Cathode structure for preparing nitrogen trifluoride gas

Abstract

The invention discloses a cathode structure for preparing nitrogen trifluoride gas, which comprises a conductive shell, two tubular conductive binding posts fixedly arranged outside the shell at an interval and a heat exchange tube arranged in the shell, the two binding posts are both electrically connected with the shell, two ports of the heat exchange tube are respectively and fixedly communicated with the two binding posts, and the heat exchange tube is arranged in the shell. An insulated heat exchange medium circulates in the heat exchange tube, and the heat exchange medium flows in from one binding post and flows out from the other binding post to heat or cool the electrolyte, so that the heat exchange tube does not need to be independently arranged in the electrolyte. Due to the fact that the heat exchange tube does not make contact with the electrolyte, the heat exchange tube is not corroded by the electrolyte, the risk that the heat exchange tube leaks is avoided, and the situation that the heat-conducting medium leaks from the heat exchange tube and enters the electrolyte, and then normal electrolysis operation is affected is avoided.

Description

Technical Field

[0001] This invention relates to the field of nitrogen trifluoride preparation, and more particularly to a cathode structure for preparing nitrogen trifluoride gas. Background Technology

[0002] Nitrogen trifluoride (NF3), as a specialty electronic gas, has wide and important applications in the semiconductor, LCD panel, and new energy industries as a cleaning agent and etchant. The main method for preparing NF3 gas is molten salt electrolysis, using a nickel anode, NH3·xHF molten salt as the electrolyte, an electrolysis temperature of 90℃ to 140℃, an electrolysis voltage of 5V to 10V, and an electrolysis current density of 30mA / cm³. 2 Up to 200mA / cm 2 The anode produces NF3, and the cathode produces H2. During NF3 electrolysis, at the beginning of the process, NF3 production is in a low-current stage, requiring heating to ensure the electrolyte remains molten. Once NF3 production stabilizes, it enters a high-current stage. Since the NF3 reaction is exothermic, it generates a large amount of heat. When the NF3 electrolysis temperature exceeds 150°C, an abnormality occurs: a decrease in current, a reduction in NF3 yield, and an increase in H2 content. Therefore, a heat exchange medium is needed to remove the heat generated during electrolysis and ensure the stability of the electrolysis temperature.

[0003] Currently, there are two heat exchange methods used in NF3 production to ensure electrolysis temperature. The first method involves installing electric heating and cooling devices on the electrolysis equipment, with water or organic substances such as ethylene glycol aqueous solution and heat transfer oil as the cooling medium. The second method involves installing a heat exchange device on the electrolysis equipment, using steam or high-temperature heat transfer oil as the heating medium during heating, and water or organic substances such as ethylene glycol aqueous solution and heat transfer oil as the cooling medium during cooling. Existing NF3 electrolysis equipment heat exchange structures use tubes or perforated plates welded inside the electrolysis cell, with the heat exchange medium contacting the electrolyte through pipes within the cell. The main problem with this design is the inability to avoid the potential corrosion risk of the heat exchange tubes due to electrochemical and electrical factors. Using a 220V / 380V electric heating structure, if the insulation layer between the heating rod and the electrolysis equipment is damaged, or if the equipment encounters a humid environment, the 220V / 380V electricity can directly puncture the heating tube, causing electrolyte leakage and the formation of hazardous waste containing sulfur (F). In NF3 electrolysis equipment, there is a potential difference between the tank and the cathode. Compared with the cathode potential, the tank is at a positive potential. Since water or organic heat exchange medium circulates in the internal pipeline of the electrolysis cell through a pump, there is pressure. However, the internal pressure of the electrolysis cell is generally flat or negative. Therefore, under the influence of pressure and defects in the heat exchange medium pipeline, the circulation pipeline may be damaged by corrosion. Water or organic substances will enter the electrolyte, causing abnormalities such as a decrease in current, a decrease in NF3 content, and an increase in H2 and CF4, leading to the cessation of electrolysis in the electrolysis cell. Moreover, the electrolyte mixed with water or organic substances is a fluorine-containing solid hazardous waste. Once it seeps into water or soil, it will form fluorine-containing wastewater or pollute the soil.

