CN111282983A - Electrothermal coupling chemical oxidation method and device - Google Patents

Abstract

The invention provides an electrothermal coupling chemical oxidation method and a device, wherein the device comprises an oxidant preparation and injection unit, a monitoring control unit and a power regulation unit, wherein the oxidant preparation and injection unit can inject an oxidant into polluted soil; the monitoring control unit can detect the change conditions of the conductivity and the oxidation-reduction potential in the polluted soil; the electric power regulating unit comprises an isolation voltage regulator, a rectifier and a change-over switch, wherein the input end of the isolation voltage regulator is connected with an alternating current power supply, the output end of the isolation voltage regulator is directly connected with an electrode in polluted soil through the change-over switch, or the output end of the isolation voltage regulator is connected with the electrode through the rectifier, and therefore alternating current or direct current is transmitted to the electrode. According to the invention, direct current is firstly applied to lead the oxidant to migrate directionally, and then alternating current is applied to lead the oxidant to be activated under the heating action of the alternating current field, so that the polluted soil is efficiently oxidized.

Description

Electrothermal coupled chemical oxidation method and device

technical field

The invention relates to the technical field of soil remediation.

Background technique

In-situ chemical oxidation technology is a high-efficiency in-situ remediation technology suitable for treating source areas. By injecting oxidants into soil or groundwater polluted areas, the oxidants contact the pollutants to oxidize, so that the pollutants are converted into non-toxic or relatively less toxic. It has the characteristics of good economy, quick repair and remarkable effect. However, for low-permeability formations, there is a problem of poor mass transfer of oxidants. Because the transport and diffusion of oxidants are affected by the permeability of soil, sufficient contact between oxidants and pollutants cannot be achieved, resulting in poor in-situ chemical oxidation effects.

Sodium persulfate is a new type of oxidant, which has the advantages of strong oxidizing ability (E ⁰ =2.01V), various types of pollutants, wide pH adaptability, strong stability, high solubility, low economic cost and high safety. After activation, it can form sulfate radicals (E ⁰ =2.5-3.1V), and the oxidizing ability is further improved, which can increase the types of pollutants to be treated, speed up the reaction rate, and reduce the amount of oxidants. Therefore, advanced oxidation technology based on sodium persulfate has been widely used in organic pollution site remediation projects.

Sodium persulfate can be activated by heating or by adding activators, such as iron activation (Fe ²⁺ /Fe ⁰⁺ ), strong oxidant activation (H ₂ O ₂ ) and alkali activation (NaOH), etc. However, the ratio of activator to persulfate is difficult to control (if the activator is added too much, the activator will react with the generated sulfate radicals, resulting in unnecessary consumption of free radicals; if the activator is added too little, the oxidant cannot be fully activated) , low activation efficiency (one persulfate ion can only produce one sulfate radical), poor environmental friendliness (pH>10 for alkali activation) and other problems. In contrast, thermal activation is a more efficient and environmentally friendly activation method. The bond energy of the OO bond in persulfate is 140kJ/mol. The input energy of heating (>50°C) will cause the cleavage of the OO bond to generate sulfate free radicals. The temperature of thermal activation of persulfate is about 50°C. Due to the poor stability of the free radicals generated by activation, there is a problem of short time (about 4s). For the thermal activation of the oxidant, the optimal activation time is after the oxidant is transported to the polluted area, and then the thermal activation of the oxidant is carried out, so as to improve the performance of the oxidant. Oxidant activation efficiency, the purpose of reducing the amount of oxidant.

Therefore, the key to in-situ chemical oxidation technology is to achieve uniform migration and dispersion technology of oxidant and efficient heating activation technology.

SUMMARY OF THE INVENTION

In order to solve the problems of poor mass transfer in low-permeability formations and low oxidant activation efficiency in in-situ chemical oxidation technology, the present invention provides an electrothermal coupled chemical oxidation method and device.

For achieving the above object, the technical scheme adopted in the present invention is:

An electrothermal coupled chemical oxidation device, characterized in that it comprises an oxidant preparation and injection unit, a monitoring control unit and a power adjustment unit, wherein:

The oxidant preparation and injection unit is capable of injecting oxidant into the contaminated soil;

The monitoring and control unit is capable of detecting changes in conductivity and redox potential in the contaminated soil;

The power conditioning unit includes an isolation voltage regulator, a rectifier and a switch. The input end of the isolation voltage regulator is connected to the AC power source, and the output end is selected to be directly connected to the electrode in the polluted soil through the switch, or to the electrode through the rectifier. The electrodes are connected to deliver alternating current or direct current to the electrodes.

