Patent Application
20140284929
The present invention relates to an apparatus in which low-concentration water having a low osmotic pressure and high-concentration water having a high osmotic pressure are brought into contact with each other through a semi-permeable membrane interposed therebetween and the resultant permeation flow due to forward osmosis phenomenon is utilized as energy to conduct hydroelectric power generation. The invention further relates to a method for operating the apparatus.
In recent years, various global environmental issues such as consumption of fossil fuels, depletion of resources, and increases in carbon dioxide emission have come to be actualized as a result of the economic growth of the world. Under such circumstances, novel carbon-free energy technologies including photovoltaic power generation, wind power generation, and temperature-difference power generation have been developed as energy production means and are coming to be put to practical use.
Among those technologies, the concentration-difference power generation, in particular, is a technology in which a difference in salt concentration between, for example, seawater and river water is taken out as energy, and is highly expected because this power generation utilizes natural energy sources that are substantially inexhaustible. Representative techniques for converting a difference in salt concentration into energy include concentration cells.
Furthermore, a pressure-retarded osmosis method, in which an osmotic pressure generated through a semi-permeable membrane is utilized, was proposed by Sidney Loeb as a technique for generating electricity by utilizing a concentration difference (S. Loeb, Journal of Membrane Science, Vol. 1, p. 49, 1976). When two solutions differing in salt concentration (i.e., low-concentration water and high-concentration water) are separated from each other by a semi-permeable membrane, water moves from the fresh-water side to the brine side by forward osmosis phenomenon. In the pressure-retarded osmosis method, this movement is utilized to operate a hydroelectric generator.
At the time when this technique was proposed, it was thought that the possibility of practical use thereof was low from the standpoint of cost performance including the performance of the semi-permeable membrane and the efficiency of the hydroelectric generator. Because of this, little investigation has been made on practical use of that technique. However, as a result of the recent increases in energy cost and the recent improvements in the performance of semi-permeable membranes and electric generators, the possibility of practically using the concentration-difference power generation employing the pressure-retarded osmosis method has come to be reconsidered. In Japan, an attempt to simultaneously conduct wastewater treatment and power generation while utilizing the concentrated discharge water from a seawater desalination plant is being made in Fukuoka Prefecture (Non-patent Document 1 and Patent Document 1).
In the pressure-retarded osmosis method, the larger the amount of water which moves from the fresh water to brine, the more the cost performance improves. However, since the difference in osmotic pressure in the method in which seawater and fresh water are utilized is exceedingly large, organic substances contained in the fresh water are pushed strongly against the surface of the semi-permeable membrane. As a result, there is a problem that the so-called fouling is apt to occur, in which the semi-permeable membrane is fouled to decrease in performance. In view of such a problem, a technique has been developed in which the pressure difference imposed on the semi-permeable membrane is controlled, while diminishing energy loss, by applying an energy recovery unit (Patent Document 2). With respect to such techniques, investigations for practical use thereof are accelerating, and performance demonstration plants designed for practical use were construed in Norway and have come to be operated.
However, the conventional techniques have the following problem.
The movement of a large amount of water from the low-concentration-water side to the high-concentration-water side results in a considerable decrease in the concentration of the high-concentration water. Consequently, even in one semi-permeable membrane unit in which high-concentration water is brought into contact with low-concentration water through a semi-permeable membrane, the high-concentration water has a large difference in concentration between the upstream side and the downstream side. A difference in the concentration of the high-concentration water causes a difference in osmotic pressure. Namely, in the vicinity of the inlet for high-concentration water (e.g., seawater) in a semi-permeable membrane unit, the difference in concentration between the fresh water and the seawater which are located on the surfaces of the semi-permeable membrane is large and, hence, a large forward-osmosis permeation flow per unit membrane area occurs. One the other hand, at the outlet for high-concentration water, the difference in concentration between the high-concentration water and the low-concentration water is decreased due to the fresh water which has already flowed in, resulting in a small forward-osmosis permeation flow.
