Coal gas desorption and diffusion device capable of applying overburden pressure and experimental method

Abstract

The invention discloses a coal gas desorption and diffusion device capable of applying overburden pressure and an experimental method.The coal gas desorption and diffusion device comprises a coal sample tank, a steel pipe of an upper cavity of the coal sample tank is connected with a pressure pump, the pressure pump is connected with a hydraulic oil tank, and a gas outlet pipe and a gas conveying pipe are installed on the left side of a lower cavity of the coal sample tank; the gas delivery pipe is communicated with a pressure reduction tank, the pressure reduction tank is communicated with a high-pressure gas cylinder, the right side of the lower cavity of the coal sample tank is connected with a pressure sensor, and the pressure sensor is connected with an overburden pressure display screen in the data control and monitoring unit; and the data control and monitoring unit is connected with the computer. According to the coal gas desorption and diffusion device capable of applying overburden pressure and the experimental method, the gas diffusion coefficients of microscopic coal powder with different pore sizes and large-size raw coal test pieces can be tested, and the influence of different external unconventional pressure environments on the gas desorption behavior can be analyzed.

Description

Technical Field

[0001] The present invention relates to the technical field of mine safety and environmental engineering, and in particular to a pressurizable coal gas desorption and diffusion device and an experimental method. Background Art

[0002] Coalbed methane (CBM) travels from the reservoir interior to the outside world through three stages: desorption from the inner surface, diffusion within pores, and seepage within fractures. Diffusion takes the longest time of the entire process, and the duration of this stage significantly determines the CBM production rate. Therefore, in-depth research into the diffusion and migration patterns of coal reservoir gas and the multi-factor influencing mechanisms will help address current challenges in CBM extraction in my country, particularly in deep coal seams, such as poor permeability and unstable extraction rates, and improve the efficiency of CBM extraction and utilization.

[0003] At present, the depth of coalbed methane extraction in my country is constantly expanding. The physical properties of coal reservoirs and the migration status of coalbed methane are significantly affected by changes in geothermal and geostress fields. The coupling of temperature and pressure can not only affect the gas movement state, but also affect the physical and structural characteristics of coal seams and thus change the gas diffusion path, resulting in differentiated sensitivity of coal body structure and gas migration status. Therefore, clarifying the mechanism of the influence of temperature and pressure changes on gas diffusion characteristics is crucial for studying the gas transport phenomenon and its dynamic process in coal reservoirs.

[0004] Currently, existing research methods (CN113281234A, CN107063934A, and CN112903519A) primarily measure the gas desorption and diffusion of pulverized coal of varying particle sizes in a stress-free state in the laboratory. This method primarily investigates the desorption and diffusion of coal around the decompression borehole. However, outside the influence of the decompression borehole, coal gas desorption and diffusion are affected by geostress, leading to large errors in the coal desorption rate and diffusion coefficient tests. Consequently, this method fails to provide sufficient scientific reference for the gas adsorption-desorption-diffusion mechanism in undecompression zones. In undecompression zones, some devices proposed by relevant scholars (CN116519545A and CN114689480A) primarily apply effective stress through a confining pressure control system and are only applicable to raw coal specimens. However, in deep coal seams, overburden pressure plays a dominant role in gas migration. Therefore, it is necessary to investigate the diffusion characteristics of gas in raw coal / pulverized coal particles under the influence of overburden pressure and temperature. Summary of the Invention

[0005] The purpose of the present invention is to provide a coal gas desorption and diffusion device and experimental method that can be over-pressurized, which can test the gas diffusion coefficient of coal powder with different microscopic pore scales and larger-scale raw coal specimens, analyze the influence of different external unconventional pressure environments on gas desorption behavior, and more clearly understand and grasp the actual gas desorption and migration laws under certain specific conditions in underground coal seams, thereby enriching the means of investigating gas desorption and diffusion characteristics.

