JPH0822434B2 - Method and apparatus for treating salt-containing water - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for treating salt-containing water containing a large amount of salt through a multi-stage high pressure and low pressure reverse osmosis membrane module. is there.

[Conventional technology]

For example, in Eastern Europe, a coal mine and a water vein coexist, and the water vein passes through a rock salt layer, so the salt concentration of water discharged from the coal mine is 30,000.
It is as high as ~ 80,000ppm, and this salt water flows into rivers, lakes and marshes, causing serious environmental pollution in some areas.

In order to solve this problem without causing secondary pollution, drinking water or industrial water and concentrated water or solid salt containing a high concentration of salt without discharging salt-containing water to rivers, lakes, etc. Must be fully processed to be

For this purpose, the conventional evaporation method alone, the combination of the single-stage reverse osmosis membrane method and the evaporation method, and the combination of the electrodialysis method and the evaporation method can be considered.

On the other hand, in JP-A-55-31459, in order to obtain fresh water from seawater, seawater is passed through a high pressure reverse osmosis membrane module,
An apparatus for supplying demineralized water to a low pressure reverse osmosis membrane module is described. By the way, the salt concentration of seawater is around 35,000ppm.

Further, Japanese Utility Model Application Laid-Open No. 58-108195 discloses a reverse osmosis membrane module having a small desalination rate and a reverse osmosis membrane module having a large desalination rate in one vessel. Devices are described which are connected in series in a downstream manner.

[Problems to be Solved by the Invention]

If only the evaporation method is applied, all drinking water will
It will be obtained by condensation, and energy consumption will be large (the evaporation method involves a phase change, so the energy cost is higher than that of the water production method using a reverse osmosis membrane or the like).

When the single-stage reverse osmosis membrane method and the evaporation method are applied in combination, a considerable reduction in energy is possible compared to the evaporation method, but the single-stage reverse osmosis membrane has a low degree of concentration and requires a considerable amount of water. The reduction in energy usage is not sufficient as it needs to be evaporated.

Further, when the salt concentration of the water supplied to the reverse osmosis membrane exceeds 60,000 ppm, the general reverse osmosis membrane for seawater desalination cannot be used due to the osmotic pressure (because the pressure becomes too high). On the other hand, low-pressure reverse osmosis membranes cannot obtain drinking water-level demineralized water.

When the electrodialysis method and the evaporation method are applied in combination, the electrodialysis method generally consumes a large amount of energy when the salt concentration is high. Further, the electrodialysis method can be used for the purpose of concentration, but in this case, a large amount of waste water having a medium salt concentration is discharged from the desalting side of the electrodialysis device, which is not preferable.

In addition, the method described in JP-A-55-31459 has the main purpose of obtaining fresh water from seawater, and the degree of concentration of concentrated water is
The concentration is lower than the concentration in the present invention, and the concentrated water is discarded. Further, in the method described in Japanese Utility Model Publication No. 58-108195, salt water pressurized to a predetermined pressure is sequentially passed through a plurality of membrane modules. What is the technical idea of reducing the pressure of the medium-concentrated concentrated water supplied to the second-stage low-pressure membrane module or increasing the pressure of the crude demineralized water supplied to the second-stage high-pressure membrane module? Is also not listed.

The present invention has been made in view of the above points, by treating salt-containing water with a multi-stage reverse osmosis membrane module, or by combining a multi-stage reverse osmosis membrane module and an evaporator, to reduce energy consumption, It is an object of the present invention to provide a method and an apparatus for treating salt-containing water that enables efficient treatment.

[Means and Actions for Solving the Problems]

In order to achieve the above object, the method for treating salt-containing water according to claim 1 is, as shown in FIG.
80,000 ppm relatively high concentration salt water is passed through low pressure reverse osmosis membrane module 20 at 30-70 kg / cm ² G to separate into crude demineralized water and high concentration concentrated water with salt concentration of 80,000-120,000 ppm. Then, this crude demineralized water is pressurized to 40 to 70 kg / cm ² and passed through a high pressure reverse osmosis membrane module 22 to separate into drinking water level demineralized water and medium concentration concentrated water.

