WO2012113958A1

WO2012113958A1 - Brine treatment method

Info

Publication number: WO2012113958A1
Application number: PCT/ES2012/070103
Authority: WO
Inventors: Arturo BUENAVENTURA POUYFAUCON
Original assignee: Abengoa Water, S. L. U.
Priority date: 2011-02-23
Filing date: 2012-02-22
Publication date: 2012-08-30
Also published as: ES2390166A1; ES2390166B1

Abstract

The invention relates to a brine treatment method consisting of the injection of a suitable dose of pre-determined reagents, followed by an extraction step for recovering the different agents obtained so that they can be re-used, while simultaneously rendering the brine suitable for other types of industrial processes, thereby offsetting part of the costs and the environmental impact of desalination plants.

Description

SALMUERA TREATMENT PROCEDURE.

The present invention relates to a method of brine treatment, consisting of the injection of certain reagents in the appropriate dose followed by an extraction step to recover the different agents obtained in order to reuse them while also being able to adapt the brines to another type of industrial processes, managing to compensate part of the costs and the environmental impact of the desalination plants. The present invention falls within the technical field of fluid treatment. More specifically, the invention falls within the technical field of brine treatment. More specifically, the invention fits in the technical field of the recovery of brines from desalination plants for the recovery of useful products for various purposes and accelerated setting C0 _2.

STATE OF THE PREVIOUS TECHNIQUE

Desalination technologies are processes widely used in the generation of water for different uses. The main byproduct of these processes is the concentrated solution called brine or rejection stream, which has a high salt content and is usually poured into the receiving medium.

Nowadays, due to the environmental problems that its discharge can cause and due to the physical-chemical properties of the brines, this waste can be subject to a recovery that has a direct impact on the reduction of costs and environmental impact.

In this sense, the valuation of the brines can be directed to different purposes, including the recovery of useful products for self-supply of the same desalination plant or also for sale to other industries that employ such agents in their processes, adaptation of the same as raw material in other industries, fixation of CO ₂ , ... Therefore, different physical-chemical processes of extraction of useful products from brines have been developed, usually calcium carbonate, magnesium carbonate, sodium carbonate, sodium chloride, calcium chloride, calcium sulfate, sodium sulfate, magnesium sulfate, magnesium hydroxide, joint salts, etc.

The recovery of the brine basically consists in providing certain chemical agents to it, which by various reaction mechanisms will generate precipitates that can be used and / or adapt the brine for other types of purposes after previously separating them.

Preferably, some of these reagents to be added are hydroxides such as NaOH or Ca (OH) ₂ .

In the literature there are different methods of extracting chemical agents that have been patented. Some examples of patents are discussed below: - US7595001 "Process for the treatment of saline water", in which useful products are recovered from saline waters with the problem of a high content of total dissolved solids, in the range of 1 at 60 g / l. In this patent CaO, Ca (OH) ₂ or mixture of both are used to obtain, in a first stage, precipitated CaC0 ₃ (PCC) or a magnesium and gypsum hydroxide (GMH), according to the type of water. In a second stage they add CaCl ₂ , NaOH, etc. (depending on the type of water) to obtain more PCC, Na ₂ CO ₃ , etc.

- US7198722 "Process for pre-treating and desalinating sea water", in which CaSO ₄ , CaCI ₂ , MgSO ₄ , MgCI ₂ , Na ₂ CO ₃ , NaCI, are recovered

Na ₂ SO ₄ , Ca (HCO3) 2, and other combined salts of seawater (not brine, as in the case of the present invention) using, between others, NaOH, Na ₂ C0 ₃ , KOH, K ₂ C0 ₃ , Ca (OH) ₂ , CaC0 ₃ , AI (OH) ₃ , AI ₂ (S04) ₃ , K ₂ S0 ₄ , and then removed to feed the Stream of purified seawater to a desalination process. - US2793099 "Processes for the manufacture of various chemicals from sea water" in which Mg (OH) ₂ , Ca ₂ S0 ₄ and NaCI are recovered by adding to seawater (not the case of residual brine), in a first stage , dolomite or lime for precipitation of Mg (OH) ₂ , separating by gravity and subsequently concentrating the other two compounds by evaporation.

Therefore, it is necessary to develop new brine treatment procedures, through which it can be valued in order to achieve the milestones discussed previously.

