A high-purity nitrogen preparation device with double-tower double-condensation belt liquid pump

Abstract

The application provides a high-purity nitrogen preparation device with double towers, double condensations and a liquid pump, and relates to the technical field of air cryogenic separation and purification. The high-purity nitrogen preparation device with double towers, double condensations and a liquid pump comprises a lower tower, a lower condensation evaporator, an upper tower, an upper condensation evaporator and a liquid nitrogen pump. The liquid nitrogen pump is used to deliver the liquid nitrogen generated by the upper condensation evaporator to the top of the lower tower after pressurization. A storage tank is arranged in front of the liquid nitrogen pump inlet. In the starting stage, the liquid nitrogen pump sends the liquid nitrogen stored in the storage tank to the top of the lower tower. The application stores the liquid nitrogen discharged by the upper condensation evaporator through the storage tank arranged in front of the liquid nitrogen pump, solves the problem of fluctuation caused by small flow of liquid nitrogen, uses the liquid nitrogen in the storage tank to deliver the liquid nitrogen to the top of the lower tower in the starting stage, enables the lower tower to enter the stable state more quickly, delivers the liquid nitrogen to the lower condensation evaporator, completes the initial liquid filling, enables the nitrogen to complete heat exchange to form liquid nitrogen in the starting stage, and promotes the promotion of the stable state.

Description

Technical Field

[0001] This invention relates to the field of air cryogenic separation and purification technology, and in particular to a high-purity nitrogen preparation device with a double-tower double-condenser and liquid pump. Background Technology

[0002] With the rapid development of high-precision technology in China, the demand for nitrogen at various pressures is also increasing, particularly for users requiring nitrogen at pressures of 1500~2000 Nm. 3 Small-scale nitrogen generators with a capacity of [number] / h typically employ a single-tower nitrogen generation process. This process has significant drawbacks, including low extraction rates and higher energy consumption compared to a dual-tower process. However, using a dual-tower pump-equipped design is limited by the availability of liquid nitrogen pumps; the minimum flow rate for liquid nitrogen pumps, both domestically and internationally, is 3 m³ / h. 3 / h is also far greater than the total amount of liquid nitrogen in the nitrogen generator at that flow rate, making it difficult to achieve nitrogen production using a dual-tower pump process.

[0003] Based on the dual-tower distillation technology, a liquid nitrogen pump is added to utilize the secondary distillation of oxygen-enriched liquid air in the upper tower to improve the air extraction rate of the unit. The liquid nitrogen obtained from the secondary distillation in the upper tower is pressurized by the liquid nitrogen pump and sent to the lower tower to increase the liquid nitrogen reflux flow rate in the lower tower, thereby achieving the goal of obtaining more nitrogen from a small volume of air.

[0004] However, when the flow rate of liquid nitrogen entering the liquid nitrogen pump is low, cavitation or pressure instability is likely to occur. When the liquid nitrogen pump is at a low flow rate, insufficient pump inlet pressure causes local vaporization of liquid nitrogen, forming bubbles. When the bubbles enter the high-pressure area and burst, they cause violent impact, causing the flow rate to fluctuate by up to 20%, accompanied by abnormal noise and vibration. When the flow rate of liquid nitrogen is lower than the design value, reverse flow occurs at the impeller inlet of the liquid nitrogen pump, forming a vortex zone and disrupting fluid continuity.

[0005] Furthermore, during the initial startup of the high-purity nitrogen preparation equipment, both nitrogen gas and oxygen-enriched liquid air in the lower condenser evaporator are insufficient. The oxygen-enriched liquid air cannot adequately cover the pipeline containing nitrogen, making heat exchange difficult and resulting in insufficient heat exchange between the two. During the cold start of the unit, the air distillation in the lower column has not yet stabilized, and the accumulation of oxygen-enriched liquid air is insufficient, resulting in a limited liquid air coverage area entering the lower condenser evaporator. At the same time, the nitrogen production at the top of the lower column is unstable, making it impossible to form a continuous and uniform airflow that can fully contact the liquid air.

[0006] Therefore, in order to solve the above problems, this invention proposes a high-purity nitrogen preparation device with a double tower and double condenser and a liquid pump, which aims to improve the operational stability of the liquid nitrogen pump in small nitrogen production equipment under low flow conditions and the ability of cold start heat exchange. Summary of the Invention

[0007] The purpose of this invention is to provide a high-purity nitrogen preparation device with a dual-tower, dual-condenser liquid pump, which aims to solve the problems of insufficient operational stability and long cold start time of liquid nitrogen pumps under low flow conditions.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a high-purity nitrogen preparation device with a double-tower, double-condenser, and liquid pump, comprising a lower tower, a lower condenser-evaporator, an upper tower, and an upper condenser-evaporator, and further comprising:

[0009] A liquid nitrogen pump is used to pressurize the liquid nitrogen generated by the upper condenser evaporator and deliver it to the top of the lower column. The output end of the liquid nitrogen pump is connected to the top of the lower column, and a storage tank is provided in front of the inlet of the liquid nitrogen pump. During the start-up phase, the liquid nitrogen pump delivers the liquid nitrogen stored in the storage tank to the top of the lower column.

