Method and system for removing lead and zinc from flue gas

Abstract

The present invention relates to a method and system for removing lead and zinc from flue gas. The method involves passing flue gas into a flue gas sorting system, which is used to grade and collect dust particles in the flue gas to obtain lead-zinc dust ash of different grades and particle sizes. The method comprises a lead-zinc removal device, which includes a flue gas duct, a filter belt, and a main exhaust fan. The filter belt and the transverse cross-section of the flue gas duct are arranged perpendicular to each other. The flue gas is filtered by the filter belt in the flue gas duct, and the main exhaust fan is arranged in the flue gas duct. The advantages of the present invention are: the flue gas sorting system is used to initially capture lead-zinc dust in the flue gas, achieving classification of the lead-zinc dust ash, and then the lead-zinc removal device is used to effectively reduce the content of heavy metal lead and zinc in the flue gas of a rotary hearth furnace or rotary kiln, eliminating its pollution and harm to the environment. This method overcomes the shortcomings of existing dust removal technologies in their poor ability to capture fine dust particles rich in lead and zinc, achieving a dust particle removal rate of over 93%, which is much higher than that of existing wet processes.

Description

Technical Field

[0001] The present invention relates to the field of comprehensive utilization of wastes, and is a method and system for removing lead and zinc from flue gas. Background Art

[0002] Research has found that when the lead and zinc content of the waste feedstock is low in a rotary hearth furnace or rotary kiln, the amount of lead and zinc released into the atmosphere with the flue gas is also extremely low, causing little impact on the environment. However, when the lead and zinc content of the waste feedstock exceeds a certain critical value, the lead and zinc content in the flue gas entering the rotary hearth furnace or rotary kiln after treatment increases dramatically, causing serious environmental impacts. Studies of the flue gas from rotary hearth furnaces and rotary kilns have revealed that, unlike general flue gas, the flue dust from these furnaces contains significant amounts of heavy metals such as lead and zinc. The finer the dust, the higher the content. These heavy metals can enter the human lungs through air and can cause cancer. Currently, there is no effective, low-cost method for controlling the heavy metal content in rotary hearth furnaces and rotary kilns.

[0003] Application number CN201921036591.2, patented "Tail Gas Treatment Equipment for the Disposal of Chromium-Containing Heavy Metal Hazardous Waste," includes a dust purification device, an acid gas purification tank, and a sludge settling tank. The dust purification device mixes the steam generated during water quenching with the flue gas, utilizing the condensation of the steam to settle the dust in the flue gas. The dust-removed flue gas is then fed into the acid gas purification tank below the liquid level, allowing the acid gas in the flue gas to fully react with the solution, thereby purifying the acid gas. This equipment requires a large amount of steam for condensation during operation, consuming significant resources and energy, resulting in high operating costs. Furthermore, the steam condensation method is limited in its effectiveness in purifying chromium-containing dust particles, resulting in a low chromium dust removal rate.

[0004] Application number CN201811373734.9, patent name "Purification system for flue gas generated by harmless disposal of chromium-containing sludge using a double-drum rotary kiln", includes a tilted double-drum rotary kiln, which effectively solves the waste gas treatment problems of dust, acidic gas, and nitrogen oxides in the process of chromium-containing sludge disposal. The device passes the flue gas through a settling chamber and a cyclone dust collector in sequence, and then through a first water film dust removal and desulfurization spray tower for water washing, and then through a second water film dust removal and desulfurization spray tower, and then through a third water film dust removal and desulfurization spray tower. The entire system has a complex structure, and through sedimentation, cyclone dust removal, and three-stage spraying, the equipment cost and operating cost are high. The choice of reagents does not specifically capture chromium-containing dust, and the chromium-containing fine dust cannot be completely captured.

