A method and system for the innocuous disposal of toxic hazardous waste

Abstract

The present application relates to a hazardous waste detoxification disposal method and system, including a chromium removal device, the chromium removal device includes a flue gas pipeline, a filter belt, a main exhaust fan, the filter belt and the flue gas pipeline cross section are perpendicular to each other, sintering flue gas is filtered in the flue gas pipeline through the filter belt, the main exhaust fan is used for producing negative pressure by exhausting, so that sintering flue gas does not overflow in the process of chromium removal.The present application has the advantages that: the sintering process is used to realize the compliance disposal of hazardous waste, eliminate its pollution and harm to the environment, save disposal cost and cost; through the sintering process, the proportion coefficient of chromium element in the sintered raw material is calculated to control the adding amount of chromium-containing sludge, so that the problem of environmental pollution or low treatment efficiency caused by improper adding amount of chromium-containing sludge is avoided; through the flue gas chromium removal process, the secondary pollution caused in the process of chromium-containing sludge treatment is solved, the chromium removal rate is improved, and the cost is much lower than that of the existing process.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of waste, and to a method and system for the harmless disposal of toxic and hazardous waste. Background Technology

[0002] According to national hazardous waste identification standards, some chromium-containing wastes from steel enterprises are classified as hazardous waste. For example, chromium-containing sludge generated from the production of cold-rolled silicon steel is classified as HW17 in the national hazardous waste list. Common valence states of chromium, trivalent and hexavalent, are both toxic substances, especially hexavalent chromium, which is highly toxic and classified as a carcinogen and mutagen. To dispose of these hazardous wastes, some steel enterprises use their own furnaces for harmless treatment, resulting in some chromium entering the atmosphere with the flue gas, causing serious secondary pollution. Research has found that when the chromium content in the sintering raw materials is low, the chromium is mainly solidified in the sintered ore after sintering, and the amount of chromium released into the atmosphere with the flue gas is extremely low. However, when the chromium content in the sintering raw materials exceeds a certain critical value, the proportion of chromium entering the sintering flue gas increases sharply after sintering. Furthermore, this critical value for chromium content is not fixed under different sintering raw material and process parameters, increasing the difficulty of treatment. There are currently no studies or reports on how to control the amount of chromium-containing sludge added in the sintering process to reduce its environmental impact.

[0003] On the other hand, studies on the forms in which chromium exists in sintering flue gas have revealed that chromium exists primarily in the form of solid particulate matter, with chromium mainly concentrated in fine-grained dust particles, and its content in larger-sized dust particles being very low. Research on dust collected from sintering flue gas also shows that the smaller the particle size of the dust collected, the higher the percentage of chromium content. Domestic and international steel companies generally use electrostatic precipitators to treat sintering flue gas, which easily captures larger dust particles, while the small particles enriched in chromium are not effectively removed and are ultimately released into the atmosphere, causing environmental harm. Currently, there is no good and economically reasonable method for removing heavy metal chromium from sintering flue gas.

[0004] Wu Yanmei's article, "Practice of Harmless Sintering Production Treatment of Chromium Slag," introduces the production practice of Sichuan Dagang in treating chromium-containing waste slag during sintering. Wang Hongjun et al.'s article, "Application Practice of Chromium Slag in Jiuquan Iron & Steel's Sintering Production," introduces Jiuquan Iron & Steel's method of treating chromium slag as a sintering auxiliary material in its sintering system. Both articles concern the application of chromium-containing solid waste in the sintering system; however, their technical research only considers the impact of chromium on sintering production yield and quality, neglecting the existence form and final destination of chromium in the sintering process, thus ignoring the environmental impact of chromium-containing waste. Chromium-containing waste is hazardous waste and requires centralized harmless treatment. Simply treating it as a sintering auxiliary material without considering environmental factors may not only fail to achieve harmless treatment but also cause the spread of hazardous chromium-containing waste through sintering flue gas emissions.

[0005] The patent with publication number CN1313407A, entitled "Production of Chromium-Containing Sinter for Blast Furnaces Using Chromium Ore Powder and Iron-Bearing Raw Materials," involves mixing chromium ore powder, iron-bearing materials, solid fuel, and auxiliary flux in a certain proportion, and sintering the mixture using ordinary sintering equipment to produce chromium-containing sinter. The patent with publication number CN104630458A, entitled "A Method for Preparing Acidic Chromium-Containing Vanadium-Titanium Sinter," involves mixing iron ore powder, quicklime, coke powder, and chromium-containing vanadium-titanium magnetite powder in a certain proportion to form sintering pellets, then distributing the pellets on a sintering machine, and performing ignition and blast sintering to finally obtain sinter. The patent, published under CN 107267749A and titled "Method for Preparing Sintered Ore from High-Grade, High-Vanadium, Chromium-Containing Vanadium-Titanium Magnetite Concentrate Mixture," uses high-grade, high-vanadium, chromium-containing vanadium-titanium magnetite concentrate powder, boron concentrate powder, iron concentrate powder, vanadium-chromium extraction waste slag, limestone, lime powder, fuel, and recycled ore as raw materials. These materials are crushed, mixed, granulated, and then sintered in a sintering machine to obtain sintered ore. However, these patents only consider the impact of chromium-containing raw materials on sintering indicators and sintered ore product quality, without considering the secondary pollution caused by chromium-containing hazardous waste.

