System and method for combined removal of soil organic matter and heavy metals using a two-stage rotary kiln

Abstract

The present invention relates to the technical field of contaminated soil regeneration, and specifically to a system and method for combining soil organic matter and heavy metal removal using a two-stage rotary kiln. The system comprises a frame, a low-temperature organic matter removal system, and a high-temperature heavy metal solidification system. The low-temperature organic matter removal system comprises a low-temperature rotary kiln and an induced draft fan, and the high-temperature heavy metal solidification system comprises an induced draft fan, an air preheater, and a combustion pipeline. The frame is provided with multiple motors. A feeding device is connected between a soil discharge port of the low-temperature rotary kiln and a material inlet of the high-temperature rotary kiln. A quenching device is installed between a flue gas outlet of the high-temperature rotary kiln and a flue gas inlet of the low-temperature rotary kiln. The quenching device can reduce the flue gas from a high temperature to below 250°C within 2 seconds, avoiding the dioxin generation temperature range of 250-700°C, thereby ensuring the stability of the system and method for combining soil organic matter and heavy metal removal using the two-stage rotary kiln during flue gas treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of contaminated soil regeneration, and in particular to a system and method for jointly removing soil organic matter and heavy metals using a two-stage rotary kiln. Background Art

[0002] Soil is a vital component of nature, not only regulating the surface water cycle but also providing nutrients for the growth of various plants and animals. Industrial wastewater, pesticide use, petrochemicals, and mineral mining all contribute to soil pollution. Soil can be categorized as organically contaminated or inorganically contaminated, depending on the type of pollutant. Organic pollutants primarily include volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and polychlorinated biphenyls (PCBs). The most common type of inorganic pollutant is heavy metals. Most heavy metals evaporate from the soil at high temperatures or combine with mineral components in the soil to form stable forms. These organic compounds and heavy metals accumulate in the soil and eventually enter the human body through biological cycles, causing harm.

[0003] When using thermal desorption to treat contaminated soil, the invention patent with patent application number CN202121758133.7 discloses a rotary kiln for soil thermal desorption. The preheating component and heating component of this solution are respectively provided with two soil holding cavities. When working, the soil to be treated will be transported in the direction of preheating outer cylinder, heating inner cylinder, heating outer cylinder, and preheating inner cylinder. Since the soil will undergo thermal desorption process inside the heating component, the soil entering the preheating inner cylinder will carry a lot of heat. At this time, the soil that has completed thermal desorption will be mixed with the newly entered soil. The soil exchanges heat inside the preheating component, thereby effectively utilizing the waste heat of thermal desorption and improving the heat utilization rate during the thermal desorption process. However, the above solutions all have some problems. Some organic matter is prone to secondary pollution during the thermal desorption process. For example, if polychlorinated biphenyls are not rapidly cooled to avoid the temperature range of 250-700°C after high-temperature combustion, the highly toxic substance dioxin will be generated. If the organic matter is volatilized and removed at low temperature, the heavy metals cannot be precipitated or solidified. Therefore, the joint removal of organic matter and heavy metals in contaminated soil is still imminent. Summary of the Invention

[0004] The present invention aims to provide a system and method for the combined removal of soil organic matter and heavy metals using a two-stage rotary kiln, thereby resolving the problem that, after high-temperature combustion of polychlorinated biphenyls (PCBs), if not rapidly cooled to avoid the temperature range of 250-700°C, will lead to the formation of highly toxic dioxins, and that, if organic matter is removed by volatilization at low temperatures alone, heavy metals cannot be precipitated or solidified.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A system and method for jointly removing soil organic matter and heavy metals using a two-stage rotary kiln, comprising a frame, a low-temperature organic matter removal system and a high-temperature heavy metal solidification system, wherein the low-temperature organic matter removal system and the high-temperature heavy metal solidification system are both installed on the frame, the low-temperature organic matter removal system comprises a low-temperature rotary kiln and an induced draft fan, the low-temperature rotary kiln is respectively provided with a flue gas inlet, a flue gas outlet, a soil inlet and a soil outlet, the induced draft fan is installed at the flue gas outlet, the high-temperature heavy metal solidification system comprises an induced draft fan, an air preheater and a combustion pipeline, the high-temperature rotary kiln is provided with a flue gas inlet, a flue gas outlet, a material inlet and a material outlet, the induced draft fan, the air preheater, the combustion pipeline and the flue gas inlet are connected in sequence, a plurality of motors are provided on the frame, the plurality of motors are respectively connected to the low-temperature rotary kiln and the high-temperature rotary kiln, the low-temperature rotary kiln soil outlet A feeding device is connected to the material inlet of the high-temperature rotary kiln, and a screw is provided in the feeding device. A quenching device is installed between the flue gas outlet of the high-temperature rotary kiln and the flue gas inlet of the low-temperature rotary kiln, and a heat exchange pipe is provided in the quenching device. The flue gas discharged from the high-temperature rotary kiln may contain dioxin precursors generated during the high-temperature combustion of organic matter such as polychlorinated biphenyls. The quenching device can reduce the flue gas from a high temperature to below 250°C within 2 seconds, avoiding the dioxin generation temperature range of 250-700°C. This avoids the generation of highly toxic dioxins if polychlorinated biphenyls are not rapidly cooled to avoid the temperature range of 250-700°C after high-temperature combustion. If the organic matter is volatilized and removed alone at low temperature, heavy metals cannot be precipitated or solidified. This ensures the stability of the system and method for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln when treating flue gas.

