Abstract:
A pressurization device is described mobilizing gravity to mobilize seawater and to employ a weight ( 56 ) for gravitionally applying a force to and thereby pressurizing an enclosed pocket ( 58 ) of seawater, resulting in low energy utilisation. Energy is further recovered from the flow of pressurized seawater that is supplied to the desalination system ( 20 ), resulting in a mechanically robust and energy efficient pressurization system.

Description:
FIELD OF INVENTION 
     The present invention relates generally to a pressurisation system. In particular, the invention relates to a pressurisation system for pressurising fluids for a desalination system. 
     BACKGROUND 
     Fluids, or water in particular, are pressurised for a multitude of applications. One such application is in a desalination system using a reverse osmosis (RO) process for producing potable water. Seawater and brackish water are often used in the RO process. However, the seawater from a water source, for example the sea, has to be highly pressurised before it is supplied to the desalination system for the RO process to be performed. 
     High pressure pumps, for example displacement pumps, are conventionally used for drawing the seawater from the water source, pressurising the drawn seawater by compressing the seawater within a volume and supplying the pressurised seawater to the desalination system. However, the energy consumption of each of these pumps is high which results in high operating costs. Systems using these high pressure pumps require a variation of components to reduce water supply pulsation and prevent over-pressurisation of downstream pipes for conveying pressurised seawater. 
     There is hence a need for a pressurisation system for addressing the deficiencies of high pressure pumps. 
     SUMMARY 
     In accordance with a first aspect of the invention, there is disclosed a pressurisation system comprising:
         a vessel having a chamber for receiving fluid thereinto, the fluid having a pressure,   a plunger for enclosing a portion of the chamber to form an enclosure, the enclosure having a volume, and the plunger being movably coupled to and for cooperation with the chamber to reduce the volume of the enclosure, the chamber is shaped and dimensioned for the passage of the plunger therethrough and for the reciprocation of the plunger therewithin, the plunger for reciprocating along a longitudinal axis of the chamber generally parallel to the direction of gravitational acceleration, the plunger having a weight for gravitationally applying a compression force to the fluid to thereby reduce the volume of the enclosure and increase the pressure of the fluid; and   a positioning device for comprising a hoist assembly and an electric actuator having a brake assembly for interacting with the hoist assembly to impede the reduction of the volume of the enclosure,   wherein positioning of the plunger within the chamber is artificially controlled by the positioning device to allow the volume of the enclosure to be pre-determinable.       

     In accordance with a second aspect of the invention, there is disclosed a pressurisation method comprising the steps of:
         providing a vessel having a chamber;   receiving fluid into the chamber, the fluid having a pressure,   enclosing a portion of the chamber with a plunger to form an enclosure, the enclosure having a volume, and the plunger being movably coupled to and for cooperation with the chamber to reduce the volume of the enclosure, the chamber is shaped and dimensioned for the passage of the plunger therethrough and for the reciprocation of the plunger therewithin, the plunger for reciprocating along a longitudinal axis of the chamber generally parallel to the direction of gravitational acceleration, the plunger having a weight for gravitationally applying a compression force to the fluid to thereby reduce the volume of the enclosure and increase the pressure of the fluid; and   providing a positioning device comprising a hoist assembly and an electric actuator having a brake assembly for interacting with the hoist assembly to impede the reduction of the volume of the enclosure,   wherein positioning of the plunger within the chamber is artificially controlled by       

     the positioning device to allow the volume of the enclosure to be pre-determinable. 
     In accordance with a third aspect of the invention, there is disclosed, a pressurisation method for pressurising fluids comprising the steps of:
         receiving fluid from a water source into a chamber of a vessel, the chamber having a longitudinal axis and being formed within the vessel, the water source having a water level and the fluid having a pressure;   enclosing a portion of the chamber with a plunger to form an enclosure having a volume, the plunger having a weight, the fluid received in the chamber being contained in the enclosure, and the plunger being movable along the longitudinal axis of the chamber to one of reduce or increase the volume of the enclosure;   gravitationally applying a force to the fluid by the plunger along the longitudinal axis of the chamber to reduce the volume of the enclosure and thereby increasing the pressure of the fluid, the pressure of the fluid being controlled by a positioning device being coupled to the plunger for positioning the plunger along the longitudinal axis thereby controlling the amount of force applied to the fluid, the positioning device comprising a hoist assembly and an electric actuator having a brake assembly for interacting with the hoist assembly to impede the reduction of the volume of the enclosure; and   wherein positioning of the plunger within the chamber is artificially controlled by the positioning device to allow the volume of the enclosure to be pre-detenninable.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are described hereafter with reference to the following drawings, in which: 
         FIG. 1  is a front sectional view of a pressurisation system in accordance to an embodiment of the invention; 
         FIG. 2  is a process flow-chart of a pressurisation process applied by the pressurisation system of  FIG. 1 ; and 
         FIG. 3  is a system representation of the pressurisation system of  FIG. 1  with a plurality of vessels. 
