A method and system for pyrolysis recycling of mobile phone circuit boards

Abstract

A method and system for pyrolysis recovery of mobile phone circuit boards, comprising the following steps: conveying the mobile phone circuit boards to a rotary kiln; providing the rotary kiln with multiple heating sections, which are arranged in series, a preheating section before the heating section, and a cooling section after the heating section, wherein the preheating section, the multiple heating sections, and the cooling section are sequentially arranged in series, and the flow direction of high-temperature pyrolysis gas is opposite to the movement direction of the mobile phone circuit boards. The high-temperature pyrolysis gas flows in the feed direction, contacts the circuit boards for heat exchange in the preheating section, and then enters a spiral feeder from the feed port of the rotary kiln. After cooling, the high-temperature pyrolysis gas enters a pyrolysis gas heating unit from the exhaust port in the middle of the spiral feeder; in the pyrolysis gas heating unit, the pyrolysis gas is heated to 400-600°C and dusted at high temperature. The dust-free pyrolysis gas is further condensed and incinerated; the pyrolysis residue is output from the cooling section of the rotary kiln for crushing and screening to separate metal recyclables.

Description

Technical Field

[0001] This invention relates to the field of waste electronic product recycling technology, and in particular to a method and system for pyrolysis recycling of mobile phone circuit boards. Background Technology

[0002] As an important component of electronic waste, discarded circuit boards contain a variety of heavy metals and harmful substances such as lead, cadmium, polyvinyl chloride plastic, and brominated flame retardants, posing a potential environmental pollution problem. On the other hand, they also contain a variety of common and rare precious metals such as copper, nickel, gold, and silver, giving them high recycling value.

[0003] With increasing demands for environmental protection, the recycling and utilization of electronic waste has become a thorny issue for most countries. Printed circuit boards (PCBs), as key components in discarded household appliances, have become a pressing issue requiring urgent attention in terms of recycling and resource recovery.

[0004] Effective treatment and recycling of scrapped circuit boards can significantly reduce the consumption of primary resources and mitigate environmental pollution. This plays a positive role and is of great significance for building a resource-saving and environmentally friendly society and developing a circular economy.

[0005] The main processing technologies for mobile phone circuit boards are: pyrometallurgy, hydrometallurgy, and physical methods.

[0006] Pyrometallurgical extraction of precious metals is simple, convenient and efficient, but it also has disadvantages such as secondary pollution caused by the generation of harmful gases during the incineration of organic matter, low metal recovery rate and expensive processing equipment.

[0007] Hydrometallurgy is a commonly used technique for extracting precious metals from waste electronic products. The basic principle of hydrometallurgy is to utilize the solubility of precious metals in nitric acid and aqua regia to remove them from waste circuit boards and recover them from the liquid phase. Compared to pyrometallurgy, hydrometallurgy emits relatively less waste gas and the residue after precious metal extraction is easier to treat. However, it generates a large amount of waste liquid, and the treatment process for this waste liquid is complex and costly. This poses a potential threat to the environment.

[0008] Physical processing methods mainly include technologies such as mechanical crushing, air separation, and magnetic adsorption. Currently, physical processing methods are primarily used for the recovery of metals such as aluminum and copper. For example, the United States uses high-powered cyclone separators to recover aluminum from PC PCBs. By controlling the feed rate, the purity of the obtained aluminum is 85%, and the recovery rate is over 90%. Sweden uses electric drum electrostatic separators to recover copper. By optimizing operating parameters, the grade of the obtained copper is 93%–99%, and the recovery rate reaches 95%–99%. However, there are problems such as significant loss of precious metals during physical recycling and the difficulty in resource recovery of non-metallic resin powder.

[0009] The existing rotary kiln pyrolysis process for circuit boards has the following main problems:

[0010] 1. During the continuous tumbling of pyrolysis products inside the rotary kiln, and the process of pyrolysis residue falling from the top of the rotary kiln, a large number of small particles do not easily fall and are easily carried by the pyrolysis gas to the pyrolysis gas treatment system outside the kiln. During the purification and condensation process of the pyrolysis gas, pyrolysis oil will condense and precipitate when the temperature drops. This oil easily adheres to the inner surface of equipment or pipelines. When it adsorbs and captures particles in the pyrolysis gas, it will form sludge. As the pyrolysis time prolongs, it may cause blockage of pipelines and condensers.