[0006] The patent, published under CN112853090A and entitled "A Method for Resource Utilization of Chromium-Containing Waste Residue Composite Pellets Using Sintering," describes a process where raw materials, including chromium-containing waste residue and a reducing agent, are mixed and pelletized to obtain pellet material. Simultaneously, raw materials, including iron ore, flux, and coke powder, are mixed and granulated to obtain granular material. The pellet material and granular material are then mixed and layered and sintered in a sintering machine to obtain chromium-containing sintered ore. By utilizing the structural advantages of the pellet material, the automatic heat storage effect of the material layer, and the thermal field of the granular material to heat the pellet material, the high-valent chromium compounds in the pellet material are rapidly reduced to metallic chromium or chromium carbide under high-temperature conditions, thus achieving complete detoxification of the chromium-containing waste residue. The patent, published under CN112853091A and titled "A Method for Efficient Co-operative Resource Utilization of Chromium-Containing Waste Residue and Carbon-Containing Waste," describes a method for efficiently and synergistically utilizing chromium-containing waste residue and carbon-containing waste. This method involves mixing raw materials, including chromium-containing waste residue and carbon-containing waste, to form spherical pellets. Simultaneously, raw materials, including iron-containing raw materials, flux, and fuel, are mixed and granulated to obtain granular material. The spherical and granular materials are then mixed and layered before being fed into a sintering machine for sintering under vacuum, ultimately yielding chromium-containing sintered ore, thus achieving complete detoxification of the chromium-containing waste residue. The advancement of these two patents lies in considering the detoxification of chromium-containing waste while simultaneously utilizing it. By using a reduction reaction between carbon-containing raw materials and chromium-containing waste at high temperatures, the highly toxic hexavalent chromium is reduced to trivalent chromium, achieving detoxification of the chromium-containing waste. However, this method still has some drawbacks. First, the sintering process is a complex process of reduction followed by oxidation, and it is not entirely a reduction reaction. The process of trivalent chromium being re-oxidized to hexavalent chromium in the second half of sintering is not taken into consideration. Second, although trivalent chromium is not as toxic as hexavalent chromium, it is still a toxic substance. Even if it is completely reduced, it will still be released into the atmosphere with the flue gas, causing serious harm to the environment.

[0007] The patent, with publication number CN 210752037 U and titled "Equipment for Tail Gas Treatment in the Disposal of Chromium-Containing Heavy Metal Hazardous Waste," includes a dust purification device, an acidic gas purification tank, and a sludge settling tank. The dust purification device mixes steam generated during water quenching with flue gas, utilizing the condensation effect of the steam to settle the dust in the flue gas. The dust-removed flue gas is then introduced into the acidic gas purification tank below the liquid level, allowing the acidic gases in the flue gas to fully react with the solution, thereby purifying the acidic gases. However, this equipment requires a large amount of steam for condensation, consuming significant resources and energy, resulting in high operating costs. Furthermore, the steam condensation effect on purifying chromium-containing dust particles is limited, and the chromium dust removal rate is low.

[0008] The patent, with announcement number CN109499238A and titled "Purification System for Flue Gas Generated from the Harmless Disposal of Chromium-Containing Sludge by a Double-Cylinder Rotary Kiln," includes an inclined double-cylinder rotary kiln. It effectively solves the problems of dust, acidic gases, and nitrogen oxides in the waste gas treatment process of chromium-containing sludge, ensuring emissions meet the requirements of the "Standard for Pollution Control of Hazardous Waste Incineration" (GB18484-2001). The device sequentially passes the flue gas through a settling chamber, a cyclone dust collector, then through a first water film dust removal and desulfurization spray tower for washing, followed by a second and third water film dust removal and desulfurization spray tower. The entire system has a complex structure, involving settling, cyclone dust removal, and three-stage spraying, resulting in high equipment and operating costs. Furthermore, the selection of reagents does not specifically target the collection of chromium-containing dust, and fine chromium-containing dust cannot be completely captured.

[0009] The patent, with publication number CN101339103A and titled "Method for Determining Heavy Metal Elements in Cigarette Smoke Using a Smoke Collection and Absorption Device," describes a smoke collection and absorption device comprising an outer sleeve (1), an inner sleeve (2), and a sealing plug (3). The outer sleeve (1) has an inlet (7) and an outlet (8). The outer sleeve (1), inner sleeve (2), and sealing plug (3) are sequentially sealed together. An upper sieve plate (6) and a lower sieve plate (4) are installed in the inner sleeve (2), with buffer filler (5) filling the space between the two sieve plates. This method, through the combined action of the upper sieve plate, lower sieve plate, and buffer filler, slightly prolongs the residence time and absorption time of the smoke in the collector. Furthermore, the dispersion of the smoke by the sieve plates and the buffering effect of the buffer filler increase the reaction surface area for smoke absorption, resulting in more complete absorption of the smoke components. However, the buffer packing only serves a buffering function, and its relatively large gaps are insufficient to filter fine dust particles in the gas. The absorption of heavy metal dust particles relies solely on the short-term contact reaction between the collector and the flue gas, resulting in a low dust collection rate. Furthermore, this device can only absorb gases with small flow rates and low flue gas velocities. When large flow rates and high velocities of sintering flue gas are introduced into the device, the resulting impact force can disperse the buffer packing and even cause the collector to splash. Moreover, the contact reaction time between the faster-flowing flue gas and the collector is even shorter, resulting in insufficient absorption.

