WO2011064252A1 - Régulation des conditions de pression dans des systèmes osmotiques - Google Patents

Régulation des conditions de pression dans des systèmes osmotiques Download PDF

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Publication number
WO2011064252A1
WO2011064252A1 PCT/EP2010/068121 EP2010068121W WO2011064252A1 WO 2011064252 A1 WO2011064252 A1 WO 2011064252A1 EP 2010068121 W EP2010068121 W EP 2010068121W WO 2011064252 A1 WO2011064252 A1 WO 2011064252A1
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Prior art keywords
pressure
draw
side compartment
solution
draw side
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PCT/EP2010/068121
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English (en)
Inventor
Stein Erik Skilhagen
Geir Magnar Brekke
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Statkraft Development As
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Priority to EP10782281A priority Critical patent/EP2504080A1/fr
Publication of WO2011064252A1 publication Critical patent/WO2011064252A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/002—Forward osmosis or direct osmosis
    • B01D61/0022—Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/002—Forward osmosis or direct osmosis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/06—Specific process operations in the permeate stream

Definitions

  • the present invention relates to controlling the pressure in osmotic systems.
  • Osmosis may also be used in other industrial applications, where the processes of forward osmosis (FO), also referred to as direct osmosis (DO), and reverse osmosis (RO) are relevant.
  • FO forward osmosis
  • DO direct osmosis
  • RO reverse osmosis
  • FO the mass flow across a semi-permeable membrane is occurring naturally only due to the difference in osmotic pressure between each side of the membrane.
  • reverse osmosis pressure is applied to force the solvent through the membrane.
  • pressure retarded osmosis pressure is applied to the solution with high solute concentration to optimize conditions for the osmotic processes.
  • GB 1 343 891 describes an osmotic power plant and a process optimized for extracting the maximum amount of osmotic potential in a volume of solvent (fluid with small molecular concentration) and solution (fluid with large molecular concentration).
  • the osmotic process are operated in cycles; osmotic flow of solvent over the membrane is continued until it stops due to the pressure being build up is equal to the osmotic pressure.
  • the pressure can be stored as potential energy or released for energy production, whereafter the flow of solvent over the membrane will start again to initiate a new cycle of pressure build up.
  • the osmotic pressure will decrease and the cycles will become shorter. At this point, additional solute can be introduced into the solution.
  • WO 2007/134226 describes a plant capable of both desalination and power production.
  • the amount of flow of mixed solution from the membrane chamber that is directed to the hydroturbine is indirectly controlled by controlling the flow rate of sea water into the membrane chamber using a booster pump.
  • the system is considered to be essentially self- controlling when a efficient rotary pressure transfer device is used. It is a drawback of WO 2007/134226 that control of a booster pump to supply a defined flow rate of seawater into the membrane chamber will control the remainder amount of flow directed to the hydroturbine. This is disadvantageous as it involves operating a booster pump at different speeds, and since it provides only an indirect control of the power yield.
  • a disadvantage with systems using FO or PRO is related to the need for a precise control of the pressure in the draw solution (the most concentrated solution) to ensure optimum conditions for FO or PRO.
  • an improved control of the pressure in the draw solution would be advantageous, and in particular a faster way of regulating the pressure of the draw solution would be advantageous to ensure an optimal energy output from an osmotic system during non-steady state conditions.
  • a pressure exchanger for transferring pressure in the draw side compartment from a second outlet to an inlet of the draw side compartment, the pressure exchanger ensuring mass balance between draw solution received by the inlet and mixed solution leaving the draw side compartment through the second outlet;
  • compartment to maintain pressure conditions for PRO by regulation of the volume of mixed solution entering the pressure conversion means from the first outlet through adjustment of an opening degree of the adjustable flow control means in response to a signal from the first pressure sensor .
  • the invention provides a method for regulating pressure conditions in an osmotic system comprising a semi-permeable membrane separating a feed side compartment holding a feed solution and a draw side compartment holding a draw solution, pressure conversion means in fluid communication with a first outlet of the draw side compartment for converting pressure generated in the draw side compartment by pressure retarded osmosis (PRO), preferably of solvent from the feed side compartment into energy, and a pressure exchanger for transferring pressure in the draw side compartment from a second outlet to an inlet of the draw side compartment, the method comprising regulating pressure in the draw side compartment to maintain pressure conditions for PRO by adjusting an opening degree of flow control means controlling a volume of mixed solution entering the pressure conversion means from the draw side compartment in response to input relating to a pressure in the draw side compartment from a first pressure sensor placed therein.
  • PRO pressure retarded osmosis
  • the present invention provides the advantage of providing a fast and energy efficient regulation of pressure conditions.
  • the pressure conditions preferably correspond to a predefined optimized pressure corresponding to optimized operation of the osmotic system. It is important to understand that osmotic systems are very complex, and that the conditions determining such predefined optimized pressure can change continuously or abruptly due to factors internal or external of the system. Examples may be internal factors such as fouling of the membrane and external factors such as changes in the feed or draw solution availability. Such changes will result in that the pressure conditions corresponding to optimized operation will change, and that fast regulation is advantageous for maintaining optimized operation also after the change.