The electrothermal coupling chemical oxidation device, wherein: the electrodes are arranged in a manner that the basic unit is an equilateral triangle, and an electrode matrix is formed;

When the electrodes are connected to direct current, there are a plurality of regular hexagonal units in the electrode matrix, wherein the six vertices of each regular hexagonal unit are negative electrodes, and the electrode at the center of the positive six deformed units is positive; The electrodes are arranged in a staggered and adjacent manner with positive and negative electrodes;

When the electrodes are connected to alternating current, the phases of each equilateral triangular basic unit are different at the three corners.

The electrothermal coupled chemical oxidation device, wherein: the electrode matrix is formed by combining the electrode injection integrated well and the electrode well.

The electrothermal coupled chemical oxidation device, wherein: the electrode injection integrated well is made of corrosion-resistant metal material.

An electrothermal coupled chemical oxidation method adopts the electrothermal coupled chemical oxidation device, wherein: firstly, the oxidant is injected into the soil through an oxidant preparation and injection unit, and then the first and second operation stages are operated in sequence, and the oxidant injection and operation are repeated. Phase 1 and Operation Phase 2, where:

The first operation stage is the DC directional migration stage: the switch of the power conditioning unit is connected to the rectifier to realize the conversion of AC to DC, and the DC is transmitted to the electrodes to form a DC electric field underground; The electric field strength of the DC electric field controls the migration rate of the oxidant; driven by the DC electric field, the oxidant migrates and diffuses directionally to the designated pollution area;

The second operation stage is the AC heating activation stage: after the monitoring and control unit determines that the oxidant has been transferred to the designated pollution area, the switch of the power conditioning unit is connected to another circuit, so that the AC power is directly transmitted to the electrodes, thereby forming an AC electric field underground; The voltage regulator adjusts the DC voltage and the electric field strength of the AC electric field, thereby controlling the soil heating rate and heating temperature; the oxidant is activated under the heating of the AC electric field to produce sulfate radicals with stronger oxidizing ability.

The electrothermal coupled chemical oxidation method, wherein: the electrodes are arranged in a manner that the basic unit is an equilateral triangle, and an electrode matrix is formed;

In the first operation stage, there are multiple regular hexagonal units in the electrode matrix, wherein, the six vertices of each regular hexagonal unit are negative electrodes, and the electrode at the center of the regular six deformed units is the positive electrode;

In the second phase of operation, the phase of each equilateral triangular basic unit is different at the three corners.

The electrothermal coupling chemical oxidation method, wherein: the electrode matrix is formed by combining the electrode injection integrated well and the electrode well.

The electrothermal coupled chemical oxidation method, wherein: the electrode injection integrated well is made of corrosion-resistant metal material.

The electrothermal coupled chemical oxidation method, wherein: in the first stage of operation, for the single electrode existing in the regular hexagonal layout, the rotation switching method is also used to optimize the layout of the electrodes, so that the regular hexagonal electrode unit is combined. Move horizontally and vertically in the electrode matrix, and incorporate the single electrode into a new regular hexagonal unit to eliminate the dead angle of drug delivery.

In the electrothermal coupled chemical oxidation method, the oxidant is also re-injected, and the first operation stage and the second operation stage are carried out in sequence.

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

(1) The present invention uses electrode injection into an integrated well, which can realize the compound function of chemical injection and introduction of direct current and alternating current, and the function is integrated, which reduces the cost and time of well construction;

(2) In the stage of DC enhanced oxidant directional migration, by adjusting the distribution of DC positive and negative electrodes, the electrode matrix can be formed into any number of regular hexagonal electrode units, so that the effective area of a single electrode is maximized and the average field intensity induced is the highest. , thereby reducing the operating energy consumption, improving the uniformity of drug diffusion, and reducing the dosage of the drug;

(3) In the AC heating activation stage, by adjusting the AC phase distribution of the electrodes, the electrodes form an equilateral triangle layout, and the current can be heated between any two adjacent electrodes to avoid heating cold spots (if the two adjacent electrodes are If the alternating current phase is the same, there will be no current flow between the two, and heating cannot be performed), so that the heating effect is better and uniform, the activation efficiency of the oxidant is higher, and the heating energy consumption is reduced;

(4) In the first stage of operation, by periodically switching the polarity of the electric field by means of rotation switching, the dead angle of drug transmission can be eliminated, and the drug diffusion can be made more uniform.