[0010] The patent, with publication number CN211725299U and titled "An Asphalt Fume Absorption Device," comprises a cylindrical body, a resistive layer, an ozone layer, an ultraviolet lamp, a spray covering layer, a fan, and an exhaust port. Its key feature is that the bottom of the cylindrical body is equipped with a multi-layered filter plate. The first layer of the filter plate has an asbestos mesh screen, the second layer has activated carbon with honeycomb pores, and the third layer has a screen plate covered with quicklime. There is a height of 300mm-500mm between adjacent absorption layers. From top to bottom, starting at the center section of the cylindrical body, the layers are the resistive layer, the spray covering layer, and the exhaust fan inlet. The spray covering layer contains an organic solvent capable of absorbing asphalt particles. This device uses an organic solvent to absorb particulate matter in asphalt fumes, and through the combined action of the resistive layer, ozone layer, and ultraviolet lamp, the asphalt fumes react further with oxygen at high temperatures, achieving excellent absorption results. However, the use of this device has certain limitations and drawbacks: First, the device has a complex structure and high cost. The activated carbon honeycomb pore material needs to be replaced regularly because it will fail after use. The ozone layer and the resistance layer also consume high resources and energy, which significantly increases the operating cost of the equipment. Second, among the several layers of filtration structure of this device, the asbestos mesh has limited filtering and interception effect on fine dust in the flue gas. 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. The sprayed organic solvent is sprayed through tiny water droplets, and the collision between the spray liquid and the small asphalt particles in the flue gas is random, so the spray absorption effect is poor. The combined effect of the resistance layer, ozone layer and ultraviolet lamp is only effective against organic particles in asphalt flue gas, and its effect is also very limited.

[0011] The patent, with publication number CN213467325U and titled "A Petrochemical Flue Gas Absorption Device," includes an absorption tower, a gas washing section, a chemical absorption section, and a water vapor recovery section. The gas washing 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 water vapor recovery section is located at the top of the absorption tower. The water vapor recovery section includes a water vapor baffle plate, which comprises a water vapor baffle channel and a water vapor recovery channel. A cold air channel is provided at the top of the water vapor baffle channel, and a water outlet is provided at the bottom of the water vapor recovery channel. A heat-conducting plate is provided on the cold air channel, and a water collection plate is provided on the water outlet channel. A water outlet is provided at the bottom of the water outlet channel. This device introduces flue gas into the bottom of the absorption tower, where it undergoes gas washing and cooling, followed by chemical absorption of acidic gases, and finally water vapor recovery. This device effectively solves the problem of catalysts and water in flue gas after conventional absorption tower treatment, but it still has certain limitations and drawbacks: when the flue gas passes through the gas washing section of the device, it usually rises 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. The chemical absorption and water vapor absorption sections also cannot achieve the purpose of absorbing dust particles in the flue gas.

[0012] The patent, CN103969324A, entitled "A Method for Detecting Chromium, Nickel, Arsenic, Selenium, Cadmium, and Lead in Cigarette Sidestream Smoke," uses a fishtail hood with a series of quartz fiber filters to collect particulate matter from cigarette sidestream smoke. A three-stage series of nitric acid solutions collects the gaseous phase of the sidestream smoke. The sample is digested using microwave digestion, and the content of chromium, nickel, arsenic, selenium, cadmium, and lead in the particulate and gaseous samples is detected by inductively coupled plasma mass spectrometry (ICP-MS). This method absorbs and neutralizes particulate and gaseous heavy metals in the smoke separately before detection. However, this method requires separate processing of particulate and gaseous matter, involving a series of processes such as washing, extraction, digestion, ultrasonic vibration, and heating concentration. The operation is complex, time-consuming, and costly. More importantly, the method of collecting particulate matter using quartz fiber filters cannot completely absorb particulate matter in the smoke; some extremely small heavy metal particles cannot be captured.

[0013] Currently, there is no economical and reasonable method for the harmless disposal of chromium-containing sludge in China that can both avoid secondary environmental pollution and permanently eliminate the harmful effects of chromium-containing hazardous waste. Summary of the Invention

[0014] The purpose of this invention is to provide a method and system for the harmless disposal of toxic hazardous waste. This method solves the problem that existing treatment processes do not consider the impact of chromium-containing hazardous waste on sintering flue gas, which leads to the diffusion of chromium pollutants and secondary environmental pollution. By dynamically controlling the amount of chromium-containing hazardous waste added by balancing the chromium content in raw materials and products, the method minimizes the proportion of chromium entering the sintering flue gas and absorbs the heavy metal chromium in the sintering flue gas, thus achieving the harmless disposal of chromium-containing waste. This not only saves high hazardous waste treatment costs but also makes full use of resources, creating considerable economic and environmental benefits.

[0015] To achieve the above objectives, the present invention provides the following technical solution:

[0016] A method for harmlessly disposing of toxic hazardous waste includes:

[0017] S1. Pretreatment of chromium-containing sludge

[0018] The chromium-containing sludge is air-dried or oven-dried to ensure a moisture content of ≤2%, and then crushed. The crushed material must meet the requirement of a particle size of less than 2mm, with a proportion of greater than or equal to 95%, to obtain chromium-containing dust.

[0019] S2. Mix the crushed chromium-containing dust with other dust and sludge waste materials evenly to obtain dust and sludge mixture, wherein the mass ratio of chromium-containing dust to dust and sludge waste materials is 1:50 to 1:10.

[0020] S3. The dust and sludge mixture is then mixed with various iron-containing materials to obtain a premixed material. The dust and sludge mixture accounts for 14% to 17% of the total iron-containing material ratio.

