Method and system for repairing polluted soil through solar thermal activation oxidation

Abstract

The invention relates to a method and system for repairing polluted soil through solar thermal activation oxidation. The method comprises the steps that the pollution condition of polluted soil is detected, and remediation agent preparation parameters and the set temperature of a heat medium are determined; the heated thermal medium is introduced into the polluted soil, the temperature of the polluted soil is monitored in real time, and the introduction amount of the thermal medium is fed back and adjusted according to the feedback so that the temperature of the polluted soil can be maintained at the set temperature; the prepared remediation agent is introduced into the contaminated soil, multi-phase extraction is conducted on the contaminated soil, the contamination condition of the contaminated soil is monitored in real time, and remediation agent preparation parameters and / or the set temperature of a thermal medium are / is adjusted according to feedback. Clean energy is adopted for heat supply, the heating mode is improved, energy consumption is reduced, in the remediation process, the temperature and the pollution condition of the contaminated soil are detected in real time, regulation and control are conducted according to the detection result, it can be guaranteed that the contaminated soil is heated evenly, remediation operation of the contaminated soil is conducted efficiently, the use amount of remediation agents is saved, and the treatment period is shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a method and system for remediating contaminated soil by solar thermal activated oxidation. Background Art

[0002] With the rapid development of social economy, environmental issues have gradually attracted people's attention, among which soil pollution is becoming more and more serious. Chemical oxidation remediation is mainly a remediation technology that adds chemical oxidants to the soil, enhances the decomposition or volatilization of pollutants through heating, causes oxidation reactions with pollutants, and finally degrades pollutants or converts them into low-toxic and low-transfer products.

[0003] The existing chemical oxidation remediation of contaminated soil has the following problems: high energy consumption, uneven temperature distribution, difficult to control the thermal activation temperature of the remediation agent, and the temperature of some remediation agents is not within the optimal temperature range of thermal activation, resulting in reduced remediation effect and affecting remediation efficiency. Therefore, a solar thermal activated oxidation remediation system and method for contaminated soil is urgently needed to solve the above problems. Summary of the invention

[0004] In order to solve the above problems, on the one hand, the present invention provides a method for remediating contaminated soil by solar thermal activated oxidation, comprising the following steps:

[0005] Detect the contamination status of the contaminated soil, and determine the preparation parameters of the remediation agent and the set temperature of the heat medium used to heat the contaminated soil according to the contamination status;

[0006] The heat medium heated by the solar heating unit is introduced into the contaminated soil, and the temperature of the contaminated soil is monitored in real time, and the amount of heat medium introduced is adjusted based on the feedback to maintain the internal temperature of the contaminated soil at the set temperature;

[0007] The prepared remediation agent is introduced into the contaminated soil and subjected to multiphase extraction. During the remediation process, the contamination status of the contaminated soil is monitored in real time, and the remediation agent preparation parameters and / or the set temperature of the heat medium are adjusted based on the feedback.

[0008] Furthermore, real-time monitoring of the contamination of contaminated soil specifically includes:

[0009] According to the real-time monitoring results of the pollution situation, the concentration of the remediation agent introduced into the contaminated soil is adjusted. When it is detected that the pollutant degradation rate is less than the set range of the pollutant degradation rate over a period of time, the set temperature of the heat medium introduced into the contaminated soil is increased.

[0010] Further, the set temperature of the heat medium includes an initial set temperature of the heat medium, and the determination of the initial set temperature of the heat medium specifically includes:

[0011] Detect the type and concentration of pollutants in the contaminated soil, and determine the type and concentration of the remediation agent used to repair the contaminated soil and the initial set temperature of the heat medium used to activate the remediation agent based on the detection results.

[0012] Furthermore, the set temperature of the heat medium also includes an optimal set temperature of the heat medium, and the determination of the optimal set temperature of the heat medium specifically includes:

[0013] The set temperature of the heat medium is adjusted at regular intervals, and the pollution data of the contaminated soil at the corresponding set temperature is collected. The degradation rate, energy consumption and the ratio of the degradation rate to the energy consumption of the pollutants are obtained through multiple sets of pollution data. The set temperature of the heat medium corresponding to the largest ratio is selected as the optimal set temperature, and the temperature of the heat medium passing into the contaminated soil is adjusted to the optimal set temperature.

[0014] Furthermore, if the contaminated soil temperature is less than the set temperature of the heat medium, the solar heating unit supplies the heat medium to the contaminated soil until the contaminated soil temperature is not less than the set temperature of the heat medium; if the contaminated soil temperature is greater than or equal to the set temperature of the heat medium, the solar heating unit stops supplying the heat medium to the contaminated soil, and the heat medium is stored and kept warm in the solar heating unit.

[0015] Furthermore, the solar heating unit includes a solar heating component and a storage component for storing heat medium, and the storage component is connected to the solar heating component; if the heating temperature of the solar heating component is ≥ the set temperature of the heat medium, the heat medium heated to the set temperature is sent to the storage component for storage and standby; if the heating temperature of the solar heating component is < the set temperature of the heat medium, the heat medium in the storage component is heated to the set temperature.

[0016] Furthermore, if it is detected that the pollutant concentration of the contaminated soil is greater than the pollutant concentration control value, the prepared remediation agent is sent to the contaminated soil to undergo an oxidation reaction with the pollutants in the soil; if it is detected that the pollutant concentration of the contaminated soil is less than or equal to the pollutant concentration control value, the introduction of the remediation agent into the contaminated soil and the introduction of the heat medium into the contaminated soil are stopped.

[0017] Furthermore, if the multiphase extraction pressure of the contaminated soil is less than the pressure setting value, the multiphase extraction pressure is adjusted until the multiphase extraction pressure is greater than or equal to the pressure setting value, and the multiphase extraction is continued for a period of time.

[0018] Furthermore, the waste gas and waste water collected by the multiphase extraction of the contaminated soil are purified and discharged after purification.

