KR20140114197A - Salinity gradient electric generating device - Google Patents

Abstract

The present invention relates to a pressure-retarded osmosis (PRO) power generation apparatus generating power using osmotic pressure between salt water and fresh water and, more specifically, to a power generation apparatus capable of using a pressure increase as a driving source of a power generation turbine, wherein the pressure increase is induced when water at a fresh water side flows to a salt water side through an osmotic membrane by a cross flow between the fresh water and the salt water with respect to the osmotic membrane. According to the present invention, provided are a process configuration and an operation method thereof which are capable of improving an output per the area of a separation membrane by increasing the operation pressure of a module in order to improve efficiency in osmosis power generation. According to the present invention, the power generation apparatus using a salinity difference has pressurization units for salt water and fresh water, wherein the pressurization units supply the salt water and the fresh water with increased pressure to an osmosis module, so pressure increase due to osmotic pressure removes a water permeability reduction factor due to the loss of the separation membrane or both of a tight contact between the separation membrane and a spacer and the loss of the separation membrane, thereby allowing a water permeable speed through the separation membrane to be improved to increase the efficiency of a power generation system.

Description

Salinity gradient electric generating device (Salinity gradient electric generating device)

The present invention relates to a power generation apparatus using a difference in ion concentration between brine and fresh water, and more particularly, to an apparatus for generating electricity by crossing fresh water and brine with a boundary of an osmosis membrane, And a power generating device using the power source as a driving source.

Due to the recent rise in fossil fuel prices and the accident at the Fukushima Nuclear Power Plant in Japan, it is required to abandon the existing production methods that relied solely on fossil fuels and nuclear power.

Hydroelectric power plant has a limitation in place to construct a power plant, and there is a huge problem of construction cost of a power plant. In addition, the electric power generation amount is insufficient, so that it is possible to supply electric power locally, but there is a limit to the stable electric power supply of the whole country.

There is a problem in that it is difficult to produce a constant intensity of power because wind power is not only limited in place but also changes in intensity with time. In addition, as in the case of hydroelectric power generation, the amount of electric power generated is small, so it is possible to supply electric power locally, but there is a limit to the stable supply of electric power throughout the country.

In addition, solar power generation requires a huge space for power generation, but also has a problem in that it generates only a small amount of electric power and a power generation efficiency varies greatly according to the weather, which is an auxiliary power supply source.

As a new and renewable energy source, attention is focused on marine energy, and marine renewable energy sources are ocean temperature difference, wave power, tidal power and salinity difference power generation. The development of the power generation technology using the wave, tidal force and the ocean temperature difference has been progressed, but the research on the salinity power generation has not been carried out relatively.

In order to solve the above problems, an object of the present invention is to provide a construction and operation method of a power generation apparatus with increased utilization efficiency of osmotic pressure between brine and fresh water.

The PRO (pressure retarded osmosis) process was developed with excellent efficiency in the development process using the salt concentration difference. In order for the above process to be economical as a new and renewable energy source commercial power generation facility, the power production density of the moisture permeable membrane is required to be 5 W / m 2 or more (T. Thorsen, T. Holt, "Potential for power generation from pressure gradients by pressure retarded osmosis ", J. Membr. Sci., 335 (2009), 103-110). In order to improve the competitiveness of the separation module, it is possible to improve the specific surface area per unit volume of the module using the hollow fiber membrane rather than the bare wound module, thereby improving the competitiveness (Shuren Chou, et al., "Thin -film composite hollow fiber membranes for pressure retarded osmosis (PRO) process with high power density ", Journal of Membrane Science, 389, (2012), 25-33).

The performance characteristics of the PRO process operating conditions can be improved by increasing the operating pressure (W / ㎡) per unit area. For example, using 11.5% high salt water and 2.9% low salt water, 3.0W / m2 power density can be obtained at 12 bar operation on the draw (high concentration brine) side, while 6.5 W / m2 power density can be obtained at 35 bar operation . That is, the output density can be increased by 110% by increasing the operating pressure (Yu Chang Kim, " Potential of osmotic power generation by pressure retarded osmosis using sea water as feed solution: Analysis and experiments "JMS 429, 330-337 2013). This means that the efficiency of the PRO process can be improved by reducing the separation membrane by more than 50%.