[0010] The lower condenser evaporator is equipped with multiple vortex-shaped condenser tubes, which are connected to the top of the lower tower. A connecting pipe is provided in the middle of the condenser tubes, which connects the multiple condenser tubes.

[0011] Preferably, the lower condenser evaporator further includes a shell, and all the condenser tubes are located inside the shell, with the central end of each condenser tube lower than the peripheral end.

[0012] Preferably, the lower end of the connecting pipe is provided with a bundle tube, and the bottom of the housing is provided with a lower convex cavity. The bundle tube is located in the lower convex cavity to ensure that the liquid is still concentrated in the lower convex cavity and in contact with the bundle tube when the liquid level is low.

[0013] Preferably, each of the condenser tubes has a first valve at its air inlet, and the state of the first valve is controlled by the amount of liquid in the lower condenser evaporator.

[0014] Preferably, the shell is further provided with a nozzle, which is connected to the bottom of the lower tower to transport the oxygen-enriched liquid air at the bottom of the lower tower into the lower condenser evaporator.

[0015] Preferably, the output end of the liquid nitrogen pump is also connected to a lower condenser evaporator to transport the liquid nitrogen in the storage tank to the lower condenser evaporator.

[0016] Preferably, the lower condenser evaporator is further provided with a partition to divide the interior of the lower condenser evaporator into two chambers. The partition is funnel-shaped to facilitate the discharge of nitrogen gas. The partition is provided with a second valve to control the connection between the two chambers.

[0017] Preferably, during initial startup, the second valve is closed to prevent liquid nitrogen from contacting oxygen-enriched liquid air. Once the liquid nitrogen in the lower condenser evaporator has completely vaporized and a certain amount of oxygen-enriched liquid air has been stored, the second valve is opened, and the oxygen-enriched liquid air covers all of the condenser tubes.

[0018] Preferably, the bottom of the upper tower is provided with an automatic regulating valve, which controls the flow rate of oxygen-enriched liquid air entering the upper main condenser evaporator.

[0019] Preferably, an electric heater is integrated at the bottom of the upper condenser evaporator to force vaporization of the accumulated liquid when the liquid level in the upper condenser evaporator is too high.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This invention addresses the issue of fluctuations caused by low liquid nitrogen flow by installing a storage tank before the liquid nitrogen pump to store liquid nitrogen discharged from the upper condenser-evaporator. This ensures a stable flow of liquid nitrogen into the pump and prevents damage. During startup, the liquid nitrogen in the storage tank is used to transport it to the top of the lower column, allowing it to reach a stable state more quickly. The liquid nitrogen is then transported to the lower condenser-evaporator for initial filling, enabling heat exchange and liquid nitrogen formation during startup, thus promoting steady-state operation. A funnel-shaped baffle and a second valve provide staged control, achieving initial isolation to prevent mixing. Full coverage of the condenser tubes during operation enhances heat exchange efficiency. The lower convex cavity maintains heat exchange even at low liquid levels, preventing heat exchange interruptions due to insufficient liquid. Attached Figure Description

[0022] Figure 1 This is an overall schematic diagram of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of the lower condenser evaporator in this invention.

[0024] Figure 3 This is a three-dimensional schematic diagram of the lower condenser evaporator in this invention.

[0025] Figure 4 This is a schematic diagram of the structure of the upper condenser evaporator in this invention.

[0026] Figure label:

[0027] 1. Main heat exchanger; 2. Turbine expander; 3. Lower column; 4. Lower condenser-evaporator; 41. Shell; 411. Lower cavity; 412. Liquid nitrogen inlet; 413. Nitrogen outlet; 42. Condenser tube; 421. First valve; 43. Connecting pipe; 44. Bundle tube; 45. Nitrogen pipeline; 46. Nozzle; 461. Atomizing nozzle; 47. Oxygen-enriched liquid air pipeline; 471. Oxygen-enriched liquid air inlet pipe; 472. Oxygen-enriched liquid air outlet pipe; 473. Oxygen-enriched air outlet pipe; 48. Baffle; 481. Second valve; 49. Liquid nitrogen pipeline; 491. Liquid nitrogen first branch pipe; 492. Liquid nitrogen second branch pipe; 5. Upper column; 6. Upper condenser-evaporator; 7. Liquid nitrogen pump; 8. Storage tank; 9. Cold box. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] To improve the operational stability of the liquid nitrogen pump 7 in small nitrogen generators under low flow conditions and its cold start heat exchange capability, such as... Figures 1 to 4 As shown, the present invention proposes a high-purity nitrogen preparation device with a double tower, double condenser, and liquid pump, including a lower tower 3, a lower condenser-evaporator 4, an upper tower 5, an upper condenser-evaporator 6, and a liquid nitrogen pump 7.

[0031] The lower column 3 is used for the initial distillation of air, obtaining oxygen-enriched liquid air at the bottom and high-pressure nitrogen at the top. The lower condenser-evaporator 4 is used to exchange heat between the nitrogen produced at the top of the lower column 3 and the oxygen-enriched liquid air produced at the bottom of the lower column 3, so that the nitrogen and the oxygen-enriched liquid air complete the phase exchange. The upper column 5 is used for the secondary distillation of the oxygen-enriched air produced by the lower condenser-evaporator 4. The upper condenser-evaporator 6 is used to exchange heat between the low-pressure nitrogen produced at the top of the upper column 5 and the oxygen-enriched liquid air after secondary distillation at the bottom of the upper column 5, thereby condensing part of the nitrogen into liquid nitrogen and vaporizing the oxygen-enriched liquid air into waste nitrogen.