[0004] Patent CN210176967U discloses a medium-temperature electrolytic cell for fluorides, including an electrolytic cell body, a sealing cover fixedly atop the electrolytic cell body, a cooling tank body fitted over the electrolytic cell body, and a stirring assembly. An electric heating rod is installed outside the tank body for heating the cell body. However, because the electric heating rod heats the sidewalls of the tank body, thereby heating the electrolyte inside the tank, the heating effect is poor. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a cathode structure for preparing nitrogen trifluoride gas, which solves the problem that in the current preparation of nitrogen trifluoride, heat exchange is required through the contact of the pipeline in the tank with the electrolyte, which makes the heat exchange tube easy to be corroded and damaged by the electrolyte, and allows the heat exchange medium in the heat exchange tube to enter the electrolyte.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A cathode structure for preparing nitrogen trifluoride gas includes a conductive shell, two tubular conductive terminals fixedly disposed outside the shell at intervals, and a heat exchange tube disposed inside the shell. Both terminals are electrically connected to the shell. The two ports of the heat exchange tube are fixedly connected to the two terminals respectively. An insulating heat exchange medium flows through the heat exchange tube. The heat exchange medium flows in from one terminal and flows out from the other terminal.

[0008] Furthermore, the heat exchange medium is pure water, steam, or heat transfer oil.

[0009] Furthermore, when the heat exchange medium is pure water, it is used to cool the shell. The pressure flowing into the corresponding terminal is 0.1 MPa to 1 MPa, the temperature is 45°C to 75°C, the outlet water temperature is 60°C to 85°C, the conductivity of the pure water is 3 μS / cm to 8 μS / cm, and the salt content is 3 mg / L to 5 mg / L.

[0010] Furthermore, when the heat exchange medium is water vapor, it is used to heat the shell. The water vapor pressure entering the corresponding terminal is 0.1 MPa to 0.6 MPa, and the temperature is 150°C to 200°C. The water vapor temperature exiting the corresponding terminal is 110°C to 125°C.

[0011] Furthermore, when the heat exchange medium is heat transfer oil, it is used to heat or cool the shell. When the heat transfer oil is used to heat the shell, the pressure of the heat transfer oil entering the corresponding terminal is 0.1 MPa to 0.6 MPa, the temperature is 150°C to 180°C, and the temperature of the heat transfer oil flowing out of the corresponding terminal is 100°C to 120°C. When the heat transfer oil is used to cool the shell, the pressure of the heat transfer oil entering the corresponding terminal is 0.2 MPa to 0.8 MPa, the temperature is 70°C to 85°C, and the temperature of the heat transfer oil flowing out of the corresponding terminal is 100°C to 120°C.

[0012] Furthermore, each of the two terminals is connected to an insulated connecting tube, which is made of fluororubber, fluoroplastic, or fluorometal-lined tubing.

[0013] Furthermore, the terminal block is fitted with a sealing ring.

[0014] Furthermore, the housing is omitted.

[0015] Furthermore, the heat exchange tube is omitted, and both terminals are connected to the inside of the casing.

[0016] The positive effects of this invention are:

[0017] This invention comprises a shell containing a heat exchange tube, and two terminals connected to both ends of the heat exchange tube on the outside of the shell. The shell acts as the cathode; when the heat exchange medium flows through the heat exchange tube, it exchanges heat with the cathode (i.e., the shell), thereby heating or cooling the electrolyte. Therefore, there is no need for a separate heat exchange tube within the electrolyte. Since the heat exchange tube does not come into contact with the electrolyte, it is not subject to corrosion, eliminating the risk of leakage. Consequently, the heat transfer medium will not leak from the heat exchange tube into the electrolyte, thus preventing disruption to normal electrolysis operations. Attached Figure Description

[0018] Figure 1 These are schematic diagrams of the external appearance of embodiments 1 and 2 of the present invention;

[0019] Figure 2 This is a schematic diagram of the internal structure of Embodiment 1 of the present invention;

[0020] Figure 3 This is a schematic diagram of the external appearance of Embodiment 3 of the present invention;

[0021] In the picture:

[0022] 1. Terminal block; 2. Sealing ring; 3. Housing; 4. Connector; 5. Heat exchange tube; 6. Heat exchange chamber. Detailed Implementation

[0023] Example 1

[0024] like Figures 1 to 2 As shown, a cathode structure for preparing nitrogen trifluoride gas includes a cubic conductive shell 3, two tubular conductive terminals 1 fixedly disposed at intervals outside the shell 3, and a heat exchange tube 5 disposed in a hollow heat exchange cavity 6 inside the shell 3. The lower ends of the two terminals 1 are electrically connected to the top of the shell 3 near the left and right sides, respectively.

