A device and method for purifying nitrogen and removing methane

Abstract

The present invention discloses a purified nitrogen demethanization device and method, comprising: a controller, a mass flow controller, a heat exchanger, a heater and a reactor; the refrigerant inlet of the heat exchanger is connected to the nitrogen inlet and the oxygen inlet through a pipeline, the refrigerant outlet of the heat exchanger is connected to the inlet of the reactor, the heater is arranged on the pipeline between the refrigerant outlet of the heat exchanger and the inlet of the reactor, the outlet of the reactor is connected to the heat medium inlet of the heat exchanger, and the heat medium outlet of the heat exchanger is connected to the gas outlet; the mass flow controller is arranged on the pipeline between the refrigerant inlet and the oxygen inlet of the heat exchanger, the controller calculates the gas volume flow rate of the nitrogen flowing into the reactor and the gas volume flow rate of the oxygen injected into the reactor according to the gas volume flow formula, and the mass flow controller adjusts the oxygen injection amount. The problem that the existing purifier uses a flow meter to measure the flow rate with large deviation, which affects the oxygen injection amount and the quality of the prepared ultra-pure nitrogen is overcome.

Description

Technical Field

[0001] The invention relates to the field of nitrogen purification, and in particular to a device and method for purifying nitrogen and removing methane. Background Art

[0002] In the semiconductor chip manufacturing process, the purity of nitrogen is required to be ≥9N. In conventional processes, there are no special regulations on the methane content in nitrogen. However, the methane content of ultra-pure nitrogen (PN2) used in key processes must be less than 1PPb. In some specific cases, the methane content is even required to be less than 0.1PPb. Given that the carbon-hydrogen bond of methane is relatively stable and difficult to remove at room temperature, catalytic methods are usually used to remove methane from high-purity nitrogen (GN2). The catalytic method uses precious metal catalysts such as palladium and platinum to inject an appropriate amount of high-purity oxygen (GO2) into GN2, and oxidize methane into CO2 and H2O at a high temperature of 250 to 330 degrees Celsius, and then remove the generated CO2 and H2O in the subsequent adsorption process.

[0003] In view of the continuous development of the semiconductor industry, the demand for PN2 is gradually increasing. In order to cope with this growth, purifiers that can efficiently purify GN2 per unit time are generally used, and flow meters with a large range are equipped to measure the flow of GN2 to meet the gas supply needs of different flow rates. The detection range of the flow meter is between 5% and 100%, and there is a measurement error of ±3%. 3 Taking the purifier with a flow rate of 1000 Nm / h as an example, the flow meter with the matching flow rate has a measurement range of 0 to 6000 Nm 3 / h. When the flow rate is less than 300Nm 3 / h, the error of the flow meter increases significantly. The purifier calculates the amount of GO2 required to be injected based on the GN2 flow data provided by the flow meter, which may result in failure to inject oxygen or excessive oxygen injection under low flow conditions.

[0004] During the catalytic process, the injected GO2 flow rate must match the GN2 flow rate to meet the process requirements. If the amount of injected GO2 far exceeds the process requirements, GO2 will not be completely adsorbed after entering the subsequent adsorption process, resulting in excessive oxygen impurity content in the product gas PN2. If the amount of injected GO2 is far below the process requirements, methane cannot be completely removed, which will affect the quality of PN2 and make it unable to meet the use standards. Summary of the invention

[0005] The present invention provides a purified nitrogen demethanization device and method to overcome the problem that the flow data of GN2 measured by a flow meter in an existing purifier has a large deviation, which affects the amount of injected GO2 and further affects the quality of prepared PN2.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A purified nitrogen demethanization device comprises: a controller, a mass flow controller, a heat exchanger, a heater and a reactor;

[0008] The refrigerant inlet of the heat exchanger is connected to the nitrogen inlet and the oxygen inlet through a pipeline, the refrigerant outlet of the heat exchanger is connected to the inlet of the reactor through a pipeline, the heater is arranged on the pipeline between the refrigerant outlet of the heat exchanger and the inlet of the reactor, the outlet of the reactor is connected to the heat medium inlet of the heat exchanger through a pipeline, and the heat medium outlet of the heat exchanger is connected to the gas outlet through a pipeline;