[0032] Oxygen-enriched liquid air refers to liquid air with a high oxygen content that accumulates at the bottom of a distillation column.

[0033] The liquid nitrogen pump 7 is used to pressurize the low-pressure liquid nitrogen generated by the upper condenser evaporator 6 and deliver it to the top of the lower tower 3 to increase the liquid nitrogen reflux flow. The liquid nitrogen pump 7 is located near the lower main condenser evaporator. The output end of the liquid nitrogen pump 7 is connected to the top of the lower tower 3. A storage tank 8 is provided in front of the inlet of the liquid nitrogen pump 7. The inlet of the storage tank 8 is connected to the nitrogen pipeline 45 that delivers liquid nitrogen from the upper condenser evaporator 6 to the upper tower 5, so that a portion of the liquid nitrogen discharged from the upper condenser evaporator 6 enters the storage tank 8. The outlet of the storage tank 8 is connected to the inlet of the liquid nitrogen pump 7 to concentrate small flow rates of liquid nitrogen and ensure the stable operation of the liquid nitrogen pump 7.

[0034] Low-pressure liquid nitrogen refers to liquid nitrogen in a low-pressure state formed by initial condensation in the upper condenser evaporator 6. During the start-up phase, the liquid nitrogen pump 7 sends the liquid nitrogen stored in the storage tank 8 to the top of the lower tower 3. The top of the lower tower 3 is equipped with a liquid nitrogen spray distribution device to ensure uniform distribution of the pressurized liquid nitrogen.

[0035] The storage tank 8 can be a cylindrical tank with an inclined inlet, allowing liquid nitrogen to enter along the tangential edge of the tank. Inside the storage tank 8, there is a guide plate spirally arranged to reduce the liquid nitrogen flow rate, promote bubble aggregation and collapse, and reduce the risk of cavitation in the liquid nitrogen pump 7. The storage tank 8 stores the liquid nitrogen discharged from the condenser evaporator 6, solving the problem of fluctuations caused by small liquid nitrogen flow rates, ensuring that liquid nitrogen enters the liquid nitrogen pump 7 stably, and preventing damage to the liquid nitrogen pump 7.

[0036] Storage tank 8 is equipped with a liquid level sensor, which is linked to the liquid nitrogen pump 7 for control, preventing the pump from running dry. Storage tank 8 stores the liquid nitrogen discharged from the upper main condenser evaporator, solving the problem of fluctuations caused by low flow rates. It also replenishes the nitrogen in the lower tower 3 during startup, solving the problems of uneven gas-liquid distribution and insufficient heat exchange in the lower main condenser evaporator.

[0037] Liquid nitrogen pump 7 delivers liquid nitrogen through liquid nitrogen pipeline 49, which is sequentially connected to the upper condenser evaporator 6, storage tank 8, liquid nitrogen pump 7, and the top of the lower tower 3. A separate reflux pipeline can be added to liquid nitrogen pump 7 to stabilize it. Liquid nitrogen pump 7 is a cryogenic liquid pump with frequency conversion control, and its output flow rate can be adjusted according to liquid level or pressure feedback.

[0038] The lower condenser evaporator 4 is equipped with multiple condenser tubes 42, which are connected to the top of the lower tower 3 via nitrogen pipelines. A connecting pipe 43 is provided in the middle of the condenser tubes 42, which connects the multiple condenser tubes 42. The lower condenser evaporator 4 also includes a shell 41, and the condenser tubes 42 are all located inside the shell 41. Each condenser tube 42 is arranged in a vortex shape, and the end of each condenser tube 42 located in the center is lower than the end located in the periphery.

[0039] The condenser tube 42 has a vortex structure with higher periphery and lower center. The connecting pipe 43 is located in the middle of the condenser tube 42, that is, the lowest position of the condenser tube 42, so that the liquid nitrogen generated at each position of the condenser tube 42 can be sent into the connecting pipe 43, preventing the flow of nitrogen from being hindered by the surface tension of the liquid.

[0040] The lower end of the connecting pipe 43 is provided with a bundle tube 44, and the bottom of the housing 41 is provided with a lower convex cavity 411. The bundle tube 44 is located in the lower convex cavity 411, ensuring that the liquid is still concentrated in the lower convex cavity 411 and in contact with the bundle tube 44 when the liquid level is low. Even if there is little liquid in the lower condenser evaporator 4, the liquid can be concentrated in the lower convex cavity 411, so that the liquid is in contact with the bundle tube 44 and heat exchange is guaranteed.

[0041] The bundle tube 44 is connected to the connecting tube 43. The bundle tube 44 divides the nitrogen gas into multiple bundles, increasing the overall flow area of ​​the nitrogen gas and slowing down the flow speed of the nitrogen gas. In addition, the multi-bundle structure allows the nitrogen gas to fully contact the liquid in the recessed cavity, thereby improving the heat exchange efficiency.