DESCRIPTION OF THE INVENTION

The present invention relates to a new process for treating brine preferably from desalination plants by means of which the following advantages are obtained:

- Extraction of chemical agents from the brine generated as a by-product (CaC0 ₃ , Mg (OH) ₂ , etc.) for self-supply of the desalination plant in order to reduce costs and environmental impact since the fair amount can be produced remineralizing agent and also at a lower price than if purchased externally in any of its variants.

- Extraction of chemical agents from the brine generated as a by-product (CaC0 ₃ , Mg (OH) ₂ , etc.) to supply other industries that use these agents in their processes, such as the sale of Mg (OH ) ₂ as a dietary supplement in feed or mixed calcium carbonate magnesium MgCaC0 ₃ as a fertilizer to regulate soil pH. - Adaptation of the brine generated as a by-product in the desalination process for supply in foreign industries that use brines in their

processes A non-limiting example is found in the chlor-alkaline industry since, with the present invention, part of the agents that this industry considers impurities and that are pretreated before entering the production process are removed from the brine. Therefore, a suitable brine minimizes the amount of NaCI in solid form that this industry has to provide since the brine contains it in greater concentration than the seawater that is usually used as the starting raw material.

- Possibility of using CO2 and / or combustion gases with greater or lesser richness in CO2 in order to complement the process and fix CO2 (emission reduction)

- Total or partial combination of the four previous points simultaneously. - Possibility of working continuously, discontinuously, etc. Versatility and flexibility

- Possibility of qualitatively and quantitatively controlling the chemical agents that must be extracted (eg, each product that is formed by selective precipitation at its typical pH can be separated and varies depending on ionic activities, pKs, ... Without being limiting and depending on each case, in general, working at a pH greater than or equal to 9 favors carbonates precipitating while at a pH greater than or equal to 10.5 the precipitation of hydroxides is favored.

- Versatility in the system to extract precipitated chemicals press, decanter, evaporation of water in the generated sludge, etc. - Possibility of recirculating part of the sludge generated to accelerate the decantation / sedimentation of the generated compounds.

- Possibility of controlling the pressure and / or the temperature of the system to increase the dilution of the reagents and increase the yield of the process.

- System strategically aligned with the idea of zero discharge in desalination plants and with the idea of brines as a CO ₂ sink (sustainability).

Therefore, a first aspect of the present invention relates to a brine treatment process comprising the following steps: a) Addition of chemical agents to a brine stream; b) Injection of the mixture from step a) into a reaction chamber; c) Extraction of the products obtained in stage b) d) Separation of the products obtained after stage c); e) Drying of the resulting products in stage c).

According to a preferred embodiment, the chemical agents that are added to the brine stream are selected from the group consisting of NaOH, Ca (OH) ₂ , CaCI ₂ and / or CaO. According to a preferred embodiment, the chemical agents are added online before a reaction chamber. According to another preferred embodiment, the chemical agents are added directly to the reaction and mixing chamber.

According to another preferred embodiment, the chemical agents are added in preferably excess amounts to ensure that the reaction reaches the desired conditions and that they are calculated based on the balances of the species present in the fluid.

According to another preferred embodiment, in addition to the chemical agents supplements are added.

According to another preferred embodiment, the supplements are selected from carbon dioxide or flue gases containing CO ₂ . According to another preferred embodiment, the dosage of CO ₂ , either pure (without other components) or from combustion gases, is carried out by one of the following possibilities:

- online

- in a mixing and reaction chamber by bubbling

- bubbling in a totally or partially flooded absorber, with or without internal filling, in order to achieve greater efficiency in the collection of this gas

- a partially flooded absorption tower with a rain sprayer or a spray type sprayer, and with or without internal filling

According to another preferred embodiment, the excess of unreacted CO ₂ (pure or from combustion gases) is recirculated from head to tail of the corresponding dosing system, for example from head to tail of the absorption tower. According to another preferred embodiment, the chemical agents added to the brine stream must remain in the reaction chamber a sufficient hydraulic residence time (THR) to allow the reaction to be quantitative, that is a hydraulic residence time of less than or equal to 120 minutes, preferably less than or equal to 60 minutes, and more preferably less than or equal to 30 minutes.

In another preferred embodiment, the mixture present in the reaction chamber is maintained at a pH between 7 and 14, preferably between 9 and 12 and more preferably between 10 and 1 1.