[0009] The mass flow controller is arranged on the pipeline between the refrigerant inlet and the oxygen inlet of the heat exchanger. The controller calculates the gas volume flow rate V1 of the nitrogen flowing into the reactor and the gas volume flow rate V2 of the oxygen injected into the reactor according to the gas volume flow formula, and the mass flow controller adjusts the oxygen injection amount;

[0010] The gas volume flow formula for nitrogen is:

[0011] ,

[0012] Where V1 is the gas volume flow rate of nitrogen (Nm 3 / h); P is the output power of the heater (kW); ΔT is the temperature difference before and after the nitrogen enters the heater (℃); q is the nitrogen empirical constant; is the operating time coefficient of the heater;

[0013] The gas volume flow formula for oxygen is:

[0014] V2=V1×S / 60

[0015] Wherein, V2 is the gas volume flow rate (sccm) of oxygen introduced into the reactor; S is the gas concentration (ppm) of methane in nitrogen.

[0016] Furthermore, the nitrogen empirical constant q=1.03.

[0017] Furthermore, the heater is provided with a heating rod, and the heater can automatically control the start and stop of the heating rod according to a set temperature threshold. The operating time coefficient of the heater is According to the following formula:

[0018] ,

[0019] is the running time coefficient, dimensionless;

[0020] t1 is the working time of the heating rod in a fixed cycle (s);

[0021] t2 is the stop working time of the heating rod in a fixed cycle (s).

[0022] Furthermore, the heat exchanger is a shell and tube heat exchanger.

[0023] Furthermore, it also includes an intake air temperature sensor and an outlet air temperature sensor, wherein the intake air temperature sensor is arranged on the pipeline between the refrigerant outlet of the heat exchanger and the inlet of the heater, and the outlet air temperature sensor is arranged between the outlet of the heater and the inlet of the reactor, and the controller can calculate the temperature difference ΔT before and after the nitrogen enters the heater according to the data fed back by the intake air temperature sensor and the outlet air temperature sensor.

[0024] Furthermore, a filter and a one-way valve are provided on the pipeline between the oxygen inlet and the refrigerant inlet of the heat exchanger.

[0025] Furthermore, a pneumatic valve is provided on the pipeline between the oxygen inlet and the refrigerant inlet of the heat exchanger.

[0026] Furthermore, a manual valve, a temperature sensor and a pressure gauge are provided on the pipeline between the nitrogen inlet and the refrigerant inlet of the heat exchanger, and a manual valve and a pressure gauge are provided on the pipeline between the oxygen inlet and the refrigerant inlet of the heat exchanger.

[0027] The present invention also includes a control method for the aforementioned purified nitrogen demethanization device, comprising the following steps:

[0028] Parameter setting: setting the output power of the heater, the nitrogen empirical constant and the gas concentration of methane in the nitrogen in the controller;

[0029] Parameter calculation: obtaining the temperature difference before and after the nitrogen passes into the heater and the operating time coefficient of the heater through the controller, and calculating the gas volume flow rate of the nitrogen;

[0030] Flow rate adjustment: The controller calculates the gas volume flow rate of oxygen according to the gas volume flow rate of nitrogen to control the mass flow controller, and adjusts the gas volume flow rate of oxygen injected into the reactor based on the gas volume flow rate of oxygen.

[0031] Beneficial effects of the present invention:

[0032] Different from the existing purifiers that use flow meters to measure flow, the present invention provides a purified nitrogen demethanization device and method. Based on the heat exchange principle, the controller calculates the nitrogen gas volume flow rate using the nitrogen gas volume flow formula according to the output power of the heater, the temperature difference before and after the nitrogen is introduced into the heater and other parameters. Then, based on the calculated nitrogen gas volume flow rate, the mass flow controller is controlled to adjust the gas volume flow rate of oxygen injected into the reactor to ensure that the purified nitrogen demethanization device will not be affected by the flow meter error under low flow conditions, thereby avoiding the quality of high-purity nitrogen being affected by the inability to inject oxygen or excessive injection of oxygen. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0034] Figure 1 It is a structural schematic diagram of a purified nitrogen demethanization device disclosed in the present invention;

[0035] Figure 2 This is a calculation example diagram of the HTRI software in a verification test of a purified nitrogen demethanization device disclosed in the present invention.

