Gradient separation and recovery method for halogen in combustion tail gas

Abstract

The invention discloses a gradient separation and recovery method for halogen in combustion tail gas, and belongs to the technical field of environmental protection. The method comprises the following steps: spraying combustion tail gas introduced into a spraying tower by utilizing spraying liquid containing alkaline earth metal ions, reacting calcium ions in the spraying liquid with hydrogen fluoride to generate alkaline earth metal fluoride precipitate, and filtering to separate calcium chloride precipitate and tail gas absorption liquid; the tail gas absorption liquid is conveyed into the electrochemical treatment tank for electrochemical treatment, and bromide ions in the tail gas absorption liquid are oxidized into bromate ions, so that chloride and bromate in reaction effluent can be separated by using a nanofiltration membrane in subsequent steps; the halogen is separated and recycled from the tail gas through an integrated process of spraying, electrochemical treatment and membrane separation, so that the integration of pollution reduction and recycling is realized, the waste gas treatment process is simplified, the waste gas treatment cost is favorably reduced, and the conversion from the halogen pollution attribute to the resource attribute is innovatively realized.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection, and in particular to a method for cascade separation and recovery of halogens in combustion tail gas. Background Art

[0002] Liquid crystal displays (LCDs) boast rich colors, a compact size, light weight, and fast response times, making them widely used in electronic display devices such as color televisions. As these electronic display devices reach the end of their useful life, a large number of discarded LCDs are generated. The liquid crystal materials in discarded LCDs are both hazardous and valuable resources. Improper recycling methods can pollute the atmosphere, soil, and other environments. However, the organic matter, glass, and metal materials contained in the LCD material can be recycled through processing. Currently, discarded LCDs are primarily disassembled manually, separating them into components such as the LCD panel, fluorescent tube, metal frame, and waste plastic. Discarded LCD panels are first sorted and recycled before their valuable materials are processed. The liquid crystal material, polarizer, and glass in discarded LCD panels are separated by mechanical grinding. The liquid crystal material, after mechanical grinding, is then transported to a pyrolysis furnace for pyrolysis. Pyrolysis, a commonly used method for treating organic solid waste, can reduce the amount of organic matter in discarded LCDs and convert large organic molecules into small compounds, thus realizing their resource utilization. However, because liquid crystal materials contain halogens, halogen-containing pyrolysis oil and gas are produced during the pyrolysis process, posing a threat to the environment. In-situ combustion can effectively remove the halogenated organic matter in the waste liquid crystal pyrolysis oil and gas, but the halogen-containing acidic gases in the combustion exhaust are highly corrosive and irritating, requiring further removal and absorption.

[0003] In response to the problem that the tail gas generated by the in-situ combustion of pyrolysis oil and gas from liquid crystal materials contains halogen-containing acidic gases such as hydrogen fluoride, hydrogen bromide, and hydrogen chloride, there is currently a lack of a mature and feasible treatment and recovery technology that can achieve the tiered separation and resource utilization of halogens after the tail gas is generated.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] Based on the defects of the prior art, the purpose of the present invention is to provide a method for the cascade separation and recovery of halogens in combustion tail gas.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a method for cascade separation and recovery of halogens in combustion tail gas, comprising the following steps:

[0008] S1. Passing the combustion exhaust gas into a spray tower, passing a spray liquid containing alkaline earth metal ions into the spray tower, spraying the combustion exhaust gas with the spray liquid containing alkaline earth metal ions in the spray tower, filtering the solution obtained after the spraying to separate the alkaline earth metal fluoride precipitate and the exhaust gas absorption liquid; the combustion exhaust gas contains hydrogen fluoride, hydrogen chloride and hydrogen bromide;

[0009] S2, inputting the tail gas absorption liquid obtained in step S1 into an electrochemical treatment cell for electrochemical treatment to obtain reaction effluent;

[0010] S3. The reaction effluent obtained in step S2 is subjected to membrane separation treatment using a nanofiltration membrane to obtain a bromate solution and a chlorine-containing solution.

[0011] It is understood that the method for cascade separation and recovery of halogens in combustion tail gas of the present invention may further comprise the following steps:

[0012] collecting the alkaline earth metal fluoride precipitate from the spray tower in step S1, and obtaining the alkaline earth metal fluoride product after drying;

[0013] The chlorine-containing solution obtained in step S3 is evaporated and concentrated to obtain a chloride crystal product;

[0014] The bromate solution obtained in step S3 is concentrated, enriched and recovered to obtain a bromate product.

[0015] Theoretically, drying and recovery of the alkaline earth metal fluoride product can be performed after step S1, before or after steps S2 and S3, or simultaneously with steps S2 and S3. The steps of recovering the chloride crystal product and bromate product can be performed after step S3, and the order of the two steps is not critical.

[0016] Waste liquid crystal materials are both resource-based and hazardous. The halogens in the tail gas of the in-situ combustion of waste liquid crystal pyrolysis oil and gas mainly exist in the form of acidic gases, such as hydrogen fluoride gas, hydrogen chloride gas, hydrogen bromide gas, etc. The method for the cascade separation and recovery of halogens in the combustion tail gas provided by the present invention is suitable for recovering and separating the halogens in the in-situ combustion tail gas of waste liquid crystal pyrolysis oil and gas. Specifically, the present invention realizes the pollution reduction of combustion tail gas and the reuse of halogens in combustion tail gas through the integrated process of "spraying + electrochemical treatment + membrane separation", simplifies the waste gas treatment process, and is conducive to reducing the cost of waste gas treatment. The recovered alkaline earth metal fluorides, bromates and chlorides can be directly used in metallurgy, chemical industry and other fields. In summary, the method of the present invention separates and recovers halogens from tail gas, and innovatively realizes the transformation from halogen pollution attributes to resource attributes.