Although an energy recovery unit can be used to control the pressure difference between high-concentration water and low-concentration water in a semi-permeable membrane unit, this configuration cannot accommodate such fluctuations in osmotic pressure which occur between the inlet and outlet for high-concentration water. As a result, those portions of the semi-permeable membrane through which a large permeation flow occurs are apt to be fouled, and there is a problem that attempts to inhibit the fouling result in a decrease in overall osmotic permeation amount and this in turn results in a decrease in power generation amount. There are cases where a high-concentration brine, such as a high-concentration discharge water obtained through seawater desalination or Dead Sea brine, is used for the purpose of utilizing a large concentration difference to highly efficiently generate electricity. However, the higher the concentration, the more the problem becomes severe. Consequently, it is difficult to attain stable high-efficiency power generation.
An object of the invention is to provide an apparatus in which low-concentration water having a low osmotic pressure and high-concentration water having a high osmotic pressure are brought into contact with each other through a semi-permeable membrane interposed therebetween and the permeation flow caused by forward osmosis phenomenon is utilized as energy to efficiently and stably conduct hydroelectric power generation, and is to provide a method for operating the apparatus.
In order to solve the above-mentioned problem, a concentration-difference power generation apparatus of the present invention is a concentration-difference power generation apparatus in which high-concentration water and low-concentration water which differ in their concentrations are brought into contact with each other through a semi-permeable membrane unit including a semi-permeable membrane, and a resultant increase in an amount of the high-concentration water due to permeation of water from a low-concentration side to a high-concentration side caused by a forward osmotic pressure is utilized to drive an electric generator to generate electricity, in which the semi-permeable membrane unit is divided into a plurality of subunits and includes a high-concentration-side intermediate channel and a low-concentration-side intermediate channel which connect the subunits, and the concentration-difference power generation apparatus includes a pressure change mechanism disposed on at least one of the high-concentration-side intermediate channel and the low-concentration-side intermediate channel.
According to the invention, it becomes possible to efficiently and stably conduct hydroelectric power generation by a technique in which low-concentration water having a low osmotic pressure and high-concentration water having a high osmotic pressure are brought into contact with each other through a semi-permeable membrane interposed therebetween and the permeation flow caused by forward osmosis phenomenon is utilized as energy.
Embodiments for carrying out the invention are explained below by reference to the drawings. However, the scope of the invention should not be construed as being limited to the following embodiments.
In each embodiment, configurations in the other embodiments can be applied to the configurations which are not especially mentioned. There are cases where with respect to each figure, constituent elements having like functions as in other figures are designated by the same signs and explanations thereof are omitted.
In the configurations shown in
Meanwhile, in the configurations shown in
In
In the following explanations, the terms “upstream” and “preceding stage” may be replaced with each other, and the term “downstream” and the term “subsequent-stage” or “next-stage” may be replaced with each other.
Furthermore, the terms “concentration-difference power generation apparatus” and “osmotic-pressure power generation apparatus” may be replaced with each other.
The concentration-difference power generation apparatus shown in
The concentration-difference power generation apparatus shown in
According to need, some of the devices and members shown in the figure may be omitted, and devices and members not shown in the figure, such as, for example, a booster pump, an intermediate tank, and a protection filter, may be additionally disposed.
As shown in
Furthermore, as shown in
The semi-permeable membrane unit 101 causes water movement from the low-concentration water to the high-concentration water by a difference in osmotic pressure between the high-concentration water and the low-concentration water. The semi-permeable membrane unit 101 is divided into a plurality of subunits. Specifically, the semi-permeable membrane unit 101 includes a first subunit 8, a second subunit 12, an intermediate channel L3 for low-concentration water, and an intermediate channel L4 for high-concentration water, the intermediate channels L3 and L4 connecting the first subunit 8 and the second subunit 12 to each other. Incidentally, the number of subunits, with which one semi-permeable membrane unit is equipped, is not limited to 2 and may be 3 or larger.
The first subunit 8 and the second subunit 12 include a semi-permeable membrane, a channel through which low-concentration water flows, and a channel through which high-concentration water flows, respectively.
The intermediate channel L3 for low-concentration water connects the low-concentration-side channel of the first subunit 8 and the low-concentration-side channel of the second subunit 12 to each other, while the intermediate channel L4 for high-concentration water connects the high-concentration-side channel of the first subunit 8 and the high-concentration-side channel of the second subunit 12 to each other.
