KR20020094526A - System making fresh water from sea water using revertse osmosis - Google Patents

Abstract

PURPOSE: A seawater desalination system using two step reverse osmosis is provided to promote the reclamation efficiency of disposed water with high pressure and can prevent the performance decline of membrane due to high pressure. CONSTITUTION: The system comprises a pretreatment part(20) which filters suspended solids in sea water by a filter unit(26) using hollow fiber membrane; an equipment protection part(30) in which a first treatment tank(32), a supply pump(34) and a protection filter(36) are installed; an energy recovery part(40) which discharges primarily treated water with high pressure using a high pressure pump(42) and mixes that with sea water using a return pump(44); a reverse osmosis part(50) which mixes main freshwater from a first reverse osmosis unit(52) and sub freshwater and returns sub concentrated water discharged to the energy recovery part; a membrane washing part(60) which takes suspended solids off the surface of hollow fiber membrane by supplying reverse washing water by the reverse washing pump.

Description

Reverse osmosis desalination system for energy savings {SYSTEM MAKING FRESH WATER FROM SEA WATER USING REVERTSE OSMOSIS}

[Industrial use field]

The present invention relates to a reverse osmosis process system for producing fresh water or drinking water from sea water, and more particularly, to produce fresh water or drinking water with the same water quality as the existing process when producing fresh water or drinking water from sea water using reverse osmosis. The present invention relates to a reverse osmosis desalination system for energy saving.

[Prior art]

In general, in order to obtain fresh water from seawater, it is necessary to remove dissolved or suspended components in seawater to meet the water and drinking water standards. The components contained in seawater are almost constant except in certain regions.

The desalination method of seawater is divided into evaporation method and reverse osmosis method. Recently, the reverse osmosis method which is relatively energy efficient has been widely used.

Reverse osmosis separates the components contained in seawater into produced water and concentrated water using a polymer membrane, and the produced water side makes the concentration of the component thin and utilizes it as drinking water and drinking water and discharges the concentrated water back to the sea.

In this process, the components to be removed to produce fresh water from seawater are mainly ionic components. Hardness components such as Na, Cl, Ca, and Mg, SO ₄ , B, and the like, which are ionic components, should be removed below the reference value. Organic chemicals and aesthetic influencers included in other drinking water standards are not a problem because the amount of dissolved water in seawater is lower than the standard water and drinking water standards.

As described above, in the polymer membrane in which seawater is separated and purified, in order to separate seawater, separation begins to be applied to the incoming seawater by applying a pressure greater than the osmotic pressure caused by the components dissolved in the seawater. The concentration of seawater is typically 3.5% or 35,000 ppm, with an osmotic pressure of about 350 psig. That is, in order to obtain a small amount of fresh water from the sea water, it is necessary to apply a pressure of 350 psig or more.

The motor is used as a driving force necessary to overcome the osmotic pressure of seawater and produce freshwater, and the magnitude of the driving force of the motor depends on the ionic components dissolved in the water and the amount of freshwater obtained from the seawater, that is, the recovery rate. The power cost of the motor accounts for more than 60% of the total production cost, excluding depreciation, of the freshwater produced by reverse osmosis.

In general, in the seawater desalination process using reverse osmosis, seawater (2) taken from the sea is stored in a raw water tank (4), and the seawater (2) is sanded using a seawater supply pump (6). The seawater (2) passed through the filter (8) and the suspended matter is removed from the sand filter (8) flows into the reverse osmosis unit (10), and the reverse osmosis unit (10) receives 20 to 35% of the introduced seawater as fresh water. To produce.

The membrane facility, the main process of the reverse osmosis seawater desalination system, is used by mounting six modular separators in series in a pressure vessel that withstands high pressure and connects the membranes in parallel according to the fresh water to be produced. Has been increased.

The connection of 6 membranes in series is called 1st stage. In order to produce 1m3 of fresh water from seawater using 1st stage reverse osmosis process, energy of 10kw / ㎥ or more is required.

Therefore, there is a difficulty in spreading the seawater desalination system in places where the cost of water and drinking water is low, such as in Korea, due to the high cost of electricity.