[0007] It should be noted that the system also includes a soil pretreatment system, a montmorillonite feeding system and an exhaust gas treatment system. The soil pretreatment system includes a soil crusher, a vibrating screen, an inorganic acid storage tank, a leaching tower and a leachate storage tank. The leaching tower is provided with a leachate inlet and a leachate outlet. The outlet of the soil crusher is connected to the inlet of the vibrating screen, the outlet of the vibrating screen is connected to the soil feeding port, the outlet of the inorganic acid storage tank is connected to the leachate inlet, the leachate outlet of the leaching tower is connected to the leachate storage tank, the induced draft fan outlet is connected to the air inlet, the soil discharge port of the leaching tower is connected to the soil feeding port of the low-temperature rotary kiln, the high-temperature heavy metal solidification system includes an induced draft fan, an air preheater and a combustion pipe, an air preheater and a combustion device; the high-temperature rotary kiln also includes a gas inlet, the outlet of the combustion device is connected to the gas inlet, the soil discharge port of the low-temperature rotary kiln is connected to the feeding inlet of the feeding device, and the material inlet of the high-temperature rotary kiln is connected to the feeding outlet of the feeding device.

[0008] The montmorillonite feeding system includes a heat exchange calcining device, the material outlet of the heat exchange calcining device is respectively connected to the leachate recovery tank and the material inlet of the high-temperature rotary kiln, the flue gas inlet of the heat exchange calcining device is connected to the flue gas outlet of the high-temperature rotary kiln, the flue gas outlet of the heat exchange calcining device is respectively connected to the air inlet of the induced draft fan and the quenching device, and the montmorillonite outlet of the heat exchange calcining device is respectively connected to the leachate storage tank and the material inlet of the high-temperature rotary kiln.

[0009] The tail gas treatment system includes a dust collector and a chimney. The inlet of the dust collector is connected to the flue gas outlet of the low-temperature rotary kiln and the flue gas outlet of the high-temperature rotary kiln respectively, and the outlet of the dust collector is connected to the chimney.

[0010] Preferably, the feeding device includes a feeding pipe and a gear set, the feeding pipe is installed on the frame, and the feeding pipe is located between the soil discharge port and the material inlet, the screw is coaxially connected to the feeding pipe, the feeding pipe is provided with a feeding inlet and a feeding outlet, the feeding inlet and the feeding outlet are respectively communicated with the soil discharge port and the material inlet, the gear set is installed on the frame, the gear set is provided with an input end and an output end, the input end and the output end are respectively connected to the motor and the screw; the rotation of the screw in the feeding pipe can push the material to be continuously and stably transported from the soil discharge port of the low-temperature rotary kiln to the material inlet of the high-temperature rotary kiln, prevent the material from accumulating and clogging during the transportation process, and ensure the material transmission of the entire system. Smoothness is ensured to avoid system shutdown or efficiency reduction due to material blockage. At the same time, the gear set transmits the power of the motor to the screw, so that the screw can rotate according to the rotation speed of the high-temperature rotary kiln and the low-temperature rotary kiln, thereby ensuring uniform material transportation. At the same time, when the screw in the feed pipe pushes the material to move, the flue gas in the high-temperature rotary kiln cannot enter the low-temperature rotary kiln through the feed pipe, avoiding the problem of the generation of highly toxic dioxins if polychlorinated biphenyls are not rapidly cooled to avoid the temperature range of 250-700℃ after high-temperature combustion. This ensures the stability of the system and method for removing soil organic matter and heavy metals in a two-stage rotary kiln, as well as the consistency of material treatment effects.

[0011] Preferably, the quenching device includes a quenching box and heat exchange fins, the quenching box is installed on the frame, a heat exchange cavity is provided in the quenching box, the heat exchange tube is installed in the heat exchange cavity, a plurality of heat exchange fins are evenly distributed on the heat exchange tube, and an air inlet and an air outlet are provided on the quenching box, the air inlet and the air outlet are respectively connected to the flue gas outlet of the high-temperature rotary kiln and the flue gas inlet of the low-temperature rotary kiln; as mentioned above, the flue gas after high-temperature combustion may contain dioxin precursors, and the quenching device can quickly cool the flue gas, avoid the dioxin generation temperature range of 250-700°C, prevent the generation of highly toxic dioxins, avoid serious harm to the environment and human health, and ensure the environmental protection performance of the system and method for combined removal of soil organic matter and heavy metals by a two-stage rotary kiln.

