System and method for jointly removing organic matters and heavy metals in soil through two-section rotary kiln

Abstract

The invention relates to the technical field of polluted soil regeneration, in particular to a system and method for jointly removing soil organic matter and heavy metal through a two-section type rotary kiln, and the system comprises a rack, a low-temperature organic matter removal system and a high-temperature heavy metal solidification system. The high-temperature heavy metal solidification system comprises an induced draft fan, an air preheater and a combustion pipeline, a plurality of motors are arranged on the rack, a feeding device is communicated between a low-temperature rotary kiln soil discharge port and a high-temperature rotary kiln material inlet, and a quenching device is installed between a high-temperature rotary kiln flue gas outlet and a low-temperature rotary kiln flue gas inlet; the quenching device can reduce the temperature of the flue gas from the high temperature to 250 DEG C or below within 2 seconds, the dioxin generation temperature interval of 250-700 DEG C is avoided, and the stability of the system and method for jointly removing the soil organic matter and the heavy metal through the two-section rotary kiln in the flue gas treatment process is guaranteed.

Description

Technical Field

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

[0002] Soil is one of the important components of nature. It not only has a certain regulating effect on the surface water cycle but also provides nutrients for the growth of various plants and animals. Industrial sewage, pesticide use, petrochemical industry, and mineral exploitation can all cause soil pollution. According to the types of pollutants, it can be divided into organic pollutant-contaminated soil and inorganic pollutant-contaminated soil. Organic pollutants mainly include volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and polychlorinated biphenyls (PCBs), etc. The most common type of inorganic pollutant is heavy metal, and most heavy metals will volatilize from the soil at high temperatures or combine with some mineral components in the soil to form a stable form. Various organic matters and heavy metals continuously accumulate in the soil and will eventually enter the human body through the biological cycle and cause harm.

[0003] When using the thermal desorption method to treat contaminated soil, for example, the invention patent with the patent application number CN202121758133.7 discloses a rotary kiln for soil thermal desorption. In this scheme, two soil accommodation cavities are respectively arranged inside the preheating component and the heating component. During operation, the soil to be treated will be conveyed along the directions of the preheating outer cylinder, heating inner cylinder, heating outer cylinder, and preheating inner cylinder. Since the soil will undergo the thermal desorption process inside the heating component, the soil entering the preheating inner cylinder will carry a large amount of heat. At this time, the soil that has completed thermal desorption will exchange heat with the newly incoming soil inside the preheating component, thereby effectively utilizing the waste heat of thermal desorption and further improving the heat utilization rate during the thermal desorption process. However, there are some problems in the above-mentioned schemes. Some organic matters are prone to generate secondary pollution during the thermal desorption process. For example, if polychlorinated biphenyls do not avoid the temperature range of 250-700°C through rapid cooling after high-temperature combustion, it will lead to the generation of highly toxic dioxins. If the volatilization and removal of organic matters are carried out at low temperature alone, heavy metals cannot be precipitated or solidified. Therefore, the joint removal of organic matter and heavy metals in contaminated soil is still extremely urgent. Summary of the Invention

[0004] The purpose of the present invention is to provide a system and method for jointly removing soil organic matter and heavy metals by a two-stage rotary kiln to solve the problem that if polychlorinated biphenyls do not avoid the temperature range of 250-700°C through rapid cooling after high-temperature combustion, it will lead to the generation of highly toxic dioxins, and if the volatilization and removal of organic matters are carried out at low temperature alone, heavy metals cannot be precipitated or solidified.