[0021] S4. The premixed material is mixed with flux and fuel again, and after one mixing and two mixing and granulation, a sintering mixture is finally obtained for the production of sintered ore.

[0022] S5. Weighing and chromium content detection;

[0023] S6. Calculate the proportion coefficient η of chromium element entering the sinter from the sintering raw materials;

[0024] S7. The proportional coefficient η is used to determine whether the chromium-containing sludge in the raw material has been added in excess. When the proportional coefficient η is greater than or equal to 0.97, it can be determined that the chromium-containing sludge in the raw material has been added in excess, and the proportion of chromium-containing sludge added needs to be increased. If the chromium-containing sludge has not been added in excess, when the proportional coefficient η is less than 0.97, it can be determined that the chromium-containing sludge in the raw material has not been added in excess, and the proportion of chromium-containing sludge added in the sintering raw material needs to be reduced immediately.

[0025] S8. The sintering flue gas generated during the sintering process is successively treated by a dust collector, a chromium removal device, and desulfurization and denitrification before being discharged in compliance with regulations.

[0026] Various iron-containing materials include rich ore powder and concentrate.

[0027] In S6, the proportionality coefficient η is calculated using the following formula:

[0028]

[0029] In formula ①, η represents the proportion coefficient of chromium in the sintering raw material entering the sinter, M1 represents the mass of the sintering mixture weighed before feeding, M2 represents the mass of all sintered products between the starting and ending positions of the sintering machine trolley as recorded after sintering, X% represents the chromium content of the mixture (wet basis), and Y% represents the chromium content of the sinter.

[0030] In S8, the dust collectors include gravity dust collectors and electrostatic precipitators.

[0031] In S5, the content is as follows:

[0032] Before feeding, weigh the mass of the sintering mixture, feed the mixture, number the sintering trolley, record the starting and ending positions of the trolley corresponding to the feeding process of the weighed sintering mixture, and then ignite and sinter.

[0033] After sintering, the mass of all sintered ore products between the starting and ending positions of the sintering machine trolley is weighed. Multiple samples are taken from the sintering mixture and sintered ore products during the process, and the chromium content is tested. The chromium content of the mixture (wet basis) and the chromium content of the sinter are analyzed.

[0034] A harmless disposal system for toxic hazardous waste includes a chromium removal device, which includes a flue gas duct, a filter belt, and a main exhaust fan. The filter belt and the flue gas duct are arranged perpendicular to each other in their transverse sections. The sintering flue gas is filtered by the filter belt in the flue gas duct. The main exhaust fan is installed in the flue gas duct to generate negative pressure, so that the sintering flue gas does not overflow during the chromium removal process.

[0035] The chromium removal equipment also includes a filter belt cleaning tank, an absorbent wetting tank, and filter belt rotating shafts. There are an even number of filter belt rotating shafts, which are arranged symmetrically in parallel with the middle being lower and the sides being higher. The filter belt rotating shafts are connected to the filter belt, so that the filter belt rotates clockwise with the filter belt rotating shafts. The absorbent wetting tank is placed inside the annular space surrounded by the filter belt, and the filter belt rotating shaft located at the upper center is located inside the absorbent 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 located inside the filter belt cleaning tank.

[0036] The horizontal width of the filter belt cleaning tank is greater than the distance between the two filter belts with the furthest horizontal spacing; the horizontal width of the absorbent wetting tank is less than the distance between the two filter belts with the furthest horizontal spacing.

[0037] Both the filter belt cleaning tank and the absorbent wetting tank are filled with immersion solution. The immersion solution is a mixed solution of NaOH and Ca(OH)2. The immersion solution is used to clean the residue on the filter belt. The percentage concentration of NaOH in the mixed solution is 3% to 6%, and the percentage concentration of Ca(OH)2 is 2% to 4%. The linear running speed of the filter belt is 16 to 20 m / min, and the ultrasonic vibration frequency is 25 to 40 kHz.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. Harmless disposal of chromium-containing hazardous waste: The sintering process was used in conjunction with other methods to achieve compliant disposal of hazardous waste, eliminating its pollution and harm to the environment, and saving disposal costs.

[0040] 2. By co-treating chromium-containing sludge through sintering process, the amount of chromium-containing sludge added is controlled by calculating the proportion coefficient of chromium element in sintering raw materials entering the sintered ore, thus avoiding environmental pollution or low treatment efficiency caused by improper addition of chromium-containing sludge.

[0041] 3. By using a low-cost and high-efficiency flue gas chromium removal process, the secondary pollution caused by chromium-containing sludge treatment is solved, the chromium removal rate is improved, and the removal rate is much higher than that of the existing wet process (below 70%), while the cost is much lower than that of the existing process.

[0042] 4. By using sintering to co-process chromium-containing hazardous waste, steel companies can achieve the self-harmless disposal of existing chromium-containing hazardous waste sludge, reducing the various hazards of chromium to the environment. Moreover, it makes reasonable use of resources such as iron, silicon, and calcium in the waste, saves hazardous waste disposal costs, and creates considerable economic benefits.

[0043] 5. By treating the sintering flue gas with gravity dust collectors and electrostatic precipitators, the dust content of the sintering flue gas can be significantly reduced, thereby reducing the operating burden of the chromium removal equipment and ensuring the operating effect of the chromium removal equipment.

[0044] 6. Chromium removal equipment can further reduce the dust content of sintering flue gas, which not only has the effect of further dust removal, but also reduces the operating burden of desulfurization and denitrification processes, and ultimately achieves compliant ultra-low emissions.