[0012] Preferably, a plurality of inertial separation plates are provided at the connection between the flue gas outlet and the air inlet of the high-temperature rotary kiln, and the plurality of inertial separation plates are arranged in parallel in a louver shape; when the flue gas is discharged from the high-temperature rotary kiln, it may carry some solid particulate matter, such as incompletely reacted soil particles, metal oxides, etc.; the inertial separation plates can utilize the inertia of the particulate matter to cause it to collide with the separation plates during the flow of the flue gas and be separated, thereby preventing these particulate matter from entering the quenching device and subsequent pipelines, preventing blockage problems caused by the accumulation of particulate matter, and ensuring the smooth flow of the flue gas channel. At the same time, if particulate matter enters the quenching device and adheres to the heat exchange tubes and heat exchange fins, it will reduce the heat exchange efficiency, affect the quenching effect and heat recovery efficiency; the inertial separation plates separate the particulate matter in advance, reduce the deposition of particulate matter on the heat exchange equipment, maintain the normal heat exchange performance of the quenching device, avoid the decline in system performance due to the reduction in heat exchange efficiency, and ensure the heat exchange efficiency of the heat exchange tubes in the system and method for the combined removal of soil organic matter and heavy metals by a two-stage rotary kiln.

[0013] Preferably, a guide groove is provided at the bottom of the quench box, and the guide groove is funnel-shaped, and the bottom of the guide groove is connected to the feed pipe; during the flue gas treatment process, some fine soil particles or reaction products may enter the quench box with the flue gas, and some particles will settle to the bottom of the quench box. The guide groove introduces these particles into the feed pipe, so that the material can return to the material conveying system, avoiding material loss and accumulation; at the same time, during the rapid cooling process, water vapor and some volatile substances in the flue gas may condense into liquid. If there is no guide groove, the condensate may accumulate at the bottom of the quench box, which may cause equipment corrosion, bacterial growth and other problems. The setting of the guide groove can make the condensate flow along the funnel-shaped trough body to the feed pipe, avoiding the accumulation of condensate at the bottom of the quench box, reducing the corrosion risk of the quench box, extending the service life of the equipment, and ensuring the continuity and integrity of material transmission in the system and method for combined removal of soil organic matter and heavy metals by a two-stage rotary kiln.

[0014] Preferably, a guide pipe is installed at the connection between the air inlet and the heat exchange chamber, and the central axis of the guide pipe is tangent to the inclined surface of the guide groove; the dust-laden gas or gas-liquid mixture flows from the guide pipe at a high speed along the tangential direction of the guide groove side wall to form a rotating airflow. Under the action of centrifugal force, solid particles or liquid droplets in the gas are thrown to the inner wall of the separator. Since the density of the particles or liquid droplets is greater than that of the gas, the centrifugal force causes them to obtain a greater outward acceleration, thereby separating from the gas, avoiding direct contact between fine soil particles and the heat exchange tubes and heat exchange fins, resulting in soil particles adhering to the heat exchange tubes and heat exchange fins. On the heat exchange tubes and heat exchange fins, soil particles adhere to the surface of the heat exchange tubes and heat exchange fins, which is equivalent to adding a layer of thermal resistance between the heat transfer medium and the heat exchange surface. This layer of thermal resistance will hinder the transfer of heat, making the heat exchange effect worse. It is difficult for heat to be effectively transferred from the flue gas to the cooling medium, resulting in poor rapid cooling effect and the inability to quickly cool the flue gas to a suitable temperature, which in turn affects the removal effect of the entire system on soil organic matter and heavy metals. This ensures the heat exchange efficiency of the heat exchange tubes in the system and method for combined removal of soil organic matter and heavy metals in a two-stage rotary kiln, as well as the stability and reliability of the system.

[0015] Preferably, a plurality of tumbling plates are evenly distributed around the circumference of the high-temperature rotary kiln and the low-temperature rotary kiln, and the longitudinal cross-sections of the plurality of tumbling plates are arc-shaped, and the arc opening directions of the plurality of tumbling plates are consistent with the rotation directions of the high-temperature rotary kiln and the low-temperature rotary kiln; if there are no tumbling plates, the materials may accumulate and agglomerate in the rotary kiln, resulting in uneven heating of the materials, affecting the removal of organic matter and the solidification of heavy metals; the tumbling plates can continuously lift and tumble the materials, avoiding local accumulation of the materials in the kiln and making the materials evenly distributed in the kiln, It is beneficial to improve the consistency of treatment effect. At the same time, when the material moves in the rotary kiln, it may stick to the kiln wall due to high temperature, humidity and other reasons. The tumbling plate can reduce the direct contact time and area between the material and the kiln wall in the process of turning the material, and reduce the possibility of material sticking to the wall. Once the material sticks to the wall, it will not only affect the heat transfer effect, but may also cause local overheating and damage the kiln wall lining. The existence of the tumbling plate effectively avoids this problem and ensures the uniformity of material treatment in the system and method for combined removal of soil organic matter and heavy metals in a two-stage rotary kiln.