[0006] To achieve the above-mentioned purpose, the present invention provides a coal gas desorption and diffusion device that can be pressurized, including a coal sample tank, a steel pipe in the upper chamber of the coal sample tank is connected to a pressure pump, the pressure pump is connected to a hydraulic oil tank, an air outlet pipe and an air supply pipe are installed on the left side of the lower chamber of the coal sample tank, the air outlet pipe is connected to a vacuum tank line system, the vacuum tank line system is connected to the vacuum pump, the air supply pipe is connected to a pressure reducing tank, the pressure reducing tank is connected to a high-pressure gas cylinder, a pressure sensor is connected to the right side of the lower chamber of the coal sample tank, the pressure sensor is connected to the pressure display screen in the data control and monitoring unit, the data control and monitoring unit is connected to a computer, and a constant temperature water tank is fixedly connected below the coal sample tank.

[0007] Preferably, a coal sample tank cover is installed on the top of the coal sample tank, and the coal sample tank cover is equipped with sealing bolts and sealing nuts. A pressure piston is provided inside the coal sample tank, and the pressure piston is located in the middle of the coal sample tank and transitionally matched with the tank wall. A sealing ring is installed on the side of the pressure piston.

[0008] Preferably, the data control and monitoring unit is equipped with a gas flow meter, a water bath temperature display screen, a pressure display screen, an instantaneous flow display screen, a cumulative flow display screen, a water bath temperature control unit and a temperature control and monitoring system. The right side of the gas flow meter is connected to the instantaneous flow display screen and the cumulative flow display screen, and the left side of the gas flow meter is connected to the right side of the lower cavity of the coal sample tank.

[0009] Preferably, a pressure gauge is installed on the gas pipeline between the high-pressure gas cylinder and the pressure reducing tank, and a gas injection pipeline valve is installed on the gas pipeline between the pressure reducing tank and the coal sample tank.

[0010] Preferably, an oil filling valve is installed between the coal sample tank and the pressure pump, the hydraulic oil tank and the coal sample tank are connected through an oil outlet pipe, and an oil outlet valve is installed on the oil outlet pipe.

[0011] Preferably, the right side of the constant temperature water tank is connected to the water bath temperature control unit and the water bath temperature display screen.

[0012] A pressurized coal gas desorption and diffusion experimental method, using the pressurized coal gas desorption and diffusion device described above, comprises the following steps:

[0013] S1. The raw coal sample is crushed by a pulverizer and the coal powder is dried in a drying oven to obtain a coal powder / raw coal specimen to be tested; the prepared coal powder particles are placed in the lower chamber of the tank body and the coal particles are ensured to have a uniform texture. A piston is installed at the top of the lower chamber of the tank body, and the tank cover is fixed with a sealing nut and a sealing screw to achieve a sealed tank body;

[0014] S2. Test the air tightness of the device: First, fill the coal sample tank with high-pressure gas, close all the valves of the coal sample tank and immerse it in water to observe whether bubbles are generated. If no bubbles appear after standing for 5 seconds, it means that the coal sample tank is airtight. Then connect the experimental device so that the high-pressure gas spreads throughout the device. Apply soapy water to all the joints of the experimental device and observe whether bubbles are generated. If there are no bubbles, it means that the device is airtight.

[0015] S3, overpressure loading: open the oil filling port valve, start the pressure pump to increase the pressure to the overpressure value specified in the experimental plan, and turn on the data control and monitoring unit to prepare for the next step of experimental data measurement;

[0016] S4. Vacuum degassing treatment: Connect the vacuum pump and the coal sample tank, open the vacuum pipeline valve; fill the water bath box with water to the top of the tank, set the water bath temperature, and immerse the coal sample tank in the constant temperature water tank; turn on the vacuum pump, and when the vacuum gauge shows 4Pa, close the vacuum pipeline valve and the vacuum pump in turn;

[0017] S5. High-pressure gas injection: Connect the degassed coal sample tank to the gas injection device, open the high-pressure gas cylinder valve, and allow the gas in the high-pressure gas cylinder to enter the pressure-reducing tank and the connecting pipe. When the pressure in the pressure-reducing tank is slightly higher than the preset adsorption equilibrium pressure, close the high-pressure gas cylinder valve and slowly open the gas injection pipeline valve to allow the gas in the pressure-reducing tank to enter the coal sample tank until the gas pressure in the coal sample tank is slightly higher than the set adsorption equilibrium pressure.