[0042] The condenser tube 42 is connected to the top of the lower column 3 by a nitrogen pipeline 45. One end of the nitrogen pipeline 45 is connected to the top of the lower column 3, and the other end is connected to the condenser tube 42. One end of the bundle tube 44 is connected to the top of the lower column 3 by another nitrogen pipeline 45. The two nitrogen pipelines 45, the condenser tube 42, the connecting pipe 43 and the bundle tube 44 together form a nitrogen circuit.

[0043] Each condenser tube 42 has a first valve 421 at its air inlet. The state of the first valve 421 is controlled by the amount of liquid in the lower condenser evaporator 4. When there is little liquid in the lower condenser evaporator 4, only the first valve 421 of the lowest condenser tube 42 is opened. As the liquid level in the lower condenser evaporator 4 rises, the remaining first valves 421 are opened gradually from low to high.

[0044] The first valve 421 can change its opening state according to the liquid level in the lower condenser evaporator 4. When the liquid completely covers a condenser tube 42, the first valve 421 corresponding to that condenser tube 42 opens. The first valve 421 is a low-temperature special valve, which can maintain normal opening and closing at low temperatures. Furthermore, the first valve 421 is an electromagnetic control valve, and its opening and closing state is controlled by the feedback signal from the liquid level sensor. When the liquid level is lower than the set value, the air inlet of part of the condenser tube 42 is closed to maintain the condensation efficiency of the remaining condenser tube 42.

[0045] The lower condenser evaporator 4 is equipped with an oxygen-enriched liquid air pipeline 47, which includes an oxygen-enriched liquid air inlet pipe 471, an oxygen-enriched liquid air outlet pipe 472, and an oxygen-enriched air outlet pipe 473. The oxygen-enriched liquid air outlet pipe 472 and the oxygen-enriched air outlet pipe 473 are both connected to the lower condenser evaporator 4. The oxygen-enriched liquid air outlet pipe 472 transports the excess oxygen-enriched liquid air in the lower condenser evaporator 4 to the bottom of the upper tower 5, and the oxygen-enriched air outlet pipe 473 transports the excess oxygen-enriched air in the lower condenser evaporator 4 to the bottom of the upper tower 5.

[0046] The shell 41 is also equipped with a nozzle 46, which is located at the top inside the shell 41. The nozzle 46 is connected to the bottom of the lower tower 3 and transports the oxygen-enriched liquid air at the bottom of the lower tower 3 into the lower condenser evaporator 4. Multiple mist nozzles 461 are provided below the nozzle 46. The mist nozzles 461 can spray the oxygen-enriched liquid air into the lower condenser evaporator 4 in a mist form. The nozzle 46 is connected to the bottom of the lower tower 3 through the oxygen-enriched liquid air inlet pipe 471.

[0047] The nozzle 46 is equipped with a venturi structure to enhance the atomization effect of the oxygen-enriched liquid air; the nozzle 46 can spray the oxygen-enriched liquid air onto the condenser tube 42, and the upper condenser tube 42 contacts the oxygen-enriched liquid air sprayed from the nozzle 46, converting a portion of the nitrogen inside the condenser tube 42 into liquid nitrogen. Through the spiral shape of the condenser tube 42, the liquid nitrogen is concentrated into the connecting pipe 43, and after passing through the bundle tube 44, it is discharged from the lower condenser evaporator 4.

[0048] The condenser tubes 42 are arranged in multiple layers, which can make multiple contacts with the oxygen-rich liquid air sprayed under the lower condenser evaporator 4 when the liquid is low, thereby improving the heat exchange efficiency. When the liquid is high in the lower condenser evaporator 4, the time of nitrogen in the condenser tubes 42 is increased, thereby improving the heat exchange efficiency. The lower convex cavity 411 is set to keep the condenser evaporator in heat exchange state when the liquid level is low, thus solving the problem of heat exchange interruption when the liquid is insufficient.

[0049] This high-purity nitrogen preparation equipment with dual towers, dual condensers, and liquid pumps also includes a turbine expander 2, a main heat exchanger 1, and a cold box 9. In the main heat exchanger 1, air exchanges heat with the reflux low-temperature oxygen-enriched air and product nitrogen, and after cooling to the dew point, it enters the bottom of the lower tower 3. The oxygen-enriched liquid air in the upper condenser evaporator 6 is evaporated into waste nitrogen by nitrogen. Due to the change from liquid to gas, it returns to the main heat exchanger 1 for reheating and is then drawn into the middle. It is expanded and cooled in the turbine expander 2 and returns to the main heat exchanger 1 to exchange heat with the incoming air. After reheating, it is discharged from the cold box 9, thereby achieving the replenishment of the cooling capacity of the entire system.

[0050] The normal working process of a high-purity nitrogen preparation equipment is as follows:

[0051] After purification, the air is sent into the cold box 9 and first enters the main heat exchanger 1. In the main heat exchanger 1, the air exchanges heat with the reflux low-temperature oxygen-enriched air and product nitrogen. After being cooled to the dew point, it enters the bottom of the lower column 3. In the lower column 3, the air is continuously refined by rising steam and falling liquid. Finally, oxygen-enriched liquid air with a high oxygen content is obtained at the bottom of the lower column 3, and nitrogen with high purity is obtained at the top of the lower column 3. A portion of the nitrogen is reheated by the main heat exchanger 1 and sent out of the cold box 9 as nitrogen product for users. The other portion of the nitrogen enters the lower condenser evaporator 4.