[0016] The present invention also provides a method for jointly removing soil organic matter and heavy metals using the above-mentioned two-stage rotary kiln, comprising the following steps:

[0017] S1: The crushed soil is screened by screening equipment to obtain the particle size. The screened soil is mixed with the inorganic acid leaching liquid and the soil is pretreated. The pretreated filtrate is recovered and stored.

[0018] S2: After pretreatment in S1, the soil enters the low-temperature rotary kiln through the soil inlet for drying and removal of organic matter volatilization; part of the flue gas generated by the high-temperature rotary kiln is subjected to heat exchange with montmorillonite and then enters the quenching device through the air inlet for heat exchange, and then enters the low-temperature rotary kiln through the air outlet to directly contact the soil and provide a heat source; the soil is discharged from the soil outlet and transported to the high-temperature rotary kiln through the feeding device for heavy metal solidification.

[0019] S3: In the heavy metal high-temperature solidification system, air enters the air preheater through the induced draft fan and then enters the combustion pipe to assist in generating fuel gas. The fuel gas enters the high-temperature rotary kiln through the combustion pipe for full combustion and heat exchange with the soil. Part of the flue gas generated by the high-temperature rotary kiln is heat-exchanged by the heat exchange and calcination device and then enters the high-temperature rotary kiln from the flue gas inlet as the circulating flue gas in the kiln. The soil after organic matter removal is used as one of the raw materials and enters the high-temperature rotary kiln through the material inlet for high-temperature calcination. The product is discharged from the material outlet and collected.

[0020] S4: After the montmorillonite enters the heat exchange calcination device for heat treatment, a portion of the product is recovered and stored, and the other portion of the product enters the high-temperature rotary kiln through the material inlet as another raw material.

[0021] S5: The outlet flue gas from the medium and low temperature rotary kiln in S2 and the outlet fuel gas from the medium and high temperature rotary kiln in S3 enter the dust collector and chimney for treatment and are discharged in compliance with emission standards.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention incorporates a low-temperature organic matter removal system and a high-temperature heavy metal solidification system on a frame. A feeding device is connected between the soil discharge port of the low-temperature rotary kiln and the material inlet of the high-temperature rotary kiln. A quenching device is installed between the flue gas outlet of the high-temperature rotary kiln and the flue gas inlet of the low-temperature rotary kiln. The quenching device can cool the flue gas from a high temperature to below 250°C within 2 seconds, avoiding the dioxin-forming temperature range of 250-700°C. This ensures the stability of the two-stage rotary kiln combined soil organic matter and heavy metal removal system and method during flue gas treatment.

[0024] 2. The present invention provides a plurality of inertial separation plates at the connection point between the flue gas outlet and the air inlet of the high-temperature rotary kiln. When the flue gas is discharged from the high-temperature rotary kiln, it may carry some solid particles. The inertial separation plates can utilize the inertia of the particles to cause them to collide with the separation plates during the flow of the flue gas and be separated, thereby preventing these particles from entering the quenching device and subsequent pipelines, and preventing blockage problems caused by the accumulation of particles. At the same time, if particles enter the quenching device and adhere to the heat exchange tubes and heat exchange fins, the heat exchange efficiency will be reduced, affecting the quenching effect and heat recovery efficiency.

[0025] 3. The present invention provides a guide groove at the bottom of the quench box. During the flue gas treatment process, some fine soil particles or reaction products may enter the quench box along with the flue gas, and some particles will settle to the bottom of the quench box. The guide groove introduces these particles into the feed pipe, so that the material can return to the material conveying system, avoiding material loss and accumulation, and ensuring the continuity and integrity of material transmission in the system and method for combined removal of soil organic matter and heavy metals in a two-stage rotary kiln. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a working diagram of the system for removing soil organic matter and heavy metals using a two-stage rotary kiln according to the present invention;

[0027] Figure 2 This is a schematic structural diagram of a two-stage rotary kiln system for combined removal of soil organic matter and heavy metals according to the present invention;

[0028] Figure 3 It is an isometric view of a system for combined removal of soil organic matter and heavy metals using a two-stage rotary kiln according to the present invention;

[0029] Figure 4 A cross-sectional view of a two-stage rotary kiln system for combined removal of soil organic matter and heavy metals according to the present invention;

[0030] Figure 5 For the present invention Figure 4 Cross-sectional view at AA in the middle;

[0031] Figure 6 This is an exploded view of the driving wheel in the system of the two-stage rotary kiln for combined removal of soil organic matter and heavy metals of the present invention.

