Method in chlor-alkali industry for treating chlorine and oxychloride in light salt brine subjected to electrolysis, and apparatus using same

Abstract

An apparatus in the chlor-alkali industry for treating light salt brine subjected to electrolysis. Under a weak acid working condition, light salt brine subjected to electrolysis and active chlorine (Cl2, ClO-) in chlorine water disproportionate to chlorate (ClO3 -), which and an electrolysis byproduct ClO3 - are then concentrated in a chlorate full-decomposition apparatus, such that disproportionation and decomposition are organically combined together to implement centralized recycle of NaCl, Cl2, H2O. In addition, provided are two methods for recycling waste heat of light salt brine subjected to electrolysis, in which salt brine first disproportionates and then is heated, and light salt brine disproportionates while being concentrated- alkali production by a halogeno salt. The apparatus can be used for eliminating outdated and energy-wasting processes such as dechlorination of light salt brine and chlorine water, evaporation of well and rock salt brine for salt production followed by adding water to dissolve the salt for alkali production, using halide after dechlorination and dehydration, and dechlorinated light salt brine returning to mines to dissolve, so as to promote the development of the chlor-alkali industry in low-carbon environment-friendly and sustainable directions.

Description

A method and device for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine Technical Field

[0001] The present invention relates to a method and device for treating chlorine and chlorine oxides in chlor-alkali electrolysis brine, which belongs to the field of chlor-alkali industrial brine electrolysis production technology (including NaOH and KOH production). Specifically, the refined brine discharged from the anode chamber after electrolysis is dissolved in the brine, and the by-product chlorine and chlorine oxides (ClO3 - , ClO - The technology completely removes Cl2) from the brine out of the tank. The qualified rate of residual chlorine in the treated brine is 100%, and the heat energy released by electrolysis carried by the brine is not lost. The salt is recycled and dissolved to produce caustic soda in an efficient and energy-saving manner. Background Art

[0002] The electrolysis dechlorination process of salt water is now commonly used, refer to Figure 2

[0003] The brine leaving the ion-exchange membrane electrolyzer is ~87℃ and acid is added to adjust the pH value to 2±0.5 before entering the dechlorination tower. Under the suction of the vacuum pump, the absolute pressure in the dechlorination tower is maintained at about 33.3kPa. Most of the chlorine in the brine in the dechlorination tower flashes out from the liquid phase with water vapor and enters the cooler to be cooled to below 40℃. The wet chlorine is separated from the chlorine water. A part of the chlorine is condensed into chlorine water and recovered to the chlorine water tank. At the same time, the chlorine water condensed in the wet chlorine main pipe is also collected in the chlorine water tank, circulated and heated to ~90℃ and then enters the dechlorination tower for dechlorination. The chlorine leaving the cooler is non-condensable gas and is pumped into the water ring vacuum pump. After cooling and separation, the wet chlorine enters the wet chlorine main pipe. The chlorine water is used as the working fluid of the water ring vacuum pump. The excess chlorine water is collected in the chlorination water tank. The brine containing a small amount of active chlorine leaving the dechlorination tower is adjusted to a pH value of 9-11 with caustic soda, and then a liquid concentration of 5%-10% Na2SO3 is added to reduce it to Cl - , eliminate the remaining active chlorine; the chemical equation is as follows:

[0004] Na2SO3+Cl2+2NaOH=Na2SO4+2NaCl+H2O

[0005] After the residual active chlorine is chemically reduced, the brine is desaturated with NaCl, and Na2SO4 is removed by the denitrification process.

[0006] Purchased solid Na2SO3 is manually added to the preparation tank, and water is added to heat it up to dissolve it into liquid, with a concentration of 5% to 10% Na2SO3. A centrifugal pump is used to add it to the brine under the control of a control valve to remove residual active chlorine. The redox potential of the brine is controlled at -500mv to +500mv to be qualified.

[0007] Current operating status of chlorate decomposition process in desalinated brine

[0008] A portion of the electrolytically generated brine is diverted from the vacuum dechlorination main pipe. It is then mixed with high-purity hydrochloric acid (31% HCl) in proportion to its chlorate content and fed into a chlorate decomposition tank. Heating steam is added to raise the temperature to between 90 and 95°C, decomposing the chlorate in the brine. The gaseous phase is diluted with process air to remove harmful absorption, while components insoluble in alkaline liquids are vented. After sufficient reaction, the liquid phase overflows and is recycled into the brine main pipe, where it is then fed into a dechlorination tower to remove residual chlorine. The chlorate decomposition solution contains 2 to 3 g / L of NaClO and 20 to 25 g / L of HCl, with the decomposition temperature controlled between 90 and 95°C. This chlorate decomposition technology only involves partial decomposition, not complete decomposition (including a gas phase). The process principle clearly states that complete chlorate decomposition (including a gas phase) is impossible. The presence of a large amount of incompletely decomposed ClO in the gas phase is reasonable, and the theoretical basis only supports incomplete decomposition. The liquid phase decomposition is not complete, and a certain amount of chlorate still remains in the liquid after the chlorate decomposition is completed.

