Chlorine dioxide preparation system adopting electrolysis combined reduction method

Abstract

The invention provides an electrolysis combined reduction method chlorine dioxide preparation system, which belongs to the technical field of chlorine dioxide preparation, and comprises a brine refining unit, a brine washing unit, a sodium chlorate electrolysis unit, a sodium chlorate crystallization unit, a sodium chlorate dissolving device and a chlorine dioxide generation and absorption unit, the saline water refining unit is connected with the saline water washing unit, the saline water washing unit is connected with the sodium chlorate electrolysis unit, the sodium chlorate electrolysis unit is respectively connected with the saline water washing unit and the sodium chlorate crystallization unit, and the sodium chlorate crystallization unit is respectively connected with the sodium chlorate electrolysis unit and the sodium chlorate dissolving equipment. And the sodium chlorate dissolving equipment is connected with the chlorine dioxide generation and absorption unit. Chlorine or hydrochloric acid does not need to be purchased as a production raw material, safety requirements and safety control of chlorine and hydrochloric acid in the aspects of production, storage and emergency disposal are avoided, and higher operation safety guarantee of the system is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of chlorine dioxide preparation, and particularly relates to a chlorine dioxide preparation system by an electrolytic combination reduction method. Background Art

[0002] The chemical formula of chlorine dioxide is ClO₂, and its relative molecular mass is 67.45. Under normal temperature and pressure, chlorine dioxide is an orange-yellow gas, with an irritating spicy smell similar to the mixture of chlorine and ozone. Its boiling point is 11°C, freezing point is -59°C, and the gaseous density at 11°C is 3.09 g / m 3 . Chlorine dioxide is extremely soluble in water without reacting with water. Its solubility is 5-8 times that of chlorine, and the aqueous solution is yellow. The solubility of chlorine dioxide in water decreases with the increase of temperature. Therefore, generally, ice water at 5-7°C is used to absorb chlorine dioxide, and the temperature of the chlorine dioxide aqueous solution is generally controlled at 10-14°C to ensure that the concentration of the chlorine dioxide aqueous solution is 8-10 g / L.

[0003] Chlorine dioxide gas is unstable and prone to decomposition. The concentration of chlorine dioxide gas cannot be too high, otherwise it will decompose and explode. The partial pressure of chlorine dioxide gas needs to be controlled below 100 mmHg (absolute pressure). When the partial pressure exceeds 100 mmHg, it will decompose into chlorine and oxygen and release heat (24.7 kJ / mol). Therefore, it can only be prepared and used on-site. Chlorine dioxide has extremely strong oxidizing properties and can oxidize and degrade the residual lignin in pulp, thus playing a role in bleaching pulp. Chlorine dioxide has strong selectivity for lignin. After bleaching, the pulp has high whiteness, less yellowing, good strength, and low AOX content in the wastewater. Chlorine dioxide is the main bleaching agent in the ECF bleaching process.

[0004] The reduction method for chlorine dioxide preparation technology is the most commonly used method in pulp mills at present. Sodium chlorate is the largest consumed raw material in the system and needs to be purchased externally. The cost of purchasing sodium chlorate accounts for a large proportion of the system operation cost. Solid sodium chlorate is a Class A hazardous chemical, and the safety risk of raw material storage is high. A sodium chlorate warehouse with a stock of more than 100 T belongs to a major hazard source. A series of safety hazards will occur when purchasing sodium chlorate externally, resulting in an increase in cost. There is too much manual operation during transportation, storage, and use, and the increase of external uncertain factors increases the possibility of accidents, making the enterprise face uncontrollable operation hazards. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a chlorine dioxide preparation system by an electrolytic combination reduction method with high productivity, no need to purchase sodium chlorate externally, comprehensive utilization of system materials, energy conservation and emission reduction.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] An electrolytic combined reduction method chlorine dioxide preparation system, the system includes a brine refining unit, a brine washing unit, a sodium chlorate electrolysis unit, a sodium chlorate crystallization unit, a sodium chlorate dissolving device, and a chlorine dioxide generation and absorption unit. The brine refining unit is connected to the brine washing unit, the brine washing unit is connected to the sodium chlorate electrolysis unit, the sodium chlorate electrolysis unit is respectively connected to the brine washing unit and the sodium chlorate crystallization unit, the sodium chlorate crystallization unit is respectively connected to the sodium chlorate electrolysis unit and the sodium chlorate dissolving device, and the sodium chlorate dissolving device is connected to the chlorine dioxide generation and absorption unit.

[0008] Further, the discharge end of the brine refining unit is connected to the brine washing unit through a pipeline, and the brine refining unit is used to make raw salt into refined brine.