[0011] 2. Precious metals, such as gold, in mobile phone circuit boards often exist as plating layers, typically less than 0.1µm thick. After pyrolysis, these easily form tiny gold-containing ash particles. During pyrolysis, these ash particles are easily carried into the exhaust gas system by the pyrolysis gas flow. There, they are adsorbed by tar on the inner walls of the piping system, turning into sludge that is difficult to recover, resulting in losses. Therefore, existing rotary kiln pyrolysis systems for circuit boards cannot achieve long-term stable operation, nor can they obtain high recovery rates for precious metals such as gold and silver. Summary of the Invention

[0012] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the present invention provides a pyrolysis recovery system and method for mobile phone circuit boards, aiming to solve the problems of easy coking and pipeline blockage caused by existing pyrolysis gas treatment systems and low precious metal recovery efficiency.

[0013] Technical solution: A method for pyrolytic recycling of mobile phone circuit boards, comprising the following steps:

[0014] Circuit board feeding and pyrolysis;

[0015] The mobile phone circuit boards are continuously fed into the rotary kiln via the feeding unit. The rotary kiln rotates, pushing the circuit boards from the feed inlet towards the discharge direction while simultaneously heating them to the pyrolysis temperature to begin pyrolysis. Pyrolysis is completed within the specified time within the kiln. The pyrolysis gas generated during the pyrolysis process is drawn from the feed inlet at the kiln head by a pyrolysis gas induced draft fan and enters the screw feeder. The gas pressure inside the rotary kiln is controlled to be slightly negative by adjusting the draft speed. The pyrolysis residue is discharged from the slag outlet at the kiln tail and enters the discharge unit.

[0016] The temperature of the preheating section is 400–500°C, and the temperature of the cooling section is 500–600°C.

[0017] The pyrolysis temperature of the circuit board is controlled at 600–800°C.

[0018] The time the circuit board spends in the rotary kiln is controlled to be 30 to 60 minutes.

[0019] The pressure of the pyrolysis gas inside the rotary kiln is controlled at a slight negative pressure of -50 to 0 Pa.

[0020] The temperature of the pyrolysis residue discharged from the rotary kiln slag outlet is 500–600°C.

[0021] The temperature of the pyrolysis gas leaving the rotary kiln feed inlet is 400–500°C.

[0022] The mobile phone circuit board is fed into the rotary kiln through a hopper, a feeder, and a screw feeder. The hopper, feeder, and screw feeder are sealed and transported, and nitrogen is injected into the hopper to maintain a slight positive pressure.

[0023] Discharge and treatment of pyrolysis residue from circuit boards

[0024] The pyrolysis residue discharged from the rotary kiln slag discharge port enters the screw conveyor through the feeding valve. Driven by the screw conveyor, it is fed into the pyrolysis residue storage tank. Cooling water at 20-40°C is circulated through the jacket of the screw conveyor to cool the pyrolysis residue at 500-600°C to 200-300°C. At the same time, nitrogen gas is introduced into the pyrolysis residue storage tank to maintain a slight positive pressure of 0-10 kPa.

[0025] Extraction and treatment of pyrolysis gas from circuit boards

[0026] Under the action of the induced draft fan, high-temperature pyrolysis gas enters the screw feeder from the rotary kiln inlet. Circulating cooling water at 20–40°C is introduced into the screw feeder jacket to further cool the pyrolysis gas to 200–300°C. The condensed pyrolysis oil is then returned to the rotary kiln along with the circuit board. The oil-removed pyrolysis gas enters the induced draft distributor from the exhaust port in the middle of the screw feeder.

[0027] The induced draft diverter divides the pyrolysis gas into two parts: one part (first pyrolysis gas) is mixed with an appropriate amount of air and then subjected to oxygen-deficient combustion to produce high-temperature flue gas at 900-1200°C. This flue gas is then mixed with the other part (second pyrolysis gas) from the induced draft diverter. The temperature of the mixed gas rises to 400-600°C and is then sent to a dust collector for dust removal at high temperature. The dust-removed pyrolysis gas enters a condenser for further cooling and pyrolysis oil is precipitated. The non-condensable pyrolysis gas is transported by a fan to an incinerator for high-temperature incineration. The flue gas produced by incineration is purified and then discharged in compliance with standards.

[0028] Among them, the oxygen-deficient combustion of pyrolysis gas means controlling the input air volume to be 70-90% of the theoretical air requirement for the combustion of the first pyrolysis gas (the air volume required for the stoichiometric combustion of pyrolysis gas), and controlling the residual oxygen concentration in the flue gas to be no more than 1%.

[0029] Among them, the pyrolysis gas dust removal method can be any one of cyclone dust removal, electrostatic dust removal, bag dust removal, or any combination thereof.

[0030] The process involves using circulating cooling water at 20–40°C to cool the dust-removed pyrolysis gas to below 50°C, collecting the condensed pyrolysis oil, and then sending the non-condensable pyrolysis gas into the waste gas treatment area. The condensation of the pyrolysis gas involves introducing circulating cooling water at 20–40°C into the condenser to cool the pyrolysis gas to 30–50°C, causing the pyrolysis oil to precipitate.

