Abstract:
Disclosed is a self-reciprocating energy recovery device utilized in driving of a seawater pump by self-reciprocating a piston of a power recovery chamber and recovering energy not using an electronic drive unit but using the hydraulic power of concentrated water. The self-reciprocating energy recovery device including a pair of power recovery chambers having pistons therein respectively, a high-pressure concentrated supply pipe, a low-pressure concentrated discharge pipe, and a high-pressure seawater discharge pipe to enable the power recovery chambers to recover hydraulic power supplied through the high-pressure concentrated water supply pipe and utilize the hydraulic power in driving of a seawater pump.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates generally to an energy recovery device for a desalination system and, more particularly, to a self-reciprocating energy recovery device utilized in driving of a seawater pump by self-reciprocating a piston of a power recovery chamber and recovering energy not using an electronic drive unit but using the hydraulic power of concentrated water. 
     2. Description of the Related Art 
     In general, in order to acquire freshwater from seawater, substances dissolved or floating in seawater need to be removed to satisfy the standards for water and drinking water. Desalination methods mainly include reverse osmosis and electric dialysis using special membranes, and evaporation for changing seawater into vapor to desalinate seawater, and also may use freezing and solar heat. 
     A desalination plant using electric dialysis uses semi-permeable membranes that entirely exclude ion materials dissolved in water and pass pure water to filter ionic materials dissolved in seawater. 
     A process using high pressure above standard osmosis pressure is needed to separate ionic materials and pure water from seawater is referred to reverse osmosis, and a high pressure of 42 to 70 bars is needed in desalination of seawater. 
     The operation of the desalination system using reverse osmosis is as follows. 
     First, the seawater introduced from the sea is supplied through a low-pressure pump for reverse osmosis via a pre-treatment process. 
     Some of the seawater supplied through the low-pressure pump is supplied to a membrane after being pressurized by a high-pressure pump, and some of the seawater supplied to the membrane is discharged to treated water from which salt is removed by reverse osmosis and the remainder is supplied to an energy recovery device as high-pressure concentrated water. 
     The energy recovery device includes a pair of power recovery chambers recovering hydraulic power of concentrated water, a plurality of check valves for interrupting the seawater supplied to the power recovery chambers, and an electric actuator drive spool valve for controlling pistons inside the power recovery chambers to alternately reciprocate. 
     In a simple explanation of the operation of such an energy recovery device, some of the high-pressure seawater that has passed through a high-pressure pump is discharged to treated water from which salt is removed through a membrane and the remainder is provided to the energy recovery device as high-pressure concentrated water. 
     High-pressure concentrated water is alternately supplied to the power recovery chambers by interrupting the electric actuator drive spool valve. Then, the pistons are moved by the pressure of the high-pressure concentrated water, whereby high-pressure seawater is supplied to a membrane module and low-pressure seawater is selectively supplied to the power recovery chambers through a boost pump by selective opening/closing of a check valve. 
     In the desalination system using reverse osmosis, the energy recovery device can make the capacities of the low-pressure pump and the high-pressure pump smaller and the power of electric motors driving the low-pressure pump and the high-pressure pump less by recovering the hydraulic power of the concentrated water that has been treated in the membranes, saving energy. 
     However, such an energy recovery device separately includes a chamber having a cylindrical piston to use hydraulic pressure in reverse osmosis, and a linearly moved spool valve selectively controlling driving of a cylindrical piston in the chamber. 
     In other words, since the rotational movement of the electric motor needs to be converted to linear movement and the electric actuator drive spool valve such as an electric linear motor and a proportional control valve needs to be provided outside a chamber, the device becomes complex and the size of the device increases. 
     In order to overcome the above-mentioned disadvantages, the present applicant has disclosed an energy recovery device in Korean Patent Application No. 2008-0054464. 
     The technology enables reduction of the size of the device, precise control of the device, and linear flow of fluid by using a conventional spool valve selectively supplying concentrated water to a power recovery chamber as a concentrated water control valve block having a fluctuating plate-like concentrated water valve and directly controlling rotation using an electric motor. 
     However, since the technology uses a separate electric motor for driving a fluctuating plate-like concentrated water valve, power for driving of an electric motor is consumed and a waterproof structure for interrupting contact with water is needed, making the device complex and larger. 
     BRIEF SUMMARY 
     The present invention has been made in view of the above problems, and the present invention provides a self-reciprocating energy recovery device that can reciprocally move pistons in power recovery chambers without using any external electric drive actuator or electronic valve, using a fluctuating actuator integrated plate valve fluctuating by a high pressure of concentrated water by selectively interrupting high pressure of the concentrated water without using a drive unit by a separate electric drive. 