[0009] Further, the discharge end of the brine washing unit is connected to the sodium chlorate electrolysis unit through a pipeline, and the brine washing unit is used to wash the refined brine and absorb the generated chlorine gas.

[0010] Further, a hydrogen tail gas treatment device is connected to the discharge end of the brine washing unit. The hydrogen tail gas treatment device is used to dechlorinate hydrogen, and the discharge end of the hydrogen tail gas treatment device is connected to the brine refining unit.

[0011] Further, the discharge end of the sodium chlorate electrolysis unit is connected to the sodium chlorate crystallization unit through a pipeline, and the sodium chlorate electrolysis unit is used to electrolyze brine.

[0012] Further, the discharge end of the sodium chlorate crystallization unit is connected to the sodium chlorate dissolving device through a pipeline, and the sodium chlorate crystallization unit is used to crystallize sodium chlorate.

[0013] Further, a sulfate removal device is connected to the discharge end of the sodium chlorate crystallization unit. The sulfate removal device is used to remove sulfate from the mother liquor generated by the sodium chlorate crystallization unit, and the discharge end of the sulfate removal device is connected to the brine refining unit.

[0014] Further, the discharge end of the sodium chlorate dissolving device is connected to the chlorine dioxide generation and absorption unit through a pipeline, and the sodium chlorate dissolving device is used to dissolve sodium chlorate crystals.

[0015] Further, a chlorine dioxide tail gas treatment system is connected to the discharge end of the chlorine dioxide generation and absorption unit. The chlorine dioxide tail gas treatment system is used to wash and absorb chlorine dioxide, and the discharge end of the chlorine dioxide tail gas treatment system is connected to the brine refining unit.

[0016] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0017] 1. The present invention uses a sodium chlorate electrolysis unit to produce sodium chlorate and a by-product hydrogen gas. The by-product hydrogen gas can be used to prepare hydrogen peroxide or as fuel, achieving comprehensive utilization of by-products and improving economic benefits.

[0018] 2. The present invention only needs to provide electricity, raw salt, methanol, and sulfuric acid to continuously prepare chlorine dioxide, without the need to purchase sodium chlorate externally. This reduces the procurement, transportation, and manual operation costs of sodium chlorate and lowers the system operation cost.

[0019] 3. The present invention does not require the external purchase of chlorine gas or hydrochloric acid as production raw materials, avoiding the safety requirements and safety control in the production, storage, and emergency disposal of chlorine gas and hydrochloric acid, and achieving a higher level of system operation safety guarantee.

[0020] 4. The raw material salt used in the patent of the present invention is very safe during transportation, storage, and use, and has higher production safety than the existing technologies that require the external purchase of sodium chlorate.

[0021] 5. In the chlorine dioxide generation system of the present invention, by-products mirabilite are produced while synthesizing chlorine dioxide. The mirabilite can be sent to the alkali recovery workshop for use, achieving comprehensive utilization of system materials and facilitating the balance of enterprise production.

[0022] 6. The present invention collects all the chlorine-containing gas and performs alkali washing. The resulting sodium thiosulfate solution is sent to the brine purification unit for salt dissolution and recycled use, without discharging by-product sodium thiosulfate solution and chlorine-containing tail gas.

[0023] 7. The present invention treats the mother liquor to remove sulfate ions, and the clear liquid is sent to the brine purification process for reuse, without discharging chromium-containing wastewater.

[0024] 8. The sodium chlorate electrolysis unit and the chlorine dioxide generation and absorption unit of the present invention can operate independently. The production of these two units can be independent of each other, providing a favorable guarantee for the stable and continuous operation of enterprise production.

[0025] 9. The chlorine dioxide tail gas treatment system of the present invention absorbs and treats all the chlorine gas generated by the chlorine dioxide preparation system, without chlorine gas emission. The resulting sodium thiosulfate solution is used for salt dissolution, and the sodium thiosulfate solution circulates to form a closed loop system for the entire electrolysis combination reduction chlorine dioxide preparation system. Description of the Drawings

[0026] Figure 1 is a schematic diagram of the electrolysis combination reduction method chlorine dioxide preparation system of the present invention.

[0027] In the drawings, 1 - brine purification unit, 2 - brine washing unit, 3 - sodium chlorate electrolysis unit, 4 - sodium chlorate crystallization unit, 5 - sodium chlorate dissolution equipment, 6 - chlorine dioxide generation and absorption unit, 7 - hydrogen tail gas treatment equipment, 8 - sulfate removal equipment, 9 - chlorine dioxide tail gas treatment system. Detailed Embodiments

[0028] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following provides preferred embodiments with reference to the accompanying drawings and further elaborates on the present invention in detail. However, it should be noted that many details listed in the specification are only for enabling the reader to have a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be implemented even without these specific details.

