Mobile phone circuit board pyrolysis recovery method and system

Abstract

The invention discloses a mobile phone circuit board pyrolysis recovery method and system. The method comprises the following steps that mobile phone circuit boards are conveyed to a rotary furnace; the rotary furnace is provided with a plurality of heating sections, the heating sections are arranged in series, a preheating section is arranged in front of the heating sections, a cooling section is arranged behind the heating sections, the preheating section, the plurality of heating sections and the cooling section are sequentially arranged in series, the flowing direction of high-temperature pyrolysis gas is opposite to the moving direction of the mobile phone circuit board, and the high-temperature pyrolysis gas flows in the feeding direction. The pyrolysis gas is in contact with the circuit board at the preheating section for heat exchange, then enters the spiral feeder from a feed port of the rotary furnace, and enters the pyrolysis gas heating unit from an exhaust port in the middle of the spiral feeder after being cooled; in the pyrolysis gas heating unit, pyrolysis gas is heated to 400-600 DEG C and subjected to dust removal at high temperature, and the pyrolysis gas subjected to dust removal is further condensed and incinerated; and the pyrolysis residues are output from the cooling section of the rotary furnace and can be crushed and screened, and metal recycled materials are separated out.

Description

Technical Field

[0001] The invention relates to the technical field of recycling waste electronic products, and in particular to a method and system for pyrolysis recycling of mobile phone circuit boards. Background Art

[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 plastics, and brominated flame retardants, which pose potential environmental pollution. On the other hand, they also contain a variety of common metals and rare precious metals such as copper, nickel, gold, and silver, and have high recycling value.

[0003] With higher requirements for environmental protection, the recycling and utilization of electronic waste has become a thorny issue faced by most countries. As a key component of discarded home appliances, the recycling and resource utilization of printed circuit boards (PCBs) has become a hot issue that needs to be solved urgently.

[0004] Effective treatment and resource recycling of scrapped circuit boards can greatly slow down the consumption of primary resources, reduce environmental pollution, and play a positive role and important role in establishing a resource-saving and environmentally friendly society and developing a circular economy.

[0005] At present, the main processing technologies for mobile phone circuit boards are: pyrometallurgy, hydrometallurgy, and physical method.

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

[0007] Hydrometallurgy is a commonly used technology for extracting precious metals from discarded electronic products. The basic principle of hydrometallurgy is to use the characteristics of precious metals that can be dissolved in nitric acid and aqua regia to remove them from discarded circuit boards and recover them from the liquid phase. Compared with pyrometallurgy, hydrometallurgy emits relatively less waste gas and the residues after extracting precious metals are also easy to handle, but it produces more waste liquid, and the waste liquid treatment process is complicated and costly. It poses a certain potential threat to the environment

[0008] Physical treatment methods mainly include mechanical crushing, air sorting and magnetic adsorption and other technologies. At present, physical treatment methods are mainly used for the recovery of metals such as aluminum and copper. For example, the United States uses a strong cyclone separator to recover aluminum from the PCB of personal computers. By controlling the feed speed, the purity of the obtained metal aluminum is 85%, and the recovery rate is above 90%; Sweden uses an electric roller electrostatic separator to recover copper. By optimizing the operating parameters, the grade of the obtained metal copper is 93% to 99%, and the recovery rate is 95% to 99%. However, there are problems such as the loss of precious metals in the physical recovery process and the difficulty of resource utilization of non-metallic resin powder.

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

[0010] 1. The pyrolysis products in the rotary furnace are constantly turning, and the pyrolysis residues fall from the top of the rotary furnace. A large number of small-sized particles are not easy to fall and are easily carried by the pyrolysis gas to the pyrolysis gas treatment system outside the furnace. In the purification and condensation process of the pyrolysis gas, when the temperature is lowered, pyrolysis oil will condense and precipitate. These oils are easy to attach to the inner surface of the equipment or pipelines, and will form sludge when adsorbing and capturing the particles in the pyrolysis gas. As the pyrolysis time increases, it may cause blockage of the pipeline and condenser.

[0011] 2. Precious metals in mobile phone circuit boards, such as gold, mostly exist in the form of plating, with a thickness of generally less than 0.1um. After pyrolysis, they are prone to form tiny gold-containing ash, which is easily entrained into the exhaust system by the pyrolysis airflow during the pyrolysis process and is adsorbed by the tar on the inner wall surface of the pipeline system to become sludge, which is difficult to recover and causes losses.