     In order to achieve the object, the present invention provides a self-reciprocating energy recovery device including a pair of power recovery chambers having pistons therein respectively, a high-pressure concentrated supply pipe, a low-pressure concentrated discharge pipe, and a high-pressure seawater discharge pipe to enable the power recovery chambers to recover hydraulic power supplied through the high-pressure concentrated water supply pipe and utilize the hydraulic power in driving of a seawater pump, the energy recovery device comprising: a concentrated water control valve block selectively interrupting introduction and discharge of concentrated water to and from the power recovery chambers through fluctuation of a fluctuating plate-like concentrated water valve having pinion gear teeth on the outer peripheral surface thereof; a rack gear having rack gear teeth enmeshed with the pinion gear teeth and inserted into opposite spools; first and second high-pressure concentrated water pilots branched out from the high-pressure concentrated water supply pipe to pilots and connected to sides of the spools to alternately supply high-pressure concentrated water; first and second high-pressure concentrated water pilot valve interrupting supply of high-pressure concentrated water to the first and second high-pressure concentrated water pilots respectively; first and second low-pressure concentrated water pilots connected to opposite sides of the spools to discharge low-pressure concentrated water; and first and second low-pressure concentrated water pilot valves interrupting discharge of low-pressure concentrated water through the first and second low-pressure concentrated water pilots. 
     The concentrated water control valve block includes: a concentrated water chamber cover having chamber ports communicated with the power recovery chambers respectively; a concentrated water inlet/outlet cover having a concentrated water supply hole communicated with the high-pressure concentrated water supply pipe and a concentrated water outlet hole communicated with the low-pressure concentrated water supply pipe; and a fluctuating plate-like concentrated water valve functioning as a hydrostatic bearing by a pressure of supplied water between the concentrated water chamber cover and the concentrated water inlet/outlet cover and having opened holes. 
     The self-reciprocating energy recovery device further comprises a fluctuating plate-like check valve block provided on one side of the power recovery chambers and connected to the fluctuating plate-like concentrated water valve, the fluctuating plate-like check valve block being moved in association with the fluctuation of the fluctuating plate-like concentrated valve to selectively interrupt introduction and discharge of seawater to and from the first power recovery chamber and the second power recovery chamber. 
     The fluctuating plate-like check valve block includes: a seawater chamber cover having chamber ports communicated with the power recovery chambers respectively; a seawater inlet/outlet cover having a seawater supply hole connected to the low-pressure seawater supply pipe and a seawater outlet hole connected the high-pressure seawater discharge pipe; and a fluctuating plate-like concentrated water valve functioning as a hydrostatic bearing by a pressure of supply water between the seawater chamber cover and the seawater inlet/outlet cover and having opened holes. 
     The first and second high-pressure concentrated water pilot valves and the first and second low-pressure concentrated water pilot valves pass through sides of the power recovery chambers and are connected to resilient members outside the power recovery chambers. 
     The present invention also provides a self-reciprocating energy recovery device including a pair of power recovery chambers having pistons therein respectively, a high-pressure concentrated supply pipe, a low-pressure concentrated discharge pipe, and a high-pressure seawater discharge pipe to enable the power recovery chambers to recover hydraulic power supplied through the high-pressure concentrated water supply pipe and utilize the hydraulic power in driving of a seawater pump, the energy recovery device comprising: a fluctuating plate-like concentrated water valve having a fixed vane to selectively interrupt introduction and discharge of concentrated water to and from the first power recovery chamber and the second power recovery chamber through fluctuation thereof; a fluctuating plate-like concentrated water valve block having a space into which the fluctuating plate-like concentrated water valve and in which the fixed vane is accommodated and a first block outlet hole and a first block inlet hole, and a second block outlet hole and a second block inlet hole symmetrically disposed on opposite sides of the space; first and second high-pressure concentrated water pilots branched out from the high-pressure concentrated water supply pipe to pilots and connected to the first and second block inlet holes to alternately supply the high-pressure concentrated water; first and second high-pressure concentrated pilot valves interrupting supply of high-pressure concentrated water to the first and second high-pressure concentrated water pilots; first and second low-pressure concentrated water pilots connected to the first and second block outlet holes to alternately discharge the low-pressure concentrated water; and first and second low-pressure concentrated water pilot valves interrupting discharge of low-pressure concentrated water through the first and second low-pressure concentrated water pilots. 
     The fluctuating plate-like concentrated water valve block includes: a concentrated water chamber cover having chamber ports communicated with the power recovery chambers respectively; a concentrated water inlet/outlet cover having a concentrated water supply hole communicated with the high-pressure concentrated water supply pipe and a concentrated water outlet hole communicated with the low-pressure concentrated water supply pipe; and a fluctuating plate-like concentrated water valve functioning as a hydrostatic bearing by a pressure of supplied water between the concentrated water chamber cover and the concentrated water inlet/outlet cover and having opened holes. 
     The self-reciprocating energy recovery device further comprises: a fluctuating plate-like check valve provided on one side of the power recovery chambers and having a fixed vane at the outer periphery thereof to selectively interrupt introduction and discharge of seawater into and from the first power recovery chamber and the second power recovery chamber through fluctuation thereof; a fluctuating plate-like concentrated water valve block having a space into which the fluctuating plate-like concentrated water valve and in which the fixed vane is accommodated and a first block outlet hole and a check valve block having a first block inlet hole, and a second block outlet hole and a second block inlet hole symmetrically disposed on opposite sides of the space; wherein the first and second high-pressure concentrated water pilots alternately supplying high-pressure concentrated water are connected to the first and second check valve inlet holes, and first and second low-pressure concentrated water pilots alternately discharging low-pressure concentrated are connected to the first and second check valve outlet holes. 