[0019] On the other hand, the present invention also provides a solar thermal activated oxidation remediation system for contaminated soil, comprising:

[0020] A solar heating unit for heating the medium and storing the heat medium, the solar heating unit being connected to a heat medium heating pipe inserted into the contaminated soil;

[0021] A dispensing unit, used for preparing and storing remediation agents, wherein the dispensing unit is connected to a dosing pipe inserted into the contaminated soil;

[0022] A multiphase extraction unit, wherein the multiphase extraction unit is connected to a multiphase extraction pipeline inserted into the contaminated soil;

[0023] The data acquisition unit includes a temperature detection device and a pollutant detection device. The temperature detection device is interlocked with the solar heating unit to monitor the temperature of the contaminated soil and feedback interlock control the amount of heat medium introduced into the heat medium heating pipeline. The pollutant detection device is interlocked with the solar heating unit and the dispensing unit respectively to monitor the contamination of the contaminated soil and feedback interlock control the set temperature of the heat medium of the solar heating unit and the preparation parameters of the remediation agent of the dispensing unit.

[0024] Due to the adoption of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0025] 1) The method for remediating contaminated soil by solar thermal activated oxidation provided by the present invention adopts clean energy solar energy for heating, improves the heating method, reduces energy consumption, and during the remediation process, detects the temperature and pollution status of the contaminated soil in real time and regulates according to the detection results, thereby ensuring uniform heating of the contaminated soil and efficient implementation of the contaminated soil remediation operation, saving the use of remediation agents and shortening the treatment cycle.

[0026] 2) The method for solar thermal activated oxidation remediation of contaminated soil provided by the present invention adopts a combined heating system of solar energy and electric heating, which can not only realize green energy powered by solar energy, but also ensure the stability of heating, thereby making up for the disadvantage of unstable heating of solar energy due to the influence of weather and collection area. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 This is a schematic diagram of the structure of the solar thermal activated oxidation remediation system for contaminated soil in the present invention;

[0029] Figure 2 Schematic diagram of pollutant degradation in the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In the drawings, the size and relative size of some parts may be enlarged for clarity.

[0031] In the description of the present invention, unless otherwise clearly stipulated and limited, the terms "connection" and "connected" should be interpreted in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] In the description of the present invention, terms such as "up", "down", "left", "right", "front", "back", etc., and the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0033] In addition, in the description of the present invention, the terms "first" and "second" are only used to distinguish in the description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. In addition, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0034] Example 1

[0035] The present invention provides a method for remediating contaminated soil by solar thermal activated oxidation, comprising the following steps:

[0036] Detect the contamination status of the contaminated soil, and determine the preparation parameters of the remediation agent and the set temperature of the heat medium used to heat the contaminated soil according to the contamination status;

[0037] The heat medium heated by the solar heating unit 1 is introduced into the contaminated soil, and the temperature of the contaminated soil is monitored in real time, and the amount of heat medium introduced is adjusted based on the feedback to maintain the internal temperature of the contaminated soil at the set temperature;

[0038] The prepared remediation agent is introduced into the contaminated soil and subjected to multiphase extraction. During the remediation process, the contamination status of the contaminated soil is monitored in real time, and the remediation agent preparation parameters and / or the set temperature of the heat medium are adjusted based on the feedback.

[0039] Specifically, the present invention can perform in-situ remediation of contaminated soil. When in use, the solar heating unit 1 provides a heat source, and its heat medium can be hot water or steam, but is not limited to hot water. In this embodiment, the heat medium is preferably hot water. The heat medium is passed into the contaminated soil, and the contaminated soil is heated by thermal radiation. The prepared remediation agent is transported into the contaminated soil, and the remediation agent is fully in contact with the contaminated soil. During the dosing process, the contaminated soil is subjected to multiphase extraction, so that a negative pressure is formed inside the contaminated soil. The remediation agent can quickly extend into the soil and react with the pollutants in the contaminated soil to undergo a chemical oxidation reaction, thereby remediating the contaminated soil. The gaseous or liquid pollutants generated by the oxidation reaction are guided out of the contaminated soil through multiphase extraction to be collected and processed outside the contaminated soil for centralized collection, so as to avoid secondary pollution caused by the diffusion of the generated pollutants, and also reduce the concentration of the products in the contaminated soil, promote the oxidation reaction to move in the direction of the products, and increase the reaction rate. During the entire remediation process, the temperature change of the contaminated soil can be detected in real time, so as to feedback and adjust the amount of heat medium introduced into the contaminated soil by the solar heating unit 1, and ensure that the temperature of the contaminated soil remains within the set range.

[0040] Preferably, before injecting the remediation agent, a heat medium can be introduced to preheat the contaminated soil. The preheating temperature is lower than the set temperature of the heat medium. After the temperature of the contaminated soil reaches the preheating temperature, the remediation agent is introduced. This can improve the reaction efficiency between the remediation agent and the pollutant and shorten the remediation time. Of course, the heat medium can also be introduced into the contaminated soil while the remediation agent is introduced. While introducing the remediation agent, multiphase extraction is performed on the contaminated soil. Multiphase extraction is used to accelerate the diffusion of the agent in the soil, so that the remediation agent is evenly distributed in the contaminated soil to ensure that the contaminated soil is completely remediated. At the same time, the pressure generated when the agent is injected by in-situ chemical oxidation is used to keep the soil in a state of pressure balance. Organic pollutants in different forms in the soil can be removed synchronously, solving the shortcomings of single technologies such as in-situ chemical oxidation (ISCO) only for oxidizable substances (adsorbed state) and multiphase extraction (MPE) only for volatile and free substances.

[0041] Optimize the implementation method, and detect the pollution of contaminated soil, specifically including detecting the type, concentration and volume of pollutants in the contaminated soil, so as to fully grasp the pollution distribution of the contaminated soil; prepare the agent, including setting the repair agent according to the type of pollutant, using a suitable repair agent to oxidize the pollutant, and determining the concentration of the repair agent according to the concentration of the pollutant, and passing the prepared repair agent into the contaminated soil for oxidation repair. As the oxidation reaction proceeds, the concentration of pollutants in the contaminated soil will gradually decrease, and the concentration of pollutants in the contaminated soil will be monitored in real time, and the concentration of the repair agent passed into the contaminated soil will be adjusted according to the monitoring results. While ensuring the oxidation reaction, the use of repair agents is saved, costs are saved and environmental pollution is avoided. When it is monitored that the degradation rate of pollutants within a period of time is less than the set range of the degradation rate of pollutants, it means that the repair effect is not good, and the set temperature of the heat medium passed into the contaminated soil can be increased, that is, the temperature of the heat medium passed into the contaminated soil is increased to ensure that the reaction between the repair agent and the pollutant proceeds smoothly. For example, the set temperature of the heat medium can be increased by 10°C in sequence to ensure that the degradation rate of pollutants in the contaminated soil is within the set range. When the temperature of the heat medium increases, the vapor pressure of the reagent increases. In order to ensure that the reagent remains in liquid form and circulates in the system, it is necessary to increase the pressure setting value of the multiphase extraction pipeline in the multiphase extraction unit.

