JPH01123605A - Method for recovering energy in brine desalting plant using reverse-osmosis membrane - Google Patents

Abstract

PURPOSE:To efficiently recover the pressure energy of concd. brine by driving the piston of the main booster of a desalting equipment by the reverse-osmosis membrane concd. brine to pressurize the brine. CONSTITUTION:The seawater stored in a seawater tank 1 is pressurized by a high-pressure pump 2, and supplied to the desalting equipment 3. The fresh water generated by reverse osmosis is discharged from a pipeline 6, and the concd. seawater retaining high residual pressure is introduced into an energy conversion train from a pipeline 8. Namely, the seawater is sent into a cylinder 13 from a change-over valve 14a, and discharged from a change-over valve 14b. The piston 12 is moved to the left and to the right by switching the change- over valves 14a and 14b to the left and to the right, and the seawater is moved to the left and to the right in the cylinder 13. The piston 17 of the booster cylinder 18 is reciprocated by the movement of the piston, and the seawater supplied into the cylinder from pipelines 16a and 16b is pressurized, discharged, and supplied to the desalting equipment 3 along with the seawater supplied from the high-pressure pump 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for recovering pressure energy of concentrated salt water in equipment for desalinating salt water using a desalination apparatus using a reverse osmosis membrane.

[Prior Art] Desalination of salt water such as seawater by reverse osmosis is a method that is attracting attention because it consumes very little energy compared to other methods. Reverse osmosis is a desalination method that reversely utilizes the action of a so-called semipermeable membrane that only allows water in an aqueous solution to pass through.
This method is based on the principle that if a mechanical pressure higher than the osmotic pressure of the aqueous solution is applied to the aqueous solution side isolated by a reverse osmosis membrane, only water will pass through the membrane and fresh water will be obtained. At this time,
Concentrated salt water is discharged along with fresh water, but in actual desalination facilities, the salt water is put under high pressure and passed through a reverse osmosis membrane, so the concentrated salt water is discharged with a high residual pressure, wasting energy. being consumed. For this reason, how efficiently the residual pressure energy of concentrated salt water can be recovered is a major factor in reducing power consumption and, by extension, freshwater production costs.

In response to this need, there is an introduction to a technology that recovers the residual pressure energy of concentrated salt water (Water Supply Technology - All About Water Treatment, pp. 379-380, published by the Water Desalination Promotion Center, 1981). This method uses the residual pressure energy of concentrated salt water to rotate a turbine and recovers it as auxiliary power for a high-pressure pump that boosts the pressure of salt water. FIG. 2 is an explanatory diagram of an apparatus in which an energy recovery experiment was conducted in the prior art, and is a diagram showing only the main parts of the drawing described in the above-mentioned document. In FIG. 2, the high-pressure pump 2 is arranged in series with a motor 30 and a turbine 31,
It is designed to rotate by a single, connected shaft. Although this experimental device does not include a desalination device, the flow rate and pressure of salt water are the same as those of the desalination equipment. Salt water stored in a salt water tank 1 is pressurized by a high pressure pump 2. The salt water discharged from the high-pressure pump 2 is controlled by a flow meter 32 and a control valve 3 so that the production ratio of fresh water and concentrated salt water in the salt water desalination equipment is maintained.
3, one is made into a flow rate equivalent to fresh water and directly returned to the salt water tank 1, and the other is adjusted to a flow rate equivalent to concentrated salt water and sent to the turbine 31, which rotates the turbine 31. The rotational energy generated by the rotation of the turbine 31 serves as auxiliary power for the high-pressure pump 1. In this way, the pressure energy of the concentrated salt water is converted into rotational energy by the turbine 31 and the energy is recovered. The energy recovery rate in this case is 1 of the power consumed by the high-pressure pump.
It is 8%.

[Problems to be solved by the invention] However, in the above-mentioned conventional technology, a turbine is used as a means of energy recovery, but the loss during energy conversion is large, and the energy recovery rate cannot be said to be sufficient. However, there is still much room for improvement in recovery rates.

The present invention was made in order to solve the problems of the prior art, and it is an object of the present invention to provide an energy recovery method for a salt water desalination facility that has an extremely high energy recovery rate.

[Measures to Avoid Solving Problems] The problem is that a piston is driven by the reverse osmosis membrane concentrated salt water of the desalination equipment, and the pressure of the salt water is increased by a booster piston driven by the piston, and the main pressure booster is This problem can be solved by supplying the desalination device together with salt water supplied by the above desalination apparatus.