[0045] 7. In addition to generating negative pressure in the pipeline and promoting the combustion of sintered materials, the main exhaust fan also prevents flue gas from overflowing during the chromium removal process. Attached Figure Description

[0046] Figure 1 This is a flowchart of the method for harmless disposal of toxic hazardous waste.

[0047] Figure 2 This is a schematic diagram of the chromium removal equipment.

[0048] Figure 3 This is a schematic diagram of the connection structure between the flue gas duct and the filter belt.

[0049] Figure 4 This is a schematic diagram of the cross-section of the joint between the flue gas duct and the filter belt.

[0050] In the diagram: 1-Filter belt cleaning tank; 2-Absorbent liquid wetting tank; 3-Ultrasonic generator; 4-Filter belt rotating shaft; 5-Flue gas duct; 6-Seam 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-Sealed outer shell of chromium removal equipment. Detailed Implementation

[0051] The present invention will now be described in detail 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.

[0052] Extensive experimental research on the fate and distribution of chromium during the sintering process in major steel plants across the country revealed that as the chromium content in the sintering raw materials increases, the proportion of chromium entering the sintering flue gas surges when a certain critical value is reached. Chromium in the sintering flue gas exists in the form of small particles; the chromium content in large dust particles is extremely low, and the smaller the dust particle size, the higher the chromium content. This invention utilizes a sintering process in conjunction with the treatment of chromium-containing waste to completely achieve the harmless treatment of chromium-containing hazardous waste without causing secondary pollution. A method and system for the harmless treatment of toxic hazardous waste is described below:

[0053] 1. Pretreatment of chromium-containing sludge

[0054] The chromium-containing sludge is air-dried or oven-dried to ensure a moisture content of ≤2%, and then crushed. The crushed material must meet the requirement of a particle size of less than 2mm, with a proportion of greater than or equal to 95%, to obtain chromium-containing dust.

[0055] 2. Mix the crushed chromium-containing dust with other dust and sludge waste materials to obtain a dust and sludge mixture, wherein the mass ratio of chromium-containing dust to dust and sludge waste materials is between 1:50 and 1:10.

[0056] 3. The dust and sludge mixture is then mixed with various iron-containing materials such as rich ore powder and concentrate to obtain a premixed material. In this process, the dust and sludge mixture accounts for 14% to 17% of the total iron-containing material.

[0057] 4. The premixed material is mixed with flux and fuel again, and after one mixing and two mixing and granulation, a sintering mixture is finally obtained for the production of sintered ore.

[0058] 5. Before feeding the sintering mixture, weigh the mass of the sintering mixture (denoted as M1), feed the mixture, number the sintering trolleys, and record the starting and ending positions of the trolleys corresponding to the feeding process of the weighed sintering mixture. Ignite and sinter. The starting time of sintering at the starting position of the trolley is the starting time of the sintering flue gas flow measurement, and the ending time of sintering at the ending position of the trolley is the ending time of the sintering flue gas flow measurement. After sintering, weigh the mass of all sintered ore products between the recorded starting and ending positions of the sintering machine trolleys (denoted as M2). During this process, perform multi-point sampling and chromium content testing on the sintering mixture and sintered ore products. The chromium content of the mixture (wet basis) is denoted as X%, and the chromium content of the sintered ore is denoted as Y.

[0059] 6. Calculate the proportion coefficient η of chromium in the sintering raw materials into the sinter, using the following formula:

[0060]

[0061] 7. Determine whether excessive amounts of chromium-containing sludge have been added to the raw materials based on the coefficient η:

[0062] When the η value is ≥0.97, the proportion of chromium-containing sludge added can be increased appropriately according to the treatment volume requirements, or the addition volume parameter can be maintained.

[0063] When the η value is less than 0.97, the proportion of chromium-containing sludge added to the sintering raw materials needs to be reduced immediately.

[0064] 8. The sintering flue gas generated during the sintering process, under the negative pressure generated by the main exhaust fan, first passes through a gravity dust collector, then enters an electrostatic precipitator for treatment. The flue gas exiting the electrostatic precipitator is then treated by a chromium removal device. See [link to relevant documentation]. Figure 2 In the chromium removal equipment, the immersion solution is a mixed solution of NaOH and Ca(OH)2, in which the percentage concentration of NaOH is 3% to 6% and the percentage concentration of Ca(OH)2 is 2% to 4%. The filter belt runs clockwise at a linear speed of 16 to 20 m / min and the ultrasonic vibration frequency is 25 to 40 kHz.

[0065] 9. After chromium removal, the flue gas undergoes desulfurization and denitrification to ultimately achieve emission standards.

[0066] The chromium removal equipment used in the above method includes a filter belt cleaning tank 1, an absorbent wetting tank 2, an ultrasonic generator 3, a filter belt rotating shaft 4, a flue gas duct 5, a filter belt 7, and a chromium removal equipment sealing housing 10. The connection method of this equipment is as follows:

[0067] Inside the sealed housing 10 of the chromium removal equipment, six filter belt rotating shafts 4 are placed parallel to each other with a lower center and higher sides. The rotating shafts 4 connect to the filter belts 7, allowing the filter belts 7 to rotate clockwise with the shafts. The absorbent wetting tank 2 is placed inside the annular space surrounded by the filter belts 7. The filter belt rotating shaft located at the upper center is surrounded by the absorbent wetting tank 2 on three sides. The filter belt cleaning tank 1 is placed directly below the annular space surrounded by the filter belts 7, and its width is greater than the distance between the two horizontally furthest rotating shafts 4. The filter belt rotating shaft located at the lower center is surrounded by the filter belt cleaning tank 1 on three sides. An ultrasonic generator 3 is suspended inside the filter belt cleaning tank 1. Through the cavitation effect of the generated ultrasonic waves in the liquid, the dust particles on the filter belts are separated and peeled off, thus achieving the cleaning purpose. The horizontally placed flue gas duct 5 is connected to the vertically placed filter belts 7, see... Figure 3 , Figure 4 .

