Electrolytic combined reduction method chlorine dioxide preparation system

Abstract

The utility model discloses a kind of chlorine dioxide preparation systems of electrolytic combined reduction method, including brine refining unit, brine washing unit, electrolytic unit, crystallization unit, dissolving unit, formation and absorption unit, it is characterized by: the discharge outlet of the brine refining unit is connected with the feed inlet pipeline of brine washing unit;The discharge outlet of the brine washing unit is connected with the feed inlet pipeline of electrolytic unit;The discharge outlet of the electrolytic unit is respectively connected with the feed inlet pipeline of crystallization unit and brine washing unit;The discharge outlet of the crystallization unit is respectively connected with the feed inlet of dissolving unit and electrolytic unit;The discharge outlet of the dissolving unit is connected with the feed inlet pipeline of formation and absorption unit;The discharge outlet of the formation and absorption unit is connected with bleaching plant pipeline.The utility model is high in production efficiency, and energy-saving emission-reduction effect is good, and safety is high.

Description

Technical Field

[0001] This invention belongs to the field of chlorine dioxide preparation technology, and particularly relates to an electrolytic combined reduction method for chlorine dioxide preparation system. Background Technology

[0002] Chlorine dioxide has the chemical formula ClO2 and a relative molecular mass of 67.45. At room temperature and pressure, chlorine dioxide is an orange-yellow gas with a pungent, irritating odor similar to a mixture of chlorine and ozone. It has a boiling point of 11°C, a freezing point of -59°C, and a gaseous density of 3.09 g / m³ at 11°C. 3 Chlorine dioxide is highly soluble in water and does not react with it; its solubility is 5-8 times that of chlorine gas, and its aqueous solution is yellow. Solubility decreases with increasing temperature, so ice water at 5-7°C is generally used to absorb chlorine dioxide. The temperature of the chlorine dioxide aqueous solution is generally controlled at 10-14°C to ensure a concentration of 8-10 g / L.

[0003] Chlorine dioxide gas is unstable and easily decomposes. Its concentration cannot be too high, otherwise a decomposition explosion will occur. The partial pressure of chlorine dioxide gas must be controlled below 100 mmHg (absolute pressure). If the partial pressure exceeds 100 mmHg, it will decompose into chlorine and oxygen, releasing heat (24.7 kJ / mol). Therefore, it must be prepared and used on-site. Chlorine dioxide has extremely strong oxidizing properties and can oxidize and degrade residual lignin in pulp, thus bleaching the pulp. Chlorine dioxide has strong selectivity for lignin, resulting in bleached pulp with high brightness, less yellowing, good strength, and low AOX content in wastewater. Chlorine dioxide is the main bleaching agent in the ECF bleaching process.

[0004] The reduction method for preparing chlorine dioxide is currently the most common method used by pulping companies. This method uses sodium chlorate as one of the main raw materials, which companies usually obtain directly from external sources. However, solid sodium chlorate is a Class A hazardous chemical, posing a high safety risk to raw material storage. Sodium chlorate warehouses with a storage capacity of more than 100 tons are considered major hazard sources. When purchasing sodium chlorate, manual operation is required in all aspects of transportation, storage, and use, leading to an increase in external uncertainties and a series of safety hazards, increasing the possibility of accidents and exposing companies to uncontrollable operational risks. Furthermore, the reduction method for preparing chlorine dioxide consumes a large amount of sodium chlorate, resulting in high production costs. Utility Model Content

[0005] The purpose of this invention is to provide an electrolytic combined reduction method for preparing chlorine dioxide, so as to solve the technical problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An electrolytic combined reduction method for chlorine dioxide preparation system includes a brine purification unit, a brine washing unit, an electrolysis unit, a crystallization unit, a dissolution unit, and a generation and absorption unit. The outlet of the brine purification unit is connected to the inlet of the brine washing unit; the outlet of the brine washing unit is connected to the inlet of the electrolysis unit; the outlet of the electrolysis unit is connected to the inlets of both the crystallization unit and the brine washing unit; the outlet of the crystallization unit is connected to the inlets of both the dissolution unit and the electrolysis unit; the outlet of the dissolution unit is connected to the inlet of the generation and absorption unit; and the outlet of the generation and absorption unit is connected to a bleaching workshop.