[0012] Therefore, the existing circuit board rotary furnace pyrolysis system cannot achieve long-term stable operation, nor can it obtain a high recovery rate of precious metals such as gold and silver. Summary of the invention

[0013] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a mobile phone circuit board pyrolysis recovery system and method, aiming to provide a solution to the problems of easy coking of the existing pyrolysis gas treatment system causing pipeline blockage and low precious metal recovery efficiency.

[0014] Technical solution: A method for pyrolysis recovery of mobile phone circuit boards, including the following steps:

[0015] Feeding and pyrolysis of circuit boards

[0016] The mobile phone circuit board is continuously transported to the rotary kiln through the feeding unit. The rotary kiln pushes the circuit board from the feeding port to the discharging direction by rotating. At the same time, the circuit board is heated to the pyrolysis temperature to start pyrolysis, and the pyrolysis is completed within the residence time in the furnace. The pyrolysis gas generated during the pyrolysis process is extracted from the feeding port of the rotary kiln head by the pyrolysis gas induced draft fan and enters the spiral feeder. By adjusting the exhaust speed, the air pressure in the rotary kiln is controlled to be slightly negative. The pyrolysis residue is discharged from the slag discharge port at the end of the furnace and enters the discharging unit.

[0017] The temperature of the preheating section is 400-500°C, and the temperature of the cooling section is 500-600°C.

[0018] The pyrolysis temperature of the circuit board is controlled at 600-800℃

[0019] The circuit board stays in the rotary kiln for 30 to 60 minutes.

[0020] The pyrolysis gas pressure in the rotary furnace is controlled to be a slight negative pressure of -50 to 0 Pa.

[0021] The temperature of the pyrolysis residue discharged from the rotary furnace slag outlet is 500-600℃.

[0022] The temperature of the pyrolysis gas leaving the rotary furnace feed port is 400-500℃.

[0023] Mobile phone circuit boards are fed into the rotary kiln through the silo, feeder and screw feeder. The silo, feeder and screw feeder are sealed for transportation, and nitrogen is filled into the silo to maintain a slight positive pressure.

[0024] Discharge and treatment of PCB pyrolysis residues

[0025] The pyrolysis residue discharged from the slag discharge port of the rotary furnace enters the screw discharger through the discharge valve and is sent to the pyrolysis residue storage tank under the push of the screw discharger. Cooling water at 20-40°C is passed through the jacket of the screw discharger to cool the pyrolysis residue at 500-600°C to 200-300°C. At the same time, nitrogen is passed into the pyrolysis residue storage tank to maintain a slight positive pressure of 0-10kPa.

[0026] Extraction and treatment of PCB pyrolysis gas

[0027] Under the action of the induced draft fan, the high-temperature pyrolysis gas enters the screw feeder from the feed port of the rotary kiln. Circulating cooling water at 20-40°C is passed into the jacket of the screw feeder to further cool the pyrolysis gas to 200-300°C. The condensed pyrolysis oil is sent back to the rotary kiln together with the circuit board. The pyrolysis gas after oil removal enters the induced draft diverter from the exhaust port in the middle of the spiral feeder. The induced draft diverter divides the pyrolysis gas into two parts: one part of the pyrolysis gas (the first pyrolysis gas) is mixed with an appropriate amount of air and then burned in the absence of oxygen to produce high-temperature flue gas of 900-1200°C, which is then mixed with the other part of the pyrolysis gas (the second pyrolysis gas) coming out of the induced draft diverter. The temperature of the mixed gas rises to 400-600°C and is then sent to the dust collector for dust removal at high temperature. The pyrolysis gas after dust removal enters the condenser for further cooling and precipitation of pyrolysis oil. The non-condensable pyrolysis gas is transported to the incinerator by the fan for high-temperature incineration treatment. The flue gas generated by incineration is purified and discharged in compliance with the standards.

[0028] The oxygen-deficient combustion of pyrolysis gas means controlling the input air volume to 70-90% of the theoretical air demand for the first pyrolysis gas combustion (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] The pyrolysis gas dust removal method may adopt any one of cyclone dust removal, electrostatic dust removal, bag dust removal or any combination thereof.

