An in-situ removal and resource utilization method for high-concentration 1,2-dichloroethane in deep low-permeability medium

Abstract

The present application relates to the field of environmental remediation technology, specifically, a method for in-situ removal and resource utilization of high-concentration 1,2-dichloroethane in deep low-permeability medium. The present application alternately performs asymmetric microcirculation of air pumping-pressure stabilizing-gas injection in the remediation well penetrating the vadose zone and aquifer, uses micro-negative pressure to strip pollutants in large pores, and provides desorption relaxation time through pressure stabilization. The modular adsorption unit in the well uses a 2-15mm radial gap and a liquid guide apron to build a low-resistance airflow preferential channel, prevent liquid phase plugging, and achieve in-situ efficient adsorption. After adsorption saturation, the unit is taken out and placed in a closed reactor for closed-loop thermal nitrogen desorption. The desorbed gas is condensed, separated, and rectified to recover high-purity 1,2-dichloroethane liquid product. The present application breaks through the mass transfer bottleneck and realizes complete remediation and economic resource utilization of deep pollution.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation technology, and more specifically, to a method for in-situ removal and resource recovery of high concentrations of 1,2-dichloroethane in deep, low-permeability media. Background Technology

[0002] 1,2-Dichloroethane is an important chemical raw material and industrial solvent, possessing high toxicity and readily undergoing phase partitioning and migration in deep underground environments. When it leaks during production, storage, or transportation and enters low-permeability media (typically with a permeability coefficient below 10⁻⁶ cm / s), such as clay and silty clay, it can easily form a deep, complex pollution source penetrating both the vadose zone (soil) and the saturation zone (groundwater). Due to the small pore size and extremely high capillary resistance of these media, the pollutants persist for a long time, and conventional fluid mass transfer is exceptionally difficult.

[0003] Currently, existing technologies for addressing the aforementioned deep and complex pollution mainly rely on in-situ chemical oxidation, conventional soil vapor extraction, or groundwater extraction. However, these technologies have revealed significant inherent limitations in practical engineering applications: First, in-situ chemical oxidation technology faces a severe bottleneck in reagent mass transfer in low-permeability formations. Oxidants struggle to effectively penetrate and distribute evenly into micropores, easily leading to fingering effects and short-circuit flows along macropores, resulting in large remediation blind zones and incomplete degradation. Simultaneously, this method undermines the resource recovery value of high-concentration 1,2-dichloroethane and easily triggers secondary environmental risks such as alterations in the physicochemical properties of groundwater.

[0004] Secondly, conventional soil vapor extraction and groundwater extraction treatments rely on a single steady-state negative pressure or pump suction. In low-permeability environments where deep gas and water coexist, continuous strong negative pressure can easily cause soil dehydration and cracking, as well as pore water phase blockage (water-locking effect), leading to rapid paralysis of gas-phase mass transfer channels. Furthermore, the desorption rate of pollutants in low-permeability media is much lower than the steady-state extraction rate, and long-term operation will produce severe extraction concentration tailing and rebound phenomena, resulting in extremely high energy consumption.

[0005] Furthermore, technologies related to ex-situ thermal desorption of soil and tail gas distillation recovery after excavation are not directly applicable to in-situ deep remediation scenarios due to the enormous amount of deep media excavation work, high foundation pit support costs, and the inability to simultaneously address groundwater pollution. While some publicly available in-situ groundwater adsorption well structures do not require excavation, they rely solely on the natural concentration gradient diffusion of pollutants, resulting in an effective radiation mass transfer radius of less than 0.5 meters in low-permeability soil layers, thus lacking practical engineering remediation significance.

[0006] In summary, the existing research and development logic generally severs the intrinsic connection between in-situ multiphase flow field control, gas-liquid interface mass transfer breakthroughs, and ex-situ high-purity recovery, treating deep media remediation merely as a mechanical superposition of single-dimensional extraction, degradation, or static adsorption. In fact, the contradiction in pollutant removal from low-permeability media lies in the fact that inherently high capillary resistance limits gas-liquid phase mass transfer under conventional extraction conditions, while blindly increasing the extraction intensity inevitably leads to water-locking effects and paralysis of mass transfer channels, ultimately resulting in extremely low concentrations of the extracted mixture, completely eliminating the technical and economic feasibility of subsequent distillation recovery. Summary of the Invention

[0007] The purpose of this invention is to provide an in-situ removal and resource recovery method for high concentrations of 1,2-dichloroethane in deep, low-permeability media, in order to solve the problems mentioned in the background art, such as difficulty in in-situ mass transfer, easy generation of water-locking effect, and high energy consumption for high-purity recovery.