[0029] As Figure 1 shown, an electrolytic combined reduction method chlorine dioxide preparation system, the system includes a brine purification unit 1, a brine washing unit 2, a sodium chlorate electrolysis unit 3, a sodium chlorate crystallization unit 4, a sodium chlorate dissolving device 5 and a chlorine dioxide generation and absorption unit 6. The brine purification unit 1 is connected to the brine washing unit 2, the brine washing unit 2 is connected to the sodium chlorate electrolysis unit 3, the sodium chlorate electrolysis unit 3 is respectively connected to the brine washing unit 2 and the sodium chlorate crystallization unit 4, the sodium chlorate crystallization unit 4 is respectively connected to the sodium chlorate electrolysis unit 3 and the sodium chlorate dissolving device 5, and the sodium chlorate dissolving device 5 is connected to the chlorine dioxide generation and absorption unit 6. The preparation system of the present invention does not need to purchase sodium chlorate externally. Only by providing electricity and raw salt, sodium chlorate solution can be continuously produced. Enterprises do not need to purchase sodium chlorate hazardous chemicals, avoiding the safety risks of sodium chlorate raw material transportation and storage, and at the same time reducing the operating costs of enterprises.

[0030] In the present invention, the discharge end of the brine purification unit 1 is connected to the brine washing unit 2 through a pipeline. The brine purification unit 1 is used to make raw salt into refined brine. The raw material salt is added to the brine purification unit, and then water is added to prepare qualified refined brine. The refined brine comes out from the discharge end of the brine purification unit and is transported to the brine washing unit through a pipeline. The discharge end of the brine washing unit 2 is connected to the sodium chlorate electrolysis unit 3 through a pipeline. The brine washing unit 2 is used to wash the refined brine and absorb the chlorine generated by the electrolysis of the sodium chlorate electrolysis unit. After the brine washing tower of the brine washing unit washes the brine, it is transported to the sodium chlorate electrolysis unit through a pipeline.

[0031] In the present invention, the discharge end of the sodium chlorate electrolysis unit 3 is connected to the sodium chlorate crystallization unit 4 through a pipeline, and the sodium chlorate electrolysis unit 3 is used for electrolyzing brine. The sodium chlorate electrolysis unit feeds the brine coming out from the discharge end of the brine washing unit and the mother liquor coming out from the discharge end of the sodium chlorate crystallization unit into the sodium chlorate electrolysis unit, and electrolyzes them to generate an electrolytic solution containing sodium chlorate, sodium hypochlorite, hypochlorous acid solution, by-product hydrogen and a small amount of chlorine gas; the electrolytic solution generated by the sodium chlorate electrolysis unit, after being subjected to sodium hypochlorite removal treatment, enters the sodium chlorate crystallization unit. The discharge end of the brine washing unit 2 is connected to a hydrogen tail gas treatment device 7, and the hydrogen tail gas treatment device 7 is used for dechlorinating hydrogen. The discharge end of the hydrogen tail gas treatment device 7 is connected to the brine purification unit 1. The hydrogen and chlorine gas generated by the sodium chlorate electrolysis unit enter the hydrogen washing tower of the hydrogen tail gas treatment device through the brine washing tower of the brine washing unit. By adding sodium hydroxide solution to the hydrogen washing tower (not marked in the figure) of the hydrogen tail gas treatment device for treatment, the generated sodium thiosulfate solution is transported to the brine purification unit for salt dissolution, and there is no by-product sodium thiosulfate solution discharged, realizing internal circulation utilization in the system; all the chlorine gas generated by the preparation system of the present invention passes through the brine washing tower (not marked in the figure) of the brine washing unit and the hydrogen washing tower of the hydrogen tail gas treatment device. The chlorine gas is removed by alkali absorption. The sodium thiosulfate solution generated by the hydrogen washing tower of the hydrogen tail gas treatment device is sent to the brine purification unit for salt dissolution, and there is no by-product sodium thiosulfate solution discharged. In the sodium chlorate electrolysis unit of the preparation system of the present invention, the discharged electrolytic solution contains sodium hypochlorite. The electrolytic solution subjected to sodium hypochlorite removal treatment is sent to the crystallizer of the sodium chlorate crystallization unit for heating crystallization. The sodium chlorate crystals separated by the crystallizer of the sodium chlorate crystallization unit are dissolved to obtain a sodium chlorate solution. The mother liquor separated by the crystallizer of the sodium chlorate crystallization unit is returned to the electrolytic cell of the sodium chlorate electrolysis unit. The mother liquor circulation between the electrolytic cell of the sodium chlorate electrolysis unit and the crystallizer of the sodium chlorate crystallization unit is a closed system circulation. The preparation system of the present invention can generate by-product hydrogen, which can be sent by the enterprise to downstream processes for use, such as for the preparation of hydrogen peroxide or as fuel, reducing or eliminating the need to purchase hydrogen externally and reducing the operating cost of the enterprise.