[0008] Furthermore, the discharge port of the generation and absorption unit is also connected to the pipeline of the alkali recovery workshop.

[0009] Furthermore, it also includes a sulfate reaction unit; the inlet of the sulfate reaction unit is connected to the outlet of the crystallization unit via a pipeline.

[0010] Furthermore, the outlet of the sulfate reaction unit is connected to the inlet of the brine purification unit via a pipeline.

[0011] Furthermore, it also includes a hydrogen scrubbing unit; the inlet of the hydrogen scrubbing unit is connected to the outlet of the brine scrubbing unit via a pipeline.

[0012] Furthermore, the outlet of the hydrogen scrubbing unit is connected to the inlet pipe of the brine refining system.

[0013] Furthermore, it also includes an exhaust gas treatment unit; the inlet of the exhaust gas treatment unit is connected to the outlet pipeline of the generation and absorption unit.

[0014] Furthermore, the outlet of the exhaust gas treatment unit is connected to the inlet of the brine refining unit.

[0015] Furthermore, the outlet of the exhaust gas treatment unit is also connected to the inlet of the generation and absorption unit.

[0016] The advantages of this utility model compared to the prior art are as follows:

[0017] 1. This utility model produces sodium chlorate by electrolysis using an electrolysis unit, resulting in high production efficiency and good energy-saving and emission-reduction effects. It only requires electricity and raw salt to continuously produce sodium chlorate solution, unaffected by the quality of purchased sodium chlorate, thus improving the stability of chlorine dioxide preparation. Furthermore, the raw salt used in this utility model offers higher production safety during transportation, storage, and use compared to purchased sodium chlorate. In addition, the preparation system of this utility model does not require the purchase of chlorine or hydrochloric acid as raw materials, avoiding the safety requirements and control associated with the production, storage, and emergency response of chlorine and hydrochloric acid, thus achieving higher operational safety assurance for the system.

[0018] 2. The byproduct Glauber's salt produced by the chlorine dioxide generation system of this utility model can be sent to the alkali recovery workshop for use, which is conducive to balancing the overall production of the plant and reducing the production cost of the enterprise.

[0019] 3. This utility model, by setting up a hydrogen scrubbing unit, can scrub and purify the tail gas generated by electrolysis, with no chlorine emissions. The sodium hypochlorite solution generated by the tail gas scrubbing is returned to the brine refining system for recycling and is used for salt dissolution, with no residual sodium hypochlorite solution as a byproduct.

[0020] 4. This utility model sets up a sulfate reaction unit to remove impurities from the mother liquor produced by the crystallization unit, and the resulting clarified filtrate is sent to the brine refining unit for salt dissolution, with no chromium-containing wastewater discharged.

[0021] 5. By setting up a tail gas treatment unit, this utility model can treat the chlorine gas generated by the generation and treatment unit, achieving zero chlorine gas emissions. The generated sodium thiosulfate solution is used for salt dissolution, and the sodium thiosulfate solution circulation makes the connection of the entire electrolytic combination reduction chlorine dioxide preparation system form a closed loop system.

[0022] 6. The electrolysis unit and the generation and absorption unit of this utility model can operate independently, which can provide a favorable guarantee for the stable and continuous operation of production. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of this utility model;

[0024] Figure 2 This is a schematic diagram of the structure of the electrolysis unit of this utility model;

[0025] In the attached diagram, 1-Brine refining unit; 2-Brine washing unit;

[0026] 3-Electrolysis unit; 301-Electrolytic cell; 302-Inlet manifold; 303-Reactor; 304-Degasser; 305-Cooler;

[0027] 4-Crystallization unit; 5-Dissolution unit; 6-Generation and absorption unit; 7-Sulfate reaction unit; 8-Hydrogen scrubbing unit; 9-Tail gas treatment unit. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this utility model clearer, the following detailed description is provided with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of this utility model, and these aspects can be achieved even without these specific details.

[0029] like Figure 1 As shown, an electrolytic combined reduction method for preparing chlorine dioxide includes a brine purification unit 1, a brine washing unit 2, an electrolysis unit 3, a crystallization unit 4, a dissolution unit 5, and a generation and absorption unit 6.