[0018] S6. Adsorption equilibrium: Set the water bath test temperature and immerse the coal sample tank in a constant temperature water tank for 10 hours to allow the coal sample to fully adsorb and the pressure to reach equilibrium. Read the actual equilibrium pressure.

[0019] S7. Gas desorption: Close the valve of the gas injection pipeline, open the gas flow meter first, and then open the gas outlet valve. After the internal pressure is relieved to zero, quickly connect the coal sample tank and the gas flow meter, and observe the gas flow meter reading. When the cumulative gas flow does not change for 10 consecutive minutes, the desorption is considered to be completed.

[0020] Therefore, the present invention adopts the above-mentioned coal gas desorption and diffusion device and experimental method that can be pressurized, and takes the coal gas desorption and diffusion experimental device as the basis. By applying pressure to the sample, the desorption and diffusion characteristics of the gas in the unpressurized area of the coal seam are measured, which effectively avoids the traditional method of only being able to investigate the coal sample in the pressure relief area. The pressure change of the sample tank is monitored in real time by the pressure sensor, and the flow rate and temperature and pressure changes in the adsorption and desorption process are automatically identified by the data control and monitoring unit. At the same time, the external environment pressure and temperature in the gas adsorption and desorption process can also be customized and controlled, which effectively avoids the problem of only being able to investigate the gas in the pressure relief situation. Desorption is carried out under certain conditions to meet the research on gas adsorption and desorption laws in multi-scale pressure environments; based on the data control and monitoring unit, the automation of the experimental process is improved, and the errors caused by human operation and recording are effectively avoided; the adsorption and desorption rate and cumulative adsorption and desorption amount of gas under certain specific pressures are measured, and the influence of different external unconventional pressure environments on gas desorption behavior is analyzed, so as to have a clearer understanding and grasp of the actual gas desorption and migration laws under certain specific conditions in underground coal seams, enrich the means of investigating gas desorption and diffusion characteristics, and provide a basis for formulating gas extraction and control measures and ensuring safe production in coal mines.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic structural diagram of a coal-gas desorption and diffusion device capable of applying pressure;

[0023] Figure 2 This is a schematic structural diagram of a coal sample tank of a coal gas desorption and diffusion device capable of adding pressure according to the present invention;

[0024] Figure 3 This is a top view of a coal sample tank of a coal gas desorption and diffusion device capable of adding pressure according to the present invention;

[0025] Figure 4 The invention discloses a cross-sectional view of the connection between a sealing screw and a sealing nut of a coal-gas desorption and diffusion device capable of applying pressure.

[0026] Reference numerals

[0027] 1. Coal sample tank; 2. Data control and monitoring unit; 3. Computer; 4. High-pressure gas cylinder; 5. Pressure reducing tank; 6. Vacuum pump; 7. Vacuum tank line system; 8. Hydraulic oil tank; 9. Pressure pump; 10. Constant temperature water tank; 11. Coal sample tank cover; 12. Sealing nut; 13. Sealing screw; 14. Pressure piston; 15. Sealing ring; 16. Pressure sensor; 21. Water bath temperature display; 22. Overpressure display; 23. Instantaneous flow display; 24. Accumulated flow display; 25. Water bath temperature control unit; 26. Gas flow meter; 31. Oil outlet valve; 32. Oil filling valve; 33. Gas injection pipeline valve; 34. Vacuum pipeline valve; 35. Gas outlet valve; 51. Pressure gauge. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0029] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0030] Example 1

[0031] like Figures 1 to 4 As shown, the present invention provides a coal gas desorption and diffusion device that can be pressurized, including a coal sample tank 1, which can be added with coal powder particles of different mesh sizes to obtain the diffusion coefficients of coal samples with different pore sizes under the action of temperature and pressure, and can also test the diffusion coefficients of gas in larger-scale raw coal specimens. A coal sample tank cover 11 is installed on the top of the coal sample tank 1, and the coal sample tank cover 11 is equipped with sealing bolts and sealing nuts 12. The sealing bolts installed on the coal sample tank cover 11 can ensure the sealing and safety of the coal sample tank 1. A pressure piston 14 is provided inside the coal sample tank 1. The pressure piston 14 is located in the middle of the coal sample tank 1 and transitionally matched with the tank wall. A sealing ring 15 is installed on the side of the pressure piston 14 to achieve the separation of the upper and lower cavities of the coal sample tank 1.