The low-concentration water which has undergone the pretreatment first flows into the low-concentration-side channel of the first subunit 8. The high-concentration water pumped out from the booster pump 7 flows into the high-concentration-side channel of the first subunit 8. Thus, the low-concentration water and the high-concentration water come into contact with each other through the semi-permeable membrane. Due to this contact, water moves from the low-concentration-side channel to the high-concentration-side channel through the semi-permeable membrane on the basis of osmotic pressure. As a result, the flow rate of the low-concentration water as measured downstream from the first subunit 8 becomes lower than the flow rate thereof as measured upstream, while the flow rate of the high-concentration water as measured downstream from the first subunit 8 becomes higher than the flow rate thereof as measured upstream.
The low-concentration water, the amount of which has thus decreased, flows out from the first subunit 8 and is then supplied through the intermediate channel L3 for low-concentration water to the low-concentration-side channel of the second subunit 12. On the other hand, the high-concentration water, the amount of which has increased, flows out from the first subunit 8 and is then supplied through the intermediate channel L4 for high-concentration water to the high-concentration-side channel of the second subunit 12. In the second subunit 12, water moves from the low-concentration-side channel to the high-concentration-side channel as in the first subunit 8.
In this stage, the difference in concentration between the low-concentration water and the high-concentration water in the second subunit 12 is smaller than the difference in concentration between the low-concentration water and the high-concentration water in the first subunit 8. Namely, the permeation flux (i.e., permeation amount per membrane area) in the second subunit 12 is lower than the permeation flux in the first subunit 8.
However, in case where the difference in concentration between the low-concentration water and high-concentration water to be supplied to the first subunit 8 is increased in order to obtain a high permeation flux in the second subunit 12, the first subunit 8 comes to have an exceedingly high permeation flux. As a result, impurities contained in the low-concentration water are more apt to accumulate on the surface of the semi-permeable membrane and, hence, the resultant fouling is apt to reduce the performance of the semi-permeable membrane. Meanwhile, in case where the permeation flux in the first subunit 8 is regulated to a low value for the purpose of inhibiting the fouling in the first subunit, the second subunit 12 has an even lower permeation flux, making it difficult to obtain a high power generation efficiency.
The present inventors found that such problems can be overcome by disposing a pressure change mechanism in a channel between the subunits. The pressure change mechanism is a mechanism which causes a difference between the pressure on the upstream of the pressure change mechanism and the pressure on the downstream thereof.
As an example of the pressure change mechanism, a valve 11 is disposed on the intermediate channel L4 for high-concentration water, in the apparatus shown in
The high-concentration water is supplied from the second subunit 12 through the high-concentration discharge channel L6 to the hydroelectric generator 13 and is then discharged from the system. The hydroelectric generator 13 converts the pressure energy possessed by the high-concentration water into electric power.
On the other hand, the low-concentration water is discharged from the second subunit 12 through the low-concentration discharge channel L5.
As explained above, in the configuration shown in
The configuration of the hydroelectric generator 13 is not particularly limited, and examples of the hydroelectric generator 13 include a Francis turbine, propeller turbine, Pelton turbine, cross-flow turbine, and reverse pump. A configuration of the hydroelectric generator 13 is selected in accordance with flow rate, generated pressure, etc.
As shown in
Due to the intermediate energy recovery unit 16, the pressure of the high-concentration water located downstream from the intermediate energy recovery unit 16 is rendered lower than the pressure of the high-concentration water located upstream therefrom. Incidentally, even when the intermediate energy recovery unit 16 is disposed, the high-concentration water to be supplied to the second subunit 12 is made to still have a pressure suitable for the water. Preferred as the intermediate energy recovery unit 16 is, for example, a hydroelectric generator of the in-line type capable of maintaining a pressure as measured on the downstream side of the intermediate energy recovery unit 16 (i.e., a permeation-side pressure). Examples of such a hydroelectric generator include a Francis turbine and a propeller turbine.