[0042] If the pollutant concentration in the soil exceeds the pollutant concentration control value, it means that the pollutants exceed the standard and the contaminated soil needs to be repaired; if the pollutant concentration in the soil is less than or equal to the pollutant concentration control value, it means that the pollutants do not exceed the standard and the soil does not need to be repaired. In the present invention, the pollutant concentration of the contaminated soil is monitored in real time. When the pollutant concentration exceeds the pollutant concentration control value, the repair agent is introduced to repair the soil until the pollutant concentration in the soil is detected to be equal to or less than the pollutant concentration control value, and the introduction of the repair agent is stopped. When the pollutant concentration in the soil exceeds the standard, the above-mentioned contaminated soil repair operation is repeated.

[0043] In an optimized implementation mode, the set temperature of the heat medium includes the initial set temperature of the heat medium. The determination of the initial set temperature of the heat medium specifically includes: detecting the type and concentration of pollutants in the contaminated soil, and determining the type and concentration of the remediation agent used to remediate the contaminated soil and the initial set temperature of the heat medium used to activate the remediation agent according to the detection results. The initial set temperature of the heat medium can be determined according to the type of pollutants detected, and the initial set temperature of the heat medium is the thermal activation temperature of the remediation agent. When the contaminated soil is initially remediated, the heat medium is heated to the initial set temperature, and then introduced into the contaminated soil to heat the soil to activate the remediation agent.

[0044] There are mainly the following types of soil and groundwater pollution: polycyclic aromatic hydrocarbons-based contaminated sites, pesticide-based contaminated sites, and petroleum hydrocarbon-based contaminated sites. Different pollutants correspond to different pollutant concentration control values, concentration screening values, types of remediation agents, and thermal activation temperatures. Persulfate can be used for the remediation of polycyclic aromatic hydrocarbons-based contaminated sites, potassium permanganate can be used for the remediation of pesticide-based contaminated sites, and Fenton reagent (H2O2+Fe 2+ ) is used for the remediation of contaminated sites mainly composed of petroleum hydrocarbons. The following table shows the remediation parameters for some pollutants. When the pollutant concentration is detected to exceed the concentration control value, pollutant remediation is required until the pollutant concentration is lower than the concentration screening value.

[0045] Table 1 Remediation parameters of pollutants (unit: mg / kg)

[0046]

[0047] The initial set temperature of the above-mentioned heat medium is not the optimal thermal activation oxidation temperature. The optimal set temperature of the heat medium needs to be determined through the degradation rate of pollutant concentration and energy consumption during the remediation process. Specifically, the set temperature of the heat medium is adjusted at regular intervals, and the pollution status data of the contaminated soil at the corresponding set temperature is collected. The degradation rate of pollutants, energy consumption, and the ratio of degradation rate to energy consumption are obtained through multiple sets of pollution status data. The set temperature of the heat medium corresponding to the largest ratio is selected as the optimal set temperature. The degradation effect of pollutants at this temperature is good and the energy consumption is relatively low. It can be used as the optimal set temperature of the heat medium, and this optimal set temperature is fed back to the solar heating unit.

[0048] During the remediation process, the temperature of the contaminated soil is detected. If the temperature of the contaminated soil is less than the set temperature of the soil, the solar heating unit is operated to provide heat medium to the contaminated soil to ensure that the temperature of the contaminated soil reaches the set temperature of the soil; if the temperature of the contaminated soil is greater than or equal to the set temperature of the soil, it means that the temperature of the contaminated soil has reached the activation temperature of the remediation agent, and the soil has a heat preservation function, and the heating of the contaminated soil can be suspended. The solar heating unit stops providing heat medium to the contaminated soil, and the heat medium can be stored for standby to save energy. The set temperature of the soil is equal to the set temperature of the heat medium.

[0049] In the optimized implementation mode, the solar heating unit 1 includes a solar heating component and a storage component for storing a heat medium. The storage component is connected to the solar heating component. The storage component can be used to store the heat medium and perform secondary heating on the heat medium. If the heating temperature of the solar heating component is greater than or equal to the set temperature of the heat medium, the heat medium heated to the set temperature is sent to the storage component for storage and standby. If the heating temperature of the solar heating component is less than the set temperature of the heat medium, the heat medium in the storage component is heated to the set temperature. The solar heating component can use sunlight to heat water. Under sufficient sunshine conditions, it can fully heat the medium and pass the heated hot water into the contaminated soil to activate the remediation agent. In order to save energy and reduce energy loss, the excess hot water can be sent to the storage component for storage. The storage component is provided with an insulation layer to reduce energy loss. At the same time, the storage component is also provided with a heating device for secondary heating of the heat medium. When the solar heating component cannot heat the medium to the set temperature, the heat medium can be heated to the set temperature in the storage component and then passed into the contaminated soil to heat the contaminated soil.

