Method and system for recovering bromine from smelting smoke of waste printed circuit board of bromine flame retardant

Abstract

The present application relates to waste circuit board resource utilization and flue gas treatment technical field, disclose a kind of method and system for recovering bromine from bromine flame retardant waste circuit board smelting flue gas, the method includes oxygen-rich molten pool smelting, flue gas cooling, bag dust collection and bromine ion leaching, double-stage gradient absorption, bromine salt solution pretreatment, preheating oxidation, distillation condensation separation, finished product separation and reflux eight steps;System includes molten pool smelting unit, flue gas cooling unit, bag dust collection and leaching unit, double-stage gradient absorption unit, pretreatment unit, preheating oxidation unit, distillation condensation unit, separation reflux unit;The present application realizes the efficient release of bromine element by oxygen-rich smelting, combined with gradient cooling, double-stage absorption, molecular distillation and other processes, high-purity recovery of bromine is realized, and the purity of finished product bromine is ≥99.5%;While using waste heat boiler to recover flue gas heat, provide heat source for distillation process, reduce energy consumption.

Description

Technical Field

[0001] This invention relates to the field of waste circuit board resource utilization and flue gas treatment technology, and in particular to a method and system for recovering bromine from the smelting flue gas of waste circuit boards containing bromine-based flame retardants. Background Technology

[0002] According to statistics, around 2000, more than 90% of rigid circuit boards used FR-4 substrates containing bromine (mainly tetrabromobisphenol A). Currently, halogen-free and bromine-based flame retardant circuit boards are in a stable period of "binary structure" distribution. A large number of low- and mid-range electronic products, industrial control equipment, home appliances, and some automotive parts commonly use bromine-based FR-4 circuit boards. The industry estimates that its market share is between 50% and 65%. At present, most of the waste circuit boards in China are recycled using pyrometallurgical methods to recover valuable metal elements, while bromine elements enter the flue gas for treatment without being recycled and reused. Moreover, most of the bromine elements in my country are extracted from seawater with extremely low content, resulting in a huge waste of bromine resources.

[0003] Currently, existing methods for bromine recovery from waste circuit board smelting gas have many shortcomings, such as low bromine recovery rate, low purity of finished product, inability to meet industrial requirements, high energy consumption in some methods, failure to effectively utilize the waste heat of smelting gas, and the generation of secondary pollutants during the treatment process, resulting in poor environmental performance. Therefore, there is an urgent need to develop a high-efficiency, low-consumption, and environmentally friendly bromine-based flame retardant waste circuit board smelting gas bromine recovery technology. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method and system for recovering bromine from the smelting flue gas of bromine-based flame retardants used in waste circuit boards. This method aims to solve the technical problems of low bromine recovery rate, low purity of finished products, inability to meet industrial use requirements, high energy consumption in some methods, ineffective utilization of waste heat from smelting flue gas, easy generation of secondary pollutants during treatment, and poor environmental performance.

[0005] A method and system for recovering bromine from smelting flue gas of waste circuit boards containing brominated flame retardants, comprising the following steps:

[0006] S1: Oxygen-enriched molten pool smelting: Waste circuit boards with bromine flame retardants and a particle size ≤100mm are added to the molten pool smelting furnace. High-pressure oxygen-enriched air and natural gas are blown into the melt for stirring and smelting. The furnace temperature is controlled at 1200~1250℃, and the flue gas residence time in the flue gas zone of the furnace is >2 seconds. A waste heat boiler is installed in the furnace to cool down the high-temperature flue gas and generate saturated steam. The treated high-temperature flue gas is discharged from the top of the furnace.

[0007] S2: Flue gas cooling: The high-temperature flue gas discharged in step 1 is cooled to 150°C through a two-stage cooling device, with the first stage cooling to 550°C and the second stage rapidly cooling to 150°C.

[0008] S3: Baghouse dust collection and bromide ion leaching: The cooled flue gas is passed into a baghouse dust collector to collect bromine-containing dust. The dust is added to a debrominating agent solution with a pH of 8-10 and reacted at 50-70℃ for 1-2 hours to allow 95% of the bromine to migrate to the leaching solution in the form of bromide ions.

[0009] S4: Two-stage gradient absorption: The flue gas after passing through the bag filter dust collector is passed into the first-stage acidic absorption tower with an inlet temperature ≤160℃ and an outlet temperature ≥80℃. The pH of the absorbent is controlled at 2-3. Then it enters the second-stage alkaline absorption tower with an outlet temperature ≥50℃ and the pH of the absorbent is controlled at 10-12.

[0010] S5: Bromine salt solution pretreatment: Mix the leachate from step 3 with the absorbent from step 4, add dilute hydrochloric acid or dilute sulfuric acid to adjust the pH to 2.5-3.5, and filter to remove suspended solids;

[0011] S6: Preheating oxidation: Preheat the pretreated bromide salt solution to ≥60℃, add 5-10% excess oxidant, and react at 60-90℃ for 30-60 minutes to oxidize 90-95% of the bromide ions to elemental bromide.

[0012] S7: Distillation and condensation separation: The oxidized solution is added to a falling film molecular distillation column, and the distillation temperature is controlled at 65-75℃. The solution is heated by the saturated vapor generated in step S1 to vaporize the free bromine. The mixed vapor generated by vaporization is passed into a condenser to condense into liquid.

[0013] S8: Product separation and reflux: The condensed liquid is introduced into a centrifugal phase separator to separate and obtain bromine with a purity of ≥99.5%. After filtering to remove trace organic matter, the bromine concentration is detected. If the concentration is >10%, it is refluxed to the distillation tower. If the concentration is low, it is returned to the secondary absorption tower of step S4 as makeup water.

[0014] Furthermore: the specific steps of oxygen-enriched molten pool smelting in step S1 are as follows:

[0015] S1.1: The waste circuit boards containing bromine-based flame retardants are crushed and screened to control the particle size of the material to ≤100mm, remove large metal impurities, and ensure uniform feeding.

[0016] S1.2: The pretreated waste circuit boards are continuously fed into the molten pool furnace through the feed inlet. The oxygen-enriched air supply device and the natural gas supply device are started to blow high-pressure oxygen-enriched air with a pressure of 0.3-0.5MPa and an oxygen concentration of 80-90vol% into the molten material in the furnace. At the same time, natural gas is blown in. The mass ratio of natural gas to waste circuit board feed is controlled at 0.08-0.12:1. Through the stirring action of oxygen-enriched air and natural gas, the waste circuit boards and the molten material are fully mixed and reacted.

[0017] S1.3: The furnace temperature is monitored in real time by an in-furnace temperature sensor, and the amount of oxygen-enriched air and natural gas injected is adjusted to stabilize the furnace temperature at 1200-1250℃; at the same time, the flue gas residence time detection device ensures that the residence time of the flue gas in the flue gas zone of the furnace is >2 seconds, so that the bromine flame retardant in the waste circuit board is fully decomposed and the bromine element enters the flue gas.

[0018] S1.4: High-temperature flue gas is discharged from the flue gas outlet at the top of the molten pool furnace and enters the waste heat boiler. The waste heat boiler uses the heat of the high-temperature flue gas for heat exchange, cooling the flue gas while generating saturated steam with a pressure of 0.8-1.2MPa. The saturated steam is stored in a steam storage tank and used for heating in subsequent distillation steps. The high-temperature flue gas treated by the waste heat boiler enters the next step.

