CN112210788B - Method and equipment for decomposing chlorate in light salt water for producing chlor-alkali - Google Patents
Method and equipment for decomposing chlorate in light salt water for producing chlor-alkali Download PDFInfo
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- CN112210788B CN112210788B CN202011100956.0A CN202011100956A CN112210788B CN 112210788 B CN112210788 B CN 112210788B CN 202011100956 A CN202011100956 A CN 202011100956A CN 112210788 B CN112210788 B CN 112210788B
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
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- C25B1/24—Halogens or compounds thereof
- C25B1/26—Chlorine; Compounds thereof
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
Abstract
The invention provides a method and equipment for decomposing chlorate in dilute brine for chlor-alkali production, which belong to the technical field of brine electrolysis production in chlor-alkali industry, comply with the oxidation-reduction theory of chlorate generation and decomposition, overcome the defect that the gas-liquid phase of the conventional chlorate decomposition equipment cannot be completely decomposed, creatively enable materials to flow in the equipment in an inverted U-shaped mode, increase the purification and decomposition of gas-phase miscellaneous materials and complete the liquid heat recovery, sequentially communicate the working steps of the equipment, integrate preheating, heating, decomposition, gas purification and gas-liquid separation into a whole, and optimize the structure in the equipment; several stages of chlorate decomposition are organically combined together, chlorate in the fresh brine is quickly and completely decomposed once, and decomposition products are completely recycled, so that environmental protection treatment zero emission is realized, and the chlorate decomposition cost is greatly reduced. The electrolytic bath does not need to add acid any more, prolongs the service life of the ionic membrane, reduces the power consumption of caustic soda and relieves the worries of the improvement of the electrolytic technology.
Description
Technical Field
The chlorate decomposition method and the chlorate decomposition equipment are applied to the field of brine electrolysis production technology (containing NaOH and KOH production) in the chlor-alkali industry, and particularly relate to the chlorate decomposition method and the chlorate decomposition equipment, which have the function of decomposing chlorate generated by side reaction in the ionic membrane caustic soda electrolysis process to convert the chlorate into high-quality chlorine, sodium chloride and water.
Background
In the existing production process of caustic soda by an ion-exchange membrane method in chlor-alkali industry, a plurality of different chlorides and oxychlorides can be generated by side reaction of an anode chamber of an electrolytic cell, wherein NaClO3The chlorine oxide is a final and stable chlorine oxide, can exist in circulating brine for a long time, and can influence the concentration of saturated sodium chloride of refined brine when the enrichment amount is too high. A small amount of chlorate ions in the brine in the anode chamber of the electrolytic cell can penetrate through the ion membrane and enter the cathode chamber to circulate caustic soda to influence the quality of liquid caustic soda, and the chlorate process control index in the quality of 32 percent finished caustic soda is NaClO3Less than or equal to 10ppm, and the chlorate in the liquid caustic soda can strongly corrode the concentration equipment when producing solid caustic soda. In the process of refining brine, the concentration of hydrochloric acid is sometimes high locally, so that the oxidation-reduction potential of chlorate in the brine is increased, and the chlorate has very strong oxidizability, so that an anticorrosive layer can be corroded to damage pipelines and equipment exposed out of metal materials, and high-value chelate resin can be pulverized and a nanofiltration membrane can be inactivated. Therefore, there is a need to design a device capable of decomposing chlorate efficiently, which can complete chlorate decomposition at one time, rapidly eliminate chlorate in a brine system, and enable the whole refined brine system to be ClO3 -Less than or equal to 2.5g/L, and optimizes the operation conditions of the whole brine and electrolysis. In the existing chlorate decomposition equipment, a part of impurity gas ClO exists in chlorine gas generated after decomposition2Remains in the liquid phaseThe equivalent chlorine oxide is necessarily purified and reduced into chlorine with the quality equivalent to that of chlorine generated by the electric cell, and only NaCl and Cl can be contained in the final product of chlorate decomposition2、H2O。
Under normal operating conditions, the existing equipment is used for decomposing chlorate in weak brine, and the chlorate decomposition has two directions, and the chemical equation of the chlorate decomposition is as follows:
NaClO3+2HCl→NaCl+ClO2+1/2Cl2+H2O (a)
NaClO3+6HCl→NaCl+3Cl2+3H2O (b)
during the whole process of heating the strong acid weak brine and decomposing chlorate, the temperature and HCl content of the strong acid weak brine and ClO in the weak brine3 -The concentration of (a) and (b) are changed, the above two formulas are reacted, and the decomposed chlorine gas contains a certain amount of ClO2ClO in chlorine under different operating conditions2The proportions are different, so that the ClO is finished at one time3 -Decomposed to pure Cl2The method cannot be completed, the chlorine purity which can be recycled cannot be achieved, and the decomposition is not complete. And ClO2Is also an unstable gas, has a high concentration of aggregates and risks to be rapidly decomposed by impact, resulting in the possibility of explosion. In the existing ClO3 -Air is added into the decomposition device to dilute the decomposed gas, the low-concentration chlorine-containing gas is removed and absorbed for environmental protection treatment, but the discharged qualified gas still contains chlorine below 1mg/L, and zero emission of toxic and harmful gas cannot be achieved in the environmental protection treatment.