[0050] For details, please refer to the attached manual. Figure 1As shown, the solar heating component includes a heat collecting plate 11 and a heat collecting tank 12, and a circulation loop is formed between the heat collecting plate 11 and the heat collecting tank 12 through a pipeline. The heat collecting tank 12 is also connected to a water inlet pipe 13, and the water inlet pipe 13 can replenish water to the heat collecting tank 12 so that the water level in the heat collecting tank 12 is within the water level setting range; the storage component includes a hot water supply tank 14, and the hot water supply tank 14 is provided with an electric heater for secondary heating. The hot water supply tank 14 is connected to the heat collecting tank 12 through a first water supply pipeline 15, and the heat collecting plate 11 can preliminarily heat the water in the heat collecting tank 12. After the water in the heat collecting tank 12 is heated, it is sent to the hot water supply tank 14 through the first water supply pipeline 15 for storage and use. In order to detect the water temperature, the heat collecting tank 12 is provided with a first temperature detector, and the heat supply tank 14 is provided with a second temperature detector, which are respectively used to monitor the water temperature in the tank in real time. The heat collecting tank 12 and the heat supply tank 14 are respectively provided with water level sensors for water level detection. A heat medium heating pipe 2 is buried in the contaminated soil, and the heat medium heating pipe 2 is inserted into the contaminated soil. The water inlet end of the heat medium heating pipe 2 is connected to the heat supply tank 14 through the second water pipeline 16, and the water outlet end is connected to the heat collecting tank 11 through the third water pipeline 17. When the contaminated soil needs to be heated, the hot water in the heat supply tank 14 is sent to the heat medium heating pipe 2 through the second water pipeline 16 to heat the soil. The heat medium heating pipe 2 is provided with a third temperature detector. When the third temperature detector detects that the water temperature in the pipe is lower than the pipe set value, the water in the heat medium heating pipe 2 flows back to the heat collecting tank 12 through the third water pipeline 17 for reheating. A fourth water delivery pipeline 18 is provided between the heat collection tank 12 and the second water delivery pipeline 16, and the hot water in the heat collection tank 12 can also be directly delivered to the heat medium heating pipeline 2 for use. There are a plurality of heat medium heating pipelines 2, and each heat medium heating pipeline 2 is evenly spaced in the contaminated soil, so that the contaminated soil can be evenly heated.

[0051] Preferably, the water inlet pipeline 13 is provided with a first water pump 19, a first valve 110 and a second valve 111, the pipelines of the heat collecting plate 11 and the heat collecting tank 12 are provided with a second water pump 112, a third valve 113 and a fourth valve 114, the first water supply pipeline 15 is provided with a third water pump 115, a fifth valve 116 and a sixth valve 117, the second water supply pipeline 16 is provided with a fourth water pump 118, a seventh valve 119 and an eighth valve 120, the third water supply pipeline 17 is provided with a fifth water pump 121, a ninth valve 122 and a tenth valve 123, and the fourth water supply pipeline is provided with an eleventh valve 124.

[0052] Preferably, in order to monitor the temperature of the contaminated soil in real time, a temperature detection device 3 is also provided. The temperature detection device 3 includes a plurality of temperature sensors. A plurality of temperature monitoring points are provided in the contaminated soil. Each temperature monitoring point is provided with a temperature sensor. Multi-point temperature collection is performed in the contaminated soil, and the detection is more accurate.

[0053] The above-mentioned water pumps, temperature detectors, water level sensors, and temperature detection devices are respectively connected to the controller 4. The controller 4 can collect and analyze the detection data, and then feed back to the corresponding water pump to open and close the pipeline.

[0054] Set the minimum and maximum water levels of the heat collecting tank 12, and the water level sensor can detect the measured water level of the heat collecting tank in real time. If the measured water level is ≥ the maximum set water level, the controller controls the first water pump 19, the first valve 110 and the second valve 111 to close, and controls the second water pump 112, the third valve 113 and the fourth valve 114 to open, so as to perform circulation heating of the central heat collecting plate; set the temperature of the heat collecting tank 12, and the first temperature detector in the heat collecting tank 12 collects the actual temperature value of the water tank, and compares the actual temperature value with the set temperature value; if the actual temperature value is ≥ the set temperature, the fourth water pump 118, the seventh valve 119 and the eighth valve 120, the eleventh valve 124 are opened to supply hot water to the heat medium heating pipe 2 ... If the temperature value is less than the set temperature, the eleventh valve 124 is closed, and the water in the heat collection tank 12 is transported to the heat supply tank 14, the secondary heating mode is started, the water in the heat supply tank 14 is heated to the set temperature of the heat medium, and then is transported to the heat medium heating pipeline 2 through the second water delivery pipeline 16; when the hot water in the heat collection tank 12 is used up to a water level lower than the minimum set water level, the controller controls the first water pump 19, the first valve 110 and the second valve 111 to open, and continue to supply water to the heat collection tank 12; the controller starts the secondary heating mode, and the controller opens the third water pump 115, the fifth valve 116 and the sixth valve 117. The minimum water level and the maximum water level of the hot water supply tank 14 are set, the actual water level value of the hot water supply tank 14 is collected, and the actual water level is compared with the set water level. If the actual water level value is ≥ the maximum set water level, the controller controls the third water pump 115, the fifth valve 116 and the sixth valve 117 to close; the temperature setting value of the hot water supply tank 14 is set, and the second temperature detector in the hot water supply tank 14 collects the temperature and compares it with the temperature setting value; if the actual temperature value is ≥ the set temperature value, the controller turns off the electric heating, turns on the fourth water pump 118, the seventh valve 119 and the eighth valve 120, and supplies hot water to the heat medium heating pipeline 2; when the hot water in the hot water supply tank 14 is used up to the water level less than the minimum set water level, the third water pump 115, the fifth valve 116 and the sixth valve 117 are continued to be opened to supply water to the hot water supply tank 14. The third temperature detector in the heat medium heating pipeline 2 monitors the water temperature in the pipeline. When the actual temperature in the pipeline is less than the set temperature in the pipeline, the controller turns on the fifth water pump 121, the ninth valve 122 and the tenth valve 123 to return the water in the pipeline to the heat collection tank 12 for solar heating again.

[0055] In this embodiment, the set temperature of the heat collecting tank is equal to the set temperature of the heat medium, and the set temperature of the heat supply tank is equal to the set temperature of the heat medium. When the contaminated soil temperature is lower than the set value of the soil temperature, the solar heating unit passes the heat medium into the heat medium heating pipe. If the solar heating unit is already providing heat, but the contaminated soil temperature is still lower than the set value of the soil temperature, the amount of heat medium introduced can be increased or the heating time can be extended.

