JPH06320169A - Method and apparatus for recovering silica in aqueous solution - Google Patents

Abstract

PURPOSE:To recover efficiently dissolved silica in aqueous solutions such as geothermal hot water. CONSTITUTION:Geothermal hot water supplied from a passage 3 is introduced by a valve 4 to either of the branched passages 3a, 3b which are opened at the upper ends of containers 1, 1a filled with modified material 2. Branched passages 5a, 5b are connected to the lower ends of the containers 1, 1a, and the passages 5a, 5b is combined into a passage 5. A chemical containing multivalent cations which is supplied from a chemical tank 6 through a circulating passage 7 is introduced by a valve 8 to either of the branched passages 7a, 7b which are opened at the upper ends of the container 1, 1a. Branched circulating passages 11a, 11b are connected to the branched passages 5a, 5b through valves 9, 10, and the geothermal hot water or the chemical in the containers 1, 1a is introduced by the valves 9, 10 to the passages 5 or either of the branched circulating passages 11a, 11b. The branched circulating passages 11a, 11b are combined into a circulating passage 11 connected to the chemical tank 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adsorbing and recovering silica in an aqueous solution containing silica (silicate ions) such as geothermal hot water to prevent the formation of silica scale in the flow path of the aqueous solution.

[0002]

2. Description of the Related Art Geothermal power generation is a method in which a high-temperature geothermal fluid in the ground is ejected and power is generated using separated steam. In this case, geothermal heat containing silica at a concentration of several hundred ppm together with steam. Water gushes. The ejected geothermal hot water is returned to the ground through an underground reduction well, but the temperature of the geothermal fluid is 2
While the temperature of the refluxed geothermal hot water is as low as 97 ° C to 98 ° C while the temperature is 50 ° C to 350 ° C, the solubility of silica in the geothermal hot water is relatively reduced. Moreover, since silica is concentrated as it is separated from water vapor, some of the silica contained in the geothermal hot water becomes supersaturated.

This supersaturated silica is in the form of colloid and easily deposits and adheres to the hot water path in the geothermal power plant, the inner wall of the above-mentioned underground reduction well, etc. as silica scale, so that the thermal efficiency of the heat exchanger is reduced and the hot water path This is a cause of blockage or reduction of the capacity of the above-mentioned underground reduction well. Moreover, since this silica scale is firmly attached to the inner wall or the like and is difficult to remove, when the silica scale is attached, the use of the hot water passage or the underground reduction well is stopped,
The scale must be removed. As described above, the presence of silica in the geothermal hot water is a major obstacle to the utilization of the geothermal hot water.

Therefore, there has been conventionally developed a method of removing silica contained in geothermal hot water to prevent silica scale from adhering to the hot water path or the underground reduction well. Specifically, a method in which colloidal silica is further flocculated and then recovered by flotation or ultrafiltration, a sedimentable seed is added to geothermal hot water, and supersaturated silica is deposited on the sedimentable seed to precipitate sedimentation. Examples include a method in which colloidal silica remaining in the supernatant after being removed together with the seed is recovered by ultrafiltration. Further, as a method of aggregating colloidal silica, cations such as aluminum and iron are added, or the geothermal hot water is aerated after addition of iron powder or the like, and the resulting hydroxide is treated with colloidal silica. There are methods such as adsorption and aggregation.

[0005]

However, among the above-mentioned conventional methods, in the method by floatation separation, it is necessary to add a chemical such as a flotation agent in order to float the aggregated silica, and the recovery method There is a problem that the cost increases because a power facility is required. Further, in the method using the ultrafiltration method, there is a problem that the filtration membrane is easily clogged, and it is necessary to wash or replace it each time, so that the recovery efficiency is low, and the cost increases with the replacement of the filtration membrane. It was

Moreover, if cations, iron powder, etc. are added to agglomerate the colloidal silica, surplus cations remain in the geothermal hot water, which may adversely accelerate the precipitation of silica scale. there were. The present invention has been made in view of the above circumstances, in a method of recovering silica in an aqueous solution using cations, while improving the recovery efficiency of silica, the residual amount of cations in geothermal hot water after silica removal Its purpose is to reduce.

[0007]

According to the present invention, a substance that is negatively charged in a neutral pH range is contacted with a polyvalent cation to modify the surface of the substance, and the obtained positively charged substance is modified. A method for recovering silica in an aqueous solution in which a substance is brought into contact with an aqueous solution containing silica such as geothermal hot water, and the silica dissolved in the aqueous solution is adsorbed on the surface of the modified product, and a silica recovery device applied to the recovery method. .