[0005] Application number CN200810058792.2, patent name "Method for determining heavy metal elements in cigarette smoke using a smoke capture and absorption device", the smoke capture and absorption device includes an outer sleeve (1), an inner sleeve (2) and a sealing plug (3), the outer sleeve (1) is provided with an inlet (7) and an outlet (8), the outer sleeve (1), the inner sleeve (2) and the sealing plug (3) are sealed in sequence, the inner sleeve (2) is provided with an upper sieve plate (6) and a lower sieve plate (4), and a buffer filler (5) is filled between the two sieve plates. The method slightly prolongs the residence time and absorption time of the smoke in the capture agent through the combined action of the upper sieve plate, the lower sieve plate, the buffer filler and other structures. In addition, the smoke is dispersed by the sieve plate and buffered by the buffer filler, the reaction surface area of ​​the smoke absorption is increased, and the smoke components are more fully absorbed. However, the buffer filler only serves as a buffer. Its large gaps are insufficient to filter tiny dust particles from the gas. Dust particle absorption relies solely on the short-term contact reaction between the collector and the flue gas, resulting in a low dust capture rate. Furthermore, the device can only absorb gases with low flow rates and flue gas velocities. The impact of high-flow, high-velocity gases, such as those from a rotary hearth furnace, can disperse the buffer filler and even cause the collector to splash. Furthermore, the faster-flowing flue gas has a shorter contact reaction time with the collector, resulting in inadequate absorption.

[0006] Application number CN201921879172.5, titled "A Asphalt Fume Absorption Device," describes the device, which comprises a cylinder, a resistor layer, an ozone layer, an ultraviolet lamp, a spray cover, a fan, and an exhaust port. The device is characterized by a multi-layer filter plate installed at the bottom of the cylinder. The first layer of the filter plate is made of asbestos mesh, the second layer is made of activated carbon honeycomb pores, and the third layer is a screen plate covered with quicklime. The height between two adjacent absorption layers is 300mm-500mm. From the center cross-section of the cylinder, from top to bottom, it consists of a resistor layer, a spray cover, and a return fan air intake. The spray cover incorporates an organic solvent capable of absorbing asphalt particles. The device uses an organic solvent to absorb particulate matter from the asphalt fume. The combined action of the resistor layer, ozone layer, and ultraviolet lamp allows the asphalt fume to further react with oxygen at high temperatures, achieving excellent absorption results. However, the use of this device has certain limitations and disadvantages: First, the device has a complex structure and high cost. The material of the activated carbon honeycomb holes will become ineffective after use and needs to be replaced regularly. The resources and energy costs consumed in the operation of the ozone layer and the resistance layer are also high, which significantly increases the operating cost of the equipment; Second, in the several layers of filtering structure of the device, the asbestos mesh has limited filtering and intercepting effect on tiny dust in the flue gas, and the screen plate covered with quicklime only has an absorption effect on some acidic gases in the flue gas, and the absorption is not complete enough. The spraying of organic solvents is to spray the spray liquid through tiny water droplets, and its collision with small asphalt particles in the flue gas is random, so the spraying absorption effect is poor. The combined effect of the resistance layer, ozone layer, and ultraviolet lamp only has a certain effect on organic particles in asphalt flue gas, and its effect is also very limited.

[0007] Application number CN202021710826.4, patent name "A Petrochemical Flue Gas Absorption Device," features an absorption tower, a scrubbing section, a chemical absorption section, and a vapor recovery section. The scrubbing section is located at the bottom of the absorption tower, the chemical absorption section is located in the middle of the absorption tower, and the vapor recovery section is located at the top of the absorption tower. The vapor recovery section includes a vapor baffle, which includes a vapor baffle trough and a vapor recovery trough. The vapor baffle trough has a cold air channel at the top, and the vapor recovery trough has a water outlet trough at the bottom. The cold air channel is equipped with a heat conduction plate, the water outlet trough is equipped with a water collecting plate, and the bottom of the water outlet trough is equipped with a water outlet. The device passes the flue gas into the bottom of the absorption tower, where it is scrubbed and cooled, then chemically absorbed by the acidic gas, and finally vapor is recovered. This device effectively solves the problem of catalysts and water in flue gas after treatment in conventional absorption towers, but it still has certain limitations and disadvantages: when the flue gas passes through the scrubbing part of the device, it usually moves upward rapidly in the form of bubbles. The reaction time between the flue gas and the absorption liquid is limited and the contact area is small, resulting in insufficient absorption of dust particles in the flue gas, and the chemical absorption and water vapor absorption parts cannot achieve the purpose of absorbing dust particles in the flue gas.