[0017] The implementation principle of the present invention's "spraying + electrochemical treatment + membrane separation" is as follows:

[0018] In step S1 of the present invention, a spray liquid containing alkaline earth metal ions is used to spray the combustion exhaust gas introduced into the spray tower. During the spray treatment process, the spray liquid can fully absorb components such as hydrogen fluoride, hydrogen chloride, and bromine chloride in the combustion exhaust gas. The calcium ions in the spray liquid react with the hydrogen fluoride to form an alkaline earth metal fluoride precipitate. The calcium chloride precipitate and the exhaust gas absorption liquid containing chloride ions and bromide ions are separated by filtration.

[0019] In step S2 of the present invention, the tail gas absorption liquid after spraying treatment and filtration is transported to the electrochemical treatment cell for electrochemical treatment, and the ions with a radius of The bromide ion (Br - ) is oxidized to an ionic radius of The bromate ion (BrO3 - ), while the chloride ions (Cl - ) has stable chemical properties and will not undergo oxidation reactions, thereby achieving differential construction of the ionic radius of the two elements, so that in the subsequent steps, the chloride ions (Cl - ) of chloride and bromate ions (BrO3 - ) of bromate, solving the problem of bromide ions (Br - ) and chloride ions (Cl - ) The problem of difficulty in separation due to the similar ionic radius.

[0020] Preferably, in step S1, the flow ratio of the combustion exhaust gas to the spray liquid containing alkaline earth metal ions is (5-12):1.

[0021] For example, in step S1, the flow ratio of the combustion exhaust gas to the spray liquid containing alkaline earth metal ions can be 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or a range consisting of any two groups of flow ratios therein.

[0022] Preferably, in step S1, the spray liquid containing alkaline earth metal ions includes a first spray liquid and a second spray liquid, the pH value of the first spray liquid is 8-10, and the pH value of the second spray liquid is 7-8; the flow rate ratio of the first spray liquid to the second spray liquid is (0.5-2):1;

[0023] The first spray liquid is formed by mixing a soluble alkaline earth metal salt, a pH regulator and water, the soluble alkaline earth metal salt includes at least one of calcium chloride, barium chloride, strontium chloride and magnesium chloride, the pH regulator includes at least one of potassium hydroxide and sodium hydroxide, the mass concentration of the soluble alkaline earth metal salt in the first spray liquid is 13 to 18 mg / L, and the solute in the second spray liquid includes at least one of calcium bicarbonate and sodium bicarbonate.

[0024] For example, in step S1, the pH value of the first spray liquid can be 8, 8.5, 9, 9.5, 10 or a range consisting of any two groups of values ​​therein; the pH value of the second spray liquid can be 7, 7.3, 7.5, 7.7, 8 or a range consisting of any two groups of values ​​therein; the inlet flow ratio of the first spray liquid and the second spray liquid is 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1 or a range consisting of any two groups of values ​​therein.

[0025] It can be understood that, in step S1, the first spray liquid and the second spray liquid can be combined and then introduced into the spray tower, or the first spray liquid and the second spray liquid can be introduced into the spray tower separately and simultaneously.

[0026] Further preferably, in step S1, the soluble alkaline earth metal salt is calcium chloride.

[0027] The first spray liquid is formed by mixing a soluble alkaline earth metal salt, a pH regulator and water, the soluble alkaline earth metal salt includes at least one of calcium chloride, barium chloride, strontium chloride and magnesium chloride, the pH regulator includes at least one of potassium hydroxide and sodium hydroxide, the mass concentration of the soluble alkaline earth metal salt in the first spray liquid is 13 to 18 mg / L, and the solute in the second spray liquid includes at least one of calcium bicarbonate and sodium bicarbonate.

[0028] The inventors have found through research that, in step S1, the pH value of the first spray liquid is adjusted to 8.5-9.5, the pH value of the second spray liquid is adjusted to 7.3-7.7, the flow rate ratio of the first spray liquid to the second spray liquid is (0.8-1):1, and the flow rate ratio of the combustion exhaust gas to the spray liquid containing alkaline earth metal ions is adjusted to (7-9):1. This can enable the spray liquid to fully absorb fluoride, chloride and bromide in the combustion exhaust gas, and at the same time, the calcium ions in the spray liquid containing alkaline earth metal ions preferentially react with fluoride to fully react to form alkaline earth metal fluoride precipitate, thereby improving the recovery rate of fluorine, chlorine and bromine in the combustion exhaust gas.

[0029] Preferably, step S2 specifically includes:

[0030] The tail gas absorption liquid obtained in step S1 is input into an electrochemical treatment cell for electrochemical treatment in stages to obtain reaction effluent.

[0031] Further preferably, the electrochemical treatment is carried out in stages and is specifically divided into two stages:

[0032] The first electrochemical treatment stage: the current density is 15-30A / m 2, the voltage is 1-3 V, the ratio between the flow rate of air and the volume of the liquid in the electrochemical treatment cell is 0.5-5 L / (L·min), and the reaction time is 10-30 min;

[0033] The second electrochemical treatment stage: the current density is 500~1500A / m 2 , the voltage is 2 to 5 V, the ratio between the flow rate of air and the volume of the liquid in the electrochemical treatment cell is 0.5 to 5 L / (L·min), and the reaction time is 30 to 90 min.

[0034] For example, in the first electrochemical treatment stage, the current density may be 15 A / m 2 , 20A / m 2 , 22A / m 2 , 24A / m 2 , 25A / m 2 , 27A / m 2 、30A / m 2 Or a range consisting of any two groups of values ​​therein; the voltage can be 1V, 1.5V, 1.8V, 2V, 2.3V, 2.5V, 3V or a range consisting of any two groups of values ​​therein; the ratio between the flow rate of the air introduced and the volume of the liquid in the electrochemical treatment cell can be 0.5L / (L·min), 1L / (L·min), 1.5L / (L·min), 2L / (L·min), 2.5L / (L·min), 3L / (L·min) or a range consisting of any two groups of values ​​therein; the reaction time can be 10min, 15min, 20min, 25min, 30min or a range consisting of any two groups of values ​​therein.