[0025] When the heat exchange medium flows through the heat exchange tube 5, it heats or cools the electrolyte, thus eliminating the need for a separate heat exchange tube within the electrolyte. Since the heat exchange tube 5 does not contact the electrolyte, it is not subject to corrosion, eliminating the risk of leakage. Consequently, the heat transfer medium will not leak from the heat exchange tube 5 into the electrolyte, thus preventing disruption to normal electrolysis operations. Because the shell 3 acts as the cathode inserted into the electrolyte, the heat exchange effect is improved (to further enhance the heat exchange effect, the number of tubes in the electrolyte can be increased).

[0026] The following is a further explanation of this embodiment. The wall of the heat exchange tube 5 and the shell 3 are fitted with a clearance (i.e., the wall of the heat exchange tube 5 does not contact the shell 3). Heat exchange between the heat exchange tube 5 and the shell 3 is achieved through the air in the heat exchange chamber 6, thereby preventing the temperature of the shell 3 from changing too rapidly.

[0027] The two ports of the heat exchange tube 5 are fixedly connected to the lower ends of the two terminals 1 respectively. An insulating heat exchange medium flows inside the heat exchange tube 5. The heat exchange medium flows in from the left terminal 1 and flows out from the right terminal 1.

[0028] The shell 3 (i.e., the cathode) is made of nickel, nickel alloy, or carbon steel, serving a dual purpose of heat exchange and providing an electrolysis circuit. As the cathode, shell 3 generates hydrogen gas. As the most negatively charged component in the electrolysis system, it effectively prevents leakage problems caused by electrochemical corrosion. During operation, this invention achieves two main functions: first, it forms an electrolysis circuit to produce hydrogen gas; second, the heat exchange medium flowing within the heat exchange tube 5 ensures that the NF3 electrolysis temperature remains within the range of 90°C to 140°C.

[0029] The terminal block 1 is fitted with a sealing ring 2. In use, the terminal block 1 is connected to the tank cover of the NF3 electrolysis equipment, and the housing 3 is immersed in the electrolyte of the electrolysis equipment. The two terminals 1 are connected to insulated connecting pipes via top connectors 4. These connecting pipes are made of fluororubber, fluoroplastic, or fluoropolymer-lined metal, with a heat resistance exceeding 80°C. The connecting pipes are connected to the heat exchange medium supply equipment, ensuring insulation between the terminal block 1 and the heat exchange medium supply equipment. The terminal block 1 is connected to the negative terminal of the power supply. Because the heat exchange medium inlet and outlet (i.e., the positions of terminal block 1 and connector 4) are energized during NF3 electrolysis, and both the connecting pipes and the heat-conducting medium are insulated, stray current flowing from the terminal block 1 to the heat exchange medium supply equipment can be reduced, thus preventing corrosion of the connecting pipes or the heat exchange medium supply equipment.

[0030] The sealing ring 2 ensures a tight seal between the shell 3 and the tank cover of the NF3 electrolysis equipment. The heat exchange medium is pure water, steam, or heat transfer oil. A combination of water and steam can be used, with water providing cooling and steam providing heating. It is strictly forbidden to interchange or mix water or steam with heat transfer oil. This is because residual heat exchange medium may remain in the heat exchange tube 5. If water or steam is interchanged or mixed with heat transfer oil, the water may boil violently during heating, causing the heat transfer oil to decompose into flammable and explosive gases, posing a safety hazard.

[0031] When the heat exchange medium is pure water, it is used to cool the shell 3, thereby lowering the temperature of the electrolyte. The pressure flowing into the left terminal 1 is 0.1 MPa to 1 MPa, and the temperature is 45°C to 75°C. The outlet water temperature from the right terminal 1 is 60°C to 85°C. The conductivity of the pure water is 3 μS / cm to 8 μS / cm, and the salt content is 3 mg / L to 5 mg / L.