According to another preferred embodiment, the injected mixture present in the reaction chamber is maintained at a pressure less than or equal to 20 atm preferably of less than or equal to 10, and more preferably less than or equal to 5 atm.

According to another preferred embodiment the extraction step is carried out by a pH controlled precipitation. In this way the controlled precipitation occurs in a pH range between 7 and 14; preferably it is given at a pH range of 9 to 12.

According to another preferred embodiment, after the extraction stage of the products obtained from the brine, these are partially redirected in an amount less than or equal to 25% to the extraction stage to facilitate the decantation / sedimentation thereof. Preferably it is redirected in an amount less than or equal to 10%.

According to another preferred embodiment, the separation step is carried out by microfiltration, ultrafiltration, ring filters, centrifuges, decantation or any combination thereof. According to another preferred embodiment, the drying step is carried out by thickeners, evaporation of the mud water, vacuum filters, press filters, band filters, centrifuges or any combination thereof. According to another preferred embodiment, the process is continuous.

According to another preferred embodiment, the process is discontinuous.

In this way, with the procedure described above, different products will be obtained depending on the type of brine and the process applied. CaC03 calcium carbonate is usually obtained (with applications in water treatment, as raw material for gypsum production, oil industry, chemical industry, food industry, salt manufacturing, etc.), magnesium hydroxide or brucite Mg (OH) ₂ (with applications such as additives for rubber, feed manufacturing, water treatment, agriculture, refractories, pharmaceutical industry, etc.), gypsum CaS0 ₄ (with applications in construction, ceramics, agriculture, medicine, chemical and food industry, etc.) , or mixed calcium carbonate magnesium MgCa (C0 ₃ ) (with applications in refractory manufacturing, fertilizers to regulate soil pH, thermal insulators, building material, flux in metallurgy, paints, etc.).

A great advantage of this procedure is that the brine can also serve as a CO2 sink taking into account the balance of carbonic species and the presence of certain elements. It is known that sea water and certain brackish or brines water may have an ion imbalance and therefore are capable of fixing a large amount of C0 ₂ to at suitable pH, be in the form of bicarbonate and / or carbonate mainly.

Therefore, in the present invention, in addition to the recovery of brines from desalination plants, CO2 fixation can be achieved or CO2-rich combustion gases, independently or in combination with the other variants as mentioned above, which gives added value to the residual brines. Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and are not intended to be limiting of the present invention.

DESCRIPTION OF THE FIGURES Figure 1. General scheme of the procedure for carrying out the recovery of brines from desalination plants of seawater, where (1) represents the total flow to be treated as brine, (2) represents the step of adding reagents in line prior to the reaction and mixing chamber, (3) represents the current of chemicals to be added (NaOH, Ca (OH) ₂ , CaCl2, CaO ...), (4) represents the CO2 or gas stream of combustion, (5) is the reaction chamber, (6) represents the extraction and separation stage, where (7) represents the separation extraction stage that can be done by filtration, (8) represents the separation extraction stage that can be done by decantation followed by sludge thickening, (9) represents the alternative of recirculating part of the products obtained, (10) represents the output current of the treated brine, (1 1) represents the output current of the products obtained that are gave The drying stage is governed by (12) Finally, the output current of the products obtained is represented by (13). Optionally, the lime slurry can be prepared with fluid to be remineralized (14). Figure 2. Scheme of the procedure to carry out the recovery of the brine with the addition of the reagents in a reaction and mixing chamber where the CO2 is bubbled, and where the currents are those explained in Figure 1 and (2) represents the dosage of reagents in the reaction chamber itself and mixture (5).

Figure 3. Scheme of the procedure for carrying out the recovery of the brine with the addition of CO2 by means of a partially flooded absorber with internal filling, where the currents are those explained in Figure 1 and also (16) represents the absorber, (14 ) represents the flow rate of (1) diverted to prepare the slurry and (15) represents the flow rate of (1) diverted to the absorber.

EXAMPLES

The present invention is further illustrated by 3 preferred embodiments that are not intended to limit the scope thereof. EXAMPLE 1. Treatment of a brine stream using NaOH as chemical agent.

