CN113996644B - Catalyst-loaded medium circulation thermal desorption soil remediation method and system thereof - Google Patents
Catalyst-loaded medium circulation thermal desorption soil remediation method and system thereof Download PDFInfo
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- CN113996644B CN113996644B CN202111274546.2A CN202111274546A CN113996644B CN 113996644 B CN113996644 B CN 113996644B CN 202111274546 A CN202111274546 A CN 202111274546A CN 113996644 B CN113996644 B CN 113996644B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/06—Reclamation of contaminated soil thermally
Abstract
The invention discloses a medium circulation thermal desorption soil remediation system loaded with a catalyst, and belongs to the technical field of soil remediation. The rotary drum structure and the screening circulation system contained in the system realize the recycling of the medium, the circulating medium loaded with the catalyst efficiently reduces the temperature required by soil thermal desorption, and the energy consumption of the system is obviously reduced while the thermal desorption efficiency is improved on the premise of not increasing the scale of the equipment. After the circulating medium is crushed, the catalytic material is decomposed into beneficial components such as calcium oxide and the like which have an improvement effect on soil.
Description
Technical Field
The invention belongs to the technical field of remediation of contaminated site soil, is suitable for remediation of organic contaminated site soil, and particularly relates to a medium circulation thermal desorption soil remediation system loaded with a catalyst.
Background
The soil is a loose surface layer which has fertility and can grow plants on the surface of the land, when harmful substances discharged into the soil exceed the self-cleaning capacity of the soil, the composition, the structure and the function of the soil are changed, the activity of microorganisms is inhibited, the harmful substances or decomposition products thereof are gradually accumulated in the soil and absorbed by the human body through soil → plants → the human body or through (soil → water → the human body) indirectly, and the soil pollution is caused to the extent of harming the health of the human body.
At present, sites with serious pollution mainly comprise chemical plants, pesticide plants, smelting plants, gas stations, chemical storage tanks and the like, pollutants in the sites mainly comprise organic pollution, and the sites can be divided into volatile organic compounds, semi-volatile organic compounds, persistent organic compounds, pesticides and the like according to the difference of melting boiling points of the volatile organic compounds, the semi-volatile organic compounds, the persistent organic compounds and the like. The restoration technology of the polluted soil comprises incineration (cement kiln cooperative treatment), phytoremediation, bioremediation, chemical restoration, thermal desorption and the like, wherein the thermal desorption technology has the advantages of high treatment efficiency, short restoration period, movable device and the like, is widely applied to restoration of volatile/semi-volatile organic polluted sites, and is one of the main site restoration technologies, wherein the thermal desorption accounts for 20-30% in European and American site restoration cases, as shown by American EPA statistics.
Thermal desorption is divided into two technologies, direct thermal desorption and indirect thermal desorption, according to different heating modes. The indirect thermal desorption technology is widely applied due to the advantages of high safety, low risk of secondary pollution, recyclability of the repaired soil and the like.
The indirect thermal desorption technology is that high-temperature flue gas generated by combustion indirectly heats the polluted soil through a metal shell of the reactor, so that the polluted soil is heated to a temperature higher than a target temperature, and the high-temperature flue gas is not directly contacted with the polluted soil in the heating process. The organic pollutants are selectively gasified and volatilized by controlling the temperature of the system and the residence time of the materials, so that the organic pollutants are separated and removed from the soil particles.
Generally, the amount of the polluted soil to be restored in a polluted site is thousands of tons as a result, and tens of thousands of tons as a result, real estate needs to be developed again after the land is restored, so that the restoration equipment is required to have high treatment efficiency and strong capacity so as to shorten the restoration period. The polluted soil is distributed all over the country, and the equipment needs to be frequently disassembled and assembled to replace the use field so as to realize the repeated utilization of the equipment. Considering the installation, transportation and disassembly of equipment, skid-mounted integration is required, and the size of a single structure is generally not more than 3m multiplied by 12m.
On the premise of not increasing the size of equipment, the single heating mode of indirect heat transfer of high-temperature flue gas, the metal shell and soil is relied on, so that the heat transfer efficiency is limited, the treatment efficiency of indirect thermal desorption equipment is low, generally 3-4 tons per hour, and the requirement of soil remediation of medium and large polluted sites cannot be met.
On the other hand, some large-block soils are compact, heat is difficult to effectively transfer to the interior, central organic pollutants are prevented from volatilizing, the pollutant removal rate is low and is generally 90-95%, and the thermal desorption effect of the heavily polluted soil cannot meet the restoration requirement.
In addition, the heat of the existing thermal desorption technology is derived from fuel combustion, a large amount of fuel needs to be consumed, and the repair cost is high.