  • the regulation according to the invention is fast because the regulation is made in response to a sensed pressure which is immediately affected by changes in flux over the membrane.
  • the regulation according to the invention is energy efficient because the efficiency of the osmosis (i.e. the flux) is affected by the pressure, so that by regulating the amount of mixed solution to the pressure conversion means in response to the pressure (the cause) instead of the flux (the effect) renders it possible to maintain predefined (e.g. optimum) PRO or FO pressure conditions during fluctuations in the operation conditions.
  • predefined e.g. optimum
  • osmosis is to be understood as PRO and/or FO unless otherwise specified.
  • the feed and draw side compartments designate fluid systems on each side of the membrane. These comprise both piping and sub-compartments which can be separated by valves, faucets, or similar.
  • the fluid system is limited at the entrance to the pressure exchanging means and at the exits to the flow control means of the pressure converting means and
  • the semi-permeable membrane is a membrane that will allow certain molecules or ions to pass through it by diffusion, depending on the size, solubility, properties, or chemistry of the molecules or ions.
  • the semi-permeable membrane designates the entire membrane in contact with the fluid systems, typically comprising a plurality of smaller pieces of semi-permeable membrane in arranged in membrane modules.
  • An example of an applicable semi-permeable membrane is a flat sheet cellulose acetate membrane.
  • a membrane module is a compartment divided into separate feed and draw side sub-compartments by a semi-permeable membrane, the feed and draw side sub- compartments having inlets for influx of feed and draw solution, respectively.
  • the draw side sub-compartment also comprises an outlet for outflow of solution, the inlet and outlet being arranged so that solution adjacent to the semi-permeable membrane in the draw side sub-compartment is continuously replaced by flow of draw solution into the membrane module.
  • a plurality of membrane modules are combined so that their respective feed and draw side sub-compartments form at least part of the feed and draw side compartments of the plant.
  • the feed and draw solutions are any solutions that, when separated by the semipermeable membrane, will result in diffusion of solvent from the feed solution to the draw solution via osmosis. Where feed solution diffuses through the membrane, a mixture of feed and draw solution will be formed in the draw side compartment. This mixture is referred to as mixed solution or simply solution.
  • the draw solution is a solution of high solute concentration, for example, but not limited to, a solution of inorganic or organic salts in water or any other electrolytic solution.
  • Typical draw solutions may contain ions naturally occurring in seawater such as Chloride (CI " ), Sodium (Na + ), Sulfate (S0 4 2 ⁇ ), Magnesium (Mg 2+ ), Calcium (Ca 2+ ), Potassium (K + ), Bicarbonate (HC0 3 " ), Bromide (Br " ), Iodine ( ⁇ ), Borate (B0 3 3” ), or Strontium (Sr 2+ ).
  • common salt-forming cations comprising Ammonium (NH 4
  • Draw solution is also sometimes referred to as the hypertonic solution.
  • the feed solution is a solution with lower overall solute concentration than the draw solution. It may be that the feed solution for some single solutes has a higher concentration than the draw solution (referred to as a partial concentration when only looking at the concentration of some solutes in the solutions). But overall, taking into consideration the molar concentration of all solutes in the feed and draw solution, the feed solution has a smaller concentration. Feed solution is also sometimes referred to as the hypotonic solution.
  • the adjustable flow control means for controlling volume entering the pressure conversion means comprise all possible ways of limiting, controlling or adjusting a liquid flow such as valves, nozzles, jets, vanes, etc.
  • Pressure conversion means is any type of device that will transform hydraulic pressure to another type of energy, such as kinetic energy, electric potential, potential energy, internal energy (e.g. thermal, chemical or latent energy), etc.
  • the pressure conversion means can comprise any number of separate units which in unity enables conversion of energy.
  • the flow control means may be a nozzle generating a flowing solution from the pressurized solution, converting the pressure (potential energy) into kinetic energy.
  • the pressure conversion means may then further comprise a turbine transforming the flowing solution into mechanical rotation (linear kinetic energy into rotational kinetic energy), and finally a generator transforming rotational kinetic energy into alternating electrical potential.
  • Pressure conversion means may also provide other functions and is not limited to converting energy.
  • Pressure retarded osmosis is osmosis through a semi-permeable membrane separating a feed and a draw solution, where the draw solution is subdued to a pressure load relative to the feed solution which is larger than zero.
  • Forward or direct osmosis is osmosis where the pressure difference between the draw and feed solution is zero or at least substantially zero, such as small in relation to the absolute pressure in the draw solution.
  • Pi is the draw solution pressure
  • P 2 is the feed solution pressure
  • Pressure of a liquid is sometimes also referred to as water potential or pressure potential designating the potential energy of the solution relative to the surroundings.