[0030] Among them, the pyrolysis gas after dust removal is cooled to below 50°C by circulating cooling water at 20-40°C, the condensed pyrolysis oil is collected, and then the non-condensable pyrolysis gas is sent to the waste gas treatment area. The condensation of the pyrolysis gas is to pass the circulating cooling water at 20-40°C into the condenser, cool the pyrolysis gas to 30-50°C, and precipitate the pyrolysis oil.

[0031] Among them, in the waste gas treatment area, the pyrolysis gas is introduced into the incinerator for combustion, the incineration temperature is controlled to be not lower than 1100℃, the residence time is not shorter than 2s, and the waste gas after incineration is purified and meets the emission standards.

[0032] Incineration of non-condensable pyrolysis gas, control the incineration temperature of non-condensable gas to be no less than 1100℃, and the residence time to be no less than 2s

[0033] This patented technical solution invents 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 incineration unit:

[0034] Feeding unit: includes silo, feeder, screw feeder and its piping system. The outlet at the lower end of the silo is connected to the inlet of the feeder, the outlet of the feeder is connected to the feed port of the screw feeder, the outlet of the screw feeder is connected to the feed port of the rotary kiln, and an exhaust port is set in the middle of the screw feeder, and the gas discharge is connected to the pyrolysis gas heating unit. The circuit board enters the screw feeder from the outlet of the silo through the feeder, and is driven by the screw into the rotary kiln. The high-temperature pyrolysis gas from the rotary kiln enters from the outlet of the screw feeder, and contacts with the circuit board in countercurrent in the screw feeder. The spiral feeder jacket is passed through the circulating cooling water of 20-40℃. After the pyrolysis gas is cooled to 200-300℃ in 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 0-10kpa (gauge pressure) to prevent the pyrolysis gas from entering the silo and also prevent the outside air from entering the system. The nitrogen is introduced into the pyrolysis gas heating unit after merging with the pyrolysis gas from the exhaust port in the middle of the screw feeder.

[0035] Pyrolysis unit: includes rotary kiln, electric heating system, drive motor, etc. The furnace body of the rotary kiln is tilted at a certain angle so that the feed port end (head) is higher than the discharge port end (tail), and the tilt angle is adjustable between 0 and 5 degrees. The motor drives the furnace body to rotate, and the speed is adjustable between 2 and 20r / min. In the rotary kiln, the circuit board rolls as the rotary kiln rotates and moves in a spiral direction from the furnace head to the discharge direction of the furnace tail. The flow direction of the pyrolysis gas is opposite to the movement direction of the circuit board. The pressure of the pyrolysis gas in the furnace is controlled at -50 to 0pa by adjusting the speed of the pyrolysis gas induced draft fan. The residence time of the circuit board in the rotary kiln can be controlled between 30 and 60min by adjusting the tilt angle of the rotary kiln and the speed of the furnace body. An electric heating block is arranged outside the furnace body of the rotary kiln. According to the heating temperature and control requirements of the furnace body, the furnace of the rotary kiln is divided into six sections:

[0036] The first section is the preheating section. There is no electric heating block in this section. The high-temperature pyrolysis gas generated during the pyrolysis process is used to preheat the circuit board. After preheating, the temperature of the circuit board rises to 400-500°C.

[0037] The second to fifth sections are the heating sections of the pyrolysis furnace, where electric heating blocks are set to heat the furnace body. The preheated circuit boards are further heated to and maintained at 600-800°C in the heating section.

[0038] The sixth section is the pyrolysis residue cooling section. This section does not have an electric heating block, 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.

[0039] Pyrolysis gas heating unit: including induced draft diverter, burner, gas pipeline mixer, the exhaust port in the middle of the screw feeder is connected to the inlet of the induced draft diverter, the first outlet of the induced draft diverter 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, and the second outlet of the induced draft diverter 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. In order to keep the temperature of the pyrolysis gas in the pipeline and equipment basically unchanged during the flow process, sufficient insulation layer and high-temperature steam heating are installed outside the pipeline and equipment.

