG. 10  is a schematic exploded perspective view of a power recovery device according to a second embodiment. 
           [0016]      FIG. 11  is a perspective view showing a rotary member of the power recovery device of  FIG. 10 , with a half of the rotary member being horizontally cut. 
           [0017]      FIG. 12  is a perspective view of a center shaft of  FIG. 10 . 
           [0018]      FIG. 13  is a schematic perspective view of a lower portion of the center shaft shown of  FIG. 12 , after the center shaft is cut along a line XIII-XIII. 
           [0019]      FIG. 14  is a schematic perspective view of a lower end part portion of the lower portion of the center shaft of  FIG. 13 , after the lower portion is further cut along a line XIV-XIV. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    A power recovery device of a liquid processing apparatus, according to an embodiment is a power recovery device which is used in a liquid processing apparatus in which raw water as externally supplied water containing a plurality of components is supplied to a reverse osmosis membrane through a pressure raising unit and extracts a part of fresh water from the pressure raised raw water by the reverse osmosis membrane, and which supplies raw water a pressure of which is raised by using a pressure of remaining raw water from which the part of the fresh water is extracted by the reverse osmosis membrane to the reverse osmosis membrane, in addition to the pressure raised raw water from the pressure raising unit. 
         [0021]    The power recovery device comprises: a housing having an internal space; a center shaft fixed in the internal space of the housing and having an outer circumferential surface and at least one end portion protruding outside the housing; and a rotary member accommodated in the internal space of the housing such that the rotary member is rotatable on the outer circumferential surface of the center shaft, having an inner circumferential surface opposing the outer circumferential surface of the center shaft and an outer circumferential surface positioned outside the center shaft in a radial direction of the center shaft, and including a plurality of channels arranged at equal intervals in a circumferential direction of the center shaft and each extending between the inner circumferential surface thereof and the outer circumferential surface thereof. 
         [0022]    At least one set of two pairs of chambers opposing the outer circumferential surface of the rotary member and divided from each other is provided in the internal space of the housing. 
         [0023]    At least one set of two pairs of openings opening in the outer circumferential surface of the center shaft to be equal in number to the chambers to oppose the at least one set of the chambers in the internal space of the housing through the rotary member, and at least one set of two pairs of passages extending through the center shaft from the at least one set of the openings and opening in the at least one end portion of the center shaft, are formed in the center shaft. 
         [0024]    One pair of the chambers symmetrically arranged with respect to the center shaft in the one set of the chambers in the internal space of the housing is configured to be introduced with the externally supplied raw water and to cause the externally supplied raw water to push the plurality of channels in the outer circumferential surface of the rotary member exposed in the one pair of chambers, in a predetermined circumferential direction of the outer circumferential surface so as to rotate the rotary member. 
         [0025]    The other pair of the chambers symmetrically arranged with respect to the center shaft in the one set of the chambers is connected to a channel of the raw water between the pressure raising unit and the reverse osmosis membrane. 
         [0026]    One pair of the openings of the one set of the openings in the outer circumferential surface of the center shaft, opposing the one pair of the chambers through the rotary member are communicated with an outside through one pair of the passages corresponding to the one pair of the openings in the center shaft. 
         [0027]    The other pair of the openings of the one set of the openings in the outer circumferential surface of the center shaft, opposing the other pair of the chambers through the rotary member is introduced with the remaining raw water through the other pair of the passages corresponding to the other pair of the openings in the center shaft. 
         [0028]    First of all, a schematic structure of the whole of an example of a liquid processing apparatus in which a power recovery device according to a first embodiment will be explained with reference to  FIG. 1 . 
         [0029]    The liquid processing apparatus of the example is a seawater desalination apparatus. In this seawater desalination apparatus, raw water as externally supplied water containing a plurality of components is seawater. Seawater SW pumped up from the sea is supplied to a preprocessing unit  10 . The preprocessing unit  10  preprocesses the supplied seawater SW by adding, e.g., a germicide  10   a,  flocculant  10   b,  scale inhibitor  10   c,  dechlorine agent  10   d,  etc. to the seawater SW. Seawater (preprocessed seawater) PSW which is preprocessed is led to pass through a water supply pump  12  and safety filter  14  by a pipe. The preprocessed seawater PSW passed through the safety filter  14  is branched into two parts by branched pipes. 
         [0030]    One branched pipe is connected to a reverse osmosis membrane unit  18  containing a reverse osmosis membrane  18   a  through a pressure raising unit  16 . In this example, the pressure raising unit  16  is provided by a high-pressure pump. The preprocessed seawater PSW on which a predetermined high pressure is loaded by the pressure raising unit  16  is supplied to the reverse osmosis membrane unit  18  by the one branched pipe. In the reverse osmosis membrane unit  18 , the reverse osmosis membrane  18   a  extracts a part of water (fresh water) FW from the high-pressure preprocessed seawater HPSW. 