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

[0006] System and method for jointly removing soil organic matter and heavy metals by a two-stage rotary kiln, comprising a frame, a low-temperature organic matter removal system and a high-temperature heavy metal solidification system. 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 includes a low-temperature rotary kiln and a draft fan. A flue gas inlet, a flue gas outlet, a soil feed inlet and a soil discharge outlet are respectively arranged on the low-temperature rotary kiln. The draft fan is installed at the flue gas outlet. The high-temperature heavy metal solidification system includes a 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 draft fan, the air preheater, the combustion pipeline and the flue gas inlet are sequentially connected. A plurality of motors are arranged on the frame, and the plurality of motors are respectively connected to the low-temperature rotary kiln and the high-temperature rotary kiln. A feeding device is connected between the soil discharge outlet of the low-temperature rotary kiln and the material inlet of the high-temperature rotary kiln. A screw is arranged 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. Heat exchange tubes are arranged in the quenching device; Dioxin precursors generated by organic matters such as polychlorinated biphenyls may be contained in the flue gas discharged from the high-temperature rotary kiln during the high-temperature combustion process. The quenching device can cool the flue gas from a high temperature to below 250°C within 2 seconds, avoiding the dioxin formation temperature range of 250-700°C, and avoiding 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 only by low temperature, the heavy metals cannot be precipitated or solidified, ensuring 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 further includes a soil pretreatment system, a montmorillonite feeding system and a tail 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. A leachate inlet and a leachate outlet are arranged on the leaching tower. 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 feed inlet, 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 outlet of the draft fan is connected to the air inlet, the soil discharge outlet of the leaching tower is connected to the soil feed inlet of the low-temperature rotary kiln. The high-temperature heavy metal solidification system includes a draft fan, an air preheater and a combustion pipeline, an air preheater and a combustion device; The high-temperature rotary kiln further includes a gas inlet, and the outlet of the combustion device is connected to the gas inlet. The soil discharge outlet of the low-temperature rotary kiln soil is connected to the feed inlet of the feeding device, and the material inlet of the high-temperature rotary kiln is connected to the feed outlet of the feeding device.

[0008] The montmorillonite feeding system includes a heat exchange and calcination device. The material outlet of the heat exchange and calcination 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 and calcination device is connected to the flue gas outlet of the high-temperature rotary kiln. The flue gas outlet of the heat exchange and calcination device is respectively connected to the inlet of the induced draft fan and the quenching device. The montmorillonite outlet of the heat exchange and calcination 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 respectively connected to the flue gas outlet of the low-temperature rotary kiln and the flue gas outlet of the high-temperature rotary kiln. 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 is located between the soil discharge port and the material inlet. The screw rod is coaxially and rotationally connected inside the feeding pipe. The feeding pipe is provided with a feeding inlet and a feeding outlet, and 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, and the input end and the output end are respectively connected to the motor and the screw rod. The rotation of the screw rod inside the feeding pipe can push the material to continuously and stably be transported from the soil discharge port of the low-temperature rotary kiln to the material inlet of the high-temperature rotary kiln, preventing the material from accumulating and blocking during the transportation process, ensuring the smoothness of the material transmission of the entire system, and avoiding problems such as system shutdown or efficiency reduction caused by material blockage. At the same time, the gear set transmits the power of the motor to the screw rod, enabling the screw rod to rotate following the rotation speed of the high-temperature rotary kiln and the low-temperature rotary kiln, thereby ensuring the uniform transportation of the material. Additionally, when the screw rod inside the feeding pipe pushes the material to move, the flue gas inside the high-temperature rotary kiln cannot enter the low-temperature rotary kiln through the feeding pipe, avoiding the problem that if polychlorinated biphenyls are not rapidly cooled to avoid the temperature range of 250 - 700 °C after high-temperature combustion, it will lead to the generation of highly toxic dioxins, ensuring the stability of the operation of the system and method for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln, and the consistency of the material treatment effect.

[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 tubes are installed in the heat exchange cavity. A plurality of the heat exchange fins are evenly distributed and installed on the heat exchange tubes. An air inlet and an air outlet are provided on the quenching box. The air inlet and the air outlet are respectively communicated with the flue gas outlet of the high-temperature rotary kiln and the flue gas inlet of the low-temperature rotary kiln. As described above, the flue gas after high-temperature combustion may contain dioxin precursors. The quenching device can rapidly cool the flue gas, avoid the dioxin formation temperature range of 250-700°C, prevent the formation of the highly toxic substance dioxin, avoid causing serious harm to the environment and human health, and ensure the environmental protection performance of the system and method for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln.

