Tail gas treatment system for repairing polluted soil through thermal desorption

Abstract

The invention relates to the technical field of contaminated soil remediation, in particular to a tail gas treatment system for contaminated soil remediation through thermal desorption. The invention discloses a tail gas treatment system for repairing polluted soil through thermal desorption. The tail gas treatment system comprises a dust removal unit, an adsorption unit, a degradation unit and a detection unit, magnesium chloride loaded modified zeolite is used as an adsorption material in the adsorption unit; a porous MnO2-RuO2 composite catalyst is used as a catalytic degradation catalyst in the degradation unit, and catalytic degradation is carried out under the action of the porous MnO2-RuO2 composite catalyst. After the tail gas containing 90 mg / m < 3 > of polycyclic aromatic hydrocarbon, 13.2 mg / m < 3 > of nitrogen oxide and 15.5 mg / m < 3 > of sulfur dioxide is treated by the method, the concentration of the polycyclic aromatic hydrocarbon in the tail gas can reach 142-215 mu g / m, the concentration of the nitrogen oxide can reach 125-150 mu g / m, the concentration of the sulfur dioxide can reach 70-83 mu g / m, and the effect of removing pollutants in the tail gas is excellent.

Description

Technical Field

[0001] The present application relates to the technical field of contaminated soil remediation, and in particular to an exhaust gas treatment system for thermal desorption remediation of contaminated soil. Background Art

[0002] Soil is one of the main resources for human survival and an important part of the human ecological environment. With the rapid development of my country's economy, the problem of soil pollution has become increasingly prominent.

[0003] In recent years, various remediation technologies and equipment for organic contaminated sites have been widely studied, and relevant research results have been applied to the remediation of contaminated sites. Thermal desorption remediation technology has been widely used in the treatment of soil, sludge, sediment and other sites containing volatile and semi-volatile organic pollutants due to its advantages of high treatment efficiency, short remediation cycle and wide application range.

[0004] After the organically contaminated soil is heated, the tail gas will be desorbed from the soil. The tail gas contains high concentrations of VOCs (especially naphthalene, benzopyrene and other difficult-to-degrade benzene ring macromolecules), as well as heavy metals, alkali metals, alkaline earth metals, and particulate matter, with a complex composition.

[0005] Some existing technologies use incineration to treat thermal desorption tail gas. The incineration method is more suitable for direct thermal desorption tail gas treatment, but this method has high energy consumption and cost, and there is a risk of dioxin pollution. Other existing technologies use condensation to transfer most of the organic pollutants in the tail gas to the liquid phase. Although some of them also use plasma to remove the remaining very small amount of organic pollutants, the wastewater generated in this technology still needs to be further treated, which increases the difficulty of wastewater treatment.

[0006] Currently, researchers in this field have tried to use catalysts to catalytically oxidize the desorbed exhaust gas to reduce its combustion temperature, but the effect is not good. Secondary pollution control technology is still immature, with a low level of specialization and high cost, resulting in a greater risk of secondary pollution. Summary of the invention

[0007] In order to improve the exhaust gas treatment effect of thermal desorption remediation of contaminated soil, the present application provides an exhaust gas treatment system for thermal desorption remediation of contaminated soil.

[0008] A tail gas treatment system for thermal desorption remediation of contaminated soil adopts the following technical solution.

[0009] A tail gas treatment system for thermal desorption remediation of contaminated soil, comprising a dust removal unit, an adsorption unit, a degradation unit, and a detection unit; In the adsorption unit, magnesium chloride-loaded modified zeolite is used as the adsorption material; Porous MnO 2 -RuO2 The composite catalyst is used as a catalytic degradation catalyst in porous MnO 2 -RuO 2 Catalytic degradation is carried out under the action of a composite catalyst.

[0010] By adopting the above technical solution, after the contaminated soil is heated and desorbed, the tail gas enters the tail gas treatment system. The tail gas entering the tail gas treatment system is firstly sent to the dust removal unit to remove the particulate soil materials in the tail gas; the tail gas after dust removal enters the degradation unit, and the tail gas in the degradation unit is heated and desorbed in the porous MnO 2 -RuO 2 Under the action of the composite catalyst, the pollutants in the tail gas are degraded by heating and catalysis; the tail gas degraded by the degradation unit enters the adsorption unit, and the magnesium chloride-loaded modified zeolite in the adsorption unit effectively removes the gasified tar-containing components and sulfur-containing components in the tail gas. The treated tail gas can be discharged after being tested by the detection unit to meet the emission standards.