  • Pressure sensors are sensors capable of extracting information on the pressure in a liquid. Pressure sensors can directly measure the pressure in a liquid or indirectly measure the pressure of a liquid by directly measuring some property of an adjacent material such as a thin wall in contact with the liquid etc. Numerous types of applicable pressure sensors are known by the person skilled in the art.
  • the pressure will typically vary depending on position in the draw compartment.
  • the first pressure sensor for measuring Pi is placed in the draw side compartment between the semi-permeable membrane and the flow control means, such as preferably immediately before the flow control means.
  • the pressure in the feed side compartment is kept approximately constant, in which case Pi is proportional to the differential pressure, ⁇ .
  • the regulation of the draw side pressure can occur solely by input of Pi.
  • the flow control means is operated in response to the differential pressure, ⁇ , in front of and behind the semi-permeable membrane in the feed and draw side compartments, respectively, using signals Pi and P 2 from the first pressure sensor and a second pressure sensor placed in the feed side
  • the term 'working pressure' is used to refer to the actual pressure conditions in the plant, i or ⁇ , as these may often be used interchangeably.
  • the term 'predefined pressure' is used to designate the value of Pi, ⁇ , or similar that the regulation of pressure seeks to achieve.
  • the draw solution pressure is preferably regulated to establish or maintain pressure conditions for PRO or FO, i.e. so that 0 ⁇ ⁇ ⁇ Posmo t io where P OS mo t ic is the osmotic pressure in the specific set-up.
  • the regulation of pressure in the draw side compartment, or the operation of the flow control means may be carried out manually by an operator, mechanically by a mechanical or electrical connection between the first pressure sensor and the flow control means (here it is understood that 'signal' may also be a mechanical connection), or electronically by an electronic processor such as computer or a computer system.
  • the osmotic system comprises a pressure regulation unit for regulating working pressure in the draw side compartment by operation of the flow control means.
  • the pressure regulation unit may comprise an electronic processor connected to receive at least signal from the first pressure sensor, and typically forms part of an overall control system for the osmotic system.
  • the pressure regulation unit preferably involves a pressure regulation algorithm configured to generate an operation signal to the flow control means determined by the sensed working pressure and the set desired pressure.
  • the algorithm may perform proportional-integral-differential (PID) regulation of the opening degree of the needle valve, which ensures a fast and precise control of the pressure conditions.
  • PID proportional-integral-differential
  • the PID algorithm can be optimized to resist large fluctuations in working pressure, to do fast regulation on small fluctuations etc., depending on the special needs for a specific plant.
  • the pressure regulation algorithm may also involve utilization of modeled or planned changes in
  • the pressure regulation unit may be manually controlled by an operator entering a desired pressure to be steered after or feeding parameter values manually to the pressure regulation algorithm.
  • the flow control means after start-up and establishment of stable pressure conditions for PRO or FO of the osmotic system, is operated to regulate pressure in the draw side compartment to maintain pressure conditions for PRO or FO by:
  • the regulating of pressure conditions further comprises:
  • the three regulations described above may constitute examples of pressure regulation algorithms as used by a pressure regulation unit described previously.
  • the osmotic system is an osmotic power plant operating by PRO.
  • pressure conditions for PRO designates operation under fulfilling 0 ⁇ ⁇ ⁇ P OS mo t ic-
  • the optimal pressure conditions are preferably those leading to the largest possible power yield.
  • the power yield obtainable from the pressurized mixed solution is proportional to the volume of mixed solution entering the draw side compartment (i.e. the flux of feed solution solute over the membrane) and to the pressure build-up created by this flux. The more liquid and the higher its pressure build-up, the larger power yield.
  • the power yield (W) may therefore be expressed as proportional to a product of the flux (F) over the membrane and the draw-side pressure build-up (Pi) created by this flux, W ⁇ F- ⁇ .
  • flux and draw-side pressure is also related.
  • a situation with a first salt concentration in the draw solution represented by osmotic pressure OP1 and optimal pressure PI corresponding to optimum power production is illustrated by the full curve 81.
  • the draw side pressure may be regulated to PI to have pressure conditions with higest power yield.
  • the stipled curve 82 shows a situation where the draw solution concentration has been lowered, which leads to that the osmotic pressure (OP2) as well as the optimum pressure (P2) is shifted towards the left. Accordingly, it will be necessary to regulate the actual pressure down to maintain pressure conditions with higest power yield. If instead the supply of one of the fliuds is restricted, a simular change in situation would occur in that the flow would then be reduced.
  • Curves 83 and 84 show the flow trough the membrane at different pressures, wherecurve 83 is related to curve 81 and curve 84 is related to curve 82. A reduction in the flow would also make a regulation ofthe pressure necessary to maintain an optimum power production.
  • the power yield may be controlled directly by controlling the working pressure on the draw side compartment.
  • the power yield is indirectly controlled by controlling the flow of sea water into the membrane chamber.
  • the flow of draw fluid is controlled. This makes it difficult/impossible to adjust the optimal pressure and thereby the power production based on other parameters than the flow. Examples may be concentration variations in the draw solution, changes in membrane performance, temperature changes, membrane fouling, limitations in available fluid, etc.