[0008] Patent application number CN201410223759.6, entitled "A Method for Detecting Chromium, Nickel, Arsenic, Selenium, Cadmium, and Lead in Cigarette Sidestream Smoke," features the following: using a fishtail cap connected in series with a quartz fiber filter to collect particulate matter from cigarette sidestream smoke, a three-stage nitric acid solution connected in series to collect gaseous matter from the sidestream smoke, microwave digestion of the sample, and inductively coupled plasma-mass spectrometry to detect the chromium, nickel, arsenic, selenium, cadmium, and lead content in both the particulate and gaseous samples. This method absorbs toxic substances from the smoke separately before detection. This method requires separate processing of the particulate and gaseous phases, involving a series of steps including elution, extraction, digestion, ultrasonic vibration, and heating and concentration. This is complex, time-consuming, and costly. More importantly, the quartz fiber filter method for collecting particulate matter does not completely absorb particulate matter from the smoke, and some extremely small particles are not captured.

[0009] Currently, there is no economical and efficient method for removing heavy metals from flue gas in China. The present invention removes heavy metals from flue gas from a rotary hearth furnace or rotary kiln under certain process conditions, which is highly economical and reasonable, and provides a new route for treating flue gas from rotary hearth furnaces or rotary kilns. Summary of the Invention

[0010] The purpose of the present invention is to provide a method and system for removing lead and zinc from flue gas, which can remove heavy metals from the flue gas of a rotary hearth furnace or a rotary kiln, thereby solving the problems of high treatment cost and poor treatment effect of the existing treatment process and providing a new route for the treatment of flue gas from a rotary hearth furnace or a rotary kiln.

[0011] To achieve the above object, the present invention is implemented through the following technical solutions:

[0012] A method for removing lead and zinc from flue gas, wherein the flue gas is passed through a flue gas sorting system to collect dust particles in the flue gas by classification to obtain lead-zinc dust ash of different grades and particle sizes, specifically comprising:

[0013] S1. Adjust the air volume in the flue to between 110 and 170 m3 / min, and the air pressure in the flue to between 1400 and 1700 Pa, so that the dust with high iron content and large particle size settles under the action of gravity in the front section of the flue and is separated;

[0014] S2. The dust with smaller particle size and specific gravity continues to move forward along the flue. A weak magnetic separation device is installed in the middle section of the flue. The magnetic field strength of the weak magnetic separation device is adjusted between 6000 and 8000 Oe to separate the magnetic materials with relatively high iron content.

[0015] S3. The flue gas enters the rear section of the flue, where a strong magnetic separation device is installed. The magnetic field strength is adjusted between 11,000 and 13,000 Oe to separate the magnetic materials with relatively low iron content.

[0016] S4. The flue gas coming out of the flue gas sorting system is then processed by the lead and zinc removal equipment to further capture the lead and zinc elements in the flue gas.

[0017] In S4, the flue gas from the flue gas separation system is then processed by the lead and zinc removal equipment, including:

[0018] S41, prepare immersion solution;

[0019] S42, respectively loading the prepared leaching liquid into the filter belt cleaning tank and the absorption liquid wetting tank;

[0020] S43, turn on the ultrasonic generator and adjust the ultrasonic vibration frequency to 25~29kHz;

[0021] S44, the filter belt rotating shaft rotates, so that the filter belt linear running speed reaches 28~32m / min;

[0022] S45, passing the flue gas after the electrostatic precipitator into the flue gas duct, and controlling the flow rate of the flue gas in the duct to be 8-14 m / s;

[0023] S46. Regularly drain and add the leaching liquid in the filter belt cleaning tank and the absorption liquid wetting tank.