[0031] In the waste gas treatment area, pyrolysis gas is introduced into the incinerator for combustion, and the combustion temperature is controlled to be no less than 1100°C and the residence time is no less than 2 seconds. The waste gas after combustion is purified and discharged in compliance with standards.

[0032] For the combustion of non-condensable pyrolysis gas, the combustion temperature of the non-condensable gas shall be controlled at not less than 1100°C and the residence time shall be not less than 2 seconds.

[0033] This patented technical solution discloses a circuit board pyrolysis system, including a feeding unit, a pyrolysis unit, a discharging unit, a pyrolysis gas heating unit, a dust removal unit, a condensation unit, and a pyrolysis gas combustion unit.

[0034] Feeding Unit: Includes a hopper, feeder, screw feeder, and its piping system. The lower outlet of the hopper is connected to the inlet of the feeder, the outlet of the feeder is connected to the inlet of the screw feeder, and the outlet of the screw feeder is connected to the inlet of the rotary kiln. An exhaust port is located in the middle of the screw feeder, and this gas discharge is connected to the pyrolysis gas heating unit. The circuit board enters the screw feeder from the outlet of the hopper via the feeder and is driven into the rotary kiln by the screw. High-temperature pyrolysis gas from the rotary kiln enters from the outlet of the screw feeder and comes into countercurrent contact with the circuit board inside the screw feeder. Circulating cooling water at 20-40°C is introduced into the jacket of the screw feeder. After the pyrolysis gas is cooled to 200-300°C inside the screw feeder, it flows out from the exhaust port in the middle of the screw feeder and enters the pyrolysis heating unit. After the circuit board is added to the silo, it is sealed with a cover plate, and nitrogen is introduced into the silo to maintain a slight positive pressure of 0-10 kPa (gauge pressure) to prevent pyrolysis gas from entering the silo and also to prevent outside air from entering the system. The introduced nitrogen gas merges with the pyrolysis gas from the exhaust port in the middle of the screw feeder and then enters the pyrolysis gas heating unit.

[0035] The pyrolysis unit includes a rotary kiln, an electric heating system, and a drive motor.

[0036] The rotary kiln body is tilted at a certain angle so that the feed inlet (head) is higher than the discharge outlet (tail), and the tilt angle is adjustable between 0 and 5 degrees. A motor drives the kiln body to rotate, with a speed adjustable between 2 and 20 r / min. Inside the rotary kiln, the circuit board tumbles as the kiln rotates and moves in a spiral direction from the kiln head towards the discharge direction at the kiln tail. The flow direction of the pyrolysis gas is opposite to the movement direction of the circuit board.

[0037] The pressure of the pyrolysis gas inside the furnace is controlled between -50 and 0 Pa by adjusting the speed of the pyrolysis gas induced draft fan. By adjusting the tilt angle of the rotary furnace and the rotation speed of the furnace body, the residence time of the circuit board in the rotary furnace can be controlled between 30 and 60 minutes.

[0038] The rotary kiln is equipped with electric heating blocks outside the furnace body. Depending on the heating temperature and control requirements of the furnace body, the furnace chamber is divided into six sections:

[0039] The first section is the preheating section. No electric heating blocks are installed in this section. The high-temperature pyrolysis gas generated during the pyrolysis process is used to preheat the circuit board. After preheating, the circuit board is heated to 400-500°C.

[0040] The second to fifth sections are the heating sections of the pyrolysis furnace, where electric heating blocks are installed to heat the furnace body. The preheated circuit boards are further heated to and maintained at 600-800°C in the heating sections.

[0041] The sixth section is the pyrolysis residue cooling section. This section is not equipped with electric heating blocks and uses air to dissipate heat and cool the furnace wall. After the circuit board pyrolysis residue passes through the cooling section, the temperature drops to 500-600°C.

[0042] The pyrolysis gas heating unit includes an induced draft fan distributor, a burner, and a gas pipeline mixer. The exhaust port in the middle of the screw feeder is connected to the inlet of the induced draft fan distributor. The first outlet of the induced draft fan distributor is connected to the inlet of the burner. The flue gas outlet of the burner is connected to one inlet of the gas pipeline mixer. The second outlet of the induced draft fan distributor is connected to the other inlet of the gas pipeline mixer. The outlet of the pipeline mixer is connected to the gas inlet of the dust collector. To maintain a relatively constant temperature of the pyrolysis gas flowing through the pipelines and equipment, sufficient insulation and high-temperature steam heating are installed outside the pipelines and equipment.