[0009] Summary of the Invention

[0010] The technical task of the present invention is to convert the chlorine and chlorine oxides (ClO3 - , ClO - , Cl2) is completely removed, so that the residual chlorine is zero in a nearly neutral environment, and the gaseous products after decomposition are pure and easy to recycle as resources.

[0011] 1 The basic idea of ​​the present invention to complete the above tasks

[0012] The correctness of the electrochemical theoretical basis on which the industrial device design of this innovative technology is based is demonstrated from the electrochemical reaction mechanism of chlorine and chlorine oxides.

[0013] 1.1 Complete decomposition of chlorate in salt water (including gas phase)

[0014] In a strong acidic working environment (T = 298k, [H + ]=1mol / L, standard electrode potential) The electrode potential diagram is shown in Figure 1, in which the redox standard electrode potential related to chlorate decomposition is:

[0015] E A θ ClO3 - / ClO2=1.75V,E A θ ClO2 / HClO2=1.188V,

[0016] E A θ ClO3 - / Cl2=1.468V,E A θ ClO3- / HClO2=1.181V,

[0017] E A θ HClO2 / Cl2=1.659V,E A θ HClO2 / HClO=1.701V,

[0018] E A θ HClO / Cl2=1.630V. E A θ Cl2 / Cl - =1.35828V

[0019] According to the standard electrode potential pair in Figure 1:

[0020] (E A θ ClO2 / HClO2=1.188V)-(E A θ Cl2 / Cl - =1.35828V) = -0.17028V → reaction to the left

[0021] (E A θ ClO3 - / HClO2=1.181V)-(E A θ Cl2 / Cl - =1.35828V) = -0.17728V → reaction to the left

[0022] (E A θ ClO3 - / ClO2=1.75V)-(E A θ Cl2 / Cl - =1.35828V) = 0.39172V → reaction to the right

[0023] (E A θ ClO3 - / Cl2=1.468V)-(E A θ Cl2 / Cl - =1.35828V) = 0.1097V → reaction to the right

[0024] Right now:

[0025] NaClO3+2HCl=NaCl+ClO2+1 / 2Cl2+H2O (1)

[0026] NaClO3+6HCl=NaCl+3Cl2+3H2O (2)

[0027] and,

[0028] ClO2+HCl≠HClO2+1 / 2Cl2

[0029] This is also the chlorate decomposition process principle recognized by the chlor-alkali industry since the emergence of the ion-exchange membrane electrolysis process. It is the only theoretical basis for all current equipment, process configurations, process control indicators and operating methods. However, it has not achieved the ultimate goal of chlorate decomposition in brine. To date, the chlorate decomposition unit has not solved the problem of the existence of a large amount of ClO2 in the gas phase products of chlorate decomposition. The chlorate decomposition is not thorough, and other better brine treatment technologies cannot be used in chlor-alkali equipment.

[0030] This problem can be solved from another perspective. Under non-standard conditions, the difference between the above electrode potentials can change. + ] in 0.5~1.5mol / L dilute hydrochloric acid working environment to [H + ]~10mol / L, T=298K unchanged. Among them, E A θ ClO2 / HClO2=1.188V,E A θ Cl2 / Cl - =1.35828V;

[0031] Oxidation side: Cl - -e=1 / 2Cl2,

[0032] E A Cl2 / Cl - =1.35828+0.0592 / 2*lg(1 / 10 2 )V=1.29908V;

[0033] Reduction side: ClO2+H + +e=HClO2,

[0034] E A ClO2 / HClO2=1.188+0.0592 / 1*lg(10 / 0.01)V=1.3656V;

[0035] Electrode potential difference:

[0036] (E AClO2 / HClO2=1.3656V)-(E A Cl2 / Cl - =1.29908V)=0.06652V;

[0037] This redox reaction proceeds to the right.

[0038] ClO2+HCl=HClO2+1 / 2Cl2 (3).

[0039] In fact, HClO2 is extremely unstable in strong acidic solutions.

[0040] Chlorite reduction electrode potential difference:

[0041] (E A θ HClO2 / Cl2=1.659V)-(E A θ Cl2 / Cl - =1.35828V)=0.30072V,

[0042] Chemical reaction equation:

[0043] HClO2+3HCl=2Cl2+2H2O (4).