[0056] In some embodiments, if there is excess hot water in the heat collection tank after supplying the heat medium heating pipe, the heat medium can be sent to the hot water supply tank for storage. The hot water supply tank is provided with an insulation layer to keep the hot water warm and reduce the energy loss of the hot water. The hot water stored in the hot water supply tank can be used to heat the contaminated soil at night or on rainy days, which can effectively reduce energy consumption.

[0057] An optimized implementation method is as follows: if it is detected that the pollutant concentration of the contaminated soil is greater than the pollutant concentration control value, the prepared remediation agent is delivered to the contaminated soil to undergo an oxidation reaction with the pollutants in the soil; if it is detected that the pollutant concentration of the contaminated soil is less than or equal to the pollutant concentration control value, the introduction of the remediation agent into the contaminated soil and the introduction of the heat medium into the contaminated soil are stopped.

[0058] For details, please refer to the attached manual. Figure 1 As shown, the repair agent is prepared by the dispensing unit 5, and the dispensing unit 5 includes a dissolving tank 51 and a liquid storage tank 52. The liquid storage tank 52 is connected to the dissolving tank 51 through a first drug delivery pipeline 53. The repair agent is dissolved and prepared in the dissolving tank 51, and then sent to the liquid storage tank 52 for storage. The first drug delivery pipeline 53 is provided with a sixth water pump 54, a twelfth valve 55 and a thirteenth valve 56. The dissolving tank 51 is provided with an agitator. The dissolving tank 51 is connected with a dosing pipe 57 and a water adding pipe 58. The dosing pipe 57 is provided with a flow meter 59 and a dosing solenoid valve 510. The water adding pipe 58 is provided with a water adding solenoid valve 511. The dissolving tank 51 and the liquid storage tank 52 are respectively connected with water level sensors for monitoring the water levels in the tanks. A dosing pipe 6 is buried in the contaminated soil, and the dosing pipe 6 is connected to the liquid storage tank 52 through a second drug delivery pipeline 512, and a discharge pump 513, a fourteenth valve 514 and a fifteenth valve 515 are provided on the second drug delivery pipeline 512. There are multiple dosing pipes 6, and each dosing pipe is evenly spaced in the contaminated soil. A plurality of dosing holes are respectively opened on each dosing pipe 6, and the remediation agent can enter the soil through the dosing holes to remediate the contaminated soil.

[0059] When the pollutant concentration exceeds the standard, the dispensing unit 5 starts to prepare and supply the repair agent. The repair agent is prepared according to the type of pollutant, mixed evenly in the dissolving tank 51, and then sent to the liquid storage tank and sent to the dosing pipeline through the second drug delivery pipeline.

[0060] The dispensing unit 5 is started, and the oxidizing agent is configured according to the main pollutant site, and the set water level of the agent in the dissolution tank is set. The water level sensor in the dissolution tank collects the actual water level data and compares the actual water level with the set water level; if the actual water level in the dissolution tank is ≥ the set water level, the controller controls the dosing solenoid valve and the water adding solenoid valve to be closed; the controller turns on the agitator, sets the running time of the agitator, and compares the actual running time with the set running time. If the actual running time = the set running time, the agitator is turned off, the sixth water pump 54, the twelfth valve 55 and the thirteenth valve 56 are turned on, and the prepared repair agent is sent to the liquid storage tank; the set water level of the agent in the liquid storage tank is set, and the water level sensor located in the liquid storage tank collects the actual water level data and compares the data with the set water level. If the actual water level is ≥ the set water level, the controller controls the sixth water pump 54, the twelfth valve 55 and the thirteenth valve 56 to be closed. The prepared repair agent is stored in the liquid storage tank, waiting for the agent delivery instruction. When the concentration of soil pollutants is detected to exceed the control value, repair is required, and the discharge pump 513, the fourteenth valve 514 and the fifteenth valve 515 are controlled to open to deliver the agent to the dosing pipeline; if the concentration of soil pollutants is detected to be lower than the screening value, there is no need to supply the agent, and the discharge pump 513, the fourteenth valve 514 and the fifteenth valve 515 are closed. When the agent in the liquid storage tank is used up, the dispensing unit starts to continue dispensing. The sixth water pump, the discharge pump, the water level sensor, and the agitator are all connected to the controller to achieve intelligent regulation.

[0061] The contaminated soil is subjected to multiphase extraction through a multiphase extraction unit 7. A multiphase extraction pipeline 8 is buried in the contaminated soil, and the multiphase extraction pipeline 8 is connected to the multiphase extraction unit 7. The multiphase extraction unit 7 includes an extraction well, which is connected to the multiphase extraction pipeline 8. The extraction well is provided with a gas-liquid separator 71 and an oil-water separator 72 for waste gas and wastewater treatment. The gas-liquid separator 71 is connected to a tail gas treatment device 73, and the oil-water separator 72 is connected to a hazardous waste treatment device 74 and a sewage treatment device 75. There are multiple multiphase extraction pipelines 8, each of which is evenly spaced in the contaminated soil, and each of which is provided with a plurality of extraction holes for multiphase extraction. At least part of the multiphase extraction pipelines 8 is connected to the gas-liquid separator 71, and at least part of the multiphase extraction pipelines 8 is connected to the oil-water separator 72. A vacuum pump 76 is provided at the front end of each of the multiphase extraction pipes 8. When the vacuum pump is turned on, negative pressure is formed in the pipe, which can accelerate the circulation of the remediation agent in the contaminated soil. The waste gas and wastewater generated by the oxidation reaction can also be recovered and treated, and then discharged after the treatment meets the standards.