[0008] To achieve the above objectives, this invention provides an in-situ removal and resource recovery method for high concentrations of 1,2-dichloroethane in deep, low-permeability media, comprising the following steps: S1. In-situ well construction: Deploying remediation wells that penetrate the vadose zone and aquifer in the contaminated area; S2. Asymmetric microcirculation mass transfer: The microcirculation operation of pumping, stabilizing and injecting gas is alternately performed in the repair well. 1,2-dichloroethane in the large pores is stripped by micro-negative pressure and introduced into the repair well. Then, pumping and injection are stopped to maintain load and stabilize pressure. Finally, micro-positive pressure gas injection is performed to disturb the aquifer. S3, In-situ channel adsorption: During the execution of S2, the modular adsorption unit placed in the repair well is used to perform in-situ adsorption and enrichment of gaseous 1,2-dichloroethane through the preferential airflow channel constructed inside it. S4. Ex-situ desorption and resource recovery: The saturated modular adsorption unit is removed and placed in a closed reactor for hot nitrogen purging desorption. The desorbed mixed gas is then purified by condensation and gas-liquid separation, and liquid 1,2-dichloroethane is recovered.

[0009] Furthermore, the specific timing sequence of the micro-circulation of air extraction-pressure stabilization-injection in S2 is as follows: Each micro-circulation cycle lasts 4 to 24 hours; the pulsed gas extraction stage lasts 5 to 30 minutes, with the negative pressure inside the well controlled at -0.5 kPa to -5 kPa; then it enters the pressure stabilization and static stage; the micro-positive pressure gas injection stage is performed after the pressure stabilization stage, with the gas injection pressure being 0.01 to 0.05 MPa higher than the hydrostatic pressure of the aquifer.

[0010] Furthermore, the duration of the pressure stabilization and settling stage is determined based on the desorption relaxation time of 1,2-dichloroethane in the low-permeability medium as it diffuses from micropores to macropores; the micro-negative pressure of -0.5 kPa to -5 kPa is used to overcome the capillary resistance of pore water in the low-permeability medium while suppressing the generation of short-circuit flow in the soil microcracks.

[0011] Furthermore, in step S4, the temperature of hot nitrogen purging and desorption is controlled at 80~130℃; during the distillation purification process, the top temperature of the distillation column is controlled at 83~87℃.

[0012] Furthermore, in step S4, the low-temperature nitrogen gas generated after condensation and gas-liquid separation is heated and then circulated back into the closed reactor for hot nitrogen purging.

[0013] The present invention also provides a repair system for implementing the above method, comprising: The remediation well penetrates the vadose zone and aquifer of the contaminated site; An external gas injection device is connected to the repair well via a pipeline and is equipped with an automatic control program for performing asymmetric microcirculation operations; The modular adsorption unit is detachably suspended inside the repair well, and its interior is equipped with a gas-liquid two-phase adaptive flow guiding structure. The off-site resource recovery equipment includes a closed desorption reactor, a condensation separation unit, and a distillation column connected in sequence by pipelines.

[0014] Furthermore, the modular adsorption unit includes a central guide tube that is a cylindrical hollow tube, an adsorption material layer that is cylindrically wrapped around the outer peripheral wall of the central guide tube, and a cylindrical protective net cage with an inner diameter larger than the outer diameter of the adsorption material layer. The sidewall of the central guide tube has through holes; the protective mesh cage and the adsorption material layer are coaxially nested, and an annular columnar cavity is formed between them as a radial gap. The radial cross-sectional width of the radial gap is maintained equally between 2 and 15 mm to form a priority channel for the passage of micro-negative pressure airflow.