     The fluctuating plate-like check valve block includes: a seawater chamber cover having chamber ports communicated with the power recovery chambers respectively; a seawater inlet/outlet cover having a seawater supply hole connected to the low-pressure supply pipe and a seawater outlet hole connected to the high-pressure seawater discharge pipe; and a fluctuating plate-like check valve functioning as a hydrostatic bearing by a pressure of supply water between the seawater chamber cover and the seawater inlet/outlet cover and having opened holes. 
     The first and second high-pressure concentrated water pilot valves and the first and second low-pressure concentrated water pilot valves pass through sides of the power recovery chambers and are connected to resilient members outside the power recovery chambers. 
     The present invention enables self-reciprocating movement of pistons by recovering high-pressure power by hydraulic pressure of concentrated water with no power unit by an electric drive, increasing energy saving efficiency. Furthermore, the present invention does not use an electric drive in an environment in which water is treated, increasing the reliability of operation of a device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIGS. 1 and 2  are views illustrating the structure and operation of a self-reciprocating energy recovery device according to the first embodiment of the present invention; 
         FIGS. 3 and 4  are views illustrating the structure and operation of a self-reciprocating energy recovery device according to the second embodiment of the present invention; 
         FIGS. 5 and 6  are views illustrating the structure and operation of a self-reciprocating energy recovery device according to the third embodiment of the present invention; and 
         FIGS. 7 and 8  are views illustrating the structure and operation of a self-reciprocating energy recovery device according to the fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIGS. 1 and 2  are views illustrating the structure and operation of a self-reciprocating energy recovery device according to the first embodiment of the present invention. The present invention relates to a self-reciprocating energy recovery device utilized in driving of a seawater pump by recovering hydraulic power of high-pressure concentrated water from a power recovery chamber in discharging treated water and concentrated water obtained by removing salt from sea water using reverse osmosis. 
     Referring to  FIGS. 1 and 2 , the self-reciprocating energy recovery device includes a pair of power recovery chambers  1   a  and  1   b , a low-pressure seawater supply pipe  2 , a high-pressure seawater discharge pipe  3 , a high-pressure concentrated water supply pipe  4 , a low-pressure concentrated water discharge pipe  5 , a concentrated water control value block  6 , a pair of high-pressure concentrated water pilots  73   a  and  73   b , a pair of high-pressure concentrated water pilot valves  74   a  and  74   b , a pair of low-pressure concentrated water pilots  75   a  and  75   b , and a pair of low-pressure concentrated water pilot valves  76   a  and  76   b.    
     The pair of power recovery chambers  1   a  and  1   b  are a first power recovery chamber  1   a  and a second power recovery chamber  1   b  having pistons  11   a  and  11   b  therein respectively, and alternately introduce and discharge concentrated water. 
     Then, the pistons  11   a  and  11   b  may be floating ball-shaped pistons reciprocating inside the chambers without using piston rods. 
     The high-pressure concentrated water treated by a membrane module (not shown) is supplied to the high-pressure concentrated water pipe  4 , and the low-pressure concentrated water that has been used in recovery of energy in the power recovery chambers  1   a  and  1   b  is discharged through the low-pressure concentrated water discharge pipe  5 . 
     The low-pressure seawater supplied through a low-pressure pump (not shown) is supplied to the power recovery chambers  1   a  and  1   b  through the low-pressure seawater supply pipe  2 , and the high-pressure seawater that has been used in the power recovery chambers  1   a  and  1   b  is discharged to the high-pressure seawater discharge pipe  3  through a boost pump (not shown) and is supplied to a membrane (not shown). 
     The concentrated water control valve block  6  functions as a valve selectively interrupting introduction and discharge of concentrated water to the first power recovery chamber  1   a  and the second power recovery chamber  1   b  through fluctuation of a fluctuating plate-like concentrated water valve  63  having pinion gear teeth  631  on the outer peripheral surface thereof. 
     In this case, the concentrated water control valve block  6  includes a concentrated water chamber cover  61  functioning as a hydrostatic bearing using the pressure of supplied water, a concentrated water inlet/outlet cover  62 , and a fluctuating plate-like concentrated valve  63 . 
     A first concentrated water chamber port  61   a  communicated with the first power recovery chamber  1   a  and a second concentrated water chamber port  61   b  are formed in the concentrated water chamber cover  61 . The ports  61   a  and  61   b  may be circular or arc shaped. 
     A concentrated water supply hole  62   a  communicated with the high-pressure concentrated water supply pipe  4  and a concentrated water discharge hole  62   b  communicated with the low-pressure concentrated water discharge pipe  5  are formed in the concentrated water inlet/outlet cover  62 . The concentrated water supply hole  62   a  and the concentrated water discharge hole  62   b  may be circular or arc shaped. 