         [0031]    The extracted water FW is led to a clear water tank  20  by a pipe. In the clear water tank  20 , clear water CW is produced by adding, e.g., a hardness control agent  20   a,  pH adjuster  20   b,  disinfectant  20   c,  etc. to the water FW. The clear water CW produced in the clear water tank  20  is supplied to a water pipe  23  through a clear water supply pump  22 . 
         [0032]    The other branched pipe is connected to the power recovery device  24  according to the first embodiment. 
         [0033]    The low-pressure preprocessed seawater PSW to be supplied to the power recovery device  24  through the other branched pipe is called as low-pressure feed LPF. Seawater (high-concentration seawater) in which concentrations of the various components including salt are increased because a part of the water FW is extracted by the reverse osmosis membrane unit  18  and the pressure is more or less decreased, is led to the power recovery device  24  through a pipe. This high-concentration seawater supplied from the reverse osmosis membrane unit  18  to the power recovery device  24  is called as high-pressure brine HPB. 
         [0034]    In the power recovery device  24 , a pressure of the high-pressure brine HPB is raised by the energy of the low-pressure feed LPF, and then the high-pressure brine HPB the pressure of which is raised pushes the low-pressure feed LPF and raises a pressure of the low-pressure feed LPF, and finally high-pressure feed HPF is discharged. That is, the energy of the high-pressure feed HPF is generated by using most of the energy of the high-pressure brine HPB, and by adding a part of the energy of the low-pressure feed LPF. 
         [0035]    The high-pressure feed HPF is led by a pipe from the power recovery device  24  to a pipe between the pressure raising unit  16  and the reverse osmosis membrane unit  18 . In this pipe, the high-pressure feed HPF is added to the high-pressure preprocessed seawater HPSW flowing from the pressure raising unit  16  to the reverse osmosis membrane unit  18 , and flows together with the high-pressure preprocessed seawater HPSW toward the reverse osmosis membrane unit  18 . 
         [0036]    In the power recovery device  24 , the low-pressure feed LPF used to raise the pressure of the high-pressure brine HPB becomes the high-pressure feed HPF in a next stage in which the pressure of the low-pressure feed LPF is raised by the high-pressure brine HPB whose pressure is further raised by using a part of the energy of the low-pressure feed LPF. After raising the pressure of the low-pressure feed LPF, the high-pressure brine HPB loses its pressure and is discharged outside as low-pressure brine LPB from the power recovery device  24 . 
       First Embodiment 
       [0037]    Next, a structure of the power recovery device  24  of the first embodiment will be explained with reference to  FIGS. 2-7 . 
         [0038]    As shown in  FIGS. 2-4 , the power recovery device  24  comprises a housing  32  having an internal space  30 . In this embodiment, the housing  32  includes a case  32   a  having an almost circular recess that provides the internal space  30 , and a lid  32   b  that liquid-tightly covers one opening of the recess of the case  32   a.  The lid  32   b  is detachably fixed to the case  32   a  by a well-known fixing means (not shown). 
         [0039]    The power recovery device  24  further comprises a center shaft  34  fixed in the internal space  30  of the housing  32 , and having an outer circumferential surface and at least one end portion protruding outside the housing  32 . More specifically, the center shaft  34  is long and narrow, and a portion of its outer circumferential surface is liquid-tightly fixed in a through hole  32   c  formed in a center of a bottom surface of the recess of the case  32   a.  The One end portion of the center shaft  34  is positioned at one end along a longitudinal central line of the center shaft  34  and protrudes from the through hole  32   c  into an external space below the case  32   a.  The other end portion of the center shaft  34  is positioned at the other end along the longitudinal central line and protrudes from a through hole  32   d  in a center of the lid  32   b  into the external space above the lid  32   b.    
         [0040]    The power recovery device  24  further comprises a rotary member  36  accommodated in the internal space  30  of the housing  32  so as to be rotatable on the outer circumferential surface of the center shaft  34 . The rotary member  36  includes an inner circumferential surface  36   a  opposing the outer circumferential surface of the center shaft  34 , and an outer circumferential surface  36   b  positioned outside in a radial direction of the center shaft  34 . As is well shown in  FIG. 5 , the rotary member  36  further includes a plurality of channels  36   c  arranged at equal intervals in a circumferential direction of the center shaft  34  and each extending between the inner circumferential surface  36   a  and the outer circumferential surface  36   b.    
         [0041]    As is well shown in  FIG. 3 , at least one set of two pairs of chambers  38   a  and  38   b  opposing the outer circumferential surface  36   b  of the rotary member  36  and divided from each other is provided in the internal space  30  of the housing  32 . In this embodiment, one set of two pairs of the chambers  38   a  and  38   b  is provided. 
         [0042]    The low-pressure feed LPF supplied to the power recovery device  24  as shown in  FIG. 1  is led, as shown in  FIG. 2 , into one pair of the chambers  38   a,    38   a  symmetrically arranged with respect to the center shaft  34  in the one set of the chambers  38   a  and  38   b  in the internal space  30  of the housing  32 . The one pair of the chambers  38   a,    38   a  are configured such that the supplied low-pressure feed LPF flows along the outer circumferential surface  36   b  of the rotary member  36 , which is exposed in the one pair of the chambers  38   a,    38   a  in a predetermined circumferential direction (in  FIG. 3 , in a counterclockwise direction) of the outer circumferential surface  36   b.    