[0032] In the figure: 1, frame; 2, low-temperature rotary kiln; 3, high-temperature rotary kiln; 4, combustion pipe; 501, flue gas inlet; 502, flue gas outlet; 503, soil inlet; 504, soil outlet; 505, material inlet; 506, material outlet; 507, motor; 601, feed pipe; 602, screw; 603, gear set; 604, feed inlet; 605, feed outlet; 701, quench box; 702, heat exchange chamber; 703, Heat exchange tube; 704, heat exchange fin; 705, air inlet; 706, air outlet; 801, inertial separation plate; 802, guide trough; 803, guide pipe; 804, tumbling plate; 901, soil crusher; 902, vibrating screen; 903, inorganic acid storage tank; 904, leaching tower; 905, leaching liquid storage tank; 906, feeding device; 907, induced draft fan; 908, quenching device; 909, air preheater; 910, heat exchange calcining device. DETAILED DESCRIPTION

[0033] See also Figures 1 to 5The present invention provides a system and method for removing soil organic matter and heavy metals by a two-stage rotary kiln. The technical solution is as follows:

[0034] Two-stage rotary kiln combined removal of soil organic matter and heavy metals system, please refer to Figures 1 to 6, including a frame 1, a soil pretreatment system, a low-temperature organic matter removal system, a high-temperature heavy metal solidification system, a montmorillonite feeding system and an exhaust gas treatment system. The soil pretreatment system includes a soil crusher 901, a vibrating screen 902, an inorganic acid storage tank 903, a leaching tower 904 and a leachate storage tank 905. The leaching tower 904 is provided with a leachate inlet, a leachate outlet, a soil feeding port 503, and a soil discharge port 504. The outlet of the soil crusher 901 is connected to the inlet of the vibrating screen 902, the outlet of the vibrating screen 902 is connected to the soil feeding port 503, the outlet of the inorganic acid storage tank is connected to the inlet of the leaching tower 904, the leachate outlet of the leaching tower 904 is connected to the leachate storage tank 905, the low-temperature organic matter removal system and the high-temperature heavy metal solidification system are connected. The curing systems are all installed on the frame 1. The low-temperature organic matter removal system includes a low-temperature rotary kiln 2. The low-temperature rotary kiln 2 is respectively provided with a flue gas inlet 501, a flue gas outlet 502, a soil feed port 503 and a soil discharge port 504. The high-temperature heavy metal curing system includes a high-temperature rotary kiln 3 induced draft fan 907, an air preheater 909 and a combustion pipe 4. The high-temperature rotary kiln 3 is provided with a flue gas inlet 501, a flue gas outlet 502, a material inlet 505 and a material outlet 506. The induced draft fan 907, the air preheater 909, the combustion pipe 4 and the flue gas inlet 501 are connected in sequence. The soil discharge port 504 of the leaching tower 904 is connected to the soil feed port 503 of the low-temperature rotary kiln 2. A plurality of motors 507 are provided on the frame 1. The plurality of motors 507 are respectively It is connected to the low-temperature rotary kiln 2 and the high-temperature rotary kiln 3. A plurality of tumbling plates 804 are evenly distributed around the circumference of the high-temperature rotary kiln 3 and the low-temperature rotary kiln 2. The longitudinal cross-section of the plurality of tumbling plates 804 is arc-shaped, and the arc opening direction of the plurality of tumbling plates 804 is consistent with the rotation direction of the high-temperature rotary kiln 3 and the low-temperature rotary kiln 2. A feeding device 906 is connected between the soil discharge port 504 of the low-temperature rotary kiln 2 and the material inlet 505 of the high-temperature rotary kiln 3. The feeding device 906 includes a feeding pipe 601, a screw 602 and a gear set 603. The feeding pipe 601 is installed on the frame 1, and the feeding pipe 601 is located between the soil discharge port 504 and the material inlet 505. The screw 602 is coaxially connected to the feeding pipe 601. The feeding pipe 601 is provided with a feeding device. The inlet 604 and the feeding outlet 605 are connected to the soil discharge port 504 and the material inlet 505 respectively. The gear set 603 is installed on the frame 1. The gear set 603 is provided with an input end and an output end. The input end and the output end are connected to the motor 507 and the screw 602 respectively. A quenching device 908 is installed between the flue gas outlet 502 of the high-temperature rotary kiln 3 and the flue gas inlet 501 of the low-temperature rotary kiln 2. The quenching device 908 includes a quenching box 701, a heat exchange tube 703 and a heat exchange fin 704. The quenching box 701 is installed on the frame 1. A heat exchange cavity 702 is opened in the quenching box 701. The heat exchange tube 703 is installed in the heat exchange cavity 702. A plurality of heat exchange fins 704 are evenly distributed on the heat exchange tube 703.The quench box 701 is provided with an air inlet 705 and an air outlet 706, which are connected to the flue gas outlet 502 of the high-temperature rotary kiln 3 and the flue gas inlet 501 of the low-temperature rotary kiln 2, respectively. Multiple inertial separation plates 801 are installed at the connection between the flue gas outlet 502 of the high-temperature rotary kiln 3 and the air inlet 705. These inertial separation plates 801 are arranged in parallel in a louver-like pattern. A funnel-shaped guide groove 802 is provided at the bottom of the quench box 701. The bottom of the guide groove 802 is connected to the feed pipe 601. A flow guide pipe 803 is installed at the connection between the air inlet 705 and the heat exchange chamber 702. The central axis of the flow guide pipe 803 is tangent to the inclined surface of the guide groove 802.

