Abstract:
An apparatus and method suitable for use in a reverse osmosis desalinization system having a first process chamber has a first reverse osmosis membrane therein, a first feed inlet, a first permeate outlet, and a first concentrate outlet. A second process chamber having a second reverse osmosis membrane has a second feed inlet, a second permeate outlet, and a second concentrate outlet.

Description:
RELATED APPLICATIONS 
     The present application relates to U.S. patent application Ser. No. 09/491,769 entitled “Hydraulic Energy Recovery Device” filed Jan. 26, 2000, and U.S. Provisional Application No. 60/163,042, filled Nov. 2, 1999 entitled “Method and Apparatus for Membrane Recirculation and Concentrate Energy Recovery a Reverse Osmosis System” filed simultaneous herewith, each of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a reverse osmosis systems for desalinization of water, and more specifically, to an interstage pressure boosting system of a multiple stage reverse osmosis system. 
     BACKGROUND OF THE INVENTION 
     Reverse osmosis (RO) is a process widely used for desalinization of water. Reverse osmosis membranes are contained in a process chamber into which pressurized feedwater is admitted. A portion of the pressurized water permeates across the membrane and exits the process chamber as purified water at a low pressure and is referred to as permeate. The remainder of the water, still at high pressure, exits the process chamber and is referred to as a concentrate. 
     During the life of a membrane the fluid pressure must be adjusted slightly to ensure optimum operation. Without such optimization, the system will needlessly use energy or not produce the desired amount of permeate. 
     The concentrate from reverse osmosis systems may be used in three ways. The first way is to dispose of the concentrate by throttling the pressure with an orifice plate. The second way in which the high pressure concentrate may be used is to drive an energy recovery turbine (ERT). The output of the turbine is used to drive the feedwater into the system. The use of a turbine reduces the net energy consumption of the system. A third way in which to use the high pressure concentrate is to increase the pressure of the high level concentrate and admit the concentrate to a second reverse osmosis chamber to extract additional permeate. The high pressure concentrate from the second reverse osmosis chamber may then be handled in the above-mentioned three manners. 
     Referring now to FIG. 1, a known reverse osmosis system  10  is illustrated having a feed pump  12  which is driven by a motor  14  to pressurize feed fluid from a feed input  16 . Pressurized fluid leaves pump  12  through an output  18  and enters a first reverse osmosis process chamber  20 . The process chamber  20  has a permeate header  22  through which permeate is removed from the reverse osmosis chamber  20 . Reverse osmosis chamber  20  also has a concentrate output  24  which removes concentrate from the reverse osmosis chamber  20  at a high pressure. The concentrate output  24  is coupled to a booster pump  26  which is driven by a booster pump motor  28 . The booster pump  26  with booster pump motor  28  boosts the pressure of the concentrate before it is admitted into a second reverse osmosis chamber  30 . The reverse osmosis chamber  30  has a permeate output  32  coupled to permeate header  22 . A concentrate output  34  is coupled to an energy recovery turbine  36  which is coupled to a shaft  38  common to both motor  14  and pump  12 . In this manner, some of the load of pump  12  is relieved by energy recovery turbine  36 . 
     Another known arrangement similar to FIG. 1 is illustrated having the same components illustrated with the same reference numerals. In this embodiment, second energy recovery turbine  40  is coupled to concentrate output  34  is used to drive booster pump  26  on a common shaft  42 . The energy recovery turbine  36  is thus used to recover any remaining energy in the concentrate. 
     One problem in known systems is that energy-wasting throttle valves and bypass lines are typically used to control the flow and the pressure of fluids to and from the reverse osmosis chambers. It would therefore be desirable to provide a reverse osmosis system that allows independent control of the flow and pressure of each reverse osmosis chamber without the use of energy wasting throttle valves and bypass lines. 
     SUMMARY OF THE INVENTION 
     It is therefore one object of the invention to provide a reverse osmosis system that may easily and energy-efficiently be adjusted to operate at its design capacity despite changes in the membrane characteristics due to fouling or other operating parameters. 