[0024] In S41, a leaching solution is prepared using a mixed solution of H2SO4 and H3PO4, with the percentage concentration of H2SO4 being 5% to 8% and the percentage concentration of H3PO4 being 2% to 3%.

[0025] A system for removing lead and zinc from flue gas includes lead and zinc removal equipment, which includes a flue gas duct, a filter belt, and a main exhaust fan. The filter belt and the transverse cross-section of the flue gas duct are arranged perpendicular to each other. The flue gas is filtered by the filter belt in the flue gas duct. The main exhaust fan is arranged in the flue gas duct and is used to extract air to generate negative pressure, so that the flue gas does not overflow during the lead and zinc removal process.

[0026] The lead-zinc removal equipment also includes a filter belt cleaning tank, an absorption liquid wetting tank, and a filter belt rotating shaft. The number of the filter belt rotating shafts is an even number, and the filter belt rotating shafts are arranged in parallel and symmetrically with the middle being low and the two sides being high. The filter belt rotating shaft is connected to the filter belt so that the filter belt rotates clockwise along with the filter belt rotating shaft. The absorption liquid wetting tank is placed inside the annular space surrounded by the filter belt, the filter belt rotating shaft located at the upper center is arranged inside the absorption liquid wetting tank, the filter belt cleaning tank is placed directly below the annular space surrounded by the filter belt, and the filter belt rotating shaft located at the lower center is arranged inside the filter belt cleaning tank.

[0027] The horizontal width of the filter belt cleaning tank is greater than the distance between the two filter belt rotation axes with the farthest horizontal spacing; the horizontal width of the absorption liquid wetting tank is less than the distance between the two filter belt rotation axes with the farthest horizontal spacing.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. A flue gas sorting system is used to preliminarily capture lead-zinc dust in the flue gas, achieving lead-zinc dust grading and creating considerable economic value. Then, lead-zinc removal equipment is used to effectively reduce the content of heavy metal lead and zinc in the flue gas of the rotary hearth furnace or rotary kiln, eliminating its pollution and harm to the environment, significantly reducing disposal fees and costs, and making up for the shortcomings of existing dust removal technologies in their poor ability to capture fine particles rich in lead and zinc. The dust particle removal rate reaches over 93%, which is much higher than the existing wet process (below 70%), and the cost is much lower than the existing process.

[0030] 2. The flue gas is passed horizontally through the wet rolling filter belt. The micropores on the filter belt and the water film work together to effectively wet and intercept the tiny dust particles in the flue gas, reducing the concentration of dust particles. The intercepted small dust particles are then washed away in the cleaning tank, eliminating the cleaning process of wet electrostatic precipitators and the bag replacement process of bag filters. It is low-cost, easy and quick to operate, and does not affect production operations.

[0031] 3. The cleaning tank is equipped with an ultrasonic generator, which can clean the intercepted small dust particles through the rotation of the filter belt and ultrasonic cleaning. It has a simple structure and is easy to implement.

[0032] 4. The immersion liquid is a mixed solution of H2SO4 and H3PO4. During the immersion, it can react chemically with the dust particles in the filter belt to achieve better immersion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a structural diagram of the lead and zinc removal equipment.

[0034] Figure 2 It is a schematic diagram of the connection structure between the flue gas duct and the filter belt.

[0035] Figure 3 It is a cross-sectional diagram of the joint between the flue gas duct and the filter belt.