[0011] Furthermore, a spray gun for spraying urea solution is provided in the degradation unit, and the spraying speed of the urea solution is 1.6-1.8 L / min.

[0012] Furthermore, the mass percentage concentration of the urea solution is 15-30%.

[0013] By adopting the above technical solution, urea solution is sprayed into the exhaust gas flow, and urea decomposes at high temperature to produce ammonia and carbon dioxide. Ammonia and nitrogen oxides in the exhaust gas undergo selective catalytic reduction reaction under the action of the catalyst, converting NOx into harmless nitrogen and water. Urea solution can also absorb organic matter in the exhaust gas, capture it through physical or chemical action, and reduce the content of organic matter discharged into the atmosphere.

[0014] Furthermore, the temperature in the degradation unit is 450-600° C., and the tail gas residence time is 1-5 s.

[0015] Furthermore, the preparation method of the magnesium chloride loaded modified zeolite is: a) Prepare a magnesium chloride solution with a concentration of 0.4-0.7 mol / L; b) calcining the zeolite at 500-700° C. for 10-12 h, then mixing the zeolite with a magnesium chloride solution at a solid-liquid ratio of 1:(5-10), and heating and stirring the mixture for 40-70 min to obtain a reaction solution; c) drying the reaction solution, and then washing and drying to obtain magnesium chloride loaded modified zeolite.

[0016] Natural zeolite has a stable structure with a large number of pores and cavities, but the activity of silicon and aluminum is low. By adopting the above technical solution, the performance is activated after high-temperature calcination to form larger cavities, thereby obtaining a higher adsorption force, allowing pollutant molecules to be adsorbed or stored in it. After calcination, magnesium chloride is loaded, Mg 2+ There is a strong electrostatic field between the zeolite structure, which polarizes and dissociates water molecules, so that the zeolite obtains a more stable charge distribution. After loading magnesium chloride, a large number of small particles appear on the surface of the zeolite, and the lamellar structure is more obvious. The pore structure of the zeolite is changed, the adsorption capacity of the zeolite is increased, and the zeolite can more completely adsorb pollutants in the exhaust gas.

[0017] Furthermore, the solid-to-liquid ratio of the zeolite to the magnesium chloride solution is 1:8.

[0018] Furthermore, the particle size of the zeolite is 5-25 μm and the pore size is 0.5-1 nm.

[0019] Furthermore, the MnO 2 -RuO 2 The preparation method of the composite catalyst is: 1) treating the cordierite honeycomb ceramic substrate with a nitric acid solution at 80° C. for 2-3 hours, then washing to neutrality, drying at 110-120° C. for 3 hours, and then calcining at 550-600° C. for 4 hours to obtain a pretreated substrate; 2) Mix manganese sulfate and ammonium persulfate in a weight ratio of (1-1.5):1 and dissolve in water to obtain MnO 2 Precursor solution; 3) Immerse the pretreated substrate in MnO 2 The precursor solution is then reacted at 170-190°C for 12-14 hours. After the reaction is completed, centrifugation, washing, and drying are performed to obtain the loaded MnO 2 the matrix; 4) dissolving ruthenium trichloride in water to obtain a ruthenium trichloride solution; 5) Load MnO 2 The substrate is immersed in a ruthenium trichloride solution and reacted at 70-80°C for 8-10 hours; after the reaction, the precipitate is filtered out and washed; 6) Dry the washed precipitate at 100-120℃ for 3-5h, and then calcine at 400-600℃ for 8-10h to obtain MnO 2 -RuO 2 Composite catalyst.