  • the flow control means is operated to regulate pressure in the draw side compartment to establish or maintain a predefined pressure in the draw side compartment.
  • the predefined pressure may preferably correspond to pressure conditions ⁇ £
  • an expression of power yield as a function of pressure conditions, and possibly also as a function of time is determined empirically for the osmotic power plant or for specific parameters of an osmotic power plant, such as membrane type.
  • the flow control means preferably being operated to regulate pressure in the draw side compartment to establish or maintain a predefined pressure corresponding to maximum power yield as determined from such expression.
  • the pressure regulation algorithm of the pressure regulation unit is configured to receive an input related to the feed solution availability and: in case of a decrease in the availability, increase the desired pressure; and in case of an increase in the availability, decrease the desired pressure. Based on the newly set desired pressure and the sensed working pressure, the algorithm causes the pressure regulation unit to adjust the flow control means accordingly. Such adjustment will ensure a that flux of feed solution over the membrane is reduced in case of lower feed solution availability, while the power yield is kept high.
  • the flow of mixed solution entering the pressure conversion means is adjusted, using the flow control means, to at least
  • the flow control means is operated in response to a pressure in the draw compartment and not in reponse to a determination or estimation of the flow over the membrane.
  • the pressure at which the condition is fulfilled may be estimated so that it can be used to control the flow control means. It may be estimated by the module characteristics (determined before the modules are insertes into the plant) such as the response to salt concentration, temperature and cross flow consitions on both sides. During power production the pressure might then be changed depending on the above parameters so that the flow of mixed solution entering the pressure conversion means correspond to the flow, F OS mosis, of feed solution over the semi-permeable membrane which will in this case give optimal pressure conditions and thus power yield.
  • the pressure is preferably built up by osmosis during start-up.
  • the draw-side compartment is filled with draw solution and a flow through the compartment is generated from an inlet, past the semi-permeable membrane to the first outlet connected to the pressure conversion means and/or a second outlet for discharging solution.
  • the feed-side compartment is filled with feed solution. Permeation of feed solution through the membrane caused by osmosis will initiate irrespective of the pressure on the draw-side (as long as the pressure is not larger than osmotic pressure), and this will build up pressure in the draw side compartment.
  • the flow control means are preferably operated to regulate pressure in the draw side compartment to establish pressure conditions for PRO by:
  • the osmotic power plant preferably further comprises one or more of:
  • ⁇ means for generating a flow of draw solution through the draw side
  • ⁇ means for generating a flow of feed solution through the feed side
  • the means for generating a flow is provided by a draw solution supply pump in connection with an inlet of the draw side compartment for providing draw solution to the draw side compartment in a continuous manner, the semi-permeable membrane being arranged so that solution in front of the semi-permeable membrane in the draw side compartment is continuously replaced by the flow generated by the draw solution supply pump.
  • Figure 1 describes an exemplary PRO plant serving to describing the preferred features of the invention relating to the regulation of pressure and flow.
  • fresh water as well as sea water is fed into separate water filters prior to the streams are passing by one another on each side of a semi-permeable membrane.
  • a portion of the mixture of permeate and salt water with elevated pressure is passed to a turbine for the production of electric power.
  • the balance of the permeate stream is passed to a pressure exchanger where incoming sea water is pressurized. The pressurized sea water is then fed into the membrane module.
  • Figure 2 shows an enlarged portion of Figure 1, with further details and data flows related to the pressure regulation unit 26.
  • Figure 3 is an embodiment according to the invention, where the pressure conversion means is a long tube reaching into a water tower. The osmotic pressure from the osmotic membrane module is converted to potential energy of the fluid. The potential energy of the liquid can then subsequently be utilized for convenient purposes.
  • Figure 4 is an embodiment according to the invention, where the pressure conversion means comprises a pressure exchanger.
  • the osmotic pressure from the osmotic membrane module is converted to potential energy of a second fluid.
  • the potential energy can in this embodiment be stored in a different liquid such as drinking water.
  • Figure 5 is a schematic drawing with emphasis on the extent of the draw side compartment and the feed side compartment.
  • Figure 6 is a graph 80 of the power yield W as a function of pressure ( ⁇ ) and flow (F).
  • Adjustable flow control means 20.
  • One embodiment of the present invention is an osmotic power plant using the difference in salinity between seawater (draw solution) and freshwater (feed solution) to produce electrical energy by a turbine.
  • a prototype example of such a 30 plant which is to be opened in Tofte, Norway, will be described in detail below with reference to Figure 1.
  • the osmotic power plant 19 utilizes a semi-permeable membrane 2 separating the seawater 3 from the freshwater 4 to create energy.
  • the feed side compartment 41 comprises the fluid system below the membrane 2 in Figure 1, and the draw side compartment 31 comprises the fluid system above the membrane 2.