[0043] The induced draft splitter divides the pyrolysis gas into first pyrolysis gas and second pyrolysis gas. After the first pyrolysis gas is mixed with air, it enters the burner to complete oxygen-deficient combustion at 900-1200°C, controlling the residual oxygen concentration in the flue gas to be no more than 1%. The high-temperature flue gas generated by combustion is mixed with the second pyrolysis gas in the gas pipeline mixer, controlling the temperature of the mixed gas to reach 400-600°C.

[0044] Dust collection unit: Includes a dust collector, dust storage tank, etc. The dust collector inlet is connected to the outlet of the pipeline mixer, and the dust collector gas outlet is connected to the gas inlet of the pyrolysis gas condenser. The dust separated by the dust collector is collected in the dust storage tank. The dust collector can be any one of a cyclone dust collector, electrostatic precipitator, or bag filter, or any combination thereof. The inlet gas temperature of the dust collector is controlled to be no less than 400°C, and the outlet gas temperature is controlled to be no less than 300°C. To maintain a relatively constant temperature of the pyrolysis gas flowing through the pipelines and equipment, sufficient insulation and high-temperature steam heating are installed on the outside of the pipelines and equipment.

[0045] Condensation Unit: The pyrolysis gas condensation unit consists of a condenser, an oil storage tank, and a circulating cooling water system. The gas inlet of the condenser is connected to the gas outlet of the dust collector, and the gas outlet of the condenser is conveyed to the pyrolysis gas incineration unit by an induced draft fan. Circulating cooling water at 20–40°C is introduced into the condenser jacket to cool the pyrolysis gas to 30–50°C. The condensed pyrolysis oil is collected in the oil storage tank, while the non-condensable pyrolysis gas is sent to the waste gas incineration unit.

[0046] Non-condensable gas incineration unit: The incineration unit includes an induced draft fan, a burner, and a flue gas purifier. The inlet of the induced draft fan is connected to the gas outlet of the pyrolysis gas condenser, and the outlet of the induced draft fan is connected to the gas inlet of the burner. The flue gas generated during incineration is connected to the inlet of the flue gas purifier. The non-condensable pyrolysis gas from the condensation unit is mixed with air and then fully combusted in the burner, with the combustion temperature controlled at no less than 1100°C and the residence time at no less than 2 seconds. The flue gas is purified to meet emission standards.

[0047] The discharge unit consists of a rotary feeder, a screw conveyor, and a residue storage tank. The feeder inlet is connected to the slag discharge port at the tail of the rotary kiln, the feeder outlet is connected to the screw conveyor inlet, and the screw conveyor outlet is connected to the storage tank inlet. Pyrolysis residue enters the screw conveyor from the rotary kiln slag discharge port via the feeder, and then enters the residue storage tank under the propulsion of the screw. Circulating cooling water at 20–40°C is introduced into the screw conveyor jacket to cool the pyrolysis residue, controlling the temperature of the cooled pyrolysis residue to 200–300°C. The discharge system is a sealed system. To prevent pyrolysis gas from entering the discharge system and to prevent outside air from entering, nitrogen is introduced into the residue storage tank to maintain a slight positive pressure of 1–10 kPa. The introduced nitrogen passes through the screw feeder and the feeder, and then enters the rotary kiln again from the slag discharge port at the tail of the rotary kiln to merge with the pyrolysis gas. Beneficial effects

[0048] The system and method of this invention enable the pyrolysis treatment of mobile phone circuit boards, allowing for complete pyrolysis and recycling. Pre-pyrolysis of the circuit boards eliminates the need for crushing, reducing dust generation and precious metal loss. Therefore, the system of this invention achieves a higher precious metal recovery rate when processing waste mobile phone circuit boards. Compared with existing pyrolysis systems, other advantages of this invention are as follows:

[0049] 1. By controlling the temperature and residence time of each heating section in the rotary furnace, the full pyrolysis of the mobile phone circuit board can be achieved;

[0050] 2. To prevent pyrolysis oil precipitation during the dust removal process, which could cause pipeline blockage, this invention employs a scheme of first cooling the pyrolysis gas to remove oil, and then heating it up to remove dust. The high-temperature pyrolysis gas from the rotary kiln is cooled to 200–300°C in a water-cooled screw feeder, thus effectively separating the tar with a boiling point above 300°C. Subsequently, by maintaining the pyrolysis gas temperature at no less than 300°C during the dust removal process, the precipitation of pyrolysis oil can be effectively avoided. This effectively solves the problem of blockage caused by coking in the dust removal and condensation pipelines.

[0051] 3. To heat the pyrolysis gas, this invention uses high-temperature flue gas generated from the anoxic combustion of a portion of the pyrolysis gas to raise its temperature. This not only avoids additional fuel requirements but also prevents residual oxygen by employing anoxic combustion, ensuring system safety. Furthermore, the carbon monoxide formed during the anoxic combustion process can be utilized in subsequent pyrolysis gas combustion treatment.