[0052] The liquid air at the bottom of the lower column 3 enters the lower condenser-evaporator 4 through a throttling valve, where it exchanges heat with the nitrogen in the lower condenser-evaporator 4. The nitrogen is liquefied into liquid nitrogen and flows back to the top of the lower column 3. The oxygen-enriched liquid air is evaporated into a gaseous state in the lower condenser-evaporator 4 and then passes through the throttling valve again to the bottom of the upper column 5 for secondary distillation. At the same time, the oxygen-enriched liquid air in the main condenser-evaporator of the lower column 3 is also throttled into the bottom of the upper column 5. Through the continuous distillation of rising steam and falling liquid, oxygen-enriched liquid air with a high oxygen content is finally obtained at the bottom of the upper column 5, and nitrogen with high purity is obtained at the top of the upper column 5.

[0053] At this point, nitrogen gas is introduced into the upper condenser evaporator 6 and exchanges heat with the oxygen-enriched liquid air throttled to the upper condenser evaporator 6 from the bottom of the upper column 5. The nitrogen gas is liquefied into liquid nitrogen, part of which flows back to the top of the upper column 5, and the other part of the liquid nitrogen is sent into the storage tank 8. After the flow rate is stabilized by the storage tank 8, it is sent to the liquid nitrogen pump 7. The liquid nitrogen pump 7 pressurizes the liquid nitrogen gas and introduces it into the top of the lower column 3 to increase the nitrogen extraction rate.

[0054] In the upper condenser evaporator 6, the oxygen-rich liquid air is evaporated into polluted nitrogen by nitrogen, changing from liquid to gas. It returns to the main heat exchanger 1 for reheating and is then drawn into the middle. After expansion and cooling in the turbine expander 2, it returns to the main heat exchanger 1 to exchange heat with the incoming air. After reheating, it is discharged from the cold box 9, thus achieving the replenishment of the cooling capacity of the entire system.

[0055] Start-up process of high-purity nitrogen preparation equipment:

[0056] During the start-up phase, purified air is sent into the cold box 9 and then into the main heat exchanger 1 to complete heat exchange with the reflux low-temperature oxygen-enriched air and product nitrogen. After cooling, it enters the bottom of the lower column 3. At the same time, liquid nitrogen is stored in the storage tank 8, and the liquid nitrogen pump 7 sends the liquid nitrogen in the storage tank 8 to the top of the lower column 3. At this time, the bottom of the lower column 3 is mostly air, and the top is liquid nitrogen. The air and liquid nitrogen come into contact and are continuously distilled through rising steam and falling liquid. Oxygen-enriched liquid air is gradually generated at the bottom of the lower column 3, and nitrogen is generated at the top of the lower column 3.

[0057] Liquid nitrogen is introduced into the top of the lower column 3 to promote distillation, accelerate the pressure rise in the lower column 3, accelerate the flow of oxygen-enriched liquid air into the lower condenser evaporator 4, accelerate the accumulation of liquid in the lower condenser evaporator 4, establish reflux in the lower column 3, and accelerate the stability of the distillation system.

[0058] In this embodiment, by setting up a storage tank 8 before the liquid nitrogen pump 7 to store the liquid nitrogen discharged from the upper condenser evaporator 6, the problem of fluctuations caused by small liquid nitrogen flow is solved, ensuring that liquid nitrogen enters the liquid nitrogen pump 7 stably and preventing damage to the liquid nitrogen pump 7. During the start-up phase, the liquid nitrogen in the storage tank 8 is used to transport the liquid nitrogen to the top of the lower column 3, so that the lower column 3 can enter a stable state more quickly. By setting up the lower convex cavity 411, the condenser evaporator is kept in heat exchange state when the liquid level is low, solving the problem of heat exchange interruption when the liquid is insufficient.

[0059] Example 2

[0060] In actual use, during the cold start of the device, the air distillation in the lower column 3 is not yet stable, and the accumulation of oxygen-rich liquid air is insufficient, resulting in a limited liquid air coverage area entering the lower condenser evaporator 4, leading to insufficient heat exchange in the lower condenser evaporator 4.

[0061] To solve the above-mentioned technical problems, in another embodiment of the present invention, the output end of the liquid nitrogen pump 7 is also connected to the lower condenser evaporator 4, so that the liquid nitrogen in the storage tank 8 is transported to the lower condenser evaporator 4 through the liquid nitrogen inlet 412.

[0062] Part of the liquid nitrogen stored in storage tank 8 is sent to the top of lower tower 3, and the other part is sent to lower condenser evaporator 4. The liquid nitrogen sent to lower condenser evaporator 4 exchanges heat with the nitrogen gas generated in lower tower 3 in condenser tube 42. The pressure of the liquid nitrogen sent to lower condenser evaporator 4 must be controlled. The pressure of liquid nitrogen is lower than that of nitrogen gas, so that liquid nitrogen vaporization and nitrogen gas liquefaction can be carried out simultaneously.