[0008] In particular, when the silica adsorbing ability of the modified product is lowered by the silica adsorbed on the surface, the modified product is brought into contact with the polyvalent cation to modify the silica adsorbed on the surface of the modified product. Then, the obtained positively-charged re-modified product may be brought into contact with the aqueous solution again, and silica dissolved in the aqueous solution may be adsorbed on the surface of the re-modified product.

More specifically, first, a plurality of containers filled with a substance that is negatively charged in a neutral pH range, cation circulation means for circulating the polyvalent cations in the container, and the container. First, an apparatus is provided which is provided with a water-passing means for passing the aqueous solution, and a switching means for switching the circulation of the polyvalent cations to the vessel and the water-flowing of the aqueous solution for each individual vessel.

Then, the polyvalent cations are circulated in the container to modify the surface of the substance to obtain a positively charged modified product, and then the switching means is switched to pass the aqueous solution through the container. Then, the recovery step of adsorbing silica dissolved in the aqueous solution onto the surface of the modified product to recover it, and switching the switching means again to circulate the polyvalent cation in the container, The re-reforming process of reforming the adsorbed silica to obtain a positively-charged re-reforming product is repeated for each container. In this case, the recovery process and the re-reforming process are performed in parallel in at least two containers of the plurality of containers.

[0011]

The dissolved silica in the aqueous solution has hydroxyl groups on its surface and is always negatively charged. On the other hand, the modified product used in the present invention is positively charged. Therefore, the silica is adsorbed and recovered by the reformate by ionic bond. Further, by repeating the recovery process and the re-reforming process for each individual container, and performing the recovery process and the re-reforming process in parallel in at least two containers out of a plurality of containers, silica can be obtained. Is always collected in any one of the plurality of containers. Furthermore, since the cation is used only for contact with a substance that is negatively charged in the neutral pH range, it is not necessary to add the cation to the aqueous solution, and the cation of the cation in the aqueous solution after silica recovery is eliminated. The residual amount decreases.

[0012]

Embodiments of the present invention will now be described in more detail with reference to the drawings. FIG. 1 shows an example of an apparatus for recovering silica in an aqueous solution according to the present invention. Reference numeral 1 in the figure
Reference numeral 1a is a container having a cylindrical shape with a bottom. The containers 1 and 1a are filled with a positively charged reformate 2. At the upper ends of the vessels 1 and 1a, ends of branch flow paths 3a and 3b branched from the flow path 3 of geothermal heat water via a valve (switching means) 4 are opened. Here, the geothermal hot water flows from the flow path 3 into the branch flow paths 3a and 3b by switching the valve 4.
It is possible to flow down to only one of them.

An opening is formed at the lower end of each of the containers 1 and 1a, and branch channels 5a and 5b are connected to the opening. The branch flow paths 5a and 5b are further combined into a flow path 5 for allowing geothermal water to flow down to a geothermal power generation facility or the like.

On the other hand, reference numeral 6 is a chemical liquid tank in which a chemical liquid containing polyvalent cations is stored, and branched flow paths 7a, 7b branched from the chemical liquid tank 6 via a circulation path 7 and a valve (switching means) 8. Ends of the container open at the upper ends of the containers 1 and 1a. Here, the chemical solution is used in the valve 8
It is possible to flow down from the circulation path 7 to only one of the branch circulation paths 7a and 7b by switching. As the polyvalent cation, for example, an ion of a substance selected from aluminum, iron, calcium and magnesium is used.

In addition, branch circulation paths 11 are provided in the branch flow paths 5a and 5b via valves (switching means) 9 and 10, respectively.
a and 11b are connected. Here, the geothermal hot water or the chemical liquid in the containers 1 and 1a is switched by switching the valves 9 and 10, respectively, and the flow path 5 or the branch circulation path 11a,
Only one of 11b can flow down. The branch circulation paths 11 a and 11 b are integrated into the circulation path 11, and the circulation path 11 is further connected to the chemical liquid tank 6. In addition,
Reference numeral 12 is a pump provided in the circulation path 7, and reference numeral 13 is a chemical liquid supply unit for supplying the chemical liquid to the chemical liquid tank 6.