[0052] 4. This patent uses the heat generated by the combustion of a portion of the pyrolysis gas to heat the pyrolysis gas. Because some air is introduced, the total gas flow rate in the dust removal process is increased, and the gas temperature is higher. Therefore, the airflow speed in the dust removal process is faster, which is beneficial to improving the dust removal effect of the cyclone separator.

[0053] 5. To prevent outside air from entering the pyrolysis system, the present invention fills the mobile phone circuit board silo and pyrolysis residue storage tank with nitrogen to maintain positive pressure. This not only prevents external oxygen from entering the system, but also prevents pyrolysis gas from entering the silo and residue storage tank, thus avoiding pyrolysis gas leakage. Attached Figure Description

[0054] Figure 1 This is a flowchart of the processing of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0056] It should be noted that the descriptions involving "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0057] The dimensions and composition of the mobile phone circuit board used in the implementation process are as follows:

[0058] The waste mobile phone circuit boards used for pyrolysis were all smaller than 10cm × 20cm. The weight loss rate of the circuit boards, measured by thermogravimetric analysis at 10°C / min and nitrogen atmosphere, was 36.98% (final temperature 800°C). After the circuit boards were crushed and dissolved into a solution, elemental analysis showed that the waste circuit boards contained 22.50% copper, 5.62% tin, 0.61% lead, 4.88% nickel, and 0.11% gold.

[0059] Example 1

[0060] The operating parameters of the rotary kiln during the pyrolysis process are controlled as follows: the tilt angle of the rotary kiln is adjusted to 2 degrees, the rotation speed of the rotary kiln is adjusted to 10 r / min, the temperature of the preheating section is 400°C, the temperature of the heating section is 600°C, the temperature of the cooling section is 500°C, and the pressure of the pyrolysis gas in the furnace fluctuates between -40 and -10 Pa (gauge pressure).

[0061] Operating parameters of the feeding unit: Mobile phone circuit board feed flow rate 200 kg / h, cooling water inlet temperature of the screw feeder 20°C, pyrolysis gas inlet flow rate of 68 kg / h and temperature of 400°C at the screw feeder outlet, and pyrolysis gas outlet flow rate of 54 kg / h and temperature of 200°C at the middle exhaust port of the screw feeder. Nitrogen pressure in the hopper fluctuates between 1 and 2 kPa (gauge pressure).

[0062] Operating parameters of the discharge unit: The flow rate of the residue entering the discharge unit is 139 kg / h and the temperature is 500°C. The inlet temperature of the cooling water for the screw feeder is 20°C. The temperature of the pyrolysis residue leaving the screw feeder is 200°C. The nitrogen pressure in the pyrolysis residue storage tank is maintained between 1 and 2 kPa (gauge pressure).

[0063] Operating parameters of the pyrolysis gas heating unit: air input is 90% of the theoretical air requirement; the flue gas temperature produced by the combustion of the first pyrolysis gas is 1200°C; the oxygen content in the flue gas is 0.8%; and the temperature of the gas after mixing the flue gas with the second pyrolysis gas is 600°C.

[0064] Dust removal unit operating parameters: A two-stage cyclone dust collector is used. The gas inlet temperature of the cyclone separator is 600°C, and the particulate matter content in the inlet gas is 2200 mg / Nm3. The gas outlet temperature of the cyclone distributor is 550°C, and the particulate matter content in the outlet gas is 170 mg / Nm3. The dust removal efficiency is 92.27%, and the average dust separation rate is 350 g / h.

[0065] The operating process parameters of the condensation unit are as follows: condenser inlet gas temperature is 550°C, condenser outlet non-condensable gas temperature is 40°C, cooling water inlet temperature is 20°C, and pyrolysis oil production is 15 kg / h.

[0066] Operating parameters of the pyrolysis gas incineration unit: incineration temperature 1100°C, residence time 2 seconds. The exhaust gas after combustion is purified to meet emission standards before being discharged.

[0067] The weight loss rate of the pyrolysis residue, determined by thermogravimetric analysis, was 0.34%. Following the calculation method provided in the "Requirements for the Treatment and Disposal of Waste Circuit Boards (GB-T44157-2024)," the pyrolysis rate of the circuit board was calculated to be 99.08%. Elemental analysis of the residue and dust obtained from the dust collector showed that the recovery rates were 99.6% for gold, 98.68% for copper, 91.69% for tin, 90.08% for lead, and 98.69% for nickel.

[0068] Example 2

[0069] The operating parameters of the rotary kiln during the pyrolysis process are controlled as follows: the tilt angle of the rotary kiln is adjusted to 2 degrees, the rotation speed of the rotary kiln is adjusted to 10 r / min, the temperature of the preheating section is 400°C, the temperature of the heating section is 600°C, the temperature of the cooling section is 500°C, and the pressure of the pyrolysis gas in the furnace fluctuates between -40 and -10 Pa (gauge pressure).