[0044] New ecological HClO2 is easily oxidized by high concentration of Cl in concentrated hydrochloric acid (31% HCl). - Reduced to Cl2, Cl - It is also oxidized to Cl2. ClO2 is reduced to HClO2 and dissolved in concentrated hydrochloric acid. The ratio of gaseous HClO2 to ClO2 in concentrated hydrochloric acid environment is very low, and 1% is only a very conservative figure.

[0045] The entire decomposition process of chlorate in light salt water (including gas phase) is as follows:

[0046] In dilute hydrochloric acid conditions,

[0047] NaClO3+2HCl=NaCl+ClO2+1 / 2Cl2+H2O and NaClO3+6HCl=NaCl+3Cl2+3H2O

[0048] Under concentrated hydrochloric acid conditions,

[0049] ClO2+HCl=HClO2+1 / 2Cl2 and HClO2+3HCl=2Cl2+2H2O

[0050] Finally, the chlorate in the salt water is completely decomposed (gas and liquid phases)

[0051] NaClO3+6HCl=NaCl+3Cl2+3H2O

[0052] Theoretically, it has been proven that ClO2 in the gas phase after chlorate decomposition is further reduced and decomposed into Cl2 in a concentrated hydrochloric acid environment, which now serves as the basis for the innovative process of complete decomposition (including gas phase) of the corresponding chlorate.

[0053] 1.2 Active chlorine in salt water (Cl2, ClO - )

[0054] Under weakly acidic conditions (T = 333k, pH = 3-7), the chemical equation for the disproportionation reaction of active chlorine in salt water is:

[0055] 2HClO≒HClO2+HCl (5)

[0056] HClO2+NaClO=NaClO3+HCl (6)

[0057] 2HClO+NaClO≒NaClO3+2HCl (7)

[0058] When active chlorine disproportionates, the product HClO2 in formula (5) is in a bimolecular reversible reaction state. The reaction rate depends on the equilibrium constant between molecules. Increasing the temperature can increase the disproportionation reaction potential difference and molecular activity, accelerating the disproportionation reaction to reach the equilibrium concentration. The disproportionation product in formula (6) is ClO3 - 、Cl - Both are completely ionized anions and the reaction is completed rapidly.

[0059] From the above chemical reaction equation, it can be seen that under the premise of complete decomposition of chlorate, especially after ClO2 can be completely decomposed, the disproportionation (chemical) method is to eliminate active chlorine (Cl2, ClO - ) is the simplest method. Under stable pH conditions, only temperature affects the reaction rate, which determines the equilibrium constant of the reversible reaction in equation (5). The reaction rate is slow at room temperature, and the appropriate reaction rate at the cell temperature (~87°C) must be determined by experimental data.

[0060] 2 Experimental evidence for the above theoretical derivation

[0061] 2.1 Pilot test plan for complete decomposition of chlorate (including gas phase)

[0062] The decomposition of chlorate in brine using dilute hydrochloric acid (HCl 0.5-1.5 mol / L) is already commercially available, so this experimental verification is no longer required. Simply confirming the reaction conditions for the second step, during which concentrated hydrochloric acid absorbs ClO2—that is, the reaction rate at an appropriate reaction temperature—completes the entire chlorate decomposition process. When the ClO2 concentration in the absorption gas phase is a commercial-grade concentration [HCl] = 10 mol / L, ClO2 is completely soluble in concentrated hydrochloric acid, achieving the optimal reaction time and temperature for complete absorption.

[0063] The pilot test involved connecting a gas conduit to the sampling port of the gas phase pipeline following decomposition in a normally operating chlorate decomposition tank. This was then connected to a gas flowmeter (3000 mL / h). Three absorption bottles (1000 mL) were then connected in series. Each of the three absorption bottles was filled with 800 mL of concentrated hydrochloric acid (31% HCl) at 45°C. The outlets were connected to an induced draft fan. The fan outlet was connected to an absorption bottle (1000 mL) containing 800 mL of 15% NaOH absorption solution. A glass tube was inserted into the bottom of the bottle stopper for venting. The sampling valve at the gas phase pipeline sampling port was opened, and the fan was started to draw in the mixed gas at a rate of 2 L / h. Concentrated hydrochloric acid was then used to purify and absorb ClO2. Then, 15% NaOH was used to absorb chlorine. Samples were taken from the absorption bottle containing 15% caustic soda after 30 and 60 minutes, respectively, and the NaClO3 and NaClO present were analyzed.