[0036] In the figure: 1 - filter belt cleaning tank 2 - absorption liquid wetting tank 3 - ultrasonic generator 4 - filter belt rotating shaft 5 - flue gas duct 6 - joint between flue gas duct and filter belt 7 - filter belt 8 - transverse section of flue gas duct 9 - longitudinal section of flue gas duct 10 - sealing shell. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0038] The flue gas from a rotary hearth furnace or rotary kiln contains a large amount of lead-zinc dust, which can be used as an important raw material for lead and zinc extraction and has a high market value. The smaller the dust particle size, the higher its lead and zinc content, and thus has a higher added value. A method for removing lead and zinc from flue gas, which passes the flue gas into a flue gas sorting system, is used to collect dust particles in the flue gas by classification, and obtain lead-zinc dust ash of different grades (low lead and zinc content, medium lead and zinc content, high lead and zinc content) and different particle sizes (large particle size, medium particle size, small particle size). The flue gas sorting system adopts the wind-magnetic separation system in the patent application number CN201710742752.9, entitled "A method for dry separation of potassium, sodium, and chlorine from sintering flue gas dust removal ash". Other methods can also be used. The specific steps are as follows:

[0039] S1. Adjust the air volume in the flue to between 110 and 170 m3 / min, and the air pressure in the flue to between 1400 and 1700 Pa, so that the dust with high iron content and large particle size settles under the action of gravity in the front section of the flue and is separated;

[0040] S2. Dust with smaller particle size and specific gravity continues to move forward along the flue. A weak magnetic separation device is provided in the middle section of the flue. The magnetic separation device provided in the second section of the air duct in the patent application number CN201710742752.9, entitled "A method for dry separation of potassium, sodium and chlorine from sintering flue gas dust removal ash" is adopted. Other methods can also be used. The magnetic field strength of the weak magnetic separation device is adjusted to between 6000 and 8000 Oe to separate the magnetic materials with relatively high iron content.

[0041] S3. Flue gas enters the rear section of the flue, where a strong magnetic separation device is provided. The magnetic separation device provided in the second section of the air duct in the patent application number CN201710742752.9, entitled "A method for dry separation of potassium, sodium and chlorine from sintering flue gas dust removal ash" is adopted. Other methods may also be used. The magnetic field strength is adjusted to a range of 11,000 to 13,000 Oe to separate magnetic materials with relatively low iron content. The flue gas separation system separates lead-zinc dust removal ash of three grades: low, medium and high. These grades are dust removal ash with low lead and zinc content (large particle size, diameter ≥ 300 μm), dust removal ash with medium lead and zinc content (medium particle size, 100 μm < diameter < 300 μm), and dust removal ash with high lead and zinc content (small particle size, diameter ≤ 100 μm), which are used as raw materials for lead and zinc extraction.

[0042] S4. The flue gas from the flue gas separation system is then processed by the lead and zinc removal equipment to further capture the lead and zinc elements in the flue gas and reduce the emission of fine lead and zinc dust into the atmosphere with the flue gas, causing environmental pollution. Specifically, it includes:

[0043] S41. Prepare the leaching solution: use a mixed solution of H2SO4 and H3PO4, with the percentage concentration of H2SO4 being 5% to 8% and the percentage concentration of H3PO4 being 2% to 3%;

[0044] S42, respectively loading the prepared leaching liquid into the filter belt cleaning tank and the absorption liquid wetting tank;

[0045] S43, turning on the ultrasonic generator and adjusting the ultrasonic vibration frequency to 25-29 kHz to achieve the best cleaning degree of the filter belt;

[0046] S44, the filter belt rotating shaft rotates, so that the filter belt linear running speed reaches 28~32m / min;

[0047] S45, passing the flue gas after the electrostatic precipitator into the flue gas duct, and controlling the flow rate of the flue gas in the duct to be 8-14 m / s;

[0048] S46. Regularly drain and add the leaching liquid in the filter belt cleaning tank and the absorption liquid wetting tank.

