An ex-situ thermal desorption coupled catalytic cracking and oxidation device for organic contaminated soil

Abstract

This invention discloses an ex-situ thermal desorption coupled catalytic cracking oxidation device for organically contaminated soil, relating to the field of soil remediation technology. It includes a feeding unit, a thermal desorption unit, a high-temperature dust removal unit, a catalytic cracking oxidation unit, and an alkaline washing unit connected in sequence, as well as a heat exchange unit connected to the thermal desorption unit and the catalytic cracking oxidation unit. The thermal desorption unit is used to thermally desorb the organically contaminated soil, resulting in effluent soil and organic waste gas. The high-temperature dust removal unit is used to remove dust from the organic waste gas. The catalytic cracking oxidation unit is used to perform a cracking-oxidation reaction on the dust-removed organic waste gas to achieve organic matter decomposition and obtain preliminarily purified waste gas. The alkaline washing unit is used to perform alkaline washing on the waste gas to obtain purified waste gas that can be emitted. The heat exchange unit is used to enhance the recycling of waste heat. This invention optimizes the waste gas treatment process of ex-situ thermal desorption, achieving reduced energy consumption and deep decomposition of pollutants.

Description

Technical Field

[0001] This utility model relates to an ex-situ thermal desorption coupled catalytic cracking oxidation device for organic polluted soil, belonging to the field of soil remediation technology. Background Technology

[0002] Ex-situ thermal desorption technology is one of the mainstream technologies in the soil remediation industry. Its principle is to heat organic pollutants in the soil to above the boiling point so that they can be physically separated and removed. This technology is frequently used in my country and has significant advantages such as high pollutant removal rate, short remediation cycle and strong applicability. It is suitable for the removal of volatile and semi-volatile organic pollutants and mercury and its compounds in soil.

[0003] However, with the engineering application of this technology in market projects, some difficulties have also been exposed, such as high energy consumption and complex end-of-pipe purification processes; the high-temperature steam from thermal desorption will cause a large amount of heat loss after condensation; the gas after condensation will generate a large amount of hazardous waste through activated carbon adsorption; the treatment of condensate wastewater and the recycling of non-condensable gas will lead to secondary treatment and increase disposal costs.

[0004] The main reason for this is the lack of efficient deep digestion and purification technologies for thermal desorption exhaust gases. There is an urgent need to develop and apply high-efficiency, low-cost, short-process, and low-investment treatment technologies and equipment. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide an ex-situ thermal desorption coupled catalytic cracking oxidation device for organic polluted soil. By optimizing the tail gas treatment process, it can reduce energy consumption and achieve deep decomposition of pollutants.

[0006] To achieve the above objectives, this utility model employs the following technical solution: This invention provides an ex-situ thermal desorption coupled catalytic cracking oxidation device for organic polluted soil, comprising a feeding unit, a thermal desorption unit, a high-temperature dust removal unit, a catalytic cracking oxidation unit and an alkaline washing unit connected in sequence, and a heat exchange unit connected to the thermal desorption unit and the catalytic cracking oxidation unit.

[0007] The thermal desorption unit is used to thermally desorb organic polluted soil and desorb it into effluent soil and organic exhaust gas. The high-temperature dust removal unit is used to remove dust from organic exhaust gas; The catalytic cracking and oxidation unit is used to carry out cracking-oxidation reaction on the organic tail gas after dust removal, so as to realize the decomposition of organic matter and obtain pre-purified tail gas. The alkaline washing unit is used to perform alkaline washing on the exhaust gas to obtain purified exhaust gas that can be emitted. The heat exchange unit is used to enhance the recycling of waste heat from the thermal desorption unit and the catalytic cracking oxidation unit.

[0008] Furthermore, the feeding unit includes a feeding bin, a conveyor belt, a feeding airlock, and a feeding screw mechanism connected in sequence. The feeding bin is used for feeding organic polluted soil, and the organic polluted soil is transported to the thermal desorption unit via the conveyor belt, the feeding airlock, and the feeding screw mechanism.