     The fluctuating plate-like concentrated water valve  63  is provided between the concentrated water chamber cover  61  and the concentrated water inlet/outlet cover  62 . Holes  63   a  and  63   b  selectively communicating the concentrated water chamber ports  61   a  and  61   b  and the concentrated water supply hole  62   a , and the concentrated water chamber ports  61   a  and  61   b  and the concentrated water discharge hole  62   b , by rotating the fluctuating plate-like concentrated water valve  63  are formed in the fluctuating plate-like concentrated water valve  63 . For example, the holes  63   a  and  63   b  may be circular or arc shaped. 
     Then, a plurality of pinion gear teeth  631  are formed on the outer peripheral surface of the fluctuating plate-like concentrated water valve  63 , and a rack gear  72  having rack gear teeth  721  enmeshed with the pinion gear teeth  631  is formed on the fluctuating plate-like concentrated water valve  63 . 
     In this case, the rack gear  72  is inserted into opposite spools  71  and is linearly reciprocated by the high-pressure concentrated water supplied to opposite ends of the spools  71 . 
     In other words, the first and second high-pressure concentrated water pilots  73   a  and  73   b  branched out from the high-pressure concentrated water supply pipes  4  are connected to opposite sides of the spools  71 , and the rack gear  72  is linearly reciprocated by the pressure of the high-pressure concentrated water alternately supplied through the high-pressure concentrated water pilots  73   a  and  73   b.    
     Then, the high-pressure concentrated water supplied to the opposite sides of the spools  71  is selectively interrupted by the first and second high-pressure concentrated water pilot valves  74   a  and  74   b.    
     The first and second high-pressure concentrated water pilot valves  74   a  and  74   b  pass through the power recovery chambers  1   a  and  1   b  lengthwise and are connected to resilient members  741  located outside the power recovery chambers  1   a  and  1   b.    
     Due to the above-mentioned structure, the first and second high-pressure concentrated water pilot valves  74   a  and  74   b  selectively open the first and second high-pressure concentrated water pilots  73   a  and  73   b  by adhesion of pistons in order to alternately supply the concentrated water to the opposite sides of the spools  71 . 
     The first and second low-pressure concentrated water pilots  75   a  and  75   b  for discharging the low-pressure concentrated water are connected to the opposite sides of the spools  71 , and the first and second low-pressure concentrated water pilot valves  76   a  and  76   b  are provided on the other sides of the power recovery chambers  1   a  and  1   b.    
     The first and second low-pressure concentrated water pilot valves  76   a  and  76   b  pass through the power recovery chambers  1   a  and  1   b  lengthwise and are connected to the resilient members  761  outside the power recovery chambers  1   a  and  1   b  respectively, so that the first and second low-pressure concentrated water pilots  75   a  and  75   b  are selectively opened by adhesion of the pistons inside the power recovery chambers  1   a  and  1   b  whereby the low-pressure concentrated water of the spools  71  is discharged. 
     A plurality of ball type check valves  21  for interrupting supply of low-pressure seawater to the first and second power recovery chambers  1   a  and  1   b  and supply of high-pressure sea water to the high-pressure sea water discharge pipe  3  are provided at a connection section of the low-pressure sea water supply pipe  2  and the high-pressure seawater discharge pipe  3 . 
     In this case, the plurality of check valves  21  include a first check valve  21   a  for supplying low-pressure seawater to the first power recovery chamber  1   a , a second check valve  21   b  for interrupting supply of the high-pressure seawater pressurized by the first power recovery chamber  1   a  to the high-pressure seawater discharge pipe  3 , a third check valve  21   c  for interrupting supply of the high-pressure seawater pressurized by the second power recovery chamber  1   b  to the high-pressure seawater discharge pipe  3 , and a fourth check valve for supplying the low-pressure seawater to the second power recovery chamber  1   b.    
     Hereinafter, the operation of the self-reciprocating energy recovery device according to the first embodiment of the present invention will be described in detail with reference to  FIGS. 1 and 2 . 
     First, as illustrated in  FIG. 1 , if the piston  11   a  in the first power recovery chamber  1   a  is moved in the direction of A, the first low-pressure concentrated water control valve  76   a  is opened by adhesion of the piston  11   a , and if the piston  11   b  in the second power recovery chamber  1   b  is moved in the direction of B, the piston  11   b  is opened to open the second high-pressure concentrated pilot valve  74   b.    
     The high-pressure concentrated water is supplied to the spool  71  on one side of the rack gear  72  through the second high-pressure concentrated water pilot  73   b  when the valves are opened. 
     Then, the rack gear  72  is linearly reciprocated due to the high pressure applied to one side of the rack gear  72  by the concentrated water, the pinion gear teeth  631  are enmeshed with the rack gear teeth  721  of the rack gear  72 , rotating the fluctuating plate-like concentrated water valve  63 , and the low-pressure concentrated water accommodated on the opposite side of the rack gear  72  is discharged to a drain through the first low-pressure concentrated water pilot  75   a.    