[0064] The analysis results all showed that the 15% caustic soda absorption bottle solution contained only NaOH and NaClO, while NaClO3 was not detected.

[0065] The experiment was repeated 20 times according to the above protocol, and the results were completely consistent.

[0066] Conclusion: This small test is only a qualitative analysis, which has proved that ClO2 is completely absorbed by 45℃ concentrated hydrochloric acid (31% HCl) and reduced to Cl2

[0067] 2.2 Experimental plan for active chlorine disproportionation technology in chlor-alkali industrial plants

[0068] The reaction rate of active chlorine elimination is slow at room temperature. Only the reaction rate at the normal operating temperature of the cell (87±3℃) is confirmed. The residual chlorine after the reversible reaction within the allowed reaction time is within the allowable range. At the same time, the residual chlorine after the concentrated brine is tested.

[0069] ① Experimental plan on chlor-alkali industrial plant

[0070] 10m is diverted from the main brine pipe sent to the dechlorination unit 3 / h of light salt water, and determine its pH value to be 4.1, and heat it to 90℃ at a constant temperature, and take samples to analyze the active chlorine (HClO, ClO - ), NaClO3, sent to the disproportionation reactor for reaction, and the reactor liquid level was controlled at 10m3 (60min), 20m 3 (120min), 30m 3 After the disproportionation reaction, ~10% Na2SO3 is added to the ~90°C brine to reduce the residual chlorine and then return it to the brine process. In addition, at 120 minutes of disproportionation, 250 mL of brine sample is taken from the disproportionation reactor outlet and concentrated to 190-200 mL.

[0071] Take a sample from the outlet of the disproportionation reactor, cool the sample to room temperature, and analyze the active chlorine (HClO, ClO - ), NaClO3; take three samples for analysis in each time period, and record the analysis results as the average value;

[0072] According to the above operation method, the pH value of the brine was adjusted to pH 5 ± 0.2, and the active chlorine (HClO, ClO - )、NaClO3;

[0073] According to the above operation method, the pH value of the brine was adjusted to pH 6 ± 0.2, and the active chlorine (HClO, ClO - )、NaClO3;

[0074] Take 250mL of light brine and concentrate it to 190-200mL, analyze the pH value, NaCl, active chlorine (HClO, ClO - ),NaClO3.

[0075] Active chlorine analysis method: iodine titration.

[0076] The experiment was repeated 20 times according to the above scheme, and the results were completely consistent.

[0077] ② Experimental results

[0078] ③ Conclusion: Under the normal operating temperature of the electrolytic cell, after 180 minutes of constant temperature disproportionation, the active chlorine (ClO - , Cl2) is sufficient to reduce the process indicators that reflect the economic value of this innovative technology. The use of a brine disproportionation and concentration device can achieve even better residual chlorine process indicators in the concentrated brine.

[0079] 3. The present invention removes chlorine and chlorine oxides (ClO3 - , ClO - 、Cl2) adopted technical solutions

[0080] Chlorate (ClO3 -) Full decomposition (including gas phase) device (see Figure 3): includes a hydrochloric acid heater, a ClO2 reduction tower, a chlorate decomposer and its connecting pipes, and process parameter measuring instruments include a thermometer, a pressure gauge, a liquid level display, a flow meter and an automatic control valve for controlling the process parameters.

[0081] The specific process is as follows: High-purity hydrochloric acid supplied from outside the boundary is heated to 25-60°C and metered into the ClO2 reduction tower according to the chlorate content in the brine. The hydrochloric acid flow rate is controlled by a regulating valve. It then countercurrently contacts the ClO2 and Cl2 mixture decomposed from the chlorate decomposer within the tower. The ClO2 is absorbed and reduced to Cl2, which is then discharged from the reduction tower's gas phase outlet and merged into the chlorine main pipe. After reducing ClO2, the concentration of concentrated hydrochloric acid decreases. The acidic brine is then added to the brine from electrolysis, mixed evenly, and then fed into the chlorate decomposer. Preheating, heating, decomposition, and cooling separation complete the decomposition of the chlorate in the brine. The gaseous phase is then combined and fed into the reduction tower for treatment. The decomposed acidic brine is controlled by an automatic regulating valve to deacidify the brine entering and exiting the electrolytic cell, neutralizing the NaOH that migrates back through the ion membrane in the cathode chamber of the cell.