[0012] Preferably, a plurality of inertial separation plates are provided at the connection between the flue gas outlet of the high-temperature rotary kiln and the air inlet. 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 particles, such as unreacted soil particles, metal oxides, etc. The inertial separation plates can utilize the inertia of the particles to make them collide with the separation plates during the flow of the flue gas and be separated, avoiding these particles from entering the quenching device and subsequent pipelines, preventing blockage problems caused by particle accumulation, ensuring the smoothness of the flue gas passage. At the same time, if the particles enter the quenching device and adhere 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 particles in advance, reduce the deposition of particles on the heat exchange equipment, maintain the normal heat exchange performance of the quenching device, avoid the decline of the system performance caused by the reduction of heat exchange efficiency, and ensure the heat exchange efficiency of the heat exchange tubes in the system and method for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln.

[0013] Preferably, a guiding groove is provided at the bottom of the quenching box. The guiding groove is in a funnel shape, and the bottom of the guiding groove is communicated with the feeding pipe. During the flue gas treatment process, some fine soil particles or reaction products may enter the quenching box along with the flue gas. Some particles will settle to the bottom of the quenching box. The guiding groove introduces these particles into the feeding pipe, enabling the material to return to the material conveying system again, avoiding material loss and accumulation. At the same time, during the quenching process, the water vapor and some volatile substances in the flue gas may condense into liquid. Without the guiding groove, the condensate may accumulate at the bottom of the quenching box, which may lead to problems such as equipment corrosion and bacteria breeding. The setting of the guiding groove allows the condensate to flow along the funnel-shaped groove body to the feeding pipe, avoiding the accumulation of condensate at the bottom of the quenching box, reducing the corrosion risk of the quenching box, extending the service life of the equipment, and ensuring the continuity and integrity of material transmission in the system and method for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln.

[0014] Preferably, a diversion pipe is installed at the connection between the air inlet and the heat exchange chamber, and the central axis of the diversion pipe is tangent to the inclined surface of the guiding groove; the dusty gas or gas-liquid mixture flows from the diversion pipe at a relatively high speed in the direction of the side wall of the guiding groove along the tangent direction, forming a swirling airflow. Under the action of centrifugal force, the solid particles or liquid droplets in the gas are thrown towards the inner wall of the separator. Since the density of the particles or droplets is greater than that of the gas, the centrifugal force gives them a greater acceleration of outward movement, thus separating from the gas, avoiding direct contact between the fine soil particles and the heat exchange tubes and heat exchange fins, resulting in the attachment of soil particles to the heat exchange tubes and heat exchange fins. The attachment of soil particles to the surface of the heat exchange tubes and heat exchange fins 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 heat transfer, making the heat exchange effect worse, and it is difficult for the heat to be effectively transferred from the flue gas to the cooling medium, resulting in poor quenching effect and inability to quickly cool the flue gas to an appropriate temperature, thereby affecting the removal effect of soil organic matter and heavy metals in the entire system, ensuring the heat exchange efficiency of the heat exchange tubes in the system and method for jointly removing soil organic matter and heavy metals by a two-stage rotary kiln, as well as the stability and reliability of the system.

[0015] Preferably, a plurality of tumbling plates are circumferentially and evenly installed in both the high-temperature rotary kiln and the low-temperature rotary kiln. The radial cross-section of the plurality of tumbling plates is 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; without the tumbling plates, the materials may accumulate and agglomerate in the rotary kiln, resulting in uneven heating of the materials and affecting the removal of organic matter and the solidification effect of heavy metals; the tumbling plates can continuously lift and turn the materials, avoiding local accumulation of the materials in the kiln, making the materials evenly distributed in the kiln, which is beneficial to improving the consistency of the treatment effect. At the same time, when the materials move in the rotary kiln, they may adhere to the kiln wall due to high temperature, humidity, etc.; during the process of turning the materials, the tumbling plates can reduce the direct contact time and area between the materials and the kiln wall, reducing the possibility of the materials sticking to the wall; once the materials stick to the wall, it will not only affect the heat transfer effect but also may cause local overheating and damage the inner lining of the kiln wall, while the existence of the tumbling plates effectively avoids this problem, ensuring the uniformity of material treatment in the system and method for jointly removing soil organic matter and heavy metals by a two-stage rotary kiln.