[0049] Conventional dust removal equipment, such as gravity dust removal, cyclone dust removal, electrostatic precipitator, and bag dust removal, has little effect on removing lead and zinc. Wet electrostatic precipitator and third-generation bag dust removal equipment have high investment and operating costs (electrostatic precipitators have a large one-time investment and high maintenance costs, while bag dust removal requires frequent bag replacement, resulting in high bag consumption). Therefore, the present invention uses a flue gas lead and zinc removal system. The flue gas is passed through the lead and zinc removal equipment for treatment. The micropores on the wet rolling filter belt and the acid wash water film work together to effectively wet, intercept, and react the lead and zinc dust particles in the flue gas. The specific details are as follows:

[0050] The system for removing lead and zinc from flue gas includes a lead and zinc removal device, which includes a flue gas duct 5, a filter belt 7, a filter belt cleaning tank 1, an absorption liquid wetting tank 2, a filter belt rotating shaft 4, and a main exhaust fan. The main exhaust fan is arranged in the flue gas duct 5 and is used to extract air to generate negative pressure so that the flue gas does not overflow during the lead and zinc removal process. The number of filter belt rotating shafts 4 is an even number, and the filter belt rotating shafts 4 are arranged in parallel and symmetrically in a manner of being low in the middle and high on both sides. The filter belt rotating shafts 4 are connected to the filter belt 7 so that the filter belt 7 rotates clockwise with the filter belt rotating shafts 4, and the filter belt 7 is evenly distributed with multiple micropores; the absorption liquid wetting tank 2 is placed inside the annular space surrounded by the filter belt 7, and the filter belt rotating shaft 4 located at the upper center is arranged in the absorption liquid wetting tank 2 The filter belt cleaning tank 1 is placed directly below the annular space surrounded by the filter belt 7. The filter belt rotating shaft 4 located at the lower center is arranged inside the filter belt cleaning tank 1. The horizontal width of the filter belt cleaning tank 1 is greater than the distance between the two filter belt rotating shafts 4 with the farthest horizontal spacing. The horizontal width of the absorption liquid wetting tank 2 is less than the distance between the two filter belt rotating shafts 4 with the farthest horizontal spacing. The filter belt 7 and the transverse cross-section of the flue gas duct 5 are arranged perpendicular to each other, and the flue gas is filtered by the filter belt 7 in the flue gas duct 5. An ultrasonic generator 3 is suspended in the filter belt cleaning tank 1. Through the cavitation effect of the ultrasonic wave generated by the ultrasonic generator in the liquid, the dust particles with lead and zinc on the filter belt are separated and peeled off, thereby achieving the purpose of cleaning.

[0051] The following examples are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0052] [Example 1]

[0053] The flue air volume was adjusted to 110 m³ / min and the flue pressure to 1400 Pa using a fan. The low-pressure magnetic separator in the middle section of the flue was adjusted to 6000 Oe, and the high-pressure magnetic separator in the rear section was adjusted to 11000 Oe. Larger dust particles in the flue gas were separated and captured, yielding large dust particles (average particle size 349.5 μm, 2.43% lead and zinc by weight), medium dust particles (average particle size 184 μm, 15.90% lead and zinc by weight), and small dust particles (average particle size 52.9 μm, 45.78% lead and zinc by weight). A leaching solution was prepared using a mixture of H₂SO₄ and H₃PO₄, with an H₂SO₄ concentration of 5% and an H₃PO₄ concentration of 2%. The prepared leaching solution was then loaded into the filter belt cleaning tank 1 and the absorption liquid wetting tank 2, respectively. Turn on ultrasonic generator 3 and adjust the ultrasonic vibration frequency to 25 kHz. Turn on filter belt rotating shaft 4 and rotate it, so that the filter belt reaches a linear speed of 28 m / min. Measure the lead and zinc concentrations in the flue gas from the rotary hearth furnace after electrostatic precipitator removal. The total lead and zinc content is 4.72 mg / m³. Pass the flue gas from the rotary hearth furnace after electrostatic precipitator removal into the flue gas duct, and control the gas flow rate within the duct at 8 m / s. Test the lead and zinc concentration of the treated flue gas. The total lead and zinc content is 0.236 mg / m³.