[0062] Preferably, each of the multiphase extraction pipelines 8 is provided with a pressure sensor for monitoring the air pressure in the pipeline. A sixteenth valve 77 and a seventeenth valve 78 are provided on the pipeline between the gas-liquid separator 71 and the multiphase extraction pipeline, a seventh water pump 79, an eighteenth valve 710 and a nineteenth valve 711 are provided on the pipeline between the oil-water separator 72 and the multiphase extraction pipeline, an eighth water pump 712, a twentieth valve 713 and a twenty-first valve 714 are provided on the pipeline between the gas-liquid separator 71 and the oil-water separator 72, and an air pump 715, a twenty-second valve 716 and a twenty-third valve 717 are provided on the pipeline between the gas-liquid separator 71 and the tail gas treatment device 73. Each of the vacuum pump, water pump, air pump, gas-liquid separator and oil-water separator is connected to the controller. When the remediation agent is injected into the contaminated soil, the vacuum pump is turned on for extraction. If the multiphase extraction pressure of the contaminated soil is less than the pressure setting value, the vacuum pump is turned on and the multiphase extraction pressure is adjusted until the multiphase extraction pressure is greater than or equal to the pressure setting value. The controller then controls the vacuum pump 76 and the water pump 7, the sixteenth valve 77, the seventeenth valve 78, the eighteenth valve 710 and the nineteenth valve 711 to be closed; the gas-liquid separator, the eighth water pump 712, the air pump 715, the oil-water separator, the twentieth valve 713, the twenty-first valve 714, the twenty-second valve 716 and the twenty-third valve 717 are turned on to perform terminal sewage treatment, tail gas treatment and hazardous waste collection.

[0063] The pressure of the multiphase extraction pipeline is related to the vapor pressure of the repair agent, the temperature, the contact time between the repair agent and the soil, etc. The extraction pressure is usually higher than the vapor pressure of the repair agent (a pressure gauge is provided in the dispensing unit to measure the vapor pressure of the repair agent) to ensure that the repair agent remains liquid and circulates in the system; an increase in temperature will cause the vapor pressure of the repair agent to increase, so the extraction pressure needs to be increased; a longer contact time requires a higher pressure to maintain the fluidity and extraction efficiency of the repair agent. As the extraction pressure increases, the fluidity of the repair agent and the transfer rate of pollutants increase, and the reaction rate increases. The extraction pressure is set to a maximum set threshold, and the pressure of the multiphase extraction pipeline is less than the maximum set threshold to avoid high pressure causing damage to the soil structure, causing the soil layer to collapse, affecting the repair effect, and reducing energy consumption.

[0064] The optimized implementation also includes a pollutant detection device, which is preferably a photoionization detector (PID sensor) and a water quality detector. The photoionization detector is set at the outlet of the extraction well and the air inlet / exhaust outlet of the tail gas treatment device. The water quality detector is set at the outlet of the extraction well and the water inlet / outlet of the sewage treatment device. The photoionization detector and the water quality detector can detect the types and concentrations of pollutants in groundwater and soil in real time. According to the test results, the remediation agent is prepared and introduced into the contaminated soil for oxidative remediation.

[0065] In this embodiment, before remediating the contaminated soil, the contamination condition of the contaminated soil is first detected and analyzed, specifically including detecting and analyzing the type and concentration of pollutants in the contaminated soil and the volume of the contaminated soil. According to the analysis results, the burial depth, burial length and burial density of the heat medium heating pipeline, the dosing pipeline and the multi-phase extraction pipeline laid in the contaminated soil are determined, and the type and concentration of the agent used to remediate the contaminated soil and the activation temperature of the remediation agent are determined.

[0066] The present invention adopts clean energy solar energy for heating, improves the heating mode and control method, solves the problem of high energy consumption and uneven heating in removing soil organic pollutants; adopts a solar energy and electric heating combined heating system, which can not only realize green energy powered by solar energy, but also ensure the stability of heating, and make up for the disadvantage of unstable heating of solar energy due to the influence of weather and heat collection area; the combination of solar energy heating unit, dispensing unit, multi-phase extraction unit and controller realizes real-time online monitoring and intelligent control, and improves the efficiency of soil repair. PID control and constant temperature and pressure control are adopted to improve the utilization of thermal energy.

[0067] The following is explained through specific embodiments.

[0068] Multiphase extraction unit 7 is turned on, and the multiphase extraction pipeline pressure F<F 设定 , open the vacuum pump 76, the seventh water pump 79, the sixteenth valve 77, the seventeenth valve 78, the eighteenth valve 710 and the nineteenth valve 711, the photoionization detector and the water quality rapid detector detect the gaseous pollution concentration and the water-soluble pollution concentration, analyze the pollutant composition, select the type of repair agent, and set the thermal activation temperature of the repair agent. The soil pollutants in this embodiment are mainly polycyclic aromatic hydrocarbons, and the detection concentration of the pollutant naphthalene is greater than 700 mg / kg. It is necessary to configure the oxidizing agent persulfate (PMS) to repair it, and set the thermal activation temperature of the repair agent to 40°C. Then the set temperature of the heat medium is 40°C.

[0069] The dispensing unit 5 starts to prepare the repair agent, the actual water level in the dissolving tank 51 is recorded as Q3, the actual water level in the liquid storage tank 52 is recorded as Q4, the stirring time of the agitator is t, and the water level sensors of the dissolving tank 51 and the liquid storage tank 52 and the agitator are electrically connected to the controller 4.

[0070] When Q3<Q 设定3 , t<t 设定 When the temperature is high, open the dosing solenoid valve, water adding solenoid valve and stirrer, add the set amount of persulfate and water into the dissolving tank, stir with the stirrer, and the persulfate is fully dissolved in the water;

[0071] When Q3 ≥ Q 设定3 , t=t 设定At this time, close the dosing solenoid valve, water adding solenoid valve and agitator, and the dissolution of persulfate is completed.

[0072] When Q4<Q 设定4 , open the sixth water pump 54, the twelfth valve 55 and the thirteenth valve 56 to deliver the prepared repair agent in the dissolving tank to the liquid storage tank;

[0073] When Q4 ≥ Q 设定4 , close the sixth water pump 54, the twelfth valve 55 and the thirteenth valve 56, open the discharge pump 513, the fourteenth valve 514 and the fifteenth valve 515, and transport the repair agent to the dosing pipeline.

[0074] The dispensing unit repeats the above preparation of the repair agent.

[0075] The solar heating unit is started, the actual water level detected by the water level sensor in the heat collection tank is recorded as Q1, the first temperature detected by the first temperature detector in the heat collection tank is recorded as T1, the real-time temperature detected in the contaminated soil is recorded as T3, the water temperature and water level in the heat supply tank are T2 and Q2, and the temperature in the heat medium heating pipe is T4. 设定1 、T 设定2 、T 设定3 、T 设定4 It is the set value, which can be set by yourself or by the user. 设定1 According to the volume of the water collection tank, Q 设定2 Set according to the volume of the hot water tank; T 设定1 、T 设定2 is 40℃.