     In one aspect of the invention, a common shaft is used to rotatably hold a first pump fluidically coupled to the first feed inlet, a pump motor, a first energy recovery turbine fluidically coupled to the first concentrate outlet, and a second energy recovery turbine fluidically coupled to the second concentrate outlet. A second pump may also be coupled to the first concentrate outlet to increase the pressure of the first concentrate prior to entering the second process chamber. 
     In a further aspect of the invention, the second pump may be rotatably coupled to a booster pump motor. In another aspect of the invention, the second pump may be coupled to a third energy recovery device that is fluidically coupled to the second concentrate outlet. 
     In a further aspect of the invention, a method for operating a reverse osmosis system comprises the steps of: 
     providing energy from a first reverse osmosis process chamber to boost the pressure of feed fluid to the first reverse osmosis process chamber; 
     providing energy from a second process chamber to boost the pressure of feed fluid to a first process chamber; and, 
     collecting permeate form the first process chamber and the second reverse osmosis process chamber. 
     One advantage of the present invention is that energy-wasting throttle valves and bypass lines have been eliminated from the reverse osmosis process. Another advantage of the invention is that more energy is recovered from the process lowering the overall cost of operating such a process. 
     Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a first known reverse osmosis system. 
     FIG. 2 is a schematic view of a second known reverse osmosis system. 
     FIG. 3 is a schematic view of a first embodiment of a reverse osmosis system according to the present invention. 
     FIG. 4 is a schematic view of a second embodiment of a reverse osmosis system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following figures, the same references numerals will be used to identify identical components in the various views. 
     The present invention is described with respect to various preferred embodiments and preferred system uses. One skilled in the art would recognize various alternatives without varying from the spirit of the invention such as nondesalinization reverse osmosis systems. 
     Referring now to FIG. 3, an improved embodiment similar to that shown in FIG. 1 is illustrated with the same components having the same reference numerals from FIG. 1 increased by 100. 
     Referring now to FIG. 1, a known reverse osmosis system  110  is illustrated having a feed pump  112  which is driven by a motor  114  to pressurize feed fluid from a feed input  116 . Pressurized feed fluid leaves pump  112  through an output  118  and enters a first reverse osmosis process chamber  120 . The first osmosis chamber  130  has a membrane  121  therein for filtering feed fluid. The process chamber  120  has a permeate header  122  through which low pressure that has passed through the membrane  121  is removed from the reverse osmosis chamber  120 . 
     Reverse osmosis chamber  120  also has a concentrate output  124  which removes concentrate from the reverse osmosis chamber  120  at a high pressure. The concentrate output  124  is coupled to a booster pump  126  which is driven by a booster pump motor  128 . The booster pump  126  with booster pump motor  128  boosts the pressure of the concentrate before it is admitted into a second reverse osmosis chamber  130  that has a membrane  131  therein for filtering fluid there through. The reverse osmosis chamber  130  has a permeate output  132  coupled to permeate header  122 . A concentrate output  134  is coupled to an energy recovery turbine  36  which is coupled to a shaft  38  common to both motor  114  and pump  112 . In this manner, some of the load of pump  112  is relieved by energy recovery turbine  136 . 
     In this embodiment, concentrate outlet  124  has a first portion  144  directed to booster pump  126  and a second portion  146  directed to an energy recovery turbine  148 . Pressure booster pump motor  128  is operated to boost the pressure into second reverse osmosis chamber  130 . 
     Both energy recovery turbine  136  and  148  along with motor  114  which drives pump  112  are coupled to a common shaft  138  for recovering energy from both the first process chamber through first portion of concentrate outlet  146  and recovering energy from the second concentrate output  134 . 
     As illustrated, each energy recovery turbine preferably comprises a nozzle valve  152 A or  152 B to adjust the flow and pressure without losing energy recovery efficiency. Throttling processes have also been eliminated which increases the efficiency of the reverse osmosis system. Advantageously, the present invention accomplishes this goal while maintaining independent control of the first and second reverse osmosis chambers. 