[0035] In the second electrochemical treatment stage, the current density can be 500A / m 2 、600A / m 2 , 700A / m 2 , 800A / m 2 , 900A / m 2 、1000A / m 2 、1100A / m 2 , 1200A / m 2 、1300A / m 2 、1400A / m 2 、1500A / m 2or a range consisting of any two groups of values ​​therein; the voltage may be 2V, 2.5V, 3V, 3.5V, 4V, 4.5V, 5V or a range consisting of any two groups of values ​​therein; the ratio between the flow rate of the air introduced and the volume of the liquid in the electrochemical treatment cell may be 0.5L / (L·min), 1L / (L·min), 1.5L / (L·min), 2L / (L·min), 2.5L / (L·min), 3L / (L·min) or a range consisting of any two groups of values ​​therein; the reaction time may be 30min, 40min, 50min, 60min, 70min, 80min, 90min or a range consisting of any two groups of values ​​therein.

[0036] In step S2 of the present invention, the tail gas absorption liquid obtained in step S1 is fed into an electrochemical treatment cell for electrochemical treatment in stages. In the first electrochemical treatment stage, the present invention effectively promotes electroflocculation and / or electroflotation of the tail gas absorption liquid by regulating the current density and voltage within suitably low ranges, causing suspended impurities such as charged colloidal particles in the tail gas absorption liquid to destabilize and aggregate to form flocs. Simultaneously, aeration drives these flocs to float to the liquid surface, forming scum, which is then scraped off to complete the initial purification of the tail gas absorption liquid.

[0037] In the second electrochemical treatment stage: the present invention increases the current density and voltage to appropriate ranges, thereby enhancing the polarization effect of the electrode and promoting the following electrolytic oxidation reaction: Br - +3H2O→BrO3 - +6H + +6e - , so that Br - Oxidized to BrO3 - ; In addition, due to Br - After oxidation, the generated bromate ion (BrO3 - ) and Cl - The large difference in ionic radius between them is conducive to the subsequent separation of chloride ions (Cl - ) of chloride and bromate ions (BrO3 - ) is separated from the bromate.

[0038] The present invention performs electrochemical treatment in stages to first remove colloidal impurities, remove a large amount of suspended matter and some organic matter in advance, thereby reducing the burden of subsequent membrane separation treatment. Then, through electrolytic oxidation reaction, the differentiated ionic radius of chlorine and bromine is constructed, making the subsequent separation process more efficient and smooth.

[0039] The inventors have found that the reaction conditions of the first electrochemical treatment stage are preferably: the current density is 20-25A / m 2, the voltage is 1.5-2.5V, the ratio between the flow rate of air and the volume of the liquid in the electrochemical treatment cell is 1-3L / (L·min), and the reaction time is 15-25min; the conditions of the second electrochemical treatment stage are preferably: the current density is 800-1200A / m 2 , the voltage is 2.5-3.5V, the ratio between the flow rate of air and the volume of the liquid in the electrochemical treatment cell is 1-3L / (L·min), and the reaction time is 50-70min. When the reaction conditions of the first electrolytic oxidation stage and the reaction conditions of the second electrolytic oxidation stage are respectively within the above-mentioned corresponding preferred ranges, it is possible to more effectively remove suspended impurities such as colloids in the tail gas absorption liquid and increase the bromide ion (Br - ) is converted into bromate ion (BrO3 - ) conversion rate, thereby improving the separation effect of chlorine and bromine, and improving the purity of bromate solution and chlorine-containing solution.

[0040] Preferably, in step S2, a cathode plate and an anode plate are provided in the electrochemical treatment cell, and the effective reaction area of ​​the cathode plate and the effective reaction area of ​​the anode plate are independently 80 to 100 cm 2 The cathode plate is made of nickel, and the anode plate is made of iron.

[0041] For example, the effective reaction area of ​​the cathode plate can be 80 cm 2 , 85cm 2 , 90cm 2 , 95cm 2 , 100cm 2 Or a range consisting of any two groups of values; the effective reaction area of ​​the anode plate can be 80cm 2 , 85cm 2 , 90cm 2 , 95cm 2 , 100cm 2 Or a range consisting of any two sets of values.

[0042] The inventors have found that the anode plate made of iron can produce iron ions (Fe 3+ ), the iron ions (Fe 3+ ) can react with OH in the tail gas absorption liquid - The highly active flocculation groups are combined to form flocculation groups, which can be used to aggregate the colloids and suspended impurities in the tail gas absorption liquid by utilizing the adsorption, bridging, net capturing and sweeping effects of the highly active flocculation groups.

[0043] Preferably, in step S3, the membrane separation process is performed in an ultrasonic wave with a frequency of 10 to 60 kHz. For example, the ultrasonic wave frequency can be 10 kHz, 20 kHz, 30 kHz, 40 kHz, 50 kHz, 60 kHz, or a range consisting of any two of these values. The present invention can effectively improve the mass transfer efficiency of the solution and reduce membrane fouling by applying an ultrasonic field during the membrane separation process.

[0044] Preferably, in step S3, the pore size of the nanofiltration membrane is 0.1 to 0.5 nm.

[0045] For example, the pore size of the nanofiltration membrane can be 0.1 nm, 0.15 nm, 0.19 nm, 0.2 nm, 0.23 nm, 0.26 nm, 0.30 nm, 0.34 nm, 0.4 nm, 0.5 nm, or a range consisting of any two groups of values ​​therein.

[0046] Preferably, the combustion tail gas is the in-situ combustion tail gas of waste liquid crystal pyrolysis oil and gas, and in the combustion tail gas, the mass concentration of hydrogen fluoride is not more than 15 mg / L, the mass concentration of hydrogen chloride is not more than 0.5 mg / L, and the mass concentration of hydrogen bromide is not more than 0.3 mg / L.