[0035] It should be noted that this specific embodiment also provides a method for removing soil organic matter and heavy metals by using the above-mentioned two-stage rotary kiln combined with the soil organic matter and heavy metal removal system. Figure 1 The specific steps are as follows: First, the contaminated soil is crushed in a soil crusher 901. After entering a vibrating screen 902, particles with a size less than 20 mm enter a leaching tower 904, where an inorganic acid is used as a leaching liquid for preliminary soil contamination removal. The leached waste liquid is collected and stored in a storage tank. The leached soil then enters a low-temperature rotary kiln 2. Simultaneously, an induced draft fan 907 introduces flue gas from a high-temperature rotary kiln 3 into the low-temperature rotary kiln 2 as a heat source. Directly contacting the flue gas with the soil, the flue gas is subjected to low-temperature removal of organic matter at temperatures between 340°C and 360°C. After organic matter removal, the soil passes from the low-temperature rotary kiln 2 to the high-temperature rotary kiln 3 for high-temperature heavy metal solidification. At this time, the high-temperature combustion gas generated by the combined air preheater 909 and the combustion device enters the high-temperature rotary kiln 3 for indirect heat exchange with the internal soil, so that the heavy metals are solidified at a temperature of 700°C to 800°C; the flue gas generated by the high-temperature rotary kiln 3 first enters the heat exchange and calcination device 910 to perform inter-wall heat exchange calcination on the montmorillonite as it is, and then enters the low-temperature rotary kiln 2 and the high-temperature rotary kiln 3 for recycling through the heat exchange and calcination device 910; the calcined montmorillonite enters the leachate storage tank 905 and the high-temperature rotary kiln 3 respectively, to further adsorb and solidify the organic matter and heavy metals in the leachate, as well as the heavy metals contained in the soil in the kiln, and at the same time, it can supplement the loss of soil components caused by leaching. The flue gas at the outlet of the low-temperature rotary kiln 2 and the gas at the outlet of the high-temperature rotary kiln 3 are both treated in the dust collector and discharged through the chimney to meet the standards.

[0036] While working, see Figures 1 to 5The soil to be treated enters the low-temperature rotary kiln 2 from the soil inlet 503 of the low-temperature rotary kiln 2. The low-temperature rotary kiln 2 rotates under the drive of the motor 507. The tumbling plates 804 evenly distributed on the inner circumference rotate with the rotary kiln. Since the arc-shaped opening direction of the tumbling plates 804 is consistent with the rotation direction of the rotary kiln, the soil will be continuously lifted and tumbled, so that the soil is evenly heated in a low-temperature environment, thereby achieving the initial removal of organic matter. The temperature, residence time and other parameters in the low-temperature rotary kiln 2 are set according to the characteristics of the organic matter in the soil and the treatment requirements. In this process, the soil transported from the high-temperature rotary kiln 3 is transported to the low-temperature rotary kiln 2. The flue gas is discharged from the flue gas outlet 502 of the low-temperature rotary kiln 2. The high-temperature flue gas discharged from the flue gas outlet 502 of the high-temperature rotary kiln 3 first passes through the quenching device 908. The flue gas first passes through a plurality of inertial separation plates 801 arranged in parallel in the shape of shutters, which are arranged at the connection between the flue gas outlet 502 of the high-temperature rotary kiln 3 and the air inlet 705 of the quenching box 701. Preliminary particle separation is performed here. Larger particles of dust and other impurities are separated due to inertia and fall into the interior of the high-temperature rotary kiln 3. The flue gas after preliminary separation enters the heat exchange chamber 702 of the quenching box 701 through the air inlet 705 and is then discharged to the hot air outlet 706 of the high-temperature rotary kiln 3. Under the action of the pipe 803, the flue gas flows in a direction tangential to the inclined surface of the guide groove 802, so that the flue gas forms a specific flow field in the heat exchange chamber 702, thereby improving the contact efficiency between the flue gas and the heat exchange pipe 703 and the heat exchange fin 704. At the same time, when the flue gas flows through the guide pipe 803 in a direction tangential to the inclined surface of the guide groove 802, a rotating airflow is formed. Under the action of centrifugal force, solid particles or droplets in the gas are thrown to the inner wall of the separator. Since the density of the particles or droplets is greater than that of the gas, the centrifugal force makes them obtain a greater outward acceleration, thereby separating from the gas, avoiding the accumulation of fine soil particles. The soil particles directly contact the heat exchange tubes 703 and the heat exchange fins 704, causing the soil particles to adhere to the heat exchange tubes 703 and the heat exchange fins 704. At this time, the heat exchange tubes 703 are filled with cooling medium, which quickly cools the flue gas through the heat exchange tubes 703 and the heat exchange fins 704, reducing the flue gas temperature to a range suitable for entering the low-temperature rotary kiln 2. At the same time, some particulate impurities in the flue gas are further cooled and settled into the guide groove 802; the cooled flue gas is discharged from the outlet 706 of the quench box 701 and enters the flue gas inlet 501 of the low-temperature rotary kiln 2 for heating in the low-temperature rotary kiln 2.