Description of drawings

Fig. 1 is the structural representation of the electrothermal coupling chemical oxidation device provided by the present invention;

Fig. 2 is the working principle diagram of the electrothermal coupled chemical oxidation device provided by the present invention in operation stage one;

3A is a schematic diagram of the polarity distribution of the electrode matrix in operation stage one;

Figure 3B is a schematic diagram of the polarity distribution of a hexagonal cell in Figure 3A;

Fig. 4 is the working principle diagram of the electrothermal coupled chemical oxidation device provided by the present invention in the second operation stage;

FIG. 5A is a schematic diagram of the polarity distribution of the electrode matrix in the second operation stage (①, ②, and ③ respectively represent the three-phase connection with the live wire);

FIG. 5B is a schematic diagram of the polarity distribution of a triangular unit in FIG. 5A (①, ②, and ③ respectively represent the three-phase connection with the live wire).

FIG. 6 is a schematic diagram of the operation of controlling the regular hexagonal electrode unit to move in the horizontal and vertical directions in the electrode matrix.

DESCRIPTION OF REFERENCE NUMERALS: Oxidant preparation and injection unit 1; Oxidant storage stirring tank 11; Pressurized injection pump 12; Electrode injection integrated well 13; Monitoring control unit 2; Monitoring well 21; Rectifier 32; changeover switch 33; electrode matrix 4.

Detailed ways

As shown in FIG. 1, the present invention provides an electrothermal coupled chemical oxidation device, comprising an oxidant preparation and injection unit 1, a monitoring control unit 2 and a power conditioning unit 3, wherein:

The oxidant preparation and injection unit 1 includes an oxidant storage and stirring tank 11, a pressurized injection pump 12 and an integrated electrode injection well 13. The integrated electrode injection well 13 is made of corrosion-resistant metal material and can be used as an oxidant injection well or as an oxidant injection well. Electrode use, direct current or alternating current into the ground;

The monitoring and control unit 2 includes a monitoring well 21, a detector (which can detect redox potential, pH value, electrical conductivity, water content and/or temperature in the soil, etc.), a display and a memory (not shown), and is configured with Intelligent "positive and negative pole/phase time-division switching" control software;

The power conditioning unit 3 includes an isolation voltage regulator 31, a rectifier 32 and a switch 33. The input end of the isolation voltage regulator 31 is connected to the AC power supply, and the output end can be selected to be directly connected to the electrode injection integrated well 13 through the switch 33. Connect, or choose to connect with the electrode injection integrated well 13 and/or the electrode well through the rectifier 32, so as to transmit alternating current or direct current to the electrode injection integrated well 13 and/or the electrode well.

When the present invention is used:

First, the oxidant (sodium persulfate) is injected into the electrode injection integrated well 13 through the oxidant preparation and injection unit, and then the operation stage 1 and the operation stage 2 are alternately performed, wherein:

The first operation stage is the direct current migration stage: the switch 33 of the power conditioning unit 3 is connected to the rectifier 32 to realize the conversion of alternating current to direct current, and the direct current is transmitted to the electrode injection integrated well 13 and/or the electrode well through the cable, so that the underground A DC electric field is formed; the DC voltage is adjusted by the isolation voltage regulator 31, and the electric field strength of the DC electric field is adjusted, thereby controlling the migration rate of the oxidant; the oxidant (sodium persulfate) is driven by the DC electric field to perform directional migration and diffusion (Fig. 2); preferably Under the circumstance, the electrode injection integrated well 13 and/or the electrode well are arranged in a manner that the basic unit is a regular triangle, and the electrode matrix 4 can be formed after the number is enlarged, and a regular hexagonal unit is formed in the electrode matrix 4, wherein each regular hexagonal unit is formed. The six vertex electrodes of the shape unit are all negative electrodes, the electrodes at the center of the positive six deformed units are positive electrodes, and the remaining single electrodes are arranged in a staggered and adjacent manner with positive and negative electrodes; "Phase time division switching" control software, adjust the positive and negative electrodes of each electrode injected into the integrated well 13 and/or the electrode well (the positive and negative electrodes are staggered adjacent to each other, forming a regular hexagonal electrode unit as shown in Figure 3A and Figure 3B), which can be Make the drug delivery effect more uniform and efficient;