[0040] The induced draft splitter divides the pyrolysis gas into the first pyrolysis gas and the 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, and the residual oxygen concentration in the flue gas is controlled to be no more than 1%. The high-temperature flue gas generated by the combustion is mixed with the second pyrolysis gas in the gas pipeline mixer, and the temperature of the mixed gas is controlled to reach 400-600°C;

[0041] Dust removal unit: including dust collector, dust storage tank, etc. The inlet of the dust collector is connected to the outlet of the pipeline mixer, the gas outlet of the dust collector is connected to the gas inlet of the pyrolysis gas condenser, and the dust separated by the dust collector is collected in the dust storage tank. The dust collector is any one of a cyclone dust collector, an electrostatic dust collector, a bag dust collector or any combination thereof. The inlet gas temperature of the dust collector is controlled to be not less than 400°C, and the outlet gas temperature of the dust collector is controlled to be not less than 300°C. In order to keep the temperature of the pyrolysis gas in the pipeline and equipment basically unchanged during the flow process, sufficient insulation layer and high-temperature steam heating are installed outside the pipeline and equipment.

[0042] 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 transported to the pyrolysis gas incineration treatment unit through an induced draft fan. The condenser jacket is passed through 20-40°C circulating cooling water to cool the pyrolysis gas to 30-50°C. The condensed pyrolysis oil is collected in the oil storage tank, and the non-condensable pyrolysis gas is sent to the waste gas incineration treatment unit.

[0043] Non-condensable gas incineration treatment unit: The incineration unit includes an induced draft fan, an incinerator, a flue gas purifier, etc. The inlet of the induced draft fan is connected to the gas outlet of the pyrolysis gas condenser, the outlet of the induced draft fan is connected to the gas inlet of the incinerator, and the flue gas generated by the incineration is connected to the inlet of the flue gas purifier. The non-condensable pyrolysis gas from the condensing unit is mixed with air and fully burned in the incinerator, and the combustion temperature is controlled to be not less than 1100℃ and the residence time is not less than 2s. After purification, the flue gas can achieve standard emission.

[0044] Discharging unit: It consists of a rotary feeder, a spiral feeder, and a residue storage tank. The inlet of the feeder is connected to the slag discharge port at the rear of the rotary furnace, the outlet of the feeder is connected to the inlet of the spiral feeder, and the outlet of the spiral feeder is connected to the inlet of the storage tank. The pyrolysis residue enters the spiral feeder from the slag discharge port of the rotary furnace through the feeder, and enters the residue storage tank under the push of the spiral. The spiral feeder jacket is passed through 20-40°C circulating cooling water to cool the pyrolysis residue, and the temperature of the cooled pyrolysis residue is controlled to be 200-300°C. The discharging system is a sealed system. In order to prevent the pyrolysis gas from entering the discharging system and prevent the outside air from entering the discharging system, nitrogen is introduced into the residue storage tank to maintain a slight positive pressure of 1-10kpa. The nitrogen introduced passes through the spiral feeder and the feeder, and then enters the rotary furnace from the slag discharge port at the rear of the rotary furnace to merge with the pyrolysis gas.

[0045] Beneficial effects:

[0046] The system and method of the present invention are used to perform pyrolysis treatment on mobile phone circuit boards, which can fully pyrolyze and recycle the circuit boards. The circuit boards do not need to be crushed before pyrolysis, which reduces the amount of dust generated during the pyrolysis process and the loss of precious metals. Therefore, the system of the present invention is used to treat waste mobile phone circuit boards, which can obtain a higher recovery rate of precious metals. Compared with the existing pyrolysis system, the other effects of the present invention are as follows:

[0047] 1. By controlling the temperature and residence time of each heating section in the rotary kiln, the mobile phone circuit board can be fully pyrolyzed;

[0048] 2. To prevent the pyrolysis gas from releasing pyrolysis oil during the dust removal process, which may cause pipeline blockage. The present invention adopts a scheme of first cooling the pyrolysis gas to remove oil, and then heating it to remove dust. The high-temperature pyrolysis gas coming out of the rotary furnace is cooled to 200-300°C in a water-cooled screw feeder, so that the tar with a boiling point higher than 300°C in the pyrolysis gas can be effectively separated. In the subsequent dust removal process, it is only necessary to keep the pyrolysis gas at no less than 300°C to better avoid the release of pyrolysis oil during the dust removal process. In this way, the blockage problem caused by coking of the dust removal and condensation pipelines can be effectively solved;

[0049] 3. In order to heat the pyrolysis gas, the present invention uses the high-temperature flue gas generated by the oxygen-deficient combustion of part of the pyrolysis gas to heat the pyrolysis gas. This not only avoids the need for additional fuel, but also adopts the oxygen-deficient combustion method to avoid oxygen residue, thereby ensuring the safety of the system. The carbon monoxide generated during the oxygen-deficient combustion process can also be used in the later pyrolysis gas combustion treatment.