     In this case, the rack gear  72  may be arbitrarily driven manually by rotation of the fluctuating plate-like concentrated valve  63  during the initial driving of the rack gear  72  or by stopping the rack gear  72 . 
     Then, the second concentrated water chamber port  61   b  and the second concentrated chamber port  61   b  are communicated with each other by rotation of the fluctuating plate-like concentrated water valve  63  whereby the first concentrated water chamber port  61   a  and the concentrated water discharge hole  62   b  are communicated with each other. 
     The low-pressure seawater supply pipe  2  and the first power recovery chamber  1   a  are communicated with each other by opening the first check valve  21   a  and closing the second check valve  21   b , and the high-pressure seawater discharge pipe  3  and the second power recovery chamber  1   b  are communicated with each other by opening the third check valve  21   c  and closing the fourth check valve  21   d.    
     Accordingly, the high-pressure concentrated water is introduced into the second power recovery chamber  1   b  so that if the second piston  11   b  is moved in the direction of A, the high-pressure seawater is discharged to the high-pressure seawater discharge pipe  3 , and the low-pressure seawater is introduced from the low-pressure seawater supply pipe  2  to the first power recovery chamber  1   a  so that the first piston  11   a  is moved in the direction of B whereby the low-pressure concentrated water is discharged to the low-pressure concentrated water discharge pipe  5 . 
     As illustrated in  FIG. 2 , if the first piston  11   a  is moved in the direction of B and the second piston  11   b  is moved in the direction of A, the first high-pressure concentrated water pilot valve  74   a  and the second low-pressure concentrated water pilot valve  76   b  are opened so that the high-pressure concentrated water is supplied to the spool  71  on the opposite side of the rack gear  72 . 
     Then, since a high pressure is applied to the opposite side of the rack gear  72  by the concentrated water, the rack gear  72  is linearly reciprocated whereby the low-pressure concentrated water accommodated on one side of the rack gear  72  is discharged to a drain through the second low-pressure concentrated water pilot  75   b  and the pinion gear teeth  631  are enmeshed with the rack gear teeth  721  of the rack gear  72 , rotating the fluctuating plate-like concentrated water valve  63 . 
     The first concentrated water chamber port  61   a  and the concentrated water supply hole  62   a  are communicated with each other and the second concentrated water chamber port  61   b  and the concentrated water discharge hole  62   b  are communicated with each other, by rotation of the fluctuating plate-like concentrated water valve  63 . 
     In addition, the high-pressure seawater discharge pipe  3  and the first power recovery chamber  1   a  are communicated with each other by closing the first check valve  21   a  and opening the second check valve  21   b , and the low-pressure seawater supply pipe  2  and the second power recovery chamber  1   b  are communicated with each other by closing the third check valve  21   c  and opening the fourth check valve  21   d.    
     Accordingly, as illustrated in  FIG. 1 , the high-pressure concentrated water is introduced into the first power recovery chamber  1   a  so that the first piston  11   a  is moved in the direction of A whereby the high-pressure seawater is discharged to the high-pressure seawater discharge pipe  3 , and the low-pressure seawater is discharged from the low-pressure seawater supply pipe  2  to the second power recovery chamber  1   b  so that the second piston  11   b  is moved in the direction of B whereby the low-pressure concentrated water is discharged to the low-pressure concentrated water discharge pipe  5 . 
     During repetition of the processes, the concentrated water is alternately introduced and discharged into and from the first power recovery chamber and the second power recovery chamber and the seawater is alternately introduced and discharged, so that the seawater is pressurized and supplied to the high-pressure seawater discharge pipe by self-reciprocating the pistons with any separate electric drive force. 
     However, since fluid needs to flow via a ball in the ball type check valve, a pressure resistance due to the flow resistance against the fluid is generated. 
     In order to improve the above disadvantage, a self-reciprocating energy recovery device according to the second embodiment of the present invention includes a fluctuating plate-like check valve as illustrated in  FIGS. 3 and 4 . In this case, detailed descriptions of the same structure and operation as those of the first embodiment of the present invention will be omitted. 
     The fluctuating plate-like check block  8  is located on one side of the pair of power recovery chambers  1   a  and  1   b  and is connected to the fluctuating plate-like concentrated water valve  63 . Introduction and discharge of seawater into and from the first power recovery chamber  1   a  and the second power recovery chamber  1   b  are selectively interrupted by fluctuation of the fluctuating plate-like concentrated water valve  63 . 
     In this case, the seawater chamber cover  81 , the seawater inlet/outlet cover  82 , and the fluctuating plate-like check valve block  8  function as a hydrostatic bearing by the pressure of the supplied water. 
     A first seawater chamber port  81   a  communicated with the first power recovery chamber  1   a  and a second seawater chamber port  81   b  communicated with the second power recovery chamber  1   b  are formed in the seawater chamber cover  81 . The ports may be circular or arc shaped. 
     A seawater supply hole  82   a  connected to the low-pressure seawater supply pipe  2  and a seawater discharge hole  82   b  connected to the high-pressure seawater discharge pipe  3  are formed in the seawater inlet/outlet cover  82 . The seawater supply hole  82   a  and the seawater discharge hole  82   b  may be circular or arc shaped. 