[0009] Furthermore, the feeding hopper is equipped with a vibrating screen and an online moisture meter. The vibrating screen is used to remove particulate impurities in the organically polluted soil that are larger than a preset threshold. The online moisture meter is used to monitor the soil moisture content of the organically polluted soil in real time. When the soil moisture content is higher than the set value, the feeding hopper stops feeding.

[0010] Furthermore, the thermal desorption unit includes a combustion chamber and an indirect thermal desorption reactor connected to the output end of the feed screw mechanism. The indirect thermal desorption reactor is connected to a main drive motor, which drives the indirect thermal desorption reactor to rotate. The indirect thermal desorption reactor is provided with a heat source inlet, a heat source outlet, an organic exhaust gas outlet, and a soil outlet. The heat source inlet is connected to the combustion chamber, which provides a heat source for the indirect thermal desorption reactor. Its inlet is connected to a combustion air pipeline and a natural gas pipeline. Both the combustion air pipeline and the natural gas pipeline are equipped with a blower pump. The organic exhaust gas outlet is connected to a high-temperature dust removal unit.

[0011] Furthermore, the soil outlet is connected in sequence to an outlet gas lock and a humidification device. The outlet gas lock is used to prevent gas leakage inside the indirect thermal desorption reactor.

[0012] Furthermore, the high-temperature dust removal unit includes an air compressor, an air storage tank, a filter, a refrigerated dryer, and a high-temperature dust collector connected in sequence. The input end of the high-temperature dust collector is connected to the output end of the indirect thermal desorption reactor. The air compressor generates compressed air, which is stored in the air storage tank, purified by the filter, dried by the refrigerated dryer, and then input to the high-temperature dust collector. The output end of the high-temperature dust collector is connected to the input end of the catalytic cracking oxidation unit.

[0013] Furthermore, the heat exchange unit includes a first heat exchanger and a second heat exchanger. The shell-side input ends of the first heat exchanger and the second heat exchanger are both connected to air filters, and the shell-side output ends are connected to the combustion chamber via combustion air pipes. The tube-side input end of the first heat exchanger is connected to the heat source output port of the indirect thermal desorption reactor, and the tube-side output end is connected to the chimney. The tube-side input end of the second heat exchanger is connected to the output end of the catalytic cracking oxidation unit, and the tube-side output end is connected to the alkaline washing unit.

[0014] Furthermore, the catalytic cracking oxidation unit includes a catalytic cracking oxidation reaction shell, which is filled with CuO@Hol HZSM-5 catalyst, with a designed flow rate of 3000 Nm³. 3 / h, inlet organic matter concentration is less than 3000 mg / m³ 3 The internal reaction temperature of the reactor is 320℃-450℃, and the reaction pressure is <10kPa. The CuO@Hol HZSM-5 catalyst is prepared from HZSM-5 zeolite molecular sieve catalyst, copper nitrate trihydrate, and tetrapropylammonium hydroxide.

[0015] Furthermore, the alkaline washing unit includes an alkaline washing tower, a wastewater storage tank, and a sewage pump connected in sequence. The alkaline washing tower is a three-stage spray tower, with the first stage spray liquid being a 5% sodium hydroxide solution, the second stage spray liquid being a 10% sodium carbonate solution, and the third stage spray liquid being clean water. The alkaline washing tower is also equipped with an alkaline pump, which is used to transport the spray liquid from the bottom of the alkaline washing tower to the top of the tower.