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

[0017] S1: The crushed soil is sieved by a screening device according to the particle size, the sieved soil is mixed with the inorganic acid leaching solution, and soil pretreatment is carried out. The filtrate after pretreatment is recycled and stored.

[0018] S2: The pre-treated soil in S1 enters the low-temperature rotary kiln through the soil inlet for drying and volatilization and removal of organic matter. Part of the flue gas generated by the high-temperature rotary kiln exchanges heat 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 heat source. After the soil is discharged through the soil outlet, it is transported to the high-temperature rotary kiln by the feeding device for heavy metal solidification.

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

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

[0021] S5: The outlet flue gas of the low-temperature rotary kiln in S2 and the outlet gas of the high-temperature rotary kiln in S3 enter the dust collector and chimney for treatment and up-to-standard discharge.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. In the present invention, a low-temperature organic matter removal system and a high-temperature heavy metal solidification system are provided on the frame. A feeding device is connected between the soil outlet of the low-temperature rotary kiln and the material inlet of the high-temperature rotary kiln, and 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 reduce the temperature of the flue gas from high temperature to below 250°C within 2 seconds, avoiding the temperature range of 250 - 700°C for dioxin generation, and ensuring 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.

[0024] 2. In the present invention, 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. When the flue gas discharges from the high-temperature rotary kiln, it may carry some solid particles. The inertial separation plates can utilize the inertia of the particles to make them collide with the separation plates during the flow of the flue gas and be separated, avoiding these particles from entering the quenching device and subsequent pipelines, preventing blockage problems caused by particle accumulation. At the same time, if the particles enter the quenching device and adhere to the heat exchange tubes and heat exchange fins, it will reduce the heat exchange efficiency and affect the quenching effect and heat recovery efficiency.

[0025] 3. In the present invention, a guiding groove is provided 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. Some of the particles will settle to the bottom of the quench box, and the guiding groove introduces these particles into the feed pipe, enabling the material to return to the material conveying system again, avoiding the loss and accumulation of the material, and ensuring the continuity and integrity of the material transmission in the system and method for jointly removing soil organic matter and heavy metals by a two-stage rotary kiln. Brief Description of the Drawings

[0026] Figure 1 It is the working flow chart of the system for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln of the present invention;

[0027] Figure 2 It is the structural schematic diagram of the system for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln of the present invention;

[0028] Figure 3 It is the orthographic axonometric sectional view of the system for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln of the present invention;

[0029] Figure 4 It is the sectional view of the system for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln of the present invention;

[0030] Figure 5 For the present invention Figure 4 The sectional view at A - A in it;

[0031] Figure 6 It is the exploded view of the driving wheel in the system for jointly removing soil organic matter and heavy metals by the two-stage rotary kiln of the present invention.

[0032] In the figure: 1, frame; 2, low-temperature rotary kiln; 3, high-temperature rotary kiln; 4, combustion pipeline; 501, flue gas inlet; 502, flue gas outlet; 503, soil feed inlet; 504, soil discharge 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 pipe; 704, heat exchange fin; 705, air inlet; 706, air outlet; 801, inertial separation plate; 802, guiding groove; 803, diversion pipe; 804, tumbling plate; 901, soil crusher; 902, vibrating screen; 903, inorganic acid storage tank; 904, leaching tower; 905, leachate storage tank; 906, feeding device; 907, induced draft fan; 908, quenching device; 909, air preheater; 910, heat exchange and calcination device. Detailed Embodiment

[0033] Please refer to Figures 1 to 5, the present invention provides a system and method for jointly removing soil organic matter and heavy metals by a two-stage rotary kiln, and the technical solutions are as follows:

[0034] For the system for jointly removing soil organic matter and heavy metals by a two-stage rotary kiln, 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 a tail 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 inlet 503 and a soil outlet 504. The outlet of the soil crusher 901 is connected to the inlet of the vibrating screen 902, and the outlet of the vibrating screen 902 is connected to the soil inlet 503. The outlet of the inorganic acid storage tank is connected to the inlet of the leaching tower 904, and 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 both installed on the frame 1. The low-temperature organic matter removal system includes a low-temperature rotary kiln 2, and the low-temperature rotary kiln 2 is respectively provided with a flue gas inlet 501, a flue gas outlet 502, a soil inlet 503 and a soil outlet 504. The high-temperature heavy metal solidification system includes a high-temperature rotary kiln 3, a blower 907, an air preheater 909 and a 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 blower 907, the air preheater 909, the combustion pipeline 4 and the flue gas inlet 501 are connected in sequence. The soil outlet 504 of the leaching tower 904 is connected to the soil inlet 503 of the low-temperature rotary kiln 2. There are multiple motors 507 on the frame 1, and the multiple motors 507 are respectively connected to the low-temperature rotary kiln 2 and the high-temperature rotary kiln 3. A plurality of tumbling plates 804 are evenly distributed and installed circumferentially inside the high-temperature rotary kiln 3 and the low-temperature rotary kiln 2. The radial cross-section of the plurality of tumbling plates 804 is arc-shaped, and the arc 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. A feeding device 906 is connected between the soil outlet 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 outlet 504 and the material inlet 505. The screw 602 is coaxially and rotatably connected inside the feeding pipe 601. The feeding pipe 601 is provided with a feeding inlet 604 and a feeding outlet 605. The feeding inlet 604 and the feeding outlet 605 are respectively connected to the soil outlet 504 and the material inlet 505. 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 respectively connected to the motor 507 and the screw 602. 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 pipe 703 and heat exchange fins 704. The quenching box 701 is installed on the frame 1. A heat exchange cavity 702 is opened inside the quenching box 701. The heat exchange pipe 703 is installed inside the heat exchange cavity 702. A plurality of heat exchange fins 704 are evenly distributed and installed on the heat exchange pipe 703.The quench box 701 is provided with an air inlet 705 and an air outlet 706. 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. A plurality of inertial separation plates 801 are arranged at the connection between the flue gas outlet 502 of the high-temperature rotary kiln 3 and the air inlet 705. The plurality of inertial separation plates 801 are arranged in parallel in a louver shape. A guiding groove 802 is provided at the bottom of the quench box 701. The guiding groove 802 is in a funnel shape. The bottom of the guiding groove 802 is communicated with the feeding pipe 601. A diversion pipe 803 is installed at the connection between the air inlet 705 and the heat exchange cavity 702. The central axis of the diversion pipe 803 is tangent to the inclined surface of the guiding 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 two-stage rotary kiln combined system for removing soil organic matter and heavy metals. Please refer to Figure 1 , and the specific steps are as follows: First, the contaminated soil is crushed in the soil crusher 901. After the crushed soil enters the vibrating screen 902, the particles with a particle size less than 20 mm enter the leaching tower 904. Inorganic acid is used as the leaching solution to preliminarily remove the pollutants from the soil, and the leaching waste liquid is collected and enters the storage tank. The leached soil enters the low-temperature rotary kiln 2. At the same time, the flue gas of the high-temperature rotary kiln 3 is introduced into the low-temperature rotary kiln 2 by the induced draft fan 907 as a heat source and directly contacts the soil to perform low-temperature removal of organic matter at 340°C to 360°C; after the organic matter is removed, the soil enters the high-temperature rotary kiln 3 from the low-temperature rotary kiln 2 for high-temperature heavy metal solidification. At this time, the high-temperature gas generated by the combined air preheater 909 and the combustion device enters the high-temperature rotary kiln 3 to indirectly exchange heat with the internal soil, so that heavy metal solidification is performed 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 wall-to-wall heat exchange and calcination on the original montmorillonite sample, and then enters the low-temperature rotary kiln 2 and the high-temperature rotary kiln 3 through the heat exchange and calcination device 910 for recycling; the calcined montmorillonite enters the leaching solution storage tank 905 and the high-temperature rotary kiln 3 respectively to further adsorb and solidify the organic matter and heavy metals in the leaching solution and the heavy metals contained in the soil in the kiln. 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 both enter the dust collector for treatment and then are discharged up to standard through the chimney.