[0047] The waste liquid crystal is a liquid crystal material removed from at least one of a liquid crystal panel of a television, a liquid crystal panel of a computer, a liquid crystal panel of a mobile phone, and a liquid crystal panel of a tablet, and the liquid crystal material contains elements such as F, Cl and Br.

[0048] Preferably, the method for cascade separation and recovery of halogens in combustion tail gas is implemented by a cascade separation and recovery system for halogens in combustion tail gas, and the cascade separation and recovery system for halogens in combustion tail gas comprises a spray device, an electrochemical treatment device, and a membrane separation device;

[0049] The spray device includes a spray tower and a spray liquid storage tank. The lower part of the spray tower is provided with an air inlet and a water outlet, the top of the spray tower is provided with an air outlet, at least one group of spray components is provided in the spray tower, the spray components are located between the air inlet and the air outlet, the water outlet of the spray tower is provided with a filter, the spray components are connected to the spray liquid storage tank through a spray water pump and a pipeline, and the spray liquid storage tank containing alkaline earth metal ions is connected to the spray water pump through a pipeline;

[0050] The electrochemical treatment device includes an electrochemical treatment cell, a cathode mechanism, an anode mechanism, and a pulse power supply. The cathode plate of the cathode mechanism and the anode plate of the anode mechanism are arranged in the electrochemical treatment cell. An aeration device is provided at the bottom of the electrochemical treatment cell. The water outlet of the spray tower is connected to the inlet of the electrochemical treatment cell through a pipeline.

[0051] The electrochemical treatment cell is connected to the membrane separation device through a pipeline.

[0052] Preferably, a control valve and a delivery pump are provided on the pipeline between the water outlet of the spray tower and the electrochemical treatment cell, and on the pipeline between the electrochemical treatment cell and the membrane separation device.

[0053] Preferably, a partition is provided in the spray liquid storage box containing alkaline earth metal ions, and the partition divides the internal space of the spray liquid storage box containing alkaline earth metal ions into a first spray liquid storage chamber and a second spray liquid storage chamber. The first spray liquid storage chamber is connected to the spray water pump through a pipe, and the second spray liquid storage chamber is connected to the spray water pump through a pipe; the first spray liquid storage chamber is used to store the first spray liquid, and the second spray liquid storage chamber is used to store the second spray liquid.

[0054] Further preferably, a flow regulating valve is provided on the pipeline between the first spray liquid storage chamber and the spray water pump, and on the pipeline between the second spray liquid storage chamber and the spray water pump, respectively.

[0055] Preferably, the spray device further includes a bubble generator, and the spray tower is connected to the bubble generator via a bubble delivery pipe, and the bubble delivery pipe extends to the interior of the spray tower and is located below the air inlet.

[0056] Preferably, the number of the spray assemblies is not less than two groups, the spray assemblies include spray pipes and a plurality of atomizing nozzles arranged on the spray pipes and at equal intervals, the first spray liquid storage tank is connected to the spray pipes of at least one group of spray assemblies through a spray water pump and a pipeline, and the second spray liquid storage tank is connected to the spray pipes of at least one group of spray assemblies through a spray water pump and a pipeline.

[0057] Preferably, a packing layer is further provided in the spray tower, and the packing layer is located between the atomizing nozzle and the air outlet.

[0058] Preferably, the cathode mechanism includes a cathode plate and a cathode connector connected to one end of the cathode plate, the anode mechanism includes an anode plate and an anode connector connected to one end of the anode plate, the cathode plate and the anode plate are respectively arranged in the electrochemical treatment cell, the cathode connector and the anode connector are respectively installed on the side walls of the electrochemical treatment cell, and the cathode connector and the anode connector are respectively used to be electrically connected to a pulse power supply.

[0059] Preferably, the cathode plate and the anode plate are parallel to each other and arranged opposite to each other, and the effective reaction area of ​​the cathode plate and the effective reaction area of ​​the anode plate are independently 80 to 100 cm 2 The cathode plate is made of nickel, and the anode plate is made of iron.

[0060] Preferably, the electrochemical treatment device also includes a scraper mechanism, which includes a scraper body and a drive motor. The drive motor is arranged on the electrochemical treatment cell, and the output end of the drive motor is connected to one end of the scraper body. The other end of the scraper body is rotatably connected to one side of the electrochemical treatment cell. The scraper body is located inside the side of the electrochemical treatment cell close to the tube.

[0061] Preferably, the membrane separation device includes a membrane separation tank, a plurality of membrane separators are provided in the membrane separation tank, the inlet end of the membrane separator is connected to the electrochemical treatment tank through a pipeline, a bromate solution discharge pipe is provided at the bottom of the membrane separation tank, a nanofiltration membrane is provided in the membrane separator, the permeate side outlet of the membrane separator is connected to the chlorine-containing solution discharge pipe, the chlorine-containing solution discharge pipe is provided with a discharge pump, the retentate side outlet of the membrane separator is connected to the retentate discharge pipe, the retentate discharge pipe is provided with a retentate discharge valve, the retentate discharge pipe is located in the membrane separation tank, and a bromate solution discharge pipe is provided at the bottom of the membrane separation tank.

[0062] Further preferably, ultrasonic rods corresponding to the membrane separators are provided in the membrane separation tank, and the ultrasonic rods are perpendicular to the height direction of the membrane separators.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] (1) The present invention utilizes a spray liquid containing alkaline earth metal ions to spray the combustion tail gas introduced into the spray tower. During the spray treatment process, the spray liquid can fully absorb components such as hydrogen fluoride, hydrogen chloride, and bromine chloride in the combustion tail gas. The calcium ions in the spray liquid react with the hydrogen fluoride to form an alkaline earth metal fluoride precipitate. The alkaline earth metal fluoride precipitate and the tail gas absorption liquid are separated by filtration.