As shown in
In any of the embodiments described in this description, the intermediate energy recovery unit 16 may be disposed above the second subunit 12. In this configuration, it is possible to use a Pelton turbine or the like to recover the pressure energy of the high-concentration water located at the outlet of the first subunit 8. Furthermore, an intermediate tank may be disposed after the intermediate energy recovery unit 16.
In another configuration for making the effective pressure difference between the subunits, a booster pump may be disposed on an intermediate channel for low-concentration water.
In the embodiment shown in
It is also possible to use an energy recovery unit such the isobaric type as pressure exchanger in place of the intermediate booster pump to utilize the pressure energy generated by the discharged water, on either the high-concentration side or the low-concentration side.
As shown in
Furthermore, as shown in
Moreover, as shown in
In
It is therefore preferred that the sectional-area ratio of the channel for high-concentration water to the channel for low-concentration water in the second subunit 12 should be larger than the sectional-area ratio of the channel for high-concentration water in the first subunit 8. This configuration can render that difference small.
Consequently, it is preferred that the channel sectional-area ratio of the channel for high-concentration water to the channel for low-concentration water in the second subunit 12 should be larger than the channel sectional-area ratio in the first subunit 8. Due to this configuration, the difference between the ratio of “(flow rate of high-concentration water)/(flow rate of low-concentration water)” in the second subunit 12 and the ratio of “(flow rate of high-concentration water)/(flow rate of low-concentration water)” in the first subunit 8 can be rendered small.
In the case, for example, where the semi-permeable membranes are hollow-fiber membranes and the hollow-fiber membranes packed in the first subunit and those packed in the second subunit have the same diameter, that configuration can be rendered possible by regulating the degree of packing with the hollow-fiber membranes in the second subunit 12 so as to differ from the degree of packing therewith in the first subunit 8. Namely, in the case where high-concentration water passes through the inside of the hollow-fiber membranes, the sectional-area ratio of the channel for high-concentration water in the second subunit 12 can be rendered large by making the degree of packing with the membranes in the second subunit 12 higher than the degree of packing with the membranes in the first subunit 8. In the case where high-concentration water passes outside the hollow-fiber membranes, the sectional-area ratio of the channel for high-concentration water in the second subunit 12 can be rendered large by making the degree of packing with the membranes in the second subunit 12 lower than the degree of packing with the membranes in the first subunit 8.
In the case where the semi-permeable membrane is the spiral type or the stacked type, the channel material may be configured so that the thickness thereof differs between the first subunit 8 and the second subunit 12.
Besides such changes in the structures of the first subunit 8 and second subunit 12, the following configurations can be used to obtain the same effect.
Namely, as shown in
A booster pump 18 and a valve 19 are disposed on the bypass channel L11 for low-concentration water. Although the booster pump 18 can be used, according to need, to impart a pressure to the low-concentration water being supplied to the second subunit 12, it is possible to omit the booster pump 18 depending on the pressure measured at the low-concentration-water outlet of the first subunit 8. By opening/closing the valve 19, the flow rate of the low-concentration water being supplied to the second subunit 12 can be controlled.
Furthermore, as shown in
Moreover, as shown in
Furthermore, as shown in
The concentration-difference power generation apparatus may include an energy recovery unit on the downstream side of each subunit, the energy recovery unit being disposed so as to boosts the pressure of the water to be supplied to the subunit or of the water to be supplied to a subunit disposed upstream from that subunit, while utilizing the pressure energy of the water which is flowing out from that subunit. Usable as this energy recovery unit are an isobaric (pressure exchange) type device and a turbocharger, which can eliminate the necessity of a pump and hence attain a high energy efficiency. Examples of such configuration are as explained below.
In the configurations shown in
In the configurations shown in
Furthermore, as illustrated in
In the embodiment shown in
In the embodiment shown in
In
In
On the other hand, the low-concentration water which has passed through a low-concentration-water intake pump 2 and a low-concentration pretreatment unit 3 is supplied to the first subunit 8. In the first subunit 8, water is moved from the low-concentration side to the high-concentration side by forward osmosis, and the low-concentration water is then supplied to the second subunit 12. In the second subunit 12 also, water moves from the low-concentration side to the high-concentration side as described above. The low-concentration water which has passed through the second subunit is discharged from the system.