[0015] Furthermore, the gas-liquid two-phase adaptive flow guiding structure includes: The portion of the protective net cage below the aquifer elevation is a non-porous blind pipe section or a low-porosity section, while the portion above the vadose zone elevation is a high-porosity section. A funnel-shaped annular interceptor plate serves as a liquid-guiding skirt at the bottom of the radial gap. The upper edge of this annular interceptor plate is sealed and fixedly connected to the inner wall of the protective net cage in the area below the aquifer elevation. The lower edge of this annular interceptor plate extends downwards and inclines towards the central axis of the central guide pipe, forming an inverted frustum-shaped water-blocking structure, and this lower edge does not contact the adsorbent material layer.

[0016] Furthermore, the adsorbent material layer is made of hydrophobic and oleophilic polypropylene fiber or polyurethane foam; the repair well outer pipe and central guide pipe are made of PVC or stainless steel.

[0017] Furthermore, the top of the condensation separation component is provided with a non-condensable gas exhaust port, which is connected to the gas inlet of the heater through a gas pipeline containing an induced draft fan; the gas outlet of the heater is connected to the nitrogen gas inlet at the bottom of the sealed desorption reactor through an insulated pipeline, forming a closed carrier gas circulation loop.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This in-situ removal and resource recovery method for high concentrations of 1,2-dichloroethane in deep, low-permeability media utilizes a sequence of pulsed pumping, desorption and load maintenance, and micro-pressure disturbance to provide sufficient relaxation equilibrium time for the desorption and diffusion of 1,2-dichloroethane in deep pores, eliminating local concentration depletion zones. Simultaneously, the precisely defined critical micro-negative pressure of -0.5 kPa to -5 kPa precisely disrupts the surface tension balance at the gas / liquid interface without inducing soil cracks, achieving efficient stripping of pollutants in the form of a micro-airflow continuum. This significantly increases the concentration extracted in a single extraction and reduces ineffective energy consumption.

[0019] Secondly, addressing the challenge of adsorbent material failure caused by deep gas-liquid coexistence environments, this invention constructs a macroscopic hydraulic priority channel within the wellbore by combining a 2-15mm radial gap with an inverted frustum-shaped fluid-guiding skirt at the bottom. This structure utilizes the Hagen-Poiseuille law to create local flow resistance differences, forcing the gas flow to precisely scour the adsorbent layer surface, forming a tangential shear flow. Simultaneously, the liquid water carried in the gas flow is effectively isolated and flows back under the interception effect of gravity and the fluid-guiding skirt, mechanically preventing the possibility of free water forming a liquid film and blocking the adsorbent layer surface.

[0020] Furthermore, this invention forms a closed loop by combining in-situ high-concentration enrichment with ex-situ desorption distillation. The low-temperature nitrogen separated at the condensation end is reheated and directly refluxed to the desorption reactor as purge gas, thus constituting a self-feedback circulation system of gas-thermal pathway. This integrated architecture not only avoids the hidden dangers of fugitive emissions of volatile toxic gases but also reduces the carrier gas consumption and heat loss in ex-situ thermal desorption, thereby making the in-situ remediation of volatile organic compounds in low-permeability media highly practical in engineering and economically beneficial. Attached Figure Description

[0021] Figure 1 This is an overall flowchart of an embodiment of the present invention; Figure 2 This is a flowchart illustrating the steps of asymmetric microcirculation mass transfer in an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: This embodiment of the invention provides an in-situ removal and resource recovery method and system for high concentrations of 1,2-dichloroethane in deep, low-permeability media. The remediation system in this embodiment mainly consists of four parts: a remediation well, an external gas injection / extraction device, a modular adsorption unit, and an ex-situ resource recovery device.

[0024] Repair the system: The modular adsorption unit centers on a cylindrical hollow tube, known as the central guide tube. Multiple through-holes are evenly distributed along the tube wall, and the tube is made of standard-diameter PVC or stainless steel. A hydrophobic and oleophilic adsorption material layer, made of polypropylene fiber or polyurethane foam, is tightly wrapped around the outer periphery of the central guide tube. A cylindrical protective mesh cage is positioned at the outermost edge of the adsorption material layer, with the inner diameter of the cage strictly larger than the outer diameter of the adsorption material layer.