In order to produce fresh water or drinking water from seawater, the ions contained in seawater must be removed to a certain level or less. The reverse osmosis method used as an ion removal process has a higher power ratio as the concentration of ions contained in raw water increases. In the case of the seawater desalination system using the conventional reverse osmosis method, it is difficult to disseminate the power cost of 1000 ~ 2000 won / ton out of operating costs 2000 ~ 3000 won / ton except the depreciation cost.

The present invention is to solve the problems as described above, an object of the present invention is to provide a reverse osmosis desalination system for energy saving to increase the recovery rate of the treated water at a higher pressure than conventional for energy saving.

Another object of the present invention is to provide a reverse osmosis desalination system for energy saving by configuring the reverse osmosis process in two stages to minimize the performance degradation of the separator due to high pressure.

Another object of the present invention is a reverse osmosis for energy saving that can minimize the contamination of the membrane due to high pressure and high recovery rate in the process of recovering the pressure energy discharged with the concentrated water after producing fresh water using the energy recovery facility. To provide a seawater desalination system.

Still another object of the present invention is to provide a reverse osmosis seawater desalination system for energy saving that can reduce the overall facility size compared to the existing system based on the same amount of treated water due to increased recovery rate.

1 is a block diagram showing a reverse osmosis seawater desalination system for energy saving according to the present invention,

2 is a graph showing a comparison of the amount of power according to the recovery rate using the seawater desalination system and the conventional seawater desalination equipment according to the present invention,

3 is a graph showing the percentage of power comparison according to the recovery rate using the seawater desalination system and the conventional seawater desalination equipment according to the present invention,

Figure 4 is a block diagram showing a conventional seawater desalination system.

<< Explanation of symbols for main part of drawing >>

12 Seawater 20 Pretreatment

22 ... water tank 24 ... sea water supply pump

26 Backwash filter 30 Equipment protection

32 ... Primary treatment tank 34 ... Supply pump

36.Protective filter 40.Energy recovery unit

42 High pressure pump 44 Recovery pump

50 ... reverse osmosis part 60 ... membrane cleaning part

[Means for solving problem]

In order to achieve the above object, the present invention is a reverse osmosis desalination system for introducing fresh water into the seawater, the pre-treatment unit for filtering the suspended solids contained in the introduced seawater with a backwash filter equipped with a hollow fiber membrane; A facility protection unit for installing a primary treatment tank, a supply pump, and a protection filter for storing primary treatment water that has passed through the backwash filter first; An energy recovery unit for discharging the primary treated water passing through the facility protection unit at a high pressure using a high pressure pump; And the first treated water discharged at a high pressure passes through a first stage reverse osmosis unit to be converted into some main freshwater, and the discharged main concentrated water is converted into some sub freshwater through a second stage reverse osmosis unit to be combined with the main freshwater and discharged. It is composed of a reverse osmosis unit for returning the sub-concentrated water to the energy recovery unit.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 is a block diagram showing a reverse osmosis seawater desalination system for energy saving according to the present invention.

The seawater desalination system of the present invention obtains fresh water by introducing the seawater filtered by the suspended solids from the backwash filter into the first stage reverse osmosis machine and the second stage reverse osmosis machine, and rotates the recovery pump with the concentrated water discharged from the second stage reverse osmosis machine with the rotational force. The high pressure primary treated water is introduced into the first stage reverse osmosis unit, and the discharged concentrated water is recovered to wash the hollow fiber membrane of the backwash filter.

The seawater 12 supplied to such a seawater desalination system is first removed from the pretreatment unit 20, the pretreatment unit 20 is to transfer and pressurize the seawater stored in the raw water tank 22 for the automation of operation It consists of a seawater supply pump 24 and a backwash filter 26 provided with a hollow fiber membrane for removing suspended matter.

The pretreatment unit 20 includes a pressure gauge for measuring the pressure of the inflowing seawater, a flowmeter for measuring the flow rate of the primary treated water 6 passing through the hollow fiber membrane, and an electric conductivity for measuring the amount of ions contained in the seawater. Measurement equipment such as an electrical conductivity meter and a water thermometer for measuring the water temperature of the incoming seawater are installed.

The seawater 12 collected from the wells installed on the surface, deep or beach of the sea is first stored in the raw water tank 22 and then backwashed with a hollow fiber membrane by the seawater supply pump 24. Inflow.