[0065] (2) The present invention transports the tail gas absorption liquid after spraying treatment and filtration to an electrochemical treatment cell for electrochemical treatment, and removes the ion radius of the tail gas absorption liquid. The bromide ion (Br - ) is oxidized to an ionic radius of The bromate ion (BrO3 - ), while the chloride ions (Cl - ) has stable chemical properties and will not undergo oxidation reactions, thereby achieving differential construction of the ionic radius of the two elements, so that in the subsequent steps, the chloride ions (Cl - ) of chloride and bromate ions (BrO3 - ) of bromate, solving the problem of bromide ions (Br -) and chloride ions (Cl - ) Problems with separation due to similar ionic radii;

[0066] (3) The present invention realizes the integration of pollution reduction and reuse through the integrated process of "spraying + electrochemical treatment + membrane separation", simplifies the waste gas treatment process, and is conducive to reducing the cost of waste gas treatment. The recovered alkaline earth metal fluorides, bromates and chlorides can be directly used in metallurgy, chemical industry and other fields.

[0067] In summary, the method of the present invention separates and recovers halogens from tail gas, innovatively achieving the transformation of halogen pollution properties into resource properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a structural schematic diagram of the halogen cascade separation and recovery system in combustion tail gas provided by the present invention.

[0069] In the figure, 1-spraying device, 11-spray tower, 111-air inlet, 112-air outlet, 113-water outlet, 12-atomizing nozzle, 13-packing layer, 14-filter, 15-bubble generator, 16-spray liquid storage box, 161-partition, 162-first spray liquid storage chamber, 163-second spray chamber storage chamber, 17-bubble conveying pipe, 2-electrochemical treatment device, 21-electrochemical treatment cell, 22-cathode mechanism, 23-anode mechanism, 24-pulse power supply, 25-scraper mechanism, 26-aeration device, 3-membrane separation device, 31-membrane separation tank, 32-membrane separator, 33-ultrasonic rod, 34-discharge pump, 35-bromate solution discharge pipe, 36-chlorine-containing solution discharge pipe. DETAILED DESCRIPTION

[0070] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to specific embodiments and comparative examples. The purpose is to provide a detailed understanding of the content of the present invention, but not to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0071] Unless otherwise specified, the components and raw materials used in the examples and comparative examples of the present invention are all commercially available raw materials, and the components and raw materials used in each parallel experiment are all of the same kind.

[0072] Examples 1 to 22

[0073] The embodiment of the present invention provides a method for halogen separation and recovery in combustion exhaust gas, which is implemented by a halogen separation and recovery system in combustion exhaust gas. The structure of the halogen separation and recovery system in combustion exhaust gas is as follows: Figure 1As shown, the halogen cascade separation and recovery system in combustion tail gas includes a spray device 1, an electrochemical treatment device 2 and a membrane separation device 3.

[0074] The spraying device 1 includes a spray tower 11, a bubble generator 15, and a spray liquid storage tank 16. The lower part of the spray tower 11 is provided with an air inlet 111 and a water outlet 113. The bottom of the spray tower 11 is provided with a sedimentation outlet, and the sedimentation outlet is provided with a movable cover (not shown in the figure). The top of the spray tower 11 is provided with an air outlet 112. The spray tower 11 is provided with a filter 14 at the water outlet 113. Three groups of spray components 12 are provided in the spray tower 11. The three groups of spray components 12 are located at the air inlet 11 1 and the air outlet 112, three groups of spray assemblies 12 are arranged at equal intervals along the height direction of the spray tower 11. The spray assembly 12 includes a spray pipe and a plurality of atomizing nozzles arranged on the spray pipe and arranged at equal intervals. A packing layer 13 is also provided in the spray tower 11, and the packing layer 13 is located between the spray assembly 12 and the air outlet 112; the spray tower 11 is connected to the bubble generator 15 through a bubble delivery pipe 17, and the bubble delivery pipe 18 extends to the interior of the spray tower 11 and is located below the air inlet 111.

[0075] A partition 161 is provided in the spray liquid storage box 16, and the partition 161 divides the internal space of the spray liquid storage box 16 into a first spray liquid storage chamber 162 and a second spray liquid storage chamber 163. The first spray liquid storage chamber 162 is used to store the first spray liquid, and the second spray liquid storage chamber 163 is used to store the second spray liquid. The first spray liquid storage chamber 162 is connected to the spray pipe of the spray assembly 12 located at the bottom through a spray water pump (not shown in the figure), a flow regulating valve (not shown in the figure) and a pipeline. The second spray liquid storage chamber 163 is connected to the spray pipes of the other two groups of spray assemblies 12 through a spray water pump (not shown in the figure), a flow regulating valve (not shown in the figure) and a pipeline.

[0076] The electrochemical treatment device 2 includes an electrochemical treatment cell 21, a cathode mechanism 22, an anode mechanism 23, a pulse power supply 24 and a scraper mechanism 25. The cathode mechanism 22 includes a cathode plate and a cathode connector connected to one end of the cathode plate. The anode mechanism 23 includes an anode plate and an anode connector connected to one end of the anode plate. The cathode plate and the anode plate are respectively arranged in the electrochemical treatment cell 21. The cathode plate and the anode plate are parallel to each other and arranged opposite to each other. The effective reaction area of ​​the cathode plate is the same as the effective reaction area of ​​the anode plate and is as shown in Table 1. The material of the cathode plate is nickel, the material of the anode plate is iron, and the cathode connector and The anode connectors are respectively installed on the side walls of the electrochemical treatment cell 21, and the cathode connector and the anode connector are respectively used to be electrically connected to the pulse power supply 24. The scraper mechanism 25 includes a scraper body and a drive motor. The drive motor is arranged on the electrochemical treatment cell 21. The output end of the drive motor is connected to one end of the scraper body, and the other end of the scraper body is rotatably connected to one side of the electrochemical treatment cell 21. The scraper body is located in the upper part of the electrochemical treatment cell 21; an aeration device 26 is provided at the bottom of the electrochemical treatment cell 21, and the water outlet 113 of the spray tower 11 is connected to the inlet of the electrochemical treatment cell 21 through a pipe 4.