The chlorate decomposer is a tank-type container, steam is directly introduced to heat (or a heating device is independently arranged) the temperature of the acidic weak brine is increased to over 90 ℃, partial chlorate is decomposed after reaction time is about 2 hours, and the partial chlorate overflows to a collecting tank for dechlorination and recycling. NaClO as control index in reaction completion liquid of chlorate discharging reaction tank33-5g/L, HCl is less than or equal to 20g/L, chlorine generated by the reaction is diluted by adding a proper amount of air (ClO generated is prevented)2Decomposition explosion) as waste gasAnd discharging to the downstream process for treatment.
The chlorate decomposition method used at present has the following defects:
1. the equipment for decomposing chlorate needs complex matched technology;
2. the chlorate decomposition method needs more than 2 hours for a long time, the decomposition rate is reduced by 50-65%, the design scale of the decomposition device is only the decomposition amount during normal production, but the byproduct amount of chlorate rises along with the reduction of current efficiency, the residual chlorate accumulates over-standard operation in a brine system for a long time, and the operation condition is deteriorated;
3. the excessive hydrochloric acid in the decomposed light brine needs caustic soda for neutralization, and compared with the shutdown of a chlorate decomposition device, the consumption of caustic soda for dechlorination is much higher;
4. high content of ClO in the decomposed chlorine and miscellaneous gases2The purity of recycling can not be achieved, and only air can be added for dilution until Cl is contained2Less than or equal to 10 percent (V), which causes resource waste and increases waste chlorine treatment facilities and operation cost.
There is also an LSZ reducing agent elimination chlorate method, which is based on the above chlorate decomposition apparatus, and uses strong reducing agent prepared by supplier to replace part of hydrochloric acid to decompose chlorate, aiming at selling chlorate decomposition medicine for profit, and has no relation with technical innovation and improvement of chlorate decomposition.
Disclosure of Invention
The technical task of the invention is to achieve the purpose of one-time complete decomposition of chlorate in weak brine in an electrolytic cell, specially design a set of chlorate decomposition method and equipment, follow the redox law in an electrochemical equation for chlorate decomposition, and (the invention patent can be checked for a chlorate decomposition device and method generated by an anode chamber side reaction of the electrolytic cell in chlor-alkali production and a related acid adding process, and the invention has the application number of 202010186563.X, the theoretical basic part in the invention content) maximally saves materials (high-purity hydrochloric acid, caustic soda, process air) and heat energy (steam, hot water and the like) used for decomposition, and NaCl is recycled to achieve the recycling use requirement, and chlorine is merged into a chlorine main pipe to achieve environment-friendly zero emission treatment.
The technical scheme adopted by the invention for solving the technical problems is as follows:
1. the invention provides a method for decomposing chlorate in dilute brine for producing chlor-alkali, which comprises the following steps:
in a preheating zone, utilizing the hot ClO of step 32Purifying the reduction product to preheat the mixed solution;
2, allowing the mixed solution obtained in the step 1 after the primary reaction to enter a decomposition reaction chamber for continuing decomposition reaction, and allowing gas to escape from the mixed solution;
Optionally, the temperature of the mixed solution is controlled to be 87-105 ℃ after the temperature of the mixed solution is increased.
Optionally, a pressure measuring instrument and a pressure valve are arranged in the decomposition reaction chamber, and the pressure of the pressure measuring instrument is controlled to be-200-400 mm water column.
Optionally, a liquid level measuring meter is arranged on the gas-liquid separation zone, and a liquid level signal measured by a liquid level transmitter is transmitted to the hydrochloric acid regulating valve to control the total amount of the added hydrochloric acid.
Optionally, a control valve is arranged at the liquid outlet of the gas-liquid separation zone, a control signal is from a pH measuring instrument on the dechlorination dilute brine manifold, and the pH value is controlled to be between 1 and 2.5.
Optionally, the method is based on a chlorate decomposition plant comprising at least: a preheating zone, a heating chamber, a decomposition reaction chamber and ClO which are communicated in sequence2A purification reduction area and a gas-liquid separation area.