[0030] The outlet of the brine refining unit 1 is connected to the inlet of the brine washing unit 2 via a pipeline. The brine refining unit 1 includes a salt dissolving and reaction device, a membrane filter, and a resin tower. The brine refining unit 1 prepares the raw salt into a solution of the required concentration and then completes the brine refining process through reaction precipitation, physical filtration, and ion exchange in sequence to obtain qualified refined brine raw material for electrolysis, which is then transported to the washing unit via a pipeline.

[0031] The outlet of the brine washing unit 2 is connected to the inlet of the electrolysis unit 3 via a pipeline; the brine washing unit 2 further purifies the brine from the brine refining unit 1, and at the same time uses the alkali remaining in the brine to absorb some of the chlorine gas generated by the sodium chlorate electrolysis unit 3.

[0032] The outlet of the electrolysis unit 3 is connected to the inlet pipes of the crystallization unit 4 and the brine washing unit 2, respectively. The electrolysis unit 3 electrolyzes the refined brine to generate an electrolyte containing sodium chlorate and hydrogen gas. The sodium chlorate is transported to the crystallization unit 4, and the hydrogen gas is returned to the brine washing unit 2. The chemical equation for the principle of producing sodium chlorate by electrolysis of refined brine is as follows:

[0033]

[0034] like Figure 2 As shown, in a further embodiment, the electrolysis unit 3 includes an electrolytic cell 301, a main inlet pipe 302, a reactor 303, a degasser 304, and a cooler 305. The electrolytic cell 301 can adopt different structural forms, such as a square electrolytic cell or a circular electrolytic cell. The electrolytic cell 301 is composed of multiple unit cells, each unit cell including a cell body, an anode, a cathode, and a current-carrying plate. The inlet pipe of each unit cell is connected to the cooler 305 through the main inlet pipe 302, and the outlet pipe is connected to the degasser 304. The degasser 304 and the cooler 305 are respectively connected to the inlet and outlet of the reactor 303. The degasser 304 and the reactor 303 are provided with hydrogen exhaust ports. The reactor 303 is provided with a concentrated sodium chlorate solution outlet and an inlet for brine from the brine refining unit 1 and mother liquor from the crystallization unit 4.

[0035] In a further embodiment, during electrolysis, chloride ions discharge to generate chlorine gas. Some of the chlorine gas reacts with water to produce hypochlorous acid. The generated hypochlorous acid then reacts with sodium hydroxide in the solution to form sodium hypochlorite. Therefore, byproducts hypochlorous acid and sodium hypochlorite are present in the electrolyte. Since sodium hypochlorite and hypochlorous acid are oxidizing, they interfere with the reaction of sodium chlorate with methanol and sulfuric acid in the subsequent chlorine dioxide generation unit, leading to instability in the reaction process and affecting the generation efficiency and purity of chlorine dioxide. In this embodiment, a hydrogen peroxide addition pipe is installed on the connecting pipe between the outlet of electrolysis unit 3 and the inlet of crystallization unit 4. Hydrogen peroxide is introduced into the connecting pipe through the hydrogen peroxide addition pipe to remove hypochlorous acid and sodium hypochlorite from the electrolyte. The chemical equation is as follows:

[0036] NaClO + H₂O₂ → NaCl + H₂O + O₂

[0037] HClO + H₂O₂ → HCl + H₂O + O₂

[0038] After removing hypochlorous acid and sodium hypochlorite from the electrolyte, the electrolyte is transported to crystallization unit 4.

[0039] The outlet of the crystallization unit 4 is connected to the dissolution unit 5, and the outlet of the crystallization unit 4 is also connected to the inlet pipeline of the electrolysis unit 3. The crystallization unit 4 evaporates and concentrates the electrolyte containing dehypochlorous acid and sodium hypochlorite, thereby removing other impurities in the electrolyte to obtain sodium chlorate crystals and mother liquor. The sodium chlorate crystals are fed into the dissolution unit 5 by a screw conveyor, and the mother liquor is returned to the electrolysis unit 3 for recycling through pipeline.

[0040] The outlet of the dissolving unit 5 is connected to the inlet of the generating and absorbing unit 6 via a pipeline; the dissolving unit 5 dissolves sodium chlorate crystals to obtain a sodium chlorate solution that meets the concentration requirements, and then sends the sodium chlorate solution into the generating and absorbing unit 6.