[Operation] In the energy recovery method of the present invention, a piston is driven by the residual pressure of concentrated salt water, and the driving of this piston increases the pressure of the salt water to make it the same pressure as the salt water discharged from the high-pressure pump. This is a method of supplying the water to the desalination equipment. Therefore, the load on the high-pressure pump is reduced by the amount of salt water supplied by increasing the pressure with the piston, and energy is saved. The energy loss in energy recovery by the piston is only due to mechanical frictional resistance of the piston, pressure loss in the salt water flow path, etc., and is very small, so it is more efficient than the conventional turbine.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described based on the drawings. 1st
The figure is an explanatory diagram showing an example of equipment for carrying out the method of the present invention. In Figure 1, 1 is a seawater tank;
Connected to the seawater tank 1 are a high-pressure pump 2 as a main pressure booster and a desalination device 3 incorporating a reverse osmosis membrane. These are connected in series by piping 4 and piping 5 to constitute the fresh water production process, which is the main part of the seawater desalination equipment.The piping 5 is connected to the high-pressure pump 2, where seawater is supplied from the energy recovery process, which will be described later. A check valve 7 is arranged to prevent backflow in the direction. The desalination device 3 is provided with a pipe 6 for discharging fresh water and a pipe 8 for discharging concentrated seawater, and the pipe 8 is connected to an energy recovery process.

The energy recovery process refers to a series of devices that boost the pressure of seawater in a separate system from the high-pressure pump 2 and supply it to the desalination device 3, and an energy conversion system that converts the pressure energy of concentrated seawater into kinetic energy. It is divided into a seawater pressurization system that supplies seawater to the desalination device 3 depending on energy.

The energy conversion series is arranged in the path of the pipe 8, and the aperture 9
．． A cylinder 13 in which a smoothing means 11 consisting of an accumulator 10 etc. and a piston 12 which is a device for converting pressure energy of concentrated seawater into kinetic energy are built-in.
, switching valves 14a and 14b arranged before and after the cylinder 13, and stroke detectors 15 and 15 for detecting the position of the piston 12. The smoothing means 11 is arranged to reduce the impact generated at the stroke end of the piston 12 and to protect the reverse osmosis membrane of the desalination device 3 from mechanical shock. The pipe 8 is connected between the front and rear of the cylinder 13, that is, between the switching valves 14a and 14b.
a and 8b, each with cylinder 1
It is connected to both sides of the piston 12 of No. 3. This piping 8a
, 8b, a switching valve 14a, such as an electromagnetic type or a pneumatic type, is used to switch the concentrated seawater introduced into the ports 8b.

14b is arranged. This switching valve 14a.

b is a simplified illustration of two valve mechanisms. Switching valve 1
4a and 14b are operated by signals from stroke detectors 15, 15, etc., so as to alternately introduce concentrated seawater into pipes 8a and 8b. The seawater boosting system is arranged in a route of a pipe 16 branched from the pipe 4, and includes a pressure boosting cylinder 18 containing a pressure boosting piston 17, which is a seawater boosting device, and check valves 19a arranged before and after the pressure boosting cylinder 18.
, 19a, 19b, 19b, and smoothing means 22 consisting of a diaphragm 20, an accumulator 21, and the like. The piping 16 is connected to 16a and 16 before and after the cylinder 18.
b, and is connected to both sides of the piston 17 of the cylinder 18. The pipes 16a and 16b are provided with check valves 19a before and after the booster cylinder 18, respectively.

19a, 19b, and 19b are arranged so as to alternately introduce seawater into the pipes 16a and 16b.

The smoothing means 22 is arranged for the same purpose as the smoothing means 11 of the energy conversion series.

Next, a boost cylinder 18 containing a boost piston 17
will be explained in more detail. The boost cylinder 18 is arranged in series adjacent to the cylinder 13, and the built-in rod 23 of the boost piston 17 is connected to the piston 12.
It is connected to the rod to form a single unit. Therefore, the boosting piston 17 is driven by operating the piston 12. In addition, the boost cylinder 18
The cross-sectional area of the cylinder 13 is smaller than that of the cylinder 13 so that the pressure of the seawater discharged from the pressurizing cylinder 18 is higher than the pressure at which the concentrated seawater is introduced into the cylinder 13. This compensates for the pressure loss in the desalination device 3 and the piping route, so that the pressure of seawater supplied from the booster cylinder 18 can be made equal to the pressure of seawater discharged from the high-pressure pump 2, which is the main booster. It has become.