[0054] [Example 2]

[0055] The flue air volume was adjusted to 140 m³ / min and the flue pressure to 1550 Pa using a fan. The low-pressure magnetic separator in the middle section of the flue was adjusted to 7000 Oe, and the high-pressure magnetic separator in the rear section was adjusted to 12000 Oe. Larger dust particles in the flue gas were separated and captured, yielding large dust particles (average particle size 378.2 μm, 2.55% lead and zinc by weight), medium dust particles (average particle size 174 μm, 12.83% lead and zinc by weight), and small dust particles (average particle size 45.2 μm, 49.45% lead and zinc by weight). A leaching solution was prepared using a mixture of H₂SO₄ and H₃PO₄, with an H₂SO₄ concentration of 8% and an H₃PO₄ concentration of 3%. The prepared leaching solution was then loaded into the filter belt cleaning tank 1 and the absorption liquid wetting tank 2, respectively. Turn on ultrasonic generator 3 and adjust the ultrasonic vibration frequency to 29 kHz. Turn on filter belt rotating shaft 4 and rotate it, so that the filter belt reaches a linear running speed of 32 m / min. Measure the lead and zinc concentrations in the rotary hearth furnace flue gas after electrostatic precipitator removal, and the result is 5.97 mg / m³. Pass the rotary hearth furnace flue gas after electrostatic precipitator removal into flue gas duct 5, and control the gas flow rate within the duct at 14 m / s. Test the lead and zinc concentration of the treated flue gas, and the result is 0.304 mg / m³.

[0056] [Example 3]

[0057] The flue air volume was adjusted to 170 m³ / min and the flue pressure to 1700 Pa using a fan. The strength of the weak magnetic separator in the middle section of the flue was adjusted to 8000 Oe, and the strength of the strong magnetic separator in the rear section was adjusted to 13000 Oe. Larger dust particles in the flue gas were separated and captured, yielding large dust particles (average particle size 387.2 μm, 1.98% lead and zinc by weight), medium dust particles (average particle size 204.2 μm, 13.39% lead and zinc by weight), and small dust particles (average particle size 58.3 μm, 44.43% lead and zinc by weight). A leaching solution was prepared using a mixture of H₂SO₄ and H₃PO₄, with an H₂SO₄ concentration of 6% and an H₃PO₄ concentration of 2.5%. The prepared leaching solution was then loaded into the filter belt cleaning tank 1 and the absorption liquid wetting tank 2, respectively. Turn on ultrasonic generator 3 and adjust the ultrasonic vibration frequency to 27 kHz. Turn on filter belt rotating shaft 4 and rotate it, so that the filter belt reaches a linear running speed of 30 m / min. Measure the lead and zinc concentrations in the rotary hearth furnace flue gas after electrostatic precipitator removal; the total lead and zinc content is 5.25 mg / m³. Pass the rotary hearth furnace flue gas after electrostatic precipitator removal into flue gas duct 5, and control the gas flow rate within the duct at 14 m / s. Test the lead and zinc concentration of the treated flue gas; the total lead and zinc content is 0.278 mg / m³.

[0058] The present invention adopts a flue gas sorting system to preliminarily capture lead-zinc dust in the flue gas, realizes lead-zinc dust ash classification, creates considerable economic value, and then adopts lead-zinc removal equipment to effectively reduce the content of heavy metal lead and zinc in the flue gas of the rotary hearth furnace or rotary kiln, eliminates its pollution and harm to the environment, significantly reduces disposal fees and costs, and makes up for the shortcomings of the existing dust removal technology for the poor capture ability of fine particles rich in lead and zinc, and achieves a dust particle removal rate of more than 93%, which is much higher than the existing wet process (below 70%), and the cost is much lower than the existing process; the flue gas is passed horizontally through the wet rolling filter belt, and the micropores on the filter belt and the water film are used together to remove the lead-zinc dust. The function is to effectively wet and intercept the tiny dust particles in the flue gas, reduce the concentration of dust particles, and wash away the intercepted small dust particles in the cleaning tank, eliminating the cleaning process of wet electrostatic precipitator and the bag replacement process of bag dust removal. It has low cost, simple and fast operation, and does not affect production operation. The cleaning tank is equipped with an ultrasonic wave generator, which can wash away the intercepted small dust particles through filter belt rotation and ultrasonic cleaning. It has a simple structure and is easy to implement. The immersion liquid adopts a mixed solution of H2SO4 and H3PO4, which can chemically react with the dust particles in the filter belt during immersion to achieve better immersion effect.