[0019] Furthermore: the specific steps for flue gas cooling in step S2 are as follows:

[0020] S2.1: First-stage cooling: The high-temperature flue gas discharged from the waste heat boiler, with a temperature of about 800-900℃, is passed into the first-stage tubular heat exchanger. Heat exchange is carried out through the circulating water in the heat exchanger. The cooling rate is controlled at 80-100℃ / min to reduce the flue gas temperature to 550℃. The cooling medium after heat exchange enters the cooling system for further cooling and is then recycled.

[0021] S2.2: Secondary Cooling: The flue gas cooled to 550°C after the primary cooling is introduced into the secondary quench tower. Cooling water is sprayed through atomizing nozzles in the quench tower to achieve rapid cooling of the flue gas. The cooling rate is controlled at 6-8°C / s to quickly reduce the flue gas temperature to 150°C, thus preventing the bromine in the flue gas from forming secondary pollutants. The rapidly cooled flue gas carries a small amount of water mist and enters the next step.

[0022] Furthermore: the specific steps of bag dust collection and bromide ion leaching in step S3 are as follows:

[0023] S3.1: The flue gas after secondary cooling is introduced into the bag filter at 150°C. The filtration velocity of the bag filter is controlled at 0.8-1.2 m / min and the dust collection efficiency is ≥99%. The dust in the flue gas is collected through the bag filter. The bromine content in the dust is 30-50%. The flue gas after dust collection enters the next step. The dust collected by the bag filter is periodically discharged into the leaching tank.

[0024] S3.2: Prepare a debrominating agent solution with a pH of 8-10. The debrominating agent is a sodium carbonate-sodium hydroxide mixed solution, wherein the sodium carbonate concentration is 5-8 g / L and the sodium hydroxide concentration is 3-5 g / L. After preparation, the solution is introduced into the leaching tank.

[0025] S3.3: Add the flue dust collected by the bag filter to the leaching tank containing the debromination agent solution, start the stirring device, control the stirring rate to 150-200 r / min, and at the same time stabilize the temperature in the leaching tank at 50-70℃ using the temperature control device. React for 1-2 hours to allow the bromine element in the flue dust to react fully, with more than 95% of the bromine migrating to the leachate in the form of bromide ions. After the reaction is completed, the leachate is temporarily stored in the leachate storage tank for subsequent pretreatment steps.

[0026] Furthermore: the specific steps of the two-level gradient absorption in step S4 are as follows:

[0027] S4.1: Primary acidic absorption: The flue gas after bag dust collection, containing a small amount of uncollected bromine vapor, is passed into the primary acidic absorption tower. The inlet temperature of the primary absorption tower is controlled to be ≤160℃ and the outlet temperature is ≥80℃. Dilute hydrochloric acid is added to the absorption tower through a pH adjustment device to control the pH of the absorbent at 2-3. The bromine vapor in the flue gas reacts with the acidic absorbent to generate bromide, which enters the absorbent. The absorbent is recycled. When the bromide ion concentration in the absorbent reaches 10-15g / L, it is discharged into the mixing tank.

[0028] S4.2: Secondary alkaline absorption. The flue gas after primary acidic absorption is passed into the secondary alkaline absorption tower. The outlet temperature of the secondary absorption tower is controlled at ≥50℃. Sodium hydroxide solution is added into the absorption tower through a pH adjustment device to control the pH of the absorbent at 10-12, further absorbing the residual bromine vapor and acidic gases in the flue gas to ensure that the flue gas meets the emission standards. The secondary absorbent is recycled. When the bromide ion concentration in the absorbent reaches 8-12 g / L, it is discharged into the mixing tank.

[0029] Furthermore: the specific steps of the bromine salt solution pretreatment in step S5 are as follows:

[0030] S5.1: Pass the leachate temporarily stored in step S3 and the primary and secondary absorbent solutions discharged in step S4 into the mixing tank, start the stirring device, and make the three solutions fully and evenly mixed.

[0031] S5.2: Add dilute hydrochloric acid or dilute sulfuric acid to the mixing tank through the pH adjustment device, and adjust the pH value of the mixed solution to 2.5-3.5 while stirring, so that the impurity ions in the solution form precipitates;

[0032] S5.3: The pH-adjusted mixed solution is passed into a filter to remove suspended solids and precipitated impurities. The filtered clear bromide solution is then sent to a pretreatment storage tank for subsequent preheating oxidation steps. The filter residue is collected and disposed of in a harmless manner.

[0033] Furthermore: the specific steps of preheating oxidation in step S6 are as follows:

[0034] S6.1: The clarified bromide solution in the pretreatment tank is passed into the preheater to preheat the solution temperature to ≥60℃, and the preheated solution is then passed into the oxidation reaction tank.

[0035] S6.2: Add an oxidant to the oxidation reaction tank. The oxidant is a sodium hypochlorite solution or chlorine gas with an effective chlorine concentration of 10-15%. The amount of oxidant added is 105-110% of the theoretical reaction amount to ensure that the bromide ions are fully oxidized.

[0036] S6.3: Start the stirring device in the oxidation reaction tank and control the stirring rate to 150-200 r / min. At the same time, stabilize the reaction temperature at 60-90℃ using the temperature control device. React for 30-60 minutes to oxidize 90-95% of the bromide ions in the solution to elemental bromine. After the reaction is completed, a mixed solution containing elemental bromine is obtained.

[0037] Furthermore: the specific steps of distillation and condensation separation in step S7 are as follows:

[0038] S7.1: Pass the bromine-containing mixed solution after the oxidation reaction into a falling film molecular distillation column, check the sealing of the distillation column, start the vacuum system, and adjust the vacuum degree in the distillation column to 0.08-0.09 MPa;

[0039] S7.2: The saturated vapor generated in step S1 is introduced into the heating jacket of the falling film molecular distillation column at a pressure of 0.8-1.2 MPa. The heat of the saturated vapor is used to heat the solution, and the temperature inside the distillation column is controlled to be stable at 65-75℃. The free bromine in the solution vaporizes under this temperature and vacuum conditions to form bromine vapor. The distillation residence time is controlled to be 15-20 min to ensure that the bromine is fully vaporized.

[0040] S7.3: The bromine vapor produced by distillation is passed into the condenser, where the low-temperature brine condenses the bromine vapor into liquid. The condensation temperature of the condenser is controlled at 5-10℃ to ensure that the bromine vapor is fully condensed. The condensed liquid then enters the centrifugal phase separator.

[0041] Furthermore: the specific steps for product separation and reflux in step S8 are as follows:

[0042] S8.1: Centrifugal phase separation. The condensed liquid is introduced into the centrifugal phase separator. The centrifugal phase separator is started and the centrifugal speed is controlled at 3000-4000 r / min. The bromine in the condensed liquid is separated from the water by centrifugal force to obtain a finished bromine with a purity ≥99.5%. The finished bromine is stored in the finished product storage tank. The separated finished bromine is passed through a filter to remove trace organic impurities to ensure that the purity of the finished bromine meets the standard.

[0043] S8.2: The concentration of bromine in the filtered product is detected by a concentration detector. If the bromine concentration is >10%, it is refluxed back to the falling film molecular distillation tower through the reflux pipe for re-distillation and separation to improve the bromine recovery rate. If the bromine concentration is low (≤10%), it is returned to the secondary alkaline absorption tower in step S4 as makeup water through the reflux pipe to achieve the recycling of bromine.

[0044] Furthermore: A bromine recovery system for waste circuit board smelting flue gas containing brominated flame retardants, comprising:

[0045] Molten pool smelting unit: includes molten pool smelting furnace, oxygen-enriched air supply device, natural gas supply device and waste heat boiler; the molten pool smelting furnace is provided with a feed inlet and flue gas outlet at the top and a blower at the bottom. The oxygen-enriched air supply device and natural gas supply device are both connected to the blower through pipelines. The waste heat boiler is connected to the flue gas outlet of the molten pool smelting furnace and is used for cooling high-temperature flue gas and generating saturated steam.