[0020] By adopting the above technical solution, MnO is first grown on the cordierite honeycomb ceramic substrate. 2 , then in MnO 2 RuO 2, and obtain a porous composite catalyst. This catalyst includes a matrix and an active component, wherein the matrix is ​​honeycomb cordierite, and the active component is MnO 2 and RuO 2 This catalyst has high catalytic efficiency in the temperature range of 450-650℃, can completely convert the tail gas of organic polluted soil thermal desorption, and has good high-temperature stability, strong resistance to sintering and carbon deposition, and good resistance to alkali, alkaline earth, heavy metals, chlorine and sulfur poisoning.

[0021] In summary, this application has the following beneficial effects: The tail gas generated by thermal desorption of the contaminated soil is collected and then enters the dust removal unit to remove particulate matter in the tail gas. The tail gas after dust removal enters the degradation unit, where the pollutants in the tail gas are degraded by porous MnO 2 -RuO 2 The composite catalyst catalyzes the degradation, and the degraded tail gas enters the adsorption unit and is adsorbed by the magnesium chloride-loaded modified zeolite to remove organic matter and nitrogen- and sulfur-containing pollutants in the tail gas. Contains 90mg / m 3 PAHs, 13.2 mg / m 3 Nitrogen oxides, 15.5mg / m 3 After the sulfur dioxide tail gas is treated by this application, the concentration of polycyclic aromatic hydrocarbons in the tail gas can reach 142-215μg / m³, the concentration of nitrogen oxides can reach 125-150μg / m³, and the concentration of sulfur dioxide can reach 70-83μg / m³, which has excellent effect on removing pollutants in the tail gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the exhaust gas treatment system of Example 1 of the present application.

[0023] In the figure, 1. dust removal unit; 2. degradation unit; 3. adsorption unit; 4. detection unit. DETAILED DESCRIPTION

[0024] The present application is further described in detail below in conjunction with embodiments.

[0025] Raw materials and intermediate preparation examples raw material Magnesium chloride, analytical grade; Manganese sulfate, anhydrous manganese sulfate, analytical grade; Ammonium persulfate, analytical grade; Ruthenium trichloride, analytical grade.

[0026] Preparation Example Preparation Example 1 A magnesium chloride-loaded modified zeolite, the preparation method of which is as follows: a) Prepare a magnesium chloride solution with a concentration of 0.6 mol / L; b) calcining the zeolite at 600° C. for 11 h, then mixing the zeolite with a magnesium chloride solution at a solid-liquid ratio of 1:8, and heating and stirring the mixture at 350° C. for 60 min to obtain a reaction solution; wherein the zeolite has a particle size of 15 μm and a pore size of 0.8 nm; c) drying the reaction solution at 120° C., then washing with deionized water until neutral, and drying at 120° C. to obtain magnesium chloride-loaded modified zeolite.

[0027] Preparation Example 2 Different from Preparation Example 1, the solid-to-liquid ratio of zeolite to magnesium chloride solution in Preparation Example 2 is 1:5.

[0028] Preparation Example 3 Different from Preparation Example 1, the solid-to-liquid ratio of zeolite to magnesium chloride solution in Preparation Example 3 is 1:10.

[0029] Preparation Example 4 Different from Preparation Example 1, the particle size of the zeolite in Preparation Example 4 is 5 μm and the pore size is 1 nm.

[0030] Preparation Example 5 Different from Preparation Example 1, the particle size of the zeolite in Preparation Example 5 is 25 μm and the pore size is 0.5 nm.

[0031] Preparation Example 6 Different from Preparation Example 1, in Preparation Example 6, the zeolite was calcined at 800° C. for 12 h.

[0032] Preparation Example 7 A porous MnO 2 -RuO 2 The composite catalyst is prepared by: 1) The cordierite honeycomb ceramic substrate was immersed in a 15% nitric acid solution at 80°C for 2 hours, then washed to neutrality, dried at 120°C for 3 hours, and then calcined at 600°C for 4 hours to obtain a pretreated substrate; 2) Mix 1.5 kg of manganese sulfate and 1.5 kg of ammonium persulfate and completely dissolve them in water to obtain MnO 2 Precursor solution; 3) The pretreated substrate is completely immersed in MnO 2 The precursor solution was then reacted at 180 °C for 12 h. After the reaction, it was centrifuged, washed, and dried at 120 °C to obtain the loaded MnO 2 the matrix; 4) dissolving 1 kg of ruthenium trichloride in water to obtain a ruthenium trichloride solution; 5) Load MnO 2The substrate is immersed in a ruthenium trichloride solution and reacted at 70-80°C for 8-10 hours; after the reaction, the precipitate is filtered out and washed; 6) The washed precipitate was dried at 120 °C for 3 h and then calcined at 500 °C for 9 h to obtain MnO 2 -RuO 2 Composite catalyst.