The preheating zone is provided with a mixed liquid inlet, the mixed liquid is prepared by mixing light salt water from an electrolytic anolyte circulating tank and hydrochloric acid according to a certain proportion, and hot ClO is utilized2Purifying the reduction product to preheat the mixed solution;
the heating chamber heats the preheated mixed liquid flowing through the heating chamber;
the decomposition reaction chamber provides a decomposition reaction place for the heated and heated mixed liquid, and the decomposed Cl2Contains a certain amount of ClO2Leaving the liquid phase with the decomposition liquid which is not completely reacted;
the ClO2The purification reduction zone is provided with a decomposition liquid distribution system in which a part of the decomposition liquid and Cl are present2、ClO2The mixed gas is contacted, HCl converts ClO in gas phase2Reduction to Cl2And H2O, the other part is continuously heated and decomposed, and partial unreacted oxychloride, ClO, in the decomposition liquid is removed2The purified reduction product returns to the preheating zone, and the mixed solution in the preheating zone absorbs heat and cools;
the gas-liquid separation zone is used for cooling the cooled ClO2The purified reduction product is separated into decomposition completion liquid and chlorine gas.
2. The invention also provides a chlorate decomposing equipment in weak brine for producing chlor-alkali, which at least comprises: a preheating zone, a heating chamber, a decomposition reaction chamber and ClO which are communicated in sequence2A purification reduction area and a gas-liquid separation area,
the preheating zone is provided with a mixed liquid inlet, the mixed liquid is prepared by mixing light salt water from an electrolytic anolyte circulating tank and hydrochloric acid according to a certain proportion, and hot ClO is utilized2Purifying the reduction product to preheat the mixed solution;
the heating chamber heats the preheated mixed liquid flowing through the heating chamber;
the decomposition reaction chamber is heatedThe heated mixed solution provides a place for the decomposition reaction of chlorate to generate Cl2Escape from the liquid phase, Cl2Contains a certain amount of ClO2In the liquid phase, there remains ClO remaining in the liquid phase without completion of the reaction3 -And ClO2 -An oxychloride;
the ClO2A decomposition liquid distribution system is arranged in the purification reduction area, and HCl and Cl in a part of decomposition liquid in the decomposition liquid2、ClO2Contacting the mixed gas to remove gas-phase ClO2Reduction to Cl2And H2O, the other part is continuously heated and decomposed to remove residual ClO in the decomposition liquid3 -And ClO2 -Oxychloride, ClO2The purified reduction product enters a preheating zone, and the mixed solution in the preheating zone absorbs heat and is cooled;
the gas-liquid separation zone is used for cooling the cooled ClO2The purified reduction product is separated into decomposition completion liquid and chlorine gas.
Optionally, the ClO2The purifying and reducing area is arranged in the heating chamber and is isolated from the heating chamber, and the dividing wall heats gas-phase and liquid-phase materials which are not completely decomposed in the central cylinder. The heating medium of the heating chamber heats the preheated mixed liquid to reach the temperature condition required by the decomposition reaction, heats the liquid partition wall which is not completely reacted in the central cylinder, and completely unreacted ClO3 -、ClO2 -、ClO-And ClO2And (4) accelerating the decomposition.
Optionally, the preheating zone, heating chamber, decomposition reaction chamber, ClO2The purifying and reducing zone and the gas-liquid separating zone are arranged in the same shell, the gas-liquid separating zone, the preheating zone, the heating chamber and the decomposition reaction chamber are sequentially arranged in the shell, the gas-liquid separating zone, the preheating zone, the heating chamber and the decomposition reaction chamber are separated by tube plates arranged in the shell, and ClO2The inlet end of the purification and reduction zone is communicated with the decomposition reaction chamber, and the outlet end is communicated with the preheating zone.
Optionally, the heating chamber uses low-pressure steam or hot air as a heating medium to heat the preheated mixed liquid to raise the temperature.
OptionallyEarth, the ClO2The purification reduction area comprises a central cylinder arranged in the heating chamber, a liquid distribution plate is covered on the central cylinder, a gas inlet pipe is arranged at the center of the central cylinder, a decomposed liquid inlet is tangentially arranged on the outer wall of the central cylinder higher than the tube plate, a part of the decomposed liquid is contacted with gas phase through the liquid distribution plate, and ClO in chlorine is removed2Reduction to Cl2And H2And O, continuously heating and decomposing the other part of the decomposition liquid under tangential rotation to further decompose and react part of the decomposition liquid containing the chlorine oxide which is not reacted in the central cylinder.
Optionally, the gas conduit inlet is closed to decomposition liquid, ClO in gas phase2The gas flow direction at the outlet of the gas conduit forms a certain included angle with the falling direction of the liquid in the liquid distribution plate.
Optionally, the gas outlet of the gas conduit has a horizontal gas flow direction, and the liquid in the liquid distribution plate falls along a vertical direction.