  • Incoming fresh- and seawater is filtered through automatic filters 24 and 25 of 50 pm mesh size or smaller.
  • the seawater 3 is pumped onto the filter using a seawater supply pump 10.
  • a seawater supply tank 13 is acting as buffer by accumulating the filtered seawater so the supply for the pressure exchanger and following process steps can be steady and furthermore to give sufficient volume to smoothen out differences in pump capacity.
  • the seawater supply tank has a volume of 1.4 m 3 i.e. 1 minute retention time at water flow of 20 l/s.
  • the freshwater supply has the same arrangement with a freshwater supply tank 14, filter 25, and, if necessary, a freshwater supply pump 11 on its inlet side if it is not possible to place the membrane modules below the water surface, typically a river or a lake.
  • a further use of these buffer tanks can be to enable to run continuously on the supply pumps during cleaning of the osmotic membrane module 1. If the plant stops running or if parts of the membrane area are sealed off during cleaning, but the rest of the membrane area continues to be utilized. No flow or flow through a limited membrane area would therefore require limited flow to the membrane module, which can be accommodated by pumping less water into the system. However since the supply pumps are optimized to a certain flow it is more energy efficient to let the water level build up in the buffer tank and keep the supply pumps running on optimum flow.
  • Extra measures can be taken to filter the incoming water by placing further filtering means upstream of the osmotic membrane module such as nanofiltering devices. Recurrent chlorination of the membrane can help to avoid fouling i.e. that the membrane gets clogged up with particles or other impurities in the water.
  • Chlorine is oxidizing natural organic material (NOM) clogged up in the membrane, and the NOM can after chlorination more easily be removed. No exact number for the frequency of chlorination can be given, but in a plant dimensioned similar to this one, the experience is that 2 times a day is appropriate using a solution of 5- 10 ppm chlorine.
  • the volume of freshwater 4 through the membrane 2 is determined by the membrane characteristics. Given a working pressure of the draw solution 3, determined by the pressure conversion means 7 and the temperature of the solution, the volume of freshwater through the osmotic membrane module 1 (or flux, I /m 2 xh) is determined by the membrane characteristics. The water surface of the freshwater supply tank is higher than the membrane modules and the freshwater 4 will therefore flow towards the membrane due to gravity. Osmosis will draw the freshwater 4 through the membrane to the seawater 3 on the other side of the membrane 2.
  • the volume of freshwater not entering the membrane is called the feed solution concentrate 42, and this volume is preferably in the vicinity of 25% of the incoming feed solution 4, which is controlled by an adjustable nozzle 12.
  • the freshwater 4 is pumped into the feed side compartment 41 from the freshwater supply tank 14/filter 25 by the pump 11, which seeks to keep the pressure constant.
  • the pump may be placed on either side of the freshwater supply tank 14/filter 25 and starts when the freshwater concentrate 42 volume exceeds a certain level and stops when it goes below the certain level.
  • a flow of 10 l/s of freshwater and 20 l/s seawater is needed.
  • the volume of the freshwater through the membrane is controlled by the pressure difference over the membrane, which is controlled by the pressure conversion means 7 connected to a first outlet 21 of the draw side compartment, more specifically by the flow control means 20 controlling the volume of mixed solution (brackish water 32) that enters a turbine 6.
  • the pressure is in the vicinity of 12 bars.
  • the optimal pressure conditions are established for ⁇ ⁇ Vi Posmotic / and for typical fresh-saltwater systems P OS motic ⁇ 26 bar.
  • the feed solution pressure is close to 1 bar, so that the draw solution pressure, also referred to as the working pressure, is around 12-14 bar.
  • the working pressure determines the efficiency of the PRO, and thereby the flow of freshwater through the membrane.
  • Applicable volume of freshwater may be restricted by water level e.g . in a river. Typically the volume of needed fresh water will be much less than the accessible amount so the plant always is able work on the maximum possible load .
  • Pressure exchanging means 5 is provided for transferring pressure from the second outlet 22 to the inlet 23 of the draw side compartment in order to pressurize the saltwater.
  • a pressure increasing pump 8 can be provided and dimensioned so as to accommodate the pressure difference between the second outlet 22 and the inlet 23, i .e. the loss in the pressure exchanger.
  • There is mass-balance in the pressure exchanger so that the flow of brackish water at outlet 22 is equal to the flow of seawater at the inlet 23, here
  • the pressure increasing pump 8 is steered according to a flow measurement, e.g. before the second outlet of the draw side, and determines how efficiently the membrane is utilized . With the right flow, the membrane will be less clogged and concentration gradient better etc. During normal operation salts, particles, etc. tend to get consentrated in the membrane area of the feed side, and on the draw side a decrase in salt concentration may occure unless the fluids flow with a certain speed and thus reduce the concentration polarization .
  • the pressure exchanging means 5 is a purely mechanical component ensuring energy transfer from the low pressure seawater 3 to the high pressure brackish water 32.