[0046] Flue gas cooling unit: includes a primary tubular heat exchanger and a secondary quench tower. The inlet of the primary tubular heat exchanger is connected to the outlet of the waste heat boiler, and the outlet of the primary tubular heat exchanger is connected to the inlet of the secondary quench tower, used to gradually cool the flue gas to 150°C.

[0047] Baghouse dust collection and leaching unit: includes a baghouse dust collector, a leaching tank and a stirring device; the inlet of the baghouse dust collector is connected to the outlet of the secondary quench tower, the bottom outlet of the baghouse dust collector is connected to the leaching tank, the stirring device is installed in the leaching tank, and the leaching tank is equipped with a debromination agent addition port and a temperature control device.

[0048] The dual-stage gradient absorption unit includes a primary acidic absorption tower and a secondary alkaline absorption tower. The inlet of the primary acidic absorption tower is connected to the flue gas outlet of the bag filter, and the outlet of the primary acidic absorption tower is connected to the inlet of the secondary alkaline absorption tower. Both absorption towers are equipped with a temperature detection device, a pH adjustment device, and an absorbent circulation device.

[0049] Pretreatment unit: includes a mixing tank, a pH adjustment device, and a filter; the inlet of the mixing tank is connected to the outlet of the leaching tank and the absorbent outlet of the secondary alkaline absorption tower, respectively; the pH adjustment device is connected to the mixing tank and is used to add dilute hydrochloric acid or dilute sulfuric acid; the filter is connected to the outlet of the mixing tank.

[0050] Preheating oxidation unit: includes a preheater, an oxidation reaction tank and an oxidant adding device; the inlet of the preheater is connected to the outlet of the filter, the outlet of the preheater is connected to the oxidation reaction tank, the oxidant adding device is connected to the oxidation reaction tank, and the oxidation reaction tank is equipped with a temperature control device and a stirring device;

[0051] Distillation and condensation unit: includes a falling film molecular distillation column and a condenser; the inlet of the falling film molecular distillation column is connected to the outlet of the oxidation reaction tank, the heating medium inlet of the falling film molecular distillation column is connected to the saturated steam outlet of the waste heat boiler, and the inlet of the condenser is connected to the steam outlet of the falling film molecular distillation column.

[0052] Separation and reflux unit: includes a centrifugal phase separator, a filter, a concentration detector, and a reflux pipeline; the inlet of the centrifugal phase separator is connected to the outlet of the condenser, the bottom outlet of the centrifugal phase separator is connected to the filter, the concentration detector is installed on the outlet pipeline of the filter, and the reflux pipeline is connected to the outlet of the concentration detector, the falling film molecular distillation column, and the secondary alkaline absorption column respectively.

[0053] The present invention has the following beneficial effects:

[0054] 1. In the oxygen-enriched molten pool smelting process, by precisely controlling the furnace temperature of 1200-1250℃ and the flue gas residence time of >2 seconds, combined with 80-90 vol% high-concentration oxygen-enriched air, the bromine-based flame retardant can be completely decomposed, with a bromine release rate of ≥98%, laying the foundation for subsequent recovery. The combination of bag filter dust collection and two-stage gradient absorption process achieves full coverage capture of different forms of bromine in the flue gas. The bag filter dust collection intercepts 30-50% of the high-bromine content flue gas dust, the acidic absorption tower captures bromine vapor to generate bromides, and the alkaline absorption tower catches the residual bromine and acidic gases at the bottom, with a total bromine recovery rate of ≥90%.

[0055] 2. The falling film molecular distillation column achieves efficient separation of bromine from impurities under precise temperature control of 0.08-0.09 MPa vacuum and 65-75℃. Combined with high-speed centrifugation of 3000-4000 r / min by a centrifugal phase separator, the final product bromine purity is stable at ≥99.5%, meeting the industrial-grade bromine standards and can be directly applied in pharmaceutical, dye and other fields.

[0056] 3. The waste heat boiler recovers heat from the high-temperature flue gas at 1200-1250℃ to generate saturated steam at 0.8-1.2MPa. This steam precisely matches the heating requirements of the falling film molecular distillation column, eliminating the need for an additional steam boiler or fuel heating system. Compared with traditional bromine recovery processes, energy consumption is reduced by 35%-45%. The circulating water cooling medium of the tubular heat exchanger can be used in a closed loop, and the atomized cooling water of the quench tower can be partially recovered to the absorbent system, reducing water consumption by 20%-30% and further compressing operating costs.

[0057] 4. Two-stage gradient cooling process specifically addresses bromine pollution risks: The first-stage tubular heat exchanger provides gentle cooling at a rate of 80-100℃ / min, while the second-stage quench tower provides rapid cooling at a rate of 6-8℃ / s, quickly bypassing the temperature range where bromine easily generates dioxins, thus preventing the generation of highly toxic byproducts at the source. The baghouse dust collector maintains a filtration velocity of 0.8-1.2 m / min with a dust collection efficiency of ≥99%, effectively trapping over 99% of particulate matter in the flue gas, significantly reducing the risk of flue gas emissions. The tail gas treated by the two-stage absorption tower has a bromide concentration below the limit and can be directly discharged in compliance with standards.

[0058] 5. The system achieves closed-loop control of core parameters: The temperature sensor of the molten pool furnace is linked with the oxygen-enriched air and natural gas supply devices, which can automatically adjust the fuel and oxygen ratio to ensure that the furnace temperature is stable at 1200-1250℃. The pH and temperature detection devices of the primary acidic and secondary alkaline absorption towers are automatically linked with the dosing system and heat exchange system, and the pH fluctuation range of the absorption liquid is controlled within ±0.2 to avoid the decrease in absorption efficiency due to parameter drift. The finished product concentration detection and reflux mechanism are automated. The concentration detector monitors the bromine concentration in real time. When the concentration is >10%, it is automatically refluxed to the distillation tower for purification. When it is ≤10%, it is automatically returned to the secondary absorption tower for water replenishment. No manual judgment is required, which ensures product purity and avoids bromine waste. The product quality fluctuation range is ≤0.3%. Attached Figure Description

[0059] Figure 1 This is a flowchart of a method for recovering bromine from the smelting flue gas of waste circuit boards containing bromine-based flame retardants.

[0060] Figure 2 This is a flowchart of a bromine recovery system for waste circuit board smelting flue gas from a brominated flame retardant process. Detailed Implementation

[0061] The present invention will be further described in detail below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0062] Please see the appendix Figure 1 The present invention provides an embodiment 1: a method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants, comprising the following specific implementation steps:

[0063] S1: Oxygen-enriched molten pool smelting: Waste circuit boards with bromine flame retardants and a particle size ≤100mm are added to the molten pool smelting furnace. High-pressure oxygen-enriched air and natural gas are blown into the melt for stirring and smelting. The furnace temperature is controlled at 1200~1250℃, and the flue gas residence time in the flue gas zone of the furnace is >2 seconds. A waste heat boiler is installed in the furnace to cool down the high-temperature flue gas and generate saturated steam. The treated high-temperature flue gas is discharged from the top of the furnace.

[0064] The specific steps of oxygen-enriched molten pool smelting in step S1 are as follows:

[0065] S1.1: The waste circuit boards containing bromine-based flame retardants are crushed and screened to control the particle size of the material to ≤100mm, remove large metal impurities, and ensure uniform feeding.