[0068] The present invention will now be described in detail 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.

[0069] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0070]

Example 1

[0071] A method for the harmless disposal of toxic hazardous waste, see Figure 1First, chromium-containing sludge was taken and dried at 105℃. The moisture content after drying was measured to be 2.0%. A jaw crusher was used for crushing. Particle size analysis of the resulting chromium-containing dust showed that particles smaller than 2mm accounted for 96.2% of the mass. The crushed chromium-containing dust was then mixed evenly with other dust and sludge waste at a mass ratio of 1:50 to obtain a dust-sludge mixture. This mixture was then premixed with various iron-containing materials such as rich ore powder and concentrate to obtain a premix. In this process, the dust-sludge mixture accounted for 14% of the total iron-containing material. The premix was then mixed again with flux and fuel, and after one mixing and two homogenization granulation processes, a sintering mixture was finally obtained. The sintering mixture was weighed, and its mass M1 was 329.4 tons. The mixture was then distributed, and the starting and ending positions of the sintering trolley were recorded. Ignition and sintering were then carried out. After sintering, the mass M2 of all sintered ore products between the recorded starting and ending positions of the sintering trolley was weighed and found to be 263.9 tons. Multiple samples of the sintering mixture and sintered ore products were taken and their chromium content was tested. The chromium content (wet basis) of the mixture was 0.032%, and the chromium content of the sintered ore was 0.040%. According to formula ①, the proportionality coefficient η was calculated to be 0.982, which is much greater than 0.97. Therefore, the proportion of chromium-containing sludge added can be appropriately increased according to the required processing volume. The sintering flue gas generated during this sintering process was first treated by a gravity dust collector, then by an electrostatic precipitator, and finally by a chromium removal device. The chromium removal equipment uses a mixed solution of NaOH and Ca(OH)₂ as the immersion solution. The NaOH concentration in this mixed solution is 3%, and the Ca(OH)₂ concentration is 2%. The filter belt operates at a linear speed of 16 m / min, and the ultrasonic generator vibrates at a frequency of 40 kHz. Samples of the sintering flue gas after electrostatic precipitator treatment and after treatment with the chromium removal equipment were taken and analyzed to determine the chromium content, denoted as C1 and C2, respectively. The analysis showed that C1 was 24.68 μg / m³. 3 C2 is 2.11 μg / m 3 The average chromium content in the conventional sintering flue gas of this sintering machine, without the addition of chromium-containing sludge, is 20–25 μg / m³. 3 It can be seen that after adding chromium-containing sludge to the sintering batch, the chromium content of the sintering flue gas produced has been reduced to a level far below this after treatment. The comparison of the effects of the chromium removal equipment before and after treatment is shown in Table 1.

[0072] Table 1 Comparison of Chromium Removal Equipment Effects Before and After Treatment Table 1 Comparison of Chromium Removal Equipment Effects Before and After Treatment

[0073] <![CDATA[Chromium content C1 in flue gas after electrostatic precipitation]]> <![CDATA[Chromium content C2 in flue gas after treatment by chromium removal equipment]]> Flue gas chromium removal rate <![CDATA[24.68μg / m 3 ]]> <![CDATA[2.11μg / m 3 ]]> 91.45％

[0074]

Example 2

[0075] A method for the harmless disposal of toxic hazardous waste, see Figure 1First, chromium-containing sludge was taken and dried at 105℃. The moisture content after drying was measured to be 0.28%. A jaw crusher was used for crushing. Particle size analysis of the resulting chromium-containing dust showed that particles smaller than 2mm accounted for 96.6% of the mass. The crushed chromium-containing dust was mixed evenly with other dust and sludge waste at a mass ratio of 1:10 to obtain a dust-sludge mixture. This mixture was then premixed with various iron-containing materials such as rich ore powder and concentrate to obtain a premix. In this process, the dust-sludge mixture accounted for 17% of the total iron-containing materials. The premix was then mixed again with flux and fuel, and after one mixing and two homogenization granulation processes, a sintering mixture was finally obtained. The sintering mixture was weighed, and its mass M1 was 352.1 tons. The mixture was then distributed, and the starting and ending positions of the sintering trolley were recorded. Ignition and sintering were then carried out. After sintering, the mass M2 of all sintered ore products between the recorded starting and ending positions of the sintering trolley was weighed and found to be 282.03 tons. Multiple samples were taken from both the sintering mixture and the sintered ore products during this process, and their chromium content was tested. The chromium content (wet basis) of the mixture was 0.076%, and the chromium content of the sintered ore was 0.099%. According to formula ①, the proportionality coefficient η was calculated to be 0.956. Since η is less than 0.97, the proportion of chromium-containing sludge added to the sintering raw materials needs to be immediately reduced. The sintering flue gas generated during this sintering process was first treated by a gravity dust collector, then by an electrostatic precipitator, and finally by a chromium removal device. The chromium removal equipment uses a mixed solution of NaOH and Ca(OH)₂ as the leaching solution, with a NaOH concentration of 6% and a Ca(OH)₂ concentration of 4%. The filter belt operates at a linear speed of 20 m / min, and the ultrasonic generator vibrates at a frequency of 25 kHz. Samples of the sintering flue gas after electrostatic precipitator treatment and after treatment with the chromium removal equipment were taken and analyzed to determine the chromium content, denoted as C1 and C2, respectively. The analysis showed that C1 was 115.03 μg / m³. 3 C2 is 9.95 μg / m 3 The average chromium content in the conventional sintering flue gas of this sintering machine, without the addition of chromium-containing sludge, is 20–25 μg / m³. 3 It can be seen that after adding chromium-containing sludge to the sintering batch, the chromium content of the sintering flue gas produced has been reduced to less than 1 / 2 of this level after treatment; the comparison of the effects of the chromium removal equipment before and after treatment is shown in Table 1.