[0070] Operating parameters of the feeding unit: Mobile phone circuit board feed flow rate 200 kg / h, cooling water inlet temperature of the screw feeder 40°C, pyrolysis gas inlet flow rate of 68 kg / h and temperature of 400°C at the screw feeder outlet, and pyrolysis gas outlet flow rate of 56 kg / h and temperature of 300°C at the exhaust port in the middle of the screw feeder outlet. Nitrogen pressure in the hopper fluctuates between 1 and 2 kPa (gauge pressure).

[0071] Operating parameters of the discharge unit: The flow rate of the residue entering the discharge unit is 139 kg / h and the temperature is 500°C. The inlet temperature of the cooling water for the screw feeder is 20°C. The temperature of the pyrolysis residue leaving the screw feeder is 200°C. The nitrogen pressure in the pyrolysis residue storage tank is maintained between 1 and 5 kPa (gauge pressure).

[0072] Operating parameters of the pyrolysis gas heating unit: the air addition is 70% of the theoretical air requirement, the flue gas temperature produced by the combustion of the first pyrolysis gas is 900°C, the oxygen content in the flue gas produced by combustion is 0.4%, and the temperature of the gas after the flue gas and the second pyrolysis gas are mixed is 400°C.

[0073] Dust collection unit operating parameters: Baghouse dust collector is used. The gas inlet temperature is 400°C, with a particulate matter content of 1900 mg / Nm³. The gas outlet temperature is 300°C, with a particulate matter content of 50 mg / Nm³. The dust collection efficiency is 97%, and the average dust separation rate is 380 g / h.

[0074] The operating parameters of the condensation unit are as follows: the condenser inlet gas temperature is 400°C, the condenser outlet non-condensable gas temperature is 30°C, the cooling water inlet temperature is 20°C, and the pyrolysis oil production rate is 16 kg / h.

[0075] Operating parameters of the pyrolysis gas incineration unit: incineration temperature 1100°C, residence time 2 seconds. The exhaust gas after combustion is purified to meet emission standards before being discharged.

[0076] The weight loss rate of the pyrolysis residue, determined by thermogravimetric analysis, was 0.37%. Following the calculation method provided in the "Requirements for the Treatment and Disposal of Waste Circuit Boards (GB-T44157-2024)," the pyrolysis rate of the circuit board was calculated to be 99%. Elemental analysis of the pyrolysis residue and dust obtained from the dust collector showed that the recovery rates were 99.2% for gold, 97.29% for copper, 90.32% for tin, 90.0% for lead, and 97.29% for nickel.

[0077] Example 3

[0078] The operating parameters of the rotary kiln during the pyrolysis process are controlled as follows: the tilt angle of the rotary kiln is adjusted to 5 degrees, the rotation speed of the rotary kiln is adjusted to 20 r / min, the temperature of the preheating section is 500°C, the temperature of the heating section is 800°C, the temperature of the cooling section is 600°C, and the pressure of the pyrolysis gas in the furnace fluctuates between -30 and -10 Pa (gauge pressure).

[0079] Operating parameters of the feeding unit: Mobile phone circuit board feed flow rate 200 kg / h, cooling water inlet temperature of the screw feeder 20°C, pyrolysis gas inlet flow rate of 69 kg / h and temperature of 500°C at the screw feeder outlet, and pyrolysis gas outlet flow rate of 57 kg / h and temperature of 300°C at the middle exhaust port of the screw feeder. Nitrogen pressure in the hopper fluctuates between 1 and 5 kPa (gauge pressure).

[0080] Operating parameters of the pyrolysis gas heating unit: the air addition is 70% of the theoretical air requirement, the temperature of the flue gas produced by the combustion of the first pyrolysis gas is 1200°C, the oxygen content in the flue gas produced by combustion is 0.2%, and the temperature of the gas after the flue gas and the second pyrolysis gas are mixed is 600°C.

[0081] Operating parameters of the discharge unit: The flow rate of the residue entering the discharge unit is 137 kg / h and the temperature is 600°C. The inlet temperature of the cooling water for the screw feeder is 20°C. The temperature of the pyrolysis residue leaving the screw feeder is 300°C. The nitrogen pressure in the pyrolysis residue storage tank is maintained between 1 and 6 kPa (gauge pressure).

[0082] Dust removal unit operating parameters: A single-stage cyclone dust collector is used in series with a single-stage electrostatic precipitator. The gas inlet temperature of the cyclone separator is 600°C, and the particulate matter content in the inlet gas is 2380 mg / Nm3. The gas outlet temperature of the cyclone distributor is 590°C, and the particulate matter content in the outlet gas is 150 mg / Nm3. The dust removal efficiency is 93.70%, and the average dust separation rate is 362 g / h.