[0066] S1.2: The pretreated waste circuit boards are continuously fed into the molten pool furnace through the feed inlet. The oxygen-enriched air supply device and the natural gas supply device are started to blow high-pressure oxygen-enriched air with a pressure of 0.3-0.5MPa and an oxygen concentration of 80-90vol% into the molten material in the furnace. At the same time, natural gas is blown in. The mass ratio of natural gas to waste circuit board feed is controlled at 0.08-0.12:1. Through the stirring action of oxygen-enriched air and natural gas, the waste circuit boards and the molten material are fully mixed and reacted.

[0067] S1.3: The furnace temperature is monitored in real time by an in-furnace temperature sensor, and the amount of oxygen-enriched air and natural gas injected is adjusted to stabilize the furnace temperature at 1200-1250℃; at the same time, the flue gas residence time detection device ensures that the residence time of the flue gas in the flue gas zone of the furnace is >2 seconds, so that the bromine flame retardant in the waste circuit board is fully decomposed and the bromine element enters the flue gas.

[0068] S1.4: High-temperature flue gas is discharged from the flue gas outlet at the top of the molten pool furnace and enters the waste heat boiler. The waste heat boiler uses the heat of the high-temperature flue gas for heat exchange, cooling the flue gas while generating saturated steam with a pressure of 0.8-1.2MPa. The saturated steam is stored in a steam storage tank and used for heating in subsequent distillation steps. The high-temperature flue gas after being treated by the waste heat boiler enters the next step.

[0069] S2: Flue gas cooling: The high-temperature flue gas discharged in step 1 is cooled to 150°C through a two-stage cooling device, with the first stage cooling to 550°C and the second stage rapidly cooling to 150°C.

[0070] The specific steps for flue gas cooling in step S2 are as follows:

[0071] S2.1: First-stage cooling: The high-temperature flue gas discharged from the waste heat boiler, with a temperature of about 800-900℃, is passed into the first-stage tubular heat exchanger. Heat exchange is carried out through the circulating water in the heat exchanger. The cooling rate is controlled at 80-100℃ / min to reduce the flue gas temperature to 550℃. The cooling medium after heat exchange enters the cooling system for further cooling and is then recycled.

[0072] S2.2: Secondary cooling: The flue gas after primary cooling is introduced into the secondary quench tower at 550°C. Cooling water is sprayed through atomizing nozzles in the quench tower to achieve rapid cooling of the flue gas. The cooling rate is controlled at 6-8°C / s to quickly reduce the flue gas temperature to 150°C, so as to avoid the formation of secondary pollutants by bromine in the flue gas. The flue gas after rapid cooling carries a small amount of water mist and enters the next step.

[0073] S3: Baghouse dust collection and bromide ion leaching: The cooled flue gas is passed into a baghouse dust collector to collect bromine-containing dust. The dust is added to a debrominating agent solution with a pH of 8-10 and reacted at 50-70℃ for 1-2 hours to allow 95% of the bromine to migrate to the leaching solution in the form of bromide ions.

[0074] The specific steps for baghouse dust collection and bromide ion leaching in step S3 are as follows:

[0075] S3.1: The flue gas after secondary cooling is introduced into the bag filter at 150°C. The filtration velocity of the bag filter is controlled at 0.8-1.2 m / min and the dust collection efficiency is ≥99%. The dust in the flue gas is collected through the bag filter. The bromine content in the dust is 30-50%. The flue gas after dust collection enters the next step. The dust collected by the bag filter is periodically discharged into the leaching tank.

[0076] S3.2: Prepare a debrominating agent solution with a pH of 8-10. The debrominating agent is a sodium carbonate-sodium hydroxide mixed solution, wherein the sodium carbonate concentration is 5-8 g / L and the sodium hydroxide concentration is 3-5 g / L. After preparation, the solution is introduced into the leaching tank.

[0077] S3.3: Add the flue dust collected by the bag filter to the leaching tank containing the debromination agent solution, start the stirring device, control the stirring rate to 150-200 r / min, and simultaneously stabilize the temperature in the leaching tank at 50-70℃ using the temperature control device. React for 1-2 hours to allow the bromine in the flue dust to react fully, with more than 95% of the bromine migrating into the leachate in the form of bromide ions. After the reaction is completed, the leachate is temporarily stored in the leachate storage tank for subsequent pretreatment steps.

[0078] S4: Two-stage gradient absorption: The flue gas after passing through the bag filter dust collector is passed into the first-stage acidic absorption tower with an inlet temperature ≤160℃ and an outlet temperature ≥80℃. The pH of the absorbent is controlled at 2-3. Then it enters the second-stage alkaline absorption tower with an outlet temperature ≥50℃ and the pH of the absorbent is controlled at 10-12.

[0079] The specific steps of the two-level gradient absorption in step S4 are as follows:

[0080] S4.1: Primary acidic absorption: The flue gas after bag dust collection, containing a small amount of uncollected bromine vapor, is passed into the primary acidic absorption tower. The inlet temperature of the primary absorption tower is controlled to be ≤160℃ and the outlet temperature is ≥80℃. Dilute hydrochloric acid is added to the absorption tower through a pH adjustment device to control the pH of the absorbent at 2-3. The bromine vapor in the flue gas reacts with the acidic absorbent to generate bromide, which enters the absorbent. The absorbent is recycled. When the bromide ion concentration in the absorbent reaches 10-15g / L, it is discharged into the mixing tank.

[0081] S4.2: Secondary alkaline absorption. The flue gas after primary acidic absorption is passed into the secondary alkaline absorption tower. The outlet temperature of the secondary absorption tower is controlled at ≥50℃. Sodium hydroxide solution is added into the absorption tower through a pH adjustment device to control the pH of the absorbent at 10-12, further absorbing the residual bromine vapor and acidic gases in the flue gas to ensure that the flue gas meets the emission standards. The secondary absorbent is recycled. When the bromide ion concentration in the absorbent reaches 8-12 g / L, it is discharged into the mixing tank.

[0082] S5: Bromine salt solution pretreatment: Mix the leachate from step 3 with the absorbent from step 4, add dilute hydrochloric acid or dilute sulfuric acid to adjust the pH to 2.5-3.5, and filter to remove suspended solids;

[0083] The specific steps for the pretreatment of the bromide solution in step S5 are as follows:

[0084] S5.1: Pass the leachate temporarily stored in step S3 and the primary and secondary absorbent solutions discharged in step S4 into the mixing tank, start the stirring device, and make the three solutions fully and evenly mixed.

[0085] S5.2: Add dilute hydrochloric acid or dilute sulfuric acid to the mixing tank through the pH adjustment device, and adjust the pH value of the mixed solution to 2.5-3.5 while stirring, so that the impurity ions in the solution form precipitates;

[0086] S5.3: The pH-adjusted mixed solution is passed into a filter to remove suspended solids and precipitated impurities from the solution. The filtered clear bromide solution is then sent to a pretreatment storage tank for subsequent preheating oxidation steps. The filter residue generated during filtration is collected and then subjected to harmless treatment.

[0087] S6: Preheating oxidation: Preheat the pretreated bromide salt solution to ≥60℃, add 5-10% excess oxidant, and react at 60-90℃ for 30-60 minutes to oxidize 90-95% of the bromide ions to elemental bromide.

[0088] The specific steps of preheating oxidation in step S6 are as follows:

[0089] S6.1: The clarified bromide solution in the pretreatment tank is passed into the preheater to preheat the solution temperature to ≥60℃, and the preheated solution is then passed into the oxidation reaction tank.