[0032] A pressure pump 9 is connected to a steel pipe in the upper chamber of coal sample tank 1. This pressure pump 9 is connected to a hydraulic oil tank 8. This pump pressurizes hydraulic oil into the upper chamber of coal sample tank 1, applying pressure to the raw coal specimen / coal dust particles. An oil inlet valve 32 is installed between coal sample tank 1 and pressure pump 9. The hydraulic oil tank 8 and coal sample tank 1 are connected via an oil outlet pipe, which is equipped with an oil outlet valve 31. These valves control the flow of oil, adjusting the hydraulic pressure within coal sample tank 1 to achieve the upward and downward movement of pressure piston 14.

[0033] An air outlet pipe and an air supply pipe are installed on the left side of the lower cavity of the coal sample tank 1. The air outlet pipe is connected to the vacuum tank line system 7, and the vacuum tank line system 7 is connected to the vacuum pump 6. The air supply pipe is connected to the pressure reducing tank 5, and the pressure reducing tank is connected to the high-pressure gas cylinder 4. A pressure gauge 51 is installed on the air supply pipe between the high-pressure gas cylinder 4 and the pressure reducing tank 5, and a gas injection pipeline valve 33 is installed on the air supply pipe between the pressure reducing tank 5 and the coal sample tank 1.

[0034] A pressure sensor 16 is connected to the right side of the lower chamber of the coal sample tank 1. The pressure sensor 16 is connected to the pressure display screen 22 in the data control and monitoring unit 2. The actual pressure value detected by the pressure sensor 16 can be quickly read through the pressure display screen 22. The data control and monitoring unit 2 is connected to the computer 3, and the user can access the data control and monitoring unit 2 remotely through the computer 3. A constant temperature water tank 10 is fixedly connected to the bottom of the coal sample tank 1. The right side of the constant temperature water tank 10 is connected to the water bath temperature control unit 25 and the water bath temperature display screen 21. The water bath temperature display screen 21 can obtain the temperature information of the water in the water tank in real time. The water bath temperature control unit 25 can adjust the water flow rate, heating or cooling position and other parameters according to the temperature data collected on the right side of the water tank, so as to make the water temperature in the water tank more uniform and avoid deviations in experimental results or product quality problems due to temperature differences.

[0035] The data control and monitoring unit 2 houses a gas flowmeter 26, a water bath temperature display 21, a pressure display 22, an instantaneous flow display 23, an accumulated flow display 24, a water bath temperature control unit 25, and a temperature control and monitoring system. These provide real-time control and monitoring of the external ambient pressure and the temperature of the constant-temperature water bath 10 during the gas adsorption and desorption process. The right side of the gas flowmeter 26 is connected to the instantaneous flow display 23 and the accumulated flow display 24, while the left side is connected to the right side of the lower chamber of the coal sample tank 1. The gas flowmeter 26 automatically monitors the instantaneous flow rate and flow rate changes of the gas during the desorption and diffusion process.

[0036] A pressurized coal gas desorption and diffusion experimental method, using the pressurized coal gas desorption and diffusion device described above, comprises the following steps:

[0037] S1. The raw coal sample is crushed by a pulverizer and the pulverized coal is dried in a drying oven to obtain a pulverized coal / raw coal specimen to be tested; the prepared pulverized coal particles are placed in the lower chamber of the tank body and the coal particles are ensured to have a uniform texture. A piston is installed at the top of the lower chamber of the tank body, and the tank cover is fixed with a sealing nut 12 and a sealing screw 13 to achieve a sealed tank body;

[0038] S2. Test the air tightness of the device: First, fill the coal sample tank 1 with high-pressure gas, close all valves of the coal sample tank 1 and immerse it in water, and observe whether bubbles are generated. If no bubbles appear after standing for 5 seconds, it means that the coal sample tank 1 is airtight. Then connect the experimental device so that the high-pressure gas spreads throughout the device. Apply soapy water to all joints of the experimental device and observe whether bubbles are generated. If there are no bubbles, it means that the device is airtight.