[0032] In the present invention, the discharge end of the sodium chlorate crystallization unit 4 is connected to a sodium chlorate dissolving device 5 through a pipeline. The sodium chlorate crystallization unit 4 is used for crystallizing sodium chlorate. The crystallizer (not marked in the figure) of the sodium chlorate crystallization unit heats and separates out sodium chlorate crystals. The sodium chlorate crystals coming out from the discharge end of the sodium chlorate crystallization unit are transported to the sodium chlorate dissolving device through a pipeline. At the same time, a part of the mother liquor separated by the crystallizer of the sodium chlorate crystallization unit is returned to the sodium chlorate electrolysis unit for recycling. The discharge end of the sodium chlorate crystallization unit 4 is connected to a sulfate removal device 8, which is used for removing sulfate radicals from the mother liquor generated by the sodium chlorate crystallization unit 4. The discharge end of the sulfate removal device 8 is connected to the brine purification unit 1. The mother liquor of the sodium chlorate crystallization equipment contains sulfate radicals, perchlorate radicals, calcium, silicon dioxide, etc. During the system circulation process, insoluble solid impurities will be formed, reducing the production efficiency of the electrolytic cell and increasing the production cost. By adding calcium chloride and potassium chloride solutions to the sulfate removal device, the mother liquor is mixed with the calcium chloride and potassium chloride solutions in the sulfate reactor of the sulfate removal device, and a reaction generates calcium sulfate and potassium perchlorate precipitates. The precipitates are separated by the sulfate clarifier of the sulfate removal device and then sent to a filter press for filtration. The clear liquid is sent to the brine purification unit for salt dissolution and can be reused. There is no discharge of chromium-containing wastewater, which can reduce the power consumption and raw salt consumption for producing sodium chlorate in the sodium chlorate electrolysis unit.

[0033] The NaCl solution reacts in the electrolytic cell to generate hypochlorite radicals, chlorate radicals and other intermediate reactants. The electrolyte solution coming out of the electrolytic cell needs to first remove sodium hypochlorite and then be sent to the crystallizer for heating and evaporation to precipitate sodium chlorate crystals. The mother liquor separated by the crystallizer is returned to the electrolytic cell for recycling, and the sodium chlorate crystals are sent for dissolution to make a sodium chlorate solution. The by-product hydrogen generated by the electrolysis system can be sent out for the preparation of hydrogen peroxide or used as fuel. The tail gas of the electrolysis system consists of hydrogen, steam, and a small amount of chlorine and oxygen. This tail gas successively enters the brine scrubbing tower and the hydrogen caustic scrubbing tower for scrubbing to remove chlorine. The sodium thiosulfate solution generated by the hydrogen caustic scrubbing can be used for salt dissolution. The mother liquor generated by the concentration of sodium chlorate crystallization contains sulfate radicals and perchlorate radicals. A sulfate removal reaction is carried out, and the separated clear liquid is used for salt dissolution and reused. There is no discharge of contaminated chromium-containing wastewater.