Application number 202010291492.X A screw type indirect thermal desorption device for organic contaminated soil remediation, comprises an outer cylinder and a screw which are arranged in the horizontal direction; the upper part of the front end of the outer cylinder is fixedly connected with a scraping feeder, and the lower part of the rear end of the outer cylinder is fixedly connected with a discharging cylinder; the upper part of the outer cylinder is provided with three branch pipelines for collecting tail gas; the three branch pipelines are converged in the central pipeline, and the central pipeline is provided with a gas sampling port. The screw is fixedly supported in the outer cylinder; a cavity for heating soil is arranged in the screw rod, the rear end of the cavity is used for introducing hot air, and the front end of the cavity is used for discharging the hot air; the direction of flow of the hot air in the cavity is opposite to the direction of movement of the soil. Application number 202020478031.9 an indirect thermal desorption system of rotary kiln for soil remediation, includes: feed arrangement, rotary kiln, discharge device, second combustion chamber and heat exchanger, the rotary kiln includes: the rotary kiln comprises a kiln head, a base, a rotary kiln outer sleeve, a rotary kiln inner sleeve and a kiln tail, wherein the rotary kiln inner sleeve is arranged on the rotary kiln outer sleeve to form a hot air interlayer, the rotary kiln outer sleeve is arranged on the base, the kiln head and the kiln tail are respectively arranged at two ends of the rotary kiln outer sleeve, a feeding device is connected with the kiln head, a discharging device is connected with the kiln tail, a heat exchanger is arranged on a secondary combustion chamber, the heat exchanger is connected with the hot air interlayer, and the secondary combustion chamber is connected with the kiln tail. The two patents disclose the structural principle of a typical indirect thermal desorption reactor, the heating mode is that hot air indirectly heats internal soil through an outer cylinder and a rotary kiln inner sleeve, the heat transfer mode is single, and the heat transfer efficiency cannot be obviously improved under the condition that the sizes of the outer cylinder and the rotary kiln inner sleeve are certain; the method is lack of a crushing measure for the massive soil, and the pollutant removal rate is low; the heat sources are all fuel combustion, and the energy consumption is higher.
Disclosure of Invention
The invention provides a medium circulation thermal desorption soil remediation system loaded with a catalyst, aiming at the defects in the prior art.
The purpose of the invention can be realized by the following technical scheme:
a method for thermal desorption soil remediation using a catalyst-loaded circulation medium, the method comprising the steps of:
(1) The method comprises the following steps that a circulating medium loaded with a catalyst and polluted soil enter a feeding device together, the soil is rotationally crushed in an electric heating shaft screw conveyor and is heated to 100-120 ℃ under the dual heating conditions of waste heat carried by the circulating medium and electric heating, water vapor evaporated in the heating process is absorbed and discharged by a vapor outlet gas collecting hood, and the crushed soil is conveyed to the rear end of the device and falls into a thermal desorption reactor which is obliquely arranged;
(2) Heating the crushed soil in a thermal desorption reactor to 200-400 ℃ and carrying out thermal desorption reaction, wherein the soil and a circulating medium after the reaction are always positioned at the lower part of the rotary drum under the action of gravity and slowly move to a discharge end, and thermal desorption tail gas is discharged from a desorption gas outlet arranged on a front material end fixing cover of the reactor;
(3) When the polluted soil and the circulating medium reach the discharge end, the circulating medium is collected by the magnetic circulating medium screening device and then conveyed to the soil feed port through the circulating pipeline, and the circulating medium carries waste heat and is added to the feed port to perform heating catalysis on the soil at the feed port.
The technical scheme of the invention is as follows: the adding mass of the circulating medium loaded with the catalyst in the polluted soil is 0.1-5%.
In some specific embodiments: the method comprises the following steps:
(1) The circulating medium (9) and the polluted soil enter the feeding device together, the polluted soil is rotationally crushed in the electric heating shaft screw conveyor, the temperature is 100-120 ℃ under the dual heating condition of waste heat carried by the circulating medium and electric heating, water vapor evaporated in the heating process is absorbed and discharged by a gas collecting hood at a water vapor outlet, and the crushed soil is conveyed to the rear end of the device and falls into a thermal desorption reactor;
(2) The thermal desorption reactor rotates around an axial line, other parts are fixed, soil and a circulating medium are always positioned at the lower part of the rotary drum and slowly move to the discharge end under the action of gravity, hot air is blown into a hot air heating box body by a hot air generating device to exchange heat with the thermal desorption reactor, the polluted soil and the circulating medium are further heated to 200-400 ℃ under the condition of heating by the hot air, organic pollutants in the polluted soil are decomposed into small molecules such as water, carbon dioxide and the like under the action of a catalytic material loaded in the circulating medium, heat is released to enhance the heating effect of the soil, thermal desorption tail gas is discharged from a desorption gas outlet arranged at a material fixing cover at the front end of the reactor, and the hot air enters a circulating pipeline from a smoke outlet at the upper end of the hot air heating box body to circulate;
(3) The circulating medium is heated simultaneously with the soil in the process of moving to the discharge end in the rotary drum, when the polluted soil and the circulating medium reach the discharge end, the circulating medium is collected by the magnetic circulating medium screening device and then conveyed to the soil feed port through the circulating pipeline, and the circulating medium carries waste heat and is added to the feed port to heat the soil at the feed port to a certain extent.
A system for realizing the method comprises a feeding device, and a thermal dehydration device, a reactor feeding end fixing cover, a thermal desorption reactor and a reactor discharging end fixing cover which are sequentially connected with the feeding device, wherein the circulating medium screening device is positioned below the reactor discharging end fixing cover.
In the above system: the front section of the shafted spiral conveyor is a feeding device, the middle section of the shafted spiral conveyor is a thermal dehydration device, and the tail end of the shafted spiral conveyor is connected with a feeding hole of the thermal desorption reactor.
In some specific embodiments: the thermal dehydration device is internally provided with a shaft spiral conveyor which has an electric heating function, the front end is a contaminated soil and circulating medium feed inlet, the middle section is provided with 1 thermal desorption steam outlet, the steam outlet is arranged above the thermal dehydration device, and the tail end is connected with a thermal desorption reactor feed inlet.