However, when a high pressure is applied to the hollow fiber membrane, breakage due to pressure occurs. Therefore, development of a membrane capable of withstanding high pressure has been a technical challenge. That is, in order to improve the pressure resistance, it is necessary to increase the density and the thickness of the separation membrane support, but the water permeation amount is inversely proportional to the decrease in water permeation amount, which is a technically difficult problem. In addition, when a module using a flat membrane is used, a space for supplying salt water and fresh water is provided by laminating a separation membrane and a spacer. When high pressure is applied, printing is performed in the same manner as a spacer shape on the front and back sides of the separation membrane. That is, there is a problem that the shadow effect of the separation membrane area occurs and the utilization rate of the separation membrane area is reduced.

Accordingly, an object of the present invention is to propose a new process that can solve the problem through a process configuration and a method of operating the new process.

In order to achieve the above object, the present invention aims to maintain the absolute pressure of the sea water at a high level to improve the output per unit area and to maintain the pressure of the fresh water side at a high level, thereby minimizing the pressure difference between both sides.

Various methods can be used as means for increasing the supply pressure of seawater and fresh water. For example, it is possible to obtain pressure using the pressure increase and salt concentration difference using a high-pressure pump, and pressurize seawater and fresh water using a pressure exchange apparatus using the pressure as a driving source, or a combination thereof. However, in consideration of energy efficiency (maximization of net production energy), it is preferable to provide the pressurizing means using the difference in salt concentration, but the present invention is not limited thereto.

Therefore, the salt differential power generation apparatus according to the present invention comprises: brine pressure means for pressurizing brine; Fresh water pressurizing means for pressurizing the fresh water; A PRO module having a brine space connected to the brine pressurizing means and a fresh water space connected to the fresh water pressurizing means and having a separation membrane at a boundary between the brine space and the fresh water space; And a turbine generating electricity by the mixed solution discharged from the PRO module.

The brine pressurizing means and the fresh water pressurizing means are a brine pressurizing pump and a fresh water pressurizing pump.

The brine pressurizing means and the fresh water pressurizing means are pressure exchangers using a mixed solution discharged from the PRO module.

The brine pressurizing means and the fresh water pressurizing means may comprise a pressure exchanger using a mixed solution discharged from the PRO module, a brine pressurizing pump for pressurizing the brine discharged from the pressure exchanger, It is also possible to include a fresh water pressurizing pump.

The separation membrane may be a flat membrane or a hollow fiber membrane.

The pressure of the fresh water is equal to or lower than the pressure of the brine, and is equal to or greater than a difference between the pressure of the brine and the allowable pressure of the separation membrane.

Through the present invention, it is possible to increase the operation amount per unit area by increasing the operating pressure of the PRO process using the salinity difference.

In addition, electricity is provided in the development direction of the separation membrane for the PRO process. In other words, the present invention provides a salinity generating device which is more competitive in the field by eliminating the necessity of simultaneously satisfying the strength and water permeability of the flat membrane and the hollow fiber membrane.

1 is a general configuration diagram of a PRO process according to the prior art.
2 is a configuration diagram of the PRO process according to the first embodiment of the present invention.
3 is a configuration diagram of the PRO process according to the second embodiment of the present invention.
4 is a graph of the experimental result according to Experimental Example 1 of the present invention.
FIG. 5 is a graph of an experimental result according to Experimental Example 2 of the present invention. FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings attached to preferred embodiments. In the drawings, the same reference numerals are used to designate the same or similar elements in the drawings, unless otherwise indicated by the same reference numerals, Detailed description of functions and configurations is omitted.

The salinity difference generation apparatus 100 by PRO, which produces energy using an osmosis membrane, is generally constructed as shown in FIG. The pressurized brine is supplied to the fresh water space 22 in the membrane module through the brine supply line 21 and the fresh water is supplied to the brine space 25 in the PRO module 20 through the fresh water supply line 24. The fresh water is then passed through the separation membrane 27 by the osmotic pressure to increase the pressure of the salt water side space 22 and the mixed solution of the pressurized brine and fresh water passes through the mixed solution supply line 23, The mixed solution of the backlash supply line 32 is used as a driving energy source of the pressure exchanger 10 for compressing the brine supplied through the brine supply line 21, The mixed solution of the power generation line 30 is supplied to the turbine 40 to produce electricity. The mixed solution having passed through the pressure exchanger 10 is discharged to the backlash discharge line 12 and the mixed solution having passed through the turbine 40 is discharged to the turbine discharge line 33. At this time, it is also possible to additionally provide a brine pressure pump 28 between the pressure exchanger 10 and the PRO module 20.