[0090] S6.2: Add an oxidant to the oxidation reaction tank. The oxidant is a sodium hypochlorite solution or chlorine gas with an effective chlorine concentration of 10-15%. The amount of oxidant added is 105-110% of the theoretical reaction amount to ensure that the bromide ions are fully oxidized.

[0091] S6.3: Start the stirring device in the oxidation reaction tank and control the stirring rate to 150-200 r / min. At the same time, stabilize the reaction temperature at 60-90℃ using the temperature control device. React for 30-60 minutes, allowing 90-95% of the bromide ions in the solution to be oxidized to elemental bromine. After the reaction is complete, a mixed solution containing elemental bromine is obtained.

[0092] S7: Distillation and condensation separation: The oxidized solution is added to a falling film molecular distillation column, and the distillation temperature is controlled at 65-75℃. The solution is heated by the saturated vapor generated in step S1 to vaporize the free bromine. The mixed vapor generated by vaporization is passed into a condenser to condense into liquid.

[0093] The specific steps of distillation and condensation separation in step S7 are as follows:

[0094] S7.1: Pass the bromine-containing mixed solution after the oxidation reaction into a falling film molecular distillation column, check the sealing of the distillation column, start the vacuum system, and adjust the vacuum degree in the distillation column to 0.08-0.09 MPa;

[0095] S7.2: The saturated vapor generated in step S1 is introduced into the heating jacket of the falling film molecular distillation column at a pressure of 0.8-1.2 MPa. The heat of the saturated vapor is used to heat the solution, and the temperature inside the distillation column is controlled to be stable at 65-75℃. The free bromine in the solution vaporizes under this temperature and vacuum conditions to form bromine vapor. The distillation residence time is controlled to be 15-20 min to ensure that the bromine is fully vaporized.

[0096] S7.3: The bromine vapor produced by distillation is passed into the condenser. The low-temperature brine in the condenser condenses the bromine vapor into liquid. The condensation temperature of the condenser is controlled at 5-10℃ to ensure that the bromine vapor is fully condensed. The condensed liquid enters the centrifugal phase separator.

[0097] S8: Product separation and reflux: The condensed liquid is introduced into a centrifugal phase separator to separate and obtain bromine with a purity ≥99.5%. After filtering to remove trace organic matter, the bromine concentration is detected. If the concentration is >10%, it is refluxed to the distillation tower. If the concentration is low, it is returned to the secondary absorption tower of step S4 as makeup water.

[0098] The specific steps for product separation and reflux in step S8 are as follows:

[0099] S8.1: Centrifugal phase separation. The condensed liquid is introduced into the centrifugal phase separator. The centrifugal phase separator is started and the centrifugal speed is controlled at 3000-4000 r / min. The bromine in the condensed liquid is separated from the water by centrifugal force to obtain a finished bromine with a purity ≥99.5%. The finished bromine is stored in the finished product storage tank. The separated finished bromine is passed through a filter to remove trace organic impurities to ensure that the purity of the finished bromine meets the standard.

[0100] S8.2: The concentration of bromine in the filtered product is detected by a concentration detector. If the bromine concentration is >10%, it is refluxed back to the falling film molecular distillation tower through the reflux pipe for re-distillation and separation to improve the bromine recovery rate. If the bromine concentration is low (≤10%), it is returned to the secondary alkaline absorption tower in step S4 as makeup water through the reflux pipe to achieve the recycling of bromine.

[0101] An embodiment 2 of the present invention provides a bromine recovery system for waste circuit board smelting flue gas containing brominated flame retardants, comprising:

[0102] Molten pool smelting unit: includes molten pool smelting furnace, oxygen-enriched air supply device, natural gas supply device and waste heat boiler; the molten pool smelting furnace is provided with a feed inlet and flue gas outlet at the top and a blower at the bottom. The oxygen-enriched air supply device and natural gas supply device are both connected to the blower through pipelines. The waste heat boiler is connected to the flue gas outlet of the molten pool smelting furnace and is used for cooling high-temperature flue gas and generating saturated steam.

[0103] Flue gas cooling unit: includes a primary tubular heat exchanger and a secondary quench tower. The inlet of the primary tubular heat exchanger is connected to the outlet of the waste heat boiler, and the outlet of the primary tubular heat exchanger is connected to the inlet of the secondary quench tower, used to gradually cool the flue gas to 150°C.

[0104] Baghouse dust collection and leaching unit: includes a baghouse dust collector, a leaching tank and a stirring device; the inlet of the baghouse dust collector is connected to the outlet of the secondary quench tower, the bottom outlet of the baghouse dust collector is connected to the leaching tank, the stirring device is installed in the leaching tank, and the leaching tank is equipped with a debromination agent addition port and a temperature control device.

[0105] The dual-stage gradient absorption unit includes a primary acidic absorption tower and a secondary alkaline absorption tower. The inlet of the primary acidic absorption tower is connected to the flue gas outlet of the bag filter, and the outlet of the primary acidic absorption tower is connected to the inlet of the secondary alkaline absorption tower. Both absorption towers are equipped with a temperature detection device, a pH adjustment device, and an absorbent circulation device.

[0106] Pretreatment unit: includes a mixing tank, a pH adjustment device, and a filter; the inlet of the mixing tank is connected to the outlet of the leaching tank and the absorbent outlet of the secondary alkaline absorption tower, respectively; the pH adjustment device is connected to the mixing tank and is used to add dilute hydrochloric acid or dilute sulfuric acid; the filter is connected to the outlet of the mixing tank.

[0107] Preheating oxidation unit: includes a preheater, an oxidation reaction tank and an oxidant adding device; the inlet of the preheater is connected to the outlet of the filter, the outlet of the preheater is connected to the oxidation reaction tank, the oxidant adding device is connected to the oxidation reaction tank, and the oxidation reaction tank is equipped with a temperature control device and a stirring device;

[0108] Distillation and condensation unit: includes a falling film molecular distillation column and a condenser; the inlet of the falling film molecular distillation column is connected to the outlet of the oxidation reaction tank, the heating medium inlet of the falling film molecular distillation column is connected to the saturated steam outlet of the waste heat boiler, and the inlet of the condenser is connected to the steam outlet of the falling film molecular distillation column.

[0109] Separation and reflux unit: includes a centrifugal phase separator, a filter, a concentration detector, and a reflux pipeline; the inlet of the centrifugal phase separator is connected to the outlet of the condenser, the bottom outlet of the centrifugal phase separator is connected to the filter, the concentration detector is installed on the outlet pipeline of the filter, and the reflux pipeline is connected to the outlet of the concentration detector, the falling film molecular distillation column, and the secondary alkaline absorption column respectively.

[0110] An embodiment 3 of this invention: This embodiment conducts an industrial-scale test on waste circuit boards containing bromine-based flame retardants with a bromine content of 28%, and sets a waste circuit board processing volume. The natural gas purity is ≥95%. The entire system uses a PLC automatic control system to achieve closed-loop adjustment of process parameters. All function formula coefficients are taken according to the optimal operating conditions, and the core coefficients are uniformly set as follows: , , , , , , , , , , , , , , , , , , , , .

[0111] The objectives of this embodiment are: total bromine recovery rate ≥85%, finished bromine purity ≥99.5%, and all process parameters controlled within the patent requirements.

[0112] Step S1: Oxygen-enriched molten pool smelting (application of temperature control formula and closed-loop control algorithm 1)

[0113] Feed preparation: The waste circuit boards containing bromine flame retardants are crushed and screened to control the particle size to ≤100mm and remove large metal impurities. The feed is then continuously fed at a rate of 10t / h.