[0033] Preparation Example 8 Different from Preparation Example 7, in Step 2) of Preparation Example 8, 2 kg of manganese sulfate and 2 kg of ammonium persulfate were mixed and then completely dissolved in water.

[0034] Preparation Example 9 Different from Preparation Example 7, in Step 2) of Preparation Example 9, 3 kg of manganese sulfate and 3 kg of ammonium persulfate were mixed and then completely dissolved in water.

[0035] Preparation Example 10 Different from Preparation Example 7, in Step 2) of Preparation Example 9, 1.5 kg of manganese sulfate and 1 kg of ammonium persulfate were mixed and then completely dissolved in water.

[0036] Preparation Example 11 A catalyst, the preparation method of which is: 1) The cordierite honeycomb ceramic substrate was immersed in a 15% nitric acid solution at 80°C for 2 hours, then washed to neutrality, dried at 120°C for 3 hours, and then calcined at 600°C for 4 hours to obtain a pretreated substrate; 2) Mix 1.5 kg of manganese sulfate and 1.5 kg of ammonium persulfate and completely dissolve them in water to obtain MnO 2 Precursor solution; 3) The pretreated substrate is completely immersed in MnO 2 The precursor solution was then reacted at 180 °C for 12 h. After the reaction, it was centrifuged, washed, and dried at 120 °C to obtain the loaded MnO 2 catalyst.

[0037] Preparation Example 12 A catalyst, the preparation method of which is: 1) The cordierite honeycomb ceramic substrate was immersed in a 15% nitric acid solution at 80°C for 2 hours, then washed to neutrality, dried at 120°C for 3 hours, and then calcined at 600°C for 4 hours to obtain a pretreated substrate; 2) dissolving 1 kg of ruthenium trichloride in water to obtain a ruthenium trichloride solution; 3) Immerse the pretreated substrate in a ruthenium chloride solution and react at 70-80°C for 8-10 hours; after the reaction is completed, filter out the precipitate and wash it; 4) The washed precipitate was dried at 120 °C for 3 h and then calcined at 500 °C for 9 h to obtain the loaded RuO 2 catalyst.

[0038] Performance Testing The anti-poisoning ability of the catalysts in Preparation Examples 7-12 was tested, and the test results are shown in Table 1.

[0039] Anti-lead poisoning test: The catalyst was soaked in lead solution (lead nitrate solution, concentration of 0.05mol / L) for 6 hours, and the soaked catalyst was loaded into a stainless steel fixed bed reactor with an inner diameter of 16mm, and the raw gas was introduced into the reactor for catalytic oxidation. The raw gas is composed of organic polluted soil thermal desorption waste gas, including: 90mg / m 3 PAHs, 13.2 mg / m 3 Nitrogen oxides, 15.5mg / m 3 Sulfur dioxide, set the reaction space velocity to 10000h -1 The reaction pressure is normal pressure, the test temperature at the beginning of the reaction is 250℃, and the T 90 Indicates the catalytic activity of the catalyst, T 90 It indicates the reaction temperature when the conversion rate of PAHs reaches 90%. The T 90 , and T after lead poisoning 90 , calculate the activity difference, activity difference = T after poisoning 90 -Fresh T 90 .

[0040] Table 1 Catalyst performance test results Example

[0041] Example 1 Reference Figure 1 A tail gas treatment system for thermal desorption remediation of contaminated soil includes a dust removal unit 1, a degradation unit 2, an adsorption unit 3, and a detection unit 4 connected in sequence. The dust removal unit 1 is a cyclone dust collector. The degradation unit 2 includes a degrader, in which the porous MnO obtained in Preparation Example 7 is arranged. 2 -RuO 2 The composite catalyst, the temperature in the degrader is 500°C, and the tail gas residence time is 3s. The adsorption unit 3 includes an adsorber filled with the magnesium chloride-loaded modified zeolite obtained in Preparation Example 1. The detection unit 4 is an online detector.

