JP2015188850A - Method and apparatus for treating geothermal water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for treating geothermal water, in each of which silica in the geothermal water can be removed satisfactorily and the purity of the silica in the produced sludge can be made higher.SOLUTION: The method for treating geothermal water comprises: a polymerization reaction step of bringing raw water into contact with the returned sludge to polymerize silicic acid in the raw water; an anion polymer addition step of adding an anion polymer to the liquid obtained at the polymerization reaction step; a cation polymer addition step of adding a cation polymer to the liquid obtained at the anion polymer addition step; a solid-liquid separation step of subjecting the liquid obtained at the cation polymer addition step to solid-liquid separation; and a sludge return step of returning at least a part of the sludge separated at the solid-liquid separation step to the polymerization reaction step. The apparatus for treating geothermal water is also provided.

Description

  The present invention relates to a method and an apparatus for treating geothermal water containing silica in a supersaturated state, and more particularly, to remove silica in geothermal water efficiently and recover a silica-containing solid having a low water content. The present invention relates to a hot water treatment method and apparatus.

  Geothermal power generation involves generating high-temperature geothermal fluid in the ground and generating power using separated water vapor. In this case, geothermal water (geothermal water) containing silica at a concentration of several hundred ppm with water vapor is used. ) Erupts. The ejected geothermal water is returned to the ground through an underground reduction well, whereas the temperature of the geothermal fluid is 250 ° C. to 350 ° C., whereas the temperature of the returned geothermal water is 90 in an open reduction type. Since the temperature is as low as 110 ° C. to 95 ° C., 110 ° C. to 140 ° C. in the high temperature reduction method, and 90 ° C. to 95 ° C. in the flash binary method or the double flash method, the solubility of silica in geothermal water is relatively lowered. Moreover, since silica is concentrated with the separation from water vapor, a part of the silica contained in the geothermal water is supersaturated.

  This supersaturated silica is likely to deposit and adhere as a silica scale on the hot water path in the geothermal power plant and the inner wall of the underground reduction well, etc., so that the heat efficiency of the heat exchanger is reduced, the hot water path is blocked, or the underground reduction well This causes a decrease in capacity. In addition, since the silica scale adheres firmly to the inner wall and the like and is difficult to remove, when the silica scale adheres, the use of the hot water path or the underground reduction well is interrupted, and the silica scale is removed. Must be removed. Thus, the presence of silica in geothermal water is a major obstacle to the use of geothermal water.

  Japanese Patent Publication No. 3-24278 (Japanese Patent Laid-Open No. 58-86864) discloses a method for removing silica contained in geothermal water and preventing silica scale from adhering to the hydrothermal channel or underground reduction well. Alternatively, the geothermal water after steam production is retained in a retention tank and the supersaturated silica in the geothermal water is changed to polymerized silica, and then an inorganic flocculant (Al salt, Fe salt, Ca salt or Mg salt) in the coagulation sedimentation tank. Describes a method of coagulating and precipitating to remove silica in hot water to a saturation solubility or lower.

  Further, in JP-A-7-24475, a seed having silica adsorptivity is added to geothermal water, and silica in geothermal water is adsorbed to the seed, followed by solid-liquid separation, and a part of the obtained solid content is obtained. A method for treating geothermal water to be reused as a seed, and after adding calcium chloride to the geothermal water as necessary, the gel is obtained by heating and concentrating the geothermal water until the silica in the geothermal water gels. A method is described in which a part of is reused as the seed.

3-24278 JP-A-7-24475

  As described in Patent Document 1, after the geothermal water is retained and polymerized, the silica is efficiently removed by adding the Al salt, Fe salt, Ca salt or Mg salt to agglomerate and remove the silica. In addition, sludge having a low moisture content can be obtained. However, the addition of the above salt lowers the silica purity in the sludge, making it difficult to effectively use it as a valuable material such as a cement raw material.

As in Patent Document 2, in the method of generating silica gel and adding it to geothermal water as a seed, dissolved silica in water can be efficiently removed by increasing the polymerization reaction area, and high-purity silica can be recovered. If the added silica gel is not removed from the geothermal water, the silica will return to the reduction well along with the treated water as a scale nucleus, which may increase the silica scaling risk. In the polymerization reaction by circulation of mere silica gel, activated reactive silanol groups of the silica polymer surface ^{(≡Si-OH + OH - ⇔≡Si} -O - + H 2 O) and the polymerization of the silanol group active sites and molecular silica monomer Reactions such as reaction (≡Si—O ⁻ + Si (OH) ₄ ⇔≡Si—O—Si (OH) ₃ + OH ⁻ ) do not proceed sufficiently.