In the above system: the thermal desorption reactor is of a rotary drum structure, the feeding end of the rotary drum is higher than the discharging end, and the theta angle between the axial lead of the rotary drum and the horizontal line is 2-5 degrees;
the top end of the feeding end fixing cover is provided with a thermal desorption gas outlet, the hot air heating box body is positioned on the outer peripheral side of the thermal desorption reactor, and the hot air heating box body is provided with a hot air inlet and a flue gas outlet; the hot air generating device is connected with the hot air inlet.
In some specific embodiments: the front end of the reactor is connected with a feed end fixing cover provided with a thermal desorption gas outlet, and the thermal desorption gas outlet is arranged above the fixing cover. The outside is equipped with 1 exhanst gas outlet, 1 hot-air inlet and hot-blast generating device's hot-blast heating box, and the exhanst gas outlet sets up in hot-blast heating box top, and the air inlet setting is in hot-blast heating box below.
In the above system: the circulating medium screening device is of a round hole type screen structure, and round holes of the screen are larger than the soil particle size and smaller than the circulating medium; the device has a weak electromagnetic function and can effectively magnetically attract a circulating medium containing an iron oxide catalyst, the lower end of the device is obliquely placed and connected with a medium circulating pipeline, and the circulating medium is conveyed to a feed port by the pipeline for recycling.
In the above system: the diameter of the spiral blade of the axial spiral conveyor is 4/5-1 of the inner diameter of the conveying pipeline, the pitch is 1/5-1/2 of the diameter of the spiral blade, the rotating speed is 2-10 r/min, and the rotating speed of the rotary drum is 0.5-5 r/min.
In the technical scheme of the invention: the circulating medium is a spherical structure, the outer diameter is 1-2cm larger than the soil particle size, the material is microporous ceramic, the mass of the microporous ceramic is taken as the reference, and 5% -20% of Co-Ca-K @ Fe is loaded in the micropores 3 O 4 The catalyst material can synchronously catalyze and oxidize organic pollutants in the thermal desorption process of soil to divide the organic pollutants intoDecomposing into water, carbon dioxide and the like, and releasing heat; after a period of use, the circulating medium is abraded and broken, and the catalytic material is inactivated and decomposed into beneficial components such as calcium oxide and potassium oxide which have the effect of improving soil.
The technical scheme of the invention is as follows: the Co-Ca-K @ Fe 3 O 4 In the catalyst: calcium potassium cobalt oxide is used as a catalytic active component, citric acid is used as a carrier complexing agent, nano ferroferric oxide particles are used as a carrier, and sodium dodecyl sulfate is used as a circulating medium dispersing agent; based on the mass of the carrier, the mass percentage of the catalytic active component is 5-25%, the calcium potassium cobalt oxide in the active component is cobaltosic oxide, calcium oxide and potassium oxide, and the mass ratio of the cobaltosic oxide to the calcium oxide to the potassium oxide is 1: (0.1-2): (0.1-2).
The technical scheme of the invention is as follows: the grain diameter of the microporous ceramic circulating body is 1-2cm.
And further: based on the mass of the carrier, the mass percentage of the active components of the catalyst is 6-10%, and the mass ratio of cobaltosic oxide, calcium oxide and potassium oxide in the active components is 1: (0.1-0.5): (0.1-0.5).
The technical scheme of the invention is as follows: microporous ceramics: the mass ratio of the sodium dodecyl sulfate is 1: (0.01 to 0.1); further preferably: microporous ceramics: the mass ratio of the sodium dodecyl sulfate is 1: (0.02-0.08).
In the technical scheme of the invention: nano ferroferric oxide: the mass ratio of the citric acid is 1: (0.01-0.2); further preferably: nano ferroferric oxide: the mass ratio of the citric acid is 1: (0.05-0.15).
A preparation method of the circulation medium comprises the following steps:
(1) Preparation of active ingredient precursor solution
Adding cobalt salt, calcium salt and potassium salt into deionized water, and stirring at normal temperature to obtain an active component precursor solution;
(2) Preparation of the catalyst
Sequentially transferring ferric salt, citric acid and the active component precursor ion solution prepared in the step (1) into a polytetrafluoroethylene hydrothermal reaction kettle for hydrothermal reaction, and placing a mixture obtained after the reaction into an air-blowing drying box for heat preservation and drying to obtain a catalyst required by the load of a circulating medium;
(3) Preparation of the endless body
Dissolving sodium dodecyl sulfate in deionized water, stirring until the sodium dodecyl sulfate is uniformly mixed, adding the microporous ceramic and the sodium dodecyl sulfate solution into an ultrasonic cleaner, and ultrasonically dispersing for 1-2 hours to obtain a microporous ceramic circulating body with charges on the surface;
(4) Preparation of circulating Medium
And (3) adding the microporous ceramic circulating body prepared in the step (3) and the catalyst prepared in the step (2) into deionized water, stirring until the load is full, and placing the mixture into a forced air drying oven for heat preservation and drying to obtain the catalyst-loaded thermal desorption circulating medium for the organic contaminated soil.
The preparation method comprises the following steps: the cobalt salt in the step (1) is cobalt nitrate hexahydrate or cobalt acetate tetrahydrate or cobalt sulfate heptahydrate, the calcium salt is calcium chloride hexahydrate or calcium acetate monohydrate, and the potassium salt is potassium nitrate or potassium sulfate.
The preparation method comprises the following steps: the ferric salt in the step (2) is ferric nitrate hexahydrate or ferric trichloride hexahydrate, and the citric acid is citric acid monohydrate.
The preparation method comprises the following steps: the hydrothermal reaction temperature in the step (2) is 100-160 ℃, the hydrothermal time is 4-12 h, the drying temperature is 80-120 ℃, and the drying time is 6-12 h.