[0063] The lower condenser evaporator 4 is also equipped with a baffle 48, which divides the interior of the lower condenser evaporator 4 into two chambers. During initial operation, one chamber is filled with liquid nitrogen, and the other chamber is prepared to store oxygen-enriched liquid air. The lower chamber is filled with liquid nitrogen, and the upper chamber stores oxygen-enriched liquid air. The baffle 48 is funnel-shaped to facilitate the discharge of nitrogen gas, allowing the generated nitrogen gas to be better discharged from the lower condenser evaporator 4. A second valve 481 is provided on the baffle 48, which can control the connection between the two chambers.

[0064] The lower chamber of the lower condenser evaporator 4 is provided with a liquid nitrogen inlet 412 for filling liquid nitrogen and a nitrogen outlet 413 for discharging nitrogen. The upper chamber is provided with an oxygen-enriched liquid air inlet, an oxygen-enriched liquid air outlet and an oxygen-enriched air outlet, wherein the oxygen-enriched air outlet is located at the top of the lower condenser evaporator 4.

[0065] The liquid nitrogen pipeline 49 includes a first liquid nitrogen branch pipe 491 and a second liquid nitrogen branch pipe 492. The first liquid nitrogen branch pipe 491 connects the top of the lower tower 3 to the liquid nitrogen pump 7, and sends the liquid nitrogen pumped by the liquid nitrogen pump 7 into the top of the lower tower 3. The second liquid nitrogen branch pipe 492 connects the lower condenser evaporator 4 and the liquid nitrogen pump 7, and sends the liquid nitrogen pumped by the liquid nitrogen pump 7 into the lower cavity of the lower condenser evaporator 4 through the liquid nitrogen inlet 412. The nitrogen gas converted by heat exchange is discharged from the lower condenser evaporator 4 through the nitrogen outlet 413. Since the nitrogen gas discharged from the nitrogen outlet 413 is pure nitrogen gas, it can be reheated by the main heat exchanger 1 and then sent out of the cold box 9.

[0066] During initial startup, the second valve 481 is closed to prevent liquid nitrogen from contacting oxygen-enriched liquid air. Once the liquid nitrogen in the current condenser-evaporator 4 is completely vaporized and a certain amount of oxygen-enriched liquid air is stored, the second valve 481 opens, allowing the oxygen-enriched liquid air to enter the original liquid nitrogen chamber. During normal operation, the second valve 481 remains open, with the oxygen-enriched liquid air located in both chambers, covering all the condenser tubes 42 and ensuring efficient heat exchange.

[0067] The nitrogen outlet 413 is equipped with a valve. When liquid nitrogen is filled into the lower condenser evaporator 4, the valve of the nitrogen outlet 413 is opened. When the liquid nitrogen is completely vaporized and a certain amount of oxygen-enriched liquid air is stored, the valve of the nitrogen outlet 413 is closed to ensure that the output is nitrogen gas, rather than a mixture of nitrogen gas and oxygen-enriched air.

[0068] The second valve 481 can be controlled by a PLC controller. Its opening conditions include complete vaporization of liquid nitrogen in the condenser and the oxygen-rich liquid air level reaching a set threshold. The control logic can include multiple signal linkage judgments of temperature, pressure, and liquid level.

[0069] The output end of the liquid nitrogen pump 7 can be equipped with a three-way switching valve to select the liquid nitrogen delivery path according to the equipment operation stage. In the initial stage of equipment startup, liquid is supplied to the lower condenser evaporator 4 first to speed up the precooling process. After sufficient liquid nitrogen is stored in the lower condenser evaporator 4, liquid nitrogen is supplied to the top of the lower tower 3 to speed up the stabilization of the lower tower 3.

[0070] In this embodiment, the liquid nitrogen first branch pipe 491 and liquid nitrogen second branch pipe 492 connected to the output end of the liquid nitrogen pump 7 can each be equipped with a valve, so that the liquid nitrogen pump 7 can simultaneously supply liquid nitrogen to the top of the lower tower 3 and the lower condenser evaporator 4 at the initial stage of equipment startup. At this time, the opening and closing state of the valves on the liquid nitrogen first branch pipe 491 and liquid nitrogen second branch pipe 492 is controlled so that the pressure in the liquid nitrogen second branch pipe 492 is lower than the pressure in the liquid nitrogen first branch pipe 491; and when the liquid nitrogen in the lower condenser evaporator 4 reaches the set amount, the valve on the liquid nitrogen second branch pipe 492 is closed, and the liquid nitrogen pump 7 only supplies liquid nitrogen to the top of the lower tower 3.

[0071] In this embodiment, the start-up process of the high-purity nitrogen preparation equipment is as follows:

[0072] Air is sent to the bottom of the lower tower 3 after passing through the main heat exchanger 1. At the same time, the liquid nitrogen pump 7 sends liquid nitrogen from the storage tank 8 to the top of the lower tower 3 and the lower chamber of the lower condenser-evaporator 4. At this time, the second valve 481 is closed. When the liquid nitrogen in the lower condenser-evaporator 4 reaches the set amount, the liquid nitrogen pump 7 stops sending liquid nitrogen to the lower condenser-evaporator 4. The liquid nitrogen in the lower tower 3 comes into contact with the air, and nitrogen gas and oxygen-enriched liquid air are produced. The pressure in the lower tower 3 gradually increases. The nitrogen gas enters the condenser tube 42, and the oxygen-enriched liquid air enters the upper chamber of the lower condenser-evaporator 4. Since the amount of oxygen-enriched liquid air entering the lower condenser-evaporator 4 is not large, the nitrogen gas exchanges heat with the liquid nitrogen in the lower chamber. The nitrogen gas is liquefied and flows back to the top of the lower tower 3 through the nitrogen gas pipeline 45. The liquid nitrogen is vaporized and discharged from the nitrogen gas outlet 413. At this time, only the bottom of the first valve 421 is open. After the accumulation of oxygen-enriched liquid air, the first valve 421 opens sequentially from low to high.