The backwash filter 26 has a pore size of 0.001 to 0.5 µm and is selected from the group of hollow fiber membranes consisting of polysulfone, polyacrylonitrile, polyethylene, and polypropylene, and is hydrophilic. It is preferable that it is a film | membrane of the material which processed.

The suspended solids filtered in the backwash filter 26 is attached to the surface of the hollow fiber membrane and removed by a membrane washing unit described later.

The primary treatment water from which the suspended solids are removed from the pretreatment unit 20 as described above is primarily stored in the primary treatment tank 32 which is a component of the facility protection unit 30.

The primary treatment tank 32 should secure a storage capacity of at least 30 minutes so that the reverse osmosis unit to be described later can be continuously operated without stopping the flow due to the insufficient flow rate of the primary treatment water.

In addition, the facility protection unit 30 is a supply pump 34 and a protective filter continuously connected to the primary treatment water tank 32 to protect the energy recovery unit and reverse osmosis unit to supply the primary treatment water at a high pressure ( 36).

The operation of the supply pump 34 is controlled by the water level meter 32a and the PLC 32b installed in the primary treatment tank 32, and the supply pump 34 has a constant number of primary treatments that have passed through the protective filter 36. More than the pressure to be introduced into the energy recovery unit described later.

The energy recovery unit 40 transfers the primary treated water at high pressure to the high pressure pump 42 for transferring the primary treated water to the reverse osmosis unit, which will be described later, and the recovered sub-condensed water. The recovery pump 44 is made.

The operation of the high pressure pump 42 is started by the pressure gauge 42a installed at the front of the high pressure pump 42 detecting the pressure of the primary treated water, and if the above-described water level gauge 32a and the PLC 32b are malfunctioning, When the supply pump 34 is operated without the transfer of the first treatment water, the pressure gauge 42a senses the corresponding pressure to stop the operation of the high pressure pump described later.

The recovery pump 44 supplies the first treatment water to the reverse osmosis unit 50 at a high pressure together with the high pressure pump 42, which passes through the protection filter 36 at the beginning of operation before the high pressure pump 42 is operated. The primary treated water is first introduced into the recovery pump 44 to operate the recovery pump 44 and to operate the turbine of the sub-condensed water discharged from the reverse osmosis unit 50 to be described later.

That is, the pressure energy of the sub-condensate of high pressure is converted into mechanical energy while passing through the recovery pump 44 to pressurize the primary treated water flowing through the supply pump 34.

After sufficient flow of the primary treated water is made, the primary treated water that has passed through the facility protection unit 30 according to the features of the present invention is evenly distributed to the high pressure pump 42 and the recovery pump 44.

Accordingly, the first treated water passing through the high pressure pump 42 and the recovery pump 44 is supplied at a high pressure to the reverse osmosis unit 50 to be described later, and the fresh water from the reverse osmosis unit 50 according to the increase in pressure. To be produced. Freshwater production and recovery rates are determined by the inflow of subconcentrated water from the recovery pump 44 designed based on the specifications determined during initial system design.

Reverse osmosis unit 50 is composed of a first stage reverse osmosis unit 52 and a second stage reverse osmosis unit 54, the high-pressure primary treatment water introduced into the first stage reverse osmosis unit 52 is a first stage reverse osmosis unit 52 While passing through the main fresh water 56a, the remainder is discharged to the main concentrated water 56b, and the discharged main concentrated water 56b is converted into the sub fresh water 58a while passing through the two-stage reverse osmosis unit 54. The remainder is discharged to the sub-concentrated water 58b and introduced to the above-described recovery pump 44.

Thus, the main fresh water 56a and the sub fresh water 58a obtained from the two reverse osmosis units 52 and 54 are combined and used as drinking water or drinking water.

When used as drinking water, boron (B) ions contained in seawater have a low removal rate in the reverse osmosis membrane, so the sub freshwater (58a) obtained in the two-stage reverse osmosis unit (54) may exceed the standard value of drinking water. The sub fresh water 58a of 54 may be circulated to the primary treatment tank 32 and reprocessed in the first stage reverse osmosis machine 52 to produce fresh water based on drinking water quality standards. When the treated water 58a of the two-stage reverse osmosis machine 54 is circulated to the primary treated water tank 32, all of the fresh water is produced by the first-stage reverse osmosis machine 52.