In the equipment configured as described above, seawater stored in a seawater tank 1 and adjusted to conditions that do not inhibit the performance of the reverse osmosis membrane is pressurized by a high-pressure pump 2, which is the main pressure booster, and then supplied to a desalination device 3. be done. In the desalination device 3, fresh water is generated by the action of the reverse osmosis membrane and discharged from the pipe 6, and at the same time concentrated seawater, which still retains a high residual pressure, is discharged from the pipe 8 and introduced into the energy conversion train.

In the energy conversion series, concentrated seawater in the pipe 8 flows into the cylinder 13 via the smoothing means 11 and the switching valve 14a, and is discharged via the switching valve 14b. At this time, the flow path of the concentrated seawater is determined by the switching valves 14a and 14b,
For example, when concentrated seawater flows through either piping 8a or 8b, the operation of the switching valves 14a and 14b is such that the switching valve 14a is open on the piping 8a side and closed on the piping 8b side. In the valve 14b, the pipe 8
The a side is closed and the piping 8b side is open. When the concentrated seawater flows through the line of the piping 8a in this manner, the concentrated seawater supplied to the cylinder 13 flows to the right side of the piston 12 in the representation of the figure. However, since the piping 8a side of the switching valve 14b is closed, the piston 12 moves to the left due to the pressure of the concentrated seawater. When the piston 12 reaches the end of its stroke, the switching valves 14a and 14b are opened and closed in the opposite manner to the above, and the flow of concentrated seawater supplied to the cylinder 13 is switched to the left side of the piston 12 according to the signal from the stroke detector 15.15. In this case, the piston 12
moves to the right side, and the concentrated seawater supplied to the right side of the cylinder 13 through the pipe 8a is discharged via the switching valve 14b. Such operations are repeated, and the piston 12 reciprocates.

Next, the seawater pressurization series will be explained. Seawater in the pipe 16 is introduced into the pressure increase cylinder 18.

At this time, the boost piston 17 is driven by the piston 12 and is reciprocating, so the right and left sides of the boost piston 17 in the figure of the boost cylinder 18 are respectively suction areas and compression areas. When moving to the left, the right side becomes the suction area and the left side becomes the compression area, and the seawater flows into the pressure boosting cylinder 18 through the pipe 16a. When the boost piston 17 moves to the right, the right side becomes the compression area and the left side becomes the suction area, and seawater flows into the boost cylinder 18 through the pipe 16b. At the same time, the seawater that previously flowed into the right side of the pressurizing cylinder 18 is pressurized and discharged, and is supplied to the desalination device 3 along with the seawater supplied from the high-pressure pump 2 via the smoothing means 22.

Note that the present invention is not limited to the above-described embodiments. For example, if a method of providing multiple rows of energy recovery steps is adopted, the pulsation of the seawater flow will be reduced and smooth operation will be possible.

The results of a seawater desalination experiment using the apparatus configured as shown in FIG. 1 will be described. 5. Seawater with high pressure pump 2
Pressure increased to 6 kg/cm2 and 0.4
It was supplied to the desalination device 3 at a flow rate of 8 m'/hour. The amount of concentrated seawater discharged was 54 kg/cm2. This concentrated seawater drives the piston 12, pressurizes the seawater to 56K g/cm2 by the booster piston 17, and supplies it to the desalination device 3 together with the seawater supplied from the high-pressure pump 2 at a flow rate of 0.52 m'/hour. and total 1m3/
The seawater of the time was treated. The power consumption of the high pressure pump 2 at this time was i, 28 KWH. In addition, the power consumption of high pressure pump 2 without energy recovery is 2.24KW.
H, and the power consumption was reduced by about 43%.

[Effects of the Invention] The present invention drives a piston with concentrated salt water, increases the pressure of the salt water with a booster piston driven by the piston, and supplies the salt water to the desalination equipment together with the salt water supplied from the main pressure booster. Since this method recovers the pressure energy of salt water, the energy recovery rate is extremely high.The energy recovery rate is approximately 2.4 times that of conventional technology, making it an extremely economical method that can reduce freshwater production costs. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of equipment for carrying out the method of the present invention, and FIG. 2 is an explanatory diagram of a conventional method. 2... High pressure pump, 3... Desalination equipment, 12...
Piston, 13... cylinder, 17... booster piston. 18... Boost cylinder, 23... Rod. Application° Large Nippon Kokan Co., Ltd. Figure 1

Claims (1)

[Claims] In a method for recovering pressure energy of concentrated salt water in a facility where salt water is desalinated by a desalination device using a reverse osmosis membrane through a main pressure booster, a piston is driven by the reverse osmosis membrane concentrated salt water of the desalination device; An energy recovery method for a salt water desalination facility, characterized in that salt water is pressurized by a driven pressure boosting piston and is supplied to the desalination device together with salt water supplied from a main pressure boosting device.