[0025] The protective mesh cage and the internal absorbent material layer are coaxially nested. Due to the difference in their radial dimensions, they form an annular cylindrical cavity inside, which is the radial gap. The radial cross-sectional width of the radial gap is uniformly maintained between 2 and 15 mm.

[0026] The protective mesh cage is divided into two axial sections: the section below the aquifer elevation is designated as a non-porous blind pipe section or a low-porosity section, while the section above the vadose zone elevation is designated as a high-porosity section. At the bottom of the radial gap, corresponding to the groundwater fluctuation zone, a funnel-shaped annular interceptor plate serves as a liquid-guiding skirt. The upper edge of the annular interceptor plate is fully sealed and fixed to the inner wall of the protective mesh cage in the area below the aquifer elevation; the lower edge of the annular interceptor plate extends downwards towards the central axis of the central guide pipe, forming an inverted frustum-shaped water-blocking structure within the radial gap. As the lower edge of the liquid-guiding skirt extends inwards, it does not physically contact the outer surface of the adsorbent material layer, leaving a narrow annular slit between them for airflow to penetrate from bottom to top.

[0027] The ex-situ resource recovery equipment consists of a closed desorption reactor, a condensation separation unit, and a distillation column connected sequentially by pipelines. The condensation separation unit includes an induced draft fan, a condenser, and a gas-liquid separator. The exhaust port of the induced draft fan at the top of the condensation separation unit is connected to the inlet of an independent heater via an insulated pipeline. The outlet of the heater is connected to the inlet at the bottom of the closed desorption reactor, thus creating a closed nitrogen circulation loop outside the system.

[0028] Using the above-mentioned repair system, according to Figure 1 As shown, the in-situ removal and resource recovery method for 1,2-dichloroethane in this embodiment specifically includes the following steps: S1. In-situ well construction: In the low-permeability contaminated area confirmed by exploration, a remediation well is drilled vertically through the vadose zone and into the aquifer. The aforementioned modular adsorption unit is suspended inside the remediation well.

[0029] S2. Asymmetric Micro-circulation Mass Transfer: Through a PLC control program of an external gas extraction and injection device, alternating gas extraction-pressure stabilization-injection micro-circulation is performed within the repair well. The complete micro-circulation cycle is set to 4-24 hours, depending on... Figure 2 As shown, it includes: (1) Pulse pumping stage: lasts 5 to 30 minutes. Start the vacuum pump and precisely control the negative pressure in the repair well within the range of -0.5 kPa to -5 kPa. The slight negative pressure in this range breaks the surface tension balance of the gas-liquid interface, causing the 1,2-dichloroethane stored in the large pores to be forcibly stripped into the repair well in the form of a micro-flow continuous flow, without damaging the original soil skeleton.

[0030] (2) Stabilization and settling stage: Stop pumping and injecting gas. This stage provides desorption relaxation time for 1,2-dichloroethane in the deep micropores to diffuse into the macropores, ensuring the pumping concentration for the next pumping cycle.

[0031] (3) Micro-positive pressure gas injection stage: This is performed at the end of the cycle, injecting gas with a pressure 0.01~0.05 MPa higher than the hydrostatic pressure into the aquifer. The micro-positive pressure disturbs the surrounding groundwater, breaks the liquid film stagnant layer at the interface between water and pollutants, and promotes the accelerated volatilization and escape of dissolved 1,2-dichloroethane into the gas phase space.

[0032] S3. In-situ channel adsorption and prevention of liquid phase blockage: Driven by the directional pressure gradient induced by S2, the chlorinated organic gas flow enters the remediation well. After passing through the protective mesh cage, the gas flow enters a radial gap of 2-15 mm. The hydraulic diameter of the radial gap is much larger than the capillary pore size inside the adsorbent material, forming a preferential channel with extremely low resistance. The negative pressure gas flow preferentially sweeps across the preferential channel at high speed, forming a tangential shear flow on the surface of the adsorbent material layer. The groundwater or condensate droplets accompanying the gas flow fall back to the bottom of the remediation well along the funnel wall under the physical interception effect of gravity and the inverted frustum-shaped liquid-guiding skirt, avoiding the water-locking effect.