[0032] If the inlet water temperature flowing into the left-hand terminal 1 is lower than the aforementioned temperature range, the electrolyte will solidify and precipitate on the cathode surface (i.e., the surface of the shell 3) during the cooling process, forming a non-conductive solid substance, causing a sudden drop in the electrolysis current. If the inlet water temperature flowing into the left-hand terminal 1 exceeds the aforementioned temperature range, the pure water easily evaporates into water vapor. This causes two problems: firstly, it hinders the flow of pure water within the heat exchange tube 5 and obstructs the flow in and out of the two terminals 1, leading to unstable temperature control; secondly, it increases the rate of salt precipitation in the pure water, causing blockage of the heat exchange tube 5, resulting in low electrolytic heat exchange efficiency and inability to control the temperature. If the conductivity or salt content of the pure water is lower than the aforementioned range, it will increase the cost of producing pure water. If the conductivity of the pure water is higher than the aforementioned range, it will increase the stray current in the heat exchange tube 5. If the salt content of the pure water exceeds the aforementioned range, it will increase the rate of salt precipitation in the pure water, causing blockage of the heat exchange tube 5.

[0033] When the heat exchange medium is water vapor, it heats the shell 3. During heating, the water vapor inlet pressure entering the left terminal 1 is 0.1 MPa to 0.6 MPa, and the inlet temperature is 150°C to 200°C. The water vapor exhaust temperature exiting the right terminal 1 is 110°C to 125°C. Excessive inlet pressure poses a safety hazard. Insufficient inlet temperature will prevent effective heating and easily lead to condensation in the heat exchange tube 5. When condensed water forms and accumulates in the heat exchange tube 5, it cannot be discharged, significantly reducing heat exchange efficiency and preventing the NF3 electrolyte from maintaining a molten state, thus causing electrolysis to stop.

[0034] When the heat exchange medium is heat transfer oil, it serves a dual purpose of heating and cooling the shell 3. The operating temperature range of the selected heat transfer oil is 60℃ to 200℃. If the operating temperature of the heat transfer oil is lower than this range, during the cooling process, the electrolyte will solidify and precipitate on the surface of the cathode (i.e., shell 3), forming a non-conductive solid substance, causing a sudden drop in the electrolysis current. If the operating temperature of the heat transfer oil is too high, the connecting pipe connected to the connector 4 will fail to seal at the interface due to the high temperature, leading to leakage and smoke. If the leaked high-temperature heat transfer oil drips onto the sealing ring 4, it will soften the insulating components between the terminal 1 and the tank cover of the electrolysis equipment, as well as the sealing ring 4, causing hydrogen leakage inside the electrolysis equipment and potential fire.

[0035] During heating, the inlet oil pressure is 0.1 MPa to 0.6 MPa, the inlet temperature of the heat transfer oil flowing in from the left-hand terminal 1 is 150°C to 190°C, and the outlet temperature of the heat transfer oil flowing out from the right-hand terminal 1 is 100°C to 120°C. During cooling, the inlet oil pressure of the heat transfer oil flowing in from the left-hand terminal 1 is 0.2 MPa to 0.8 MPa, the inlet temperature is 70°C to 85°C, and the outlet temperature of the heat transfer oil flowing out from the right-hand terminal 1 is 100°C to 120°C. If the inlet oil temperature is too low, the viscosity of the heat transfer oil will increase, making it easy to adhere to the inner wall of the heat exchange tube 5, or even solidify on the heat exchange tube, affecting the heat exchange efficiency. If the inlet oil temperature is too high, the heat transfer oil is prone to decomposition, which firstly increases the pressure inside the heat exchange tube, hindering the flow of the heat transfer oil, and secondly, produces flammable and explosive gases, increasing safety hazards.

[0036] In this embodiment, the working process is as follows:

[0037] HF and NH3 were mixed in a molar ratio of 2.6:1 to form a molten salt. The electrolysis temperature was set at 120℃, the electrolysis dehydration voltage was 6V, and the electrolysis collection voltage was 7.2V. During the dehydration stage, heating was required, with steam as the heat exchange medium. The inlet pressure was 0.3MPa, the steam inlet temperature was 180℃, and the outlet temperature was 115℃. The electrolysis temperature was controlled between 115℃ and 125℃. During the collection stage, cooling was required, with pure water as the heat exchange medium. The inlet water temperature was 60℃, the inlet pressure was 0.25MPa, and the outlet temperature was 80℃. The electrolysis temperature was controlled between 115℃ and 125℃. The electrolysis system operated stably for 90 days without any abnormalities.