[0036] In the figure:

[0037] 1. Nitrogen inlet; 2. Nitrogen temperature sensor; 3. Nitrogen manual valve; 4. Nitrogen pressure sensor; 5. Inlet temperature sensor; 6. Heater; 7. Heating rod temperature sensor; 8. Outlet temperature sensor; 9. Reactor; 10. Reactor first temperature sensor; 11. Reactor second temperature sensor; 12. Reactor third temperature sensor; 13. Heat exchanger; 14. Outlet valve; 15. Gas outlet; 16. Oxygen inlet; 17. Oxygen manual valve; 18. Filter; 19. Local pressure gauge; 20. Mass flow controller; 21. Check valve; 22. Pneumatic valve. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of 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.

[0039] Example 1

[0040] This embodiment provides a purified nitrogen demethanization device, such as Figure 1 As shown, it includes: a controller, a mass flow controller 20, a heat exchanger 13, a heater 6 and a reactor 9;

[0041] The refrigerant inlet of the heat exchanger 13 is connected to the nitrogen inlet 1 and the oxygen inlet 16 through a pipeline, the refrigerant outlet of the heat exchanger 13 is connected to the inlet of the reactor 9 through a pipeline, the heater 6 is arranged on the pipeline between the refrigerant outlet of the heat exchanger 13 and the inlet of the reactor 9, the outlet of the reactor 9 is connected to the heat medium inlet of the heat exchanger 13 through a pipeline, and the heat medium outlet of the heat exchanger 13 is connected to the gas outlet 15 through a pipeline provided with an outlet valve 14;

[0042] The mass flow controller 20 is disposed on the pipeline between the refrigerant inlet and the oxygen inlet 16 of the heat exchanger 13. The controller calculates the gas volume flow rate V1 of the nitrogen flowing into the reactor 9 and the gas volume flow rate V2 of the oxygen injected into the reactor 9 according to the gas volume flow formula, and the mass flow controller 20 adjusts the oxygen injection amount;

[0043] The gas volume flow formula for nitrogen is:

[0044] ,

[0045] Where V1 is the gas volume flow rate of nitrogen (Nm 3 / h); P is the output power of the heater (kW); ΔT is the temperature difference before and after the nitrogen enters the heater (℃); q is the nitrogen empirical constant; is the operating time coefficient of the heater;

[0046] The gas volume flow formula for oxygen is:

[0047] V2=V1×S / 60

[0048] Wherein, V2 is the gas volume flow rate (sccm) of oxygen introduced into the reactor; S is the gas concentration (ppm) of methane in nitrogen.

[0049] Different from the existing purifiers that use flow meters to measure flow, the purified nitrogen demethanization device provided in this embodiment is based on the heat exchange principle. The controller calculates the nitrogen gas volume flow rate V1 using the nitrogen gas volume flow formula according to the output power of the heater 6, the temperature difference before and after the nitrogen is introduced into the heater 6 and other parameters. Then, based on the calculated nitrogen gas volume flow rate V1, the mass flow controller 20 is controlled to adjust the gas volume flow rate V2 of the oxygen injected into the reactor 9. The oxygen flow rate required to be injected for the catalytic reaction is relatively small, and the unit is generally sccm. The purified nitrogen demethanization device provided in this embodiment can ensure that under the condition of small flow, the purified nitrogen demethanization device will not be affected by the error of the flow meter, thereby avoiding the quality of the high-purity nitrogen being affected by the inability to inject oxygen or excessive injection of oxygen.

[0050] In a specific embodiment, the nitrogen empirical constant q=1.03.

[0051] In a specific embodiment, a heating rod and a heating rod temperature sensor 7 are provided in the heater 6. The heating rod temperature sensor 7 is used to monitor the temperature of the heating rod. The heater 6 can automatically control the start and stop of the heating rod according to the set temperature threshold. The control of the heating rod is PID controlled by the PLC program, that is, periodic heating. In a fixed time period, part of the time is heating and part of the time is stopped. The operating time coefficient of the heater 6 is According to the following formula:

[0052] ,

[0053] is the running time coefficient, dimensionless;

[0054] t1 is the working time of the heating rod in a fixed cycle (s);

[0055] t2 is the stop working time of the heating rod in a fixed cycle (s).

[0056] In a specific embodiment, the heat exchanger 13 is a shell and tube heat exchanger, and the reactor 9 is a fixed bed reactor. The fixed bed reactor is provided with a first reactor temperature sensor 10, a second reactor temperature sensor 11 and a third reactor temperature sensor 12 to detect the bed temperature of the reactor 9. The first reactor temperature sensor 10, the second reactor temperature sensor 11 and the third reactor temperature sensor 12 are all provided with high / low temperature alarm interlocks.