[0016] Compared with the prior art, the beneficial effects achieved by this utility model are as follows: The ex-situ thermal desorption coupled catalytic cracking oxidation device for organic polluted soil provided by this utility model has advantages such as high efficiency, energy saving and low cost. It eliminates the multiple end-of-pipe purification processes such as condensation, activated carbon adsorption and secondary treatment of sewage and non-condensable gas in the traditional ex-situ thermal desorption process, greatly shortens the treatment process and reduces the process cost by about 90 yuan / ton of soil. This invention employs a cracking-oxidation reaction to deeply decompose organic matter, greatly reducing the generation of hazardous waste. Combined with an alkaline washing module, it achieves synergistic control of multiple pollutants. Through a heat exchanger, it realizes the cascade utilization of reaction heat and exhaust gas waste heat, reducing natural gas consumption by approximately 26-40%. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of an ex-situ thermal desorption coupled catalytic cracking and oxidation device for organic contaminated soil in one embodiment of this utility model; In the diagram: 1-Feed hopper, 2-Conveyor belt, 3-Feed airlock, 4-Feed screw mechanism, 5-Main drive motor, 6-Indirect thermal desorption reactor, 71-First heat exchanger, 72-Second heat exchanger, 8-Air filter, 9-Chimney, 10-Fan pump, 11-Combustion chamber, 12-Discharge airlock, 13-Humidification device, 14-Air compressor, 15-Air storage tank, 16-Filter, 17-Refrigerated dryer, 18-High temperature dust collector, 19-Catalytic cracking oxidation unit, 20-Alkali washing tower, 21-Alkali pump, 22-Sewage storage tank, 23-Sewage pump. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0019] like Figure 1 As shown in the figure, this utility model embodiment provides an ex-situ thermal desorption coupled catalytic cracking oxidation device for organic contaminated soil, including a feeding unit, a thermal desorption unit, a high-temperature dust removal unit, a catalytic cracking oxidation unit, an alkaline washing unit, and a heat exchange unit connected in sequence. In this embodiment, the various units are connected by pipes, but it is not limited to this; any other form that can achieve the connection of the various units should be possible, such as a conveyor belt.

[0020] The feeding unit includes a feeding hopper 1, a conveyor belt 2, a feeding airlock 3, and a feeding screw mechanism 4 connected in sequence. Organically contaminated soil is fed into the feeding hopper 1. In this embodiment, the feeding hopper 1 is equipped with a vibrating screen with a 50mm mesh size, which can effectively separate stone impurities with a particle size >50mm, preventing large particles from clogging subsequent equipment. The feeding hopper 1 is also equipped with an online moisture meter, which is used to monitor the soil moisture content of the organically contaminated soil in real time. In this embodiment, a suitable soil moisture content range is set to 5~25%. When the soil moisture content exceeds this range, an alarm is automatically triggered, causing the feeding hopper 1 to stop feeding. After adding a desiccant such as lime and mixing thoroughly, feeding resumes once the moisture content reaches the standard.

[0021] Conveyor belt 2 is a quantitative and uniform speed conveying device. The main body is a stainless steel belt conveyor, equipped with a variable frequency speed control motor. The motor speed is set through the PLC control system to control the belt conveying speed within the range of 0.15~0.2 m / s, ensuring that the organic polluted soil is sent into the thermal desorption unit at a stable rate of 8~10 tons / hour through the feed airlock 3 and the feed screw conveyor mechanism 4.

[0022] The thermal desorption unit includes an indirect thermal desorption reactor 6 and a combustion chamber 11 connected in sequence. The indirect thermal desorption reactor 6 is connected to the output end of the feed screw conveyor 4. The organic polluted soil completes the thermal desorption process in the indirect thermal desorption reactor 6. In this embodiment, the length of the indirect thermal desorption reactor 6 is 12m and the inner diameter is 2m. It is connected to the main drive motor 5 for transmission, and the main drive motor 5 provides the rotation power for the indirect thermal desorption reactor 6.

[0023] The indirect thermal desorption reactor 6 uses a distributed burner to control the temperature in sections. Each section is equipped with an independent temperature control module, so that the soil goes through a preheating section (150~200℃), a main heating section (300~500℃), and a heat preservation section (200~250℃) in the kiln. The total residence time is ≥30 minutes, and the high-temperature flue gas temperature can reach 800℃, ensuring that the removal rate of VOCs and SVOCs is ≥99.99%.