  The present invention provides a method and apparatus for treating geothermal water that solves the above-mentioned conventional problems, can sufficiently remove silica of geothermal water, and has high silica purity in the generated sludge. With the goal.

  The method for treating geothermal water of the present invention includes a polymerization reaction step in which geothermal water and return sludge are brought into contact with each other to polymerize silica in geothermal water, and an anionic polymer addition step in which an anionic polymer is added to the liquid from the polymerization reaction step. A cationic polymer addition step for adding a cationic polymer to the liquid from the anionic polymer addition step, a solid-liquid separation step for solid-liquid separation of the liquid from the cationic polymer addition step, and sludge separated in the solid-liquid separation step A sludge returning step of returning at least a part of the sludge to the polymerization reaction step.

  The geothermal water treatment apparatus of the present invention comprises a polymerization reaction tank for bringing geothermal water and return sludge into contact with each other to polymerize silica in geothermal water, and an anionic polymer addition tank for adding an anionic polymer to the liquid from the polymerization reaction tank. A cationic polymer addition tank for adding a cationic polymer to the liquid from the anion polymer addition tank, a solid-liquid separation means for solid-liquid separation of the liquid from the cationic polymer addition tank, and sludge separated by the solid-liquid separation means And a sludge returning means for returning at least a part thereof to the polymerization reaction step.

  In the present invention, the pH in the polymerization reaction step is preferably 7.0 to 8.7. In addition, when raw | natural water pH is lower than 7.0, an acid addition process is added and it adjusts so that it may become the said pH. Although there is no restriction | limiting in particular as said acid, Hydrochloric acid, a sulfuric acid, etc. can be used.

  In the present invention, it is preferable to add alkali to part or all of the returned sludge so that the pH becomes 8.5 to 11, and then return it to the polymerization reaction step.

  In the present invention, it is preferable to adjust the addition amount of the cationic polymer by measuring the turbidity of the liquid from the cationic polymer addition step or the separated water from the solid-liquid separation step.

  In the present invention, the silica in the geothermal water is polymerized by adjusting the pH of the geothermal water to 7.0 to 8.7, then an anionic polymer is added, and then a cationic polymer is added to generate a floc. Is separated from geothermal water by solid-liquid separation. By the addition of this anionic polymer, the polymerized silica is uniformly dispersed in geothermal water, and the subsequent addition of the cationic polymer causes the polymerized silica to agglomerate in a form involving the anionic polymer, thereby growing a floc with good solid-liquid separation properties. To do. By separating this floc into solid and liquid, treated water having a low silica concentration can be obtained.

  In the present invention, the silica polymerization reaction and agglomeration reaction are allowed to proceed without adding any Al salt, Fe salt, Ca salt or Mg salt, so that high-purity silica can be recovered. It can be used as a product.

It is a flowchart explaining the processing method and apparatus of the geothermal water of this invention. It is a flowchart of the apparatus used in the Example.

  Hereinafter, the present invention will be described in more detail.

  The geothermal water to be treated in the present invention is hot water immediately after jetting or after steam production (usually 80 ° C. or higher, pH is 7.0 to 9.0). The geothermal water usually contains about 500 to 1000 mg / L of silica.

In the present invention, this silica is removed in the following four steps as shown in FIG.
1) Geothermal water is introduced into the polymerization reaction tank 1, and silica sludge (at least part of which is modified in the chemical reaction tank 2) from the subsequent stage is added to cause the silica to undergo a polymerization reaction. . This polymerization reaction increases the amount of SS.
2) Add an anionic polymer in the first coagulation tank 3 and disperse it uniformly.
3) A cationic polymer is added in the second aggregating tank 4 to crosslink the polymerized silica and the anionic polymer to form (aggregate) flocs with good sedimentation.
4) The floc is removed by the solid-liquid separation means (precipitation tank in FIG. 1) 5.

  As the polymerization reaction in the polymerization reaction tank 1 proceeds sufficiently, the addition amount of the cationic polymer necessary for charge neutralization of the silica and the anion polymer in the second aggregation tank 4 can be reduced. The residence time in the polymerization reactor 1 is preferably about 0.1 to 1 h, particularly about 0.3 to 0.6 h. The pH of the polymerization reactor 1 is preferably 7.0 to 8.7, particularly preferably 7.4 to 8.3. If the pH is too low, the polymerization reaction is difficult to proceed. If the pH is too high, the silica is easily ionized, and even if polymerized, it is easily dissolved. Further, since boron and bicarbonate ions in water serve as a pH buffer, the amount of acid / alkali used is greatly affected as the pH deviates from the raw water pH.