The preparation method comprises the following steps: in the step (4), the drying temperature is 80-100 ℃, and the drying time is 2-8 h.
In the technical scheme of the invention, the circulating medium is applied to thermal desorption of organic-polluted soil.
In some specific embodiments: the organic matters in the organic contaminated soil include but are not limited to volatile organic pollutants such as benzene, chlorobenzene, o-xylene, styrene and the like.
In the technical scheme of the invention: the cobalt-calcium-potassium composite oxide is a mixture of cobaltosic oxide, calcium oxide and potassium oxide.
The invention has the beneficial effects that:
the invention discloses a catalyst-loaded medium circulating thermal desorption soil remediation system and a method thereof, which reduce the soil moisture content before the thermal desorption process by heating and crushing an electric heating screw conveyor, and provide a way for heating soil by using a catalyst-loaded circulating medium to oxidize and decompose organic pollutants, thereby effectively reducing the thermal desorption temperature of the organic pollutants, realizing the recycling of the catalyst-loaded medium through a separation and conveying system, and enabling a medium catalytic material after abrasion and breakage to belong to beneficial soil components. The system strengthens the thermal desorption process of the polluted soil through the action of four aspects. On the first hand, the water contained in the polluted soil is removed in a steam mode in the conveying process through the heating effect of the electric heating spiral conveyor, and the reduction of the water content is beneficial to improving the thermal desorption effect of the polluted soil; in the second aspect, the circulating medium extrudes and crushes the soil, which is beneficial to the volatilization of organic pollutants in the soil; in the third aspect, the circulating medium loaded with the catalyst can efficiently oxidize and decompose the organic pollutants, the heat generated in the decomposition process cooperates with hot air to heat soil, and meanwhile, the temperature required by thermal desorption of the organic pollutants is reduced; in the fourth aspect, the residual heat of the circulating medium when the circulating medium is conveyed from the discharge end to the feed end has a heating effect on the soil at the feed end.
Drawings
FIG. 1 is a schematic cross-sectional view of a reactor according to the present invention.
FIG. 2 is a schematic longitudinal sectional view of the reactor of the present invention.
Wherein: 1 is feed arrangement, 2 is thermal dehydration device, 3 is the fixed cover of feed end, 4 is thermal desorption reactor, 5 is hot-blast heating box, 6 is the fixed cover of discharge end, 7 is circulating medium screening plant, 8 is medium circulation pipeline, 9 is circulating medium, 10 is for having a spiral conveyer, 11 is hot-blast generating device, 12 is soil.
Detailed Description
The invention is further illustrated by the following examples, without limiting the scope of the invention:
as shown in fig. 1-2, a catalyst-loaded media-cycle thermal desorption soil remediation system: the system comprises a feeding device 1, a thermal dehydration device 2, a reactor feeding end fixing cover 3, a thermal desorption reactor 4 and a reactor discharging end fixing cover 6 which are sequentially connected with the feeding device, wherein a circulating medium screening device 7 is positioned below the reactor discharging end fixing cover 6. The front section of the spiral conveyer with the shaft 10 is a feeding device 1, the middle section is a thermal dehydration device 2, and the tail end is connected with a feeding hole of the thermal desorption reactor. The thermal desorption reactor is of a rotary drum structure, the feeding end of the rotary drum is higher than the discharging end, and the theta angle between the axial lead of the rotary drum and the horizontal line is 4 degrees; the top end of the feeding end fixing cover 3 is provided with a thermal desorption gas outlet, the hot air heating box body 5 is positioned on the outer peripheral side of the thermal desorption reactor 4, and the hot air heating box body 5 is provided with a hot air inlet and a flue gas outlet; the hot air generating device 11 is connected with a hot air inlet. The circulating medium screening device 7 is of a round hole type screen structure, and the round holes of the screen are larger than the soil particle size and smaller than the circulating medium; the device has a weak electromagnetic function, can effectively magnetically attract a circulating medium containing the iron oxide catalyst, is obliquely arranged, and is connected with a medium circulating pipeline 8 at the lower end, and the circulating medium is conveyed to a feed inlet by the pipeline for recycling. The diameter of the spiral blade of the axial spiral conveyor 10 is 4/5-1 of the inner diameter of the conveying pipeline, the pitch is 1/5-1/2 of the diameter of the spiral blade, the rotating speed is 2-10 r/min, and the rotating speed of the rotary drum is 0.5-5 r/min.
The feeding device is mixed with the circulating medium 9 loaded with the catalyst while entering the raw soil; the circulating medium 9 is spherical structure, the outer diameter is 1-2cm larger than the soil grain diameter, the material is microporous ceramic, the mass of the microporous ceramic is taken as the reference, and 5% -20% of Co-Ca-K @ Fe is loaded in the micropores 3 O 4 The catalytic material can synchronously catalyze and oxidize organic pollutants in the thermal desorption process of soil, decompose the organic pollutants into water, carbon dioxide and the like, and release heat; after a period of use, the circulating medium is abraded and broken, and the catalytic material is inactivated and decomposed into beneficial components such as calcium oxide and potassium oxide which have the effect of improving soil.
