JP2014144435A - Treatment apparatus of salt-containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently take valuable salts of a low environmental load out of salt-containing wastewater (accompanying water, etc.) that contains much of sodium hydrogencarbonate and sodium carbonate and has a large fluctuation of water quality.SOLUTION: An treatment apparatus includes a thickening mechanism for thickening salt-containing wastewater containing sodium chloride and an electrolysis tank that is partitioned into a positive electrode chamber and a negative electrode chamber by a sodium-ion-permeable ion-exchange membrane and electrolyzes the salt-containing wastewater to produce sodium hydroxide. The treatment apparatus further includes between the thickening mechanism and the electrolysis tank a decarbonation mechanism for removing sodium carbonate and sodium hydrogencarbonate from the salt-containing wastewater, a flocculation filtration mechanism for removing divalent ions as a flocculate from the salt-containing wastewater, and a chelate resin for removing divalent ions by adsorption from the salt-containing wastewater.

Description

  The present invention relates to a salt wastewater treatment apparatus containing sodium bicarbonate at a high concentration represented by water associated with a gas field.

  In the mining of oil and gas fields, accompanying water containing salt is generated along with oil and natural gas. In recent years, from the viewpoint of environmental protection, it has been required to treat this accompanying water by a method with a small amount of waste generation. The feature of accompanying water is that it contains a high concentration of a mixed salt of sodium hydrogen carbonate, sodium carbonate and sodium chloride.

  As a technique for treating sodium chloride drainage containing sodium carbonate, Patent Document 1 describes a technique in which hydrochloric acid is added to the drainage for decarboxylation to extract high-purity sodium chloride.

  As a method for treating waste water containing sodium chloride, Patent Document 2 describes a technique using electrolysis. In this method, as in general electrolysis, an electrolytic cell in which a positive electrode chamber and a negative electrode chamber are partitioned by an ion exchange membrane is used, drainage containing sodium chloride is injected into the positive electrode chamber, and sodium hydroxide is extracted from the negative electrode chamber. .

JP 2008-247647 A Special table 2003-514666 gazette

  The accompanying water has a large variation in water quality and contains a large amount of impurities such as divalent ions that significantly reduce the efficiency and life of the electrolytic cell. Therefore, in order to treat the accompanying water with an electrolytic cell and take out valuable salt (for example, sodium hydroxide) efficiently, it is necessary to reduce the fluctuation of the quality of the treated water injected into the electrolytic cell.

  An object of the present invention is to take out highly valuable salt with low environmental load from salt drainage (eg, associated water) containing a large amount of sodium hydrogen carbonate and sodium carbonate and having a large fluctuation in water quality.

  In order to achieve the above object, the present invention provides a concentration mechanism for concentrating salt wastewater containing sodium chloride, and a positive electrode chamber and a negative electrode chamber separated by an ion exchange membrane that transmits sodium ions, and the salt wastewater is electrolyzed. An electrolyzer that generates sodium hydroxide, and a decarboxylation mechanism that removes sodium carbonate and sodium bicarbonate from the salt drainage between the concentration mechanism and the electrolyzer, and a divalent ion from the salt drainage And a chelating resin that adsorbs and removes divalent ions from the salt drainage.

  ADVANTAGE OF THE INVENTION According to this invention, valuable salt with low environmental impact can be taken out from salt waste water with high efficiency.

It is a system block diagram which shows an example of the Example of the salt waste water treatment apparatus of this invention. It is a system block diagram which shows an example of the Example of the salt waste water treatment apparatus of this invention. It is a system block diagram which shows an example of the Example of the salt waste water treatment apparatus of this invention. It is a system block diagram which shows an example of the Example of the salt waste water treatment apparatus of this invention. It is a system block diagram which shows an example of the Example of the salt waste water treatment apparatus of this invention. It is a system block diagram which shows an example of the Example of the salt waste water treatment apparatus of this invention. It is a system block diagram which shows an example of the Example of the salt waste water treatment apparatus of this invention. It is a system block diagram which shows the example in the case of applying the salt drainage processing apparatus of this invention to a gas field accompanying water treatment.

  In the present invention, sodium hydroxide is obtained by electrolysis after removing carbonate radicals (bicarbonate ions, carbonate ions, etc.) and divalent ions from a salt drainage obtained by separating and concentrating water.