  When the amorphous (total) silica concentration is reduced from about 800 mg / L to about 400 mg / L, the amount of the anionic polymer added in the first aggregating tank 3 is preferably about 1 to 10 mg / L, particularly preferably 2 to 5 mg / L. The addition amount of the anionic polymer is preferably determined based on this addition amount in proportion to the silica concentration in the geothermal water. When there is too much addition amount of an anionic polymer, in order to neutralize the charge derived from an anion polymer, the required addition amount of the cationic polymer in the 2nd aggregation tank 4 will increase. When the amount of the anionic polymer added is too small, the floc strength is not sufficient and the sedimentation property is deteriorated. The anionic polymer is not particularly limited, but polyacrylic acid, a copolymer of acrylic acid and acrylamide, a polyacrylamide hydrolyzate, a copolymer of acrylamide and 2-methylpropanesulfonic acid, A salt or the like can be used, and the addition amount depends on the anion degree of the polymer, but is preferably about 1 to 10 mg / L, particularly about 2 to 5 mg / L.

  If the addition amount of the cationic polymer in the second flocculation tank 4 is too small, turbidity remains in the treated water after solid-liquid separation. On the other hand, even if added excessively, floc is dispersed and a lot of turbidity is generated. In order to generate flocs with good sedimentation properties, the turbidity of the liquid after the addition of the cationic polymer or the treated water after the solid-liquid separation treatment is measured, and the amount of the cationic polymer added is adjusted so that this turbidity is minimized. It is preferable to adjust. Here, since the residence time is short when the solid-liquid separation means 5 is a centrifuge, the turbidity of treated water after solid-liquid separation may be measured. Therefore, the turbidity measurement location in the case of using a sedimentation tank is preferably the upper part of the feed well 5a from which the supernatant from which the floc has been removed can be collected.

  The turbidimeter may be any of a transmitted light method, a scattered light method, a surface scattered light method and the like, but a non-contact type surface scattered light method which is not easily affected by silica scale is desirable. However, since there is a limit to heat resistance, it is preferable to take measures such as measurement after dilution and cooling with pure water or tap water. In addition, in order to remove a small amount of growth flocs contained in the collected water and measure the concentration of only turbidity that is difficult to settle or non-sediment, It is desirable to dilute and measure water that has passed through a solid-liquid separation tank at a flow rate. The standard for minimizing turbidity should be 20 NTU or less, more preferably 10 NTU or less.

Normally, control is performed to increase the amount of cationic polymer added in order to minimize the turbidity of solid / liquid separation treated water, but if the turbidity of solid / liquid separation treated water tends to increase even if the amount of cationic polymer added is increased, It is preferable to perform control so as to switch the control so that the addition amount of the cationic polymer is regarded as excessive. The cationic polymer is not particularly limited, but polyethyleneimine, polyallylamine, polyvinylamine, poly (2-dimethylaminoethyl methacrylate), poly (2-vinyl-1-methylpyridinium), poly (diallyl) Dimethylammonium), dialkylamine-epichlorohydrin polycondensate, polylysine, chitosan, and the like, and the addition amount depends on the cation degree of the polymer,
1-20 mg / L, especially about 2-10 mg / L is preferable.

  The silica removal treatment is possible even if the cationic polymer is added in the first flocculating tank 3 and the anionic polymer is added in the second flocculating tank 4, but in this case, the required amount of the cationic polymer is not clear. According to the flow of FIG. 1, after the floc grows to some extent, the turbidity of the liquid can be measured to determine the necessary amount of the cationic polymer, so that the amount of the cationic polymer added can be appropriately controlled. .

  As the solid-liquid separation means 5, a precipitation tank, a centrifuge, an MF membrane, or the like can be used. However, in membrane filtration, there is a possibility of clogging with colloidal silica, and thus a precipitation tank or a centrifuge is desirable. In the solid-liquid separation means 5, turbidity management of the treated water is very important. The turbidity of the supernatant is measured, and when the measured value rises, it is preferable to take measures such as filtering with a subsequent emergency filter.