     Holes  83   a  and  83   b  for selectively communicating the seawater chamber ports  81   a  and  81   b  and the seawater supply hole  82   a , and the seawater chamber ports  81   a  and  81   b  and the seawater discharge hole  82   b  by rotation of the fluctuating plate-like check valve  83  are formed in the fluctuating plate-like check valve  83 . For example, the holes may be circular or arc shaped. 
     Then, a plurality of pinion gear teeth  831  are formed on the outer peripheral surface of the fluctuating plate-like check valve  83  for movement of the fluctuating plate-like check valve  83  that is associated with the fluctuating plate-like concentrated water valve  63 , and a rack gear  72  has rack gear teeth  721  enmeshed with the pinion gear teeth  831 . 
     In this case, the rack gear  72  is inserted into opposite spools  71  and is linearly reciprocated by the high-pressure concentrated water supplied to opposite ends of the spools  71 . 
     The fluctuating plate-like check valve  83  is moved in association with rotation of the fluctuating plate-like concentrated water valve  63 . 
     In other words, if the fluctuating plate-like concentrated water valve  63  is rotated in the direction of C, the fluctuating plate-like check valve  83  is simultaneously rotated together with the fluctuating plate-like concentrated water valve  63 , so that the low-pressure seawater supply pipe  2  and the first power recovery chamber  1   a  are communicated with each other and the high-pressure seawater discharge pipe  3  and the second power recovery chamber  1   b  are communicated with each other. 
     In addition, if the fluctuating plate-like concentrated water valve  63  is rotated in the direction of D, the fluctuating plate-like check valve  83  is simultaneously rotated together with the fluctuating plate-like concentrated water valve  63 , so that the low-pressure seawater supply pipe  2  and the second power recovery chamber  1   b  are communicated with each other and the high-pressure seawater discharge pipe  3  and the first power recovery chamber  1   a  are communicated with each other. 
     Accordingly, since a check valve interrupting introduction and discharge of seawater into the power recovery chambers in the second embodiment of the present invention is realized by a fluctuating plate-like check valve, the flow resistance generated by balls of a conventional ball type check valve is prevented, making the flow of fluid linear. 
       FIGS. 5 and 6  are views illustrating the structure and operation of a self-reciprocating energy recovery device according to the third embodiment of the present invention. In this case, detailed descriptions of the same structure and operation as those of the first and second embodiments of the present invention will be omitted. 
     The self-reciprocating energy recovery device according to the third embodiment of the present invention includes a pair of power recovery chambers  1   a  and  1   b , a low-pressure seawater supply pipe  2 , a high-pressure seawater discharge pipe  3 , a high-pressure concentrated water supply pipe  4 , a low-pressure concentrated water discharge pipe  5 , a concentrated water control valve block  6 , a rack gear  72 , a pair of high-pressure concentrated water pilots  73   a  and  73   b , a pair of high-pressure concentrated water pilot valves  74   a  and  74   b , a pair of low-pressure concentrated water pilots  75   a  and  75   b , and a pair of low-pressure concentrated water pilot valves  76   a  and  76   b.    
     The concentrated water control valve block  6  functions as a valve for selectively interrupting introduction and discharge of the concentrated water to the first power recovery chamber  1   a  and the second power recovery chamber  1   b , and includes a fluctuating plate-like concentrated water valve  63  having a fixed vane  632  on the outer periphery thereof to selectively interrupt introduction and discharge of the concentrated water to the first power recovery chamber  1   a  and the second power recovery chamber  1   b  by the fluctuation thereof. 
     A concentrated water chamber cover  61  and a concentrated water inlet/outlet cover  62  functioning as a hydrostatic bearing by the pressure of supplied water are provided on both sides of the fluctuating plate-like concentrated water valve  63 . 
     The fluctuating plate-like concentrated water valve  63  is inserted into the fluctuating plate-like valve block  64  having a space in which the fixed vane  632  is accommodated. 
     A first block inlet hole  642   a  and a first block outlet hole  643   a , and a second block inlet hole  642   b  and a second block outlet hole  643   b  are symmetrically formed on opposite sides of the fluctuating plate-like concentrated water valve block  64 . 
     First and second high-pressure concentrated water pilots  73   a  and  73   b  branched out from the high-pressure concentrated water supply pipe  4  to alternately supply high-pressure concentrated water are connected to the first and second block inlet holes  642   a  and  642   b.    
     In addition, first and second low-pressure concentrated water pilots  75   a  and  75   b  alternately discharging low-pressure concentrated water are connected to the first and second block outlet holes  643   a  and  643   b.    
     First and second high-pressure concentrated water pilot valves  74   b  pass through the power recovery chambers  1   a  and  1   b  lengthwise and are connected to resilient members  741  outside the power recovery chambers  1   a  and  1   b  to interrupt supply of high-pressure concentrated water to the first and second high-pressure concentrated water pilots  73   a  and  73   b.    