The configuration of Figure 1 is used to valorize a typical brine from a seawater desalination plant that has pH characteristics of 7.7, Conductivity of 84.5 mS / cm, Ca ²⁺ of 1058 mg / l, Mg ²⁺ of 1884 mg / l, CO3 ^{2 "} of 72 mg / l, HC0 ₃ ^" of 628.3 mg / l, SO4 ^{2 "} of 4907, TDS (total dissolved solids) of 59.1 g / l, Alkalinity of 515 mg / l CaC0 ₃ , Hardness of 10400 mg / l CaC0 ₃ and LSI (Langelier Saturation Index) of 1.59

At the flow rate Qt = 14000 m ³ / d representing the total brine flow rate obtained from the reverse osmosis of a desalination plant, 977.1 is injected. 1 / min of a 1M NaOH sodium hydroxide solution and the flow is directed to an open reaction and mixing chamber.

The mixture is left with gentle stirring in the reaction chamber and mixes a residence time of 20 minutes after the pH control indicates that the working pH 12 has been reached so that the reaction is quantitative.

Finally, this solution is passed through a pressure microfiltration system and the solids obtained are taken to the final stage of dehydration in a band filter that provides 99.12 tons / day (ton / d) of dry precipitates, of which 41 .04 ton / d, correspond to the brucite (Mg (OH) ₂ ) generated, 19.92 ton / d are of calcium carbonate (CaCO ₃ ) in the aragonite phase and 10.7 ton / d is calcium carbonate (CaCO ₃ ) in calcite phase

EXAMPLE 2. Treatment of a brine stream using NaOH and C0 ₂ as chemical agent.

The configuration of Figure 2 is used to titrate a typical brine from a seawater desalination plant that has pH characteristics of 7.7, Conductivity of 84.5 mS / cm, Ca ²⁺ of 1058 mg / l, Mg ²⁺ 1884 mg / l, CO ₃ ^{2 "} 72 mg / l, HCO ₃ ^2" 628.3 mg / l, SO ₄ ^{2 "} 4907, TDS 59.1 g / l, Alkalinity 515 mg / l CaCO ₃ , Hardness of 10400 mg / l CaCO ₃ and LSI of 1.59

At the flow rate Qt = 36,000 m ³ / d representing the total brine flow rate obtained from the reverse osmosis of a desalination plant, CO ₂ and a 1 M NaOH sodium hydroxide solution are injected. At the total flow rate of 36,000 m ³ / d, 25,000 and 400 l / min of CO ₂ and 1 M NaOH are injected directly into the reaction chamber and mix respectively 5,000 l / min. The mixture is left with gentle stirring in the reaction chamber and mixes a residence time of 20 minutes after the pH control indicates that the working pH 9 has been reached so that the reaction is sufficiently completed.

Finally, this solution is passed through a microfiltration system under pressure and the solids obtained are taken to the final stage of dehydration in a press filter that provides 32.6 tons / d of precipitates, of which 24.25 tons / d correspond to mixed calcium carbonate magnesium or dolomite MgCa (C03) 2 and 6.1 ton / d are calcium carbonate (CaC0 ₃ ) in the calcite phase.

EXAMPLE 3. Treatment of a brine stream using as chemical agent Ca (OH) ₂ and CO2.

The configuration of Figure 3 is used to valorize a typical brine from a seawater desalination plant that has pH characteristics of 7.7, Conductivity of 84.5 mS / cm, Ca ²⁺ of 1058 mg / l, Mg ²⁺ of 1884 mg / l, C0 ₃ ^{2 "} of 72 mg / l, HCO3 ^2" of 628.3 mg / l, S0 ₄ ^{2 "} of 4907, TDS of 59.1 g / l, Alkalinity of 515 mg / l CaC0 ₃ , Hardness of 10400 mg / l CaC0 ₃ and LSI of 1.59

The flow rate Qt = 54000 m ³ / d (2250 m ³ / h) representing the total brine flow rate obtained from the reverse osmosis of a desalination plant is separated into 2 flows, the first 90% of the flow rate Qt, that is, Q1 = 2025 m ³ / h that is introduced into a partially flooded absorption tower with spray type spray and internal filling. In this way, the brine is sprayed on the filling bed, where it comes into contact with the CO2 that is bubbled from the bottom with a flow rate of 4050 m ³ / h.

Ca (OH) 2 is added directly in the form of a slurry in the reaction chamber and mix where the acidified water leaving the absorbed arrives. For the preparation of the slurry, the remaining 10% of the flow rate Qt is used, that is, Q ₂ = 225 m3 / h, using 2385 kg / h of Ca (OH) ₂ .