In
Also in the case where low-concentration water and high-concentration water are supplied as countercurrent flows, the same bypass channel L11 as in
Furthermore, as shown in
Moreover, as shown in
It is a matter of course that those bypass channels each may be disposed at one position or at a plurality of positions. Also in the case of countercurrent supply, it is possible to boost the low-concentration-side pressure before the second subunit 12, besides lowering the high-concentration-side pressure before the second subunit 12, as in the case of parallel supply. The case where both are applied is illustrated in
In this description, the following should be noted. In countercurrent supply, although low-concentration water and high-concentration water flow between the subunits countercurrently with each other as described above, it is not essential that in each subunit, the low-concentration water and the high-concentration water flow countercurrently with each other. However, when low-concentration water and high-concentration water countercurrently flow also in each subunit, an even better balance of osmotic pressure is attained. This configuration is hence effective.
Suitable examples in which an energy recovery unit is applied in the countercurrent supply mode include, for example, the configuration shown in
This energy recovery device 23 preferably is an isobaric type device or a turbocharger. With these devices, energy can be directly recovered (namely, pressure of the high-concentration water can be directly boosted) without using a pump.
In this case, the high-concentration-side intermediate water 25 discharged from the energy recovery unit 23 frequently has a pressure close to the pressure possessed by the high-concentration water discharged from the second subunit 12, and pressure is applied to all of the high-pressure-side and low-pressure-side channels. Because of this, a device having suitable pressure resistance is used as the energy recovery unit.
Furthermore, an electric generator 13a may be disposed on the channel where the energy recovery unit 23 is disposed. In
Incidentally, in
The high-concentration-side intermediate water 25 from the energy recovery unit 23 can be utilized, for example, for boosting the pressure of high-concentration water as illustrated in
Cases where the semi-permeable membrane unit is configured of two subunits were explained above. However, the semi-permeable membrane unit may be configured of three or more subunits. When there is a large difference in concentration between low-concentration water and initial high-concentration water, a large amount of water permeates in the upstream subunit and, hence, a more even permeation flux can be rendered possible by increasing the number of subunits.
As shown in
The high-concentration water discharged from the first subunit 8 is supplied through an intermediate channel L4 for high-concentration water to the desalination unit 27. In the desalination unit 27, pressure energy is utilized to obtain desalinated water and concentrate. The concentrate is supplied as high-concentration water to the second subunit 12. In this embodiment, a desalinated-water tank 29 and a channel L7 extending from the desalination unit 27 to the desalinated-water tank 29 are further disposed. After supplied through the channel L7 and stored in the desalinated-water tank 29, the desalinated water may be utilized outside the system.
In the configuration shown in
The desalination unit 27 to be applied here may be any desalination unit which has suitable desalination performance. The suitable desalination performance may be such performance that in the case where the desalinated water obtained is to be utilized as low-concentration water, this desalinated water has a lower salt concentration than the high-concentration water that is to flow into the subunit to which this desalinated water is to be supplied. Specifically, use may be made of a method in which the configuration of the semi-permeable membrane and the conditions for operating the desalination unit are set so as to result in a salt rejection of 90% or higher, more preferably 95% or higher.
As described above, the semi-permeable membrane desalination unit 27 may be disposed on the intermediate channel L4 for high-concentration water as shown in
The configuration, size, etc. of each subunit are not limited to specific ones. For example, a separation device including a pressure vessel and a fluid separation element (separation element) disposed in the pressure vessel is applicable as the subunit. The fluid separation element includes a housing and a semi-permeable membrane packed in the housing, the membrane being in the form of either hollow-fiber membranes or a flat sheet membrane. When the semi-permeable membrane is a flat sheet membrane, the fluid separation element includes, for example, a multilayer structure formed by stacking the semi-permeable membrane and a channel material and with a cylindrical center pipe in which a large number of holes are formed in the wall thereof. In such a fluid separation element, the semi-permeable membrane and the channel material are attached to the periphery of the center pipe and may be either in a flat state or in the state of being wound around the center pipe.
As the material of the semi-permeable membrane, use may be made of a polymeric material such as a cellulose acetate-based polymer, polyamide, polyester, polyimide, vinyl polymer, or the like.