         [0043]    The other paired chambers  38   b,    38   b  of the one set of the chambers  38   a  and  38   b,  symmetrically arranged with respect to the center shaft  34 , are connected to the pipe for the high-pressure feed HPF extending from the power recovery device  24  toward the pipe between the pressure raising unit  16  and the reverse osmosis membrane unit  18  as shown in  FIGS. 1 and 2 . 
         [0044]    As is well shown in  FIGS. 6 and 7 , at least one set of two pairs of openings  40   a  and  40   b  equal in number to the at least one set of the chambers  38   a  and  38   b  in the internal space  30  of the housing  32  is formed in the outer circumferential surface of the center shaft  34  so as to oppose the chambers  38   a  and  38   b  through the rotary member  36 . In this embodiment, one set of the two pairs of the openings  40   a  and  40   b  is formed in the outer circumferential surface of the center shaft  34  so that the openings  40   a  and  40   b  are arranged at equal intervals in a circumferential direction of the outer circumferential surface. 
         [0045]    One pair of passages  42   a,    42   a  (see  FIG. 7 ) extends through the center shaft  34  from the one pair of the openings  40   a,    40   a  corresponding to the one pair of the chambers  38   a,    38   a  in the internal space  30  of the housing  32  to the other end portion of the center shaft  34 , which is positioned upwardly in  FIG. 6 , and the pair of passages  42   a,    42   a  is opened at an end surface of the other end portion. As shown in  FIGS. 2 ,  3 , and  6 , the paired passages  42   a,    42   a  can be integrated into one passage  42   a  in the center shaft  34  before they reach the other end portion. As shown in  FIGS. 1 and 2 , the opening of the integrated passage  42   a  in the end surface of the other end portion of the center shaft  34  is connected to a pipe for the low-pressure brine LPB, which extends from the power recovery device  24 . 
         [0046]    Another pair of passages  42   b,    42   b  (see  FIG. 7 ) extends through the center shaft  34  from the other pair of the openings  40   b,    40   b  corresponding to the other pair of the chambers  38   b,    38   b  in the internal space  30  of the housing  32  to the one end portion of the center shaft  34 , which is positioned downwardly in  FIG. 6 , and opens at an end surface of the one end portion. As shown in  FIG. 4 , the paired passages  42   b,    42   b  can be integrated into one passage  42   b  in the center shaft  34  before they reach the one end portion. As shown in  FIGS. 1 and 2 , the opening of the integrated passage  42   b  in the end surface of the one end portion of the center shaft  34  is connected to the pipe for the high-pressure brine HPB, which extends from the reverse osmosis membrane unit  18  to the power recovery device  24 . 
         [0047]    Next, an operation of the power recovery device  24  described above with reference to  FIGS. 2-7  will now be explained with reference to  FIGS. 8 and 9 . 
         [0048]    As shown in  FIGS. 8 and 9 , the high-pressure brine HPB supplied from the reverse osmosis membrane unit  18  shown in  FIG. 1  to the power recovery device  24  reaches the paired openings  40   b,    40   b  in the outer circumferential surface of the center shaft  34  through the passage  42   b  (see  FIG. 4 ) opened in the end surface of the downward one end portion of the center shaft  34  of the power recovery device  24 , and flows into several channels  36   c  inner ends of which are exposed to the other paired openings  40   b,    40   b  among the plurality of channels  36   c  of the rotary member  36 . Meanwhile, as shown in  FIGS. 8 and 9 , the low-pressure feed LPF supplied from the preprocessing unit  10  shown in  FIG. 1  to the power recovery device  24  through the water supply pump  12  and safety filter  14  flows into the one pair of the chambers  38   a,    38   a  of the case  32   a  of the housing  32  of the power recovery device  24 . The low-pressure feed LPF flowed into the one pair of the chambers  38   a,    38   a  pushes parts of the outer circumferential surface of the rotary member  36 , which are exposed in the one pair of the chambers  38   a,    38   a,  in a predetermined circumferential direction of the outer circumferential surface of the rotary member  36 . As a result, the low-pressure feed LPF in the one pair of the chambers  38   a,    38   a  flows into several channels  36   c  outer ends of which are exposed to the one pair of the chambers  38   a,    38   a  among the plurality of channels  36   c  of the rotary member  36 , and pushes side surfaces of the several channels  36   c.  A part of energy of the low-pressure feed LPF is consumed to rotate the rotary member  36  in a predetermined direction R. 