[0024] The indirect thermal desorption reactor 6 is equipped with a heat source inlet and a heat source outlet. The heat source inlet is connected to the combustion chamber. The inlet of the combustion chamber 11 is connected to the combustion air pipeline and the natural gas pipeline. Both the combustion air pipeline and the natural gas pipeline are equipped with a blower pump 10. The combustion air and natural gas enter the combustion chamber 11 through the blower pump 10, mix and burn to generate high-temperature flue gas, which provides a heat source for the indirect thermal desorption reactor 6.

[0025] After being desorbed at high temperature by the indirect thermal desorption reactor 6, the organic polluted soil is decomposed into organic tail gas and effluent soil. The indirect thermal desorption reactor 6 is equipped with an organic tail gas outlet and an effluent soil outlet. The effluent soil passes through an effluent air lock 12, which is used to prevent air leakage and maintain a slightly negative pressure environment inside the indirect thermal desorption reactor 6 to prevent untreated organic tail gas from escaping into the workshop. After being cooled by the humidification device 13, it is transferred to a temporary storage area for inspection.

[0026] The organic exhaust outlet is connected to a high-temperature dust removal unit, which includes an air compressor 14, an air tank 15, a filter 16, a refrigerated dryer 17, and a high-temperature dust collector 18 connected in sequence. It employs a high-temperature ceramic pulse jet dust removal principle. The air compressor 14 generates compressed air (typically 0.7~1.0 MPa) as the power source for pulse jet cleaning. The air tank 15 stores compressed air to balance the intermittent operation of the air compressor with the instantaneous high flow demand of the pulse valve. The filter 16 purifies the compressed air, preventing impurities from clogging the pulse valve and wearing down the ceramic filter element. The refrigerated dryer 17 provides a dry and clean air source, ensuring that the jet air does not freeze in low-temperature environments and that water vapor does not enter the high-temperature dust collector 18 in high-temperature environments (preventing dust adhesion to the filter element) and extending the filter element's lifespan. The high-temperature dust collector 18 operates at a temperature ≥250℃ and uses a silicon carbide / ceramic fiber filter element to trap ≥99.99% of the dust in the high-temperature flue gas. After dust removal, the dust content in the exhaust gas is <5mg / Nm³. 3 It meets the protection requirements for oxygen-induced cracking catalysts.

[0027] The organic exhaust gas treated by the high-temperature dust collector 18 enters the catalytic cracking oxidation unit 19. The catalytic cracking oxidation unit 19 includes a catalytic cracking oxidation reaction shell, and the inside of the catalytic cracking oxidation reaction shell is filled with CuO@Hol HZSM-5 catalyst.

[0028] In this embodiment, the CuO@Hol HZSM-5 catalyst was prepared by the following method: HZSM-5 zeolite molecular sieve was impregnated in copper nitrate trihydrate solution and magnetically stirred at room temperature for 8 hours, followed by drying at 80°C for 8 hours. After drying and grinding, it was placed in a tube furnace and calcined at 500°C for 4 hours under air atmosphere with a heating rate of 4°C. Then, tetrapropylammonium hydroxide was added, and hydrothermal crystallization was carried out at 170°C for 72 hours, followed by drying at 80°C for 24 hours. After drying and grinding, it was placed in a tube furnace and calcined at 500°C for 4 hours under air atmosphere with a heating rate of 4°C, finally achieving the desired shape. The catalyst's lifespan is approximately 2 years.

[0029] Catalytic cracking oxidation unit 19, under conditions of 320~450℃ and pressure <10kPa, introduces an appropriate amount of oxygen, triggering a series of reactions of cracking followed by oxidation through CuO active sites on the catalyst surface, decomposing large molecular organics (such as polycyclic aromatic hydrocarbons and chlorinated hydrocarbons) into small molecules such as CO2, H2O, N2 and HCl, with a pollutant degradation rate ≥99%.