Example 1
The preparation process of the catalyst is as follows:
(1) Preparation of active ingredient precursor solution
30.215g of cobalt nitrate hexahydrate, 1.649g of calcium chloride hexahydrate and 1.789g of potassium nitrate are weighed, added into 242.055g of deionized water and stirred at normal temperature for 30min to obtain an active component precursor solution, wherein the mass ratio of active components of cobaltosic oxide, calcium oxide and potassium oxide is 1:0.1:0.1;
(2) Preparation of the catalyst
And (2) taking the mass of the carrier as a reference, weighing 313.381g of ferric nitrate hexahydrate, 15.000g of citric acid and the active component precursor ion solution prepared in the step (1) according to the active component accounting for 10% of the mass of the carrier, sequentially transferring the weighed materials and the active component precursor ion solution into a 500ml polytetrafluoroethylene hydrothermal reaction kettle, reacting for 4 hours at 160 ℃, taking out, cooling, filtering, taking out the precipitate, placing the precipitate in a forced air drying oven, preserving the heat at 80 ℃ and drying for 12 hours to obtain the catalyst required by the circulation medium loading. Wherein, the nano ferroferric oxide: the mass ratio of the citric acid is 1:0.15;
(3) Preparation of the endless body
Weighing 4.400g of sodium dodecyl sulfate, dissolving in 500.000g of deionized water, stirring until the mixture is uniformly mixed, and then adding 220.000g of microporous ceramic and the sodium dodecyl sulfate solution into an ultrasonic cleaner for ultrasonic dispersion for 1 hour to obtain the microporous ceramic circulating body with charges on the surface. Wherein the microporous ceramic: the mass ratio of the sodium dodecyl sulfate is 1:0.02;
(4) Preparation of circulating Medium
Weighing 156.570g of the microporous ceramic circulating body prepared in the step (3) and 15.657g of the catalyst prepared in the step (2) according to the mass percentage of the catalyst loaded by 10 percent by taking the mass of the circulating body as a reference, adding the weighed materials into 343.578g of ionized water, stirring for 30min, placing the materials into a forced air drying oven after stirring till full loading, and carrying out heat preservation and drying for 2h at 100 ℃ to obtain the catalyst-loaded organic matter contaminated soil thermal desorption circulating medium;
a method for thermal desorption soil remediation by using the catalyst-loaded medium circulation thermal desorption soil remediation system comprises the following steps:
(1) The method comprises the steps of taking the mass of polluted soil as a reference, controlling a medium circulation pipeline 8 to add a circulation medium 9 with the mass percentage of 0.1%, enabling the circulation medium and the polluted soil to enter a feeding device 1 together, enabling the soil to rotate and be crushed in an electric heating shaft screw conveyor 10, enabling the diameter of a screw blade of the electric heating shaft screw conveyor 10 to be 4/5 of the inner diameter of a conveying pipeline, enabling a screw pitch to be 1/2 of the diameter of the screw blade, enabling the rotation speed to be 10r/min, enabling the temperature to reach 120 ℃ under the double heating condition of waste heat carried by the circulation medium and electric heating, enabling water vapor evaporated in the heating process to be absorbed and discharged by a gas collecting hood at a water vapor outlet, and conveying the crushed soil to the rear end of the device to fall into a thermal desorption reactor 4.
(2) The thermal desorption reactor 4 rotates around an axial line, the rotating speed is 0.5r/min, other parts are fixed, soil and a circulating medium are always positioned at the lower part of the rotary drum and slowly move to a discharge end under the action of gravity, hot air is blown into the hot air heating box body 5 by the hot air generating device 11 to exchange heat with the thermal desorption reactor, the polluted soil and the circulating medium are further heated to 400 ℃ under the condition of heating of the hot air, organic pollutants in the polluted soil are decomposed into small molecules such as water, carbon dioxide and the like under the action of a catalytic material loaded in the circulating medium, heat is released to enhance the heating effect of the soil, thermal desorption tail gas is discharged from a desorption gas outlet arranged at the front end fixing cover 3 of the reactor, and the hot air enters a circulating pipeline from a smoke outlet at the upper end of the hot air heating box body to circulate.
(3) The circulating medium is heated simultaneously with the soil in the process of moving to the discharge end in the rotary drum, when the polluted soil and the circulating medium reach the discharge end, the circulating medium is collected by the magnetic circulating medium screening device 7 and then conveyed to the soil feed port through the circulating pipeline 8, and the circulating medium carries waste heat and is added to the feed port to heat the soil at the feed port to a certain extent.