     
    
    
     DETAILED DESCRIPTION 
     A pressurisation system for addressing the aforementioned deficiencies of conventional high pressure pump-based systems is described in this section. 
     An embodiment of the invention, a pressurisation system  20  is described with reference to  FIG. 1 , which shows a front sectional view of the pressurisation system  20 . The pressurisation system  20  comprises of a vessel  22  with an internally disposed chamber  24 . The chamber  24  is preferably cylindrical with a longitudinal axis  28 . The vessel  22  is disposed generally upright on a support surface  26  with the longitudinal axis  28  of the chamber  24  generally parallel to the direction of gravitational acceleration and generally perpendicular to the support surface  26 . The chamber  24  has a base  30  and an opening  32  constituting two extremities of the chamber  24 , with the base  30  being proximal to the support surface  26  and the opening  32  being distal to the support surface  26 . The chamber  24  of the vessel  22  is preferably for containing water or the like fluids. 
     An inlet  34  is formed in the vessel  22  and adjacent to the opening  32  for receiving water into the chamber  24 . An inlet conduit  36 , preferably a pipe, connects a water source  38  to the inlet  34  of the vessel  22  with the water source  38  having a water level  40 . The inlet  34  of the vessel  22  is positioned below the water level  40  of the water source  38  to create a pressure gradient (not shown) between the water source  38  and the chamber  24 . This pressure gradient draws water from the water source  38  through the inlet conduit  36  and into the chamber  24  of the vessel  22 . Pressure equilibrium is achieved when water in the chamber  24  reaches an equalised level  42 . 
     The pressurisation system  20  is used with a desalination system  44  for water desalination, and is located within the proximity of an abundant water source, preferably the sea. The sea provides an abundance of seawater for the desalination system  44 . However, seawater contains impurities that are harmful to both the pressurisation system  20  and the desalination system  44 . 
     The pressurisation system  20  further comprises of a filtration assembly  46  and an inlet valve  48 . Both the filtration assembly  46  and the inlet valve  48  are disposed along the inlet conduit  36  with the filtration assembly  46  being adjacent to the inlet valve  48 . The filtration assembly  46  is for filtering particles of differing coarseness, for example silt, impurities and the like foreign bodies, from the seawater. The inlet valve  48  has two operating positions: an open position and a closed position (both not shown). When the inlet valve  48  is in the open position, seawater flows freely through the inlet  34  and into the chamber  24 . However, when the inlet valve  48  is in the closed position, the seawater is prevented from reaching the inlet  34 . The inlet conduit  36  is therefore in fluid communication with the chamber  24  when the inlet valve  48  is in the open position. 
     An outlet  50  is formed in the vessel  22  adjacent to the base  30  for discharging seawater from the chamber  24  therethrough. An outlet conduit  52 , preferably a pipe, connects the outlet  50  of the vessel  22  to the desalination system  44 . An outlet valve  54  is disposed along the outlet conduit  52  for controlling the supply of seawater from the vessel  22  to the desalination system  44 . The outlet valve  54  is positionable between an open position and a closed position to respectively permit or restrict the flow of seawater from the vessel  22  to the desalination system  44 . The outlet conduit  52  is in fluid communication with the vessel  22  and the desalination system  44  when the outlet valve  54  is in the open position. 
     The pressurisation system  20  further comprises a plunger  56  being slidably coupled to the vessel  22 . The plunger  56  is shaped and dimensioned for sliding within the chamber  24  along the longitudinal axis  28 . The opening  32  of the chamber  24  is shaped and sized for passage of the plunger  56  therethrough. The plunger  56  is disposed in the chamber  24  to form an enclosure  58  within the chamber  24 , the enclosure having a volume dependent on the position of the plunger  56  along the longitudinal axis  88 . A mechanical seal (not shown) is coupled to the plunger  56  and disposed along the circumference of the plunger  56  to seal the space between the periphery of the plunger  56  and the internal wall of the vessel  22  for creating a water-tight seal therebetween. 