[0076] Table 2 Comparison of Chromium Removal Equipment Effects Before and After Treatment

[0077] <![CDATA[Chromium content C1 in flue gas after electrostatic precipitation]]> <![CDATA[Chromium content C2 in flue gas after treatment by chromium removal equipment]]> Flue gas chromium removal rate <![CDATA[115.03μg / m 3 ]]> <![CDATA[9.95μg / m 3 ]]> 91.35％

[0078]

Example 3

[0079] A method for the harmless disposal of toxic hazardous waste, see Figure 1First, chromium-containing sludge was taken and dried at 105℃. The moisture content after drying was measured to be 0.48%. A jaw crusher was used for crushing. Particle size analysis of the resulting chromium-containing dust showed that particles smaller than 2mm accounted for 96.3% of the mass. The crushed chromium-containing dust was mixed evenly with other dust and sludge waste at a mass ratio of 1:30 to obtain a dust-sludge mixture. This mixture was then premixed with rich ore powder, concentrate, and other iron-containing materials to obtain a premix. In this process, the dust-sludge mixture accounted for 16% of the total iron-containing materials. The premix was then mixed again with flux and fuel, and after one mixing and two homogenization granulation processes, a sintering mixture was finally obtained. The sintering mixture was weighed, and its mass M1 was 346.2 tons. The mixture was then distributed, and the starting and ending positions of the trolleys during the distribution process were recorded. Ignition and sintering were then carried out. After sintering, the mass M2 of all sintered ore products between the starting and ending positions of the sintering machine trolleys was measured, and it was found to be 277.65 tons. Multiple samples were taken from the sintering mixture and sintered ore products during the process, and the chromium content was tested. The chromium content (wet basis) of the mixture was 0.049%, and the chromium content of the sintered ore was 0.063%. According to formula (1), the proportionality coefficient η was calculated to be 0.976. Since the value of η is greater than 0.97, the proportion of chromium-containing sludge added can be increased appropriately according to the processing volume, or the addition volume parameter can be maintained. The sintering flue gas generated during the sintering process was first treated by a gravity dust collector, then by an electrostatic precipitator, and finally by a chromium removal device. The chromium removal equipment uses a mixed solution of NaOH and Ca(OH)₂ as the immersion solution. The percentage concentration of NaOH in this mixed solution is 4.5%, and the percentage concentration of Ca(OH)₂ is 3%. The linear running speed of the filter belt is 18 m / min, and the vibration frequency of the ultrasonic generator is 32 kHz. Samples of the sintering flue gas after electrostatic precipitator treatment and the sintering flue gas after treatment with the chromium removal equipment were taken and analyzed to determine the chromium content, denoted as C1 and C2, respectively. Analysis showed that C1 was 26.72 μg / m³, and C2 was 2.53 μg / m³. The average chromium content in the conventional sintering flue gas of this sintering machine without the addition of chromium-containing sludge is 20–25 μg / m³. It is evident that after treatment, the chromium content of the sintering flue gas produced by adding chromium-containing sludge to the sintering batch is reduced to a level far below this. A comparison of the effects before and after treatment with the chromium removal equipment is shown in Table 3.

[0080] Table 3 Comparison of Chromium Removal Equipment Effects Before and After Treatment

[0081] <![CDATA[Chromium content C1 in flue gas after electrostatic precipitation]]> <![CDATA[Chromium content C2 in flue gas after treatment by chromium removal equipment]]> Flue gas chromium removal rate <![CDATA[26.72μg / m 3 ]]> <![CDATA[2.53μg / m 3 ]]> 90.53％

[0082] This invention relates to the harmless disposal of chromium-containing hazardous waste. It employs a sintering process in conjunction with other methods to achieve compliant disposal of hazardous waste, eliminating its pollution and harm to the environment while saving disposal costs. By co-processing chromium-containing sludge with sintering, the amount of chromium-containing sludge added is controlled by calculating the proportion of chromium in the sintering raw materials, thus avoiding environmental pollution or low treatment efficiency caused by improper addition of chromium-containing sludge. Furthermore, a low-cost, high-efficiency flue gas chromium removal process solves the problem of secondary pollution caused during chromium-containing sludge treatment, achieving a chromium removal rate of over 90%, far exceeding that of existing wet processes (below 70%), and at a significantly lower cost. Through the co-processing of chromium-containing hazardous waste with sintering, it achieves... This system enables steel enterprises to utilize existing chromium-containing hazardous waste sludge for self-harmless disposal, reducing the various environmental hazards caused by chromium. It also rationally utilizes resources such as iron, silicon, and calcium in the waste, saving hazardous waste disposal costs and creating considerable economic benefits. By treating sintering flue gas with gravity dust collectors and electrostatic precipitators, the dust content of the sintering flue gas can be significantly reduced, thereby reducing the operating burden of the chromium removal equipment and ensuring its operational effectiveness. The chromium removal equipment can further reduce the dust content of the sintering flue gas, achieving further dust removal and reducing the operating burden of the desulfurization and denitrification processes, ultimately achieving compliant ultra-low emissions. In addition to generating negative pressure in the pipeline and promoting the combustion of sintered materials, the main exhaust fan also prevents flue gas from overflowing during the chromium removal process.