[0030] The heat exchange unit includes a first heat exchanger 71 and a second heat exchanger 72. The first heat exchanger 71 and the second heat exchanger 72 adopt a partitioned spiral tube heat exchange method. The heat exchange tube is made of 316L stainless steel, with a tube diameter of Φ25×2mm and a spiral pitch of 50mm.

[0031] Both the shell-side inlet of the first heat exchanger 71 and the second heat exchanger 72 are connected to air filters 8, and their shell-side outlets are connected to the combustion chamber 11 via combustion air ducts. This allows the combustion air to be preheated to 330°C and 230°C respectively before being delivered to the combustion chamber 11, achieving heat recovery from the thermal desorption unit and the catalytic cracking oxidation unit 19 through counter-current heat exchange. The tube-side inlet of the first heat exchanger 71 is connected to the heat source outlet of the indirect thermal desorption reactor 6, and its tube-side outlet is connected to the chimney, allowing the waste heat flue gas (350°C) from the indirect thermal desorption reactor 6 to be cooled to 205°C before being discharged through the chimney in compliance with standards. The tube-side inlet of the second heat exchanger 72 is connected to the outlet of the catalytic cracking oxidation unit 19, and its tube-side outlet is connected to the alkaline scrubbing unit, allowing the high-temperature cracked gas (450°C) from the catalytic cracking oxidation unit 19 to be cooled to 150°C before entering the alkaline scrubbing unit.

[0032] The alkaline washing unit includes an alkaline washing tower 20, a wastewater storage tank 22, and a sewage pump 23 connected in sequence. The alkaline washing tower 20 is a three-stage spray tower, with each stage 4m high and 1.5m in diameter. In this embodiment, the first stage sprays a 5% NaOH solution, with the pH value controlled at 9-11 by an automatic dosing system; the second stage sprays a 10% Na2CO3 solution, with the pH value controlled at 8-9; and the third stage uses industrial clean water with a conductivity <100μS / cm. The spray liquid is pressurized by a circulating pump and atomized through a spiral nozzle, with a gas-liquid ratio controlled at 1.5:1 and a droplet size <800μm. The alkaline washing tower 20 is equipped with an alkaline solution pump 21, which provides the circulating power source to pressurize and transport the alkaline solution from the bottom circulation tank to the top spray system. The exhaust gas is finally dehydrated by a demister and output, with an outlet non-methane total hydrocarbon concentration ≤40mg / m³. 3 HCl concentration <10mg / m³ 3 .

[0033] Wastewater storage tank 22 is used to collect saturated waste alkali solution discharged from the alkali washing tower. It is generally lined with corrosion-resistant material and made of PE / PP or FRP. Sewage pump 23 is used to pump the high-salt wastewater in the wastewater storage tank to the subsequent wastewater treatment system for purification and discharge after meeting standards.

[0034] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. An apparatus for ex situ thermal desorption coupled with catalytic cracking oxidation of organic contaminated soil, characterized in that, It includes a feeding unit, a thermal desorption unit, a high-temperature dust removal unit, a catalytic cracking oxidation unit and an alkaline washing unit connected in sequence, as well as a heat exchange unit connected to the thermal desorption unit and the catalytic cracking oxidation unit; The thermal desorption unit is used to thermally desorb organic polluted soil and desorb it into effluent soil and organic exhaust gas. The high-temperature dust removal unit is used to remove dust from organic exhaust gas; The catalytic cracking and oxidation unit is used to carry out cracking-oxidation reaction on the organic tail gas after dust removal, so as to realize the decomposition of organic matter and obtain pre-purified tail gas. The alkaline washing unit is used to perform alkaline washing on the preliminarily purified exhaust gas to obtain purified exhaust gas that can be emitted. The heat exchange unit is used to enhance the recycling of waste heat from the thermal desorption unit and the catalytic cracking oxidation unit.

2. The apparatus for ex situ thermal desorption coupled with catalytic cracking oxidation of organic contaminated soil according to claim 1, characterized in that, The feeding unit includes a feeding bin, a conveyor belt, a feeding airlock, and a feeding screw mechanism connected in sequence. The feeding bin is used for feeding organic polluted soil, and the organic polluted soil is transported to the thermal desorption unit via the conveyor belt, the feeding airlock, and the feeding screw mechanism.