Example 2
The catalyst process is as follows:
(1) Preparation of active ingredient precursor solution
Weighing 24.825g of cobaltous acetate tetrahydrate, 12.567g of calcium acetate monohydrate and 7.400g of potassium sulfate, adding the weighed materials into 360.023g of deionized water, and stirring the materials for 30min at normal temperature to obtain an active component precursor solution, wherein the mass ratio of cobaltosic oxide, calcium oxide and potassium oxide of the active components is 1:0.5:0.5;
(2) Preparation of the catalyst
Taking the mass of the carrier as a reference, weighing 700.462g of ferric trichloride hexahydrate, 20.000g of citric acid and the active component precursor ion solution prepared in the step (1) according to the active component accounting for 8% of the mass of the carrier, sequentially transferring the mixture into a 500ml polytetrafluoroethylene hydrothermal reaction kettle, reacting at 100 ℃ for 12h, taking out, cooling, filtering, taking out the precipitate, and placing the precipitate in a forced air drying oven for heat preservation and drying at 120 ℃ for 6h to obtain the catalyst required by the load of the circulating medium. Wherein, the nano ferroferric oxide: the mass ratio of the citric acid is 1:0.10;
(3) Preparation of the endless body
Weighing 8.640g of sodium dodecyl sulfate, dissolving in 500.000g of deionized water, stirring until the mixture is uniformly mixed, and adding 216.000g of microporous ceramic and a sodium dodecyl sulfate solution into an ultrasonic cleaner for ultrasonic dispersion for 2 hours to obtain a microporous ceramic circulating body with a charged surface. Wherein, the microporous ceramic: the mass ratio of the sodium dodecyl sulfate is 1:0.04;
(4) Preparation of circulating Medium
Weighing 125.480g of the microporous ceramic circulating body prepared in the step (3) and 6.274g of the catalyst prepared in the step (2) according to the mass percentage of the catalyst loaded by 5 percent by taking the mass of the circulating body as a reference, adding the weighed circulating body and the catalyst into 246.420g of deionized water, stirring for 30min, placing the mixture into a forced air drying oven after fully loading, and performing heat preservation and drying for 8h at the temperature of 80 ℃ to obtain the catalyst-loaded organic matter contaminated soil thermal desorption circulating medium;
a method for thermal desorption soil remediation by using the catalyst-loaded medium circulation thermal desorption soil remediation system comprises the following steps:
(1) The method comprises the steps of taking the mass of polluted soil as a reference, controlling a medium circulation pipeline 8 to add 3% by mass of a circulation medium 9 and the polluted soil to enter a feeding device 1 together, rotationally crushing the soil in an electric heating shaft screw conveyor 10, enabling the diameter of a screw blade of the electric heating shaft screw conveyor 10 to be 4/5 of the inner diameter of a conveying pipeline, enabling a screw pitch to be 1/3 of the diameter of the screw blade, enabling the rotation speed to be 6r/min, enabling the soil to reach 110 ℃ under the double heating condition of waste heat carried by the circulation medium and electric heating, absorbing and discharging water vapor evaporated in the heating process through a water vapor outlet gas collecting hood, and conveying the crushed soil to the rear end of the device to fall into a thermal desorption reactor 4.
(2) The thermal desorption reactor 4 rotates around an axial lead, the rotating speed is 3r/min, other parts are fixed, soil and a circulating medium are always positioned at the lower part of the rotary drum and slowly move to a discharge end under the action of gravity, hot air is blown into a hot air heating box body 5 by a hot air generating device 11 to exchange heat with the thermal desorption reactor, the polluted soil and the circulating medium are further heated to 300 ℃ under the condition of heating of the hot air, organic pollutants in the polluted soil are decomposed into water, carbon dioxide and other micromolecules under the action of a catalytic material loaded in the circulating medium, heat is released to enhance the heating effect of the soil, thermal desorption tail gas is discharged from a desorption gas outlet arranged on a front material end fixing cover 3 of the reactor, and the hot air enters a circulating pipeline from a flue gas outlet at the upper end of the hot air heating box body to circulate.
(3) The circulating medium is heated simultaneously with the soil in the process of moving to the discharge end in the rotary drum, when the polluted soil and the circulating medium reach the discharge end, the circulating medium is collected by the magnetic circulating medium screening device 7 and then conveyed to the soil feed port through the circulating pipeline 8, and the circulating medium carries waste heat and is added to the feed port to heat the soil at the feed port to a certain extent.
Example 3
The catalyst process is as follows:
(1) Preparation of active ingredient precursor solution
Weighing 28.022g of cobaltous sulfate heptahydrate, 6.284g of calcium acetate monohydrate and 4.293g of potassium nitrate, adding into 416.409g of deionized water, and stirring at normal temperature for 30min to obtain an active component precursor solution, wherein the active component cobaltosic oxide, calcium oxide and potassium oxide are mixed in a mass ratio of 1:0.25:0.25;
(2) Preparation of the catalyst
And (2) taking the mass of the carrier as a reference, weighing 626.762g of ferric nitrate hexahydrate, 10.000g of citric acid and the active component precursor ion solution prepared in the step (1) according to the active component accounting for 6% of the mass of the carrier, sequentially transferring the weighed active component ferric nitrate hexahydrate and citric acid and the active component precursor ion solution into a 500ml polytetrafluoroethylene hydrothermal reaction kettle, reacting for 8 hours at 120 ℃, taking out, cooling, filtering, taking out the precipitate, placing the precipitate in a forced air drying oven, and keeping the temperature at 100 ℃ for drying for 8 hours to obtain the catalyst required by the circulation medium loading. Wherein, the nanometer ferroferric oxide: the mass ratio of the citric acid is 1:0.05;
(3) Preparation of the endless body
Weighing 8.480g of sodium dodecyl sulfate, dissolving in 500.000g of deionized water, stirring until the mixture is uniformly mixed, adding 106.000g of microporous ceramic and the sodium dodecyl sulfate solution into an ultrasonic cleaner, and ultrasonically dispersing for 1.5h to obtain the microporous ceramic circulating body with the surface charge. Wherein, the microporous ceramic: the mass ratio of the sodium dodecyl sulfate is 1:0.08;
(4) Preparation of circulating Medium
Weighing 88.680g of the microporous ceramic circulating body prepared in the step (3) and 17.736g of the catalyst prepared in the step (2) according to the mass percent of the catalyst loaded on the circulating body by taking the mass of the circulating body as a reference, adding the microporous ceramic circulating body prepared in the step (3) and the catalyst prepared in the step (2) into 120.034g of ionized water, stirring for 30min, placing the mixture into a forced air drying oven after stirring till full loading, and performing heat preservation and drying at 90 ℃ for 5h to obtain a catalyst-loaded organic matter-contaminated soil thermal desorption circulating medium;
a method for thermal desorption soil remediation by using the catalyst-loaded medium circulation thermal desorption soil remediation system comprises the following steps:
(1) The method comprises the steps of taking the mass of polluted soil as a reference, controlling a medium circulation pipeline 8 to add 5% by mass of a circulation medium 9 and the polluted soil to enter a feeding device 1 together, rotationally crushing the soil in an electric heating shaft screw conveyor 10, enabling the diameter of a screw blade of the electric heating shaft screw conveyor 10 to be the inner diameter of a conveying pipeline, enabling the screw pitch to be 1/5 of the diameter of the screw blade, enabling the rotation speed to be 2r/min, enabling the soil to reach 120 ℃ under the double heating condition of waste heat brought by the circulation medium and electric heating, absorbing and discharging water vapor evaporated in the heating process through a vapor outlet gas collecting hood, and conveying the crushed soil to the rear end of the device to fall into a thermal desorption reactor 4.