Optionally, the top surface of the central cylinder is higher than the upper surface of the upper tube plate, and the decomposition liquid inlet is tangentially arranged below the liquid distribution plate and at the part of the central cylinder higher than the upper tube plate.
Optionally, the preheating zone is of a shell and tube configuration and the tube-side medium is hot ClO2Purifying the reduction product, wherein the shell pass medium is a mixed liquid, and a baffling baffle is arranged in the shell pass to improve the heat exchange effect.
Optionally, the tube pass is a falling film tube array, a guide vane is arranged at the inlet, the guide vane is in threaded connection with the tube pass inlet, the hollow side wall of the guide vane is tangentially provided with a purified reducing liquid inlet, and the purified reducing liquid tangentially rotates to form a film and enters the tube pass.
Optionally, the liquid phase region of the decomposition reaction chamber is provided with a temperature measuring instrument, and a temperature signal of the heated mixed liquid measured by the temperature measuring instrument is transmitted to the steam regulating valve to control the adding amount of the steam. The temperature of the temperature measuring instrument is controlled between 87 ℃ and 105 ℃.
Optionally, a pressure measuring instrument and a pressure valve are arranged in the decomposition reaction chamber, and the pressure of the pressure measuring instrument is controlled to be-200-400 mm water column.
Optionally, a liquid level measuring meter is arranged on the gas-liquid separation zone, and a liquid level signal measured by a liquid level transmitter is transmitted to the hydrochloric acid regulating valve to control the total amount of the added hydrochloric acid.
Optionally, a control valve is arranged at the liquid outlet of the gas-liquid separation zone, a control signal is from a pH measuring instrument on the dechlorination dilute brine manifold, and the pH value is controlled to be between 1 and 2.5.
Compared with the prior art, the method and the equipment for decomposing the chlorate in the light salt water for producing the chlor-alkali have the beneficial effects that:
1. the invention realizes the rapid decomposition of chlorate in the light brine, and the volume of a decomposition device and the equipment investment are both greatly reduced within 10min from more than 2h in the past.
2. The decomposition efficiency is high, the decomposition rate of the chlorate can reach more than 99.5 percent at one time, the decomposition rate is improved by 50 to 65 percent compared with the decomposition rate of the existing device, the light saline water participating in the chlorate decomposition is greatly reduced, the residual amount of the byproduct chlorate in the whole electrolytic saline water system is lower than 2.5g/L, the newly generated chlorate in the electric tank can be completely decomposed, the accumulated chlorate is quickly consumed, and the operation quality of electrolysis and saline water is optimized.
3. The chlorate is decomposed completely, and ClO is specially arranged in the equipment2Decontamination of reduction zone to reduce associated ClO2Gas phase of wet Cl2The purity is high, reaches more than 98.5 percent (V), exceeds the purity of chlorine at the outlet of the electric cell, the air dilution process of the prior device is cancelled, harmful waste gas becomes high-quality resource, and NaClO in the liquid phase3The disappearance is converted into NaCl for repeated use, so that the complete resource recycling of harmful impurities in the light brine is realized, and the zero discharge is controlled in an environment-friendly way.
4. Energy is saved, the preheating zone almost completely recovers heat input by heating chlorate reaction, the gas-liquid phase outlet temperature is lower than 85 ℃, and the energy is saved by more than 70 percent compared with the existing device for discharging liquid at 95 ℃.
5. The strong acid weak brine of the chlorate decomposition equipment is used for replacing high-purity hydrochloric acid, the simplest acid adding process is adopted, the requirement of high excess acid amount during chlorate decomposition in the effluent weak brine is met, the accurate requirement of acid amount for dechlorination and electrolysis is guaranteed, the acidity index of the dechlorinated weak brine directly meets the process requirement of pH value of 1-2.5, the total acid amount is the lowest, and the caustic soda amount used for neutralization during recycling of the dechlorinated weak brine is the lowest.
Drawings
FIG. 1 is a view showing the structure of a chlorate decomposing tank of the prior art;
FIG. 2 is a schematic structural diagram of a chloride decomposition apparatus for producing chlor-alkali of the present invention;
FIG. 3 is a gas-liquid inlet ClO2A partial enlargement of the purge reduction zone.
The reference numerals in the figures denote:
1. preheating zone, 2 heating chamber, 3 decomposition reaction chamber, 4 ClO2The purification and reduction area is provided with a purification and reduction area,
5. a gas-liquid separation zone, 6, a baffle plate, 71, an upper tube plate, 72, a middle tube plate, 73, a lower tube plate,
8. liquid distributing plate 81, small hole 9, decomposition liquid inlet 10, gas guide pipe,
11. a purified reducing liquid inlet, 12, and a guide vane.