Finally, the membrane washing unit 60, the membrane washing unit 60 is to use the backwash water (sub-concentrated water) discharged from the recovery pump 44, the backwash water (through the recovery pump 44) A backwash tank 62 storing 66a), a backwash pump 60 transferring backwash water, a timer, a PLC, and an inverter (not shown) for effectively controlling the backwash tank 62 and the backwash pump 64.

The backwash water 66a transferred by the backwash pump 64 flows into the center of the hollow fiber membrane installed in the backwash filter 26 and then penetrates to the outside to wash the suspended matter attached to the surface of the hollow fiber membrane.

In addition, the blower 70 installed in the lower portion of the backwash filter 26 blows air out of the hollow fiber membrane of the backwash filter 26 to shake off the suspended matter secondarily.

The reverse osmosis seawater desalination system for energy saving according to the present invention configured as described above has the following effects.

First, the introduced seawater 12 is stored in the raw water tank 22, and then the seawater 12 is supplied to the backwash filter 26 using the seawater supply pump 24.

As the seawater 12 passes through the backwash filter 26, the suspended solids are filtered by the hollow fiber membrane, and the filtered suspended matter is supplied from the backwash pump 64 of the membrane washing unit 60. In addition, the air blown by the blower 70 also washes the outside of the hollow fiber membrane.

That is, the seawater supply pump 24 operates for 0.5 to 24 hours to produce primary treated water, and stops the operation of the seawater supply pump 24 for 30 seconds to 2 minutes, at which time the backwash supply pump 24 is used. Injecting the backwash water for backwashing to the center of the hollow fiber membrane of the backwashing filter (26) to remove the floating material on the membrane surface first, and the air introduced into the backwashing filter (26) by the second blower (70) The permeation performance of the hollow fiber membrane is restored by shaking the surface of the hollow fiber membrane to remove residual suspended matter.

The primary treated water from which the suspended solids are removed from the backwash filter 26 is stored in the primary treated water tank 32, and the energy recovery unit 40 is operated via the protection filter 36 through the operation of the supply pump 34. Flows into the recovery pump (44).

Accordingly, the recovery pump 44 is operated, and the sub-condensed water discharged from the reverse osmosis unit 50 also operates the turbine of the recovery pump 44 to pressurize the primary treated water.

When sufficient flow of the primary treated water is made, the primary treated water passing through the facility protection unit 30 according to the characteristics of the present invention is equally distributed to the high pressure pump 42 and the recovery pump 44, and the high pressure pump The primary treatment water passed through the 42 and the recovery pump 44 is supplied to the first stage reverse osmosis unit 52 at high pressure.

As the pressure is increased in the first stage reverse osmosis unit 52, the main fresh water 56a starts to be produced, and the remaining fresh main water 56b is introduced into the second stage reverse osmosis unit 54.

The sub fresh water 58a is also produced in the two-stage reverse osmosis machine 54, and the remaining sub-condensed water 58b is introduced into the recovery pump 44 to rotate the turbine and then flows into the backwash tank 62. .

In the seawater desalination process, the pressure of the seawater supplied to the first stage reverse osmosis unit is applied at a high pressure of 70 kg / cm 2 G or more, and more preferably 70 to 100 kg / cm 2 G or less.

Under these pressures, the recovery of freshwater produced to the entire influent seawater is about 50 to 65%, because the recovery rate of the first stage reverse osmosis machine is 30 to 60% and the recovery rate of the two stage reverse osmosis machine is 5 to 20%.

In particular, when the recovery rate is 50%, for example, the first stage recovery rate is 30%, the second stage recovery rate is 20%, and the first stage recovery rate is 35%, the second stage recovery rate is 15%, and the first stage recovery rate is 40%. The second stage recovery rate is 10%, and the second stage recovery rate is 5% when the first stage recovery rate is 45%.

Meanwhile, the backwash water stored in the backwash tank 62 is supplied to the backwash filter 26 by the backwash pump 64 to wash the suspended matter attached to the surface of the hollow fiber membrane.