[0036] During operation, please refer to Figures 1 to 5, the soil to be processed 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 driven by the motor 507. The tumbling plates 804 evenly distributed on the inner circumference thereof rotate with the rotary kiln. Since the arc opening direction of the tumbling plate 804 is consistent with the rotation direction of the rotary kiln, it will continuously lift and tumble the soil, enabling the soil to be evenly heated in a low-temperature environment and achieving the preliminary removal of organic matter. The parameters such as the temperature and residence time in the low-temperature rotary kiln 2 are set according to the characteristics of the organic matter in the soil and the treatment requirements. During this process, the flue gas transported from the high-temperature rotary kiln 3 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 a louver shape at the connection between the flue gas outlet 502 of the high-temperature rotary kiln 3 and the air inlet 705 of the quench box 701, where preliminary particle separation is carried out. Larger particle 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 quench box 701 through the air inlet 705. Under the action of the guide pipe 803, the flue gas flows along the direction tangent to the inclined plane of the guide groove 802, enabling the flue gas to form a specific flow field in the heat exchange chamber 702 and improving the contact efficiency between the flue gas and the heat exchange pipes 703 and heat exchange fins 704. At the same time, when the flue gas flows through the guide pipe 803 in the direction tangent to the inclined plane of the guide groove 802, a rotating airflow is formed. Under the action of centrifugal force, the solid particles or droplets in the gas are thrown towards the inner wall of the separator. Since the density of the particles or droplets is greater than that of the gas, the centrifugal force gives them a greater acceleration of outward movement, thereby separating from the gas and avoiding the direct contact between the fine soil particles and the heat exchange pipes 703 and heat exchange fins 704, which may cause the soil particles to adhere to the heat exchange pipes 703 and heat exchange fins 704. At this time, a cooling medium is passed through the heat exchange pipes 703, and the flue gas is rapidly cooled through the heat exchange pipes 703 and heat exchange fins 704, reducing the flue gas temperature to a range suitable for entering the low-temperature rotary kiln 2, and at the same time further causing some particle impurities in the flue gas to cool and settle to the guide groove 802; the cooled flue gas is discharged from the air 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 should be noted that the screw 602 in the feed pipe 601 rotates under the drive of the motor 507 through the gear set 603, pushing the materials that fall from the guiding groove 802 of the quenching box 701 and the materials that enter the feed pipe 601 from the soil discharge port 504 of the low-temperature rotary kiln 2 to the feed outlet 605 of the feed pipe 601 through the rotation of the screw 602, and then conveying them to the material inlet 505 of the high-temperature rotary kiln 3. After the materials enter the high-temperature rotary kiln 3, the high-temperature rotary kiln 3 rotates driven by the motor 507, and the tumbling plate 804 inside also makes the materials tumble fully. The materials are in full contact with the heat source provided by the combustion pipe 4 in a high-temperature environment, and at the same time, some additives such as curing agents may be added as needed to cause the heavy metals to undergo a curing reaction, achieving the effective curing of 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 specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principles and ideas of the present invention, various changes, modifications, substitutions, and variations made to these embodiments should still fall within the protection scope of the present invention.

Claims

1. A system for jointly removing soil organic matter and heavy metals by a two-stage rotary kiln, characterized in that, It includes a frame (1), a low-temperature organic matter removal system and a high-temperature heavy metal solidification system. 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 includes a low-temperature rotary kiln (2). A flue gas inlet (501), a flue gas outlet (502), a soil feed inlet (503) and a soil discharge outlet (504) are respectively arranged on the low-temperature rotary kiln (2). The high-temperature heavy metal solidification system includes a high-temperature rotary kiln (3), a draft fan (907), an air preheater (909) and a combustion pipeline (4). A flue gas inlet (501), a flue gas outlet (502), a material inlet (505) and a material outlet (506) are arranged on the high-temperature rotary kiln (3). The draft fan (907), the air preheater (909), the combustion pipeline (4) and the flue gas inlet (501) are connected in sequence. A feeding device (906) is connected between the soil discharge outlet (504) of the low-temperature rotary kiln (2) and the material inlet (505) of the high-temperature rotary kiln (3). A heat exchange and calcination device (910) is connected to the material inlet (505) of the high-temperature rotary kiln (3). A screw (602) is arranged in the feeding device (906). 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). A heat exchange tube (703) is arranged in the quenching device (908).

