Process and apparatus for removing calcium from brine by phosphoric acid

Abstract

The application relates to the technical field of industrial water treatment and electrolysis, and discloses a process device and method for removing calcium from brine by phosphoric acid. The method comprises the following steps: adding pressure and heating to brine, adding phosphoric acid to remove calcium, adding alkali liquor to adjust pH, adopting ceramic membrane filtration to obtain refined brine, and finally adding acid liquor to adjust the pH of the product. The device comprises a brine dissolving pump, a brine dissolving heat exchanger, a brine dissolving pool, a baffle tank, a reaction pool group, a ceramic membrane filter and a static mixer which are sequentially connected and correspondingly realize the functions of conveying, heating, brine dissolving, phosphoric acid reaction, alkali adjustment, filtration and pH fine adjustment. According to the principle of removing calcium by phosphoric acid, the calcium and magnesium content in the primary brine in the ion-exchange membrane potassium caustic soda process is effectively reduced, the reaction process is simple, the operation is convenient, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of industrial water treatment and electrolysis technology, and in particular to a process apparatus and method for calcium removal from brine using phosphoric acid. Background Technology

[0002] In the chlor-alkali industry, the production of potassium hydroxide is a crucial industrial process. Its raw material, potassium chloride, typically contains large amounts of impurity ions such as calcium and magnesium. The presence of these impurities severely damages subsequent electrolysis processes. In particular, if calcium ions are not effectively removed, they will form deposits in the ion-exchange membrane electrolyzer, leading to increased cell voltage, decreased current efficiency, and even damage to the ion-exchange membrane, shortening equipment lifespan. Therefore, brine purification is a critical pretreatment step in potassium hydroxide production, aiming to deeply remove calcium and magnesium ions and ensure the stability and economy of the electrolysis process.

[0003] Traditional brine purification methods primarily employ a two-stage purification process. The primary purification typically uses potassium carbonate as a calcium removal agent, generating calcium carbonate precipitate for initial calcium ion removal. However, the fine particles and slow settling rate of the calcium carbonate precipitate in this method lead to difficulties in solid-liquid separation, resulting in low filtration efficiency. This often necessitates large sedimentation tanks and complex filtration equipment, increasing equipment investment and operational complexity. More importantly, the high solubility product of calcium carbonate makes it difficult to reduce the residual calcium ion concentration to a low level. In actual operation, the calcium ion concentration is usually maintained above several ppm, failing to meet the high brine quality requirements of ion-exchange membrane electrolyzers. This residual calcium ion gradually accumulates in the electrolyzer, causing membrane fouling and electrode damage, thereby increasing maintenance costs and the risk of production downtime. In the secondary brine purification, due to the unsatisfactory effect of the primary purification, the resin tower requires frequent regeneration to adsorb residual calcium ions. This not only increases acid and alkali consumption and wastewater treatment burden but also shortens the resin's lifespan. Therefore, this invention provides a process apparatus and method for calcium removal from brine using phosphoric acid to solve the aforementioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a process device and method for calcium removal from brine using phosphoric acid. This method effectively reduces the calcium and magnesium content in the primary brine of the potassium alkali process using phosphoric acid, based on the principle of calcium removal from phosphoric acid. At the same time, the reaction process is simple, easy to operate, and reduces production costs.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A process for calcium removal from brine using phosphoric acid includes the following steps:

[0007] S1. After pressurizing and heating the brine, send it into the salt dissolving tank to dissolve the salt and obtain brine.

[0008] S2: Add phosphoric acid to the brine obtained in step S1, so that the calcium ions in it react with the phosphate ions to form calcium phosphate precipitate.

[0009] S3. Add alkaline solution to the brine after the reaction in step S2 to adjust the pH value of the brine.

[0010] S4. Filter the brine obtained in step S3 to obtain refined brine;

[0011] S5. Add acid to the purified brine obtained in step S4 to adjust its pH value to the target range.

[0012] Preferably, in step S1, the brine is pressurized by a brine pump and heated by steam through a brine heat exchanger. After heating, the brine temperature is 60-65℃, and the resulting brine concentration is 300-310g / L.