  In the following description, an evaporative concentration apparatus that evaporates and concentrates salt water is used. Provide a decarbonation mechanism that removes carbonate radicals, an aggregation filtration mechanism that removes most of the divalent ions as aggregates, and a chelate resin that removes divalent ions with high accuracy between the evaporation concentrator and the electrolytic cell. Therefore, the fluctuation | variation of the water quality of the salt waste_water | drain supplied to an electrolytic cell can be suppressed, and sodium hydroxide which is valuable salt can be produced | generated efficiently.

FIG. 1 is a diagram in the case where carbonate radicals are removed by a decarboxylation mechanism 4 after removing divalent ions from the concentrated salt drainage by the coagulation filtration mechanism 2 and the chelate resin 3. The salt water 11 is concentrated by the evaporative concentration mechanism 1 and separated into purified water and concentrated salt water. The divalent ions in the concentrated salt effluent are removed as secondary waste 13 by the coagulation filtration mechanism 2 to be roughly purified, and the divalent ions are further removed by the chelate resin 3 at the subsequent stage to perform precise purification. The divalent ions adsorbed on the chelate resin 3 are washed away by the chemical washing solution 14. Concentrated salt drainage from which divalent ions have been removed is sent to the decarboxylation mechanism 4 and acid such as hydrochloric acid is added to convert carbonate radicals to sodium chloride to remove carbonate radicals. Turn into. The reaction in the decarboxylation mechanism 4 is represented by the following formula.
[Chemical formula 1]
[Na ₂ CO ₃ + HCl → NaCl + NaHCO ₃
[Chemical formula 2]
NaHCO ₃ + HCl → NaCl + H ₂ O + CO ₂

The salt drainage is converted into a high-concentration sodium chloride solution with high purity by the coagulation filtration mechanism 2, the chelate resin 3, and the decarboxylation mechanism 4. This solution and dilute sodium hydroxide solution 12 are poured into the electrolytic cell 5 and electrolyzed to produce sodium hydroxide. The reaction in the electrolytic cell 5 is represented by the following formula.
[Chemical formula 3]
2NaCl → 2Na ⁺ + 2Cl ⁻ → 2Na ⁺ + Cl ₂ + 2e ⁻
[Chemical formula 4]
2H ₂ O + 2e ⁻ → 2OH ⁻ + H ₂
[Chemical formula 5]
Na ⁺ + OH ⁻ → NaOH

At this time, since the diluted salt water 15 is discharged from the positive electrode chamber of the electrolytic cell 5, it may be returned to the previous apparatus (for example, the evaporation and concentration mechanism 1) and used again for electrolysis. Carbonates contained in the salt wastewater CO ₃ ^2- and HCO ^- because anions are also separated and removed as a reaction to the carbonate with a cation in the aggregation filtration step. Therefore, by providing the decarboxylation mechanism 4 at the subsequent stage of the coagulation filtration mechanism 2 and the chelate resin 3, the amount of hydrochloric acid used during decarboxylation can be reduced.

  FIG. 2 is a diagram in the case where another concentration mechanism 1b is provided at the subsequent stage of the decarbonation mechanism 4 to concentrate the salt drainage again, and the aggregation filtration mechanism 2 and the chelate resin 3 are provided at the subsequent stage. The concentration mechanism 1b may be the same as the evaporation concentration mechanism 1a. Since the acid is added in the decarboxylation mechanism 4, the pH of the salt drainage downstream of the decarboxylation mechanism 4 is low, and scale formation in the concentration mechanism 1b can be prevented. Since the dilute salt water 15 discharged from the positive electrode chamber of the electrolytic cell 5 contains almost no carbonate radicals, when returning the dilute salt water 15 to the concentrating mechanism 1b, the dilute salt water 15 is removed compared to returning it to the evaporating and concentrating mechanism 1a. The amount of treatment liquid in the carbonic acid mechanism 4 can be reduced.