[0038] Example 2

[0039] like Figure 1 As shown, the difference between this embodiment and Embodiment 1 is that:

[0040] The heat exchange tube 5 is no longer installed. Both terminals 1 are connected to the heat exchange cavity 6 inside the shell 3. Therefore, after the heat exchange medium enters the heat exchange cavity 6 from the left terminal 1, the heat transfer oil exchanges heat with the shell 3 in the heat exchange cavity 6 and then flows out from the right terminal 1.

[0041] In this embodiment, the working process is as follows:

[0042] HF and NH3 were mixed at a molar ratio of 2.5:1 to form a molten salt. The electrolysis temperature was set at 115℃, the electrolysis dehydration voltage was 6V, and the electrolysis collection voltage was 7.2V. During the dehydration stage, heating was required, using heat transfer oil as the heat exchange medium. The inlet oil pressure was 0.3MPa, the inlet oil temperature was 170℃, and the outlet oil temperature was 110℃. The electrolysis temperature was controlled between 110℃ and 120℃. During the collection stage, cooling was required, using heat transfer oil as the heat exchange medium. The inlet oil pressure was 0.4MPa, the inlet oil temperature was 80℃, and the outlet oil temperature was 120℃. The electrolysis temperature was controlled between 110℃ and 120℃. The electrolysis system operated stably for 90 days without any abnormalities.

[0043] Example 3

[0044] like Figure 3 As shown, the difference between this embodiment and Embodiment 1 is that:

[0045] The shell 3 is no longer set up. The cathode is a conductive heat exchange tube 5, and the two terminals 1 are fixedly connected to the two ends of the heat exchange tube 5 respectively.

[0046] In this embodiment, the working process is as follows:

[0047] HF and NH3 were mixed in a molar ratio of 2.7:1 to form a molten salt. The electrolysis temperature was set at 125℃, the electrolysis dehydration voltage was 6V, and the electrolysis collection voltage was 7.2V. During the dehydration stage, heating was required, using heat transfer oil as the heat exchange medium. The inlet oil pressure was 0.3MPa, the inlet oil temperature was 180℃, and the outlet oil temperature was 120℃. The electrolysis temperature was controlled between 120℃ and 130℃. During the collection stage, cooling was required, using heat transfer oil as the heat exchange medium. The inlet oil pressure was 0.4MPa, the inlet oil temperature was 80℃, and the outlet oil temperature was 125℃. The electrolysis temperature was controlled between 120℃ and 130℃. The electrolysis system operated stably for 90 days without any abnormalities.

[0048] Comparative Example 1

[0049] Some parameters differ from those in Example 1. The specific working process is as follows:

[0050] HF and NH3 were mixed in a molar ratio of 2.6:1 to form a molten salt. The electrolysis temperature was set at 120℃, the electrolysis dehydration voltage was 6V, and the electrolysis collection voltage was 7.2V. During the dehydration stage, heating was required, with steam as the heat exchange medium. The inlet pressure was 0.3MPa, the steam inlet temperature was 180℃, and the outlet temperature was 115℃. The electrolysis temperature was controlled between 115℃ and 125℃. During the collection stage, cooling was required, with water as the heat exchange medium. The inlet water temperature was 30℃ (relatively low), and the inlet water pressure was 0.25MPa. The electrolysis temperature continuously decreased from 115℃ to below 80℃, causing a drop in the electrolysis current. This was because during the cooling process, the electrolyte solidified and precipitated on the cathode surface (i.e., the surface of shell 3), forming a non-conductive solid substance, causing a sudden drop in the electrolysis current. At this point, the water supply was stopped, and steam was replaced. The electrolysis temperature slowly recovered to 110℃, and the electrolysis current recovered.