In addition, some of the fresh water supplied through the fresh water supply line (24), which has not passed through the separation membrane (27), is discharged through the fresh water discharge line (26). At this time, the fresh water discharged through the fresh water discharge line 26 is supplied with the salt contained in the fresh water discharged through the fresh water supply line 24 and the salt passing through the separation membrane 27 in the opposite direction, And is operated to maximize the concentration difference on both sides of the separation membrane 27 through the discharge thereof.

As described above, the process efficiency can be as high as the energy per unit area of the membrane during high-pressure operation. However, the separation membrane 27 increases the expansion pressure in accordance with an increase in the pressure of the saline-side space 22 and acts as a cause of loss of the separation membrane. Further, the separation membrane 27 is provided with a spacer (not shown in the figure) As the gap narrows, the degree of moisture permeability decreases. In the case of hollow fiber membranes, it causes loss of expansion or compression. That is, it acts as a negative factor irrespective of the form of the film.

As mentioned above, the efficiency of the process depends on the operating pressure and the output per membrane area can be maximized when operating at the theoretical osmosis pressure of 50% of the brine used. According to literature data, a maximum output of 80 W / m 2 can be obtained at an operating pressure of 70 bar with a 20 wt% sodium chloride solution (Elimelech et al., "Membrane-based processes for sustainable power generation using water", Nature v 488, 2012 ).

Therefore, when the pressure on the fresh water side is maintained at a high level (200) as shown in FIG. 2, which is an embodiment of the present invention, which can provide a high pressure while suppressing the netting of the separation membrane, DELTA P) is lowered to impart pressure resistance of the separator itself and the moisture permeability is not sacrificed, so that a low pressure semipermeable membrane having the maximum water permeability can be utilized.

The construction and operation principle of the salinity difference generator 200 according to the PRO according to the first embodiment of the present invention shown in FIG. 2 are as follows. Here, the same reference numerals are used for the same components as those used in FIG. 1, and a detailed description thereof will be omitted.

The brine and fresh water pressurized in the multiple pressure exchanger 50 are supplied to the brine space 22 and the fresh water space 25 of the PRO module 20 through the respective brine supply lines 21 and fresh water supply lines 24, do. Then, the moisture in the fresh water passes through the semipermeable membrane 27 to increase the pressure on the salt water side. Then, the mixed solution of brine and fresh water with increased pressure is discharged to the mixed solution supply line 23, the power generation supply line 30 and the backlash supply line 32 are branched in the mixed solution supply line 23, The backlash supply line 32 is connected to the multiple pressure exchanger 50 and the power supply line 30 is connected to the turbine 40. The mixed solution supplied to the multiple pressure exchanger (50) raises the pressure of the brine and the fresh water and is discharged through the backlash discharge line (52). The mixed solution having passed through the turbine (40) is discharged to the turbine discharge line (33).

With this configuration, the same separation membrane 27 can be used and the pressure difference? P between both sides of the separation membrane 27 (brine, fresh water) can be reduced while increasing the pressure on the fresh water side.

A fresh water pressurizing pump 29 and a brine pressurizing pump 29 are installed in the fresh water supply line 24 and the brine supply line 21 between the multiple pressure exchanger 50 and the PRO module 20 It is also possible.

Therefore, in the process shown in Fig. 2, the pressurizing means may be replaced with only the fresh water pressurizing pump 29 and the brine pressurizing pump 29, instead of the multiple pressure exchanger 50. It is also possible to use another kind of pressurizing means, for example, a pumping facility using wind power or the like. However, considering the efficiency, the configuration of FIG. 2 using the pressure generated by using the saline-freshwater osmotic pressure difference as a driving source may be effective.

Although the pressure exchanger 50 for multiple pressurization is specified as the means for pressurizing the brine and the fresh water in the construction of FIG. 2, the present invention can be modified within the scope of the present invention. For example, the saline solution generator 300 according to the second embodiment of the present invention shown in FIG. 3 can be divided into two separate pressure exchangers 60 and 70, . Thus, the backlash supply line 32 is branched to the branch backlash supply line 76 and supplied to the pressure exchangers 60 and 70, respectively. As a result, the brine supply line 62 passes through the brine side pressure exchanger 60 and the fresh water supply line 72 passes through the fresh water side pressure exchanger 70. The pressure exchangers 60 and 70 discharge the mixed solution through the backlash discharge lines 64 and 74, respectively.

Such a configuration can be selected in consideration of the price and stability of the pressure exchanger. However, in any case, it is within the scope of the present invention to include a means for pressurizing to cancel the pressure applied to the separation membrane, and pressurize and supply fresh water using the means.