Then, in the method of claim 1, the medium-concentrated concentrated water from the high-pressure reverse osmosis membrane module 22 is supplied to the low-pressure reverse osmosis membrane module 20 (claim 2).

As shown in FIG. 1, the apparatus for treating salt-containing water according to claim 4 introduces a relatively high-concentration salt-containing water having a salt concentration of 50,000 to 80,000 ppm at 30 to 70 kg / cm ² G to obtain crude desalinated water. And salt concentration 80,000
Reverse pressure osmosis module 20 for low pressure that separates to highly concentrated water of ~ 120,000 ppm, pressurizing pump 24 to pressurize this crude demineralized water to 40 to 70 kg / cm ² G, and pressurized salt-containing water High pressure reverse osmosis membrane module that introduces water and separates it into demineralized water at the level of drinking water and concentrated water
It is characterized by including 22 and. 26 is a decompression means.

The method according to claim 1 or 2, wherein the high-concentration concentrated water having a salt concentration of 80,000 to 120,000 ppm from the low-pressure reverse osmosis membrane module 20 is sent to the evaporation step to obtain the salt as crystals. desirable.

In the system shown in FIG. 1, the salinity of the medium concentration concentrated water from the high pressure reverse osmosis membrane module 22 is 40,000 to 70,000 ppm.
Then, the salinity of the demineralized water at the drinking water level from the membrane module 22 is 1,000 ppm or less, preferably 500 ppm or less.

Reverse osmosis membrane module for high pressure has a desalination rate of about 99% or more, and generally 40 to 70 kg / cm ² G, preferably 50 kg / cm
Refers to a membrane module used under high pressure of ² G or more.

On the other hand, the low-pressure membrane module has a high desalination ratio (5,
But 90% or less than 000 ppm), generally, in the following salt concentration 5,000ppm, 10~40kg / cm ² G, preferably 30kg / cm ² G
The following refers to a membrane module used under low pressure.

Both membrane modules are hollow fiber type, spiral type,
It has a tubular shape, a pleat shape, a flat plate shape, or the like, and as a material thereof, a polymer material such as cellulose acetate is used. In particular, in a low pressure membrane module, a synthetic polymer composite membrane has been widely used.

Low-pressure membranes are generally low-concentration salt water (about 5,000 ppm or less)
Used for desalting. In the present invention, by utilizing the characteristic that the low-pressure membrane has a low desalination rate, a relatively high concentration of salt-containing water having a salt concentration of about 50,000-80,000 ppm is treated at a pressure of about 30-70 kg / cm ^2. Is.

Further, as the pressure reducing means 26 , a pressure reducing valve, a restriction orifice, or the like is used.

〔Example〕

 Examples of the present invention will be described below.

Example 1 This example shows the case of treating salt-containing water having a flow rate of 5,000 T / D and a salt concentration of 70,000 ppm by a combined method of a two-stage reverse osmosis membrane method and an evaporation method as shown in FIG. ing.

Salt-containing water is first introduced into the pretreatment device 23, the solid content, and iron contained in a trace amount in the salt-containing water, manganese is removed, further, Ca is removed, the pH was adjusted to about 6.5. After that (pH before treatment is about 7.5), it is pressurized to about 60 kg / cm ² G and supplied to the first-stage low pressure reverse osmosis membrane module 20.

The first-stage membrane module 20 uses a synthetic composite membrane with the characteristics of low operating pressure and low salt rejection. About 50% of the feed water permeates the low-pressure membrane, and the salt concentration is about 27,000 ppm. Demineralized water, and the remaining about 50% is concentrated to a salt concentration of 110,000 ppm, and is supplied to the next evaporator 25 (for example, a multi-effect evaporator).