[0114] Initial parameter settings: target furnace temperature Initial setting of oxygen-enriched air intake volume Natural gas injection volume (The mass ratio of natural gas to feed is 0.1:1, which meets the requirements).

[0115] The furnace pressure is controlled at 0.015 MPa, according to... Calculate the flue gas emission rate, and obtain .

[0116] Temperature closed-loop control (Algorithm 1)

[0117] Parameter acquisition: The PLC acquires data every 10 seconds, initially acquiring the furnace temperature. Calculate the deviation (Temperature too low);

[0118] Parameter adjustment: because Maximum value not reached ,according to Calculate the adjustment amount. ,Will Adjusted to ;

[0119] Feedback Correction: Adjusted furnace temperature collection , ( Maintain parameter stability; verify by substituting into the furnace temperature control formula:

[0120]

[0121] Substituting the values ​​into the equation:

[0122] This meets the target requirements.

[0123] Waste heat recovery: High-temperature flue gas enters the waste heat boiler, generating saturated steam pressure. It is stored in a steam tank for subsequent distillation.

[0124] Step S2: Flue gas cooling (applying formula 5 for cooling rate)

[0125] First-stage cooling: The flue gas temperature at the waste heat boiler is 850℃. It is then introduced into a tubular heat exchanger, and the cooling rate is controlled at 85℃ / min to cool down to 550℃.

[0126] Secondary rapid cooling: target cooling rate flue gas inlet temperature Substituting into the cooling rate formula:

[0127]

[0128] Back-calculation of cooling water spray volume Spray atomized cooling water at this flow rate to rapidly cool the flue gas to 150°C.

[0129] Step S3: Baghouse dust collection and bromide ion leaching (application of leaching rate formula 2 and collaborative control algorithm 2)

[0130] Baghouse dust collector: 150℃ flue gas is introduced into the baghouse dust collector, the filtration velocity is 1.0m / min (0.8-1.2m / min range), the dust collection efficiency is 99.2%, the bromine content in the collected flue gas is 42% (30-50% range), and the flue gas output is 0.8t / h.

[0131] Preparation of debromination agent: Prepare a mixed solution of 6 g / L sodium carbonate and 4 g / L sodium hydroxide, adjust the pH to 9 (8~10℃ range), and introduce it into the leaching tank.

[0132] Bromine ion leaching and Algorithm 2 control

[0133] Initial parameter settings: leaching temperature leaching time With a stirring rate of 180 r / min, substituting into the leaching rate formula:

[0134]

[0135] Calculated If the requirement of ≥95% is not met, the adjustment process will begin.

[0136] Parameter adjustment (in order of priority: temperature → time → pH)

[0137] Increase the temperature to 65℃ and calculate. It still does not meet the standard;

[0138] according to Extend the leaching time, , ,calculate It still does not meet the standard;

[0139] according to Adjust pH, The pH was adjusted to 9.2, the temperature was increased to 68℃, and the time was extended to 2 hours. The final calculations yielded... The requirement of ≥95% must be met.

[0140] Termination of operation: After the leaching rate reaches the standard, the leachate is temporarily stored in a storage tank with a bromide ion concentration of 85 g / L.

[0141] Step S4: Two-level gradient absorption (application of pH and temperature co-control algorithm 3)

[0142] Algorithm 3 is used to automatically adjust the parameters of the primary acidic absorption tower and the secondary alkaline absorption tower. The core objective is to achieve the following: primary... , , Level 2 , .

[0143] Primary acid absorption

[0144] Data collection parameters: , , ;

[0145] Adjustment logic: Reduce cooling medium flow rate Rise to 82℃; according to Calculations show that 0.1 L / h of dilute hydrochloric acid is added, and after adjustment... It meets the requirements;

[0146] Linkage control: When the bromide ion concentration in the absorbent reaches 12 g / L, it is automatically discharged into the mixing tank and replenished with fresh acidic absorbent.

[0147] Secondary alkaline absorption

[0148] Data collection parameters: , ;

[0149] Adjustment logic: Start the heating device to make Rise to 52℃;

[0150] according to Calculations show that 0.12 L / h of sodium hydroxide solution was added, and after adjustment... It meets the requirements;

[0151] Linkage control: When the bromide ion concentration in the absorbent reaches 10 g / L, it is automatically discharged into the mixing tank and replenished with fresh alkaline absorbent.

[0152] Step S5: Pretreatment of Bromine Salt Solution

[0153] The S3 leachate (85 g / L bromide ions) and the S4 two-stage absorbent (total bromide ions 11 g / L) were introduced into a mixing tank and stirred evenly. Then, dilute hydrochloric acid was added to adjust the pH to 3.0. The suspended solids were removed by a plate and frame filter to obtain a clear bromide salt solution. The bromide ion concentration was measured to be 62 g / L and then sent to the preheating oxidation unit.

[0154] Step S6: Preheating oxidation (application of oxidation conversion formula 3)

[0155] Solution preheating: The clear bromide solution is passed into the preheater and preheated to 65℃ (≥60℃) before being sent to the oxidation reaction tank.

[0156] Oxidizing agent addition: A sodium hypochlorite solution with an effective chlorine concentration of 12% was used as the oxidizing agent, and the excess oxidizing agent rate was... The amount added is 108% of the theoretical reaction amount.

[0157] Oxidation reaction: Control the reaction temperature at 75℃ (60-90℃ range), the stirring rate at 180 r / min, and the reaction time at 45 min (30-60℃ range); substitute into the oxidation conversion formula for calculation:

[0158]

[0159] Substitute the values The process requirements are met, and a mixed solution containing bromine is obtained.

[0160] Step S7: Distillation and condensation separation (application of distillation separation rate formula and distillation control algorithm 4)

[0161] Algorithm 4 is used to automatically adjust the parameters of the distillation and condensation system, while saturated steam generated by the S1 waste heat boiler is used for heating to achieve energy recovery.

[0162] Distillation preparation: Pass the oxidized mixed solution into a falling film molecular distillation column, and start the vacuum system to adjust the vacuum level. .

[0163] Steam flow rate adjustment: Distillation solution feed rate Target distillation temperature (65~75℃ range), substituting into the steam flow formula:

[0164]

[0165] Calculated Saturated steam at 1.0 MPa is introduced for heating.

[0166] Distillation parameter adjustment (Algorithm 4)

[0167] collection ,according to Calculations show an increase of 0.02 in steam volume. After adjustment ;

[0168] collection Start the vacuum system to pressurize to 0.085MPa and control the distillation residence time to 18min (15~20min range).

[0169] Distillation separation rate calculation: Substitute into the distillation separation rate formula:

[0170]

[0171] Calculated After adjusting the vacuum level to 0.082 MPa, The requirements are met.

[0172] Condensation and cooling: Adjust the condenser temperature to 8℃ (5~10℃ range) to fully condense the bromine vapor into liquid and send it into the centrifugal phase separator.

[0173] Step S8: Finished Product Separation and Recirculation

[0174] Centrifugal phase separation: Start the centrifugal phase separator and control the rotation speed to 3500 r / min (3000~4000 r / min range). The bromine solution and water are separated by centrifugal force to obtain the finished bromine product with a purity of 99.6% (≥99.5%).

[0175] Impurity filtration and concentration detection: The finished bromine is passed through a precision filter to remove trace organic matter. The bromine concentration is detected to be 12% (>10%). It is then returned to the distillation column for redistillation through the reflux pipe.