  FIG. 3 shows a case where the concentration mechanism 1b is provided at the subsequent stage of the coagulation filtration mechanism 2 and the chelate resin 3 to concentrate the salt drainage again, and the decarbonation mechanism 4 is provided at the subsequent stage. Since the diluted salt water 15 discharged from the positive electrode chamber of the electrolytic cell 5 has sufficiently removed impurities, the diluted salt water 15 is returned to the concentrating mechanism 1b and treated with the coagulation filtration mechanism 2 and the chelate resin 3. Therefore, dilute salt water can be used for re-electrolysis, and chemicals used in the coagulation filtration mechanism 2 and the chelate resin 3 can be saved.

  FIG. 4 is a diagram when the chemical washing liquid 14 discharged from the chelate resin 3 is returned to the evaporation concentration mechanism 1. The chemical washing solution 14 contains sodium chloride produced from hydrochloric acid and sodium hydroxide used for chemical washing in addition to the divalent ions adsorbed and removed by the chelate resin 3. By providing a circulation loop that returns the chemical washing liquid 14 to the evaporation and concentration mechanism 1, sodium chloride in the chemical washing liquid can be used again for electrolysis, and the amount of secondary waste can be reduced.

  FIG. 5 is a diagram in the case where sodium carbonate is obtained as a valuable salt by allowing the carbon dioxide 16 generated in the decarboxylation mechanism 4 to act on sodium hydroxide generated in the electrolytic cell 5 and neutralizing and drying. Since carbon dioxide 16 generated by the decarbonation mechanism 4 is blown into the neutralization / drying mechanism 6, solid sodium carbonate is obtained, so that transportation becomes easy. Moreover, since carbon dioxide generated in the system is used, the environmental load can be reduced. If it is desired to obtain slurry-like sodium carbonate, only neutralization reaction may be performed without drying. In addition to using carbon dioxide generated in the decarbonation mechanism 4, carbon dioxide may be introduced from outside the system and neutralized by drawing a cylinder or a pipeline.

  FIG. 6 is a diagram in the case where a carbon dioxide blowing mechanism 9 for blowing carbon dioxide 16 generated by the decarbonation mechanism 4 into the salt drainage is provided in the previous stage of the aggregation filtration mechanism 2. By blowing carbon dioxide into the salt drainage, the carbonate root concentration in the salt drainage increases, and the divalent ions in the salt drainage easily form carbonates. By separating the formed carbonate as the secondary waste 13, the concentration of divalent ions in the salt drainage is reduced, and the amount of flocculant added in the aggregation filtration mechanism 2 is reduced. Similarly to the case of FIG. 5, carbon dioxide may be introduced into the carbon dioxide blowing mechanism 9 from outside the system.

  FIG. 7 is a diagram in the case where sodium hydroxide discharged from the negative electrode chamber of the electrolytic cell 5 is reused as an injection solution added to the negative electrode chamber of the electrolytic cell 5. A part of sodium hydroxide discharged from the negative electrode chamber of the electrolytic cell 5 is taken out as valuable salt, and the remainder is diluted with water to a predetermined concentration of sodium hydroxide 12 as diluted sodium hydroxide 12 and again in the electrolytic cell (5). Inject into the negative electrode chamber. At this time, you may dilute in the electrolytic cell 5, piping, and any other place besides the inside of a tank. By reusing sodium hydroxide discharged from the negative electrode chamber of the electrolytic cell 5, it is not necessary to bring sodium hydroxide from outside the system.

  FIG. 8 is a diagram when the salt drainage treatment apparatus is applied to a coal gas field. In the salt wastewater treatment system shown in the figure, the accompanying water generated from the coal gas field 101 is treated by the reverse osmosis membrane system 8 and separated into purified water and concentrated salt wastewater by the evaporative concentrating device 1, and the concentrated salt wastewater is decarboxylated. Then, the carbonic acid radical and divalent ions are removed by the coagulation filtration device 2 and the chelate resin 3 and purified. The salt drainage which collects sodium carbonate as a valuable salt by electrolyzing the refined salt drainage in the electrolytic cell 5 to obtain sodium hydroxide, and reacting this with the carbon dioxide captured from the decarbonation mechanism 4 or the gas field 101 Processing system.

  The reverse osmosis membrane system 8 includes a microfiltration membrane unit 102 and a reverse osmosis membrane unit 103, and separates concentrated salt waste water and purified water from salt waste water.