[0051] Comparative Example 2

[0052] Some parameters differ from those in Example 3. The specific working process is as follows:

[0053] HF and NH3 were mixed in a molar ratio of 2.7:1 to form a molten salt. The electrolysis temperature was set at 125℃, the electrolysis dehydration voltage was 6V, and the electrolysis collection voltage was 7.2V. During the dehydration stage, heating was required. The heat exchange medium was heat transfer oil with an operating temperature above 250℃. The inlet oil pressure was 0.2MPa, and the inlet oil temperature was 280℃ (too high). At the sealed point of the heat transfer oil inlet (where connector 4 connects to the connecting pipe), heat transfer oil leakage and smoke occurred. The leaked heat transfer oil dripped onto the cathode insulation and sealing ring 2, and over time, it ignited, terminating the electrolysis. The cause was that the connecting pipe connected to connector 4 failed to seal at the interface due to high temperature, leading to leakage. When the leaked high-temperature heat transfer oil dripped onto sealing ring 4, it softened the insulation between terminal 1 and the tank cover of the electrolysis equipment, as well as sealing ring 4, causing hydrogen leakage and ignition within the electrolysis equipment.

[0054] The above-described embodiments are detailed and specific, illustrating preferred embodiments of the present invention. They are only used to illustrate the technical ideas and features of the present invention, with the aim of enabling those skilled in the art to understand the content of the present invention and implement it accordingly. However, they are not limited to the present invention, and the patent scope of the present invention cannot be limited by this embodiment alone. That is, any equivalent changes or modifications made to the spirit disclosed in the present invention, without departing from the structure of the present invention, such as local improvements within the system and modifications or transformations between subsystems, are still within the patent scope of the present invention.

Claims

1. A cathode structure for preparing nitrogen trifluoride gas, characterized in that, It includes a conductive shell (3), two tubular conductive terminals (1) fixedly disposed outside the shell (3) at intervals, and a heat exchange tube (5) disposed inside the shell (3). Both terminals (1) are electrically connected to the shell (3). The two ports of the heat exchange tube (5) are fixedly connected to the two terminals (1) respectively. An insulating heat exchange medium flows inside the heat exchange tube (5). The heat exchange medium flows in from one terminal (1) and flows out from the other terminal (1).

2. The cathode structure for preparing nitrogen trifluoride gas according to claim 1, characterized in that, The heat exchange medium is pure water, steam, or heat transfer oil.

3. The cathode structure for preparing nitrogen trifluoride gas according to claim 2, characterized in that, When the heat exchange medium is pure water, it is used to cool the shell (3). The pressure flowing into the corresponding terminal (1) is 0.1MPa to 1MPa, the temperature is 45℃ to 75℃, the outlet temperature of the water flowing out of the corresponding terminal (1) is 60℃ to 85℃, the conductivity of the pure water is 3μS / cm to 8μS / cm, and the salt content is 3mg / L to 5mg / L.

4. The cathode structure for preparing nitrogen trifluoride gas according to claim 2, characterized in that, When the heat exchange medium is water vapor, it is used to heat the shell (3). The water vapor pressure entering the corresponding terminal (1) is 0.1MPa to 0.6MPa, the temperature is 150℃ to 200℃, and the water vapor temperature exiting from the corresponding terminal (1) is 110℃ to 125℃.

5. The cathode structure for preparing nitrogen trifluoride gas according to claim 2, characterized in that, When the heat exchange medium is heat transfer oil, it is used to heat or cool the shell (3). When the heat transfer oil is used to heat the shell (3), the pressure of the heat transfer oil entering the corresponding terminal (1) is 0.1MPa to 0.6MPa, the temperature is 150℃ to 180℃, and the temperature of the heat transfer oil flowing out of the corresponding terminal (1) is 100℃ to 120℃. When the heat transfer oil is used to cool the shell (3), the pressure of the heat transfer oil entering the corresponding terminal (1) is 0.2MPa to 0.8MPa, the temperature is 70℃ to 85℃, and the temperature of the heat transfer oil flowing out of the corresponding terminal (1) is 100℃ to 120℃.

6. The cathode structure for preparing nitrogen trifluoride gas according to claim 1, characterized in that, Two terminals (1) are respectively connected to insulated connecting pipes, which are made of fluororubber, fluoroplastic or fluorometal.

7. The cathode structure for preparing nitrogen trifluoride gas according to claim 1, characterized in that, The terminal (1) is fitted with a sealing ring (2).

8. The cathode structure for preparing nitrogen trifluoride gas according to claim 1, characterized in that, The shell (3) is omitted.

9. The cathode structure for preparing nitrogen trifluoride gas according to claim 1, characterized in that, The heat exchange tube (5) is omitted, and both terminals (1) are connected to the inside of the shell (3).

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