[0077] The membrane separation device 3 includes a membrane separation tank 31, in which several membrane separators 32 are provided. The inlet end of the membrane separator 32 is connected to the electrochemical treatment tank 21 via a pipeline. The membrane separation tank 31 is provided with an ultrasonic rod 33 corresponding to each membrane separator 32. A bromate solution discharge pipe 35 is provided at the bottom of the membrane separation tank 31. A nanofiltration membrane with a pore size of 0.26 nm is provided in the membrane separator 32. The permeate side outlet of the membrane separator 32 is connected to a chlorine-containing solution discharge pipe 36, and the chlorine-containing solution discharge pipe 36 is provided with a discharge pump 34. The retentate side outlet of the membrane separator 32 is connected to a retentate discharge pipe (not shown in the figure), and the retentate discharge pipe is provided with a retentate discharge valve (not shown in the figure). The retentate discharge pipe is located in the membrane separation tank 31, and a bromate solution discharge pipe 35 is provided at the bottom of the membrane separation tank 31.

[0078] Control valves and delivery pumps (not shown in the figure) are provided on the pipeline between the water outlet of the spray tower 11 and the electrochemical treatment tank 21, on the pipeline between the inlet end of the membrane separator 32 and the electrochemical treatment tank 21, on the retentate discharge pipe, on the bromate solution discharge pipe 35, and on the chlorine-containing solution discharge pipe 36.

[0079] The method for cascade separation and recovery of halogens in combustion tail gas comprises the following steps:

[0080] S1. The combustion exhaust gas is introduced into the spray tower 11 through the air inlet 111. At the same time, the spray water pump is started to atomize the first spray liquid and the second spray liquid through the atomizing nozzles of the corresponding spray assemblies to form droplets and spray them into the spray tower 11 to spray the combustion exhaust gas introduced into the spray tower 11;

[0081] The solution in the spray tower 11 is filtered through the filter 14 to separate the calcium fluoride precipitate and the tail gas absorption liquid. The tail gas after the spray treatment is adsorbed by the packing layer 13 and discharged from the gas outlet 112;

[0082] In step S1, the first spray liquid is a mixed solution of NaOH, CaCl2 and water. The pH value of the first spray liquid is shown in Table 1. The mass concentration of CaCl2 in the first spray liquid is 15 mg / L.

[0083] In the other embodiments except Example 4, the second spray liquid is a mixed solution prepared by calcium bicarbonate (Ca(HCO3)2) and water. The second spray liquid in Example 4 is water, and the pH value of the second spray liquid is shown in Table 1.

[0084] In step S1, the flow rate ratio of the first spray liquid and the second spray liquid, and the ratio of the flow rate of the combustion exhaust gas to the liquid flow rate entering the spray tower 11 are shown in Table 1, wherein the liquid flow rate entering the spray tower 11 is the sum of the flow rate of the first spray liquid and the flow rate of the second spray liquid.

[0085] S2, inputting the tail gas absorption liquid obtained in step S1 into the electrochemical treatment cell 21, connecting the cathode mechanism and the anode mechanism to a pulse power supply, and performing electrochemical treatment in stages to obtain reaction effluent;

[0086] The electrochemical treatment is carried out in stages: the first electrochemical treatment stage and the second electrochemical treatment stage are carried out in sequence. The electrochemical treatment conditions of each stage are shown in Table 2;

[0087] During the electrochemical reaction, aeration is performed by the aeration device 26. The ratio between the aeration air flow rate and the volume of the tail gas absorption liquid input into the electrochemical treatment tank 21 is recorded as the gas-liquid ratio. The gas-liquid ratio in each stage is shown in Table 2.

[0088] In the first electrochemical treatment stage and the second electrochemical treatment stage, the scraper mechanism 25 is used to scrape away scum on the liquid surface.

[0089] S3. The reaction effluent obtained in step S2 is input into a membrane separator 32. Under the conditions of ultrasonic frequency as shown in Table 1, the reaction effluent is subjected to membrane separation treatment using a nanofiltration membrane (with a pore size as shown in Table 1) to separate the bromate solution and the chlorine-containing solution.

[0090] S4. Collect the calcium fluoride precipitate from the spray tower 11 and obtain the calcium fluoride product after drying; evaporate and concentrate the chlorine-containing solution to obtain a chloride crystal product; concentrate, enrich and recover the bromate solution to obtain a bromate product.

[0091] Table 1

[0092]

[0093]

[0094] Table 2

[0095]

[0096]

[0097] Comparative Example 1

[0098] The difference between this comparative example and Example 1 is that step S2 of this comparative example only performs the first electrochemical stage, and does not perform the second electrochemical stage. Step S2 of this comparative example is: the tail gas absorption liquid obtained in step S1 is input into the electrochemical treatment cell, the cathode mechanism and the anode mechanism are externally connected to a pulse power supply, and the tail gas absorption liquid is electrochemically treated in the electrochemical treatment cell. The conditions of the electrochemical treatment are: the current density is 23A / m 2 , the voltage is 2V, the gas-liquid ratio (the ratio between the aeration air flow rate and the volume of the tail gas absorption liquid input into the electrochemical treatment tank) is 2L / (L·min), the reaction time is 20min; and the scum is scraped off by a scraper mechanism during the electrochemical treatment process.

[0099] Comparative Example 2

[0100] The difference between this comparative example and Example 1 is that step S2 of this comparative example is: the tail gas absorption liquid obtained in step S1 is input into the electrochemical treatment cell, the cathode mechanism and the anode mechanism are connected to a pulse power supply, and the tail gas absorption liquid is electrochemically treated in the electrochemical treatment cell. The conditions of the electrochemical treatment are: the current density is 1000A / m 2 , voltage is 3V, gas-liquid ratio (the ratio between the aeration air flow rate and the volume of the tail gas absorption liquid input into the electrochemical treatment tank) is 2L / (L·min), reaction time is 60min; and during the electrochemical treatment process, the scum is scraped off by a scraper mechanism.