[0082] Active chlorine in salt water (ClO - , Cl2) disproportionation device (see Figure 4): includes a static mixer, a heater, a disproportionation reaction tank, a brine heat exchanger and a chlorate decomposition device. The brine main pipe is equipped with a branch pipe to remove the chlorate decomposition device, and a 32% NaOH addition pipe and an automatic regulating valve and a chlorine water pipe from the chlorine water tank after acidification are connected to the brine main pipe before the static mixer. The equipment is connected by pipes. Measuring instruments including a temperature meter and a pH meter are installed on the connecting pipes. A 5-15% Na2SO3 addition pipe and an automatic regulating valve are connected to the brine main pipe after disproportionation. The redox potential meter on the brine main pipe measures and provides process parameters to control the amount of 5-15% Na2SO3 added.

[0083] Specific process: The brine from the electrolysis tank enters the brine main pipe, 32% NaOH and acidified chlorine water are added under the control of the automatic regulating valve, and after being fully mixed in the static mixer, it enters the steam heater to control the brine temperature between 84 and 90 ° C and the pH value between 5 and 6, and then enters the disproportionation reactor. Active chlorine (ClO - , Cl2) disproportionate to ClO3 - The residual chlorine is dissolved in light salt water and discharged together, and then 5-15% Na2SO3 is added to reduce it to active chlorine (ClO -, Cl2) is zero. The 84-90°C brine heat exchanger exchanges heat with the 45-55°C refined brine from the primary brine. The primary refined brine is heated to above 65°C for secondary refining and electrolysis. The 55°C brine is then denitrated or desalinated. The electrolytic brine is fed through a branch pipe on the main pipe into a chlorate decomposition unit, where the chlorate in the brine is decomposed and chlorine is recovered and sent to the main pipe. The acidified brine after decomposition deacidifies the brine entering and exiting the electrolytic cell and the wet chlorine from the hydrogen chloride treatment, condensing into chlorine water.

[0084] Chlorinated salt water (ClO - , Cl2) disproportionation concentration device (refer to Figure 5) includes: active chlorine (ClO - , Cl2) disproportionation device and a general brine concentration device.

[0085] Specific process: the disproportionated brine is directly sent to the brine concentration device (the brine concentration device is a well-known technology) to be concentrated into brine (NaCl ≥ 225g / L), the brine is then denitrated or desalinated, and the denitrated brine is mixed with the primary refined brine according to a ratio and then subjected to secondary refining and electrolysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 Standard electrode potential diagram between different valence levels of chlorine element

[0087] Figure 2 Vacuum dechlorination of salt water (containing ClO3 - (Decomposition) Process Flow Diagram

[0088] In Figure 2, the reference numerals indicate: 1 Na2SO3 preparation tank 2 dechlorination tower 3 chlorine gas cooler 4 vacuum unit 5 chlorine water tank 6 chlorate decomposition tank

[0089] Figure 3: Schematic diagram of the process for complete decomposition of chlorate (including gas phase)

[0090] In FIG3 , the reference numerals indicate: 1 hydrochloric acid heater 2 ClO2 reduction tower 3 chlorate decomposer

[0091] Figure 4 Active chlorine (ClO - , Cl2) disproportionation process flow diagram

[0092] 4 : 1. Temperature-stabilizing heater 2. Disproportionation reactor 3. Brine heater 4. Heater 5. ClO2 reduction tower 6. Chlorate decomposer

[0093] Figure 5: Flow chart of the desalinated water disproportionation and concentration process

[0094] 5 : 1 heater 2 ClO2 reduction tower 3 chlorate decomposer 4 temperature-stabilizing heater 5 disproportionation reactor 6 concentration unit 7 denitrification unit 8 brine mixer DETAILED DESCRIPTION

[0095] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0096] Example 1

[0097] Combined with Figure 3, the chlorate (ClO3 in the light brine provided by the present invention - ) full decomposition (including gas phase) equipment;

[0098] The implementation process is as follows: The specific process is as follows: High-purity hydrochloric acid provided from outside the boundary area is heated to 25-60°C and added to the ClO2 reduction tower according to the chlorate content in the brine. The flow rate is controlled by a hydrochloric acid regulating valve. The hydrochloric acid contacts the ClO2 and Cl2 mixed gas decomposed from the chlorate decomposer in the tower in countercurrent flow. The ClO2 is absorbed and reduced to Cl2, which is discharged from the reduction tower outlet and merged into the chlorine main pipe. The concentration of concentrated hydrochloric acid after reducing ClO2 decreases slightly. The hydrochloric acid is added to the brine from electrolysis, mixed evenly, and then fed into the chlorate decomposer. After preheating, heating, decomposition, cooling and separation, the chlorate in the brine is decomposed. The gas phase is combined and then fed into the ClO2 reduction tower for treatment. The decomposed acidic brine is controlled by an automatic regulating valve to deacidify the brine out of the tank and neutralize the NaOH that migrates through the ion membrane in the cathode chamber of the electrolytic cell.