[0076] When Q1<Q 设定1 , open the first water pump 19, the second water pump 112, the first valve 110 and the second valve 111, the third valve 113 and the fourth valve 114, and start water supply and solar heating.

[0077] When Q1 ≥ Q 设定1 , close the first water pump 19, the second water pump 112, the first valve 110 and the second valve 111, the third valve 113 and the fourth valve 114 to end the water supply.

[0078] When T3<T 设定3 , T1 ≥ T 设定1 When the fourth water pump 118, the seventh valve 119, the eighth valve 120 and the eleventh valve 124 are opened, the hot water heated in the heat collection tank is supplied to the heat medium heating pipeline.

[0079] When T3>T 设定3 , T1 ≥ T 设定1When , it indicates that the temperature of the soil to be repaired is hot enough to activate the oxidant. There is no need to supply hot water to the heat medium heating pipeline. The fourth water pump 118, the seventh valve 119, the eighth valve 120 and the eleventh valve 124 are closed, and the hot water generated by solar energy is stored in the heat collection tank and the hot water supply tank.

[0080] When T3<T 设定3 , T1<T 设定1 When the solar energy cannot heat the water to the set temperature, the third water pump 115, the fifth valve 116 and the sixth valve 117 are turned on to send the water in the heat collection tank to the hot water supply tank, and the electric heater is turned on for secondary heating to heat the water to the set temperature, and then the heated water is sent to the heat medium heating pipeline.

[0081] When T3<T 设定3 , T1<T 设定1 , Q2<Q 设定2 When the first water pump 19, the second water pump 112, the first valve 110 and the second valve 111, the third valve 113 and the fourth valve 114 are closed, and the third water pump 115, the fifth valve 116 and the sixth valve 117 are opened to supply water to the hot water tank.

[0082] When T3<T 设定3 , Q2 ≥ Q 设定2 When T2<T 设定2 , close the third water pump 115, the fifth valve 116 and the sixth valve 117, and turn on the electric heater for secondary heating; if T2 ≥ T 设定2 When the electric heater is turned off, the fourth water pump 118, the seventh valve 119 and the eighth valve 120 are opened, and hot water enters the heat medium heating pipeline.

[0083] When T4<T 设定4 , open the fifth water pump 121, the ninth valve 122 and the tenth valve 123, return the water in the heat medium heating pipeline to the heat collecting tank, and restart the solar energy heating.

[0084] When T4 ≥ T 设定4 , close the fifth water pump 121, the ninth valve 122 and the tenth valve 123.

[0085] Every two hours, the set temperature of the heat medium is increased, the change of pollutant concentration is detected, a graph is drawn, and the optimal heating temperature is selected. Figure 2As shown in the figure, when the set temperature is 40℃, after 120min of reaction, the degradation rate of naphthalene in the system is about 41.5%. When the reaction temperature is increased to 50℃, 60℃ and 70℃, the degradation rate of naphthalene gradually increases to 60.5%, 66.7% and 85.9%. As the temperature increases, the energy consumption also increases successively. When the temperature rises from 40℃ to 50℃, the degradation rate increases by 19%, from 50℃ to 60℃, the degradation rate increases by 6.2%, and from 60℃ to 70℃, the degradation rate increases by 19.2%.

[0086] Considering the repair effect and energy saving, the set temperature of 50℃ with the highest degradation rate and power consumption ratio is selected as the optimal set temperature of the heat medium. The optimal set temperature is fed back to the controller and the heat medium temperature is adjusted to 50℃. 设定1 , T 设定2 , T 设定3 Set to 50℃, and correspondingly increase the pressure setting value in the multiphase extraction pipeline to ensure that the agent remains in liquid state and circulates in the system. Feedback 50℃ to the control system, readjust the set temperature of the heating system, and ensure that the pollutant degradation rate is within the set range of the degradation rate. If the pollutant degradation rate is lower than the set range of the degradation rate, the oxidation reaction rate of the repair agent and the pollutant is reduced, and the temperature of the heat medium is not enough to meet the reaction conditions. In this case, it is necessary to increase the set temperature of the heat medium so that the pollutant degradation rate is within the set range of the degradation rate.

[0087] When F = F 设定 , it indicates that the pipeline in the multiphase extraction meets the negative pressure condition, and the vacuum pump continues to operate. Promote the oxidation reaction between the repair agent and the pollutant. The detection device at the extraction well continuously monitors and collects the concentration of the pollutant. When the degradation rate of the pollutant concentration decreases, the activation temperature of the repair agent is increased, the temperature setting value of the heating system is modified, and the heating is restarted. Start the gas-liquid separator, the eighth water pump 712, the air pump 715, the oil-water separator, the twentieth valve 713, the twenty-first valve 714, the twenty-second valve 716 and the twenty-third valve 717 to treat sewage, exhaust gas and collect hazardous waste.

[0088] Photoionization detectors (PID sensors) and rapid water quality detectors are installed at the inlet and outlet of the terminal treatment device to monitor the discharged liquid and gas and ensure that the discharge complies with the emission standards. If it does not meet the emission standards, the terminal treatment will be carried out again.

[0089] Example 2

[0090] As the instruction manual Figure 1 As shown, the present invention also provides a solar thermal activated oxidation remediation system for contaminated soil, which is used to complete the remediation method described in Example 1, and the system comprises:

[0091] A solar heating unit 1, used for heating a medium and storing a heat medium, the solar heating unit being connected to a heat medium heating pipe 2 inserted into the contaminated soil;

[0092] A dispensing unit 5, used for preparing and storing remediation agents, the dispensing unit is connected to a dosing pipe 6 inserted into the contaminated soil;

[0093] A multiphase extraction unit 7, wherein the multiphase extraction unit 7 is connected to a multiphase extraction pipeline 8 inserted into the contaminated soil;

[0094] The data acquisition unit includes a temperature detection device 3 and a pollutant detection device. The temperature detection device 3 is interlocked with the solar heating unit 1 to monitor the temperature of the contaminated soil and feedback interlock control the amount of heat medium introduced into the heat medium heating pipeline 2. The pollutant detection device is interlocked with the solar heating unit 1 and the dispensing unit 5 respectively to monitor the contamination of the contaminated soil and feedback interlock control the set temperature of the heat medium of the solar heating unit and the preparation parameters of the remediation agent of the dispensing unit.