[0176] Calculation of total bromine recovery rate: Substitute into the total recovery rate formula:

[0177]

[0178] Substitution , , Calculated ;

[0179] Fine-tuning parameters , , After that, the overall recovery rate The target requirement of ≥85% has been achieved.

[0180] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants, characterized in that, Includes the following steps: S1: Oxygen-enriched molten pool smelting: Waste circuit boards with bromine flame retardants and a particle size ≤100mm are added to the molten pool smelting furnace. High-pressure oxygen-enriched air and natural gas are blown into the melt for stirring and smelting. The furnace temperature is controlled at 1200~1250℃, and the flue gas residence time in the flue gas zone of the furnace is >2 seconds. A waste heat boiler is installed in the furnace to cool down the high-temperature flue gas and generate saturated steam. The treated high-temperature flue gas is discharged from the top of the furnace. S2: Flue gas cooling: The high-temperature flue gas discharged in step 1 is cooled to 150°C through a two-stage cooling device, with the first stage cooling to 550°C and the second stage rapidly cooling to 150°C. S3: Baghouse dust collection and bromide ion leaching: The cooled flue gas is passed into a baghouse dust collector to collect bromine-containing dust. The dust is added to a debrominating agent solution with a pH of 8-10 and reacted at 50-70℃ for 1-2 hours to allow 95% of the bromine to migrate to the leaching solution in the form of bromide ions. S4: Two-stage gradient absorption: The flue gas after passing through the bag filter dust collector is passed into the first-stage acidic absorption tower with an inlet temperature ≤160℃ and an outlet temperature ≥80℃. The pH of the absorbent is controlled at 2-3. Then it enters the second-stage alkaline absorption tower with an outlet temperature ≥50℃ and the pH of the absorbent is controlled at 10-12. S5: Bromine salt solution pretreatment: Mix the leachate from step 3 with the absorbent from step 4, add dilute hydrochloric acid or dilute sulfuric acid to adjust the pH to 2.5-3.5, and filter to remove suspended solids; S6: Preheating oxidation: Preheat the pretreated bromide salt solution to ≥60℃, add 5-10% excess oxidant, and react at 60-90℃ for 30-60 minutes to oxidize 90-95% of the bromide ions to elemental bromide; S7: Distillation and condensation separation: The oxidized solution is added to a falling film molecular distillation column, and the distillation temperature is controlled at 65-75℃. The solution is heated by the saturated vapor generated in step S1 to vaporize the free bromine. The mixed vapor generated by vaporization is passed into a condenser to condense into liquid. S8: Product separation and reflux: The condensed liquid is introduced into a centrifugal phase separator to separate and obtain bromine with a purity of ≥99.5%. After filtering to remove trace organic matter, the bromine concentration is detected. If the concentration is >10%, it is refluxed to the distillation tower. If the concentration is low, it is returned to the secondary absorption tower of step S4 as makeup water.

2. The method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants according to claim 1, characterized in that, The specific steps of oxygen-enriched molten pool smelting in step S1 are as follows: S1.1: The waste circuit boards containing bromine-based flame retardants are crushed and screened to control the particle size of the material to ≤100mm, remove large metal impurities, and ensure uniform feeding. S1.2: The pretreated waste circuit boards are continuously fed into the molten pool furnace through the feed inlet. The oxygen-enriched air supply device and the natural gas supply device are started to blow high-pressure oxygen-enriched air with a pressure of 0.3-0.5MPa and an oxygen concentration of 80-90 vol% into the molten material in the furnace. At the same time, natural gas is blown in. The mass ratio of natural gas to waste circuit board feed is controlled at 0.08-0.12:

1. Through the stirring action of oxygen-enriched air and natural gas, the waste circuit boards and the molten material are fully mixed and reacted. S1.3: The furnace temperature is monitored in real time by an in-furnace temperature sensor, and the amount of oxygen-enriched air and natural gas injected is adjusted to stabilize the furnace temperature at 1200-1250℃; at the same time, the flue gas residence time detection device ensures that the residence time of the flue gas in the flue gas zone of the furnace is >2 seconds, so that the bromine flame retardant in the waste circuit board is fully decomposed and the bromine element enters the flue gas. S1.4: High-temperature flue gas is discharged from the flue gas outlet at the top of the molten pool furnace and enters the waste heat boiler. The waste heat boiler uses the heat of the high-temperature flue gas for heat exchange, cooling the flue gas while generating saturated steam with a pressure of 0.8-1.2MPa. The saturated steam is stored in a steam storage tank and used for heating in subsequent distillation steps. The high-temperature flue gas treated by the waste heat boiler enters the next step.

3. The method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants according to claim 1, characterized in that, The specific steps for flue gas cooling in step S2 are as follows: S2.1: First-stage cooling: The high-temperature flue gas discharged from the waste heat boiler, with a temperature of about 800-900℃, is passed into the first-stage tubular heat exchanger. Heat exchange is carried out through the circulating water in the heat exchanger. The cooling rate is controlled at 80-100℃ / min to reduce the flue gas temperature to 550℃. The cooling medium after heat exchange enters the cooling system for further cooling and is then recycled. S2.2: Secondary Cooling: The flue gas cooled to 550°C after the primary cooling is introduced into the secondary quench tower. Cooling water is sprayed through atomizing nozzles in the quench tower to achieve rapid cooling of the flue gas. The cooling rate is controlled at 6-8°C / s to quickly reduce the flue gas temperature to 150°C, thus preventing the bromine in the flue gas from forming secondary pollutants. The rapidly cooled flue gas carries a small amount of water mist and enters the next step.

4. The method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants according to claim 1, characterized in that, The specific steps for bag dust collection and bromide ion leaching in step S3 are as follows: S3.1: The flue gas after secondary cooling is introduced into the bag filter at 150°C. The filtration velocity of the bag filter is controlled at 0.8-1.2 m / min and the dust collection efficiency is ≥99%. The dust in the flue gas is collected through the bag filter. The bromine content in the dust is 30-50%. The flue gas after dust collection enters the next step. The dust collected by the bag filter is periodically discharged into the leaching tank. S3.2: Prepare a debrominating agent solution with a pH of 8-10. The debrominating agent is a sodium carbonate-sodium hydroxide mixed solution, wherein the sodium carbonate concentration is 5-8 g / L and the sodium hydroxide concentration is 3-5 g / L. After preparation, the solution is introduced into the leaching tank. S3.3: Add the flue dust collected by the bag filter to the leaching tank containing the debromination agent solution, start the stirring device, control the stirring rate to 150-200 r / min, and at the same time stabilize the temperature in the leaching tank at 50-70℃ using the temperature control device. React for 1-2 hours to allow the bromine element in the flue dust to react fully, with more than 95% of the bromine migrating to the leachate in the form of bromide ions. After the reaction is completed, the leachate is temporarily stored in the leachate storage tank for subsequent pretreatment steps.

5. The method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants according to claim 4, characterized in that, The specific steps of the two-level gradient absorption in step S4 are as follows: S4.1: Primary acidic absorption: The flue gas after bag dust collection, containing a small amount of uncollected bromine vapor, is passed into the primary acidic absorption tower. The inlet temperature of the primary absorption tower is controlled to be ≤160℃ and the outlet temperature is ≥80℃. Dilute hydrochloric acid is added to the absorption tower through a pH adjustment device to control the pH of the absorbent at 2-3. The bromine vapor in the flue gas reacts with the acidic absorbent to generate bromide, which enters the absorbent. The absorbent is recycled. When the bromide ion concentration in the absorbent reaches 10-15g / L, it is discharged into the mixing tank. S4.2: Secondary alkaline absorption. The flue gas after primary acidic absorption is passed into the secondary alkaline absorption tower. The outlet temperature of the secondary absorption tower is controlled at ≥50℃. Sodium hydroxide solution is added into the absorption tower through a pH adjustment device to control the pH of the absorbent at 10-12, further absorbing the residual bromine vapor and acidic gases in the flue gas to ensure that the flue gas meets the emission standards. The secondary absorbent is recycled. When the bromide ion concentration in the absorbent reaches 8-12 g / L, it is discharged into the mixing tank.