[0083] The condensation unit's operating parameters are as follows: condenser inlet gas temperature 590°C, condenser outlet non-condensable gas temperature 40°C, cooling water inlet temperature 20°C, and pyrolysis oil production 18 kg / h.

[0084] Operating parameters of the pyrolysis gas incineration unit: incineration temperature 1100°C, residence time 2 seconds. The exhaust gas after combustion is purified to meet emission standards before being discharged.

[0085] The weight loss rate of the pyrolysis residue, determined by thermogravimetric analysis, was 0.17%. Following the calculation method provided in the "Requirements for Waste Circuit Board Treatment and Disposal (GB-T44157-2024)," the pyrolysis rate of the circuit board was calculated to be 99.54%. ICP analysis of the residue and dust obtained from the dust collector showed the following metal content recovery rates: gold 99.5%, copper 97.78%, tin 90.69%, lead 88%, and nickel 97.69%.

[0086] The implementation results are as follows:

[0087] (1) Using the pyrolysis method of this patent, mobile phone circuit boards were pyrolyzed, yielding an average of 8.35% pyrolysis oil and 69% pyrolysis residue. Following the method outlined in the "Requirements for Waste Circuit Board Treatment and Disposal (GB-T44157-2024)," the pyrolysis rate was determined using a thermogravimetric analyzer. The calculation results show that the pyrolysis rate of the circuit boards treated using the system and method of this patent is greater than 99%, indicating that the circuit boards have undergone sufficient pyrolysis. Analysis results show that the recovery rates of major metal components such as gold, copper, nickel, lead, and tin are all close to or greater than 99%.

[0088] (2) The process of first cooling and removing oil from pyrolysis gas, followed by heating to remove dust, using the technology of this patent, achieves a dust removal efficiency of over 90%. No liquid oil was observed to precipitate within the dust collector, and the discharged dust was dry. After 30 days of continuous operation, the dust collector and condenser were disassembled and inspected, revealing no obvious coking and a surface dust thickness of less than 2 mm. In contrast, without the solution of this invention, a coking layer of over 2 cm appeared in the pipeline system after 7 days of dust collector operation, and the dust removal efficiency dropped from 90% to around 20%. A coking layer of 0.5–1 cm also appeared at the gas inlet of the condenser. Therefore, the technology of this invention can effectively prevent coking in the dust removal and condensation systems, improve dust removal efficiency, and achieve long-term stable operation of the pyrolysis system.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for pyrolytic recycling of mobile phone circuit boards, characterized in that, Includes the following steps: The mobile phone circuit board is continuously conveyed to the rotary kiln; the rotary kiln is equipped with multiple heating sections, which are arranged in series. The pyrolysis temperature is set to 600℃~800℃, the pressure inside the rotary kiln is controlled to -50~0Pa, and the rotation speed of the rotary kiln is controlled to 2~20r / min. The mobile phone circuit board is fed into the rotary kiln through a hopper, a feeder, and a screw feeder. Controlling the residence time of the mobile phone circuit board in the rotary kiln to obtain high-temperature pyrolysis gas and fully pyrolysis pyrolysis residue; A preheating section is set before the heating section, and a cooling section is set after the heating section. The preheating section, multiple heating sections, and cooling sections are arranged in series. The flow direction of the high-temperature pyrolysis gas generated in the heating section is opposite to the movement direction of the mobile phone circuit board. The high-temperature pyrolysis gas flows in the feeding direction and is cooled by the preheating section and the screw feeder before entering the pyrolysis gas heating unit. The pyrolysis gas is divided into first pyrolysis gas and second pyrolysis gas by the induced draft distributor in the pyrolysis gas heating unit. The first pyrolysis gas is subjected to oxygen-deficient combustion, and the high-temperature flue gas produced is mixed with the second pyrolysis gas, so that the temperature of the mixed gas is raised to 400-600℃, and then high-temperature dust removal is performed. The circulating cooling water at 20-40℃ is used to cool the pyrolysis gas after dust removal to below 50℃, collect the condensed pyrolysis oil, and then send the non-condensable pyrolysis gas into the waste gas treatment area. The pyrolysis residue is output from the cooling section and cooled to 200-300℃ by a screw conveyor. The cooled residue is then crushed and screened separately.

2. The method for pyrolytic recycling of mobile phone circuit boards according to claim 1, characterized in that, The temperature of multiple heating sections is set to 600-800℃.

3. The method for pyrolytic recycling of mobile phone circuit boards according to claim 1, characterized in that, The tilt angle of the rotary kiln is controlled between 0-5°. The dwell time of the mobile phone circuit board in the rotary kiln is controlled by adjusting the tilt angle and the rotation speed of the rotary kiln.