  • the pressure exchanging means 5 comprise a rotating cylinder with a number of cylindrical channels connecting the seawater side 51 of the pressure exchanging means with the brackish water side 52. The energy transfer is conducted like this:
  • the water pushes out brackish water with a lower pressure (LP out) which leaves the pressure exchanger.
  • LP out lower pressure
  • the difference in pressure between the LP in and LP out depends on the characteristic of the pressure exchanger and is a function of water volume through the pressure exchanger. Increasing volume results in increasing difference in pressure.
  • the pressure increasing pump 8 receives seawater 3 from the pressure
  • the exchanging means 5 after the seawater 3 has been pressurized in the pressure exchanging means 5 by the outgoing brackish water 32.
  • a normal working pressure on the seawater side of the membrane is 12 bar.
  • the pressure exchanging means the seawater only has a pressure of 11.5 bar and the pressure increasing pump then further pressurizes the seawater to the aimed pressure e.g. 12 bar.
  • the value from a first pressure sensor in the draw side compartment is used for monitoring the draw side working pressure, P i7 of the brackish water.
  • Reference numerals 9a, 9b and 9c indicate different possible positions of the first pressure sensor.
  • the pressure signal from this is used for regulating the pressure in the draw side compartment in accordance with the invention.
  • the feed pressure is preferably held approximately constant.
  • the pressure Pi from the first pressure sensor in the draw side compartment is most often also proportional to the differential pressure ⁇ over the membrane.
  • the system also comprises a pressure sensor 15 in the feed side compartment for measuring a feed side pressure, P 2 .
  • the task of the pressure conversion means 7 is to transform hydraulic pressure produced in the membrane to electrical energy, and furthermore to regulate the pressure on the seawater side of the membrane.
  • the pressure conversion means 7 is equipped with adjustable flow control means 20, in this embodiment comprising a needle valve or a nozzle on the intake of a hydroelectric turbine or Pelton device 6, which functions as a pressure regulator on the seawater side of the membrane.
  • the flow control means 20 and the turbine 6 are combined into one unit, e.g . a turbine with adjustable blades which can be used to regulate the flow therethrough (turbine turning or standing still) .
  • a certain opening degree of the flow control means 20 corresponds to a certain volume of brackish water 32 entering the turbine 6, which again corresponds to a certain change in the draw side working pressure as well as a certain effect produced by the turbine.
  • high water volume through the turbine corresponds to a high water volume through the membrane, when the pressure is kept constant.
  • a pressure regulation unit 26 operates the flow control means 20, so as to determine the flow to the turbine and to regulate the draw side pressure. The operation of the pressure regulation unit 26 is described in more detail in relation to Figure 2.
  • the pressure regulation unit 26 is preferably a computer or part of a computer system, typically forming part of an overall control system of the plant.
  • the pressure regulation unit 26 thereby involves an electronic processor 27, such as CPU, and memory 28 used to store data and software applications to be executed bu the processor 27.
  • the pressure regulation unit holds a preset desired pressure and receives the sensed working pressure 53 from at least a pressure sensor on the draw side.
  • a pressure control software application which can be stored in the memory 28 is used to control the flow control means with the object of regulating the working pressure towards the preset desired pressure.
  • This can involve a pressure regulation algorithm to generate an operation signal 56 to the flow control means 20 to regulate, adjust or set the opening degree of this.
  • the pressure regulation algorithm can comprise a regulation sub-algorithm such as proportional-integral-differential (PID) regulation.
  • PID proportional-integral-differential
  • the desired pressure towards which the working pressure is regulated, can be determined and preset in different ways. It may be entered manually (e.g . via keyboard) by an operator, which can be advantageous when unusual or highly fluctuating pressure conditions are present. During normal operation, the pressure conditions are influenced by a large number of internal and external parameters and restrictions (54, 55) as described previously. This means that the desired pressure is subject to frequent change, and based on the relevant input (54, 55), the pressure control software application of the pressure regulation unit 26 can determine the desired pressure from a table or formula, typically developed during previous extensive testing and calibration of the plant. It should be noted that the absolute values depends to a large degree of the detailed layout of the individual plant, as well as the characteristics of the sensed pressure to which it is compared (if it is Pi or ⁇ and where in the system it is measured).
  • the pressure control software application can also comprise the possibility of adjusting the desired pressure based on planned or anticipated changes in the pressure conditions. Start up procedure
  • the air in the system is evacuated.
  • the pressure increasing pump 8 starts to fill the draw side compartment; the pressure will not build up only using the pressure increasing pump 8. While filling the draw side compartment with seawater the cylinder of the pressure exchanger will start to rotate.
  • the adjustable valve 12 is opened to let freshwater 4 enter the feed side
  • needle valve 20 When a certain threshold pressure is reached, the needle valve 20 will open and the turbine 6 will start to generate power. Alternatively, needle valve 20 will be slightly open from the beginning (e.g. 10% or 20%), and will gradually be opened more and more as pressure builds up due to increased osmosis through membrane.