         [0049]    As the rotary member  36  rotates, the low-pressure feed LPF in the channels  36   c  is held in the channels  36   c  between the one pair of the chambers  38   a,    38   a  and the other pair of the chambers  38   b,    38   b  and between the one pair of the openings  40   a,    40   a  and the other pair of the openings  40   b,    40   b  of the center shaft  34 . When the channels  36   c  holding the low-pressure feed LPF oppose the other pair of the chambers  38   b,    38   b  and the other pair of the openings  40   b,    40   b  of the center shaft  34 , the low-pressure feed LPF held in the channels  36   c  is pushed out from the channels  36   c  into the other pair of the chambers  38   b,    38   b  by the high-pressure brine HPB flowed from the other pair of the openings  40   b,    40   b  into the channels  36   c  holding the low-pressure feed LPF. During this action, the pressure energy of the high-pressure brine HPB flowed from the openings  40   b,    40   b  into the channels  36   c  is given to the low-pressure feed LPF held in the channels  36   c,  so that the low-pressure feed LPF held in the channels  36  becomes the high-pressure feed HPF and is pushed into the other pair of the chambers  38   b,    38   b.    
         [0050]    The high-pressure brine HPB flowed into the channels  36   c  from the other pair of the openings  40   b,    40   b  becomes the low-pressure brine LPB because the high-pressure brine HPB gives its pressure energy to the low-pressure feed LPF in the channels  36   c  and its pressure energy is largely decreased or eliminated. After that, further rotation of the rotary member  36  makes the low-pressure brine LPB being held in the channels  36   c  between the other pair of the chambers  38   b,    38   b  and the one pair of the chambers  38   a,    38   a  and between the other pair of the openings  40   b,    40   b  and the one pair of the openings  40   a,    40   a  of the center shaft  34 . And then, when the channels  36   c  holding the low-pressure brine LPB oppose the one pair of the chambers  38   a,    38   a  and the one pair of the openings  40   a,    40   a  of the center shaft  34 , the low-pressure feed LPF is flowed from the one pair of the chambers  38   a,    38   a  into the channels  36   c  holding the low-pressure brine LPB so that the low-pressure brine LPB in the channels  36   c  is discharged out from the power recovery device  24  through the one pair of the openings  40   a,    40   a  and the one pair of the passages  42   a,    42   a  corresponding to the one pair of the openings  40   a,    40   a.    
         [0051]    As shown in  FIG. 1 , the high-pressure feed HPF in the other pair of the chambers  38   b,    38   b  is led by the pipe from the power recovery device  24  to the pipe between the pressure raising unit  16  and the reverse osmosis membrane unit  18 . In the latter pipe, the high-pressure feed HPF is added to the high-pressure preprocessed seawater HPSW flowing from the pressure raising unit  16  toward the reverse osmosis membrane unit  18 , and flows together with the high-pressure preprocessed seawater HPSW toward the reverse osmosis membrane unit  18 . 
         [0052]    AS a result of this, if an amount of the fresh water FW extracted in the reverse osmosis membrane unit  18  per unit time is constant, it is possible to reduce an amount of the high-pressure preprocessed seawater HPSW to be supplied from the pressure raising unit  16  toward the reverse osmosis membrane unit  18  per unit time. This makes it possible to reduce an amount of energy, i.e., power necessary to operate the seawater desalination apparatus as a kind of the liquid processing apparatus using the power recovery device  24 . 
         [0053]    In the power recovery device  24  of this embodiment, the one set of the two pairs of the chambers  38   a  and  38   b  are provided to be divided from each other in the internal space  30  of the case  32   a  of the housing  32 , and the same low-pressure feed LPF is supplied to the one pair of the cambers  38   a,    38   a  symmetrically arranged with respect to the center shaft  34 , and at the same time the same high-pressure brine HPB is supplied toward the other pair of the chambers  38   b,    38   b  symmetrically arranged with respect to the center shaft  34 . Accordingly, a force loaded on the case  32   a  of the housing  32  and a force loaded on the rotary member  36  accommodated in the internal space  30  of the case  32   a  so as to be rotatable on the outer circumferential surface of the center shaft  34 , by the low-pressure feed LPF in the one pair of the chambers  38   a,    38   a,  are canceled in the radial direction of the center shaft  34 , and also a force loaded on the case  32   a  and a force loaded on the rotary member  36 , by the high-pressure brine HPB in the other pair of the chambers  38   b,    38   b,  are canceled in the radial direction of the center shaft  34 . 
         [0054]    Further, a mixture of the low-pressure brine LPB and high-pressure brine HPB, entered into a gap between the outer circumferential surface of the center shaft  34  and the inner circumferential surface  36   a  of the rotary member  36  functions as a radial dynamic pressure bearing between the outer circumferential surface of the center shaft  34  and the inner circumferential surface  36   a  of the rotary member  36  with a rotation of the rotary member  36  on the outer circumferential surface of the center shaft  34 . Also, a mixture of the low-pressure feed LPF and high-pressure feed HPF, entered into gaps between the outer circumferential surface  36   b  of the rotary member  36  and regions of an inner circumferential surface of the internal space  30  of the case  32   a  of the housing  32 , the inner circumferential surface of the internal space  30  opposing the outer circumferential surface  36   b  of the rotary member  36  and the regions excepting the one set of the two pairs of the chambers  38   a  and  38   b,  functions as a radial dynamic pressure bearing between the outer circumferential surface  36   b  of the rotary member  36  and the above-mentioned regions of the inner circumferential surface of the internal space  30  of the case  32   a  of the housing  32  with the rotation of the rotary member  36  on the outer circumferential surface of the center shaft  34 . 