[0099] Example 2

[0100] 4, the active chlorine (ClO - , Cl2) disproportionation device;

[0101] The implementation process is as follows: the brine (~87°C) from the anode chamber of the electrolytic cell is added with acidic brine after decomposition of chlorate to adjust the pH value to 4±0.5, releasing most of the chlorine gas. The brine and the acidic multi-component chlorine water after the chlorine gas is used together to eliminate the remaining active chlorine in the brine. 32% NaOH (~88°C) from the cathode chamber of the electrolytic cell is added to the brine under the control of a regulating valve. After being uniformly mixed in a static mixer, it is fed into a temperature-stabilizing heater to maintain the brine temperature at 85-90°C. The pH value is measured by a pH meter to detect the pH value at 5-6. The detected value is transmitted to the caustic soda addition control valve to adjust the amount of caustic soda added in time. The caustic soda then enters the top inlet of the disproportionation reactor, where the disproportionation reaction time (h) is maintained at ≥180 minutes to allow most of the active chlorine (Cl2, ClO - ) is disproportionated to ClO3 -The residual chlorine is dissolved in the brine and discharged from the bottom. 5-15% Na2SO3 is then added to reduce the residual chlorine to zero. The brine, which is between 85 and 90°C, is heat exchanged with the refined brine at 45-55°C from the primary brine in the brine heat exchanger. The primary refined brine is heated to above 65°C for secondary refining and electrolysis. The brine at 55°C is then denitrated or desalinated. The electrolytic brine is fed into the chlorate decomposition unit through a branch pipe on the main pipe to decompose the chlorate in the brine. Chlorine is recovered and sent to the chlorine main pipe. The acidic brine after decomposition deacidifies the brine entering and exiting the electrolytic cell and the wet chlorine from the hydrogen chloride treatment to condense chlorine water.

[0102] Example 3

[0103] 5, the present invention provides a device for disproportionation and concentration of desalinated water;

[0104] The implementation process is as follows: the brine (~87°C) from the anode chamber of the electrolytic cell is added with acidic brine after chlorate decomposition to adjust the pH value to 4±0.5, releasing most of the chlorine. The brine and the acidic multi-component chlorine water after the chlorine is released and recovered are used to eliminate the remaining active chlorine in the brine. 32% NaOH (~88°C) from the cathode chamber of the electrolytic cell is added to the brine under the control of a regulating valve. After being uniformly mixed in a static mixer, it is fed into a temperature-stabilizing heater to maintain the brine temperature at 84-90°C. The pH value is measured by a pH meter to detect the pH value at 5-6. The detected value is transmitted to the caustic soda addition control valve to adjust the amount of caustic soda added in time. The caustic soda then enters the top inlet of the disproportionation reactor, where the disproportionation reaction time (h) is maintained at ≥180 minutes to allow most of the active chlorine (Cl2, ClO - ) is disproportionated to ClO3 - The residual chlorine is dissolved in the brine and discharged from the bottom. Then 5-15% Na2SO3 is added to reduce the residual chlorine to zero. The brine after disproportionation and reduction enters the brine concentration device to concentrate the brine to NaCl230-180g / L to remove SO4 in the brine. 2- The denitrified brine is mixed with the primary brine in a suitable ratio before being subjected to secondary refining and electrolysis. The electrolytic brine is fed through a branch pipe on the main pipe into a chlorate decomposition unit, where the chlorate in the brine is decomposed. Chlorine is then recovered and sent to the chlorine main pipe. The acidic brine after decomposition is then deacidified and fed into the electrolysis tank. The brine at the outlet and the wet chlorine from the hydrogen chloride treatment are then condensed into chlorine water.

[0105] Compared with the existing dechlorination technology, the method and production device for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine produced by the present invention have the following beneficial effects:

[0106] 1. Creatively electrolyze the refined brine to discharge the brine and gaseous wet chlorine gas to condense the chlorine water. After acidification, most of the chlorine is released and recovered. The remaining active chlorine is disproportionated into ClO3 under alkaline conditions. - , eliminate its oxidizing properties, ClO3 in salt water- 、Cl2、ClO - All with ClO3 - into the chlorate decomposition device, and ClO3 - Full decomposition (including gaseous Cl2) to recover NaCl, Cl2, and H2O as resources. This method is the simplest treatment process for brine and chlorine water. It eliminates the need for physical dechlorination, vacuum systems, and chlorine water dechlorination in existing dechlorination devices, and also reduces the denitrification load of brine.