2. The system for jointly removing soil organic matter and heavy metals by using a two-stage rotary kiln according to claim 1, characterized in that: The feeding device (906) includes a feeding pipe (601) 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 outlet (504) and the material inlet (505). The screw (602) is coaxially and rotationally connected in the feeding pipe (601). A feeding inlet (604) and a feeding outlet (605) are arranged on the feeding pipe (601). The feeding inlet (604) and the feeding outlet (605) are respectively communicated with the soil discharge outlet (504) and the material inlet (505). The gear set (603) is installed on the frame (1). An input end and an output end are arranged on the gear set (603). The input end and the output end are respectively connected with a motor (507) and the screw (602).

3. The system for jointly removing soil organic matter and heavy metals by using a two-stage rotary kiln according to claim 1, 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 opened in the quenching box (701). The heat exchange tube (703) is installed in the heat exchange cavity (702). A plurality of the heat exchange fins (704) are evenly arranged on the heat exchange tube (703). An air inlet (705) and an air outlet (706) are opened on the quenching box (701). The air inlet (705) and the air outlet (706) are respectively communicated with 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 system for jointly removing soil organic matters and heavy metals by a two-stage rotary kiln according to claim 3, characterized in that: At the connection between the flue gas outlet (502) and the air inlet (705) of the high-temperature rotary kiln (3), a plurality of inertial separation plates (801) are provided, and the plurality of inertial separation plates (801) are arranged in parallel in a shutter shape.

5. The system for jointly removing soil organic matter and heavy metals by using a two-stage rotary kiln according to claim 3, characterized in that: A guiding groove (802) is provided at the bottom of the quench box (701), the guiding groove (802) is in a funnel shape, and the bottom of the guiding groove (802) is communicated with the feeding pipe (601).

6. The system for jointly removing soil organic matter and heavy metals by using a two-stage rotary kiln according to claim 5, characterized in that: A diversion pipe (803) is installed at the connection between the air inlet (705) and the heat exchange chamber (702), and the central axis of the diversion pipe (803) is tangent to the inclined surface of the guiding groove (802).

7. The system for jointly removing soil organic matter and heavy metals by using a two-stage rotary kiln according to claim 1, characterized in that: A plurality of tumbling plates (804) are evenly distributed in a circumferential manner inside the high-temperature rotary kiln (3) and the low-temperature rotary kiln (2). The radial cross-section of the plurality of tumbling plates (804) is arc-shaped, and the arc 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. Method for jointly removing soil organic matters and heavy metals by a two-stage rotary kiln, characterized in that: This method is at least applied to the two-stage rotary kiln system for jointly removing soil organic matter and heavy metals according to any one of claims 1 to 7. The specific method includes: S1: The crushed soil is sieved by a screening device according to particle size. The sieved soil is mixed with an inorganic acid leaching solution, and soil pretreatment is carried out. The filtrate after pretreatment is recovered and stored. S2: The soil pretreated in S1 enters the low-temperature rotary kiln (2) through the soil inlet (503) for drying and volatilization and removal of organic matter. Part of the flue gas generated by the high-temperature rotary kiln (3) exchanges heat 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 be in direct contact with the soil and provide heat source. After the soil is discharged through the soil outlet (504), it is 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 pipeline (4) to assist in generating combustible gas. The combustible gas enters the high-temperature rotary kiln (3) through the combustion pipeline (4) to burn fully and exchange heat with the soil. Part of the flue gas generated by the high-temperature rotary kiln (3) exchanges heat through the heat exchange and 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 in-kiln circulating flue gas. The soil after organic matter removal enters the high-temperature rotary kiln (3) through the material inlet (505) as one of the raw materials for high-temperature calcination, and its product is discharged and collected through the material outlet (506). S4: After the montmorillonite enters the heat exchange and calcination device (910) for heat treatment, part of the product is recovered and stored, and the other part of the product enters the high-temperature rotary kiln (3) through the material inlet (505) as another raw material. S5: The outlet flue gas of the low-temperature rotary kiln (2) in S2 and the outlet combustible gas of the high-temperature rotary kiln (3) in S3 enter the dust collector and the chimney for treatment and up-to-standard discharge.

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