Next, a method for recovering silica in an aqueous solution using the silica recovering apparatus having the above-mentioned structure will be described.
First, substances (hereinafter referred to as seeds) that are negatively charged in a neutral pH range, such as silica scale, quartz sand, rice husk incinerated ash, and diatomaceous earth, which are precipitated in an aqueous solution described below, are placed in the containers 1 and 1a. Fill. Next, the valves 8 and 9 are switched and the pump 12 is operated to supply the chemical liquid from the chemical liquid tank 6 to the circulation passage 7, the valve 8, the branch circulation passage 7a, the container 1, the valve 9, the branch circulation passage 11a and the circulation passage 11. After that, it is circulated again to the chemical liquid tank 6. Then, the surface of the seed filled in the container 1 is modified by the action of the polyvalent cation in the chemical liquid, and the modified product 2 that is positively charged is obtained.

When the seed filled in the container 1 is reformed into the reformed product 2, the valves 4 and 9 are switched to supply geothermal hot water containing a high concentration of silica from the passage 3 to the valve 4, Branch channel 3a, container 1, valve 9 and branch channel 5
It is made to flow down to the flow path 5 via a.

In this case, the geothermal hot water comes into contact with the reformate 2 in the container 1, but silica in the geothermal hot water has hydroxyl groups on its surface and is always negatively charged. Since the substance 2 is positively charged, the silica is adsorbed on and recovered by the reformate 2 by an ionic bond. Therefore, from the flow path 5,
Geothermal hot water with a very low silica content flows out, and as a result, precipitation and adhesion of silica scale in the subsequent hot water path or underground reduction well is prevented. This is the recovery process.

Further, during the recovery process, the valves 8 and 10 are switched and the pump 12 is operated to supply the chemical liquid from the chemical liquid tank 6 to the circulation path 7, valve 8, branch circulation path 7b, container 1a, valve 10, By circulating again to the chemical liquid tank 6 via the branched circulation path 11b and the circulation path 11, the surface of the seed filled in the container 1a is modified by the action of the polyvalent cation in the chemical solution, It is referred to as modified product 2.

When the recovery process is carried out for a long time using the reformate 2 in the container 1, the surface of the reformate 2 is covered with the silica adsorbed on the surface of the reformate 2, and the silica adsorbing ability of the reformate 2 gradually increases. Fall to. In this case, the valves 8 and 9 are switched, and the pump 12 is operated to remove the chemical solution.
From the chemical liquid tank 6, the circulation path 7, the valve 8, the branch circulation path 7
The liquid is circulated again to the chemical liquid tank 6 through a, the container 1, the valve 9, the branch circulation path 11a and the circulation path 11. Then,
The silica covering the surface of the modified product 2 is modified by the action of the polyvalent cation in the chemical solution and is positively charged, and a remodified product having a silica recovery capability is obtained. This is the re-reforming process.

On the other hand, with the start of the re-reforming process in the container 1, the valves 4 and 10 are switched to supply geothermal hot water containing a high concentration of silica from the flow path 3 to the valve 4, the branch flow path 3b and the container 1a. , Through the valve 10 and the branch channel 5b to flow down to the channel 5. As a result, this time, the recovery process is performed by the reformate 2 filled in the container 1a.

Further, when the silica adsorbing ability of the reformate 2 filled in the container 1a is lowered, the valves 4 and 9 are switched so that the geothermal hot water flows from the flow path 3 to the valve 4 and the branch flow path 3.
a, the container 1, the valve 9, and the branch channel 5a
Let it flow down. As a result, the recovery step is performed again by the re-reformed product in the container 1 obtained by the re-reforming step.

At the same time, the valves 8 and 10 are switched and the pump 12 is operated to supply the chemical liquid to the chemical liquid tank 6
From the circulation path 7, valve 8, branch circulation path 7b, container 1
a, the branch flow path 5b, the valve 10, the branch circulation path 11b, and the circulation path 11 to circulate again to the chemical liquid tank 6 to perform the re-reforming process in the container 1a, and the modified container filled in the container 1a. The substance 2 is reformed again.

By alternately performing the recovery process and the re-reforming process for each of the vessels 1 and 1a, silica is recovered from the geothermal hot water by the re-reformed product and the re-reforming by the re-reforming is performed. The silica recovery function of the reformate can be restored at the same time, and the recovery process can be performed without interruption, thereby improving the silica recovery efficiency. Here, if the surface of the seed is made porous, the surface area thereof is increased, so that the recovery efficiency of silica in the case of the modified product 2 can be further improved.