Detailed Description
The method and the equipment for decomposing chlorate in dilute brine for producing chlor-alkali according to the present invention will be described in detail below with reference to the attached figures 2-3.
Example one
The invention provides a chlorate decomposing equipment in dilute brine for chlor-alkali production, which comprises a shell, wherein the shell is closed by barrel-column-shaped upper and lower oval end sockets, the middle cone is excessive, a gas-liquid separation zone 5, a preheating zone 1, a heating chamber 2 and a decomposition reaction chamber 3 which are communicated with each other are sequentially arranged in the shell from bottom to top, the gas-liquid separation zone 5, the preheating zone 1, the heating chamber 2 and the decomposition reaction chamber 3 are separated by a lower tube plate 73, a middle tube plate 72 and an upper tube plate 71 which are arranged in the shell, and ClO is2A purification reduction zone 4 is arranged in the heating chamber 2 and is isolated from the heating chamber 2, ClO2The upper part of the purification reduction zone 4 is communicated with the decomposition reaction chamber 3, and the lower part is communicated with the preheating zone 1.
The structure and the function of each part of the equipment are as follows:
the preheating zone 1 adopts a falling film type tube array heat exchanger, preheating tubes are uniformly distributed between a lower tube plate 73 and a middle tube plate 72, and falling film type tubes are arrangedThe shell side of the heat exchanger is provided with a mixed liquid inlet, and ClO is introduced into the tube side2Purifying the reduction product, arranging a baffle 6 in the shell pass to improve the heat exchange effect, wherein the baffle 6 at the uppermost part is an annular baffle. The mixed solution is prepared by mixing weak brine from an electrolytic anolyte circulation tank and hydrochloric acid according to a certain proportion to prepare strong acid weak brine, and when the low-temperature mixed solution passes through a preheating zone 1, the ClO is decomposed in an absorption falling film tube2Purifying the heat of the reduction product, raising its temperature, preheating, and carrying saturated wet Cl2High temperature ClO of2The temperature of the purified reduction product is gradually reduced and is cooled to below 85 ℃, most heat is recovered, and heating steam is saved.
The chlorate decomposition area is composed of a heating chamber 2 and a decomposition reaction chamber 3, on one hand, the preheated mixed liquid flowing through the heating chamber 2 is heated by the heating medium in the heating chamber to reach the temperature condition required by the decomposition reaction, and simultaneously, the incompletely reacted decomposition liquid in the central cylinder is heated by the heating medium through the central cylinder wall to accelerate the decomposition of the unreacted oxychloride; the decomposition reaction chamber 3 provides a place for decomposition reaction for the heated and heated mixed liquid.
Heating tubes are arranged in the heating chamber 2 and are uniformly distributed between the upper tube plate 71 and the middle tube plate 72, the preheated mixed solution flows upwards from the tube pass of the heating chamber 2, low-pressure steam is used as a heating medium, the low-pressure steam is introduced into the shell pass of the heating chamber 2, the temperature of the preheated mixed solution is increased to 87-105 ℃, the mixed solution heated to 87-105 ℃ enters the decomposition reaction chamber 3, chlorate in the mixed solution can be decomposed within 3-5 min generally, and gas-phase Cl obtained after decomposition can be decomposed within 3-5 min2Mixed with a certain amount of ClO2The liquid phase is left with the decomposition liquid which is not completely reacted.
The chlorate contained in the mixed solution can be decomposed at a temperature of more than 85 ℃, the temperature of the mixed solution is controlled between 87 ℃ and 105 ℃, the reaction rate is improved, if the temperature is lower than 85 ℃, the reaction rate is low, and if the temperature is higher than 105 ℃, moisture is easy to evaporate, so that NaCl in the decomposed solution is crystallized, separated out and attached to the inner wall of equipment, the heat transfer effect is influenced, and the equipment is corroded.
In this embodiment, the heating medium in the heating chamber 2 is steam, and the preheated mixed liquid is heated indirectly by the steam, but those skilled in the art may also heat the preheated mixed liquid by heating air with an electric heating pipe, or directly heat the mixed liquid with an electric heating pipe.