The mixture is left with gentle stirring in the chamber for a hydraulic residence time of 20 minutes after the pH control indicates that the working pH 10.5 has been reached so that the reaction is sufficiently completed.

Finally, this solution is passed through a pressure microfiltration system and the solids obtained are taken to the final stage of dehydration in a band filter that provides 848 tons / d of precipitates, of which 194 tons / d correspond to Brucite Mg (OH) ₂ , 353.6 ton / d are of calcium carbonate (CaCOs) in the calcite phase and 231.55 / d are of hemihydrated gypsum or bassanite CaS04.1 / 2H ₂ 0.

Claims

one . Chemical brine treatment process, comprising the following steps: a) Addition of chemical agents to a brine stream; b) Injection of the mixture from step a) into a reaction chamber; c) Extraction of the products obtained in stage b) d) Separation of the products obtained after stage c); and e) Drying of the resulting products in stage c).

2. The process according to claim 1, wherein the chemical agents that are added to the brine stream are selected from the group consisting of NaOH, Ca (OH) ₂ , CaCI ₂ and / or CaO.

3. The method according to any of claims 1 or 2, wherein the chemical agents are added in line before a reaction and mixing chamber.

4. The process according to any of claims 1 or 2, wherein the chemical agents are added in a reaction and mixing chamber.

5. The process according to any one of claims 1 to 4, wherein additionally selected among carbon dioxide or flue gases containing CO2 are dosed into the brine stream.

6. The method according to claim 5, wherein the supplement that is dosed is CO2.

7. The method according to claim 6, wherein the CO2 dosing is done in line.

8. The method according to claim 6, wherein the dosage of CO2 is carried out in a reaction chamber and mixture of step b) by bubbling.

9. The method according to claim 8, wherein the dosing of CO2 is carried out by bubbling in an absorber that is completely flooded, with or without submerged filling.

10. The method according to claim 6, wherein the dosage of CO2 is carried out by a partially flooded absorber with or without internal filling.

eleven . The method according to claim 10, wherein the CO2 dosing is carried out by means of a partially flooded absorption tower with a rain spray or spray type spray, with or without internal filling.

12. The method according to any of claims 10 or 1, wherein the excess of unreacted CO2 is recirculated from head to tail of the corresponding dosing system

13. The method according to any of claims 1 to 12, wherein the chemical agents added to the brine stream must remain in the reaction chamber and stage b) a hydraulic residence time of less than or equal to 120 minutes.

14. The method according to claim 13, wherein the hydraulic residence time is less than or equal to 60 minutes.

15. The method according to claim 14, wherein the hydraulic residence time is less than or equal to 30 minutes.

16. The process according to any of claims 1 to 15, wherein the mixture present in the reaction chamber and mixture of step b) is maintained at a pH of from 7 to 14.

17. The process according to claim 16, wherein the mixture is maintained at a pH of from 9 to 12.

18. The process according to claim 17, wherein the mixture is maintained at a pH of from 10 to 1 1.

19. The process according to any of claims 1 to 18, wherein the mixture present in the reaction chamber and mixture of step b) is maintained at a pressure less than or equal to 20 atmospheres.

20. The process according to claim 19, wherein the present mixture is maintained at a pressure less than or equal to 10 atmospheres.

twenty-one . The process according to claim 20, wherein the present mixture is maintained at a pressure less than or equal to 5 atmospheres.

22. The process according to any of claims 1 to 21, wherein step c) of extracting the products obtained in step b), is carried out by precipitation at a pH range of from pH 7 to 14.

23. The process according to any one of claims 1 to 22, wherein step c) of extracting the products obtained in step b), is carried out by precipitation at a pH range of from pH 9 to 12.

24. The method according to any of claims 22 or 23, wherein after step c) of extracting the products obtained from the brine, these are redirected in an amount less than or equal to 25% with respect to the total back to the stage c) extraction.

25. The method according to claim 24, wherein the percentage to be redirected is less than or equal to 10% with respect to the total.

26. The method according to any one of claims 1 to 25, wherein step d) of separation is carried out by microfiltration, ultrafiltration, ring filters, centrifugation, decantation or any combination thereof.

27. The method according to any one of claims 1 to 26, wherein step e) of drying is carried out by thickeners, by evaporation of water from the sludge in drying ages, vacuum filters, press filters, band filters, centrifuges or any combination thereof.