         [0055]    Therefore, there is no need for an independent radial bearing between the outer circumferential surface of the center shaft  34  and the inner circumferential surface  36   a  of the rotary member  36 , and it is possible to simplify the structure of the power recovery device  24  of this embodiment and to reduce a manufacturing cost thereof. 
         [0056]    More further, a mixture of the low-pressure brine LPB and high-pressure brine HPB and a mixture of the low-pressure feed LPF and high-pressure feed HPF, both mixtures entered into a gap between an inner surface of the lid  32   b  of the housing  32  and one side surface of the rotary member  36 , which opposes the above-mentioned inner surface, in the internal space  30  of the case  32   a  of the housing  32 , function as a thrust bearing between the inner surface of the lid  32   b  and the one side surface of the rotary member  36  with the rotation of the rotary member  36  on the outer circumferential surface of the center shaft  34 . Simultaneously, the mixture of the low-pressure brine LPB and high-pressure brine HPB and the mixture of the low-pressure feed LPF and high-pressure feed HPF, both entered into a gap between the bottom surface of the internal space  30  of the case  32   a  of the housing  32  and the other side surface of the rotary member  36 , which opposes the above-mentioned bottom surface, in the internal space  30  of the case  32   a  of the housing  32 , function as a thrust bearing between the bottom surface of the internal space  30  of the case  32   a  and the other side surface of the rotary member  36  with the rotation of the rotary member  36  on the outer circumferential surface of the center shaft  34 . 
         [0057]    Therefore, there is no need for independent thrust bearings between the inner surface of the lid  32   b  and the one side surface of the rotary member  36  and between the bottom surface of the internal space  30  of the case  32   a  and the other side surface of the rotary member  36 , and it is possible to simplify the structure of the power recovery device  24  of this embodiment and to reduce the manufacturing cost thereof. 
       Second Embodiment 
       [0058]    Next, a structure of a power recovery device  24 ′ according to a second embodiment and being usable in the example of the liquid processing apparatus described above with reference to  FIG. 1 , instead of the power recovery device  24  of the first embodiment described above with reference to  FIGS. 2-9 , will be explained with reference to  FIGS. 10-14 . 
         [0059]    As shown in  FIGS. 10-14 , the power recovery device  24 ′ comprises a housing  43  having an internal space  41 . In this embodiment, the housing  43  includes a case  43   a  having an almost circular recess that provides the internal space  41 , and a lid  43   b  that liquid-tightly covers an opening on one side of the recess of the case  43   a.  The lid  43   b  is detachably fixed to the case  43   a  by a well-known fixing means (not shown). 
         [0060]    The power recovery device  24 ′ comprises a center shaft  44  protruding from a center of the internal space  41  of the housing  43  into an external space above the lid  43   b  through a through hole  43   c  in a center of the lid  43   b.  More specifically, the center shaft  44  is long and narrow, and a portion of its outer circumferential surface is liquid-tightly fixed in the through hole  43   c  in the center of the lid  43   b.  One end portion of the center shaft  44 , which is positioned at one end along a longitudinal central line of the center shaft  44 , protrudes from the through hole  43   c  of the lid  42   b  into the external space above the lid  43   b.  The other end portion of the center shaft  44 , which is positioned at the other end along the longitudinal central line, is positioned slightly and upwardly away from the center of the bottom surface of the internal space  41  of the housing  43 . 
         [0061]    The power recovery device  24 ′ further comprises a rotary member  46  accommodated in the internal space  41  of the housing  43  so as to be rotatable on the outer circumferential surface of the other end portion of the center shaft  44 . More specifically, a blind hole  46   a  for receiving the other end portion of the center shaft  44  is formed in a center of the rotary member  46 . An inner circumferential surface  46   b  and bottom surface of the blind hole  46   a  relatively rotatably oppose the outer circumferential surface and end surface of the other end portion of the center shaft  44  received in the blind hole  46   a.  The rotary member  46  includes an outer circumferential surface  46   c  positioned outside the blind hole  46   a  in a radial direction thereof, and a plurality of channels  46   d  arranged at equal intervals in a circumferential direction of the blind hole  46   a  and each extending between the inner circumferential surface  46   b  and the outer circumferential surface  46   c  as is well shown in  FIG. 11 . As is well shown in  FIG. 10 , at least one set of two pairs of chambers  48   a  and  48   b  opposing the outer circumferential surface  46   c  of the rotary member  46  and divided from each other is provided in the internal space  41  of the housing  43 . In this embodiment, one set of the two pairs of the chambers  48   a  and  48   b  is provided. 