[0034] In the present invention, the discharge end of the sodium chlorate dissolving device 5 is connected to the chlorine dioxide generating and absorbing unit 6 through a pipeline. The sodium chlorate dissolving device 5 is used to dissolve sodium chlorate crystals. Water is added to the sodium chlorate dissolving tank (not marked in the figure) of the sodium chlorate dissolving device to dissolve the sodium chlorate crystals, and a sodium chlorate solution with qualified concentration is prepared. The sodium chlorate solution coming out from the discharge end of the sodium chlorate dissolving device is transported to the chlorine dioxide generating and absorbing unit 6 through a pipeline; a methanol solution and a sulfuric acid solution are added to the chlorine dioxide generating and absorbing unit 6, and they react with the sodium chlorate solution in the chlorine dioxide generating and absorbing unit 6 to prepare a qualified chlorine dioxide solution; methanol is used as a reducing agent, and the sodium chlorate solution is used as an oxidizing agent. Under a certain acidic environment, methanol, sodium chlorate, and sulfuric acid are mixed and reacted to produce chlorine dioxide; by-products mirabilite are generated during the reaction of sodium chlorate, methanol, and sulfuric acid in the chlorine dioxide reaction. The mirabilite can be sent to the alkali recovery workshop for use, reducing or eliminating the need to purchase mirabilite externally. The materials in the system are comprehensively utilized, reducing the production operation cost of the enterprise and facilitating the balanced and continuous production of the whole plant. The discharge end of the chlorine dioxide generating and absorbing unit 6 is connected to a chlorine dioxide tail gas treatment system 9. The chlorine dioxide tail gas treatment system 9 is used to wash and absorb chlorine dioxide. The discharge end of the chlorine dioxide tail gas treatment system 9 is connected to the brine purification unit 1. The chlorine dioxide tail gas treatment system 9 includes a tail gas washing tower (not marked in the figure) and an exhaust gas washing tower (not marked in the figure). The tail gas washing tower mainly uses ice water to wash and absorb chlorine dioxide and chlorine generated by the chlorine dioxide system. The dilute chlorine dioxide aqueous solution generated by the washing is sent to the absorption tower to continue absorbing chlorine dioxide. The tail gas coming out from the tail gas washing tower enters the exhaust gas washing tower, is washed with an alkali solution to remove the small amount of chlorine dioxide and chlorine contained therein, and then discharged. The hyposulfite solution generated by the exhaust gas washing tower is sent to the brine purification unit for salt dissolution, and there is no chlorine emission in the chlorine dioxide preparation system. Sodium hydroxide solution is added to the chlorine dioxide tail gas treatment system. The chlorine-containing tail gas discharged from the chlorine dioxide generating and absorbing unit enters the chlorine dioxide tail gas treatment system for absorption treatment. After being washed and absorbed by the chlorine dioxide tail gas treatment system, the tail gas contains no chlorine and can be directly discharged. The generated hyposulfite solution is transported to the brine purification unit for salt dissolution. There is no chlorine emission and no by-product hyposulfite solution is discharged externally, realizing the internal circulation utilization of the system.

[0035] Treatment process of the electrolytic combination reduction method chlorine dioxide preparation system of the present invention:

[0036] The raw salt is added to the brine purification unit 1 to prepare qualified refined brine; the refined brine is washed in the brine washing unit 2 and absorbs the chlorine gas generated by electrolysis; the brine coming from the brine washing unit 2 and the mother liquor coming from the sodium chlorate crystallization unit 4 enter the sodium chlorate electrolysis unit 3 together, and are electrolyzed to generate an electrolyte solution containing sodium chlorate, sodium hypochlorite, hypochlorous acid solution, by-product hydrogen gas and a small amount of chlorine gas; the hydrogen gas and chlorine gas generated by the sodium chlorate electrolysis unit 3 enter the hydrogen gas washing tower of the hydrogen gas tail gas treatment equipment 7 through the brine washing tower of the brine washing unit 2, and are treated by adding sodium hydroxide solution to the hydrogen gas washing tower of the hydrogen gas tail gas treatment equipment 7. The sodium thiosulfate solution generated by the treatment is transported to the brine purification unit for salt dissolution, and there is no external discharge of by-product sodium thiosulfate solution, realizing internal circulation utilization within the system; the electrolyte solution generated by the sodium chlorate electrolysis unit 3, after being treated to remove sodium hypochlorite, enters the sodium chlorate crystallization unit 4. The crystallizer of the sodium chlorate crystallization unit 4 is heated to separate out sodium chlorate crystals. At the same time, a part of the mother liquor separated by the crystallizer of the sodium chlorate crystallization unit 4 is returned to the sodium chlorate electrolysis unit 3 for recycling. A part of the mother liquor separated by the sodium chlorate crystallization unit 4 is sent to the sulfate reactor of the sulfate removal equipment 8 to remove sulfate radicals, and the separated clear liquid is sent to the brine purification unit 1 for salt dissolution and reuse, and there is no external discharge of chromium-containing wastewater; the sodium chlorate crystals separated by the sodium chlorate crystallization unit 4 are sent to the sodium chlorate dissolution tank of the sodium chlorate dissolution equipment 5 and dissolved in water to prepare a sodium chlorate solution with qualified concentration; methanol solution and sulfuric acid solution are added to the chlorine dioxide generation and absorption unit 6, and they react with the sodium chlorate solution in the chlorine dioxide generation and absorption unit 6 to prepare a qualified chlorine dioxide solution; the tail gas generated by the chlorine dioxide generation and absorption unit 6 enters the chlorine dioxide tail gas treatment system 9, and after being washed and absorbed by the chlorine dioxide tail gas treatment system, the tail gas does not contain chlorine gas and can be directly discharged. The generated sodium thiosulfate solution is transported to the brine purification unit for salt dissolution, and there is no chlorine gas discharge and no external discharge of by-product sodium thiosulfate solution, realizing internal circulation utilization within the system. The preparation system of the present invention does not need to purchase sodium chlorate externally, and only needs to provide electricity, raw salt, methanol, and sulfuric acid to continuously produce chlorine dioxide.