     The plunger  56  is preferably made of concrete or any material with large mass and generally high density. The pressurisation system  20  further comprises a positioning device  60  attached to a support structure  62 . Both the positioning device  60  and the support structure  62  are disposed above the opening  32  of the vessel  22 . The positioning device  60  comprises a pulley assembly  64  having a hoisting attachment  66  for coupling the positioning device  60  to the plunger  56 . 
     The positioning device  60  further comprises an electric motor  68  being mounted onto the support structure  62  and for engagement with the pulley assembly  64 . The electric motor  68  interacts with the pulley assembly  64  for positioning the hoisting attachment  66  generally along the longitudinal axis  28  of the chamber  24  and thereby positioning the plunger  56  generally along the longitudinal axis  28  of the chamber  24 . 
     The electric motor  68  is electrically connected to a controller (not shown) for controlling the positioning of the plunger  56  along the longitudinal axis  28  thereby varying the volume of the enclosure  58 . Both the inlet valve  48  and the outlet valve  52  are electrically connected to the controller for positioning the inlet valve  48  and the outlet valve  52  between open and closed positions. 
     The desalination system  44  uses a reverse osmosis process that requires seawater to be supplied at a pressure of generally at least 80 atm (atmosphere). A pressurisation process  100  is described with reference to  FIG. 2 , which shows a process flowchart of the pressurisation process  100 . 
     The pressurisation process  100  starts with a preparatory stage  102 . The controller initially positions both the outlet valve  52  and the inlet valve  48  to the closed position. The controller further controls the positioning device  60  to position the plunger  56  towards the opening  32  of the chamber  24 . 
     The controller then initiates an intake stage  104 , by positioning the inlet valve  48  to the open position. The pressure gradient between the water source  38  and the chamber  24  influxes seawater from the water source  38  through the inlet conduit  36  and into the enclosure  58  of the chamber  24 . Seawater from the water source  38  continues to fill the enclosure  58  until the seawater within the enclosure  58  reaches an equalised level  42 . A level sensor (not shown) is disposed within the chamber  24  and is electrically connected to the controller for transmitting a level signal to the controller when the seawater within the enclosure  58  reaches the equalised level  42 . In response to the level signal received from the level sensor, the controller positions the inlet valve  48  to the closed position. The seawater within the enclosure  58  has a pressure of approximately 1 atm before a pressurisation process. 
     The controller initiates a pressurisation stage  106 , in response to the completion of the intake stage  104 , by communicating with the positioning device  60  to position the plunger  56  towards the base  30  of the chamber  24  and thereby reducing the volume of the enclosure  58 . The reduction of the volume of the enclosure  58  increases the pressure of the seawater within the enclosure  58 . The plunger  56  is preferably made from concrete and therefore is heavily weighted. The weight of the plunger  56  applies force on the seawater within the enclosure  58  by means of gravity. The mechanical seal prevents seawater from leaking through the interface between the plunger  56  and the chamber  24 . 
     The positioning device  60  further comprises a brake assembly (not shown) built into the electric motor  68  and being electrically connected to the controller. The brake assembly is for resisting the movement of the hoisting attachment  66  along the longitudinal axis  28  when a braking signal is received from the controller. 
     In the pressurisation stage  106 , gravity pulls the plunger  56  towards the base  30  of the chamber  24 , which can lead to over-pressurisation of the seawater within the enclosure  58 . The brake assembly of the electric motor  68  is actuable to impede movement of the plunger  56  towards the base  30  of the chamber  24  and thereby maintaining the seawater at a constant pressure. Additionally, a pressure relief valve (not shown) is disposed in the chamber  24  to prevent the over-pressurisation of the seawater. The pressure of the seawater within the enclosure  58  is reducable by the positioning device  60  positioning the plunger  56  towards the opening  32  and away from the seawater within the enclosure  58 . 
     The outlet valve  54  comprises a pressure sensor (not shown) disposed therein. The pressure sensor is electrically connected to the controller for transmitting a pressure signal to the controller, the pressure signal indicating an operating pressure being the pressure of the seawater measured at the pressure sensor. An interface  70  between the plunger  56  and the seawater within the enclosure  58  is generally planar. The operating pressure is dependent on the pressure of the seawater at the interface  70  and the mass of the seawater contained within the enclosure  58 , with the mass of the seawater being a function of the distance between the interface  70  and the base  30  of the chamber  24 , and the dimensions of the chamber  24 . 