4. The method for pyrolytic recycling of mobile phone circuit boards according to claim 1, characterized in that, The temperature of the preheating section is 400-500℃, and the temperature of the cooling section is 500-600℃.

5. The method for pyrolytic recycling of mobile phone circuit boards according to claim 1, characterized in that, The silo, feeder, and screw feeder are sealed and conveyed, and nitrogen is introduced into the silo to maintain a slight positive pressure.

6. The method for pyrolytic recycling of mobile phone circuit boards according to claim 5, characterized in that, The pyrolysis residue discharged from the cooling section through the screw conveyor enters the pyrolysis residue storage tank. The screw conveyor is water-cooled by circulating cooling water, and nitrogen is introduced into the pyrolysis residue storage tank to maintain a slight positive pressure.

7. The method for pyrolytic recycling of mobile phone circuit boards according to claim 6, characterized in that, Dust is separated from pyrolysis gas by a dust collector at high temperature. Dust removal can be carried out by any one or any combination of cyclone dust collector, electrostatic dust collector, and bag filter.

8. The method for pyrolytic recycling of mobile phone circuit boards according to claim 7, characterized in that, In the waste gas treatment area, pyrolysis gas is introduced into the incinerator for combustion, and the combustion temperature is controlled to be no less than 1100℃, the residence time is no less than 2s, and the waste gas after combustion is purified and discharged in compliance with standards.

9. A recycling system using the pyrolysis recycling method for mobile phone circuit boards according to any one of claims 1-8, characterized in that, include, The feeding unit includes a hopper, a feeder, and a screw feeder. The mobile phone circuit boards are fed into the rotary kiln pyrolysis unit via the hopper, feeder, and screw feeder. The hopper, feeder, and screw feeder are used for sealed conveying. Rotary furnace pyrolysis unit: Multiple heating sections are set up in series, and the temperature is set to 600℃~800℃. The pressure of pyrolysis gas in the rotary furnace is controlled to be -50~0Pa by adjusting the exhaust speed of the pyrolysis gas induced draft fan. The rotary kiln is placed at an angle, with the feed end higher than the discharge end. The angle of inclination is adjustable between 0 and 5 degrees. The rotary kiln is driven by an electric motor, and the rotation speed is adjustable between 2 and 20 r / min. A preheating section is installed before the heating section, and a cooling section is installed after the heating section. The preheating section, multiple heating sections, and cooling sections are arranged in series. The high-temperature pyrolysis gas generated in the heating section is cooled by the preheating section of the rotary kiln and the screw feeder before being sent to the pyrolysis gas heating unit. Pyrolysis gas cooling: Pyrolysis gas cooling is completed in the screw feeder. The screw feeder jacket is circulated with 20-40℃ cooling water. The pyrolysis gas is cooled to 200-300℃ in countercurrent contact with the mobile phone circuit board in the screw feeder, and the high boiling point tar in the pyrolysis gas is condensed out. The precipitated tar is captured by the circuit board and carried back into the pyrolysis furnace. The pyrolysis gas heating unit includes an induced draft splitter, a burner, and a gas pipeline mixer. The induced draft splitter divides the pyrolysis gas into first pyrolysis gas and second pyrolysis gas. After the first pyrolysis gas is mixed with air, it enters the burner to complete oxygen-deficient combustion at 900-1200℃. The volume of the input air is 70-90% of the theoretical air requirement for the combustion of the first pyrolysis gas. The residual oxygen concentration in the flue gas is controlled to be no more than 1%. The flue gas after combustion is mixed with the second pyrolysis gas in the pipeline mixer, and the temperature of the mixed gas is controlled to reach 400-600℃. Dust removal unit: Receives the mixed high-temperature gas output from the pyrolysis gas heating unit and performs high-temperature dust removal. It adopts any one or any combination of dust removal methods such as cyclone dust removal, electrostatic dust removal, and bag dust removal. It controls the pyrolysis gas temperature at the inlet of the dust collector to be no less than 400℃ and the pyrolysis gas temperature at the outlet of the dust collector to be no less than 300℃. Condensation unit: Circulating cooling water at 20-40℃ is used to cool the pyrolysis gas after dust removal to 30-50℃, collect the condensed pyrolysis oil, and send the non-condensable pyrolysis gas to the waste gas treatment unit. Waste gas treatment unit: Pyrolysis gas is introduced into the incinerator for combustion, with an incineration temperature of not less than 1100℃ and a residence time of not less than 2s; Discharge unit: The pyrolysis residue in the cooling zone is discharged through the screw conveyor. The screw conveyor is water-cooled by circulating cooling water, and the pyrolysis residue entering the residue storage tank is cooled to 200-300℃.

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