     As those skilled in the art will recognize, feed pump  112  is assumed to be a constant flow rate positive displacement pump. However, if a centrifugal feed pump is used, additional means such as a variable feed pump, a speed or feed throttling valve may be needed as would be recognized by those skilled in the art. A turbocharger driven by concentrate streams from either the first or second chamber may be used. 
     Referring now to FIG. 4, a similar embodiment to that shown in FIG. 2 above is illustrated. In this embodiment, booster pump motor  128  has been replaced with an energy recovery turbine  140 . Energy recovery turbine  140  also has a nozzle valve  152 C to control the flow and the pressure there through. Energy recovery turbine  140  is coupled to a common shaft  142  of booster pump  126 . 
     In both embodiments in the invention, the fluid in feed input  116  is increased in pressure by pump  112  which is driven by motor  114 , and energy recovery turbines  148  and  136 . The pressurized output feed fluid from pump  112  enters the reverse osmosis chamber  20 . Permeate under low pressure exits through permeate header  122 . High pressure concentrate exits reverse osmosis chamber  120  and a portion is directed to booster pump  126  in a conventional manner. A second portion of the concentrate is directed to the energy recovery turbine  148 . Additionally with respect to FIG. 4, second energy recovery turbine  140  may be used to recover energy from the high pressure concentrate output of the second reverse osmosis chamber  130  to boost the inlet pressure at the second process chamber. 
     With respect to FIG. 3, four operating scenarios are possible. In the first scenario, if it is desired to raise the pressure of the first reverse osmosis chamber and keep the pressure in the second reverse osmosis chamber  130  constant, the nozzle valve  152 A is closed and the speed of booster pump motor  128  is increased. When the pressure of the first reverse osmosis chamber  130  is desired to be reduced, while the second reverse osmosis chamber  130  is desired to remain constant, valve  152 A is opened and the speed of the booster pump  126  is increased. 
     When the pressure of the first reverse osmosis chamber  120  is desired to remain constant while the second reverse osmosis chamber pressure is to be increased, the speed of booster pump  126  is increased while valve  152 B is closed. When first reverse osmosis chamber  120  is desired to remain constant while the second reverse osmosis chamber  130  is desired to be lowered, the booster pump speed  126  is reduced while the nozzle valve  152 B is opened. 
     Referring now to FIG. 4, the same four operating scenarios are modified slightly due to the addition of energy recovery turbine  140  with nozzle valve  152 C. When the pressure of the first reverse osmosis chamber  120  is desired to be increased while pressure in the second reverse osmosis chamber  130  is desired to remain constant, the nozzle valve  152 A is closed, nozzle valve  152 C is opened, and valve  152 B is closed. When the pressure of the first reverse osmosis chamber  120  is desired to be lowered and the pressure of the second reverse osmosis chamber  130  is desired to remain constant, the nozzle valve  152 A is opened, the nozzle valve  152 C is closed and the nozzle valve  152 B is opened. When the pressure of the first reverse osmosis chamber  120  is desired to remain constant while increasing the pressure of the second reverse osmosis chamber  130 , the nozzle valve  152 C is closed and the nozzle valve  152 B is opened. When the pressure in the first reverse osmosis chamber  120  is desired to remain constant while decreasing the second reverse osmosis chamber  130 , the nozzle valve  152 C is opened while the nozzle valve  152 B is closed. 
     In addition to the embodiments above an additional energy recovery turbine  160  may be positioned after feed pump  112  and process chamber  120  to receive a portion of the high pressure fluid from the first process chamber  120  and/or the second process chamber  130 . This embodiment allows controlled recovery of more energy in the system. 
     As is described, the present invention provides independent control of flow and pressure in each reverse osmosis chamber while providing maximum energy recovery by eliminating throttling of any fluid stream. Although two reverse osmosis chambers have been illustrated, the present invention may be applied to processes using various numbers of reverse osmosis chambers. 
     Those skilled in the art will recognize that the adjustment of the nozzle valves in response to system parameters may be controlled in an automated fashion, such as computer controlled drive to the complexity of such a system. 
     While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.