  • the working pressure of the process is controlled by the opening degree of the needle valve and by the characteristics of the membrane. After start up, the working pressure is regulated according to the invention pressure to be close to or equal to a predefined pressure for maintaining pressure conditions for PRO.
  • the membrane is delivered and installed in a plant, it is advantageous to use only the flow control means to control the working pressure of the process.
  • the needle valve and nozzle must at any time ensure that the working pressure on the seawater side of the membrane is at a predefined pressure point, measured by the pressure sensors 9a/9b.
  • the regulation of pressure by the needle valve is carried out by the pressure regulation unit using the difference between measured working pressure and the desired pressure to do a
  • PID proportional-integral-differential regulation of the opening degree of the needle valve, which ensures a fast and precise control of the pressure conditions.
  • the PID algorithm can be optimized to resist large fluctuations in pressure, to do fast regulation on small fluctuations etc. , depending on the special needs for a specific plant.
  • Osmotic power plants are very complex fluidic systems, and optimal or preferred working pressures is in general not known before the plant is operational, even though large efforts have been put into dimensioning the plant.
  • the osmotic pressure of the system may change over time which again changes the optimal working pressure. Therefore, the predefined pressure may not be known on beforehand, but may result from initial and /or regular empirical testing of different working pressures to determine working pressures or working pressure ranges which gives the largest power yield or which results in the largest product of the flux (F) over the membrane and the draw-side pressure build-up (P x ) created by the flux, F-Pi.
  • Optimal pressure conditions as a function of time after changing or cleaning of membranes may be determined, so that the predefined pressure may vary over time. The PID regulation of the needle valve 20 will ensure that the pressure is kept close or equal to the predetermined pressure during fluctuations of conditions.
  • FIG. 3 and 4 illustrates embodiments of osmotic power plants with alternative pressure converting means.
  • the power plant 19 is similar to the one described in relation to Figure 1 , except for the pressure converting means 7.
  • the pressure converting means 71 comprises flow control means 20 connected to piping or tubing 61 leading to a top tank 63 of a tower 62.
  • the top tank is elevated in relation to the first outlet 21 of the draw side compartment, the elevation being smaller than the absolute water potential at the first outlet 21.
  • the flow control means 20 can be a valve or nozzle, converting the pressure in the draw side compartment to linear kinetic energy by creating a flow of mixed solution 32 through piping 61. Upon arriving in top tank 63, the kinetic energy of the mixed solution is converted to potential energy.
  • the operation of the flow control means can be used to regulate the pressure in the draw side compartment to establish of maintain PRO pressure conditions in the plant 19.
  • the pressure converting means 72 comprises flow control means 20 and a pressure exchanger 64.
  • the pressure exchanger receives the pressurized mixed solution 32 and another liquid 66 from a tank 65 to transfer the hydraulic pressure from the mixed solution 32 to the liquid 66.
  • the mixed solution is thereafter discharged.
  • the pressurized liquid 66 can then be used in another process 67 requiring pressurized liquid. Examples could be applying pressure water to be distributed to households, such as drinking water or heated water, or liquids for used in industrial processes.
  • an osmotic system based on the forward osmosis principle is used for concentration of dilute, possibly pressurized industrial wastewater.
  • problems with dilute wastewaters containing heavy metals etc are well-known in modern society.
  • Osmotic systems can be used to concentrate dilute solutions of wastewater using forward osmosis.
  • the diluted wastewater is concentrated by entering the feed side compartment of the osmotic membrane module 1 of Figure 1.
  • An appropriate draw solution with a higher osmotic pressure than the dilute wastewater is supplied in the draw side compartment and pure water is extracted from the wastewater before it leaves the feed side compartment in concentrated form.
  • the membrane In order not to pollute the draw solution the membrane must be designed to match the specific pollutant.
  • pressure conditions may be adjusted to give PRO, possibly not optimized for power yield, but rather being a compromise between power yield and flux.
  • Another application could be within food processing, e.g. juice concentration.
  • FO has advantages over PRO in terms of the temperature of operation and the retention of sensory qualities of the products (e.g. taste, aroma etc). Therefore FO operation may be preferred in food processing.
  • pressure conditions for obtaining FO can in this embodiment be established by allowing the draw side pressure to build up by osmosis until ⁇ 0 is obtained. If none of the
  • FO pressure conditions are established as soon as the compartments are filled.
  • This increased pressure can be regulated according to the invention to maintain zero or near zero pressure difference and thereby maintain FO pressure conditions.
  • feed solution and draw solution could be others than fresh water and salt water.
  • Other examples may be solutions containing ammonium which can be artificially added to water to form a draw solution, and later removed from the mixed solution using precipitation reactions.
  • Other examples may be wastewater from industrial processes containing high solute concentrations, e.g. from washing of various materials and liquids. Especially interesting are solutions in industrial processes that nevertheless need to be diluted before being suitable for further use or discharge.