Further, since the seed or the modified product 2 is modified only by circulating the chemical solution, it is not necessary to directly add the cation to the geothermal hot water when recovering silica. Therefore, the residual cations in the geothermal hot water after silica recovery can be minimized. The chemical liquid in the chemical liquid tank 6 is replenished from the chemical liquid supply unit 13 at any time.

Further, the particle size of the re-reformed product gradually increases with the repetition of the recovery process and the re-reforming process.
The reformed product having an increased particle size is periodically withdrawn from the containers 1 and 1a after the recovery process, partially crushed and used again as the seed, and the rest is used as a cement raw material or the like.

On the other hand, as shown in FIG. 2, the ends of the branch flow passages 3a and 3b are opened at the upper ends of the containers 1 and 1a, respectively, and the branch flow passages 3a and 3b are branched from the circulation passage 7. The ends of the paths 7a and 7b may be connected via valves (switching means) 14 and 15, respectively. In this case, by switching the valves 14 and 15, only one of the geothermal hot water and the chemical liquid can flow into the containers 1 and 1a.

In the device shown in FIG. 2, the valves 9, 1
4 to switch the geothermal hot water from the flow path 3 to the flow path 5 through the valve 14, the branch flow path 3a, the container 1, the valve 9 and the branch flow path 5a, thereby performing the recovery process in the container 1. At the same time, the valves 10 and 15 are switched, and the pump 12 is operated to move the chemical liquid from the chemical liquid tank 6 to the branch circulation path 7b, the valve 15, the container 1a, the valve 1
0, the branched circulation path 11b and the circulation path 11 are circulated again to the chemical liquid tank 6 to perform the reforming or re-reforming process of the seed in the container 1a.

When carrying out the recovery process in the container 1a, the valves 10 and 15 are switched so that the geothermal hot water flows from the flow path 3 into the branch flow path 3b, the valve 15, the container 1a and the valve 10.
And the flow path 5b through the branch flow path 5b, the valves 9 and 14 are switched, and the pump 12 is operated to move the chemical solution from the chemical solution tank 6 to the branch circulation path 7
a, valve 14, container 1, valve 9, branch circuit 11a
By recirculating through the circulation path 11 to the chemical liquid tank 6 again, the reforming or re-reforming process of the seed in the container 1 is performed.

That is, in the apparatus shown in FIG. 2, the valves 9, 10, 14 and 15 are switched, and the recovery process and the re-reforming process are alternately performed between the containers 1 and 1a.
It is possible to simultaneously recover silica from geothermal hot water by the re-reformed product and recover the silica recovery function of the re-reformed product by re-reforming, and to perform the recovery process without stopping the recovery process. .

Further, as shown in FIG. 3, in the apparatus of FIG. 2, the pump 12 in the circulation passage 7 is moved into the circulation passage 11 and the upper ends of the containers 1 and 1a are closed and the branch passage 3 is formed.
By connecting a and 3b, a flow from the lower end to the upper end may be formed in the containers 1 and 1a.

In this case, the valves 9 and 14 are switched, and the geothermal hot water is supplied from the flow path 5 to the branch flow path 5a, the valve 9,
By supplying water to the flow path 3 through the container 1, the valve 14 and the branch flow path 3a, a recovery process is performed in the container 1, the valves 10 and 15 are switched, and the pump 12 is used.
To operate the chemical solution from the chemical solution tank 6 to the circulation path 1
1. Recirculation or re-reforming of the seed in the container 1a by circulating again to the chemical liquid tank 6 through the branch circulation path 11b, the valve 10, the container 1a, the valve 15, the branch circulation path 7b and the circulation path 7. Do the process.

When the recovery process is performed in the container 1a, the valves 10 and 15 are switched so that the geothermal hot water flows from the flow path 5 into the branch flow path 5b, the valve 10, the container 1a and the valve 15.
And water is sent to the flow path 3 through the branch flow path 3b. In this case, in the container 1, by switching the valves 9 and 14 and operating the pump 12, the chemical liquid flows from the chemical liquid tank 6 to the circulation passage 11, the branch circulation passage 11a, the valve 9, the container 1, the valve 14, the branch circulation. It goes without saying that the chemical solution is circulated again to the chemical liquid tank 6 via the path 7a and the circulation path 7, and as a result, the reforming or re-reforming step of the seed is performed.

In the apparatus shown in FIG. 3, the geothermal hot water and the chemical liquid form a flow from the lower end to the upper end of the vessels 1 and 1a during each of the above steps, so that the vessels 1 and 1a during each of the above steps. The reformate 2 filled in the container is the container 1, 1.
The lower end side of “a” is clogged with high density, and accordingly, the permeability of the geothermal hot water or the chemical liquid to the reformed product 2 does not decrease. In addition, there is also an effect that the accumulation of impurities on the surface of the modified product 2 is prevented.