The demineralized water of the first-stage low pressure reverse osmosis membrane module 20 is
After being pressurized to approximately 65 kg / cm ² G, the second-stage high-pressure reverse osmosis membrane module using a general seawater desalination reverse osmosis membrane 22
Supplied to About 50% of the feed water passes through the high-pressure membrane, and drinking water level demineralized water of 1,670 T / D with a salt concentration of 500 ppm or less is obtained. The remaining about 50% is concentrated to a salt concentration of 54,000 ppm. This concentrated water is returned to the supply side of the first-stage low pressure reverse osmosis membrane module 20, merges with the pretreated salt-containing water, and is treated by the first-stage low pressure reverse osmosis membrane module 20. It 27 is a bitter soup treatment device, and 29 is a produced water storage tank.

〔The invention's effect〕

Since the present invention is configured as described above, it has the following effects.

(1) Treatment of salt-containing water to obtain drinking water-level demineralized water,
Since it can be separated into high-concentration concentrated water having a salt concentration of 80,000 to 120,000 ppm, the salt can be obtained as crystals when the high-concentration concentrated water is treated in the evaporation step. In addition, energy consumption can be reduced.

(2) Conventional evaporation method, one-step reverse osmosis membrane method + evaporation method, and among the methods of the present invention, a method of permeating a relatively high-concentration salt-containing water having a salt concentration of 70,000 ppm, and then performing an evaporation treatment ( Table 1 shows a comparison of the desalination ratio with the method shown in FIG. From Table 1, the method of the present invention (method shown in FIG. 2)
It can be seen that the water production ratio is high.

(3) In case of evaporation method, energy cost for water production
25kwh / m ^3, as the case of the reverse osmosis membrane method 7 kWh / m ³ (according to desalination Promotion Center article), the results calculated for the method of the present invention shown in FIG. 2 (2), 2.5 percent about energy It can be seen that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a systematic explanatory view showing an example of an apparatus for carrying out the method for treating salt-containing water of the present invention, and FIG. 2 is a comparatively high concentration (70,0
It is a systematic explanatory view showing the case (Example 1) of treating salt-containing water of (00 ppm). 22 …… High pressure reverse osmosis membrane module, 20 …… Low pressure reverse osmosis membrane module, 23 …… Pretreatment device, 24 …… High pressure pump,
25 …… Evaporator, 26 …… Decompression means, 27 …… Bitter juice treatment device, 29 …… Generated water storage tank

Claims (4)

[Claims] 1. A relatively high-concentration salt-containing water having a salt concentration of 50,000-80,000 ppm is passed through a reverse pressure osmosis membrane module (20) for low pressure at 30-70 kg / cm ² G to obtain crude demineralized water and a salt concentration of 80,000- 120,000p
pm high-concentration concentrated water and then separate this crude demineralized water
40~70kg / cm ² pressurized, the reverse osmosis membrane module for high pressure (2
A method for treating salt-containing water, characterized in that it is separated into demineralized water at a drinking water level and concentrated concentrated water through 2). 2. The method for treating salt-containing split water according to claim 1, wherein the concentrated concentrated water from the high pressure reverse osmosis membrane module (22) is supplied to the low pressure reverse osmosis membrane module (20). . 3. The high-concentration concentrated water having a salt concentration of 80,000 to 120,000 ppm from the low-pressure reverse osmosis membrane module (20) is sent to the evaporation step to obtain the salt as crystals. Method of treating salt-containing water. 4. A relatively high-concentration salt-containing water having a salt concentration of 50,000-80,000 ppm is introduced at 30-70 kg / cm ² G and separated into crude demineralized water and high-concentration concentrated water having a salt concentration of 80,000-120,000 ppm. Low pressure reverse osmosis module (20), pressurizing pump (24) to pressurize this crude demineralized water to 40 to 70 kg / cm ² G, and pressurizing salt water An apparatus for treating salt-containing water, comprising: a high-pressure reverse osmosis membrane module (22) for separating into demineralized water and concentrated water of medium concentration.