[0073] Once the liquid nitrogen is completely vaporized and a certain amount of oxygen-enriched liquid air is stored, the valve at the nitrogen outlet 413 is closed, and the second valve 481 is opened. The oxygen-enriched liquid air on the upper side of the partition 48 enters the lower side of the partition 48 through the second valve 481, filling the lower chamber inside the lower condenser evaporator 4. The oxygen-enriched liquid air completely covers the condenser tube 42, ensuring the efficient operation of the lower condenser evaporator 4. As the amount of liquid nitrogen discharged from the lower condenser evaporator 4 entering the top of the lower tower 3 increases, the amount of liquid nitrogen pumped by the liquid nitrogen pump 7 to the top of the lower tower 3 gradually decreases until the entire device enters a stable working state, and the liquid nitrogen pump 7 also maintains a stable working state.

[0074] This invention utilizes liquid nitrogen from storage tank 8 during the startup phase to transport liquid nitrogen to the lower condenser evaporator 4, completing the initial liquid filling and enabling nitrogen to complete heat exchange to form liquid nitrogen during the startup phase, thus promoting steady-state propulsion. The funnel-shaped baffle 48 and the second valve 481 control the process in stages to achieve initial isolation and prevent mixing, while the condenser tube 42 is fully covered during operation to improve heat exchange efficiency and enhance the cold start heat exchange capability.

[0075] Example 3

[0076] In actual use, since the oxygen-enriched liquid air in the upper column 5 has already undergone rectification in the lower column 3, the nitrogen content in the oxygen-enriched liquid air here is not high, and there is less nitrogen at the top of the upper column 5. As a result, less nitrogen enters the upper main condenser and evaporator. When the rectification intensity of the upper column 5 increases, leading to an increase in liquid air production, more oxygen-enriched liquid air enters the upper main condenser and evaporator. When the oxygen-enriched liquid air exchanges heat with nitrogen, the amount of nitrogen is insufficient to convert enough oxygen-enriched liquid air into gas for discharge, causing liquid accumulation in the upper main condenser and evaporator.

[0077] To solve the above-mentioned technical problems, in another embodiment of the present invention, based on the structure in the above embodiment, an automatic regulating valve is added to the bottom of the upper tower 5. The automatic regulating valve controls the flow rate of oxygen-enriched liquid air entering the upper main condenser evaporator and adjusts it in real time according to the nitrogen production at the top and the load of the upper tower 5. When the nitrogen sensor detects a decrease in flow rate, the liquid air input is automatically reduced.

[0078] The upper condenser evaporator 6 has a similar structure to the lower condenser evaporator 4. The difference is that the upper condenser evaporator 6 does not have a baffle 48, a liquid nitrogen inlet 412, and a nitrogen outlet 413. The rest of the structure of the upper condenser evaporator 6 is the same as that of the lower condenser evaporator. The structure of the bundle tube 44 and the lower concave cavity can ensure that the oxygen-rich liquid air and nitrogen can complete the heat exchange. The lower convex cavity 411 can be equipped with a heating wire to prevent the low-temperature liquid from freezing and blocking when the liquid level is low.

[0079] By monitoring changes in oxygen-enriched liquid air flow rate in real time, the opening of the automatic regulating valve is dynamically adjusted to maintain the set flow rate value. When the distillation intensity of column 5 increases, leading to an increase in liquid air production, the opening of the automatic regulating valve automatically decreases to suppress flow overshoot; when the heat exchange load of the main condenser-evaporator decreases, the automatic regulating valve closes proportionally to reduce the medium supply. This effectively avoids a decrease in distillation efficiency caused by sudden changes in flow rate, and significantly improves the purity and stability of nitrogen products.

[0080] In this embodiment, an electric heater can also be integrated at the bottom of the upper condenser evaporator 6 to force vaporization of the accumulated liquid when the liquid level in the upper condenser evaporator 6 is too high. The electric heater is equipped with a power adjustment module, which can adjust the heating intensity according to the liquid level; the heater surface is provided with a thermal insulation layer to prevent heat loss or affecting the operation of other components.

[0081] The electric heater can be implemented using resistance wire, PTC heating element, or thin-film heater, among other methods. Resistance wire heating can be adapted to different evaporator bottom structures by adjusting the power density. The heater control module can be configured to link with a liquid level sensor, automatically initiating the heating program when the liquid level exceeds a set threshold. In practice, heat-conducting fins can be installed on the heater surface to increase the heat exchange area. Embedded mounting is preferred for bottom installation to ensure efficient heat transfer with the evaporator body. The temperature feedback system monitors the vaporization state of the accumulated liquid in real time and automatically stops heating when the liquid level returns to normal.