[0037] It is noteworthy that the screw 602 within the feed pipe 601 rotates under the drive of the motor 507 via the gear train 603. The material falling from the guide groove 802 of the quench box 701 and entering the feed pipe 601 from the soil outlet 504 of the low-temperature rotary kiln 2 are pushed to the feed outlet 605 of the feed pipe 601 by the rotation of the screw 602. The material is then transported to the material inlet 505 of the high-temperature rotary kiln 3. After entering the high-temperature rotary kiln 3, the high-temperature rotary kiln 3 rotates under the drive of the motor 507. The tumbling plate 804 within the high-temperature rotary kiln 3 also causes the material to tumble. Under the high-temperature environment, the material fully contacts the heat source provided by the combustion pipe 4. At the same time, additives such as curing agents may be added as needed to induce a curing reaction of the heavy metals, effectively solidifying the heavy metals. The treated soil is discharged from the material outlet 506 of the high-temperature rotary kiln 3, completing the entire treatment process.

[0038] The above describes the specific embodiments of the present invention in detail with reference to the accompanying drawings, but the present invention is not limited to the embodiments described above. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments without departing from the principles and ideas of the present invention should still fall within the scope of protection of the present invention.

Claims

1. A two-stage rotary kiln system for removing soil organic matter and heavy metals, characterized in that: The invention comprises a frame (1), a low-temperature organic matter removal system and a high-temperature heavy metal solidification system, wherein the low-temperature organic matter removal system and the high-temperature heavy metal solidification system are both installed on the frame (1), the low-temperature organic matter removal system comprises a low-temperature rotary kiln (2), the low-temperature rotary kiln (2) is respectively provided with a flue gas inlet (501), a flue gas outlet (502), a soil feed port (503) and a soil discharge port (504), the flue gas outlet (502) and the soil feed port (503) of the low-temperature rotary kiln (2) are located at the same end, the high-temperature heavy metal solidification system comprises a high-temperature rotary kiln (3), an induced draft fan (504), a high-temperature rotary kiln (3 ... (907), air preheater (909) and combustion pipeline (4), the high-temperature rotary kiln (3) is provided with a flue gas inlet (501), a flue gas outlet (502), a material inlet (505) and a material outlet (506), the material outlet (506) is provided on the opposite side of the material inlet (505), the induced draft fan (907), air preheater (909), combustion pipeline (4) and flue gas inlet (501) of the high-temperature rotary kiln (3) are connected in sequence, and a feeding passage is connected between the soil discharge port (504) of the low-temperature rotary kiln (2) and the material inlet (505) of the high-temperature rotary kiln (3). The device (906) is connected to the material inlet (505) of the high-temperature rotary kiln (3) with a heat exchange calcining device (910), a screw (602) is provided in the feeding device (906), a quenching device (908) is installed between the smoke outlet (502) of the high-temperature rotary kiln (3) and the smoke inlet (501) of the low-temperature rotary kiln (2), a heat exchange pipe (703) is provided in the quenching device (908), an air inlet (705) is provided on the quenching device (908), and the smoke inlet of the heat exchange calcining device (910) and the smoke outlet (502) of the high-temperature rotary kiln (3) are connected. The flue gas outlet of the heat exchange calcining device (910) is connected to the induced draft fan (907) and the air inlet (705) of the quenching device (908) respectively. The soil to be treated enters the low-temperature rotary kiln (2) through the soil inlet (503). After the soil in the low-temperature rotary kiln (2) reacts with the flue gas, it enters the feeding device (906) through the soil outlet (504). The soil is then transported to the material inlet (505) through the feeding device (906) and enters the high-temperature rotary kiln (3). After the soil in the high-temperature rotary kiln (3) reacts with the flue gas, it is discharged through the material outlet (506).Air passes through the induced draft fan (907), the air preheater (909) and the combustion pipe (4) in sequence to form high-temperature flue gas, which enters the high-temperature rotary kiln (3) through the flue gas inlet (501) of the high-temperature rotary kiln (3). The high-temperature flue gas reacts with the soil in the high-temperature rotary kiln (3) and is discharged through the flue gas outlet (502) of the high-temperature rotary kiln (3). The high-temperature flue gas enters the quenching device (908) through the air inlet (705). The flue gas cooled by the quenching device (908) enters the low-temperature rotary kiln (2) through the flue gas inlet (501) of the low-temperature rotary kiln (2). The flue gas entering the low-temperature rotary kiln (2) reacts with the soil in the low-temperature rotary kiln (2) and is discharged through the flue gas outlet (502) of the low-temperature rotary kiln (2).