[0037] Example 1

[0038] First, add raw salt to the brine refining unit 1 to prepare qualified brine with a concentration of 300 g / l. Then add the brine to the sodium chlorate electrolysis unit 3, where electrolysis generates an electrolytic solution containing sodium chlorate, sodium hypochlorite, hypochlorous acid solution, hydrogen, and a small amount of chlorine gas. The electrolytic solution produced by the sodium chlorate electrolysis unit 3 (sodium chlorate 590 g / l, sodium hypochlorite and hypochlorous acid solution about 2.6 g / l) is subjected to sodium hypochlorite removal treatment to remove sodium hypochlorite and hypochlorous acid, and then the electrolytic solution is sent into the sodium chlorate crystallization unit. 590 g / l of sodium chlorate and 110 g / l of sodium chloride crystallize by evaporation in the crystallizer, and sodium chlorate crystals are separated out. At the same time, the mother liquor separated by the crystallizer is returned to the sodium chlorate electrolysis unit 3 for recycling. The sodium chlorate crystals separated by the sodium chlorate crystallization unit 4 are sent to the sodium chlorate dissolution tank and dissolved with water to form a sodium chlorate solution with a concentration of 650 g / l, and then pumped to a sodium chlorate storage tank (not marked in the figure). Methanol, sulfuric acid, and the sodium chlorate solution from the sodium chlorate dissolution unit 5 are used to prepare chlorine dioxide in the chlorine dioxide generation and absorption unit 6. The tail gas from the sodium chlorate electrolysis unit 3 passes through the brine scrubbing tower of the brine scrubbing unit 2 and the hydrogen tail gas treatment equipment 7 to wash and absorb chlorine gas. The by-product hydrogen after tail gas treatment can be used to prepare hydrogen peroxide or as fuel, and the sodium thiosulfate solution after tail gas alkali washing can be used to dissolve salt. The mother liquor needs to be sent to the sulfate removal equipment 8 to react and remove sulfate, and the separated clear liquid is all sent to the brine refining unit for salt dissolution. There is no discharge of chromium-containing wastewater in the whole system. The chlorine-containing tail gas generated by the chlorine dioxide generation and absorption unit 6 is washed and absorbed by the chlorine dioxide tail gas treatment system 9, and there is no chlorine gas emission. The generated sodium thiosulfate solution is used to dissolve salt, and there is no discharge of by-product sodium thiosulfate solution in the whole system. The sodium thiosulfate solution is recycled to make the whole system connected to form a closed loop system.

[0039] Comparative Example 1

[0040] Using the traditional reduction method for chlorine dioxide preparation process, in a production line with a daily output of 10 t of chlorine dioxide, the sodium chlorate consumed per ton of chlorine dioxide is 1.7 t, and the daily externally purchased amount of sodium chlorate is 17 t.

[0041] While using the electrolytic combined reduction method chlorine dioxide preparation system of the present invention, the electrolysis power consumption of sodium chlorate per ton of chlorine dioxide is 8500 kwh, 9.7 t of raw salt needs to be externally purchased daily, and there is no need to externally purchase sodium chlorate.