The semi-permeable membrane may be an asymmetric membrane which includes a dense layer constituting at least one of the surfaces thereof and which has fine pores, the diameter of which gradually increases from the dense layer toward the inner part of the membrane or toward the other surface, or may be a composite membrane including a dense layer which is an asymmetric membrane and, formed thereon, an exceedingly thin functional layer made of another material.
In the embodiments described above, the low-concentration water and the high-concentration water may be any aqueous solutions which, when in contact with each other through a semi-permeable membrane, cause a permeation flow due to a difference in osmotic pressure. Namely, the “term low-concentration water” generally means water having a relatively low salt concentration, while the term “high-concentration water” means water having a higher salt concentration than the low-concentration water. The salt concentrations of the low-concentration water and high-concentration water are not limited to specific values. However, larger differences in concentration between the low-concentration water and the high-concentration water are preferred because a large quantity of energy is inherent in such water combinations. Specifically, the high-concentration water preferably is, for example, seawater, concentrated seawater, an aqueous sodium chloride solution, as aqueous sugar solution, or an aqueous solution which contains a solute having high solubility, e.g., lithium bromide, and with which a high osmotic pressure is obtained. In particular, seawater and concentrates thereof can be easily obtained from nature. On the other hand, the low-concentration water may be any liquid having a lower osmotic pressure than the high-concentration water, such as pure water, river water, ground water, or water obtained by sewage treatment. River water and water obtained by sewage treatment are suitable because these kinds of water are available at low cost and have a concentration suitable for the low-concentration water.
The pretreatment unit 3 and the pretreatment unit 6 also are not particularly limited, and removal of suspended matter, sterilization, etc. can be applied according to the quality of the feed water to be supplied to each unit, etc.
In the case where it is necessary to remove suspended matter from the feed water, sand filtration or application of a precision filtration membrane or ultrafiltration membrane is effective. In the case where this water contains microorganisms such as bacteria and algae in a large amount, addition of a germicide is also preferred. It is preferred to use chlorine as the germicide. For example, a preferred method is to add chlorine gas or sodium hypochlorite to the feed water in an amount in the range of 1 to 5 mg/L in terms of the concentration of free chlorine. Incidentally, some semi-permeable membranes have no chemical resistance to specific germicides. In such cases, it is preferred to add a germicide to the feed water as upstream as possible and to deactivate the germicide in the vicinity of the feed water inlet of the semi-permeable membrane unit. For example, in a preferred method in the case of free chlorine, the concentration thereof is measured and, on the basis of the measured value, the amount of chlorine gas or sodium hypochlorite to be added is controlled or a reducing agent, e.g., sodium hydrogen sulfite, is added. In the case where the feed water contains bacteria, proteins, natural organic matter, or the like besides suspended matter, it is effective to add a coagulant such as poly(aluminum chloride), aluminum sulfate, iron(III) chloride, or the like. The feed water which has undergone the coagulation is treated with an inclined plate or the like to sediment the coagulated matter and is then subjected to sand filtration or to filtration with a precision filtration membrane or ultrafiltration membrane constituted of a plurality of hollow-fiber membranes bundled together. Thus, the feed water can be rendered suitable for passing through the subsequent semi-permeable membrane unit. It is especially preferred that prior to the addition of a coagulant, the pH should be regulated in order to facilitate coagulation.
In the case where sand filtration is used here as a pretreatment, it is possible to apply gravity filtration in which the water flows down naturally or it is possible to apply pressure filtration which employs a pressure tank packed with sand. Although the sand to be packed thereinto can be sand constituted of a single component, it is possible to use a combination of, for example, anthracite, silica sand, garnet, pumice, and the like to heighten filtration efficiency. The precision filtration membrane and the ultrafiltration membrane also are not particularly limited, and use can be suitably made of flat sheet membranes, hollow fiber membranes, tubular membranes, pleated type membranes, and membranes of any other shapes. The material of the membrane also is not particularly limited, and use can be made of polyacrylonitrile, poly(phenyl sulfone), poly(phenylene sulfide sulfone), poly(vinylidene fluoride), polypropylene, polyethylene, polysulfones, poly(vinyl alcohol), cellulose acetate, or inorganic materials such as ceramics. With respect to filtration modes, either the pressure filtration mode in which the feed water is filtrated while being pressurized or the suction filtration mode in which the feed water is filtered while sucking the water from the permeation side is applicable. Especially in the case of the suction filtration mode, it is also preferred to apply the so-called coagulation/membrane filtration or membrane bioreactor (MBR), in which a precision filtration membrane or an ultrafiltration membrane is immersed in a coagulation sedimentation tank or biological treatment tank to conduct filtration therewith.