2. The two-stage rotary kiln combined removal system for soil organic matter and heavy metals according to claim 1 is characterized in that: The feeding device (906) comprises a feeding pipe (601) and a gear set (603), wherein the feeding pipe (601) is mounted on the frame (1) and is located between the soil discharge port (504) and the material inlet (505), and the screw (602) is coaxially rotatably connected in the feeding pipe (601), and the feeding pipe (601) is provided with a feeding inlet (604) and a feeding outlet (605), and the feeding inlet (604) and the feeding outlet (605) are respectively connected to the soil discharge port (504) and the material inlet (505), and the gear set (603) is mounted on the frame (1), and the gear set (603) is provided with an input end and an output end, and the input end and the output end are respectively connected to the motor (507) and the screw (602).

3. The two-stage rotary kiln combined removal system for soil organic matter and heavy metals according to claim 1 is characterized in that: The quenching device (908) includes a quenching box (701) and heat exchange fins (704), the quenching box (701) is installed on the frame (1), a heat exchange cavity (702) is provided in the quenching box (701), the heat exchange tube (703) is installed in the heat exchange cavity (702), and a plurality of heat exchange fins (704) are evenly distributed on the heat exchange tube (703), and an air inlet (705) and an air outlet (706) are provided on the quenching box (701), and the air inlet (705) and the air outlet (706) are respectively connected to the flue gas outlet (502) of the high-temperature rotary kiln (3) and the flue gas inlet (501) of the low-temperature rotary kiln (2).

4. The two-stage rotary kiln combined removal system for soil organic matter and heavy metals according to claim 3 is characterized in that: A plurality of inertial separation plates (801) are provided at the connection point between the smoke outlet (502) and the air inlet (705) of the high-temperature rotary kiln (3), and the plurality of inertial separation plates (801) are arranged in parallel in a louver shape.

5. The two-stage rotary kiln combined removal system for soil organic matter and heavy metals according to claim 3 is characterized in that: A guide groove (802) is provided at the bottom of the quench box (701), the guide groove (802) is funnel-shaped, and the bottom of the guide groove (802) is connected to the feeding pipe (601).

6. The two-stage rotary kiln combined removal system for soil organic matter and heavy metals according to claim 5 is characterized in that: A guide tube (803) is installed at the connection point between the air inlet (705) and the heat exchange cavity (702), and the central axis of the guide tube (803) is tangent to the inclined surface of the guide groove (802).

7. The two-stage rotary kiln combined removal system for soil organic matter and heavy metals according to claim 1 is characterized in that: A plurality of tumbling plates (804) are evenly distributed around the circumference of the high-temperature rotary kiln (3) and the low-temperature rotary kiln (2); the longitudinal cross-sections of the plurality of tumbling plates (804) are arc-shaped, and the arc-shaped opening directions of the plurality of tumbling plates (804) are consistent with the rotation directions of the high-temperature rotary kiln (3) and the low-temperature rotary kiln (2).

8. A two-stage rotary kiln combined method for removing soil organic matter and heavy metals, characterized by: The method is applied to at least the two-stage rotary kiln combined removal of soil organic matter and heavy metals system according to any one of claims 1 to 7, and the specific method includes: S1: The crushed soil is screened by screening equipment to determine the particle size. The screened soil is mixed with inorganic acid leaching liquid and the soil is pretreated. The pretreated filtrate is recovered and stored; S2: After the pretreatment in S1, the soil enters the low-temperature rotary kiln (2) through the soil inlet (503) for drying and removal of organic matter volatilization; part of the flue gas generated by the high-temperature rotary kiln (3) is subjected to heat exchange with montmorillonite and then enters the quenching device (908) through the air inlet (705) for heat exchange, and then enters the low-temperature rotary kiln (2) through the air outlet (706) to directly contact with the soil and provide a heat source; the soil is discharged through the soil outlet (504) and transported to the high-temperature rotary kiln (3) through the feeding device (906) for heavy metal solidification; S3: In the heavy metal high-temperature solidification system, air enters the air preheater (909) through the induced draft fan (907) and then enters the combustion pipe (4) to assist in generating fuel gas. The fuel gas enters the high-temperature rotary kiln (3) through the combustion pipe (4) to be fully burned and heat-exchanged with the soil. Part of the flue gas generated by the high-temperature rotary kiln (3) is heat-exchanged through the heat exchange calcination device (910) and then enters the high-temperature rotary kiln (3) from the flue gas inlet (501) of the high-temperature rotary kiln (3) as the circulating flue gas in the kiln. The soil after organic matter removal is used as one of the raw materials and enters the high-temperature rotary kiln (3) through the material inlet (505) for high-temperature calcination. The product is discharged from the material outlet (506) and collected. S4: After the montmorillonite enters the heat exchange calcination device (910) for heat treatment, a portion of the product is recovered and stored, and the other portion of the product is used as another raw material and enters the high-temperature rotary kiln (3) through the material inlet (505); S5: The outlet flue gas of the medium-low temperature rotary kiln (2) of S2 and the outlet fuel gas of the medium-high temperature rotary kiln (3) of S3 enter the dust collector and chimney for treatment and discharge in compliance with emission standards.

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