6. The method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants according to claim 1, characterized in that, The specific steps for the pretreatment of the bromide solution in step S5 are as follows: S5.1: Pass the leachate temporarily stored in step S3 and the primary and secondary absorbent solutions discharged in step S4 into the mixing tank, start the stirring device, and make the three solutions fully and evenly mixed. S5.2: Add dilute hydrochloric acid or dilute sulfuric acid to the mixing tank through the pH adjustment device, and adjust the pH value of the mixed solution to 2.5-3.5 while stirring, so that the impurity ions in the solution form precipitates; S5.3: The pH-adjusted mixed solution is passed into a filter to remove suspended solids and precipitated impurities. The filtered clear bromide solution is then sent to a pretreatment storage tank for subsequent preheating oxidation steps. The filter residue is collected and disposed of in a harmless manner.

7. The method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants according to claim 1, characterized in that, The specific steps of preheating oxidation in step S6 are as follows: S6.1: The clarified bromide solution in the pretreatment tank is passed into the preheater to preheat the solution temperature to ≥60℃, and the preheated solution is then passed into the oxidation reaction tank. S6.2: Add an oxidant to the oxidation reaction tank. The oxidant is a sodium hypochlorite solution or chlorine gas with an effective chlorine concentration of 10-15%. The amount of oxidant added is 105-110% of the theoretical reaction amount to ensure that the bromide ions are fully oxidized. S6.3: Start the stirring device in the oxidation reaction tank and control the stirring rate to 150-200 r / min. At the same time, stabilize the reaction temperature at 60-90℃ using the temperature control device. React for 30-60 minutes to oxidize 90-95% of the bromide ions in the solution to elemental bromine. After the reaction is completed, a mixed solution containing elemental bromine is obtained.

8. The method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants according to claim 1, characterized in that, The specific steps of distillation and condensation separation in step S7 are as follows: S7.1: Pass the bromine-containing mixed solution after the oxidation reaction into a falling film molecular distillation column, check the sealing of the distillation column, start the vacuum system, and adjust the vacuum degree in the distillation column to 0.08-0.09 MPa; S7.2: The saturated vapor generated in step S1 is introduced into the heating jacket of the falling film molecular distillation column at a pressure of 0.8-1.2 MPa. The heat of the saturated vapor is used to heat the solution, and the temperature inside the distillation column is controlled to be stable at 65-75℃. The free bromine in the solution vaporizes under this temperature and vacuum conditions to form bromine vapor. The distillation residence time is controlled to be 15-20 min to ensure that the bromine is fully vaporized. S7.3: The bromine vapor produced by distillation is passed into the condenser, where the low-temperature brine condenses the bromine vapor into liquid. The condensation temperature of the condenser is controlled at 5-10℃ to ensure that the bromine vapor is fully condensed. The condensed liquid then enters the centrifugal phase separator.

9. The method for recovering bromine from the smelting flue gas of waste circuit boards containing brominated flame retardants according to claim 1, characterized in that, The specific steps for product separation and reflux in step S8 are as follows: S8.1: Centrifugal phase separation. The condensed liquid is introduced into the centrifugal phase separator. The centrifugal phase separator is started and the centrifugal speed is controlled at 3000-4000 r / min. The bromine in the condensed liquid is separated from the water by centrifugal force to obtain a finished bromine with a purity ≥99.5%. The finished bromine is stored in the finished product storage tank. The separated finished bromine is passed through a filter to remove trace organic impurities to ensure that the purity of the finished bromine meets the standard. S8.2: The concentration of bromine in the filtered product is detected by a concentration detector. If the bromine concentration is >10%, it is refluxed back to the falling film molecular distillation tower through the reflux pipe for re-distillation and separation to improve the bromine recovery rate. If the bromine concentration is low (≤10%), it is returned to the secondary alkaline absorption tower in step S4 as makeup water through the reflux pipe to achieve the recycling of bromine.

10. A system for recovering bromine from the smelting flue gas of bromine-based flame retardant waste circuit boards using the method described in any one of claims 1-9, characterized in that, include: Molten pool smelting unit: includes molten pool smelting furnace, oxygen-enriched air supply device, natural gas supply device and waste heat boiler; the molten pool smelting furnace is provided with a feed inlet and flue gas outlet at the top and a blower at the bottom. The oxygen-enriched air supply device and natural gas supply device are both connected to the blower through pipelines. The waste heat boiler is connected to the flue gas outlet of the molten pool smelting furnace and is used for cooling high-temperature flue gas and generating saturated steam. Flue gas cooling unit: includes a primary tubular heat exchanger and a secondary quench tower. The inlet of the primary tubular heat exchanger is connected to the outlet of the waste heat boiler, and the outlet of the primary tubular heat exchanger is connected to the inlet of the secondary quench tower, used to gradually cool the flue gas to 150°C. Baghouse dust collection and leaching unit: includes a baghouse dust collector, a leaching tank and a stirring device; the inlet of the baghouse dust collector is connected to the outlet of the secondary quench tower, the bottom outlet of the baghouse dust collector is connected to the leaching tank, the stirring device is installed in the leaching tank, and the leaching tank is equipped with a debromination agent addition port and a temperature control device. The dual-stage gradient absorption unit includes a primary acidic absorption tower and a secondary alkaline absorption tower. The inlet of the primary acidic absorption tower is connected to the flue gas outlet of the bag filter, and the outlet of the primary acidic absorption tower is connected to the inlet of the secondary alkaline absorption tower. Both absorption towers are equipped with a temperature detection device, a pH adjustment device, and an absorbent circulation device. Pretreatment unit: includes a mixing tank, a pH adjustment device, and a filter; the inlet of the mixing tank is connected to the outlet of the leaching tank and the absorbent outlet of the secondary alkaline absorption tower, respectively; the pH adjustment device is connected to the mixing tank and is used to add dilute hydrochloric acid or dilute sulfuric acid; the filter is connected to the outlet of the mixing tank. Preheating oxidation unit: includes a preheater, an oxidation reaction tank and an oxidant adding device; the inlet of the preheater is connected to the outlet of the filter, the outlet of the preheater is connected to the oxidation reaction tank, the oxidant adding device is connected to the oxidation reaction tank, and the oxidation reaction tank is equipped with a temperature control device and a stirring device; Distillation and condensation unit: includes a falling film molecular distillation column and a condenser; the inlet of the falling film molecular distillation column is connected to the outlet of the oxidation reaction tank, the heating medium inlet of the falling film molecular distillation column is connected to the saturated steam outlet of the waste heat boiler, and the inlet of the condenser is connected to the steam outlet of the falling film molecular distillation column. Separation and reflux unit: includes a centrifugal phase separator, a filter, a concentration detector, and a reflux pipeline; the inlet of the centrifugal phase separator is connected to the outlet of the condenser, the bottom outlet of the centrifugal phase separator is connected to the filter, the concentration detector is installed on the outlet pipeline of the filter, and the reflux pipeline is connected to the outlet of the concentration detector, the falling film molecular distillation column, and the secondary alkaline absorption column respectively.

Images