[0095] The system further comprises a controller 4 .

[0096] The solar heating unit 1, the heat medium heating pipeline 2, the data acquisition unit, the dispensing unit 5, the dosing pipeline 6, the multiphase extraction unit 7, and the multiphase extraction pipeline 8 can be seen in detail in Example 1, and will not be repeated here.

[0097] Those skilled in the art will appreciate that the present invention can be implemented in many other specific forms without departing from the spirit and scope of the present invention. Although embodiments of the present invention have been described, it should be understood that the present invention should not be limited to this embodiment, and those skilled in the art can make changes and modifications within the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A method for remediating contaminated soil by solar thermal activated oxidation, characterized in that: The following steps are involved: Detect the contamination status of the contaminated soil, and determine the preparation parameters of the remediation agent and the set temperature of the heat medium used to heat the contaminated soil according to the contamination status; The heat medium heated by the solar heating unit is introduced into the contaminated soil, and the temperature of the contaminated soil is monitored in real time, and the amount of heat medium introduced is adjusted based on the feedback to maintain the internal temperature of the contaminated soil at the set temperature; The prepared remediation agent is introduced into the contaminated soil and subjected to multiphase extraction. During the remediation process, the contamination status of the contaminated soil is monitored in real time, and the remediation agent preparation parameters and / or the set temperature of the heat medium are adjusted based on the feedback.

2. The method for remediating contaminated soil by solar thermal activated oxidation according to claim 1, characterized in that: Real-time monitoring of the contamination of contaminated soil includes: According to the real-time monitoring results of the pollution situation, the concentration of the remediation agent introduced into the contaminated soil is adjusted. When it is detected that the pollutant degradation rate is less than the set range of the pollutant degradation rate over a period of time, the set temperature of the heat medium introduced into the contaminated soil is increased.

3. The method for remediating contaminated soil by solar thermal activated oxidation according to claim 1, characterized in that: The set temperature of the heat medium includes the initial set temperature of the heat medium. The determination of the initial set temperature of the heat medium specifically includes: Detect the type and concentration of pollutants in the contaminated soil, and determine the type and concentration of the remediation agent used to repair the contaminated soil and the initial set temperature of the heat medium used to activate the remediation agent based on the detection results.

4. The method for remediating contaminated soil by solar thermal activated oxidation according to claim 1, characterized in that: The set temperature of the heat medium also includes the optimal set temperature of the heat medium. The determination of the optimal set temperature of the heat medium specifically includes: The set temperature of the heat medium is adjusted at regular intervals, and the pollution data of the contaminated soil at the corresponding set temperature is collected. The degradation rate, energy consumption and the ratio of the degradation rate to the energy consumption of the pollutants are obtained through multiple sets of pollution data. The set temperature of the heat medium corresponding to the largest ratio is selected as the optimal set temperature, and the temperature of the heat medium passing into the contaminated soil is adjusted to the optimal set temperature.

5. The method for remediating contaminated soil by solar thermal activated oxidation according to claim 1, characterized in that: If the contaminated soil temperature is less than the set temperature of the heat medium, the solar heating unit supplies the heat medium to the contaminated soil until the contaminated soil temperature is not less than the set temperature of the heat medium; if the contaminated soil temperature is greater than or equal to the set temperature of the heat medium, the solar heating unit stops supplying the heat medium to the contaminated soil, and the heat medium is stored and kept warm in the solar heating unit.

6. The method for remediating contaminated soil by solar thermal activated oxidation according to claim 5, characterized in that: The solar heating unit includes a solar heating component and a storage component for storing heat medium, and the storage component is connected to the solar heating component; if the heating temperature of the solar heating component is ≥ the set temperature of the heat medium, the heat medium heated to the set temperature is sent to the storage component for storage and standby; if the heating temperature of the solar heating component is < the set temperature of the heat medium, the heat medium in the storage component is heated to the set temperature.

7. The method for remediating contaminated soil by solar thermal activated oxidation according to claim 1, characterized in that: If it is detected that the pollutant concentration of the contaminated soil is greater than the pollutant concentration control value, the prepared remediation agent will be sent to the contaminated soil to undergo an oxidation reaction with the pollutants in the soil; if it is detected that the pollutant concentration of the contaminated soil is less than or equal to the pollutant concentration control value, the introduction of the remediation agent into the contaminated soil and the introduction of the heat medium into the contaminated soil will be stopped.

8. The method for remediating contaminated soil by solar thermal activated oxidation according to claim 1, characterized in that: If the multiphase extraction pressure of the contaminated soil is less than the pressure setting value, the multiphase extraction pressure is adjusted until the multiphase extraction pressure is greater than or equal to the pressure setting value, and the multiphase extraction is continued for a period of time.

9. The method for remediating contaminated soil by solar thermal activated oxidation according to claim 1, characterized in that: The waste gas and wastewater collected by the multiphase extraction of the contaminated soil are purified and discharged after purification.

10. A solar thermal activated oxidation remediation system for contaminated soil, characterized in that: include: A solar heating unit for heating the medium and storing the heat medium, the solar heating unit being connected to a heat medium heating pipe inserted into the contaminated soil; A dispensing unit, used for preparing and storing remediation agents, wherein the dispensing unit is connected to a dosing pipe inserted into the contaminated soil; A multiphase extraction unit, wherein the multiphase extraction unit is connected to a multiphase extraction pipeline inserted into the contaminated soil; The data acquisition unit includes a temperature detection device and a pollutant detection device. The temperature detection device is interlocked with the solar heating unit to monitor the temperature of the contaminated soil and feedback interlock control the amount of heat medium introduced into the heat medium heating pipeline. The pollutant detection device is interlocked with the solar heating unit and the dispensing unit respectively to monitor the contamination of the contaminated soil and feedback interlock control the set temperature of the heat medium of the solar heating unit and the preparation parameters of the remediation agent of the dispensing unit.

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