ClO2The purifying and reducing zone 4 comprises a thicker central cylinder arranged in the center of the heating chamber 2, the top of the central cylinder extends out of the end face of the heating zone, the part of the central cylinder extending out of the end face of the heating zone is tangentially provided with a decomposed liquid inlet 9, the bottom of the central cylinder is welded with a lower tube plate 73 into a whole, and the central cylinder is covered with a liquid distribution plate 8 and is provided with a gas inlet pipe 10 in the center. Containing ClO2Is introduced from the top of the gas conduit 10 and is discharged to the ClO from the outlet of the side wall of the gas conduit 102The purifying and reducing area 4, the gas flow direction of the outlet of the gas conduit 10 and the falling direction of the showered decomposition liquid form a certain included angle. A small part of the decomposition liquid is dripped by the liquid distribution plate 8, and the strong acidic liquid and the ClO in the gas phase2Contact, scrubbing, ClO in gas phase2The following chemical reactions take place,
2ClO2+2HCl→2HClO2+Cl2(g)↑
HClO2+2HCl→HClO+Cl2(g)↑+H2O
HClO+HCl→Cl2(g)↑+H2O
through thorough washing contact, ClO2Will gradually dissolve in high temperature strong acid decomposition liquid and be reduced into Cl by HCl in liquid phase2And H2And O, most of the decomposition liquid tangentially enters the spiral flow along the decomposition liquid inlet 9 to continuously heat and raise the temperature, and meanwhile, the temperature of the material in the whole central cylinder is raised, so that the oxychloride in the decomposition liquid which is not completely reacted is decomposed in an accelerated manner, under the condition that enough HCl remains in the strong acid decomposition liquid, the oxychloride in the decomposition liquid is almost completely decomposed, the gas purity is equivalent to that of chlorine at the outlet of the electrolytic cell, and the aim of recycling harmful substances is fulfilled.
The liquid tangential inlet and the liquid distribution plate 8 are called as a decomposition liquid distribution system, the decomposition liquid of 2/3 continuously heats and reacts by swirling along the cylinder wall from the liquid tangential inlet, and the rest 1/3 is sprayed by the liquid distribution plate 8. This ratio is used because of the ratioConditions hereinafter referred to in the literature, ClO contained in chlorine gas2The decomposition with HCl is complete at this ratio, which is about 2/3 in the liquid phase, and this ratio varies slightly depending on the load.
The upper plane of the liquid distribution plate 8 is horizontal to the upper opening of the central cylinder, and the liquid distribution plate 8 is uniformly distributed with small holes 81. ClO at the level of the upper nozzle of the gas conduit 10, which is not accessible in the liquid phase2Can not be gathered, the lower pipe outlet is sealed after the liquid distribution plate 8 is closed, and the side window is opened, so that the gas flows in the horizontal direction and contacts with the leached strong acid weak brine to reduce the ClO in the chlorine2。
The gas-liquid separation zone 5 is used for cooling the cooled ClO2The purified reduction product is separated into decomposition completion liquid and chlorine gas. The preheating tube row tube side inlet is provided with a guide flow element 12, the guide flow element 12 is in threaded connection with the preheating tube row, the hollow side wall of the guide flow element 12 is cut upwards to form a purified reducing liquid inlet 11, chlorine enters the preheating tube row from the hollow part of the guide flow element 12, decomposition liquid containing a trace of unreacted oxychloride tangentially rotates to enter the preheating tube row and is in film contact with the chlorine to continuously react at a high-temperature section, and heat is gradually released. The gas-liquid separation zone 5 consists of an upper chlorine gas exhaust port and a lower decomposition completion liquid outlet pipe, and the cooled ClO2The purified reduction product T is less than or equal to 85 ℃ and is concentrated in a gas-liquid separation zone 5, a trace amount of unreacted oxychloride continuously reacts, wet chlorine enters a chlorine header pipe from an upper exhaust port, the decomposition completion liquid is discharged from a lower discharge port, and unreacted excessive hydrochloric acid is used as a substitute for dechlorinated light salt brine acidification and is removed from an anolyte circulating tank and NaOH in light salt brine discharged from an electrobath.
In summary, the design concept of this embodiment is to make the motion trajectory of the material flow in an inverted U-shape by optimizing the structure in the equipment, so that several stages of the chlorate decomposition can be organically combined together.
The low-temperature mixed liquid to be decomposed enters a shell layer from the bottom of a preheating zone 1 of chlorate decomposing equipment for preheating, rises to a tube pass of a steam heating chamber 2, is heated by shell layer steam, enters a decomposition reaction chamber 3 from a tube pass, and enters ClO from an inlet of an upper gas conduit 102The reduction zone 4 is purged. Part of the acidic light salt water rotates tangentially to form a film, adheres to the inner wall, falls, is heated and decomposed, and further promotes ClO2Purifying and reducing the gas-liquid temperature of the zone 4, and purifying and reducing Cl at high temperature by spraying the other part of the liquid through a liquid distributor2Middle ClO2The gas collected at the bottom enters the tube pass of the preheating zone 1 to be continuously purified and subjected to heat absorption and temperature reduction, the gas flows into the gas-liquid separation zone 5, the purified wet chlorine enters the chlorine main pipe from the upper exhaust pipe, and the strongly acidic decomposition finished solution HCl is discharged from the bottom pipe orifice at the concentration of more than or equal to 33 g/L.