[0013] Preferably, in step S2, the phosphoric acid is an 85% phosphoric acid solution, added in a baffled tank, and during the reaction, the brine flows sequentially through the front reaction tank, the rear reaction tank, and the intermediate tank.

[0014] Preferably, in step S3, the alkaline solution is a 32% potassium hydroxide solution, and the pH value of the adjusted brine is 10-12.

[0015] Preferably, a ceramic membrane filter is used in step S4, and the calcium ion concentration of the purified brine is less than 0.5 ppm.

[0016] According to another aspect of the present invention, a process apparatus for a brine phosphate removal method is provided, the apparatus comprising, sequentially connected along the process flow: a brine pump for pressurizing dilute brine; a brine heat exchanger connected to the brine pump for heating the pressurized dilute brine; a brine tank connected to the brine heat exchanger for preparing brine; a baffled tank connected to the brine tank and provided with a phosphate dosing port; a reaction tank group connected to the baffled tank for performing the phosphate removal reaction and pH adjustment, and provided with an alkali dosing port; a ceramic membrane filter connected to the reaction tank group for filtering and removing calcium phosphate precipitate; and a static mixer connected to the outlet of the ceramic membrane filter and provided with an acid dosing port for adjusting the pH value of the final brine.

[0017] Preferably, the reaction tank group includes a front reaction tank, a rear reaction tank, and an intermediate tank connected in sequence, and the alkali solution dosing port is located in the rear reaction tank.

[0018] Preferably, the acid dosing port is equipped with an automatic control system, which includes an online pH detection device and a regulating valve. The online pH detection device is used to detect the pH value of the refined brine output from the ceramic membrane filter, and the regulating valve is used to control the amount of acid added based on the detection results.

[0019] Preferably, the brine heat exchanger is provided with a steam inlet for receiving steam to provide a heating source; the acid added through the acid dosing port is hydrochloric acid.

[0020] The beneficial effects of this invention are:

[0021] 1. This invention utilizes phosphoric acid as a calcium removal agent, taking advantage of the extremely low solubility product of calcium phosphate, to stably control the calcium ion concentration in the primary brine below 0.5 ppm, significantly improving the purification quality of the brine. This calcium removal effect effectively reduces the load on the resin tower during the secondary brine purification process, extends the regeneration cycle of the resin tower and the service life of the ion-exchange membrane electrolyzer, and reduces the problems of increased cell voltage and decreased current efficiency caused by calcium ion deposition, thereby ensuring the stability and high efficiency of the electrolysis process.

[0022] 2. The amount of phosphoric acid used in this invention is far lower than that in the traditional potassium carbonate process, significantly reducing reagent costs. Small dosing pumps can also be used to add phosphoric acid. Due to the high calcium removal efficiency, the regeneration frequency of the resin tower in the secondary refining process is significantly reduced, saving on acid and alkali consumption and wastewater treatment costs. The calcium phosphate precipitate generated in the reaction can also be used as a raw material for phosphate fertilizer, realizing resource utilization and turning waste into treasure, further increasing economic benefits. At the same time, the process equipment of this invention has a simple structure, is easy to operate, and is easy to automate and continuously produce. The entire system requires minimal investment and can adapt to the needs of large-scale industrial production. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used, unless otherwise specified, were all purchased from conventional biochemical reagent stores. All quantitative experiments in the following examples were performed in triplicate, and the data are the average of the three replicates or the average ± standard deviation.

[0027] Example 1

[0028] This embodiment provides a process for calcium removal from brine using phosphoric acid, including the following steps:

[0029] S1. The brine is pressurized to 0.4MPa by the brine pump and enters the brine heat exchanger. It is heated to 60℃ by steam and then sent to the brine tank for stirring to produce brine with a concentration of 305g / L.

[0030] S2. Add 85% phosphoric acid to the baffle tank. The amount of phosphoric acid added is 1.1 times the molar concentration of calcium ions, so that the phosphoric acid reacts with the calcium ions in the brine to form calcium phosphate precipitate.

[0031] S3. Salt water flows sequentially through the front reaction tank and the rear reaction tank. A 32% potassium hydroxide solution is added to the rear reaction tank to adjust the pH of the system to 10.