3. The apparatus for ex situ thermal desorption coupled with catalytic cracking oxidation of organically contaminated soil according to claim 2, characterized in that, The feeding hopper is equipped with a vibrating screen and an online moisture meter. The vibrating screen is used to remove particulate impurities in the organic polluted soil that are larger than a preset threshold. The online moisture meter is used to monitor the soil moisture content of the organic polluted soil in real time. When the soil moisture content is higher than the set value, the feeding hopper stops feeding.

4. The ex-situ thermal desorption coupled catalytic cracking and oxidation device for organic contaminated soil according to claim 2, characterized in that, The thermal desorption unit includes a combustion chamber and an indirect thermal desorption reactor connected to the output end of the feed screw mechanism. The indirect thermal desorption reactor is connected to a main drive motor, which drives the indirect thermal desorption reactor to rotate. The indirect thermal desorption reactor is provided with a heat source inlet, a heat source outlet, an organic exhaust gas outlet, and a soil outlet. The heat source inlet is connected to the combustion chamber, which provides a heat source for the indirect thermal desorption reactor. Its inlet is connected to a combustion air pipeline and a natural gas pipeline. Both the combustion air pipeline and the natural gas pipeline are equipped with a fan pump. The organic exhaust gas outlet is connected to a high-temperature dust removal unit.

5. The apparatus for ex situ thermal desorption coupled with catalytic cracking oxidation of organically contaminated soil according to claim 4, characterized in that, The soil discharge port is connected in sequence to a discharge gas lock and a humidification device. The discharge gas lock is used to prevent gas leakage inside the indirect thermal desorption reactor.

6. The apparatus for ex situ thermal desorption coupled with catalytic cracking oxidation of organic contaminated soil according to claim 4, characterized in that, The high-temperature dust removal unit includes an air compressor, an air storage tank, a filter, a refrigerated dryer, and a high-temperature dust collector connected in sequence. The input end of the high-temperature dust collector is connected to the output end of the indirect thermal desorption reactor. The air compressor generates compressed air, which is stored in the air storage tank. After being purified by the filter and dried by the refrigerated dryer, the compressed air is input to the high-temperature dust collector. The output end of the high-temperature dust collector is connected to the input end of the catalytic cracking oxidation unit.

7. The apparatus for ex situ thermal desorption coupled with catalytic cracking oxidation of organically contaminated soil according to claim 6, characterized in that, The catalytic cracking oxidation unit includes a catalytic cracking oxidation reaction shell, which is filled with CuO@Hol HZSM-5 catalyst.

8. The ex-situ thermal desorption coupled catalytic cracking and oxidation device for organic contaminated soil according to claim 7, characterized in that, The heat exchange unit includes a first heat exchanger and a second heat exchanger. The shell-side input ends of the first heat exchanger and the second heat exchanger are both connected to air filters, and the shell-side output ends are connected to the combustion chamber via combustion air pipes. The tube-side input end of the first heat exchanger is connected to the heat source output port of the indirect thermal desorption reactor, and the tube-side output end is connected to the chimney. The tube-side input end of the second heat exchanger is connected to the output end of the catalytic cracking oxidation unit, and the tube-side output end is connected to the alkaline washing unit.

9. The apparatus for ex situ thermal desorption coupled with catalytic cracking oxidation of organically contaminated soil according to claim 8, characterized in that, The alkaline washing unit includes an alkaline washing tower, a wastewater storage tank, and a sewage pump connected in sequence. The alkaline washing tower is a three-stage spray tower. The first stage spray liquid is a 5% sodium hydroxide solution, the second stage spray liquid is a 10% sodium carbonate solution, and the third stage spray liquid is clean water. The alkaline washing tower is also equipped with an alkaline solution pump, which is used to transport the spray liquid from the bottom of the alkaline washing tower to the top of the tower.

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