[0057] In a specific embodiment, an intake air temperature sensor 5 and an outlet air temperature sensor 8 are further included. The intake air temperature sensor 5 is arranged on the pipeline between the refrigerant outlet of the heat exchanger 13 and the inlet of the heater 6, and the outlet air temperature sensor 8 is arranged between the outlet of the heater 6 and the inlet of the reactor 9. The controller can calculate the temperature difference ΔT before and after the nitrogen enters the heater according to the data fed back by the intake air temperature sensor 5 and the outlet air temperature sensor 8.

[0058] In a specific embodiment, a filter 18 and a one-way valve 21 are provided on the pipeline between the oxygen inlet 16 and the refrigerant inlet of the heat exchanger 13. The filter 18 is used to filter impurities, and the one-way valve 21 is used to prevent gas backflow.

[0059] In a specific embodiment, a pneumatic valve 22 is provided on the pipeline between the oxygen inlet 16 and the refrigerant inlet of the heat exchanger 13, and the pneumatic valve 22 is used to control the on and off of oxygen.

[0060] In a specific embodiment, a nitrogen temperature sensor 2, a nitrogen manual valve 3 and a nitrogen pressure sensor 4 are provided on the pipeline between the nitrogen inlet 1 and the refrigerant inlet of the heat exchanger 13. The nitrogen temperature sensor 2 is used to detect the temperature of the nitrogen raw gas, and the nitrogen pressure sensor 4 is used to detect the intake pressure of the nitrogen raw gas. An oxygen manual valve 17 and a local pressure gauge 19 are provided on the pipeline between the oxygen inlet 16 and the refrigerant inlet of the heat exchanger 13. When the pneumatic valve 22 fails, the oxygen manual valve 17 can be closed.

[0061] The nitrogen raw gas enters the device from the nitrogen inlet 1, flows through the shell side of the heat exchanger 13, the heater 6 and the reactor 9 in sequence, and oxygen enters from the oxygen inlet 16, enters the heat exchanger 13, the heater 6 and the reactor 9 together with the nitrogen raw gas, and reacts with the raw gas in the reactor 9. The ultrapure nitrogen obtained after the reaction passes through the tube side of the heat exchanger 13 and is supplied from the gas outlet 15 to the downstream equipment requiring ultrapure nitrogen;

[0062] Specifically, after the raw gas enters the heat exchanger 13, it is preheated and preheated to about 200-290 degrees Celsius through the shell side of the shell and tube heat exchanger (different flow rates result in different temperatures of the raw gas after preheating). When entering the heater 6, the temperature of the raw gas after preheating is detected by the inlet temperature sensor 5, and the outlet temperature sensor 8 monitors the temperature reached by the raw gas after passing through the heater 6. The controller calculates the temperature difference through the inlet temperature sensor 5 and the outlet temperature sensor 8, and captures the operating time coefficient of the heater through the PLC program, and then calculates the volume flow rate of nitrogen through the formula. The oxygen flow rate injected into the reactor 9 is controlled according to the gas concentration of methane in the nitrogen. After entering the reactor 9, the raw gas undergoes a catalytic reaction with oxygen to remove impurities in the raw gas. After passing through the reactor 9, the raw gas is precooled to about 50-80 degrees Celsius through the heat exchanger 13 (different flow rates result in different temperatures after precooling), reaches the gas outlet 15 through the outlet valve 14, and enters the downstream equipment.

[0063] Example 2

[0064] This embodiment provides a control method for a purified nitrogen demethanization device as described in Example 1, comprising the following steps:

[0065] Parameter setting: The process personnel preset the output power of the heater 6, the nitrogen empirical constant and the gas concentration of methane in the nitrogen in the controller;

[0066] Parameter calculation: The controller obtains the temperature difference before and after the nitrogen enters the heater and the operating time coefficient of the captured heater, and calculates the gas volume flow rate V1 of the nitrogen;

[0067] Flow adjustment: The controller calculates the gas volume flow rate V2 of oxygen based on the gas volume flow rate V1 of nitrogen and the gas concentration s of methane in nitrogen to control the mass flow controller, and adjusts the oxygen injected into the reactor 9 based on the gas volume flow rate V2 of oxygen.