  In the evaporative concentration mechanism 1, the concentrated salt drainage is further concentrated by evaporating the concentrated salt drainage discharged from the reverse osmosis membrane system 8 and separating the water.

  In the coagulation filtration mechanism 2, divalent ions in the salt drain are separated as flocs. As the flocculant, an inorganic salt, a polymer, or both an inorganic salt and a polymer are added. For example, a case where both an inorganic salt and a polymer are used as the flocculant will be described. An inorganic flocculant is added to the concentrated salt effluent discharged from the evaporation and concentration mechanism 1 to form an inorganic salt containing divalent ions. As the inorganic flocculant, for example, sodium carbonate, sodium hydroxide, phosphoric acid, sodium phosphate and the like are used. It is preferable to add the inorganic flocculant so that the sum of the inorganic flocculant and the carbonate radical previously contained is equal to or more than the equivalent to the divalent ions contained in the salt drainage. Moreover, it is preferable to adjust pH to 8-12 which is a range which does not give excessive load to the chelate resin 3 of the latter stage | paragraph easily in which precipitation formation occurs.

  A polymer flocculant is further added to the inorganic salt formed by adding the inorganic flocculant to make the fine-sized inorganic salt a floc with good sedimentation. As the polymer flocculant, it is preferable to use an anionic polymer capable of simultaneously entwining divalent ions not forming an inorganic salt. More preferably, it is a polymer having a carboxyl group in the molecule because it has high reactivity with divalent ions and is inexpensive.

  In the chelate resin 3, the salt drainage is further purified by adsorbing and separating divalent ions from the salt drainage purified by the coagulation filtration mechanism 2. The chelate resin may be a resin having a functional group capable of adsorbing a low atomic weight metal such as iminodiacetic acid type or amino-phosphate type. Examples thereof include “Diaion” (registered trademark) CR-11 manufactured by Mitsubishi Chemical Corporation.

  The chelate resin 3 is regularly washed with chemicals. In preparation for continuous operation during chemical washing, a two-stage or three-stage chelate resin 3 may be used. In the chemical washing of the chelate resin, the adsorbed ions are washed with an acid and the resin is regenerated into a sodium type with a sodium hydroxide solution. The acid used for washing is preferably hydrochloric acid. In addition, the amount of secondary waste is reduced by returning the chemical washing liquid discharged at the time of chemical washing to the evaporation concentration mechanism 1 and performing electrolysis again.

  In the decarboxylation mechanism 4, an acid is added to remove carbonate radicals in the salt effluent. As the acid, hydrochloric acid is preferred. Taking into account that not all of the added acid reacts with carbonic acid, the amount of acid added is preferably about 1.0 to 1.2 times the equivalent of the carbonate radical in the salt effluent. Further, it is preferable to increase the sodium chloride concentration to near the saturation concentration. In the decarboxylation mechanism 4, the carbonic acid radicals desorbed as carbon dioxide from the salt drainage may be captured and used for neutralization of sodium hydroxide in the drying / neutralization mechanism 6.

  In the electrolytic cell 5, electrolysis is performed on the concentrated salt drainage from which divalent ions and carbonate radicals have been removed. Sodium chloride in the salt effluent is converted into sodium hydroxide, chlorine and hydrogen by electrolysis. Sodium hydroxide is discharged from the electrolytic cell as an aqueous solution. Chlorine and hydrogen are discharged out of the electrolytic cell and then captured and sent to the hydrochloric acid production mechanism 7. The hydrochloric acid production mechanism 7 produces hydrochloric acid from chlorine produced in the positive electrode chamber of the electrolytic cell 5 and hydrogen produced in the negative electrode chamber. The manufactured hydrochloric acid can be used for cleaning when degassing mechanism 4 and gas field 101 are discharged, and chelating resin 3 is washed with chemicals.

  A part of the high-concentration sodium hydroxide solution 17 purified by electrolysis may be extracted and used for commercial or chelate resin regeneration during chemical washing. The remaining high-concentration sodium hydroxide solution 17 can be diluted with water to a predetermined concentration and used as a dilute sodium hydroxide solution 12 and again as a supply liquid to the electrolytic cell 5 negative electrode chamber. The water used at this time may be purified water separated by the reverse osmosis membrane system 8 or the evaporative concentration system 1.