[0101] Comparative Example 3

[0102] The difference between this comparative example and Example 1 is that, step S2 is: the tail gas absorption liquid obtained in step S1 is input into the electrochemical treatment cell, the cathode mechanism and the anode mechanism are connected to a pulse power supply, and electrochemical treatment is performed in stages to obtain reaction water; wherein, the electrochemical treatment in stages is: the first electrochemical treatment stage and the second electrochemical treatment stage are performed in sequence, and the conditions of the first electrochemical treatment stage are: the current density is 1000A / m 2, voltage is 3V, gas-liquid ratio (the ratio between the aeration air flow rate and the volume of the tail gas absorption liquid input into the electrochemical treatment cell) is 2L / (L·min), reaction time is 60min; the conditions of the first electrochemical treatment stage are: current density is 23A / m 2 , the voltage is 2V, the gas-liquid ratio (the ratio between the aeration air flow rate and the volume of the tail gas absorption liquid input into the electrochemical treatment tank) is 2L / (L·min), and the reaction time is 20min; during the electrochemical treatment process, the scum is scraped off by a scraper mechanism.

[0103] Comparative Example 4

[0104] The difference between this comparative example and Example 1 is that in this comparative example, the first spray liquid is not transported into the spray tower 11 in step S1 .

[0105] Comparative Example 5

[0106] The difference between this comparative example and Example 1 is that in this comparative example, the second spray liquid is not transported into the spray tower 11 in step S1 .

[0107] Comparative Example 6

[0108] The difference between this comparative example and Example 1 is that in this comparative example, there is no ultrasonic condition during filtration in step S3.

[0109] Effect test

[0110] The waste liquid crystal pyrolysis oil and gas in situ combustion tail gas from Jiangsu Ningda Environmental Protection Co., Ltd. was treated by the methods of the above embodiments and comparative examples. The treatment amount of the combustion tail gas in each embodiment and comparative example was the same. The fluorine content w1 in the waste liquid crystal pyrolysis oil and gas in situ combustion tail gas was 12906.36 mg / m 3 The bromine content w2 is 278.50 mg / m 3 The chlorine content w3 is 104.42 mg / m 3 .

[0111] The recovery rates of fluorine, chlorine and bromine were tested by the following method:

[0112] (1) Fluorine recovery rate: Weigh the mass m1 (in mg) of the calcium fluoride product obtained in step S4 and calculate the fluorine recovery rate according to the following formula: Fluorine recovery rate (%) = [(m1 × 2 × M F / M1) / (w1×V0)]×100%, where M1 is the relative molecular mass of calcium fluoride, M F is the relative atomic mass of fluorine.

[0113] (2) Bromine Recovery: The volume of the bromate solution obtained in step S3 was measured and recorded as V1 (in L). The bromate was reduced to bromide ions using thiosulfate. The mass concentration of bromine in the bromate solution obtained in step S3 was then measured by ion chromatography. The measurement result was recorded as ρ1 (in g / L). The bromine recovery (%) was calculated according to the following formula: [(ρ1 × V1) / (w2 × V0)] × 100%.

[0114] (3) Chlorine recovery rate: The volume of the chlorine-containing solution obtained in step S3 was measured and recorded as V2 (in L). The mass concentration of chlorine in the obtained chlorine-containing solution was detected by the existing silver nitrate spectrophotometry method, and the detection result was recorded as ρ1 (in g / L);

[0115] The chlorine recovery rate was calculated according to the following formula: Chlorine recovery rate (%) = [(ρ2×V2) / (w3×V0)]×100%.

[0116] The results are shown in Table 3 below.

[0117] Table 3

[0118]

[0119]

[0120] Compared with Examples 6 to 7, the recovery rates of chlorine and bromine in Examples 1 to 3 are higher. This shows that the present invention controls the process parameters of the first electrochemical treatment stage and the second electrochemical treatment stage within appropriate ranges, which can promote the progress of electrocoagulation and electroflotation, avoid excessive impurities such as colloids remaining in the reaction water and affecting the passage of chloride ions through the nanofiltration membrane, and promote the formation of bromate ions, thereby improving the separation effect of chlorine and bromine, improving the recovery rates of chlorine and bromine, and improving the purity of the chloride product and bromate product in the subsequent steps.

[0121] It can be seen from Example 1 and Examples 8 to 12 that the present invention can reduce the escape of components such as hydrogen halide during spray treatment by regulating the flow rate ratio of the first spray liquid and the second spray liquid to an appropriate range, promote the formation of calcium fluoride, and thus improve the recovery rate of each halogen.

[0122] It can be seen from Examples 1 and 13 to 15 that when the ratio of the flow rate of the combustion tail gas to the flow rate of the gas entering the spray tower is (7 to 9):1, the recovery rate of each halogen is high, the consumption of spray liquid is less, and the cost is low.

[0123] It can be seen from Example 1 and Examples 16 to 19 that selecting a nanofiltration membrane with an appropriate pore size can effectively retain bromate ions while ensuring that chloride ions pass through the nanofiltration membrane smoothly, thereby comprehensively improving the recovery rates of chlorine and bromine, and improving the purity of the chloride product and bromate product in subsequent steps.

[0124] It can be seen from Example 1, Examples 20 to 22 and Comparative Example 6 that the present invention performs a membrane separation process in ultrasound of an appropriate frequency, thereby ensuring the cleanliness of the nanofiltration membrane while avoiding membrane damage. This ensures that the nanofiltration membrane can retain bromate ions while accelerating the diffusion and mass transfer of chloride ions, thereby improving the recovery rate of chlorine and bromine, and improving the separation efficiency of chloride ions and bromate ions, thereby facilitating improvement in the purity of the chloride product and bromate product in subsequent steps.