(2) The thermal desorption reactor 4 rotates around an axial line, the rotating speed is 5r/min, other parts are fixed, soil and a circulating medium are always positioned at the lower part of the rotary drum and slowly move towards the discharge end under the action of gravity, hot air is blown into the hot air heating box body 5 through the hot air generating device 11 to exchange heat with the thermal desorption reactor, the polluted soil and the circulating medium are further heated to 200 ℃ under the condition of heating of the hot air, organic pollutants in the polluted soil are decomposed into small molecules such as water, carbon dioxide and the like under the action of catalytic materials loaded in the circulating medium, heat is released to enhance the heating effect of the soil, thermal desorption tail gas is discharged from a desorption gas outlet arranged at the front end fixing cover 3 of the reactor, and the hot air enters a circulating pipeline from a smoke outlet at the upper end of the hot air heating box body to circulate.
(3) The circulating medium is heated with the soil in the process of moving to the discharge end in the rotary drum, when the polluted soil and the circulating medium reach the discharge end, the circulating medium is collected by the magnetic circulating medium screening device 7 and then conveyed to the soil feed port through the circulating pipeline 8, and the circulating medium carries waste heat and plays a certain heating role on the soil at the feed port after being added to the feed port.
Application of example 1:
the above system structure was adopted in which the reactor drum had an inner diameter of 2.5m and a length of 10m, and the reactor scale was 3 m.times.3 m.times.10 m. The operation conditions are as follows: the soil bulk density is 1.4t/m 3 The water content is 20%, the soil pollutants are chlorobenzene and styrene with the mass ratio of 1.
The realization effect is as follows: the soil is restored by 12 tons per hour, the removal rate of organic pollutants is 99.6 percent, and 20 cubic meters of natural gas is consumed averagely for restoring each ton of polluted soil.
Application of example 2:
the above system structure was adopted in which the reactor drum had an inner diameter of 2.5m and a length of 10m, and the reactor scale was 3 m.times.3 m.times.10 m. The operation conditions are as follows: the soil bulk density is 1.4t/m 3 The water content is 20%, the soil pollutants are chlorobenzene and styrene with the mass ratio of 1.
The realization effect is as follows: the soil is restored by 12 tons per hour, the removal rate of organic pollutants is 99.5 percent, and 20.5 cubic meters of natural gas is consumed on average for restoring each ton of polluted soil.
Application of example 3:
the above system structure was adopted in which the reactor drum had an inner diameter of 2.5m and a length of 10m, and the reactor scale was 3 m.times.3 m.times.10 m. Operating conditions: the soil bulk density is 1.4t/m 3 The water content is 20%, the soil pollutants are chlorobenzene and styrene with the mass ratio of 1.
The realization effect is as follows: the soil is restored by 12 tons per hour, the removal rate of organic pollutants is 99 percent, and the polluted soil per ton is restored by 21 cubic meters of natural gas.
Comparative example 1:
the conditions were the same as in example 1 except that no circulating medium was added to the system, the inner diameter of the drum was 2.5m, the length was 10m, and the scale of the reactor was 3 m.times.3 m.times.10 m.
The operating conditions were the same as in application case 1.
The realized effects are as follows: the contaminated soil is restored by 8 tons per hour, the removal rate of organic pollutants is 93.2 percent, and 35 cubes of natural gas are consumed averagely for restoring each ton of contaminated soil.
Comparative example 2:
the mode disclosed by a screw type indirect thermal desorption device for remedying the organic contaminated soil with application number of 202010291492.X is adopted, the inner diameter of an outer cylinder is set to be 2.5m, and the scale of a reactor with the length of 10m is 3m multiplied by 10m.
The operating conditions were the same as in application case 2.
The realized effects are as follows: 3 tons of soil are restored every hour, the removal rate of organic pollutants is 91%, and 35 cubic meters of natural gas is consumed on average for restoring every ton of polluted soil.
Comparative example 3:
the method disclosed in the application No. 202020478031.9 of the indirect thermal desorption system of the rotary kiln for soil remediation is adopted, the inner diameter of the outer cylinder is set to be 2.5m, and the scale of the reactor with the length of 10m is 3m multiplied by 10m.
The operating conditions were the same as in application case 3.
The realized effects are as follows: 3 tons of soil are restored every hour, the removal rate of organic pollutants is 94%, and 35 cubic meters of natural gas is consumed on average for restoring every ton of polluted soil.
Comparison results
Treatment effects of examples and comparative examples.