In order to facilitate the control of the reaction conditions, the following design is carried out:
the liquid phase area in the decomposition reaction chamber is provided with a temperature measuring instrument, and a temperature signal of the mixed solution after the temperature is raised, which is measured by the temperature measuring instrument, is transmitted to a steam regulating valve to control the adding amount of steam, and the temperature is controlled between 87 ℃ and 105 ℃.
A pressure measuring instrument and a pressure valve are arranged in the decomposition reaction chamber 3, and the pressure of the pressure measuring instrument is controlled to be-200 mm-400 mm water column.
A liquid level measuring meter is arranged on the gas-liquid separation area 5, and a liquid level signal measured by a liquid level transmitter is transmitted to the hydrochloric acid regulating valve to control the total adding amount of the hydrochloric acid.
A control valve is arranged at a liquid outlet of the gas-liquid separation zone 5, a control signal is from a pH measuring instrument on a dechlorination dilute brine main pipe, and the pH value is controlled between 1 and 2.5.
Example two
The equipment for decomposing chlorate in weak brine for producing chlor-alkali comprises the following steps of:
in a preheating zone, utilizing the hot ClO of step 32Purifying the reduction product to preheat the mixed solution;
2, allowing the mixed solution obtained in the step 1 after the primary reaction to enter a decomposition reaction chamber for continuing decomposition reaction, and allowing gas to escape from the mixed solution;
The gas-liquid separation zone 5 is provided with a liquid level measuring meter, and a liquid level signal measured by a liquid level transmitter is transmitted to the hydrochloric acid regulating valve to control the total adding amount of the hydrochloric acid.
A control valve is arranged at a liquid outlet of the gas-liquid separation zone 5, a control signal is from a pH measuring instrument on a dechlorination dilute brine header pipe, and the pH value is controlled to be between 1 and 2.5.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. A method for decomposing chlorate in dilute brine for producing chlor-alkali is characterized by comprising the following steps:
step 1, preheating a mixed solution of dilute brine from an electrolytic anolyte circulating tank and hydrochloric acid with a certain proportion in a preheating zone (1), then heating the mixed solution in a heating chamber (2), and carrying out primary decomposition reaction under the heating condition;
in the preheating zone (1), ClO heated in step 3 is utilized2Purifying the reduction product to preheat the mixed solution;
2, allowing the mixed solution obtained in the step 1 after the primary reaction to enter a decomposition reaction chamber (3) for continuing decomposition reaction, and allowing gas to escape from the mixed solution;
step 3, Cl escaping from the decomposition reaction chamber (3)2、ClO2、H2The mixed gas and the mixed liquid enter ClO2The purification reduction area (4) is continuously heated to accelerate the reaction, and HCl in the liquid phase makes impurity gas ClO2Further reduced to Cl2And water, and continuously reducing the oxychloride in the liquid phase;
step 4, ClO2The purified reduction product enters a preheating zone (1), the mixed liquid in the step (1) absorbs heat, and the ClO is obtained after the temperature is reduced2Purification of the reduction product, ClO2The purified reduction product realizes gas-liquid separation in a gas-liquid separation zone (5), wet chlorine is separated from the liquid phase and is merged into a chlorine header pipe, and the decomposed solution is discharged from a lower discharge outlet.
2. The method as claimed in claim 1, wherein the temperature T of the mixed solution after the temperature rise is determined by the temperature T of the mixed solution1Controlling the temperature of decomposition completion liquid at 87-105 deg.C2Less than or equal to 85 ℃, and T is carried out when the adding amount of hydrochloric acid of the solution to be decomposed is fixed1、T2The decomposition rate and the decomposition amount are determined by cross-referencing.
3. The method for decomposing chlorate in dilute brine for chlor-alkali production as claimed in claim 1 or 2, wherein said decomposition reaction chamber (3) is equipped with pressure gauge and pressure valve, and the pressure of said pressure gauge is controlled within-200 to 400mm water column.
4. The method for decomposing chlorate in dilute brine for chlor-alkali production as claimed in claim 1 or 2, wherein said gas-liquid separation zone (5) is provided with a level gauge, and wherein a level signal from said level gauge is transmitted to said hydrochloric acid regulating valve to control the total amount of hydrochloric acid added.
5. The process for the chlorate decomposition in weak brine for chlor-alkali production according to claim 1 or 2 characterized in that said gas-liquid separation zone (5) is equipped with a control valve at the outlet of the liquid, the control signal coming from the pH meter of the de-dechlorinated weak brine main and the pH value being controlled between 1 and 2.5.