[0050] 4. This patent uses the heat generated by the combustion of a part of the pyrolysis gas to heat the pyrolysis gas. Since part of the air is introduced, the total gas flow rate in the dust removal process is increased, and the gas temperature is higher. Therefore, the air flow speed in the dust removal process is faster, which is beneficial to improve the dust removal effect of the cyclone splitter.

[0051] 5. In order to prevent outside air from entering the pyrolysis system, the present invention fills nitrogen into the mobile phone circuit board silo and the pyrolysis residue storage tank to maintain positive pressure, which not only prevents external oxygen from entering the system, but also prevents the pyrolysis gas from entering the silo and the residue storage tank, thereby avoiding the leakage of the pyrolysis gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0054] It should be noted that the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0055] The size and composition of the mobile phone circuit board used in the implementation process are as follows:

[0056] The size of the waste mobile phone circuit boards used for pyrolysis treatment is less than 10cm×20cm. The weight loss rate of the circuit boards measured by a thermogravimetric analyzer at 10℃ / min and nitrogen atmosphere is 36.98% (final temperature 800℃). The circuit boards are crushed and then dissolved into a solution. Elemental analysis shows that the waste circuit boards contain 22.50% copper, 5.62% tin, 0.61% lead, 4.88% nickel, and 0.11% gold.

[0057] Example 1

[0058] The operating parameters of the rotary kiln during the pyrolysis process are controlled as follows: the inclination angle of the rotary kiln is adjusted to 2 degrees, the speed of the rotary kiln is adjusted to 10r / 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 pyrolysis gas pressure in the furnace fluctuates between -40 and -10Pa (gauge pressure).

[0059] The operating parameters of the feeding unit are as follows: the mobile phone circuit board feed flow rate is 200kg / h, the cooling water inlet temperature of the screw feeder is 20℃, the pyrolysis gas flow rate entering the screw feeder outlet is 68kg / h and the temperature is 400℃, the pyrolysis gas flow rate out of the exhaust port in the middle of the screw feeder outlet is 54kg / h and the pyrolysis gas temperature is 200℃. The nitrogen pressure in the silo fluctuates between 1 and 2kpa (gauge pressure).

[0060] The operating parameters of the discharging unit are as follows: the residue flow rate discharged into the discharging unit is 139 kg / h and the temperature is 500°C; the cooling water inlet temperature of the screw discharging device 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 fluctuates between 1 and 2 kPa (gauge pressure).

[0061] The operating parameters of the pyrolysis gas heating unit are as follows: the amount of air added is 90% 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 the combustion is 0.8%, and the temperature of the gas after the flue gas and the second pyrolysis gas are mixed is 600°C

[0062] Dust removal unit operating parameters: Two-stage series cyclone dust removal. Cyclone separator gas inlet temperature is 600℃, and the particle content in the inlet gas is 2200mg / Nm 3 The gas outlet temperature of the cyclone splitter is 550°C, and the particle content in the outlet gas is 170 mg / Nm 3 The dust removal efficiency is 92.27%, and the average separation dust is 350g / h.

[0063] The operating process parameters of the condensing unit are as follows: the condenser inlet gas temperature is 550°C, the condenser outlet non-condensable gas temperature is 40°C, the cooling water inlet temperature is 20°C, and the pyrolysis oil output is 15kg / h.

[0064] The operating parameters of the pyrolysis gas incineration unit are as follows: the incineration temperature is 1100°C, the residence time is 2 seconds. The exhaust gas after combustion is purified and meets the standards before being discharged.

[0065] The weight loss rate of the pyrolysis residue measured by thermogravimetric analyzer was 0.34%. According to 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%. The metal content of the residue and the dust obtained by the dust collector was measured by an element analyzer, and the calculation showed that the recovery rate of gold was 99.6%, the recovery rate of copper was 98.68%, the recovery rate of tin was 91.69%, the recovery rate of lead was 90.08%, and the recovery rate of nickel was 98.69%.

[0066] Example 2

[0067] The operating parameters of the rotary kiln during the pyrolysis process are controlled as follows: the inclination angle of the rotary kiln is adjusted to 2 degrees, the speed of the rotary kiln is adjusted to 10r / 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 pyrolysis gas pressure in the furnace fluctuates between -40 and -10Pa (gauge pressure).