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  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

Cette invention concerne la régulation de la pression des solutions soutirées et/ou chargées dans des systèmes osmotiques tels que des centrales de production d'énergie osmotique. La régulation de pression selon l'invention exploite un nouveau principe qui permet la régulation très rapide et énergiquement performante des solutions sous pression dans les systèmes osmotiques. Selon l'invention, la régulation de la pression est gérée par une unité de régulation de pression qui administre la quantité de solution sortant du compartiment côté soutirage et/ou chargement. La régulation s'opère en fonction d'une pression de solution mesurée dans le compartiment d'où sort la solution. Les systèmes osmotiques selon l'invention peuvent fonctionner en mode Pression osmotique retardée (PRO) ou Osmose directe (FO ou DO).
PCT/EP2010/068121 2009-11-24 2010-11-24 Régulation des conditions de pression dans des systèmes osmotiques WO2011064252A1 (fr)

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NL2007353C2 (en) * 2011-09-05 2013-03-07 Kwr Water B V Solution comprising an osmotic agent and method of extracting water using said solution.
WO2013093537A1 (fr) * 2011-12-23 2013-06-27 Abb Technology Ltd Procédé et système pour surveiller et contrôler l'encrassement et son optimisation de procédé d'encrassement de membranes sur deux côtés
CN103835865A (zh) * 2012-11-20 2014-06-04 株式会社东芝 渗透压发电方法、渗透压产生器以及渗透压发电装置
JP2014526865A (ja) * 2011-09-07 2014-10-06 オズモブルー・エスアーエールエル 有用エネルギー発生装置および方法
CN105422399A (zh) * 2015-11-19 2016-03-23 浙江理工大学 超重力浓差发电装置及方法
DE102015200250A1 (de) * 2015-01-12 2016-07-14 Siemens Aktiengesellschaft Verfahren zum Betreiben eines Osmosekraftwerks und Osmosekraftwerk
EP3276170A4 (fr) * 2015-08-25 2018-09-05 Kyowakiden Industry Co., Ltd. Dispositif de commande pour appareils de production d'énergie
CN104503260B (zh) * 2014-12-05 2018-09-28 广东电网有限责任公司电力科学研究院 调速器参数设定方法及装置
WO2019027969A1 (fr) * 2017-07-31 2019-02-07 Oakland University Système de fluide
WO2020022218A1 (fr) * 2018-07-25 2020-01-30 東洋紡株式会社 Procédé de traitement par osmose directe et dispositif de traitement par osmose directe
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WO2013036111A1 (fr) * 2011-09-05 2013-03-14 Kwr Water B.V. Solution comprenant un agent osmotique et procédé d'extraction d'eau au moyen de ladite solution
NL2007353C2 (en) * 2011-09-05 2013-03-07 Kwr Water B V Solution comprising an osmotic agent and method of extracting water using said solution.
JP2014526865A (ja) * 2011-09-07 2014-10-06 オズモブルー・エスアーエールエル 有用エネルギー発生装置および方法
WO2013093537A1 (fr) * 2011-12-23 2013-06-27 Abb Technology Ltd Procédé et système pour surveiller et contrôler l'encrassement et son optimisation de procédé d'encrassement de membranes sur deux côtés
US9737858B2 (en) 2011-12-23 2017-08-22 Abb Schweiz Ag Method and a system for monitoring and control of fouling and optimization thereof of two side membrane fouling process
CN103835865A (zh) * 2012-11-20 2014-06-04 株式会社东芝 渗透压发电方法、渗透压产生器以及渗透压发电装置
CN104503260B (zh) * 2014-12-05 2018-09-28 广东电网有限责任公司电力科学研究院 调速器参数设定方法及装置
DE102015200250A1 (de) * 2015-01-12 2016-07-14 Siemens Aktiengesellschaft Verfahren zum Betreiben eines Osmosekraftwerks und Osmosekraftwerk
EP3276170A4 (fr) * 2015-08-25 2018-09-05 Kyowakiden Industry Co., Ltd. Dispositif de commande pour appareils de production d'énergie
CN105422399B (zh) * 2015-11-19 2018-01-05 浙江理工大学 超重力浓差发电装置及方法
CN105422399A (zh) * 2015-11-19 2016-03-23 浙江理工大学 超重力浓差发电装置及方法
WO2019027969A1 (fr) * 2017-07-31 2019-02-07 Oakland University Système de fluide
US11498030B2 (en) 2017-07-31 2022-11-15 Oakland University Fluid system
WO2020022218A1 (fr) * 2018-07-25 2020-01-30 東洋紡株式会社 Procédé de traitement par osmose directe et dispositif de traitement par osmose directe
WO2021185900A1 (fr) 2020-03-20 2021-09-23 Oliver Piestert Procédé de réalisation d'un travail par osmose
CN115491225A (zh) * 2021-06-17 2022-12-20 中国石油化工股份有限公司 重质润滑油基础油滤液中脱蜡溶剂的回收方法
CN115491225B (zh) * 2021-06-17 2024-03-26 中国石油化工股份有限公司 重质润滑油基础油滤液中脱蜡溶剂的回收方法

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