[0033] S4. Ex-situ Closed-Loop Desorption and Resource Utilization: After the modular adsorption unit approaches saturation, it is lifted out of the repair well and transferred in a sealed manner to the ex-situ resource utilization equipment. In the sealed desorption reactor, high-temperature nitrogen gas at 80-130℃ is introduced for bottom-up purging desorption. The mixed tail gas containing a high concentration of 1,2-dichloroethane enters the condensation separation component. The condensed liquid mixture is fed into a distillation column, where the top temperature is controlled at 83-87℃ for distillation purification. High-purity 1,2-dichloroethane liquid product is recovered by condensation. The non-condensable gas generated during gas-liquid separation is extracted by an induced draft fan and directly enters the heater to be reheated to 80-130℃ before flowing back to the sealed desorption reactor for the next round of purging, forming a bidirectional internal circulation of material and heat flow.

[0034] Comparative Example 1: Using existing technology, continuous negative pressure extraction was performed, applying a continuous negative pressure greater than -10 kPa. Initially, the extracted concentration showed a brief peak, but the high negative pressure rapidly triggered localized drying and dehydration of the low-permeability soil layer, creating interconnected micro-cracks. Airflow formed short-circuit channels along these micro-cracks, allowing a large amount of clean air to be drawn into the repair well, resulting in a sharp drop in the extracted concentration of 1,2-dichloroethane. Due to the lack of a pressure stabilization period, contaminants in the deep pores could not be effectively released.

[0035] Comparative Example 2: The modular adsorption unit configuration was modified so that the adsorption material layer directly filled the entire cross-section of the repair well, i.e., there were no radial gaps or fluid-guiding skirts inside. In the deep gas-water complex environment, the tiny pore water or condensate generated by the cooling of the gas flow was rapidly adsorbed by the capillary force on the surface of the adsorption material, forming a dense, continuous liquid film coating layer. The system's gas phase flow resistance increased sharply, and the adsorption material inside and on the leeward side completely lost its adsorption capacity, resulting in water-lock failure.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for in-situ removal and resource recovery of high concentrations of 1,2-dichloroethane in deep, low-permeability media, characterized in that, Includes the following steps: S1. In-situ well construction: Drilling a remediation well that vertically penetrates the vadose zone and extends into the aquifer in the contaminated area, and suspending a modular adsorption unit inside the remediation well; S2, Asymmetric microcirculation mass transfer: The microcirculation of pumping, stabilizing, and injecting gas is alternately performed in the repair well by an external gas pumping and injection device; S3, In-situ channel adsorption: During the execution of S2, under the drive of the directional pressure gradient, the chlorine-containing organic gas flow enters the repair well. The gas flow enters the radial gap inside the modular adsorption unit and performs in-situ adsorption and enrichment of gaseous 1,2-dichloroethane through the preferential channel formed by the radial gap. S4. Ex-situ closed-loop desorption and resource recovery: The modular adsorption unit, which is approaching saturation, is lifted out of the repair well and transferred in a sealed manner to the ex-situ resource recovery equipment. High-temperature nitrogen gas is introduced into the sealed desorption reactor for purging and desorption. The mixed tail gas containing a high concentration of 1,2-dichloroethane enters the condensation separation component. The condensed liquid mixture is fed into the distillation column for distillation and purification. High-purity 1,2-dichloroethane liquid product is recovered by condensation.

2. The method for in-situ removal and resource recovery of high concentrations of 1,2-dichloroethane in deep, low-permeability media according to claim 1, characterized in that, The complete cycle of the micro-circulation of air extraction-pressure stabilization-injection in S2 is set to 4~24 hours, specifically including: Pulse evacuation phase: lasts 5 to 30 minutes, controlling the negative pressure in the repair well within the range of -0.5 kPa to -5 kPa; Pressure stabilization and settling stage: Stop pumping and injecting gas; Micro-positive pressure gas injection stage: This stage is performed at the end of the cycle, injecting gas with a pressure 0.01~0.05 MPa higher than the hydrostatic pressure into the aquifer section.