[0068] The operating parameters of the feeding unit are as follows: the feeding flow rate of mobile phone circuit boards is 200 kg / h, the cooling water inlet temperature of the screw feeder is 40°C, the pyrolysis gas flow rate entering the screw feeder outlet is 68 kg / h and the temperature is 400°C, and the pyrolysis gas flow rate out of the exhaust port in the middle of the screw feeder outlet is 56 kg / h and the temperature is 300°C. The nitrogen pressure in the silo fluctuates between 1 and 2 kPa (gauge pressure).

[0069] The operating parameters of the discharging unit are as follows: the residue flow rate discharged into the discharging unit is 139 kg / h and the temperature is 500°C; the cooling water inlet temperature of the screw discharging device 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 fluctuates between 1 and 5 kPa (gauge pressure).

[0070] The operating parameters of the pyrolysis gas heating unit are as follows: the amount of air added is 70% of the theoretical air requirement, the temperature of the flue gas produced by the combustion of the first pyrolysis gas is 900°C, the oxygen content in the flue gas produced by the combustion is 0.4%, and the temperature of the gas after the flue gas and the second pyrolysis gas are mixed is 400°C

[0071] Dust removal unit operating parameters: Bag dust removal is used. The dust collector gas inlet temperature is 400℃, and the particle content in the inlet gas is 1900mg / Nm 3 The gas outlet temperature of the dust collector is 300°C and the particle content in the outlet gas is 50mg / Nm 3 The dust removal efficiency is 97%, and the average separation dust is 380g / h.

[0072] The operating process parameters of the condensing unit are as follows: the inlet gas temperature of the condenser is 400°C, the non-condensable gas temperature of the condenser outlet is 30°C, the cooling water inlet temperature is 20°C, and the pyrolysis oil output is 16kg / h.

[0073] The operating parameters of the pyrolysis gas incineration unit are as follows: the incineration temperature is 1100°C, the residence time is 2 seconds. The exhaust gas after combustion is purified and meets the standards before being discharged.

[0074] The weight loss rate of the pyrolysis residue measured by thermogravimetric analyzer was 0.37%. According to 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%. The metal content of the pyrolysis residue and the dust obtained by the dust collector was measured by an element analyzer. The calculation showed that the recovery rate of gold was 99.2%, the recovery rate of copper was 97.29%, the recovery rate of tin was 90.32%, the recovery rate of lead was 90.0%, and the recovery rate of nickel was 97.29%.

[0075] Example 3

[0076] The operating parameters of the rotary kiln during the pyrolysis process are controlled as follows: the inclination angle of the rotary kiln is adjusted to 5 degrees, the speed of the rotary kiln is adjusted to 20r / min, the temperature of the preheating section is 500℃, the temperature of the heating section is 800℃, the temperature of the cooling section is 600℃, and the pyrolysis gas pressure in the furnace fluctuates between -30 and -10Pa (gauge pressure).

[0077] The operating parameters of the feeding unit are as follows: the feeding flow rate of mobile phone circuit boards is 200 kg / h, the cooling water inlet temperature of the screw feeder is 20°C, the pyrolysis gas flow rate entering the screw feeder outlet is 69 kg / h and the temperature is 500°C, and the pyrolysis gas flow rate out of the exhaust port in the middle of the screw feeder outlet is 57 kg / h and the temperature is 300°C. The nitrogen pressure in the silo fluctuates between 1 and 5 kPa (gauge pressure).

[0078] The operating parameters of the pyrolysis gas heating unit are as follows: the amount of air added 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 the combustion is 0.2%, and the temperature of the gas after the flue gas and the second pyrolysis gas are mixed is 600°C

[0079] The operating parameters of the discharging unit are as follows: the residue flow rate discharged into the discharging unit is 137 kg / h, the temperature is 600°C, the cooling water inlet temperature of the screw discharging device is 20°C, the temperature of the pyrolysis residue leaving the screw feeder is 300°C, and the nitrogen pressure in the pyrolysis residue storage tank fluctuates between 1 and 6 kPa (gauge pressure).