[0042] The tail gas generated by thermal desorption of the contaminated soil is collected and enters the dust removal unit 1. The cyclone dust collector of the dust removal unit 1 removes the particulate matter in the tail gas. The tail gas after dust removal enters the degradation unit 2. The pollutants in the tail gas in the degradation unit 2 are oxidized by the porous MnO2 -RuO 2 The composite catalyst catalyzes the degradation. The degraded tail gas enters the adsorption unit 3 and is adsorbed by the magnesium chloride-loaded modified zeolite to remove organic matter and nitrogen- and sulfur-containing pollutants in the tail gas. The tail gas treated by the adsorption unit 3 is discharged after being tested by the online detector of the detection unit 4 to meet the standards.

[0043] Embodiment 2-4 Different from Example 1, the porous MnO 2 -RuO 2 The composite catalysts are from Preparation Examples 8-10 respectively.

[0044] Embodiment 5-9 Different from Example 1, the magnesium chloride-loaded modified zeolites in Examples 5-9 are from Preparation Examples 2-6, respectively.

[0045] The difference between Example 10 and Example 1 is that a dual-fluid spray gun is further provided in the degradation unit 2 in Example 10, and the dual-fluid spray gun sprays urea solution into the degradation device. The mass percentage concentration of the urea solution is 15%, and the injection speed of the urea solution is 1.8 L / min.

[0046] Embodiment 11 Different from Example 10, the mass percentage concentration of the urea solution in Example 11 is 30%, and the injection speed of the urea solution is 1.6 L / min.

[0047] Example 12 Different from Example 10, the mass percentage concentration of the urea solution in Example 12 is 20%, and the injection speed of the urea solution is 1.7 L / min.

[0048] Comparative Example Comparative Example 1 The difference from Example 1 is that in Comparative Example 1, an equal amount of zeolite is used to replace the magnesium chloride-loaded modified zeolite.

[0049] Comparative Example 2 The difference from Example 1 is that in Comparative Example 2, the porous MnO 2 -RuO 2 Composite catalyst.

[0050] Comparative Example 3 The difference from Example 1 is that in Comparative Example 3, the porous MnO 2 -RuO 2 Composite catalyst.

[0051] Comparative Example 4 Different from Example 1, in Comparative Example 4, the porous MnO 2 -RuO 2 Composite catalyst.

[0052] Performance Testing The raw gas is composed of organic polluted soil thermal desorption waste gas, including: 90mg / m 3 PAHs, 13.2 mg / m 3 Nitrogen oxides, 15.5mg / m 3 Sulfur dioxide. The raw gas was introduced into the tail gas treatment system in the embodiment and the comparative example for treatment, and the pollutant concentration of the exhaust gas was recorded. The results are shown in Table 2.

[0053] Table 2 Exhaust gas detection results

[0054] Combining the embodiments and the comparative examples, and in combination with Table 2, it can be seen that the exhaust gas treatment system in the embodiments has a greater removal effect on polycyclic aromatic hydrocarbons, nitrogen oxides, and sulfur dioxide than the comparative example, which shows that the exhaust gas treatment system of the present application can achieve better treatment effects and the treatment conditions are mild.

[0055] Combining Example 1 with Comparative Example 1 and Table 2, it can be seen that the emission concentrations of polycyclic aromatic hydrocarbons, nitrogen oxides, and sulfur dioxide in Example 1 are all lower than those in Comparative Example 1, which indicates that replacing magnesium chloride with zeolite to load the modified zeolite will affect the treatment effect of the tail gas, among which the effect on the treatment effect of nitrogen oxides and sulfur dioxide is greater. This may be because the pore structure of the zeolite is changed after the zeolite is calcined at high temperature and then loaded with magnesium chloride, which increases the adsorption amount of the zeolite, so that the zeolite can more completely adsorb pollutants in the tail gas, especially nitrogen oxides and sulfur-containing components.