Claims

1. A method for removing lead and zinc from flue gas, characterized in that: The flue gas is passed into the flue gas separation system to collect dust particles in the flue gas in a graded manner to obtain lead-zinc dust ash of different grades and particle sizes. Specifically, it includes: S1. Adjust the air volume in the flue to 110~170m 3 / min, and adjust the wind pressure in the flue to between 1400 and 1700 Pa, so that the dust with high iron content and large particle size settles under the action of gravity in the front section of the flue and is separated; S2. The dust with smaller particle size and specific gravity continues to move forward along the flue. A weak magnetic separation device is installed in the middle section of the flue. The magnetic field strength of the weak magnetic separation device is adjusted between 6000 and 8000 Oe to separate the magnetic materials with relatively high iron content. S3. The flue gas enters the rear section of the flue, where a strong magnetic separation device is installed. The magnetic field strength is adjusted between 11,000 and 13,000 Oe to separate the magnetic materials with relatively low iron content. S4. The flue gas coming out of the flue gas separation system is then processed by the lead and zinc removal equipment to further capture the lead and zinc elements in the flue gas; The lead-zinc removal equipment includes a filter belt cleaning tank, an absorption liquid wetting tank, and a filter belt rotating shaft. The number of the filter belt rotating shafts is an even number. The filter belt rotating shafts are arranged in parallel and symmetrically with the middle being low and the two sides being high. The filter belt rotating shafts are connected to the filter belt so that the filter belt rotates clockwise along with the filter belt rotating shafts. The absorption liquid wetting tank is placed inside the annular space surrounded by the filter belt. The filter belt rotating shaft located at the upper center is arranged inside the absorption liquid wetting tank. The filter belt cleaning tank is placed directly below the annular space surrounded by the filter belt. The filter belt rotating shaft located at the lower center is arranged inside the filter belt cleaning tank. The flue gas coming out of the flue gas separation system is then processed by the lead and zinc removal equipment, including: S41, prepare immersion solution; S42, respectively loading the prepared leaching liquid into the filter belt cleaning tank and the absorption liquid wetting tank; S43, turn on the ultrasonic generator and adjust the ultrasonic vibration frequency to 25~29kHz; S44, the filter belt rotating shaft rotates, so that the filter belt linear running speed reaches 28~32m / min; S45, passing the sintering flue gas after the electrostatic precipitator into the flue gas pipeline, and controlling the flow rate of the sintering flue gas in the pipeline to be 8-14 m / s; S46. Regularly drain and add the leaching liquid in the filter belt cleaning tank and the absorption liquid wetting tank; The prepared leaching solution adopts a mixed solution of H2SO4 and H3PO4, with the percentage concentration of H2SO4 being 5% to 8% and the percentage concentration of H3PO4 being 2% to 3%.

2. A system for removing lead and zinc from flue gas according to the method of claim 1, characterized in that: It includes lead and zinc removal equipment, which includes a flue gas duct, a filter belt, and a main exhaust fan. The filter belt and the transverse section of the flue gas duct are arranged perpendicular to each other. The flue gas is filtered through the filter belt in the flue gas duct. The main exhaust fan is arranged in the flue gas duct to exhaust air to generate negative pressure, so that the flue gas does not overflow during the lead and zinc removal process.

3. The system for removing lead and zinc from flue gas according to claim 2, characterized in that: The horizontal width of the filter belt cleaning tank is greater than the distance between the two filter belt rotation axes with the farthest horizontal spacing; the horizontal width of the absorption liquid wetting tank is less than the distance between the two filter belt rotation axes with the farthest horizontal spacing.

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