In this process, the production and recovery rate of fresh water is determined by the inflow of the sub-concentrated water 58b of the recovery pump 44 designed based on the specifications determined at the time of initial system design. The effect as shown in 3 is shown.

In case of applying the conventional single stage reverse osmosis machine, power consumption of 12.06kW / ton was required at 35% recovery rate of fresh water, but 5.26 in the process of obtaining 50% recovery rate when the applied two stage reverse osmosis unit was applied according to the characteristics of the present invention. Lowering the power consumption of kW / ton, as shown in Figure 3 can be seen that the energy saving rate is reduced by more than 50% compared to the percentage.

As described above, the reverse osmosis seawater desalination system for energy saving according to the present invention realizes energy saving by reducing the energy consumption by 50% or more by applying reverse osmosis in two stages.

That is, in the existing desalination system, the recovery rate of seawater was about 20 to 35% at a pressure of 50 to 70 kg / cm 2 G or less, but the desalination system of the present invention shows a recovery rate of 50% or more by applying a high pressure of 70 kg / cm 2 G or more. .

In addition, by introducing a two-stage reverse osmosis system that produces treated water using the concentrated water of the first stage reverse osmosis machine, the membrane used at a pressure of 50 to 70 kg / ㎠G or less compensates for the disadvantage that the performance falls at high pressure. Was done.

In addition, by applying the energy recovery unit to recover the pressure energy of the high-pressure concentrated water discharged to the outside of the system has the effect of reducing the power cost to less than 300 won / ton.

In addition, by reducing the pretreatment scale due to the increase in the recovery rate, it is possible to reduce the investment cost compared to the existing one-stage reverse osmosis system of the same production scale.

In addition, it is possible to smoothly operate the system by reducing the contamination of the membrane by applying a backwash filter as a pretreatment.

Claims (8)

In the seawater desalination system using a reverse osmosis method to inflow seawater to produce fresh water, A pretreatment unit for filtering the suspended solids contained in the introduced seawater with a backwash filter provided with a hollow fiber membrane; A facility protection unit for installing a primary treatment tank, a supply pump, and a protection filter for storing primary treatment water that has passed through the backwash filter first; An energy recovery unit for discharging the first treated water passing through the facility protection unit at a high pressure by using a high pressure pump; And The primary treated water discharged at the high pressure passes through the first stage reverse osmosis unit to be converted into some main fresh water, and the discharged main concentrated water is passed through the second stage reverse osmosis unit to be converted into some sub freshwater to join the main fresh water and discharged. Reverse osmosis unit for returning sub-concentrated water to the energy recovery unit Reverse osmosis desalination system for energy savings comprising a. The method of claim 1, wherein the energy recovery unit, And a recovery pump for converting the primary treated water bypassed from the primary treated water passing through the protective filter to a high pressure by using the pressure of the sub-concentrated water, and then joining the seawater discharged from the high pressure pump. Reverse osmosis desalination system for energy saving, characterized in that. The method of claim 2, Energy saving characterized in that it comprises a membrane cleaning unit for storing the backwash water exiting the recovery pump in a backwash tank to supply to the center of the hollow fiber membrane by using a backwash pump to remove suspended matter on the surface of the hollow fiber membrane Reverse osmosis desalination system for. The method of claim 3, wherein Reverse osmosis desalination system for energy saving, characterized in that the blower for blowing air to the outside of the hollow fiber membrane is installed in the lower portion of the backwash filter. The method according to any one of claims 2 to 4, The reverse osmosis seawater desalination system for energy saving, characterized in that the recovery rate of the production freshwater for the total inflow of seawater at a pressure of 70 to 100kg / ㎠G or less supplied to the first stage reverse osmosis. The method of claim 5, Recovery rate of the first stage reverse osmosis is 30 to 60%, recovery rate of the reverse osmosis desalination system for energy savings, characterized in that 5 to 20%. The method according to claim 1 or 6, Reverse osmosis desalination system for energy saving, characterized in that the pore size of the hollow fiber membrane is 0.001 to 0.5㎛. The method of claim 7, wherein The material of the hollow fiber membrane is a reverse osmosis desalination system for energy saving, characterized in that selected from the group consisting of polysulfone, polyacrylonitrile, polyethylene and polypropylene.