     First and second low-pressure concentrated water pilot valves  76   b  pass through the power recovery chambers  1   a  and  1   b  lengthwise and are connected to resilient members  761  outside the power recovery chambers  1   a  and  1   b  to interrupt discharge of low-pressure concentrated water to the first and second low-pressure concentrated water pilots  75   a  and  75   b.    
     Hereinafter, the operation of the self-reciprocating energy recovery device according to the third embodiment of the present invention will be described in detail. 
     Referring to  FIG. 5 , if the piston of the first power recovery chamber  1   a  is moved in the direction of A by the pressure of concentrated water and the piston of the second power recovery chamber  1   b  is moved in the direction of B, the second high-pressure concentrated water pilot valve  740  and the first low-pressure concentrated water pilot valve  76   a  are opened so that the high-pressure concentrated water is introduced into a first block inlet hole  642   a.    
     Then, the fluctuating plate-like concentrated water valve  63  and the fluctuating plate-like check valve  83  are rotated in the direction of C by the high pressure due to the concentrated water introduced into the first block inlet hole  642   a  whereby the low-pressure concentrated water is discharged through the second block outlet hole  643   b  and through the first low-pressure concentrated water pilot  75   a.    
     Then, when the fluctuating plate-like concentrated valve  63  is rotated in the direction of C, the second concentrated water chamber port  61   a  and the concentrated water supply hole  62   a  are communicated with each other and the first concentrated water chamber port  61   a  and the concentrated water outlet hole  62   b  are communicated with each other. 
     The low-pressure seawater supply pipe  2  and the first power recovery chamber  1   a  are communicated with each other by opening the first check valve  21   a  and closing the second check valve  21   b , and the high pressure seawater discharge pipe  3  and the second power recovery chamber  1   b  are communicated with each other by opening the third check valve  21   c  and closing the fourth check valve  21   d.    
     Accordingly, as illustrated in  FIG. 6 , when the high-pressure concentrated water is introduced into the second power recovery chamber  1   b , the second piston  11   b  is moved in the direction of A whereby the high-pressure seawater is discharged to the high-pressure seawater discharge pipe  3 , and when the low-pressure seawater is introduced from the low-pressure seawater supply pipe  2  to the first power recovery chamber  1   a , the first piston  11   a  is moved in the direction of B whereby the low-pressure concentrated water is discharged to the low-pressure concentrated water discharge pipe  5 . 
     If the first piston  11   a  is moved in the direction of B and the second piston  11   b  is moved in the direction of A, the first high-pressure concentrated water pilot valve  74   a  and the second low-pressure concentrated water pilot valve  76   b  are opened so that the high-pressure concentrated water is introduced into the second block inlet hole  742   b.    
     Then, the fluctuating plate-like concentrated water valve  63  is rotated in the direction of D by the high pressure of the introduced concentrated water, and the low-pressure concentrated water accommodated in the space  641  is discharged to the second low-pressure concentrated water pilot  75   b  through the first block outlet hole  643   b.    
     The first concentrated water chamber port  61   a  and the concentrated water supply hole  62   a  are communicated with each other and the second concentrated water chamber port  61   b  and the concentrated water outlet hole  62   b  are communicated with each other, by rotation of the fluctuating plate-like concentrated valve  63 . 
     The high-pressure seawater discharge pipe  3  and the first power recovery chamber  1   a  are communicated with each other by closing the first check valve  21   a  and opening the second check valve  21   b , and the low-pressure seawater supply pipe  2  and the second power recovery chamber  1   b  are communicated with each other by closing the third check valve  21   c  and opening the fourth valve  21   d.    
     Accordingly, as illustrated in  FIG. 5 , when the high-pressure concentrated water is introduced into the first power recovery chamber  1   a , the first piston  11   a  is moved in the direction of A whereby the high-pressure seawater is discharged to the high-pressure seawater discharge pipe  3 , and when the low-pressure seawater is introduced from the low-pressure seawater supply pipe  2  into the second power recovery chamber  1   b , the second piston  11   b  is moved in the direction of B whereby the low-pressure concentrated water is discharged to the low-pressure concentrated water discharge pipe  5 . 
     During repetition of the processes, the concentrated water is alternately introduced and discharged into and from the first power recovery chamber and the second power recovery chamber and the seawater is alternately introduced and discharged, so that the seawater is pressurized and supplied to the high-pressure seawater discharge pipe by self-reciprocating the pistons with any separate electric drive force. 
       FIGS. 7 and 8  are views illustrating the structure and operation of a self-reciprocating energy recovery device according to the fourth embodiment of the present invention. In this case, detailed descriptions of the same structure and operation as those of the first and second embodiments of the present invention will be omitted. 
     Referring to  FIGS. 7 and 8 , the self-reciprocating energy recovery device according the fourth embodiment of the present invention includes a fluctuating plate-like check valve block  8 . In the fluctuating plate-like check valve block  8 , a seawater chamber cover  812 , a seawater inlet/outlet cover  82 , and a fluctuating plate-like check valve  83  function as a hydrostatic bearing by the pressure of supplied water. The seawater chamber cover  81  and the seawater inlet/outlet cover  82  have been described in detail in the second embodiment of the present invention, and detailed descriptions thereof will be omitted. 