         [0062]    As shown in  FIG. 10 , the low-pressure feed LPF supplied to the power recovery device  24  shown in  FIG. 1  is supplied to the one pair of the chambers  48   a,    48   a  symmetrically arranged with respect to the center shaft  44  among the one set of the chambers  48   a  and  48   b  in the internal space  41  of the housing  43 . The one pair of the chambers  48   a,    48   a  are configured to flow the supplied low-pressure feed LPF along the outer circumferential surface  46   c  of the rotary member  46  exposed in the one pair of the chambers  48   a,    48   a  in a predetermined circumferential direction (in  FIG. 10 , a counterclockwise direction) of the outer circumferential surface  46   c.    
         [0063]    As shown in  FIGS. 1 and 10 , the other pair of the chambers  48   b,    48   b  symmetrically arranged with respect to the center shaft  44  in the one set of the chambers  48   a  and  48   b,  is connected to the pipe for the high-pressure feed HPF extending from the power recovery device  24 ′ toward the pipe between the pressure raising unit  16  and reverse osmosis membrane unit  18 . 
         [0064]    As is well shown in  FIGS. 10 , and  12 - 14 , at least one set of two pairs of openings  50   a  and  50   b  equal in number to the at least one set of the chambers  48   a  and  48   b  in the internal space  41  of the housing  43  is formed in the outer circumferential surface of the other end portion of the center shaft  44  so as to oppose the at least one set of the chambers  48   a  and  48   b  through the rotary member  46 . In this embodiment, one set of the two pairs of the openings  50   a  and  50   b  is formed in the outer circumferential surface of the other end portion of the center shaft  44  so that the openings  50   a  and  50   b  are arranged at equal intervals in the circumferential direction of the outer circumferential surface. 
         [0065]    One pair of passages  52   a,    52   a  (see  FIG. 14 ) extends through the center shaft  44  from the one pair of the openings  50   a  corresponding to the one pair of the chambers  48   a  in the internal space  41  of the housing  43  to the one end portion of the center shaft  44 , which is positioned upward in the center shaft  44 . The one pair of the passages  52   a,    52   a  is opened in an end surface of the one end portion. As shown in  FIGS. 10 ,  12 , and  13 , the paired passages  52   a,    52   a  can be integrated into one passage  52   a  in the center shaft  44  before they reach the one end portion. As shown in  FIGS. 1 and 12 , the opening of the integrated passage  52   a  in the end surface of the one end portion of the center shaft  44  is connected to the pipe for the low-pressure brine LPB, which extends from the power recovery device  24  (in this embodiment,  24 ′). 
         [0066]    Another pair of passages  52   b,    52   b  (see  FIG. 14 ) extends through the center shaft  44  from the other pair of the openings  50   b,    50   b  corresponding to the other pair of the chambers  48   b,    48   b  in the internal space  41  of the housing  43  to the one end portion of the center shaft  44 , which is positioned upward in the center shaft  44 . The other pair of the passages  52   b,    52   b  is opened in the end surface of the one end portion. As shown in  FIGS. 10 ,  12 , and  13 , the paired passages  52   b  can be integrated into one passage  52   b  in the center shaft  44  before they reach the one end portion. In this embodiment, the paired passages  52   b,    52   b  are integrated into the one passage  52   b  to be concentric with the above described one integrated passage  52   a  in the end surface of the one end portion of the center shaft  44 . As shown in  FIGS. 1 and 12 , the opening of the integrated passage  52   b  in the end surface of the one end portion of the center shaft  44  is connected to the pipe for the high-pressure brine HPB, which extends from the reverse osmosis membrane unit  18  to the power recovery device  24  (in this embodiment,  24 ′). 
         [0067]    A through hole  43   d  is formed in a center of a bottom surface of the internal space  41  of the housing  43  (i.e., a bottom surface of the case  42   a ) of this embodiment, and an output shaft  54   a  of a motor  54  is rotatably and liquid-tightly inserted into the through hole  43   d.  This rotatable and liquid-tight insertion of the output shaft  54   a  of the motor  54  can be performed by, e.g., interposing a well-known annular sealing member such as an O-ring or oil seal between the inner circumferential surface of the through hole  43   d  and the outer circumferential surface of the output shaft  54   a  of the motor  54 . 
         [0068]    A protruding end of the output shaft  54   a  of the motor  54  inserted into the through hole  43   d  is concentrically fixed to an out side surface a bottom wall of the blind hole  46   a  in the center of the rotary member  46  in the internal space  41  of the housing  43 . 
         [0069]    An operation of the power recovery device  24 ′ described above with reference to  FIGS. 10-14  will now be explained with reference to  FIG. 10 . 