Claims (7)
1. A method for thermal desorption soil remediation by using a circulating medium loaded with a catalyst is characterized by comprising the following steps: the method comprises the following steps:
(1) The method comprises the following steps that a circulating medium (9) loaded with a catalyst and polluted soil enter a feeding device (1) together, the soil is rotationally crushed in an electric heating shaft screw conveyor (10) and is heated to 100-120 ℃ under the dual heating condition of waste heat carried by the circulating medium and electric heating, water vapor evaporated in the heating process is absorbed and discharged by a vapor outlet gas collecting hood, and the crushed soil is conveyed to the rear end of the device and falls into a thermal desorption reactor (4) which is obliquely arranged;
(2) Heating the crushed soil in the thermal desorption reactor (4) to 200-400 ℃ for thermal desorption reaction, keeping the soil and a circulating medium after the reaction in the lower part of the rotary drum under the action of gravity and slowly moving towards a discharge end, and discharging thermal desorption tail gas from a desorption gas outlet arranged on a front material end fixing cover (3) of the reactor;
(3) When the polluted soil and the circulating medium reach the discharge end, the circulating medium is collected by the magnetic circulating medium screening device (7) and then is conveyed to the soil feed port through the medium circulating pipeline (8), and the circulating medium carries residual heat and is added to the feed port to perform heating catalysis on the soil at the feed end;
wherein: the circulating medium takes microporous ceramic as a circulating body and is loaded with 5-20% of Co-Ca-K @ Fe 3 O 4 A catalyst; based on the mass of the carrier, the mass percentage of the catalytic active component is 5-25%, the calcium potassium cobalt oxide in the catalytic active component is cobaltosic oxide, calcium oxide and potassium oxide, and the mass ratio of the cobaltosic oxide to the calcium oxide to the potassium oxide is 1: (0.1 to 2): (0.1 to 2);
calcium potassium cobalt oxide is used as a catalytic active component, citric acid is used as a carrier complexing agent, nano ferroferric oxide particles are used as a carrier, and sodium dodecyl sulfate is used as a circulating medium dispersing agent; the adding mass of the circulating medium loaded with the catalyst in the polluted soil is 0.1-5%.
2. The method of claim 1, wherein: the method comprises the following steps:
(1) The circulating medium (9) and the polluted soil enter the feeding device (1) together, the polluted soil is rotationally crushed in the electric heating shaft screw conveyor (10) and is heated to 100-120 ℃ under the dual heating condition of waste heat carried by the circulating medium and electric heating, water vapor evaporated in the heating process is absorbed and discharged by a vapor outlet gas collecting hood, and the crushed soil is conveyed to the rear end of the device and falls into the thermal desorption reactor (4);
(2) The thermal desorption reactor (4) rotates around an axis, other parts are fixed, soil and a circulating medium are always positioned at the lower part of the rotary drum under the action of gravity and slowly move to a discharge end, hot air is blown into a hot air heating box body (5) by a hot air generating device (11) to exchange heat with the thermal desorption reactor, the polluted soil and the circulating medium are further heated to 200-400 ℃ under the condition of heating of the hot air, organic pollutants in the polluted soil are decomposed into water and carbon dioxide micromolecules under the action of a catalyst loaded in the circulating medium and release heat to enhance the heating effect of the soil, thermal desorption tail gas is discharged from a desorption gas outlet arranged on a front material end fixing cover (3) of the reactor, and the hot air enters a circulating pipeline from a smoke outlet at the upper end of the hot air heating box body to circulate;
(3) The circulating medium is heated simultaneously with the soil in the process of moving to the discharge end in the rotary drum, when the polluted soil and the circulating medium reach the discharge end, the circulating medium is collected by the magnetic circulating medium screening device (7) and then conveyed to the soil feed inlet through the medium circulating pipeline (8), and the circulating medium carries waste heat and is added to the feed inlet to heat the soil at the feed inlet.
3. A system for implementing the method of claim 1, wherein: the system comprises a feeding device (1), a thermal dehydration device (2), a reactor front material end fixing cover (3), a thermal desorption reactor (4) and a reactor discharge end fixing cover (6) which are sequentially connected with the feeding device, wherein a magnetic circulating medium screening device (7) is positioned below the reactor discharge end fixing cover (6).
4. The system of claim 3, wherein: the front section of the spiral conveyer (10) with the shaft is a feeding device (1), the middle section is a thermal dehydration device (2), and the tail end is connected with a feeding hole of the thermal desorption reactor.
5. The system of claim 3, wherein: the thermal desorption reactor is of a rotary drum structure, the feed end of the rotary drum is higher than the discharge end, and the theta angle between the axial lead of the rotary drum and a horizontal line is 2 to 5 degrees;
a thermal desorption gas outlet is formed in the top end of the reactor front material end fixing cover (3), the hot air heating box body (5) is located on the outer peripheral side of the thermal desorption reactor (4), and a hot air inlet and a flue gas outlet are formed in the hot air heating box body (5); the hot air generating device (11) is connected with the hot air inlet.
6. The system of claim 3, wherein: the magnetic circulating medium screening device (7) is of a round hole type screen structure, and round holes of the screen are larger than the soil particle size and smaller than the circulating medium; the device has a weak electromagnetic function and can effectively magnetically attract a circulating medium containing an iron oxide catalyst, the lower end of the device is obliquely placed and connected with a medium circulating pipeline (8), and the medium circulating pipeline conveys the medium to a feed inlet for recycling.
7. The system of claim 3, wherein: the diameter of a screw blade of the axial screw conveyor (10) is 4/5 to 1 of the inner diameter of a conveying pipeline, the screw pitch is 1/5 to 1/2 of the diameter of the screw blade, the rotating speed is 2 to 10r/min, and the rotating speed of a rotary drum is 0.5 to 5r/min.
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