[0041] The generation and absorption unit 6 reacts the obtained sodium chlorate solution with methanol and sulfuric acid to synthesize chlorine dioxide. The chemical equation is as follows:

[0042] 12NaClO3+8H2SO4+3CH3OH→12ClO2+9H2O+4Na3H(SO4)2+3HCOOH

[0043] The discharge port of the generation and absorption unit 6 is connected to the pipeline of the bleaching workshop, so as to send the synthesized chlorine dioxide product to the bleaching workshop and realize on-site preparation and on-site use.

[0044] The discharge port of the generation and absorption unit 6 is connected to the pipeline of the alkali recovery workshop; during the synthesis of chlorine dioxide, sodium sulfate, a by-product, is generated, which can be transported to the alkali recovery workshop for use.

[0045] It also includes a sulfate reaction unit 7; the inlet of the sulfate reaction unit 7 is connected to the outlet of the crystallization unit 4, and the outlet of the sulfate reaction unit 7 is connected to the inlet of the brine purification unit 1. In the crystallization unit 4, the mother liquor after crystallization is returned to the electrolysis unit 3 for recycling through a pipeline, and another pipeline enters the sulfate reaction unit 7. The sulfate reaction unit 7 reacts the mother liquor with calcium chloride and potassium chloride to remove sulfate and perchlorate ions from the mother liquor, generating calcium sulfate and potassium perchlorate precipitates. After separation by a clarifier, the precipitate is filtered by a filter press, and the resulting clear liquid is sent back to the brine purification unit 1 for recycling. The chemical equation is:

[0046] Na₂SO₄ + CaCl₂ → CaSO₄ + 2NaCl

[0047] KCl + NaClO4 → KClO4 + NaCl

[0048] It also includes a hydrogen scrubbing unit 8; the inlet of the hydrogen scrubbing unit 8 is connected to the outlet of the brine scrubbing unit 2, and the outlet of the hydrogen scrubbing unit 8 is connected to the inlet of the brine refining system. The hydrogen generated by the electrolysis unit 3 passes through the brine scrubbing unit 2, and then enters the hydrogen scrubbing unit 8. The hydrogen scrubbing unit 8 removes chlorine from the hydrogen through alkaline washing, and the dechlorinated hydrogen is either vented or sent to other workshops for use. The generated sodium thiosulfate solution is transported to the brine refining unit 1 for recycling and reuse to dissolve the raw salt.

[0049] It also includes a tail gas treatment unit 9; the inlet of the tail gas treatment unit 9 is connected to the outlet of the generation and absorption unit 6, and the outlet of the tail gas treatment unit 9 is connected to the inlet of the brine refining unit 1. The tail gas treatment unit 9 includes a tail gas scrubbing tower and an exhaust scrubbing tower. During the synthesis of chlorine dioxide, the generation and absorption unit 6 generates tail gas containing chlorine and chlorine dioxide. The tail gas is sent to the tail gas treatment unit 9. The tail gas scrubbing tower in the tail gas treatment unit 9 uses ice water to preliminarily scrub and absorb the chlorine and chlorine dioxide in the tail gas, and then sends it to the exhaust scrubbing tower. The exhaust scrubbing tower uses alkaline solution to further scrub the chlorine and chlorine dioxide in the tail gas. Finally, the tail gas is discharged into the atmosphere. The sodium hydroxide solution generated by the exhaust scrubbing tower is sent to the brine refining unit 1 for recycling and reuse to dissolve the raw material salt.

[0050] The outlet of the exhaust gas treatment unit 9 is also connected to the inlet of the generation and absorption unit 6. The exhaust gas treatment unit 9 also includes an absorption tower; the inlet of the absorption tower is connected to the outlet of the exhaust gas scrubbing tower; after the exhaust gas is scrubbed and absorbed by the exhaust gas scrubbing tower in the exhaust gas treatment unit 9, the generated dilute chlorine dioxide returns to the absorption tower to continue absorbing chlorine dioxide.