[0125] Compared with Example 1, Comparative Example 1 did not perform electrochemical treatment in stages, which resulted in a significant decrease in the bromine recovery rate. This may be because bromide ions were not fully oxidized under lower potential conditions, resulting in a poor chlorine-bromine separation effect.

[0126] Compared with Example 1, the recovery rates of chlorine and bromine in Comparative Examples 2 to 3 were significantly reduced. This may be because the electrochemical treatment was directly carried out under higher potential conditions, so that other impurities (such as organic matter, etc.) in the tail gas absorption liquid were also electrolytically oxidized, affecting the oxidation efficiency of bromide ions and the flocculation effect of other impurities in the tail gas absorption liquid. It may also change the properties of the flocs, resulting in more residual flocs and / or colloidal particles in the reaction water, thereby affecting the subsequent membrane separation effect, resulting in a significant decrease in the recovery rates of chlorine and bromine.

[0127] Compared with Example 1, Comparative Examples 4 to 5 each use a spray liquid to spray the combustion exhaust gas, which does not fully absorb the halogen gas in the exhaust gas, resulting in a significant decrease in the halogen recovery rate.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for separating and recovering halogens from combustion tail gas in stages, characterized in that: The steps include: S1. Passing the combustion exhaust gas into a spray tower, passing a spray liquid containing alkaline earth metal ions into the spray tower, spraying the combustion exhaust gas with the spray liquid containing alkaline earth metal ions in the spray tower, filtering the solution obtained after the spraying to separate the alkaline earth metal fluoride precipitate and the exhaust gas absorption liquid; the combustion exhaust gas contains hydrogen fluoride, hydrogen chloride and hydrogen bromide; S2, inputting the tail gas absorption liquid obtained in step S1 into an electrochemical treatment cell for electrochemical treatment to obtain reaction effluent; S3. The reaction effluent obtained in step S2 is subjected to membrane separation treatment using a nanofiltration membrane to obtain a bromate solution and a chlorine-containing solution.

2. The method for separating and recovering halogens in combustion tail gas according to claim 1, wherein: In step S1, the flow ratio of the combustion exhaust gas to the spray liquid containing alkaline earth metal ions is (5-12):

1.

3. The method for separating and recovering halogens in combustion tail gas according to claim 1, wherein: In step S1, the spray liquid containing alkaline earth metal ions includes a first spray liquid and a second spray liquid, the pH value of the first spray liquid is 8-10, and the pH value of the second spray liquid is 7-8; the flow rate ratio of the first spray liquid to the second spray liquid is (0.5-2):1; The first spray liquid is formed by mixing a soluble alkaline earth metal salt, a pH regulator and water, the soluble alkaline earth metal salt includes at least one of calcium chloride, barium chloride, strontium chloride and magnesium chloride, the pH regulator includes at least one of potassium hydroxide and sodium hydroxide, the mass concentration of the soluble alkaline earth metal salt in the first spray liquid is 13 to 18 mg / L, and the solute in the second spray liquid includes at least one of calcium bicarbonate and sodium bicarbonate.

4. The method for cascade separation and recovery of halogens in combustion tail gas according to claim 1, wherein: Step S2 specifically includes: The tail gas absorption liquid obtained in step S1 is input into the electrochemical treatment cell for electrochemical treatment in stages. During the electrochemical treatment process, the scum in the electrochemical treatment cell is scraped off to obtain reaction effluent.

5. The method for cascade separation and recovery of halogens in combustion tail gas according to claim 4, characterized in that: The electrochemical treatment is specifically divided into two stages: The first electrochemical treatment stage: the current density is 15-30A / m 2 , the voltage is 1-3 V, the ratio between the flow rate of air and the volume of the liquid in the electrochemical treatment cell is 0.5-5 L / (L·min), and the reaction time is 10-30 min; The second electrochemical treatment stage: the current density is 500~1500A / m 2 , the voltage is 2 to 5 V, the ratio between the flow rate of air and the volume of the liquid in the electrochemical treatment cell is 0.5 to 5 L / (L·min), and the reaction time is 30 to 90 min.

6. The method for cascade separation and recovery of halogens in combustion tail gas according to claim 1, characterized in that: In step S2, a cathode plate and an anode plate are provided in the electrochemical treatment cell, and the effective reaction area of ​​the cathode plate and the effective reaction area of ​​the anode plate are independently 80 to 100 m 2 The cathode plate is made of nickel, and the anode plate is made of iron.

7. The method for cascade separation and recovery of halogens in combustion tail gas according to claim 1, characterized in that: In step S3, the membrane separation treatment is performed in ultrasonic waves with a frequency of 10 to 60 kHz.

8. The method for cascade separation and recovery of halogens in combustion tail gas according to claim 1, characterized in that: In step S3, the pore size of the nanofiltration membrane is 0.1-0.5 nm.

9. The method for cascade separation and recovery of halogens in combustion tail gas according to claim 1, characterized in that: The steps include: collecting the alkaline earth metal fluoride precipitate from the spray tower in step S1, and obtaining the alkaline earth metal fluoride product after drying; The chlorine-containing solution obtained in step S3 is evaporated and concentrated to obtain a chloride crystal product; The bromate solution obtained in step S3 is concentrated, enriched and recovered to obtain a bromate product.

10. The method for cascade separation and recovery of halogens in combustion tail gas according to claim 1, characterized in that: The combustion tail gas is the in-situ combustion tail gas of waste liquid crystal pyrolysis oil and gas. In the combustion tail gas, the mass concentration of hydrogen fluoride is not more than 15 mg / L, the mass concentration of hydrogen chloride is not more than 0.5 mg / L, and the mass concentration of hydrogen bromide is not more than 0.3 mg / L.

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