3. The method for in-situ removal and resource recovery of high concentrations of 1,2-dichloroethane in deep, low-permeability media according to claim 2, characterized in that, The duration of the pressure stabilization and settling phase is set according to the desorption relaxation time of 1,2-dichloroethane in a low-permeability medium as it diffuses from micropores to macropores; the micro-negative pressure of the pulse pumping phase is controlled within a threshold that does not damage the original soil skeleton.

4. The method for in-situ removal and resource recovery of high concentrations of 1,2-dichloroethane in deep, low-permeability media according to claim 1, characterized in that, In step S3, the modular adsorption unit is equipped with a liquid-guiding skirt inside, and the liquid-guiding skirt forms a radial gap with the protective mesh cage inside the modular adsorption unit; the negative pressure airflow preferentially sweeps across the preferential channel formed by the radial gap, forming a tangential shear flow on the surface of the adsorption material; the groundwater or condensate droplets that flow in with the airflow fall back to the bottom of the repair well along the liquid-guiding skirt under the interception effect of gravity and the liquid-guiding skirt.

5. The method for in-situ removal and resource recovery of high concentrations of 1,2-dichloroethane in deep, low-permeability media according to claim 1, characterized in that, In step S4, the high-temperature nitrogen gas introduced into the closed desorption reactor is at a temperature of 80~130℃; the top temperature of the distillation column is controlled at 83~87℃; the non-condensable gas generated by the gas-liquid separation of the condensation separation component is extracted by an induced draft fan, directly enters the heater to be reheated to 80~130℃, and then flows back to the closed desorption reactor for the next round of purging.

6. A remediation system for implementing the in-situ removal and resource recovery method for high concentrations of 1,2-dichloroethane in deep, low-permeability media as described in any one of claims 1-5, characterized in that, include: The remediation well vertically penetrates the vadose zone of the contaminated area and extends into the aquifer; An external gas injection device is connected to the repair well via a pipeline and is equipped with a PLC control program that performs asymmetric micro-circulation mass transfer. Modular adsorption units are suspended inside the repair well; The off-site resource recovery equipment consists of a closed desorption reactor, a condensation separation component, and a distillation column connected in sequence by pipelines.

7. The repair system according to claim 6, characterized in that, The modular adsorption unit has a central guide tube at its center, which is a cylindrical hollow tube. The tube wall of the central guide tube has multiple through holes evenly distributed. The outer peripheral wall of the central guide tube is tightly covered with a hydrophobic and oleophilic adsorption material layer in a cylindrical shape. A cylindrical protective net cage with an inner diameter larger than the outer diameter of the adsorption material layer is provided on the outermost side of the adsorption material layer. The protective net cage and the inner adsorption material layer are coaxially nested, and the annular columnar cavity formed between them is a radial gap. The radial cross-sectional width of the radial gap is evenly maintained between 2 and 15 mm.

8. The repair system according to claim 7, characterized in that, The portion of the protective net cage below the aquifer elevation is a non-porous blind pipe section or a low-porosity section, while the portion above the vadose zone elevation is a high-porosity section. A funnel-shaped annular interceptor plate serves as a liquid-guiding skirt at the bottom of the radial gap. The upper edge of the annular interceptor plate is fully sealed and fixed to the inner wall of the protective net cage in the area below the aquifer elevation. The lower edge of the annular interceptor plate extends downwards towards the central axis of the central guide pipe, forming an inverted frustum-shaped water-blocking structure within the radial gap. The lower edge does not physically contact the outer surface of the adsorbent material layer, retaining a narrow annular slit for airflow to penetrate from bottom to top.

9. The repair system according to claim 7, characterized in that, The adsorption material layer is made of polypropylene fiber or polyurethane foam; the central guide tube is made of PVC or stainless steel.

10. The repair system according to claim 6, characterized in that, The condensation separation assembly includes an induced draft fan, a condenser, and a gas-liquid separator. The exhaust port of the induced draft fan at the top of the condensation separation assembly is connected to the inlet of an independent heater through an insulated pipe. The outlet of the heater is connected to the inlet at the bottom of the sealed desorption reactor to create a closed nitrogen circulation loop outside the system.

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