[0068] To better illustrate the present invention, the principle of the present invention and the experiment to verify the practicality of the formula are described below;

[0069] The heat transfer efficiency of nitrogen with different flow rates in the heat exchanger is different, that is, the heat load of the heat exchanger is different when calculating, which makes the gas temperature entering the heater 6 from the inlet of the heater 6 different. In order to achieve the conditions required for reactor catalysis, the gas temperature discharged from the outlet of the heater 6 should meet the process requirements. In order to make nitrogen with different flow rates reach the same temperature after being heated by the heater, it is necessary to increase the working time of the heating rod in the heater 6 during the heating process, that is, to increase the operating time coefficient of the heater 6. The change of the operating time coefficient in the heater 6 is read by the automatic control program in the controller to judge the flow change. This flow measurement based on the principle of heat exchange is more accurate than the flow meter judgment, and solves the problem that the large error of the large-range flow meter in measuring small flow is too large, resulting in a large deviation in the oxygen injection amount, and saves the flow meter originally required for the purifier, reduces the failure point, saves cost, and reduces the overall size of the equipment, making the purified nitrogen demethanization device easier to meet the installation requirements on site.

[0070] In order to ensure the accuracy of the experiment to verify the practicality of the formula and avoid errors, a single large-range flow meter (0-6000Nm 3 / h) for flow measurement. The flow rates of raw gas of different sizes are measured by multiple small-range flow meters with different ranges (it is necessary to ensure that the ranges of multiple small-range flow meters with different ranges can cover 0-6000Nm 3 / h) to ensure the reliability of experimental data;

[0071] In practical applications, since the oxygen flow rate injected in the catalytic reaction is small, the unit is generally sccm, and the impact on the flow measurement and heater temperature is negligible, oxygen is not introduced in the verification experiment;

[0072] The specific process is as follows: the outlet temperature of the heater 6 is generally set at 350°C. Since there is no heating element in the reactor 9 itself, the hot gas will lose some heat when passing through the reactor 9. The temperature of the packing layer in the reactor 9 is generally 280-330°C, so that the reducing impurities can be fully burned and reacted. The gas indicators of the high-purity nitrogen used as the raw gas are different. The working pressure is 8 bar, the output power of the heater is 310kW, and the specification is 6000Nm 3 Taking a nitrogen purifier with a capacity of / h as an example, the data in Table 1 are obtained.

[0073] Table 1 Reactor outlet temperature of nitrogen under different gas indexes

[0074]

[0075] According to Table 1, for nitrogen with different gas indexes, at a working pressure of 8 bar, when the heater outlet temperature is controlled at about 350°C, the reactor outlet temperature is basically stable at about 318-324°C. Therefore, when actually calculating the heat load of the heat exchanger at different flow rates, for the convenience of calculation, the tube inlet (heat medium inlet) temperature of the heat exchanger can be set at 320°C and the shell inlet (refrigerant inlet) temperature can be set at 25°C (room temperature) in the HTRI software, and the data in Table 2 can be obtained. Figure 2 This is an example diagram calculated by HTRI software based on the above parameters.

[0076] Table 2 shows the shell outlet (refrigerant outlet) temperature of the heat exchanger calculated by HTRI software

[0077]

[0078] The experiment was conducted after rounding off the shell side outlet temperature of the heat exchanger calculated by HTRI. Nitrogen with different flow rates and temperatures was heated to a heater outlet temperature of 350°C through the heater. During the experiment, the controller captured the heater operation time coefficient through the automatic control program, and the experimenter recorded the captured heater operation time coefficient.

[0079] Based on the same experimental parameters, the experimenters used the calculation formula of nitrogen gas volume flow rate V1 to calculate and compared the calculated heater operation time coefficient with the experimentally captured heater operation time coefficient. The comparison results are shown in Table 3.

[0080] Table 3 is a comparison table of the running time coefficient calculated by the formula and the running time coefficient captured by the experiment

[0081]

[0082] It is not difficult to see from Table 3 that the difference between the heater operation time coefficient calculated according to the formula and the heater operation time coefficient obtained by experimental capture is very small, which shows that the gas flow calculated by this formula is highly consistent with the actual gas flow, with a small error, which is enough to replace the large-range flow meter and is suitable for actual production environments.