[0042] Example 2

[0043] First, add raw salt to the brine refining unit 1 to prepare qualified brine with a concentration of 300 g / l. Then add the brine to the sodium chlorate electrolysis unit 3, where electrolysis occurs to generate an electrolyte solution containing sodium chlorate, sodium hypochlorite, hypochlorous acid solution, hydrogen gas, and a small amount of chlorine gas. The electrolytic solution produced by the sodium chlorate electrolysis unit 3 (sodium chlorate 585 g / l, sodium hypochlorite and hypochlorous acid solution about 2.55 g / l), after undergoing sodium hypochlorite removal treatment to remove sodium hypochlorite and hypochlorous acid, the electrolyte solution is sent into the sodium chlorate crystallization unit. Sodium chlorate at 585 g / l and sodium chloride at 105 g / l in the crystallization unit evaporate and crystallize in the crystallizer to separate out sodium chlorate crystals. At the same time, the mother liquor separated by the crystallizer is returned to the sodium chlorate electrolysis unit 3 for recycling. The sodium chlorate crystals separated by the sodium chlorate crystallization unit 4 are sent to the sodium chlorate dissolution tank and dissolved in water to form a sodium chlorate solution with a concentration of 650 g / l, and then pumped to the sodium chlorate storage tank. Methanol, sulfuric acid, and the sodium chlorate solution from the sodium chlorate dissolution unit 5 are used to prepare chlorine dioxide in the chlorine dioxide generation and absorption unit 6. The tail gas from the sodium chlorate electrolysis unit 3 passes through the brine scrubbing tower 2 and the hydrogen tail gas treatment equipment 7 to wash and absorb chlorine gas. The by-product hydrogen gas after tail gas treatment can be used to prepare hydrogen peroxide or as fuel, and the sodium thiosulfate solution after tail gas alkali washing can be used to dissolve salt. The mother liquor needs to be sent to the sulfate removal equipment 8 to react and remove sulfate, and the separated clear liquid is all sent to the brine refining unit for salt dissolution. There is no discharge of chromium-containing wastewater in the entire system. The chlorine-containing tail gas generated by the chlorine dioxide generation and absorption unit 6 is washed and absorbed by the chlorine dioxide tail gas treatment unit 9, and there is no chlorine gas emission. The generated sodium thiosulfate solution is used to dissolve salt, and there is no discharge of by-product sodium thiosulfate solution in the entire system. The sodium thiosulfate solution circulates to make the entire system connected to form a closed circulation system.

[0044] Comparative Example 2

[0045] Using the traditional reduction method for chlorine dioxide preparation process, for a production line with a daily output of 25 t of chlorine dioxide, the sodium chlorate consumed per ton of chlorine dioxide is 1.7 t, and the daily externally purchased amount of sodium chlorate is 42.5 t.

[0046] However, when using the electrolytic combined reduction method chlorine dioxide preparation system of the present invention, the electrolysis power consumption of sodium chlorate per ton of chlorine dioxide is 8450 kwh, and 24.25 t of raw salt needs to be externally purchased daily, and there is no need to externally purchase sodium chlorate.

[0047] Example 3

[0048] First, add raw salt to the brine refining unit 1 to prepare qualified brine with a concentration of 300 g / l. Then add the brine to the sodium chlorate electrolysis unit 3, where electrolysis generates an electrolytic solution containing sodium chlorate, sodium hypochlorite, hypochlorous acid solution, hydrogen, and a small amount of chlorine gas. The electrolytic solution produced by the sodium chlorate electrolysis unit 3 (sodium chlorate 580 g / l, sodium hypochlorite and hypochlorous acid solution about 2.5 g / l) is treated to remove sodium hypochlorite and hypochlorous acid. After that, the electrolytic solution is sent to the sodium chlorate crystallization unit. Sodium chlorate at 580 g / l and sodium chloride at 100 g / l crystallize by evaporation in the crystallizer, and sodium chlorate crystals are separated out. Meanwhile, the mother liquor separated by the crystallizer is returned to the sodium chlorate electrolysis unit 3 for recycling. The sodium chlorate crystals separated by the sodium chlorate crystallization unit 4 are sent to the sodium chlorate dissolution tank and dissolved in water to form a sodium chlorate solution with a concentration of 650 g / l, and then pumped to the sodium chlorate storage tank. Methanol, sulfuric acid, and the sodium chlorate solution from the sodium chlorate dissolution unit 5 are used to prepare chlorine dioxide in the chlorine dioxide generation and absorption unit 6. The tail gas from the sodium chlorate electrolysis unit 3 passes through the brine scrubbing tower 2 and the hydrogen tail gas treatment equipment 7 to wash and absorb chlorine gas. The by-product hydrogen after tail gas treatment can be used to prepare hydrogen peroxide or as fuel, and the sodium thiosulfate solution after tail gas alkali washing can be used to dissolve salt. The mother liquor needs to be sent to the sulfate removal equipment 8 to react and remove sulfate, and the separated clear liquid is all sent to the refined brine system for salt dissolution. There is no discharge of chromium-containing wastewater in the whole system. The chlorine-containing tail gas generated by the chlorine dioxide generation and absorption unit 6 is washed and absorbed by the chlorine dioxide tail gas treatment unit 9, and there is no chlorine gas emission. The generated sodium thiosulfate solution is used to dissolve salt, and there is no discharge of by-product sodium thiosulfate solution in the whole system. The sodium thiosulfate solution is recycled, making the whole system connected to form a closed loop system.

[0049] Comparative Example 3

[0050] Using the traditional reduction method for chlorine dioxide preparation process, for a production line with a daily output of 50 t of chlorine dioxide, the sodium chlorate consumption per ton of chlorine dioxide is 1.7 t, and the daily amount of externally purchased sodium chlorate is 85 t.