         [0070]    As shown in  FIG. 12 , the high-pressure brine HPB supplied from the reverse osmosis membrane unit  18  shown in  FIG. 1  to the power recovery device  24  (in this embodiment,  24 ′) reaches the other pair of the openings  50   b,    50   b  in the outer circumferential surface of the other end portion of the center shaft  44  through the passage  52   b  opened in the end surface of the upwardly one end portion of the center shaft  44  of the power recovery device  24 ′, and flows into several channels  46   d  inner ends of which are exposed to the other pair of the openings  50   b,    50   b,  among the plurality of channels  46   d  of the rotary member  46 . Meanwhile, as shown in  FIG. 10 , the low-pressure feed LPF supplied from the preprocessing unit  10  shown in  FIG. 1  to the power recovery device  24  (in this embodiment,  24 ′) through the water supply pump  12  and safety filter  14  flows into the one pair of the chambers  48   a,    48   a  of the case  43   a  of the housing  43  of the power recovery device  24 ′. The low-pressure feed LPF flowed into the one pair of the chambers  48   a,    48   a  pushes parts of the outer circumferential surface of the rotary member  46 , which are exposed in the one pair of the chambers  48   a,    48   a,  in a predetermined circumferential direction of the outer circumferential surface of the rotary member  46 . As a result, the low-pressure feed LPF in the one pair of the chambers  48   a,    48   a  flows into several channels  46   d,  outer ends of which are exposed in the one pair of the chambers  48   a,    48   a  among the plurality of channels  46   d  of the rotary member  46 , and pushes side surfaces of the several channels  46   d.  A part of the energy of the low-pressure feed LPF is consumed to rotate the rotary member  46  in a predetermined direction R. 
         [0071]    As the rotary member  46  rotates, the low-pressure feed LPF in the channels  46   d  is held in the channels  46   d  between the one pair of the chambers  48   a,    48   a  and the other pair of the chambers  48   b,    48   b  and between the one pair of the openings  50   a,    50   a  and the other pair of the openings  50   b,    50   b  of the center shaft  44 . After that, when the channels  46   d  holding the low-pressure feed LPF oppose the other pair of the chambers  48   b,    48   b  and the other pair of the openings  50   b,    50   b  of the center shaft  44 , the low-pressure feed LPF held in the channels  46   d  is pushed out from the channels  46   d  into the other pair of the chambers  48   b,    48   b  by the high-pressure brine HPB flowed from the other pair of the openings  50   b,    50   b  into the channels  46   d  holding the low-pressure feed LPF. During this action, the pressure energy of the high-pressure brine HPB flowed from the openings  50   b,    50   b  into the channels  46   d  is given to the low-pressure feed LPF held in the channels  46   d.  As a result of this, the low-pressure feed LPF held in the channels  46   d  becomes the high-pressure feed HPF and is pushed into the other pair of the chambers  48   b,    48   b.    
         [0072]    The high-pressure brine HPB flowed into the channels  46   d  from the other pair of the openings  50   b,    50   b  gives its pressure energy to the low-pressure feed LPF in the channels  46   d  and becomes into the low-pressure brine LPB because the pressure energy of the high-pressure brine HPB is largely decreased or eliminated. After that, further rotation of the rotary member  46  causes the low-pressure brine LPB to be held in the channels  46   d  between the other pair of the chambers  48   b  and the one pair of the chambers  48   a,    48   a  and between the other pair of the openings  50   b,    50   b  and the one pair of the openings  50   a,    50   a  of the center shaft  44 . And, when the channels  46   d  holding the low-pressure brine LPB oppose the one pair of the chambers  48   a,    48   a  and the one pair of the openings  50   a,    50   a  of the center shaft  44 , the low-pressure brine LPB held in the channels  46   d  is discharged out from the power recovery device  24  (in this embodiment,  24 ′) through the one pair of the openings  50   a,    50   a  and the one pair of the passages  52   a,    52   a  corresponding to the one pair of the openings  50   a,    50   a  by the low-pressure feed LPF flowed into the passages  46   d  from the one pair of the chambers  48   a,    48   a.    
         [0073]    As shown in  FIGS. 10 and 1 , the high-pressure feed HPF in the other pair of the chambers  48   b,    48   b  is led through the pipe from the power recovery device  24  (in this embodiment,  24 ′) to the pipe between the pressure raising unit  16  and the reverse osmosis membrane unit  18 . In the latter pipe, the high-pressure feed HPF is added to the high-pressure preprocessed seawater HPSW flowing from the pressure raising unit  16  toward the reverse osmosis membrane unit  18 , and flows together with the high-pressure preprocessed seawater HPSW toward the reverse osmosis membrane unit  18 . 
         [0074]    As a result of this, if an amount of the fresh water FW extracted in the reverse osmosis membrane unit  18  per unit time is constant, it is possible to reduce an amount of the high-pressure preprocessed seawater HPSW to be supplied from the pressure raising unit  16  toward the reverse osmosis membrane unit  18  per unit time. This makes it possible to reduce an amount of the energy, i.e., a power necessary to operate the seawater desalination apparatus as a kind of the liquid processing apparatus using the power recovery device  24  (in this embodiment,  24 ′). 
         [0075]    Note that, in this embodiment, the rotation of the rotary member  46  in the internal space  41  of the housing  43  can be controlled by using the motor  54 . 