[0032] S4. The brine after the reaction enters the intermediate tank and is transported to the ceramic membrane filter by the membrane filter feed pump for solid-liquid separation. The filtration accuracy is 50nm, and refined brine is obtained.

[0033] S5. Install an online pH meter before the static mixer and automatically adjust the amount of hydrochloric acid added based on the test results to adjust the pH value of the purified brine to 7.5.

[0034] The refined brine treated by the method in this embodiment has a stable calcium ion concentration of 0.42 ppm, and the regeneration cycle of the secondary brine resin tower is extended to 251 hours.

[0035] Example 2

[0036] This embodiment provides a process for calcium removal from brine using phosphoric acid, including the following steps:

[0037] S1. The brine is pressurized to 0.45MPa by the brine pump and enters the brine heat exchanger. It is heated to 65℃ by steam and then sent to the brine tank for stirring to produce brine with a concentration of 308g / L.

[0038] S2. Add 85% phosphoric acid to the baffle tank. The amount of phosphoric acid added is 1.2 times the molar concentration of calcium ions, so that the phosphoric acid reacts with the calcium ions in the brine to form calcium phosphate precipitate.

[0039] S3. The brine flows sequentially through the front reaction tank and the rear reaction tank. A 32% potassium hydroxide solution is added to the rear reaction tank to adjust the pH of the system to 11.5.

[0040] S4. The brine after the reaction enters the intermediate tank and is transported to the ceramic membrane filter by the membrane filter feed pump for solid-liquid separation. The filtration accuracy is 50nm, and refined brine is obtained.

[0041] S5. Install an online pH meter before the static mixer and automatically adjust the amount of hydrochloric acid added according to the test results to adjust the pH value of the purified brine to 7.8.

[0042] The purified brine treated by the method in this embodiment has a stable calcium ion concentration of 0.38 ppm, and the regeneration cycle of the secondary brine resin tower is extended to 258 hours.

[0043] Example 3

[0044] This embodiment provides a process for calcium removal from brine using phosphoric acid, including the following steps:

[0045] S1. The brine is pressurized to 0.5MPa by a brine pump and enters the brine heat exchanger. It is heated to 60℃ by steam and then sent to the brine tank for stirring to produce brine with a concentration of 302g / L.

[0046] S2. Add 85% phosphoric acid to the baffle tank. The amount of phosphoric acid added is 1.08 times the molar concentration of calcium ions, so that the phosphoric acid reacts with the calcium ions in the brine to form calcium phosphate precipitate.

[0047] S3. The brine flows sequentially through the front reaction tank and the rear reaction tank. A 32% potassium hydroxide solution is added to the rear reaction tank to adjust the pH of the system to 10.8.

[0048] S4. The brine after the reaction enters the intermediate tank and is transported to the ceramic membrane filter by the membrane filter feed pump for solid-liquid separation. The filtration accuracy is 50nm, and refined brine is obtained.

[0049] S5. Install an online pH meter before the static mixer and automatically adjust the amount of hydrochloric acid added according to the test results to adjust the pH value of the purified brine to 7.2.

[0050] The purified brine treated by the method in this embodiment has a stable calcium ion concentration of 0.35 ppm, and the regeneration cycle of the secondary brine resin tower is extended to 264 hours.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 3 is that the traditional potassium carbonate decalcification method is used, and the decalcification agent is replaced with potassium carbonate solution. The amount of potassium carbonate added is 1.2 times the molar concentration of calcium ions. The remaining steps are the same as in Example 4.

[0053] The purified brine treated by this traditional potassium carbonate decalcification process has a stable calcium ion concentration of 4.2 ppm, and the regeneration cycle of the secondary brine resin tower is extended to 32 hours.