[0051] While using the electrolytic combined reduction method for chlorine dioxide preparation system of the present invention, the electrolytic power consumption of sodium chlorate per ton of chlorine dioxide is 8400 kwh, 48.5 t of raw salt needs to be externally purchased daily, and there is no need to externally purchase sodium chlorate.

[0052] By comparing the examples with the comparative examples, it can be seen that when using the chlorine dioxide preparation system by the electrolytic combination reduction method of the present invention, compared with the traditional reduction method for chlorine dioxide preparation process, at the same production capacity, the traditional reduction method for chlorine dioxide preparation process has a large consumption of sodium chlorate and strong external dependence, and a large amount of dangerous chemicals such as sodium chlorate need to be purchased externally. There are relatively large potential safety hazards during the transportation, storage, operation and use of sodium chlorate; there is no need to purchase chlorine gas or hydrochloric acid externally as production raw materials, avoiding the safety requirements and safety control in the production, storage and emergency disposal of chlorine gas and hydrochloric acid, and realizing higher operation safety guarantee for the system; while the raw material salt required by this invention patent is very safe during the transportation, storage and use processes.

[0053] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A system for preparing chlorine dioxide by electrolytic combined reduction method, characterized in that: The system comprises a brine refining unit (1), a brine washing unit (2), a sodium chlorate electrolysis unit (3), a sodium chlorate crystallization unit (4), a sodium chlorate dissolving device (5) and a chlorine dioxide generation and absorption unit (6). The brine refining unit (1) is connected to the brine washing unit (2), the brine washing unit (2) is connected to the sodium chlorate electrolysis unit (3), the sodium chlorate electrolysis unit (3) is respectively connected to the brine washing unit (2) and the sodium chlorate crystallization unit (4), the sodium chlorate crystallization unit (4) is respectively connected to the sodium chlorate electrolysis unit (3) and the sodium chlorate dissolving device (5), and the sodium chlorate dissolving device (5) is connected to the chlorine dioxide generation and absorption unit (6).

2. A chlorine dioxide production system by electrolytic combined reduction method according to claim 1, characterized in that: The discharge end of the brine refining unit (1) is connected to the brine washing unit (2) via a pipeline, and the brine refining unit (1) is used to convert raw salt into refined brine.

3. The system for preparing chlorine dioxide by electrolytic combined reduction method according to claim 1, characterized in that: The discharge end of the brine washing unit (2) is connected to the sodium chlorate electrolysis unit (3) via a pipeline, and the brine washing unit (2) is used to wash the refined brine and absorb the generated chlorine.

4. A chlorine dioxide production system by electrolytic combined reduction method according to claim 3, characterized in that: The discharge end of the brine washing unit (2) is connected to a hydrogen tail gas treatment device (7), and the hydrogen tail gas treatment device (7) is used to dechlorinate hydrogen. The discharge end of the hydrogen tail gas treatment device (7) is connected to the brine refining unit (1).

5. The system for preparing chlorine dioxide by electrolytic combined reduction method according to claim 1, characterized in that: The discharge end of the sodium chlorate electrolysis unit (3) is connected to the sodium chlorate crystallization unit (4) via a pipeline, and the sodium chlorate electrolysis unit (3) is used to electrolyze brine.

6. The system for preparing chlorine dioxide by electrolytic combined reduction method according to claim 1, characterized in that: The discharge end of the sodium chlorate crystallization unit (4) is connected to the sodium chlorate dissolving device (5) via a pipeline, and the sodium chlorate crystallization unit (4) is used to crystallize sodium chlorate.

7. A chlorine dioxide production system by electrolytic combined reduction method according to claim 6, characterized in that: The discharge end of the sodium chlorate crystallization unit (4) is connected to a sulfate removal device (8), and the sulfate removal device (8) is used to remove sulfate from the mother liquor generated by the sodium chlorate crystallization unit (4). The discharge end of the sulfate removal device (8) is connected to the brine refining unit (1).

8. The system for preparing chlorine dioxide by electrolytic combined reduction method according to claim 1, characterized in that: The discharge end of the sodium chlorate dissolving device (5) is connected to the chlorine dioxide generation and absorption unit (6) through a pipeline, and the sodium chlorate dissolving device (5) is used to dissolve sodium chlorate crystals.

9. A chlorine dioxide production system by electrolytic combined reduction method according to claim 8, characterized in that: The discharge end of the chlorine dioxide generation and absorption unit (6) is connected to a chlorine dioxide tail gas treatment system (9), and the chlorine dioxide tail gas treatment system (9) is used to wash and absorb chlorine dioxide. The discharge end of the chlorine dioxide tail gas treatment system (9) is connected to a brine refining unit (1).

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