[0056] Combining Example 1 with Comparative Examples 2-4 and Table 2, it can be seen that the emission concentrations of PAHs, NOx and SO2 in Example 1 are all lower than those in Comparative Example 1, which indicates that the type of catalyst will affect the treatment effect of tail gas, especially the effect on the treatment effect of PAHs. This may be because the porous MnO 2 -RuO 2 The composite catalyst has high catalytic efficiency and can completely transform the tail gas from thermal desorption of organically contaminated soil, greatly improving the treatment effect.

[0057] Combining Examples 1-4 and Table 2, it can be seen that porous MnO 2 -RuO 2The ratio of Mn to Ru in the composite catalyst also affects the treatment effect of tail gas, and has a greater impact on the treatment effect of polycyclic aromatic hydrocarbons. 2 -RuO 2 Composite catalysts are better.

[0058] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A tail gas treatment system for thermal desorption remediation of contaminated soil, characterized in that: It comprises a dust removal unit (1), a degradation unit (2), an adsorption unit (3), and a detection unit (4); In the adsorption unit (3), magnesium chloride-loaded modified zeolite is used as the adsorption material; In the degradation unit (2), a porous MnO2-RuO2 composite catalyst is used as a catalytic degradation catalyst, and catalytic degradation is carried out under the action of the porous MnO2-RuO2 composite catalyst.

2. The tail gas treatment system for thermal desorption remediation of contaminated soil according to claim 1, characterized in that: The degradation unit (2) is provided with a spray gun for spraying urea solution, and the spraying speed of the urea solution is 1.6-1.8 L / min.

3. The tail gas treatment system for thermal desorption remediation of contaminated soil according to claim 2 is characterized by: The mass percentage concentration of the urea solution is 15-30%.

4. The tail gas treatment system for thermal desorption remediation of contaminated soil according to claim 1, characterized in that: The temperature in the degradation unit (2) is 450-600°C, and the tail gas residence time is 1-5s.

5. The tail gas treatment system for thermal desorption remediation of contaminated soil according to claim 1, characterized in that: The preparation method of the magnesium chloride loaded modified zeolite is: a) Prepare a magnesium chloride solution with a concentration of 0.4-0.7 mol / L; b) calcining the zeolite at 500-700°C for 10-12h, then mixing the zeolite with a magnesium chloride solution at a solid-liquid ratio of 1:(5-10), and heating and stirring the mixture for 40-70min to obtain a reaction solution; c) drying the reaction solution, and then washing and drying to obtain magnesium chloride loaded modified zeolite.

6. The tail gas treatment system for thermal desorption remediation of contaminated soil according to claim 5, characterized in that: The solid-to-liquid ratio of the zeolite to the magnesium chloride solution is 1:

8.

7. The tail gas treatment system for thermal desorption remediation of contaminated soil according to claim 5, characterized in that: The particle size of the zeolite is 5-25 μm and the pore size is 0.5-1 nm.

8. The tail gas treatment system for thermal desorption remediation of contaminated soil according to claim 1, characterized in that: The preparation method of the MnO2-RuO2 composite catalyst is: 1) treating the cordierite honeycomb ceramic substrate with a nitric acid solution at 80° C. for 2-3 hours, then washing to neutrality, drying at 110-120° C. for 3 hours, and then calcining at 550-600° C. for 4 hours to obtain a pretreated substrate; 2) mixing manganese sulfate and ammonium persulfate in a weight ratio of (1-1.5):1, and dissolving the mixture in water to obtain a MnO2 precursor solution; 3) Immersing the pretreated substrate in a MnO2 precursor solution, and then reacting at 170-190°C for 12-14 hours. After the reaction is completed, centrifuging, washing, and drying are performed to obtain a MnO2-loaded substrate; 4) dissolving ruthenium trichloride in water to obtain a ruthenium trichloride solution; 5) Immerse the MnO2-loaded substrate in a ruthenium chloride solution and react at 70-80°C for 8-10 hours; after the reaction is completed, filter out the precipitate and wash it; 6) Dry the washed precipitate at 100-120°C for 3-5h, and then calcine at 400-600°C for 8-10h to obtain a MnO2-RuO2 composite catalyst.

9. The tail gas treatment system for thermal desorption remediation of contaminated soil according to claim 8, characterized in that: The weight ratio of manganese sulfate to ruthenium trichloride is (1.5-2):1.

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