[0051] The working principle of this utility model is as follows:

[0052] The brine refining system prepares refined brine and delivers it to the brine washing unit 2, which then delivers it to the electrolysis unit 3. In the electrolysis unit 3, sodium chlorate-containing electrolyte is generated through electrolysis. Chlorine and hydrogen generated during electrolysis in the electrolysis unit 3 enter the brine washing unit 2. The chlorine comes into contact with the refined brine in the washing unit 2, and the residual alkali in the refined brine absorbs the chlorine. The hydrogen passes through the brine washing unit 2 and enters the hydrogen washing unit 8. The hydrogen washing unit 8 removes the chlorine from the hydrogen through alkaline washing and then vents the dechlorinated hydrogen or sends it to other workshops for use. The generated sodium thiosulfate solution is delivered to the brine refining unit 1 for recycling.

[0053] The electrolyte generated in electrolysis unit 3, after being dechlorinated and treated with sodium hypochlorite, enters crystallization unit 4. Crystallization unit 4 evaporates and concentrates the electrolyte to obtain sodium chlorate crystals and mother liquor. The sodium chlorate crystals are sent to dissolution unit 5 via a screw conveyor. The mother liquor is divided into two paths: one path returns to electrolysis unit 3 for recycling, and the other path enters sulfate reaction unit 7. Sulfate reaction unit 7 removes sulfate and perchlorate ions from the mother liquor, and the clear liquid is sent back to brine purification unit 1 for recycling.

[0054] Dissolving unit 5 dissolves sodium chlorate crystals to obtain a sodium chlorate solution meeting the required concentration, and then sends the sodium chlorate solution to generating and absorbing unit 6. Generating and absorbing unit 6 reacts sodium chlorate with methanol and sulfuric acid to synthesize chlorine dioxide.

[0055] The exhaust gas generated by the generation and absorption unit 6 enters the exhaust gas treatment unit 9. After the exhaust gas is treated, it is discharged into the air. The generated dilute chlorine dioxide is returned to the generation and absorption unit 6 for absorption. The generated sodium hypochlorite solution is transported to the brine refining unit 1 for recycling.

[0056] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A system for producing chlorine dioxide by electrolytic combined reduction method, comprising a brine refining unit, a brine washing unit, an electrolysis unit, a crystallization unit, a dissolution unit, a generation and absorption unit, characterized in that: The outlet of the brine refining unit is connected to the inlet pipe of the brine washing unit; the outlet of the brine washing unit is connected to the inlet pipe of the electrolysis unit; the outlet of the electrolysis unit is connected to the inlet pipes of the crystallization unit and the brine washing unit respectively; the outlet of the crystallization unit is connected to the inlet pipes of the dissolving unit and the electrolysis unit respectively; the outlet of the dissolving unit is connected to the inlet pipe of the generation and absorption unit; and the outlet of the generation and absorption unit is connected to the bleaching workshop.

2. The system for preparing chlorine dioxide by electrolytic combined reduction method according to claim 1, characterized in that: The discharge port of the generation and absorption unit is also connected to the pipeline of the alkali recovery workshop.

3. The system for preparing chlorine dioxide by electrolytic combined reduction method according to claim 1, characterized in that: It also includes a sulfate reaction unit; the inlet of the sulfate reaction unit is connected to the outlet of the crystallization unit via a pipeline.

4. The system for preparing chlorine dioxide by electrolytic combined reduction method according to claim 3, characterized in that: The outlet of the sulfate reaction unit is connected to the inlet of the brine purification unit via a pipeline.

5. The system for the preparation of chlorine dioxide by electrolytic combined reduction method according to claim 1, characterized in that: It also includes a hydrogen scrubbing unit; the inlet of the hydrogen scrubbing unit is connected to the outlet of the brine scrubbing unit via a pipeline.

6. The system for the preparation of chlorine dioxide by the method of electrolytic combined reduction according to claim 5, characterized in that: The outlet of the hydrogen scrubbing unit is connected to the inlet pipe of the brine refining system.

7. The system for the preparation of chlorine dioxide by electrolytic combined reduction method according to claim 1, characterized in that: It also includes an exhaust gas treatment unit; the inlet of the exhaust gas treatment unit is connected to the outlet pipeline of the generation and absorption unit.

8. The system for the preparation of chlorine dioxide by the method of electrolytic combined reduction according to claim 7, characterized in that: The outlet of the exhaust gas treatment unit is connected to the inlet of the brine refining unit.

9. The system for the preparation of chlorine dioxide by the method of electrolytic combined reduction according to claim 7, characterized in that: The outlet of the exhaust gas treatment unit is also connected to the inlet of the generation and absorption unit.

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