     In this case, the fluctuating plate-like check valve  83  is provided on one side of the power recovery chambers  1   a  and  1   b , and a fixed vane  632  is formed at the outer periphery of the fluctuating plate-like check valve  83 . 
     The fluctuating plate-like check valve  83  is inserted into a check valve block  84  having a space  841  in which the fixed vane  832  is accommodated to selectively interrupt introduction and discharge of the seawater into the first power recovery chamber  1   a  and the second power recovery chamber  1   b  through fluctuating thereof. 
     A first check valve inlet hole  842   a  and a first check valve outlet hole  842   b , and a second check valve inlet hole  843   a  and a second check valve outlet hole  843   b  are symmetrically formed on opposite sides of the space  841  in the check valve block  84 . 
     Then, the first and second high-pressure concentrated water pilots  73   a  and  73   b  alternately supplying the high-pressure concentrated water are connected to the first and second check valve inlet holes  842   a  and  842   b.    
     The first and second low-pressure concentrated water pilots  75   a  and  75   b  alternately discharging the low-pressure concentrated water are connected to the first and second check valve outlet holes  843   a  and  843   b.    
     Hereinafter, the operation of the self-reciprocating energy recovery device according to the fourth embodiment of the present invention will be simply described. 
     As illustrated in  FIG. 7 , if the piston  11   a  of the first power recovery chamber  1   a  is moved in the direction of A and the piston  11   b  of the second power recovery chamber  1   b  is moved in the direction of B, the second high-pressure concentrated water pilot valve  74   b  and the first low-pressure concentrated water pilot valve  76   a  are opened so that the high-pressure concentrated water is introduced into the first block inlet hole  642   a  and the first check valve inlet hole  842   a.    
     Then, the fluctuating plate-like concentrated water valve  63  and the fluctuating plate-like check valve  83  are rotated in the direction of C by the high-pressure due to the concentrated water introduced into the first block inlet hole  642   a  and the first check valve inlet hole  842   a  whereby the low-pressure concentrated water is discharged through the second block outlet hole  643   b  and the second check valve outlet hole  843   b  and through the first low-pressure concentrated water pilot  75   a.    
     The second concentrated water chamber port  61   b  and the concentrated water supply hole  62   a  are communicated with each other and the first concentrated water chamber port  61   a  and the concentrated water discharge hole  62   b  are communicated with each other, by rotation of the fluctuating plate-like concentrated water valve  63 . 
     Accordingly, as illustrated in  FIG. 8 , when the high-pressure concentrated water is introduced into the second power recovery chamber  1   b , the second piston  11   b  is moved in the direction of A whereby the high-pressure seawater is discharged to the high-pressure seawater discharge pipe  5 , and when the low-pressure seawater is introduced from the low-pressure seawater supply pipe  2  into the first power recovery chamber  1   a , the first piston  11   a  is moved in the direction of B whereby the low-pressure concentrated water is discharged to the low-pressure concentrated water discharge pipe  5 . 
     If the first piston  11   a  is moved in the direction of B and the second piston  11   b  is moved in the direction of A, the first high-pressure concentrated water pilot valve  74   a  and the second low-pressure concentrated water pilot valve  76   b  are opened so that the high-pressure concentrated water is introduced into the second block inlet hole  642   b  and the second check valve inlet hole  842   b.    
     Then, the fluctuating plate-like concentrated water valve  63  and the fluctuating check valve  83  are rotated in the direction of D by the high pressure of the introduced concentrated water, whereby the low-pressure concentrated water accommodated in the space  841  is discharged to the second low-pressure concentrated water pilot  75   b  through the first block outlet hole  643   a  and the first check valve outlet hole  843   a.    
     The first concentrated water chamber port  61   a  and the concentrated water supply hole  62   a  are communicated with each other and the second concentrated water chamber port  61   b  and the concentrated water outlet hole  62   b  are communicated with each other by rotation of the fluctuating plate-like concentrated water valve  63 . 
     Accordingly, as illustrated in  FIG. 7 , when the high-pressure concentrated water is introduced into the first power recovery chamber  1   a , the first piston  11   a  is moved in the direction of A whereby the high-pressure seawater is discharged to the high-pressure seawater discharge pipe  3 , and when the low-pressure seawater is introduced into the second power recovery chamber  1   b , the second piston  11   b  is moved in the direction of B whereby the low-pressure concentrated water is discharged to the low-pressure concentrated water discharge pipe  5 . 
     During repetition of the processes, the concentrated water is alternately introduced and discharged into and from the first power recovery chamber and the second power recovery chamber and the seawater is alternately introduced and discharged, so that the seawater is pressurized and supplied to the high-pressure seawater discharge pipe by self-reciprocating the pistons with any separate electric drive force. 
     While the invention has been shown and described with respect to the exemplary embodiments, it will be understood by those skilled in the art that the system and the method are only examples of the present invention and various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.