[0039] S3, overpressure loading: open the oil filling port valve 32, start the pressure pump 9 to increase the pressure to the overpressure value specified in the experimental plan, and turn on the data control and monitoring unit 2 to prepare for the next step of experimental data measurement;

[0040] S4. Vacuum degassing: Connect the vacuum pump 6 and the coal sample tank 1, and open the vacuum pipeline valve 34; fill the water bath with water to the top of the tank, set the water bath temperature, and immerse the coal sample tank 1 in the constant temperature water tank 10; turn on the vacuum pump 6, and when the vacuum gauge shows 4 Pa, close the vacuum pipeline valve 34 and the vacuum pump 6 in sequence;

[0041] S5. High-pressure gas injection: Connect the degassed coal sample tank 1 to the gas injection device, open the valve of the high-pressure gas cylinder 4, and allow the gas in the high-pressure gas cylinder 4 to enter the pressure-reducing tank 5 and the connecting pipe. When the pressure of the pressure-reducing tank 5 is slightly higher than the preset adsorption equilibrium pressure, close the valve of the high-pressure gas cylinder 4, and slowly open the valve 33 of the gas injection pipeline to allow the gas in the pressure-reducing tank 5 to enter the coal sample tank 1 until the gas pressure in the coal sample tank 1 is slightly higher than the preset adsorption equilibrium pressure;

[0042] S6. Adsorption equilibrium: Set the water bath test temperature, immerse the coal sample tank 1 in the constant temperature water tank 10, and keep it for 10 hours to allow the coal sample to be fully adsorbed and the pressure to reach equilibrium, and read the actual equilibrium pressure;

[0043] S7. Gas desorption: Close the gas injection pipeline valve 33, open the gas flow meter 26 first, and then open the gas outlet valve 35. After the internal pressure is relieved to zero, quickly connect the coal sample tank 1 and the gas flow meter 26, and observe the reading of the gas flow meter 26. When the cumulative gas flow does not change for 10 consecutive minutes, the desorption is considered to be completed.

[0044] Therefore, the present invention adopts the above-mentioned coal gas desorption and diffusion device and experimental method that can be over-pressurized, which can test the gas diffusion coefficient of coal powder with different microscopic pore scales and larger-scale raw coal specimens, analyze the influence of different external unconventional pressure environments on gas desorption behavior, and more clearly understand and grasp the actual gas desorption and migration laws under certain specific conditions in underground coal seams, enriching the means of investigating gas desorption and diffusion characteristics.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A coal-gas desorption and diffusion device capable of applying pressure, characterized in that: It includes a coal sample tank. The steel pipe in the upper chamber of the coal sample tank is connected to a pressure pump, which is connected to the hydraulic oil tank. An air outlet pipe and an air supply pipe are installed on the left side of the lower chamber of the coal sample tank. The air outlet pipe is connected to a vacuum tank road system, which is connected to the vacuum tank road system, and the air supply pipe is connected to a pressure reducing tank, which is connected to a high-pressure gas cylinder. A pressure sensor is connected to the right side of the lower chamber of the coal sample tank, and the pressure sensor is connected to the pressure display screen in the data control and monitoring unit. The data control and monitoring unit is connected to a computer. A constant temperature water tank is fixedly connected under the coal sample tank.

2. The pressurizable coal gas desorption and diffusion device according to claim 1, characterized in that: A coal sample tank cover is installed on the top of the coal sample tank, and the coal sample tank cover is equipped with sealing bolts and sealing nuts. A pressure piston is provided inside the coal sample tank. The pressure piston is located in the middle of the coal sample tank and transitions with the tank wall. A sealing ring is installed on the side of the pressure piston.