The second operation stage is the AC heating activation stage: after the oxidant is transmitted to the designated polluted area (determined by monitoring the changes of conductivity and redox potential in the soil detected by the control unit 2), the switch 33 of the power conditioning unit 3 is turned on. Connect to another circuit, so that the alternating current is directly transmitted to the electrode matrix 4, thereby forming an alternating electric field underground; adjust the direct current voltage through the isolation voltage regulator 31, adjust the electric field strength of the alternating electric field, thereby controlling the soil heating rate and heating temperature; oxidant ( Sodium persulfate) is activated under the action of AC electric field heating to produce sulfate radicals with stronger oxidizing ability (as shown in Figure 4); The intelligent "positive and negative pole/phase time-division switching" control software of control unit 2 adjusts the basic unit of each regular triangle to have different phases at the three corners (as shown in Figure 5A and Figure 5B), so that the current can be adjusted. Flow between any two adjacent electrodes, so that the heating effect is more uniform and efficient;

After running for a period of time, according to the pollutant removal effect, re-inject the oxidant, and repeat the operation stage 1 and the operation stage 2 alternately until the restoration target is achieved; The intelligent "positive and negative pole/phase time-division switching" control software, for the single electrode existing in the regular hexagon layout, adopts the rotation switching method to optimize the layout of the electrode combination, so that the regular hexagon electrode unit is in the electrode matrix. Move along the horizontal and vertical directions (as shown in Figure 6), and incorporate the single electrode into a new regular hexagonal unit to eliminate the dead angle of drug transmission, and then achieve the purpose of uniform diffusion of the drug; in addition, the present invention can Based on the precise control of a single electrode, the repair scope is narrowed and some areas are accurately repaired.

Beneficial effects brought by the present invention:

(1) The present invention uses the electrode injection integrated well 13, which can realize the compound function of chemical injection and introduction of direct current and alternating current, and the function is integrated, which reduces the cost and time of well construction;

(2) In the stage of DC enhanced oxidant directional migration, by adjusting the distribution of DC positive and negative electrodes, the electrode matrix 4 can be formed into any number of regular hexagonal electrode units, so that the effective action area of a single electrode is maximized and the induced average field strength The highest, thereby reducing the operating energy consumption, improving the uniformity of the drug diffusion, and reducing the dosage of the drug;

(3) In the AC heating activation stage, by adjusting the AC phase distribution of the electrodes, the electrodes form an equilateral triangle layout, and the current can be heated between any two adjacent electrodes to avoid heating cold spots (if the two adjacent electrodes are If the alternating current phase is the same, there will be no current flow between the two, and heating cannot be performed), so that the heating effect is better and uniform, the activation efficiency of the oxidant is higher, and the heating energy consumption is reduced;

(4) In the first stage of operation, by periodically switching the polarity of the electric field by means of rotation switching, the dead angle of drug transmission can be eliminated, and the drug diffusion can be made more uniform.

In general, the technical method and device of the present invention can solve the problem of poor mass transfer of oxidizing agents in low-permeability formations and the problem of efficient activation of persulfate after reaching the contaminated area. By using multifunctional injection/electrode well structure, Two-dimensional electrode configuration (regular hexagonal electrode unit), equilateral triangle layout, electric field rotation switching, etc., can reduce well construction cost, reduce oxidant consumption, improve oxidant transmission rate, speed up oxidation reaction rate, and generally improve in situ Chemical oxidation removal rate, lower repair cost and shorter repair time.