Hereinafter, a method of operating the saline solution power generator 200 according to the second embodiment of the present invention will be described. The pressure difference between the brine space 22 and the fresh water space 25 is in the range of 0 to 80 bar, preferably 5 to 50 bar, more preferably 5 to 15 bar, It is preferable to use a method that minimizes the wasteful factor of compressed salt water.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It can be understood that

Next, an experimental example of the present invention will be described. In the experimental example, the power generation efficiency of the process according to the present invention was measured. In Experimental Example 1, the output according to the conventional salt-break power generation apparatus 100 was measured. In Experimental Example 2, the output was measured with respect to the configuration of the salt-difference power generation apparatus 200 according to Example 1 of the present invention. From the comparison of the two experimental results, the effect of the present invention can be clearly understood.

[Experimental Example 1]

As in the normal PRO operation conditions, fresh water is supplied at a supply pressure of 0.1 bar, the discharge of salt water and seawater is measured while increasing the pressure of the salt water, and the flux of fresh water is calculated, W / m < 2 >).

The experiment was conducted using a HTI sandwich membrane and using a small test cell (membrane active area 132 cm 2). The test cell was designed to withstand the pressure, with the porous support on the fresh water side, with a separator placed on top of it to withstand the pressure exerted from the salt water side.

The experimental results are summarized in FIG. Here, the color symbol (???) Indicates the water permeability according to the pressure increase, and the color space symbol (? O?) Indicates the output according to the pressure increase. As the pressure increases, the water permeability decreases linearly, and as the salt concentration increases, the absolute amount of water permeation increases and the maximum output value tends to exist. As a result of the salt concentration of 1.0M, the output (W / ㎡) per unit area of the membrane was 2.5 W / ㎡ at the maximum of 17 bar which is half of the osmotic pressure.

[Experimental Example 2]

A comparative experiment was conducted to confirm the effect of the present invention. The test apparatus and conditions were the same as those of Experimental Example 1 above. However, a separate fresh water pressurizing pump (29) was installed on the fresh water side, and the water permeation amount was measured while varying the pressure difference between the salt water side and the fresh water side.

Experimental results As shown in Fig. 5, when the supply pressure of fresh water was maintained at 20 bar at a salt water concentration of 1.7M and the output power of 8.5 W / m < 2 > was obtained when the operating pressure ΔP was 5 bar, , The output of 1.7 W / m < 2 > was obtained under the same conditions.

Therefore, when the pressure of the fresh water is equal to or lower than the pressure of the brine and the pressure of the brine is higher than the difference between the permissible pressure of the separator and the safety factor at the limit pressure at which the separator is not lost, It is possible to develop a considerably large output.

10, 50, 60, 70: Pressure exchanger 12, 52, 64, 74: Backlash discharge line
20: PRO module 21, 62: brine supply line
22: brine space 23: mixed solution supply line
24,72 Fresh water supply line 25 Fresh water space
26: fresh water discharge line 27: membrane
28: brine pressure pump 29: fresh water pressure pump
30: power generation supply line 32, 76: backlash supply line
33: Turbine discharge line 40: Power generation turbine
100,200,300: Salinity generator

Claims (7)

Brine pressurizing means for pressurizing the brine;
Fresh water pressurizing means for pressurizing the fresh water;
A PRO module having a brine space connected to the brine pressurizing means and a fresh water space connected to the fresh water pressurizing means and having a separation membrane at a boundary between the brine space and the fresh water space; And
And a turbine for generating electricity by the mixed solution discharged from the PRO module.
The apparatus as claimed in claim 1, wherein the salt pressurizing means and the fresh water pressurizing means are a salt pressurizing pump and a fresh water pressurizing pump.
The apparatus as claimed in claim 1, wherein the brine pressurizing means and the fresh water pressurizing means are pressure exchangers using a mixed solution discharged from the PRO module.
2. The PRO module as claimed in claim 1, wherein the brine pressurizing means and the fresh water pressurizing means comprise a pressure exchanger using a mixed solution discharged from the PRO module, a brine pressurizing pump for pressurizing the brine discharged from the pressure exchanger, And a fresh water pressurizing pump for pressurizing the fresh water.
The apparatus according to claim 1, wherein the separation membrane is a flat membrane.
The apparatus according to claim 1, wherein the osmosis membrane is a hollow fiber membrane.
The salt differential generator according to claim 1, wherein the pressure of the fresh water is equal to or lower than the pressure of the brine, and the difference between the pressure of the brine and the allowable pressure of the separation membrane.

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