Claims

1. A method for the harmless disposal of toxic hazardous waste, characterized in that, include: S1. Pretreatment of chromium-containing sludge Chromium-containing sludge is air-dried or oven-dried to ensure a moisture content of ≤2%, and then crushed. The crushed material must have a particle size of less than 2mm and a proportion of greater than or equal to 95% to obtain chromium-containing dust. S2. Mix the crushed chromium-containing dust with other dust and sludge waste materials evenly to obtain a dust and sludge mixture, wherein the mass ratio of chromium-containing dust to dust and sludge waste materials is 1:50 ~ 1:10; S3. The dust and sludge mixture is then mixed with various iron-containing materials to obtain a premixed material. The dust and sludge mixture accounts for 14% to 17% of the total iron-containing materials. S4. The premixed material is mixed with flux and fuel again, and after one mixing and two mixing and granulation, a sintering mixture is finally obtained for the production of sintered ore. S5. Weighing and chromium content detection; S6. Calculate the proportion coefficient of chromium element entering the sinter from the sintering raw materials. ; S7. The proportional coefficient η is used to determine whether the chromium-containing sludge in the raw material is added in excess: when the proportional coefficient η ≥ 0.97, it is determined that the chromium-containing sludge in the raw material is not added in excess, and the proportion of chromium-containing sludge added needs to be increased; when the proportional coefficient η < 0.97, it is determined that the chromium-containing sludge in the raw material is added in excess, and the proportion of chromium-containing sludge added in the sintering raw material needs to be reduced. S8. The sintering flue gas generated during the sintering process is successively treated by a dust collector, a chromium removal device, and desulfurization and denitrification before being discharged in compliance with regulations. proportionality coefficient The calculation formula is as follows: ① In formula ①, This indicates the proportion of chromium in the sintering raw materials that enters the sinter. This indicates the mass of the sintered mixture weighed before the fabric is laid. This indicates the total mass of sintered ore products measured and recorded between the start and end positions of the sintering machine trolley after sintering. Indicates the chromium content of the mixture (wet basis). This indicates the chromium content of the sintered ore.

2. The method for harmlessly disposing of toxic hazardous waste according to claim 1, characterized in that, The various iron-containing materials mentioned include rich ore powder and concentrate.

3. The method for harmlessly disposing of toxic hazardous waste according to claim 1, characterized in that, In S8, the dust collector includes a gravity dust collector and an electrostatic precipitator.

4. The method for harmlessly disposing of toxic hazardous waste according to claim 1, characterized in that, In S5, the content is as follows: Before feeding, weigh the mass of the sintering mixture, feed the mixture, number the sintering trolley, record the starting and ending positions of the trolley corresponding to the feeding process of the weighed sintering mixture, and then ignite and sinter. After sintering, the mass of all sintered ore products between the starting and ending positions of the sintering machine trolley is weighed. During this process, multiple samples are taken from the sintering mixture and the sintered ore products, and the chromium content is tested. The chromium content of the mixture (wet basis) and the chromium content of the sinter are analyzed.

5. A system for the harmless disposal of toxic hazardous waste according to any one of claims 1-4, characterized in that, The equipment includes a chromium removal device, which consists of a flue gas duct, a filter belt, and a main exhaust fan. The filter belt and the flue gas duct are set perpendicular to each other in their transverse cross sections. The sintering flue gas is filtered by the filter belt in the flue gas duct. The main exhaust fan is set in the flue gas duct to generate negative pressure so that the sintering flue gas does not overflow during the chromium removal process. The chromium removal equipment also includes a filter belt cleaning tank, an absorbent wetting tank, and filter belt rotating shafts. The number of filter belt rotating shafts is even, and the filter belt rotating shafts are arranged in parallel and symmetrically with the middle being lower and the two sides being higher. The filter belt rotating shafts are connected to the filter belt, so that the filter belt rotates clockwise with the filter belt rotating shafts. The absorbent wetting tank is placed inside the annular space surrounded by the filter belt. The filter belt rotating shaft located at the upper center is located inside the absorbent 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 located inside the filter belt cleaning tank.

6. The system for harmless disposal of toxic hazardous waste according to claim 5, characterized in that, The horizontal width of the filter belt cleaning tank is greater than the distance between the two filter belt rotation shafts with the furthest horizontal spacing; the horizontal width of the absorbent wetting tank is less than the distance between the two filter belt rotation shafts with the furthest horizontal spacing.

7. The system for harmless disposal of toxic hazardous waste according to claim 5, characterized in that, Both the filter belt cleaning tank and the absorbent wetting tank are filled with immersion solution. The immersion solution is a mixed solution of NaOH and Ca(OH)2. The immersion solution is used to clean the residue on the filter belt. The percentage concentration of NaOH in the mixed solution is 3% to 6%, and the percentage concentration of Ca(OH)2 is 2% to 4%. The linear running speed of the filter belt is 16 to 20 m / min, and the ultrasonic vibration frequency is 25 to 40 kHz.

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