         [0076]    That is, the amount of the energy to be given to the high-pressure feed HPF which is led through the pipe from the power recovery device  24 ′ of this embodiment to the pipe between the pressure raising unit  16  and the reverse osmosis membrane unit  18 , by the rotation of the rotary member  46  of the power recovery device  24 ′, can be controlled regardless of a value of a rotation force to be given to the rotary member  46  by the low-pressure feed LPF supplied to the power recovery device  24 ′. 
         [0077]    In the power recovery device  24 ′ of this embodiment, the one set of the two pairs of the chambers  48   a  and  48   b  are provided to be divided from each other in the internal space  41  of the case  43   a  of the housing  43 , and the same low-pressure feed LPF is supplied to the one pair of the cambers  48   a,    48   a  symmetrically arranged with respect to the center shaft  44 , and at the same time the same high-pressure brine HPB is supplied toward the other pair of the chambers  48   b,    48   b  symmetrically arranged with respect to the center shaft  34 . Accordingly, a force loaded on the case  43   a  of the housing  43  and a force loaded on the rotary member  46  accommodated in the internal space  41  of the case  43   a  so as to be rotatable on the outer circumferential surface of the center shaft  44 , by the low-pressure feed LPF in the one pair of the chambers  48   a,    48   a,  are canceled in the radial direction of the center shaft  44 , and also a force loaded on the case  43   a  and a force loaded on the rotary member  46 , by the high-pressure brine HPB in the other pair of the chambers  48   b,    48   b,  are canceled in the radial direction of the center shaft  44 . 
         [0078]    Further, a mixture of the low-pressure brine LPB and high-pressure brine HPB, entered into a gap between the outer circumferential surface of the other end portion of the center shaft  44  and the inner circumferential surface  46   b  of the blind hole  46   a  of the rotary member  46  functions as a radial dynamic pressure bearing between the outer circumferential surface of the other end portion of the center shaft  44  and the inner circumferential surface  46   b  of the blind hole  46   a  of the rotary member  46  with a rotation of the rotary member  46  on the outer circumferential surface of the center shaft  44 . Also, a mixture of the low-pressure feed LPF and high-pressure feed HPF, entered into gaps between the outer circumferential surface  46   c  of the rotary member  46  and regions of an inner circumferential surface of the internal space  41  of the case  43   a  of the housing  43 , the inner circumferential surface of the internal space  41  opposing the outer circumferential surface  46   c  of the rotary member  46  and the regions excepting the one set of the two pairs of the chambers  48   a  and  48   b,  functions as a radial dynamic pressure bearing between the outer circumferential surface  46   c  of the rotary member  46  and the above-mentioned regions of the inner circumferential surface of the internal space  41  of the case  43   a  of the housing  43  with the rotation of the rotary member  46  on the outer circumferential surface of the center shaft  44 . 
         [0079]    Therefore, there is no need for an independent radial bearing between the outer circumferential surface of the other end portion of the center shaft  44  and the inner circumferential surface  46   b  of the blind hole  46   a  of the rotary member  46 , and it is possible to simplify the structure of the power recovery device  24 ′ of this embodiment and to reduce a manufacturing cost thereof. 
         [0080]    More further, a mixture of the low-pressure brine LPB and high-pressure brine HPB and a mixture of the low-pressure feed LPF and high-pressure feed HPF, both mixtures entered into a gap between an inner surface of the lid  43   b  of the housing  43  and one side surface of the rotary member  46 , which opposes the above-mentioned inner surface, in the internal space  41  of the case  43   a  of the housing  43 , function as a thrust bearing between the inner surface of the lid  43   b  and the one side surface of the rotary member  46  with the rotation of the rotary member  46  on the outer circumferential surface of the other end portion of the center shaft  44 . Simultaneously, the mixture of the low-pressure brine LPB and high-pressure brine HPB, entered into a gap between the end surface of the other end portion of the center shaft  44  and the bottom surface of the blind hole  46   a  of the rotary member  46 , function as a thrust bearing between the end surface of the other end portion of the center shaft  44  and the bottom surface of the blind hole  46   a  of the rotary member  46  with the rotation of the rotary member  46  on the outer circumferential surface of the other end portion of the center shaft  44 . Further, the mixture of the low-pressure feed LPF and high-pressure feed HPF, entered into a gap between the bottom surface of the internal space  41  of the case  43   a  of the housing  43  and the other side surface of the rotary member  46 , which opposes the above-mentioned bottom surface, in the internal space  41  of the case  42   a  of the housing  43 , functions as a thrust bearing between the bottom surface of the internal space  41  of the case  43   a  and the other side surface of the rotary member  46  with the rotation with the rotation of the rotary member  46  on the outer circumferential surface of the other end portion of the center shaft  44 . 
         [0081]    Therefore, there is no need for independent thrust bearings between the inner surface of the lid  43   b  and the one side surface of the rotary member  46 , between the end surface of the other end portion of the center shaft  44 , and between the bottom surface of the internal space  41  of the case  43   a  and the other side surface of the rotary member  46 , and it is possible to simplify the structure of the power recovery device  24 ′ of this embodiment and to reduce the manufacturing cost thereof. 
         [0082]    While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; 
         [0083]    furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.