Meanwhile, in the case where the feed water contains dissolved organic substances in a large amount, these organic substances can be decomposed by adding chlorine gas or sodium hypochlorite. The dissolved organic substances can be removed also by conducting pressure floatation or activated-carbon filtration. In the case where dissolved inorganic substances are contained in a large amount, a preferred method is to add an organic polyelectrolyte or a chelating agent such as sodium hexametaphosphate or to use an ion-exchange resin or the like to exchange the dissolved inorganic substances for soluble ions. In the case where iron or manganese is present in a dissolved state, it is preferred to use an aeration oxidation filtration method, a contact oxidation filtration method, or the like.
It is also possible to remove specific ions and polymers or the like beforehand and to use a nanofiltration membrane in a pretreatment for the purpose of operating the power generation apparatus according to the invention at a high efficiency.
The number and position of each of the constituent elements, such as the channels, energy recovery unit, valve, and pump, explained in each embodiment can be changed. The configurations shown in separate figures can be combined with each other. Namely, embodiments obtained from the configurations explained as different embodiments through omission, addition, or combination are also included in embodiments of the invention.
Furthermore, any method of power generation using the concentration-difference power generation apparatus described herein is within the technical scope of the invention.
<Method for Operation>
With respect to all embodiments of the power generation apparatus described herein, it is preferred that the permeation flux in each subunit should be regulated so that the maximum value thereof is kept to a set value or lower, in order to prevent the permeation flux in each subunit from becoming excessively high. For thus controlling the permeation flux, use may be made of a method in which at the time when the permeation flux in each subunit has become likely to exceed a set upper limit, the high-concentration-side pressure in this subunit is boosted relative to the low-concentration-side pressure. Namely, the control may be accomplished by boosting the pressure of the high-concentration water present in the subunit, or by lowering the pressure of the low-concentration water, or by lowering the pressure of the low-concentration water while boosting the pressure of the high-concentration water.
An explanation is given using the configuration of
In the case where the permeation flux in the second subunit 12 has become likely to exceed a set upper limit, the high-concentration-side pressure in the second subunit 12 can be boosted by increasing the degree of opening of the valve 11.
Furthermore, in each of the first and second subunits, the same effect as that produced by boosting the high-concentration-side pressure can be obtained by lowering the low-concentration-side pressure.
More specifically, the permeation flux in each subunit may be controlled in accordance with the SDI (silt density index) of the low-concentration water measured in accordance with ASTM D 4189-95. For example, the permeation flux in each subunit may be regulated to 42.5 lmh or less when SDI<1 and to (50-7.5×SDI) lmh or less when 1≦SDI≦5. The symbol “lmh” is the unit which represents liter per square meter per hour (L/m2/h). This control more effectively inhibits the fouling of the subunit, rendering a more stable operation possible.
Incidentally, in the case where SDI>5, the operation may be stopped. It is, however, noted that even when SDI>5, the subunit can be operated, and that conditions for operation stopping can be set also on the basis of the state of the low-concentration water to be used, etc.
In the embodiment shown in
The present invention relates to an apparatus and a method for operating the apparatus, in which low-concentration water having a low osmotic pressure and high-concentration water having a high osmotic pressure are brought into contact with each other through a semi-permeable membrane interposed therebetween and the resultant permeation flow due to forward osmosis phenomenon is utilized as energy to conduct hydroelectric power generation. More particularly, the apparatus includes a plurality of subunits and the effective pressure difference in each subunit is optimized, thereby making it possible to efficiently and stably conduct hydroelectric power generation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-074639 | Mar 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/058389 | 3/29/2012 | WO | 00 | 9/30/2013 |