A part of the sludge generated by the solid-liquid separation in the solid-liquid separation means 5 is pulled out by the sludge pump 6 and reduced using a centrifugal concentrator or the like, and then dehydrated using a centrifugal dehydrator or the like. The remainder of the sludge is returned to the polymerization reaction tank 1 through the return lines 7 and 7a. At this time, the silanol group of the silica in the sludge is dissociated and activated, so a part or all of the returned sludge is lined up. It is preferable to add sodium hydroxide so that the pH of the chemical reaction tank 2 is about 8.5 to 10 through the chemical reaction tank 2 via 7b. The activation reaction of the silanol group on the silica polymer surface is represented by the following formula.
≡Si—OH + OH ⁻ ⇔≡Si—O ⁻ + H ₂ O

  The activated sludge is sent to the polymerization reaction tank 1 via the line 8 and reacts with the silica monomer in the hot water that also flows into the polymerization reaction tank 1 to proceed the polymerization reaction.

The polymerization reaction of the silanol group active site and the molecular silica monomer in the polymerization reaction tank 1 is represented by the following formula.
≡Si—O ⁻ + Si (OH) ₄ ⇔≡Si—O—Si (OH) ₃ + OH ⁻

  Although there is no restriction | limiting in particular in SS concentration in the polymerization reaction tank 1, Since the reaction field with the silica monomer in hot water increases so that SS concentration is high, it is desirable to set it as about 2000-10000 mg / L, and it is in this range. It is desirable to control the amount of returned sludge so that it enters. As a standard of the return amount, although it depends on the sludge SS concentration, about 1/10 to 1/4 capacity with respect to the inflow amount of hot water is desirable.

  There are no particular limitations on the ratio of the return sludge flow into the chemical reaction tank 2 and the amount of NaOH added to the chemical reaction tank 2, but the pH in the chemical reaction tank 2 tends to activate silanol groups and is 8.5 to 10.0. It is preferable to adjust so that it becomes. The remaining return sludge, although less active, still plays an important role as a reaction site for silica polymerization.

  In the present invention, the chemical reaction tank 2 is not essential and may be omitted depending on the required level of silica removal. When the chemical reaction tank 2 is omitted, NaOH is added to the polymerization reaction tank 1 so that the pH of the polymerization reaction tank 1 is 7 to 8.7, particularly 7.4 to 8.3.

  In general, in silica polymerization reaction, adhesion and growth of silica scale on a pH meter, a stirring blade, an inner wall of the apparatus and the like becomes a problem. In order to suppress the scale adhesion, the inner surface of the polymerization reaction tank 1 is made of a material that does not easily adhere to the scale (eg, a material coated with fluororesin), or the pH meter is doubled and periodically immersed in an alkali. It is preferable to take measures such as increasing the amount of returned sludge to promote preferential polymerization of silica monomer into sludge.

  Some hot water contains arsenic, and silica sludge removed and recovered from hot water may contain arsenic. Most of the arsenic in the sludge can be removed by washing with a turbine condensate containing no arsenic. Examples of the sludge washing method include a method in which the recovered silica sludge is dehydrated by a centrifugal dehydrator and then the washing water is injected to extrude arsenic adhering to the dehydrated cake.

  By passing through the above process, a silica polymer can be recovered from geothermal water with a small amount of chemical consumption, and treated water with a reduced silica concentration can be obtained. The treated water is returned to the reducing well, but the scaling risk can be further reduced by adding sulfuric acid to reduce the pH. The dehydrated cake of recovered silica has a moisture content of about 80%, but can be used as a cement raw material after natural drying or hot air drying.

  Hereinafter, examples and comparative examples will be described. In the following examples and comparative examples, the test apparatus shown in FIG. 2 was used.

  In this test apparatus, raw water is introduced from a raw water tank 11 into a 5 L pre-constant temperature tank 13 by a raw water pump 12. The pre-temperature bath 13 is maintained at 90 to 95 ° C., which is substantially equal to the return temperature to the reduction well by the heater 13a.

  The raw water in the pre-isothermal tank 13 is introduced into the neutralization tank 14, and 20 wt% hydrochloric acid in the hydrochloric acid tank 15 is added by the pump 16 to a pH of about 6 to temporarily delay the silica polymerization reaction. The liquid in the neutralization tank 14 is introduced (transferred) into the first reaction tank 17. In the first reaction tank (polymerization reaction tank) 17, the modified sludge from the chemical reaction tank 33 can be added via the line 18, and the precipitated sludge from the precipitation tank 29 can be added via the line 19. Then, a 25 wt% aqueous solution of caustic soda can be added from the caustic soda tank 21 via the line 20 a and the pump 20.