In each of the above embodiments, the valve 4
8, 9, 10, 14, 15 switching and pump 12
The operation of each of these valves is automatically controlled by timer control, etc., but these valves 4, 8, 9, 10, 1
It is of course possible to switch between 4, 15 and the operation of the pump 12 by interlocking with a sensor for measuring the silica concentration in the geothermal hot water discharged from the silica recovery device, or manually.

[0036]

As described above, in the method for recovering silica in an aqueous solution and the apparatus for recovering silica according to the present invention, since silica is adsorbed and recovered by the reformate by ionic bond, the silica recovery efficiency is high. There is. Moreover, since the recovery process and the re-reforming process are repeated for each individual container, and the recovery process and the re-reforming process are performed in parallel in at least two of the plurality of containers, silica Recovery is always performed in any one of the plurality of containers, and as a result, the silica recovery efficiency is further enhanced.

Further, since the cation is used only for contact with a substance that is negatively charged in the neutral pH range, it is not necessary to add the cation to the aqueous solution. As a result, the residual amount of the cations in the aqueous solution after silica recovery is reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a silica recovery device according to the present invention.

FIG. 2 is a diagram showing a structure of a silica recovery device according to the present invention.

FIG. 3 is a diagram showing a structure of a silica recovery device according to the present invention.

[Explanation of symbols]

1, 1a Container 2 Reformate 3,5 Flow path 3a, 3b, 5a, 5b Branch flow path 4, 8, 9, 10, 14, 15 Valve (switching means) 6 Chemical liquid tank 7, 11 Circulation path 7a, 7b, 11a, 11b Branch circuit 12 Pump 13 Chemical supply unit

Claims (7)

[Claims] 1. A substance which is negatively charged in a neutral pH range is contacted with a polyvalent cation to modify the surface of the substance, and the obtained positively charged modified product is an aqueous solution containing silica. A method for recovering silica in an aqueous solution, which comprises bringing the silica dissolved in the aqueous solution into contact with the surface of the modified product to be adsorbed. 2. The aqueous solution according to claim 1, wherein a substance selected from silica scale, quartz sand, rice husk incineration ash, and diatomaceous earth that precipitates in the aqueous solution is used as the substance. Silica recovery method. 3. The method for recovering silica in an aqueous solution according to claim 1, wherein the surface of the substance is porous. 4. The positively-charged product obtained by contacting the modified product having a reduced silica adsorption ability with silica adsorbed on the surface with the polyvalent cation to modify the silica adsorbed on the surface of the modified product. The silica recovery in the aqueous solution according to claim 1, wherein the re-modified product is brought into contact with an aqueous solution containing silica to adsorb the silica dissolved in the aqueous solution onto the surface of the re-modified product. Law. 5. The ion of a substance selected from aluminum, iron, calcium and magnesium is used as the polyvalent cation.
A method for recovering silica in an aqueous solution according to 3 or 4. 6. A plurality of containers filled with a substance that is negatively charged in a neutral pH range, a cation circulation means for circulating the polyvalent cations in the container, and the aqueous solution passing through the container. An apparatus for recovering silica in an aqueous solution, comprising: a water-passing means for allowing the water to flow; and a switching means for switching the circulation of the polyvalent cation to the vessel and the water-flowing of the aqueous solution for each individual vessel. 7. A plurality of containers filled with a substance that is negatively charged in a neutral pH range, a cation circulation means for circulating the polyvalent cations in the container, and water flow of the aqueous solution through the container. A method for recovering silica in an aqueous solution using an apparatus comprising: a water-passing means for allowing the water to flow; and a means for switching the circulation of the polyvalent cation to the vessel and the water flow of the aqueous solution for each individual vessel, After circulating the polyvalent cations in the container to modify the surface of the substance to form a positively charged modified product, the switching means is switched to pass an aqueous solution containing silica into the container, A recovery process of adsorbing and recovering silica dissolved in the aqueous solution on the surface of the modified product, and switching the switching means again to circulate the polyvalent cation in the container and adsorb it on the surface of the modified product. Modified silica The re-reforming process of positively charged re-reforming product is repeatedly performed for each individual container, and the recovery process and the re-reforming process are performed in parallel in at least two of the plurality of containers. A method for recovering silica in an aqueous solution, which is performed by