3. The pressurizable coal gas desorption and diffusion device according to claim 1, characterized in that: The data control and monitoring unit is equipped with a gas flow meter, a water bath temperature display screen, a pressure display screen, an instantaneous flow display screen, an accumulated flow display screen, a water bath temperature control unit and a temperature control and monitoring system. The right side of the gas flow meter is connected to the instantaneous flow display screen and the accumulated flow display screen, and the left side of the gas flow meter is connected to the right side of the lower cavity of the coal sample tank.

4. The pressurizable coal gas desorption and diffusion device according to claim 1, characterized in that: A pressure gauge is installed on the gas pipeline between the high-pressure gas cylinder and the pressure reducing tank, and a gas injection pipeline valve is installed on the gas pipeline between the pressure reducing tank and the coal sample tank.

5. The pressurizable coal gas desorption and diffusion device according to claim 1, characterized in that: An oil filling port valve is installed between the coal sample tank and the pressure pump. The hydraulic oil tank and the coal sample tank are connected through an oil outlet pipe, and an oil outlet valve is installed on the oil outlet pipe.

6. The pressurizable coal gas desorption and diffusion device according to claim 1, characterized in that: The right side of the constant temperature water tank is connected with the water bath temperature control unit and the water bath temperature display screen.

7. A method for the desorption and diffusion of gas in coal with pressure-reinforced coating, characterized by: The method of using the pressurizable coal gas desorption and diffusion device according to any one of claims 1 to 6 comprises the following steps: S1. The raw coal sample is crushed by a pulverizer and the coal powder is dried in a drying oven to obtain a coal powder / raw coal specimen to be tested; the prepared coal powder particles are placed in the lower chamber of the tank body and the coal particles are ensured to have a uniform texture. A piston is installed at the top of the lower chamber of the tank body, and the tank cover is fixed with a sealing nut and a sealing screw to achieve a sealed tank body; S2. Test the air tightness of the device: First, fill the coal sample tank with high-pressure gas, close all the valves of the coal sample tank and immerse it in water to observe whether bubbles are generated. If no bubbles appear after standing for 5 seconds, it means that the coal sample tank is airtight. Then connect the experimental device so that the high-pressure gas spreads throughout the device. Apply soapy water to all the joints of the experimental device and observe whether bubbles are generated. If there are no bubbles, it means that the device is airtight. S3, overpressure loading: open the oil filling port valve, start the pressure pump to increase the pressure to the overpressure value specified in the experimental plan, and turn on the data control and monitoring unit to prepare for the next step of experimental data measurement; S4. Vacuum degassing treatment: Connect the vacuum pump and the coal sample tank, open the vacuum pipeline valve; fill the water bath box with water to the top of the tank, set the water bath temperature, and immerse the coal sample tank in the constant temperature water tank; turn on the vacuum pump, and when the vacuum gauge shows 4Pa, close the vacuum pipeline valve and the vacuum pump in turn; S5. High-pressure gas injection: Connect the degassed coal sample tank to the gas injection device, open the high-pressure gas cylinder valve, and allow the gas in the high-pressure gas cylinder to enter the pressure-reducing tank and the connecting pipe. When the pressure in the pressure-reducing tank is slightly higher than the preset adsorption equilibrium pressure, close the high-pressure gas cylinder valve and slowly open the gas injection pipeline valve to allow the gas in the pressure-reducing tank to enter the coal sample tank until the gas pressure in the coal sample tank is slightly higher than the set adsorption equilibrium pressure. S6. Adsorption equilibrium: Set the water bath test temperature and immerse the coal sample tank in a constant temperature water tank for 10 hours to allow the coal sample to fully adsorb and the pressure to reach equilibrium. Read the actual equilibrium pressure. S7. Gas desorption: Close the valve of the gas injection pipeline, open the gas flow meter first, and then open the gas outlet valve. After the internal pressure is relieved to zero, quickly connect the coal sample tank and the gas flow meter, and observe the gas flow meter reading. When the cumulative gas flow does not change for 10 consecutive minutes, the desorption is considered to be completed.

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