[0080] Dust removal unit operating parameters: a first-stage cyclone dust removal system is used in series with a first-stage electrostatic dust removal system. The cyclone separator gas inlet temperature is 600°C, and the particle content in the inlet gas is 2380 mg / Nm 3 The gas outlet temperature of the cyclone splitter is 590°C, and the particle content in the outlet gas is 150mg / Nm 3 The dust removal efficiency is 93.70%, and the average separation dust is 362g / h.

[0081] The operating process parameters of the condensing unit are as follows: the condenser inlet gas temperature is 590°C, the condenser outlet non-condensable gas temperature is 40°C, the cooling water inlet temperature is 20°C, and the pyrolysis oil output is 18kg / h.

[0082] The operating parameters of the pyrolysis gas incineration unit are as follows: the incineration temperature is 1100°C, the residence time is 2 seconds. The exhaust gas after combustion is purified and meets the standards before being discharged.

[0083] The weight loss rate of the pyrolysis residue measured by thermogravimetric analyzer was 0.17%. According to 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 99.54%. The metal content of the residue and the dust obtained by the dust collector was measured by ICP. The calculation showed that the recovery rate of gold was 99.5%, the recovery rate of copper was 97.78%, the recovery rate of tin was 90.69%, the recovery rate of lead was 88%, and the recovery rate of nickel was 97.69%.

[0084] The implementation results are as follows:

[0085] (1) The patent scheme was used to pyrolyze mobile phone circuit boards, and an average of 8.35% pyrolysis oil and 69% pyrolysis residue were obtained. According to the method of "Requirements for the Treatment and Disposal of Waste Circuit Boards (GB-T 44157-2024)", the pyrolysis rate was measured by a thermogravimetric analyzer. The calculation results showed that the pyrolysis rate of the circuit boards treated by the patent system and method of the present invention was greater than 99%, indicating that the circuit boards had been fully pyrolyzed. The analysis results showed that the recovery rates of major metal components such as gold, copper, nickel, lead, and tin were close to or greater than 99%.

[0086] (2) The patented technology is used to treat the pyrolysis gas by first cooling it down to remove oil and then heating it up to remove dust, and the dust removal efficiency is greater than 90%. No liquid oil is found to precipitate in the dust collector, and the discharged dust is dry. After 30 days of continuous operation, the dust collector and condenser are disassembled and checked to find no obvious coking, and the surface dust thickness is less than 2mm. Without using the scheme of the present invention to treat the pyrolysis gas, a coking layer of more than 2cm appears in the pipeline system after the dust collector has been running for 7 days, and the dust removal efficiency drops from 90% at the beginning to about 20%. A coking layer of 0.5 to 1cm also appears at the gas inlet of the condenser. Therefore, the use of the technology of the present invention can effectively prevent the dust removal and condensation systems from coking, improve the dust removal efficiency, and achieve long-term stable operation of the pyrolysis system.

[0087] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for pyrolysis recovery of mobile phone circuit boards, characterized in that: The following steps are involved: Continuously convey the mobile phone circuit board to the rotary kiln; multiple heating sections are set in the rotary kiln, and the multiple heating sections are arranged in series. The pyrolysis temperature is set to 600℃~800℃, the pressure in the rotary kiln is controlled to -50~0Pa, and the speed of the rotary kiln is controlled to 2~20r / min; Control the residence time of mobile phone circuit boards in the rotary kiln to obtain high-temperature pyrolysis gas and fully pyrolyzed pyrolysis residue; A preheating section is provided before the heating section, and a cooling section is provided after the heating section. The preheating section, the plurality of heating sections, and the cooling section are arranged in series in sequence; 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 after being cooled by the preheating section and the spiral feeder, it enters the pyrolysis gas heating unit; In the pyrolysis gas heating unit, the pyrolysis gas is divided into the first pyrolysis gas and the second pyrolysis gas. The first pyrolysis gas is subjected to oxygen-deficient combustion, and the generated high-temperature flue gas is mixed with the second pyrolysis gas, and the mixed gas is heated to 400-600°C, and then subjected to high-temperature dust removal; The pyrolysis residue is discharged from the cooling section and cooled to 200-300°C by a spiral discharger. The cooled residue is crushed and screened separately.

2. A method for pyrolysis recovery of mobile phone circuit boards according to claim 1, characterized in that: The temperature of the multiple heating sections was set at 600-800°C.

3. A method for pyrolysis recovery of mobile phone circuit boards according to claim 1, characterized in that: The tilt angle of the rotary kiln is controlled at 0-5°, and the residence time of the mobile phone circuit board in the rotary kiln is controlled by adjusting the tilt angle of the rotary kiln and the rotation speed of the rotary kiln.