  The electrolytic cell 5 is one in which the positive electrode chamber and the negative electrode chamber are separated by a cation exchange membrane. Any cation exchange membrane may be used as long as it is generally used in an electrolytic cell. Examples thereof include “Nafion” (registered trademark) 324 manufactured by DuPont. The diluted salt water after electrolysis may be discharged from the electrolytic cell 5 and returned to the evaporative concentration apparatus 1. By returning, the sodium chloride concentration in the electrolytic cell 5 can be maintained at 18% by weight or more which is a concentration capable of maintaining the sodium passage speed of the ion exchange membrane.

  The sodium hydroxide produced in the electrolytic cell 5 is converted into solid sodium carbonate in the drying / neutralization mechanism 6. Drying and neutralization is carried out by bringing hot carbon dioxide into contact with a sodium hydroxide solution. For example, sodium hydroxide is sprayed into a chamber filled with high-temperature carbon dioxide. Carbon dioxide discharged from the gas field 101 or the decarbonation mechanism 4 can be used.

  Examples of the present invention are shown below. In addition, this invention is not restrict | limited to these Examples.

  An embodiment in accordance with the system shown in FIG. 8 will be described. After separating the oil and natural gas discharged from the gas field 101 and the accompanying water (salt drainage), the oil and the like were carried out by the pump 104a and the salt drainage by the pump 104b. The salt effluent 20t was processed by the reverse osmosis membrane system 8 to obtain 16t of purified water and 3.64t of concentrated salt effluent. The concentrated salt drainage was concentrated by the evaporative concentration mechanism 1 to obtain 2.91 t of purified water and 0.73 t of the concentrated salt drainage. In this concentrated salt water, the calcium concentration was 385 ppm, the magnesium concentration was 165 ppm, the bicarbonate ion concentration was 202,000 ppm, and the carbonate ion concentration was 45,400 ppm. Sodium hydroxide was added at 650 ppm to 0.73 t of the concentrated salt waste water, and the mixture was stirred at 500 rpm for 1 minute.

  Thereafter, a 0.5% sodium polyacrylate (PAA) solution as a polymer flocculant was added to 5 ppm, and the mixture was stirred at 250 rpm for 10 minutes. After standing, the aggregate was separated by a sand filter. After separation of the aggregates, the calcium concentration in the salt effluent was 7.7 ppm, the magnesium concentration was 3.3 ppm, and the concentration of the bicarbonate component was 202,000 ppm. This salt drainage was passed through the chelate resin 3 to remove dissolved divalent ions. The concentration of divalent ions in the salt effluent after passing 3 chelating resins was calcium: 10 ppb, magnesium: 6 ppb, barium: 0.2 ppm, strontium: 0.08 ppm, bicarbonate component: 202,000 ppm.

  Furthermore, by the decarboxylation mechanism 4, hydrochloric acid was added, sodium carbonate was converted to sodium chloride, and decarboxylation was performed. The carbon dioxide gas discharged by the decarbonation mechanism 4 was captured and transported to the drying / neutralization mechanism 6. The concentration of each component in the salt effluent that passed through the decarboxylation mechanism 4 was sodium chloride: 180,000 ppm, bicarbonate ion: 202 ppm, and carbonate ion: 6.5 ppm.

  Purified salt effluent was poured into the electrolytic cell 5 to obtain a 32 wt% sodium hydroxide solution 1 t, hydrogen gas 2 kg, and chlorine gas 82 kg. A 32 wt% sodium hydroxide solution was blown into a chamber filled with carbon dioxide gas at 150 ° C. to obtain a solid of sodium carbonate having a purity of 99.6%. 2 kg of hydrogen gas and 82 kg of chlorine gas were transported to the hydrochloric acid production mechanism 7 to produce 84 kg of hydrochloric acid.

  Even when the decarboxylation mechanism 4, the concentration mechanism 1 b, the coagulation filtration mechanism 2, and the chelate resin 3 are processed in this order between the evaporation and concentration mechanism 1 and the electrolytic cell 5 in Example 1, the same as in Example 1 A solid of sodium carbonate was obtained.