[0082] When the liquid level in the upper condenser evaporator 6 is abnormally high, the electric heater immediately provides directional heating to the liquid at the bottom, promoting rapid vaporization of the oxygen-rich liquid air and effectively preventing a decrease in heat transfer efficiency due to excessively high liquid levels. The bottom heating design ensures that heat energy acts directly on the core area of ​​the liquid accumulation, avoiding temperature interference with the upper distillation process.

[0083] This invention dynamically adjusts the amount of oxygen-enriched liquid air entering the upper condenser evaporator 6 by setting an automatic regulating valve, effectively avoiding the decrease in distillation efficiency caused by sudden changes in flow rate, and significantly improving the purity and stability of nitrogen products. By setting an electric heater, the liquid at the bottom is heated in a directional manner, which promotes the rapid vaporization of oxygen-enriched liquid air and effectively prevents the decrease in heat transfer efficiency caused by excessively high liquid levels. It is particularly suitable for small nitrogen production systems with frequent flow fluctuations. By maintaining stable liquid levels through closed-loop control, the system reliability is significantly improved compared to traditional passive adjustment methods.

[0084] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-purity nitrogen preparation device with a double-tower, double-condenser, and liquid pump, comprising a lower tower (3), a lower condenser-evaporator (4), an upper tower (5), and an upper condenser-evaporator (6), characterized in that, Also includes: A liquid nitrogen pump (7) is used to pressurize the liquid nitrogen generated by the upper condenser evaporator (6) and deliver it to the top of the lower tower (3). The output end of the liquid nitrogen pump (7) is connected to the top of the lower tower (3). A storage tank (8) is provided in front of the inlet of the liquid nitrogen pump (7). The inlet of the storage tank (8) is connected to the pipeline that outputs liquid nitrogen from the upper condenser evaporator (6), so that a portion of the liquid nitrogen discharged from the upper condenser evaporator (6) enters the storage tank (8). The inlet of the storage tank (8) is inclined, so that the liquid nitrogen enters the interior along the tangent edge of the storage tank (8). A guide plate is provided inside the storage tank (8), and the guide plate is spirally arranged inside the storage tank (8). The outlet of the storage tank (8) is connected to the inlet of the liquid nitrogen pump (7) for concentrating a small flow of liquid nitrogen. During the start-up phase, the liquid nitrogen pump (7) sends the liquid nitrogen stored in the storage tank (8) to the top of the lower tower (3). The lower condenser evaporator (4) is provided with a plurality of vortex-shaped condenser tubes (42), the condenser tubes (42) are connected to the top of the lower tower (3), and a connecting pipe (43) is provided in the middle of the condenser tubes (42), the connecting pipe (43) connects the plurality of condenser tubes (42), and the end of each condenser tube (42) located in the center is lower than the end located in the periphery; The lower condenser evaporator (4) also includes a shell (41), the condenser tubes (42) are all located inside the shell (41), the lower end of the connecting tube (43) is provided with a bundle tube (44), the bottom of the shell (41) is provided with a lower convex cavity (411), the bundle tube (44) is located in the lower convex cavity (411), ensuring that the liquid is still concentrated in the lower convex cavity (411) and in contact with the bundle tube (44) when the liquid level is low.

2. The high-purity nitrogen preparation equipment according to claim 1, characterized in that, Each of the condenser tubes (42) is provided with a first valve (421) at its air inlet, the state of which is controlled by the amount of liquid in the lower condenser evaporator (4).

3. The high-purity nitrogen preparation equipment according to claim 1, characterized in that, The shell (41) is also equipped with a nozzle (46), which is connected to the bottom of the lower tower (3) to transport the oxygen-rich liquid air at the bottom of the lower tower (3) into the lower condenser evaporator (4).

4. The high-purity nitrogen preparation equipment according to claim 1, characterized in that, The output end of the liquid nitrogen pump (7) is also connected to the lower condenser evaporator (4) to transport the liquid nitrogen in the storage tank (8) to the lower condenser evaporator (4).

5. The high-purity nitrogen preparation equipment according to claim 4, characterized in that, The lower condenser evaporator (4) is also provided with a partition (48) to divide the interior of the lower condenser evaporator (4) into two chambers. The partition (48) is funnel-shaped to facilitate the discharge of nitrogen. The partition (48) is provided with a second valve (481) to control the connection between the two chambers.

6. The high-purity nitrogen preparation equipment according to claim 5, characterized in that, During initial startup, the second valve (481) is closed to prevent liquid nitrogen from contacting oxygen-enriched liquid air. When the liquid nitrogen in the lower condenser evaporator (4) is completely vaporized and a certain amount of oxygen-enriched liquid air is stored, the second valve (481) is opened, and the oxygen-enriched liquid air covers all of the condenser tubes (42).

7. The high-purity nitrogen preparation equipment according to claim 1, characterized in that, The bottom of the upper tower (5) is equipped with an automatic regulating valve, which controls the flow rate of oxygen-enriched liquid air entering the upper main condenser evaporator.

8. The high-purity nitrogen preparation equipment according to claim 1, characterized in that, An electric heater is integrated at the bottom of the upper condenser evaporator (6) to force vaporization of the accumulated liquid when the liquid level in the upper condenser evaporator (6) is too high.

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