4. A method for pyrolysis recovery of mobile phone circuit boards according to claim 1, characterized in that: The temperature of the preheating section is 400-500°C, and the temperature of the cooling section is 500-600°C.

5. A method for pyrolysis recovery of mobile phone circuit boards according to claim 1, characterized in that: Mobile phone circuit boards are fed into the rotary kiln through the silo, feeder and screw feeder. The silo, feeder and screw feeder are sealed for transportation, and nitrogen is filled into the silo to maintain a slight positive pressure.

6. A method for pyrolysis recovery of mobile phone circuit boards according to claim 5, characterized in that: The pyrolysis residue discharged from the cooling section is outputted by the spiral discharger into the pyrolysis residue storage tank, the spiral discharger is water-cooled by circulating cooling water, and nitrogen is filled into the pyrolysis residue storage tank to maintain a slight positive pressure.

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

8. A method for pyrolysis recovery of mobile phone circuit boards according to claim 7, characterized in that: Use circulating cooling water at 20-40℃ to cool the pyrolysis gas after dust removal to below 50℃, collect the condensed pyrolysis oil, and then send the non-condensable pyrolysis gas to the waste gas treatment area.

9. A method for pyrolysis recovery of mobile phone circuit boards according to claim 8, characterized in that: In the waste gas treatment area, the pyrolysis gas is introduced into the incinerator for combustion, the combustion temperature is controlled to be no less than 1100℃, the residence time is no less than 2s, and the waste gas after incineration is purified and meets the emission standards.

10. A recycling system using the pyrolysis recycling method for mobile phone circuit boards according to any one of claims 1 to 9, characterized in that: include, Feeding unit: including silo, feeder, screw feeder. Mobile phone circuit boards are fed into the rotary furnace pyrolysis unit through silo, feeder, screw feeder. The silo, feeder, screw feeder are sealed for transportation. Rotary furnace pyrolysis unit: multiple heating sections are arranged in series, the temperature is set to 600℃~800℃, and the pressure of the pyrolysis gas in the rotary furnace is controlled to -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, and the angle of inclination is adjustable between 0 and 5 degrees. The rotary kiln is driven by a motor and the speed is adjustable between 2 and 20 r / min. A preheating section is provided before the heating section, and a cooling section is provided after the heating section. The preheating section, multiple heating sections, and the cooling section are arranged in series in sequence. The high-temperature pyrolysis gas generated in the heating section is sent to the pyrolysis gas heating unit after being cooled by the rotary furnace preheating section and the screw feeder; Pyrolysis gas cooling: Pyrolysis gas cooling is completed in the screw feeder. The screw feeder jacket is passed through 20-40℃ circulating cooling water. The pyrolysis gas is in countercurrent contact with the mobile phone circuit board in the screw feeder and is cooled to 200-300℃. The high boiling point tar in the pyrolysis gas is condensed. The precipitated tar is captured by the circuit board and brought back into the pyrolysis furnace. Pyrolysis gas heating unit: including an induced draft splitter, a burner, and a gas pipeline mixer. The induced draft splitter divides the pyrolysis gas into a first pyrolysis gas and a 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. The input air is 70-90% of the theoretical air demand required 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°C. Dust removal unit: Receive the mixed high-temperature gas output by the pyrolysis gas heating unit and perform high-temperature dust removal, using any one of cyclone dust removal, electrostatic dust removal, bag dust removal or any combination of dust removal methods, and control the pyrolysis gas temperature at the dust collector inlet to be no less than 400°C and the pyrolysis gas temperature at the dust collector outlet to be no less than 300°C; Condensation unit: Use circulating cooling water at 20-40℃ to cool the pyrolysis gas after dust removal to 30-50℃, collect the condensed pyrolysis oil, and send the non-condensed pyrolysis gas to the exhaust gas treatment unit; Waste gas treatment unit: The pyrolysis gas is passed into the incinerator for combustion, the incineration temperature is not less than 1100℃, and the residence time is not less than 2s; Discharging unit: The pyrolysis residue in the cooling zone is discharged through the spiral discharging device, and the spiral discharging device is water-cooled by circulating cooling water, so that the pyrolysis residue entering the residue storage tank is cooled to 200-300℃.

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