6. An apparatus for decomposing chlorate in dilute brine for chlor-alkali production, characterized in that the apparatus structure at least comprises: a preheating zone (1), a heating chamber (2), a decomposition reaction chamber (3), ClO which are communicated in sequence2A purification reduction zone (4), a gas-liquid separation zone (5),
the preheating zone (1) is provided with a mixed liquid inlet, the mixed liquid is prepared by mixing light salt water from an electrolytic anolyte circulating tank and hydrochloric acid according to a certain proportion, and hot ClO is utilized2Purifying the reduction product to preheat the mixed solution;
the heating chamber (2) heats the preheated mixed liquid flowing through the heating chamber;
the decomposition reaction chamber (3) provides a place for chlorate decomposition reaction for the heated and heated mixed solution, and Cl generated by decomposition is provided2Escape from the liquid phase, Cl2Contains a certain amount of ClO2In the liquid phase, there remains ClO remaining in the liquid phase without completion of the reaction3 -And ClO2 -A oxychloride;
the ClO2A decomposition liquid distribution system is arranged in the purification reduction area (4), and HCl and Cl in a part of decomposition liquid in the decomposition liquid distribution system2、ClO2Contacting the mixed gas to remove gas-phase ClO2Reduction to Cl2And H2O, the other part is heated to accelerate decomposition, and residual ClO in the decomposition liquid is removed3 -And ClO2 -Oxychloride, ClO2Purifying the reduction product into a pre-stageThe hot area (1) absorbs heat and cools the mixed liquid in the preheated area (1);
the gas-liquid separation zone (5) is used for cooling the cooled ClO2The purified reduction product is separated into decomposition completion liquid and chlorine gas.
7. The apparatus for decomposing chlorate in weak brine for chlor-alkali production as claimed in claim 6, wherein said ClO is selected from the group consisting of2The purifying and reducing area (4) is arranged in the heating chamber (2) and is isolated from the heating chamber (2), and the partition wall heats gas-phase and liquid-phase materials which are not completely decomposed in the purifying and reducing area.
8. The apparatus for decomposing chlorate in weak brine for chlor-alkali production according to claim 6 characterized by the preheating zone (1), the heating chamber (2), the decomposition reaction chamber (3), the ClO2The purification and reduction zone (4) and the gas-liquid separation zone (5) are positioned in the same shell, the gas-liquid separation zone (5), the preheating zone (1), the heating chamber (2) and the decomposition reaction chamber (3) are sequentially arranged in the shell, the gas-liquid separation zone (5), the preheating zone (1), the heating chamber (2) and the decomposition reaction chamber (3) are separated by a tube plate phase arranged in the shell, and the ClO is2The inlet end of the purification and reduction zone (4) is communicated with the decomposition reaction chamber (3), and the outlet end is communicated with the preheating zone (1).
9. The apparatus for decomposing chlorate in weak brine for chlor-alkali production as claimed in claim 6, wherein said heating chamber (2) is heated by using low pressure steam or hot air as heating medium for preheating the mixed solution.
10. The apparatus for decomposing chlorate in weak brine for chlor-alkali production as claimed in claim 6, wherein said ClO is selected from the group consisting of2The purification reduction area (4) comprises a central cylinder arranged in the heating chamber (2), a gas inlet pipe (10) is arranged in the center of the central cylinder which is covered with a liquid distribution plate (8), a decomposing liquid inlet (9) is arranged on the outer wall of the central cylinder which is higher than the tube plate in a circumferential tangential way, one part of the decomposing liquid contacts with decomposed gas through the liquid distribution plate (8), wherein HCl enables gas-phase ClO2Reduction to Cl2And H2O，The other part of the chlorine dioxide goes down spirally along the tangential direction of the cylinder wall to continue heating and accelerate decomposition of the chlorine dioxide which does not finish the reaction.
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| US4169773A (en) * | 1978-01-16 | 1979-10-02 | Hooker Chemicals & Plastics Corp. | Removal of chlorate from electrolytic cell anolyte |
| DE69118120T2 (en) * | 1990-11-28 | 1996-08-29 | Tosoh Corp | Process for the removal of chlorate from an aqueous sodium chloride solution |
| CN104928716B (en) * | 2015-05-26 | 2017-05-10 | 南通星球石墨设备有限公司 | Light salt brine pretreatment device |
| CN209507582U (en) * | 2018-11-23 | 2019-10-18 | 宜宾海丰和锐有限公司 | Chlorate decomposer |
| CN111074293B (en) * | 2020-01-14 | 2022-05-10 | 石河子天域新实化工有限公司 | Chlorate decomposition process in production of caustic soda by ion-exchange membrane method |
| CN111254455B (en) * | 2020-03-17 | 2021-04-27 | 吕子红 | Device and method for decomposing chlorate generated by side reaction of anode chamber of electrolytic cell in chlor-alkali production and related acid adding process |
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