[0083] 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 it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A purified nitrogen demethanization device, characterized in that: include: controller, a mass flow controller (20), a heat exchanger (13), a heater (6) and a reactor (9); The refrigerant inlet of the heat exchanger (13) is connected to the nitrogen inlet (1) and the oxygen inlet (16) through a pipeline, the refrigerant outlet of the heat exchanger (13) is connected to the inlet of the reactor (9) through a pipeline, the heater (6) is arranged on the pipeline between the refrigerant outlet of the heat exchanger (13) and the inlet of the reactor (9), the outlet of the reactor (9) is connected to the heat medium inlet of the heat exchanger (13) through a pipeline, and the heat medium outlet of the heat exchanger (13) is connected to the gas outlet (15) through a pipeline; The mass flow controller (20) is arranged on the pipeline between the refrigerant inlet and the oxygen inlet (16) of the heat exchanger (13), and the controller calculates the gas volume flow rate V1 of the nitrogen flowing into the reactor (9) and the gas volume flow rate V2 of the oxygen injected into the reactor (9) according to the gas volume flow formula, and the mass flow controller (20) adjusts the oxygen injection amount; The gas volume flow formula for nitrogen is: ， Where V1 is the gas volume flow rate of nitrogen (Nm 3 / h); P is the output power of the heater (kW); ΔT is the temperature difference before and after nitrogen enters the heater (°C); q is the nitrogen empirical constant; is the operating time coefficient of the heater; The gas volume flow formula for oxygen is: V2=V1×S / 60 Wherein, V2 is the gas volume flow rate (sccm) of oxygen introduced into the reactor; S is the gas concentration (ppm) of methane in nitrogen.

2. A purified nitrogen demethanization device according to claim 1, characterized in that: The nitrogen empirical constant q=1.

03.

3. A purified nitrogen demethanization device according to claim 1, characterized in that: The heater (6) is provided with a heating rod, and the heater (6) can automatically control the start and stop of the heating rod according to a set temperature threshold. The operating time coefficient of the heater (6) is According to the following formula: ， is the running time coefficient, dimensionless; t1 is the working time of the heating rod in a fixed cycle (s); t2 is the stop working time of the heating rod in a fixed cycle (s).

4. A purified nitrogen demethanization device according to claim 1, characterized in that: The heat exchanger (13) is a shell and tube heat exchanger.

5. A purified nitrogen demethanization device according to claim 1, characterized in that: The invention also comprises an inlet temperature sensor (5) and an outlet temperature sensor (8), wherein the inlet temperature sensor (5) is arranged on a pipeline between a refrigerant outlet of the heat exchanger (13) and an inlet of the heater (6), and the outlet temperature sensor (8) is arranged between the outlet of the heater (6) and the inlet of the reactor (9), and the controller is capable of calculating a temperature difference ΔT before and after the nitrogen passes into the heater based on data fed back by the inlet temperature sensor (5) and the outlet temperature sensor (8).

6. A purified nitrogen demethanization device according to claim 1, characterized in that: A filter (18) and a one-way valve (21) are provided on the pipeline between the oxygen inlet (16) and the refrigerant inlet of the heat exchanger (13).

7. A purified nitrogen demethanization device according to claim 1, characterized in that: A pneumatic valve (22) is provided on the pipeline between the oxygen inlet (16) and the refrigerant inlet of the heat exchanger (13).

8. The purified nitrogen demethanization device according to claim 1, characterized in that: A manual valve, a temperature sensor and a pressure gauge are provided on the pipeline between the nitrogen inlet (1) and the refrigerant inlet of the heat exchanger (13), and a manual valve and a pressure gauge are provided on the pipeline between the oxygen inlet (16) and the refrigerant inlet of the heat exchanger (13).

9. A control method for a purified nitrogen demethanization device as claimed in claim 1, characterized in that: The following steps are involved: Parameter setting: setting the output power of the heater, the nitrogen empirical constant and the gas concentration of methane in the nitrogen in the controller; Parameter calculation: obtaining the temperature difference before and after the nitrogen passes into the heater and the operating time coefficient of the heater through the controller, and calculating the gas volume flow rate of the nitrogen; Flow rate adjustment: The controller calculates the gas volume flow rate of oxygen according to the gas volume flow rate of nitrogen to control the mass flow controller, and adjusts the gas volume flow rate of oxygen injected into the reactor (9) based on the gas volume flow rate of oxygen.

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