  The case where the chemical washing solution of the chelate resin 3 used in Example 1 is processed by the circulation loop will be described. After the amount of adsorbed divalent ions of the chelate resin 3 reached saturation, chemical washing was performed. By recycling the sodium chloride in the chemical washing solution using the circulation loop, the amount of waste was reduced to 1/40 of that when the circulation loop was not used.

  The case where sodium hydroxide is obtained as a valuable salt without neutralization in Example 1 will be described. The salt effluent was treated and the resulting sodium hydroxide solution was dried to obtain 0.32t of solid sodium hydroxide having a purity of 99%.

1: Evaporation concentration mechanism (concentration mechanism)
1a: Evaporation concentration mechanism (concentration mechanism)
1b: Concentration mechanism 2: Coagulation filtration mechanism 3: Chelate resin 4: Decarbonation mechanism 5: Electrolysis tank 6: Drying / neutralization mechanism 7: Hydrochloric acid production mechanism 8: Reverse osmosis membrane system 9: Carbon dioxide blowing mechanism 11: Salt drainage (Accompanying water)
12: Dilute sodium hydroxide solution 13: Secondary waste
14: Drug wash
15: Dilute brine 16: Carbon dioxide 17: High concentration sodium hydroxide solution 101: Gas field 102: Microfiltration membrane unit
103: Reverse osmosis membrane unit
104a: Pump 104b: Pump

Claims (14)

A concentration mechanism for concentrating salt drainage containing sodium chloride;
The positive electrode chamber and the negative electrode chamber are partitioned by an ion exchange membrane that transmits sodium ions, and an electrolytic cell that electrolyzes the salt drainage to generate sodium hydroxide,
Between the concentration mechanism and the electrolytic cell,
A decarboxylation mechanism for removing sodium carbonate and sodium bicarbonate from the salt drainage,
A coagulation filtration mechanism for removing divalent ions as aggregates from the salt drainage;
A salt drainage treatment apparatus comprising: a chelate resin that adsorbs and removes divalent ions from the salt drainage.   The salt wastewater treatment apparatus according to claim 1, wherein the coagulation filtration mechanism and the chelate resin are provided after the decarbonation mechanism. The salt wastewater treatment apparatus according to claim 1, wherein the decarboxylation mechanism is provided downstream of the aggregation filtration mechanism and the chelate resin.   The salt wastewater treatment apparatus according to claim 1, further comprising a carbonic acid blowing mechanism that blows carbon dioxide into the salt drainage before the coagulation filtration mechanism.   The salt wastewater treatment apparatus according to claim 1, further comprising a neutralization mechanism for bringing carbon dioxide into contact with the sodium hydroxide to produce sodium carbonate or sodium bicarbonate.   6. The salt wastewater treatment apparatus according to claim 5, wherein the carbon dioxide is generated by the decarboxylation mechanism.   The salt wastewater treatment apparatus according to claim 1, further comprising another concentration mechanism between the concentration mechanism and the electrolytic cell.   The salt wastewater treatment apparatus according to claim 7, wherein at least one of the decarboxylation mechanism, the aggregation filtration mechanism, and the chelate resin is provided between the concentration mechanism and the other concentration mechanism.   The salt wastewater treatment apparatus according to claim 7, wherein a chemical washing liquid discharged when the chelate resin is washed with chemicals is returned to the concentration mechanism or the other concentration mechanism.   8. The salt wastewater treatment apparatus according to claim 7, wherein dilute salt water discharged from the positive electrode chamber of the electrolytic cell is returned to the concentration mechanism or the other concentration mechanism.   A hydrochloric acid production mechanism for generating hydrochloric acid from chlorine and hydrogen discharged from the electrolytic cell is provided, and the hydrochloric acid is returned to any one of the decarboxylation mechanism, the salt drainage supply source, or the chelate resin. The salt wastewater treatment apparatus according to claim 7.   The salt wastewater treatment apparatus according to claim 1, further comprising a reverse osmosis membrane for concentrating the salt drainage before the concentration mechanism.   2. The salt wastewater treatment apparatus according to claim 1, wherein the sodium hydroxide solution discharged from the negative electrode chamber of the electrolytic cell is returned to the electrolytic cell or the chelate resin.   The salt wastewater treatment apparatus according to claim 1, wherein the chelate resin is a resin having an iminodiacetic acid type or amino-phosphate type functional group.