[0107] 2. This method for eliminating active chlorine in brine produces high-quality brine with a stable redox potential. The qualified rate of residual chlorine in the treated brine is 100%. This method has incomparable advantages over physical vacuum dechlorination, which has complicated operations and fluctuating brine quality caused by multiple factors.

[0108] 3. The heat energy of the brine discharged from the tank is not lost. In the chlor-alkali plant without dehydration requirements, the brine at 87℃ is preheated to 45-55℃ primary brine to 60-65℃, and then the brine is refined by the chelating resin tower for the second time. The brine is cooled to 50℃ and the salt is removed without reheating.

[0109] 4. For enterprises that have advantages in using underground rock salt, the ~87℃ brine can use its heat energy to evaporate excess water multiple times. Only the insufficient steam needs to be added to realize the production of alkali by replacing salt with brine. Pipeline brine transportation greatly reduces the cost of salt for caustic soda.

[0110] 5. This invention complies with the national policy of energy conservation, emission reduction and green environmental protection, which is given priority support. From the perspective of the chlor-alkali industry chain, it can avoid the high energy consumption of existing brine extraction and evaporation for salt production, and the reuse of water-soluble salt by chlor-alkali enterprises. It subverts the theoretical basis of the current dechlorination of brine in the chlor-alkali industry, amends the brine treatment process that has been used for decades, saves more valuable energy for society, and realizes low-carbon, environmental protection and sustainable development in the treatment of chlor-alkali brine.

Claims

1. The present invention provides a method for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine, comprising: After adding acidic multi-component chlorine water to the salt water (~87°C) from the electrolytic cell that releases chlorine after acidification, add 32% NaOH (~88°C) and mix evenly. Use external heat to control the temperature of the salt water to 87±3°C, monitor its pH value online to 6±1, and disproportionate the active chlorine (Cl2, ClO - ) is chlorate (ClO3 - ), the reaction time (h) is controlled at 2-4h, the undisproportionated residual chlorine is reduced by 5%-10% Na2SO3, the redox potential (ORP) of the brine is detected to be between -500 and 500mv, which is qualified, and then it is cooled to 45-55℃ by the primary brine to denitrify or directly desalinate, and the qualified brine can also be concentrated into concentrated brine by the brine concentration device to replace the primary brine; a part of the acidified brine from the electrolytic cell is diverted to decompose the chlorate therein, according to the electrolysis After the solution tank is acidified to release chlorine, the chlorate content in the brine is diverted. High-purity hydrochloric acid (31% HCl) is heated to 25-55°C to reduce ClO2 in the mixed gas decomposed by chlorate to Cl2. The brine and the above-mentioned hydrochloric acid are proportioned according to the process requirements, and then evenly mixed and put into the chlorate decomposer. After preheating, heating, decomposition, cooling, gas-liquid separation, the gas phase is combined and then sent to the reduction tower to be reduced to pure chlorine by high-purity hydrochloric acid. The acidic brine after decomposition is used for electrolysis and neutralization of NaOH from the reverse osmosis membrane.

2. A method for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine according to claim 1, characterized in that: The acidic multi-component chlorine water is a chlorine aqueous solution formed by dissolving chlorine in the condensed water under cooling of the wet chlorine produced in the anode chamber of the electrolytic cell. The pH value of the decomposed acidic brine is adjusted to 2±0.5 before entering the chlorine water storage tank. After most of the chlorine escapes from the chlorine water tank, the residual active chlorine is only 500-200 mg / L. The chlorine water after acidification is sent to the electrolytic brine, and the escaped chlorine is recovered to the chlorine main pipe.

3. A method for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine according to claim 1 or 2, characterized in that: The decomposed acidic brine is the acidic brine obtained after chlorate in the brine out of the electrolytic cell is decomposed, wherein the components of the acidic brine are NaCl 100-200 g / L, HCl 15-50 g / L, NaClO 30-3 g / L, and T≥80°C.

4. The method for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine according to claim 1, characterized in that: When chlorate is decomposed in brine, the measured high-purity hydrochloric acid (31% HCl) is heated and firstly fed into a ClO2 reduction tower to reduce ClO2 in the gas phase of the chlorate decomposer, and then brine is added according to the known process ratio requirements to decompose the chlorate therein.

5. The method for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine according to claim 1, characterized in that: Residual chlorine after disproportionation (Cl2, ClO - ) is reduced by 5% to 10% Na2SO3. The sodium sulfite solution is generally added immediately after the disproportionation reaction. When the waste heat utilization device does not require residual chlorine in the light brine, the addition point is after the waste heat utilization.