     The controller registers a reference pressure pre-defined by a user. The reference pressure is the pressure required by the desalination system  44  and is generally at least 80 atm. During the pressurisation stage  106 , the controller controls the brake assembly to gradually increase the pressure of the seawater within the enclosure  58  and thereby increasing the operating pressure. Once the operating pressure reaches the reference pressure, the brake assembly is fully activated to prevent the plunger  56  from moving further towards the base  30  of the chamber  24 . 
     Upon completion of the pressurisation stage  106 , the controller proceeds with the supply stage  108 . The pressurised seawater is supplied to the desalination system  44  in the supply stage  108  by the controller positioning the outlet valve  54  to the open position. When the pressurised seawater is being provided from the vessel  22  to the desalination system  44 , the operating pressure of the seawater starts to decrease. During the supply stage  108 , the operating pressure is maintained at the reference pressure by controlling the rate at which the plunger  56  moves towards the base  30  of the chamber  24 , via operating the brake assembly of the electric motor  68 . 
     The supply stage  108 , is completed once the seawater within the enclosure  58  is substantially depleted. The controller responds to the completion of the supply stage  108  by re-initiating the preparatory stage  102 . In the preparatory stage  102 , both the inlet valve  48  and the outlet valve  54  are positioned to the closed position. The controller then moves the plunger  56  towards the opening  32  of the chamber  24 . 
     Once the preparatory stage  102 , is completed, the inlet valve  48  is positioned to the open position in the intake stage  104 . The pressure gradient between the water source  38  and the chamber  24  draws water from the water source  38  into the chamber  24  and thereby replenishing the enclosure  58  with seawater. The pressurisation process  100  is cyclically reiterated in accordance to requirements by the desalination system  44  for pressurised seawater. 
     The pressurisation system  20  further includes a generator (not shown) disposed along the outlet conduit  52  adjacent to the outlet valve  54 . The generator utilises a turbine array for converting the kinetic energy of the flowing pressurised seawater through the outlet conduit  52  towards the desalination system  44  during the supply stage  108 , into kinetic energy of the turbine array. The generator then converts this form of kinetic energy of the turbine array into electrical energy that is stored and reused by the pressurisation system, for example, the positioning device  60 . 
     A second embodiment of the invention, a pressurisation system  20   b  as seen in  FIG. 3 , which shows a system representation of the pressurisation system  20   b , comprises of four main elements, each of which consists of a vessel  22 , a chamber  24 , a plunger  56  and a positioning device  60 . The descriptions in relation to the structural configurations of and positional relationships among the vessel  22 , the chamber  24 , the plunger  56  and the positioning device  60  with reference to  FIG. 1  are incorporated herein. 
     The pressurisation system  20   b  comprises a plurality of vessels  22 . An inlet conduit  36  extends from a water source  38  to an inlet  34  of each vessel  22 , with the plurality of vessels  22  drawing seawater from one water source  38 . An outlet conduit  52  extends from an outlet  50  of each vessel  22  to a desalination system  44 . Both the inlet conduit  36  and the outlet conduit  52  are in fluid communication with a chamber  24  of each vessel  22 . The positional relationship between the vessel  22  and the water source  38  of  FIG. 1  is incorporated herein for each of the plurality of vessels  22 . 
     In accordance with the first embodiment, the pressurisation process  100  is also incorporated herein. However, the progress of the pressurisation process  100  for one vessel  22  lags the progress of the pressurisation process  100  for another vessel  22 . For example, when a first vessel  22  is in a preparatory stage  102  with reference to  FIG. 2 , a second vessel  22  will be in an intake stage  104 , a third vessel  22  will be in a pressurisation stage  106 , and a fourth vessel  22  will be in a supply stage  108 . This is to ensure that at any one time, one vessel  22  is in the supply stage  108 , for supplying pressurised seawater to the desalination system  44 . 
     An inlet valve  48 , an outlet valve  54  and a positioning device  60  of each vessel  22  is electrically connected to a controller to coordinate and control the pressurisation process  100  of each vessel and to ensure that the desalination system  44  is continuously supplied with pressurised seawater. 
     The pressurisation system  20 / 20   b  described in this section utilises two embodiments of the invention to illustrate how the disadvantages of conventional pressure pumps are addressed. Although only two embodiments of the invention are disclosed, numerous modifications can be made to the embodiment without departing from the scope and spirit of the invention.