  The liquid in the first reaction tank 17 is transferred to the second reaction tank 22, and further transferred from the second reaction tank 22 to the first aggregation tank 23. An anionic polymer aqueous solution can be added to the first flocculation tank 23 from an anionic polymer tank 24 through a pump 25. As the anionic polymer aqueous solution, a 0.1% aqueous solution of Cliff Rock PA-331 manufactured by Kurita Kogyo Co., Ltd. was used.

  The liquid in the first flocculation tank 23 is transferred to the second flocculation tank 26. A cationic polymer aqueous solution can be added to the second flocculation tank 26 from a cationic polymer tank 27 via a pump 28. As the cationic polymer aqueous solution, a 1% aqueous solution of Zeta Ace P-702 manufactured by Kurita Kogyo Co., Ltd. was used.

  The liquid in the second flocculation tank 26 is introduced into the lower part of the precipitation tank 29, and the supernatant water flows out as treated water from the upper part of the precipitation tank 29. The sludge settled in the settling tank 29 is taken out via the line 30 and the sludge pump 31. A part of the extracted sludge is returned to the first reaction tank 17 via the line 19. The remainder of the sludge is introduced into the chemical reaction tank 33 via the line 32. Caustic soda in the caustic soda tank 21 can be added to the chemical reaction tank 33 via the pump 20 and the line 20b. Sludge to which caustic soda is added and mixed in the chemical reaction tank 33 can be returned to the first reaction tank 17 via the line 18.

  The tanks 14, 17, 22, 23, 26, 29 and 33 are heated by a constant temperature bath 40 of 100 ° C. The tanks 14, 17, 22, 23, 26, 33 are provided with a stirrer M. The tanks 14 and 17 are provided with pH meters, and the dosages of the pumps 16 and 20 are controlled so that the tanks 14 and 17 have a predetermined pH. The tank 13 is provided with a thermometer TI.

  The volume V, residence time (RT), pH, etc. of each tank are as follows.

Neutralization tank 14: V = 100 mL, RT = 1 min, pH about 6
First reaction tank 17: V = 2L, RT = 16-20min, pH: as shown in Table 1 Second reaction tank 22: V = 2L, RT = 16-20min,
pH: almost the same as the first reaction tank 17 First coagulation tank 23: V = 500 mL, RT = 4-5 min
Second aggregation tank 26: V = 500 mL, RT = 4-5 min
Settling tank 29: horizontal sectional area A = 10 cm ² , LV = 6 m / h
Chemical reaction tank 33: V = 50 mL, RT <5 min, pH: as shown in Table 1 As raw water in the raw water tank 11, a sodium silicate aqueous solution having a total silica concentration of 800 mg / L (25 ° C., pH 12) was used.

[Example 1]
The raw water was supplied to the test apparatus shown in FIG. 2 at 6 L / h for treatment. The sludge generated in the sedimentation tank 29 was directly returned to the first reaction tank 17 at a rate of 600 mL / h, and no sludge was supplied to the chemical reaction tank 33. The amount of the anionic polymer added was 4 mg / L as the polymer amount.

  The addition amount of the cationic polymer was controlled in the range of 5 to 40 mg / L so that the turbidity of the treated water (supernatant water) from the precipitation tank 29 was 10 NTU or less. The average addition amount during this period is as shown in Table 1. The same applies to Examples 2 and 3 and Comparative Examples 1 and 2 below.

The treatment was continued for one week, and during this time, the sludge was extracted from the settling tank 29 as necessary so that the sludge interface height in the settling tank 29 was constant. After one week of continuous treatment, 1 L of sludge in the sedimentation tank 29 was collected and subjected to an interfacial sedimentation test to determine the maximum sludge interfacial sedimentation rate. Further, the moisture content of the sludge after the sludge collected from the settling tank 29 was dehydrated for 60 minutes with a 1 kg / cm ² press dehydrator was measured. Furthermore, the total silica concentration in the treated water was measured. The results are shown in Table 1.

[Example 2]
Of the sludge from the sedimentation tank 29, 500 mL / h was directly returned to the first reaction tank 17, and after 100 mL / h was introduced into the chemical reaction tank 33, it was returned to the first reaction tank 17. As a result of adjusting the amount of NaOH added so that the pH of the first reaction tank 17 was 7.8, the pH of the chemical reaction tank 33 changed around 11. Other than that, raw water was treated under the same conditions as in Example 1, and the same measurement was performed. The results are shown in Table 1.