6. The method for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine according to claim 1, characterized in that: After concentration, the brine NaCl is 225-270g / L, NaClO3 is ≤5g / L, and the active chlorine is disproportionated and the excess water in the brine is evaporated to achieve alkali production with halogenated salt.

7. A chlorine-alkali electrolysis salt water chlorine and chlorine oxide processing production device, characterized in that: Based on the method for treating chlorine and chlorine oxides in electrolyzed salt water according to claim 1, the device comprises a method for completely decomposing chlorate in salt water and electrolyzing active chlorine (Cl2, ClO - ) Connecting pipes, valves, automatic regulating valves, and various signal display instruments between the two parts and the equipment; First, the decomposition device of desalinated salt water chlorate includes a chlorate decomposer and a ClO2 reduction tower combination; The chlorate decomposer is used for decomposing chlorate in salt water. It has five functional areas inside, namely, a preheating area, a heating area, a decomposition area, a cooling area, and a gas-liquid separation storage area. The inlet is connected to the acidified salt water. The heating area has a steam addition inlet and a condensed water outlet. The decomposition area has a gas outlet and temperature and pressure measuring ports. The gas outlet pipe merges with another gas outlet pipe and is connected to the gas inlet of the ClO2 reduction tower. The gas-liquid separation storage area has a gas outlet on the top, a liquid outlet, a temperature measuring port, and a liquid level measuring port on the bottom. The gas outlet pipe is merged into the top outlet. The liquid outlet pipe is connected to the inlet and outlet pipes of the electrolytic cell salt water and the inlet pipe of the chlorine water tank. The ClO2 reduction tower is combined with a ClO2 reduction tower and an auxiliary equipment hydrochloric acid heater, which is used for reducing and purifying ClO2 in the gas phase after chlorate decomposition to Cl2. The gas phase inlet pipe of the ClO2 reduction tower is connected to the gas phase outlet pipe of the chlorate decomposer, the gas phase outlet pipe of the tower is connected to the electrolytic chlorine main pipe, its liquid inlet is connected to the hydrochloric acid pipe, the tower liquid phase outlet is connected to the chlorate decomposer after being connected to the brine pipe from electrolysis, the ClO2 reduction tower is connected to the hydrochloric acid heater outlet pipe, a temperature measuring instrument is arranged on the outlet pipe, the heater inlet pipe is connected to the high-purity hydrochloric acid (31% HCl) supply pipe, and the heater is provided with a steam inlet and a condensed water outlet; Second, the active chlorine (Cl2, ClO) from electrolyzed salt water - ) The disproportionation device includes a static mixer, a temperature-stabilizing heater, a disproportionation reactor, a brine heat exchanger, and a desalinated brine active chlorine (Cl2, ClO - ) is disproportionated in the disproportionation reactor to generate ClO3 - , there is a liquid level measuring instrument on the disproportionation reactor; the front of the desalinated brine main pipe is connected to the electrolytic desalinated brine circulation output pump, and then connected to the static mixer, which is respectively connected to the acidified chlorine water addition pipe and the 32% NaOH addition pipe, the static mixer outlet pipe is connected to the temperature-stabilizing heater, and there is a steam addition pipe and a condensed water discharge pipe on the temperature-stabilizing heater. The outlet of the temperature-stabilizing heater is connected to the inlet pipe of the desalination reactor, and there is a temperature measuring instrument on it. The outlet pipe of the desalination reactor is connected to the inlet of the brine heater, and there is a 5%-10% Na2SO3 addition pipe on it. The outlet pipe is connected to the primary brine system, and there is a redox electrode potential measuring instrument on it. The primary brine inlet pipe on the heating side of the heat exchanger is connected to the primary brine pipe, and the outlet is connected to the secondary refined brine pipeline in the area. The outlet pipe of the desalination reactor can also be connected to the desalinated brine concentration unit.

8. The device for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine according to claim 6, characterized in that: The outlet pipe of the disproportionation reactor can also be connected to the brine concentration unit, the outlet pipe of the brine concentration unit enters the inlet of the denitrification unit, the outlet pipe of the denitrification unit is connected to the primary brine main pipe, and then connected to the brine inlet pipe of the secondary refining unit.

9. The device for treating chlorine and chlorine oxides in chlor-alkali electrolyzed brine according to claim 6, characterized in that: The 5% to 10% Na2SO3 adding pipe is added at a position where the quality of the desalinated water requires that the residual chlorine is zero. The concentrating device is connected to the outlet pipe of the disproportionator, and other waste heat utilization equipment is connected to the desalinated water pipeline after the waste heat utilization is completed.

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