Claims (10)

1. An electrothermal coupling chemical oxidation device is characterized in that: the device comprises an oxidant preparing and injecting unit, a monitoring control unit and a power regulating unit, wherein:

the oxidant preparing and injecting unit can inject an oxidant into the polluted soil;

the monitoring control unit can detect the change conditions of the conductivity and the oxidation-reduction potential in the polluted soil;

the electric power regulating unit comprises an isolation voltage regulator, a rectifier and a change-over switch, wherein the input end of the isolation voltage regulator is connected with an alternating current power supply, the output end of the isolation voltage regulator is directly connected with an electrode in polluted soil through the change-over switch, or the output end of the isolation voltage regulator is connected with the electrode through the rectifier, and therefore alternating current or direct current is transmitted to the electrode.

2. The electro-thermally coupled chemical oxidation apparatus of claim 1, wherein: the electrodes are arranged in a mode that basic units are regular triangles, and an electrode matrix is formed;

when the electrode is connected with direct current, a plurality of regular hexagonal units are arranged in the electrode matrix, wherein six vertexes of each regular hexagonal unit are all negative electrodes, and the electrode at the central position of each regular hexagonal unit is a positive electrode; the rest single falling electrodes are arranged in a mode that positive and negative electrodes are staggered and adjacent;

when the electrodes are connected with alternating current, the phases of each regular triangle basic unit in three angles are different.

3. An electro-thermally coupled chemical oxidation apparatus according to claim 2, wherein: the electrode matrix is formed by combining an electrode injection integrated well and an electrode well.

4. An electro-thermally coupled chemical oxidation apparatus according to claim 3, wherein: the electrode injection integrated well is made of corrosion-resistant metal.

5. An electrothermal coupling chemical oxidation method, which adopts the electrothermal coupling chemical oxidation apparatus according to claim 1, characterized in that: firstly, an oxidant is injected into soil through an oxidant preparation and injection unit, then a first operation stage and a second operation stage are sequentially performed, and the oxidant injection, the first operation stage and the second operation stage are repeatedly performed, wherein:

the first operation stage is a direct current directional migration stage: connecting a change-over switch of the power regulating unit to a rectifier to convert alternating current into direct current and transmitting the direct current to an electrode so as to form a direct current electric field underground; the direct current voltage is regulated through an isolation voltage regulator, and the electric field intensity of a direct current electric field is regulated, so that the migration rate of the oxidant is controlled; the oxidant is driven by a direct current electric field to directionally migrate and diffuse to a specified polluted area;

the second operation stage is an alternating current heating activation stage: after the monitoring control unit judges that the oxidant is transmitted to the specified pollution area, the change-over switch of the power adjusting unit is connected to another circuit, so that alternating current is directly transmitted to the electrode, and an alternating current field is formed underground; the direct current voltage is regulated through an isolation voltage regulator, and the electric field intensity of an alternating current electric field is regulated, so that the soil heating rate and the heating temperature are controlled; the oxidant is activated under the heating action of the alternating current electric field to produce sulfate radicals with stronger oxidizing capability.

6. An electro-thermally coupled chemical oxidation process according to claim 5, characterized in that: the electrodes are arranged in a mode that basic units are regular triangles, and an electrode matrix is formed;

in the first operation stage, a plurality of regular hexagonal units are arranged in the electrode matrix, wherein six vertexes of each regular hexagonal unit are all negative electrodes, and the electrodes at the central positions of the regular hexagonal deformation units are positive electrodes;

in the second operating phase, the phases of each elementary cell in the shape of a regular triangle are different at three angles.

7. An electro-thermally coupled chemical oxidation process according to claim 6, characterized in that: the electrode matrix is formed by combining an electrode injection integrated well and an electrode well.

8. An electro-thermally coupled chemical oxidation process according to claim 7, wherein: the electrode injection integrated well is made of corrosion-resistant metal.

9. An electro-thermally coupled chemical oxidation process according to claim 6, characterized in that: in the first operation stage, aiming at single falling electrodes existing in the regular hexagonal layout, a rotary switching mode is further adopted, the layout of the electrodes is subjected to space optimization combination, so that the regular hexagonal electrode units move in the electrode matrix along the transverse direction and the longitudinal direction, and the single falling electrodes are brought into new regular hexagonal units, so that the medicament transmission dead angle is eliminated.

10. An electro-thermally coupled chemical oxidation process according to claim 5, characterized in that: and injecting the oxidant again, and performing the operation stage I and the operation stage II in sequence.

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