[Example 3]
The entire amount of return sludge from the sedimentation tank 29 of 600 mL / h was introduced into the chemical reaction tank 33 and returned to the first reaction tank 17. As a result of adjusting the amount of NaOH added so that the pH of the first reaction tank 17 was 7.8, the pH of the chemical reaction tank 33 changed around 10. Other than that, raw water was treated under the same conditions as in Example 1, and the same measurement was performed. The results are shown in Table 1.

[Comparative Example 1]
The sludge was not returned at all, the anionic polymer was not added, and the amount of cationic polymer added was 40 mg / L. Other than that, raw water was treated under the same conditions as in Example 1, and the same measurement was performed. The results are shown in Table 1.

[Comparative Example 2]
In Comparative Example 1, raw water was treated under the same conditions except that 4 mg / L of an anionic polymer was added, and the same measurement was performed. The results are shown in Table 1.

[Comparative Example 3]
In Example 1, the raw water was treated under the same conditions except that the pH of the first reaction tank 17 was set to 6 and 35 mg / L of the cationic polymer was added, and the same measurement was performed. The results are shown in Table 1.

[Comparative Example 4]
In Example 1, raw water was treated under the same conditions except that the pH of the first reaction tank 17 was set to 9, and the same measurement was performed. The results are shown in Table 1.

  As is apparent from Table 1, in Examples 1 to 3, the amount of cationic polymer added was reduced to 5 mg / L, and the sludge interface sedimentation rate was improved to 20 to 30 m / h. On the other hand, in Comparative Examples 1 to 3, the amount of cationic polymer added was large, the sludge interface sedimentation rate was decreased, and the dehydrated sludge moisture content was also increased compared to the Examples. In Comparative Example 4, although the sludge interface sedimentation rate and the dehydrated sludge moisture content are substantially the same as those in the example, the total silica concentration of the treated water is increased.

  Thus, according to the present invention, the required amount of the cationic polymer, the sludge interfacial sedimentation rate, and the water content of the dewatered sludge can be greatly improved.

DESCRIPTION OF SYMBOLS 1 Polymerization reaction tank 2 Chemical reaction tank 3 1st coagulation tank 4 2nd coagulation tank 5 Settling tank

Claims (8)

A polymerization reaction step of bringing geothermal water and return sludge into contact with each other and polymerizing silica in the geothermal water;
An anionic polymer addition step of adding an anionic polymer to the liquid from the polymerization reaction step;
A cationic polymer addition step of adding a cationic polymer to the liquid from the anionic polymer addition step;
A solid-liquid separation step for solid-liquid separation of the liquid from the cationic polymer addition step;
A method for treating geothermal water, comprising: a sludge return step of returning at least a part of the sludge separated in the solid-liquid separation step to the polymerization reaction step.   The method for treating geothermal water according to claim 1, wherein the pH in the polymerization reaction step is 7.0 to 8.7.   The method for treating geothermal water according to claim 1 or 2, wherein an alkali is added to a part or all of the returned sludge and then returned to the polymerization reaction step.   4. The method according to claim 1, further comprising a step of adjusting the addition amount of the cationic polymer by measuring the turbidity of the liquid from the cationic polymer addition step or the separated water from the solid-liquid separation step. How to treat geothermal water. A polymerization reaction tank in which geothermal water and returned sludge are contacted to polymerize silica in geothermal water;
An anionic polymer addition tank for adding an anionic polymer to the liquid from the polymerization reaction tank;
A cationic polymer addition tank for adding a cationic polymer to the liquid from the anion polymer addition tank;
Solid-liquid separation means for solid-liquid separation of the liquid from the cationic polymer addition tank;
An apparatus for treating geothermal water, comprising sludge return means for returning at least a part of the sludge separated by the solid-liquid separation means to the polymerization reaction step.   6. The apparatus for treating geothermal water according to claim 5, further comprising pH adjusting means for adjusting the pH in the polymerization reaction tank to 7.0 to 8.7.   7. The geothermal water treatment apparatus according to claim 5 or 6, further comprising a chemical reaction tank for adding an alkali to a part or all of the returned sludge by an alkali adding means and then returning it to the polymerization reaction step.   8. The method according to claim 5, further comprising a cationic polymer addition control unit that adjusts the addition amount of the cationic polymer by measuring the turbidity of the liquid from the cationic polymer addition tank or the separated water from the solid-liquid separation unit. A geothermal water treatment device.

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