[0054] A comparison of the embodiments of this invention with the comparative examples of traditional processes shows that the phosphate calcium removal technology can stably control the calcium ion concentration of the refined brine below 0.5 ppm, significantly better than the 4.2 ppm level of the traditional potassium carbonate process. This difference is mainly due to the fact that the solubility product of calcium phosphate is much lower than that of calcium carbonate, resulting in a more thorough precipitation reaction. Simultaneously, the ceramic membrane filtration system effectively separates fine precipitates, thus achieving the goal of deep calcium removal. This highly efficient calcium removal effect directly leads to a significant extension of the regeneration cycle of the secondary brine resin tower, increasing it from 32 hours in the comparative example to over 250 hours in the embodiment, greatly reducing the load on subsequent refining processes. The implementation of this invention has created significant production benefits, indirectly reducing the production cost of ion-exchange membrane alkali production, improving production levels, and enhancing the company's product competitiveness.

[0055] In the description of this specification, the reference to terms such as "example," "various examples," etc., means that a specific feature, structure, material, or characteristic described in connection with that example or preparation is included in at least one example or preparation of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparations.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for removing calcium from brine with phosphoric acid, characterized in that, Includes the following steps: S1. After the brine is pressurized by the brine pump, it is heated to 60-65℃ by steam through the brine heat exchanger, and then sent to the brine tank for brine treatment to obtain brine with a concentration of 300-310g / L. S2. Add 85% phosphoric acid to the brine obtained in step S1 in the baffle tank, so that the calcium ions in the brine react with the phosphate ions to form calcium phosphate precipitate. During the reaction, the brine flows through the front reaction tank, the rear reaction tank and the intermediate tank in sequence. S3. Add a 32% potassium hydroxide solution to the brine after the reaction in step S2 in the post-reaction tank to adjust the pH value of the brine to 10-12. S4. The brine obtained in step S3 is sent to the intermediate tank and then to a ceramic membrane filter for filtration to obtain refined brine with a calcium ion concentration of less than 0.5 ppm. S5. Add hydrochloric acid to the purified brine obtained in step S4 to adjust its pH value to 7.2, 7.5, or 7.

8.

2. The process for calcium removal from brine using phosphoric acid according to claim 1, characterized in that, The amount of phosphoric acid added in step S2 is 1.08 times, 1.1 times, or 1.2 times the molar concentration of calcium ions in the brine obtained in step S1.

3. The process for calcium removal from brine using phosphoric acid according to claim 1, characterized in that, In step S1, the brine pump pressurizes the brine to 0.4 MPa, 0.45 MPa, or 0.5 MPa.

4. The process for calcium removal from brine using phosphoric acid according to claim 1, characterized in that, In step S4, the filtration accuracy of the ceramic membrane filter is 50 nm.

5. The process for removing calcium from brine with phosphoric acid according to claim 1, characterized in that, In step S5, an online pH meter is installed before the static mixer, and the amount of hydrochloric acid added is automatically adjusted according to the detection result of the online pH meter.

6. A process apparatus for implementing the brine-phosphate decalcification method according to any one of claims 1-5, characterized in that, Including those connected sequentially along the process flow: A saline pump is used to pressurize brine. A brine heat exchanger, connected to the brine pump, is used to heat the pressurized brine using steam. A brine tank, connected to the brine heat exchanger, is used to prepare brine; A baffle trough is connected to the salt treatment tank and is equipped with a phosphoric acid dosing port; The reaction tank group, connected to the baffle tank, is used for phosphoric acid calcium removal reaction and pH adjustment. The reaction tank group includes a front reaction tank, a rear reaction tank and an intermediate tank connected in sequence, and the alkali dosing port is located in the rear reaction tank. A ceramic membrane filter, connected to the reaction tank assembly, is used to filter and remove calcium phosphate precipitate; A static mixer is connected to the outlet of the ceramic membrane filter and is equipped with an acid dosing port for adjusting the pH value of the final brine.

7. The process apparatus for calcium removal from brine using phosphoric acid according to claim 6, characterized in that, An automatic control system is provided at the acid dosing port. The system includes an online pH detection device and a regulating valve. The online pH detection device is used to detect the pH value of the refined brine output by the ceramic membrane filter, and the regulating valve is used to control the amount of acid added based on the detection results.

8. The process apparatus for calcium removal from brine using phosphoric acid according to claim 6, characterized in that, The brine heat exchanger is equipped with a steam inlet for receiving steam to provide a heating source; the acid added through the acid dosing port is hydrochloric acid.

Images