Nitrogen-making system utilizing double towers and double condensing heat exchangers for rectification
By adopting the distillation process of double tower and double condensation heat exchanger in the nitrogen production system of float glass manufacturers, the problems of low nitrogen extraction rate and high usage cost in the single tower nitrogen production process are solved, and more efficient nitrogen extraction and oxygen-rich generation are achieved, reducing energy consumption and material waste.
Patent Information
- Application Number
- CN202421918360.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-09
- Publication Date
- 2025-05-16
- Estimated Expiration
- 2034-08-09
AI Technical Summary
When floating glass manufacturers use the single tower nitrogen production process, there is a problem of high usage costs. The reason is that the nitrogen extraction rate in compressed air is low, resulting in energy consumption and material waste, which increases the cost of later use.
A distillation nitrogen production system is adopted with a double tower and a double condensation heat exchanger. By setting up an upper tower, a first main condensation heat exchanger and a lower tower in the distillation main tower, and distillation is performed multiple times using liquid nitrogen reflux and a multi-stage condensation heat exchanger to improve the nitrogen extraction rate and oxygen-rich oxygen content.
The proportion of nitrogen components extracted from compressed air is increased, the cost of use of enterprises is reduced, and an oxygen-rich nitrogen source with higher oxygen content is provided, reducing energy consumption and material waste.
Smart Images
Figure CN222881515U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the field of nitrogen production equipment, in particular to a nitrogen production system utilizing double towers and double condensation heat exchangers for rectification. Background Art
[0002] The float glass manufacturing process is a common process for glass manufacturing. The gases required in the float glass manufacturing process include the protective gas of the tin bath and the oxygen-enriched combustion-supporting gas required by the glass production line kiln. According to the load of the glass production kiln, the gas supply device needs to continuously supply protective gas to the tin bath and supply the gas source of the oxygen-enriched combustion-supporting gas to the glass production line kiln. The oxygen content of the oxygen-enriched combustion-supporting gas is required to be maintained between 33% and 38%. Therefore, the oxygen content of the oxygen-enriched combustion-supporting gas source only needs to be greater than 38%. The cryogenic distillation process only needs to meet the continuous supply of industrial nitrogen as a protective gas and the supply of gas with an oxygen content greater than 38% as an oxygen-enriched source. Therefore, most of the air separation equipment supporting cryogenic distillation of float glass production enterprises adopts a single-tower nitrogen production process. The reason is that the single-tower nitrogen production process is a relatively mature classic nitrogen production process, and the initial investment amount is relatively small.
[0003] The classic single-tower nitrogen production process is that the air enters the distillation tower after being purified. The refluxed product nitrogen and oxygen-rich air are cooled to the dew point temperature in the main heat exchanger and then enter the distillation tower for distillation. High-purity nitrogen is obtained at the top of the distillation tower. Part of the oxygen-rich liquid air is extracted from the bottom of the tower, enters the condenser evaporator after throttling, and the evaporated gas is reheated in the main heat exchanger and then enters the expander for expansion, so as to provide most of the cooling capacity of the nitrogen production equipment and provide oxygen-rich air after the evaporation of the oxygen-rich liquid air as a by-product.
[0004] Float glass enterprises have a high cost of using the classic single-tower nitrogen production process to produce nitrogen and oxygen-enriched air. The specific reason is that the gas volume of finished nitrogen produced by the distillation equipment of the single-tower nitrogen production process as a raw material accounts for a relatively low proportion of the gas volume of compressed air input. Therefore, more compressed air needs to be transported to the distillation equipment of the single-tower nitrogen production process to produce the nitrogen required by the float glass enterprise process. It is undoubtedly necessary to consume more energy costs to transport more compressed air to the distillation equipment of the single-tower nitrogen production process. And it is precisely because the single-tower nitrogen production process extracts nitrogen from compressed air at a low ratio that the oxygen content in the oxygen-enriched air produced by the single-tower nitrogen production process after evaporation of oxygen-enriched liquid air is relatively low. Therefore, the distillation equipment corresponding to the single-tower nitrogen production process has energy consumption and material waste. The corresponding float glass enterprises use this equipment although the initial investment is small, but the cost of use will increase in the later period. Therefore, targeted design and development should be carried out for the gaseous products required by float glass enterprises, and the proportion of nitrogen components extracted from compressed air should be increased as much as possible to reduce the use of finished products by enterprises to meet market demand. Summary of the invention
[0005] In view of the deficiencies in the prior art, the utility model provides a nitrogen production system using double towers and double condensing heat exchangers for distillation, which can improve the ratio of the gas volume of the distillation output nitrogen component to the gas volume of the input compressed air, and is used to overcome the defects in the prior art.
[0006] The technical solution adopted by the utility model is: a nitrogen production system using double towers and double condensing heat exchangers for distillation, comprising a main distillation tower, the main distillation tower comprising an upper tower, a first main condensing heat exchanger and a lower tower from top to bottom, a finished nitrogen gas delivery pipe is arranged on the upper tower, a second main condensing heat exchanger is arranged on the outer side of the main distillation tower, a first regulating valve is arranged on the finished nitrogen gas delivery pipe, an inlet end of a heat source channel of the first main condensing heat exchanger and an inlet end of a heat source channel of the second main condensing heat exchanger are respectively connected to the top of the lower tower, an outlet end of the heat source channel of the first main condensing heat exchanger is provided with a liquid nitrogen delivery main pipe, and the liquid nitrogen delivery main pipe is connected to the liquid nitrogen delivery main pipe. A second regulating valve, an outlet end of a first liquid nitrogen delivery branch pipe, an inlet end of a second liquid nitrogen delivery branch pipe, an inlet end of a third liquid nitrogen delivery branch pipe and a third regulating valve are sequentially arranged along the direction from close to the first main condensing heat exchanger to far away from the first main condensing heat exchanger. The inlet end of the first liquid nitrogen delivery branch pipe is connected to the outlet end of the heat source channel of the second main condensing heat exchanger, the outlet end of the second liquid nitrogen delivery branch pipe is connected to the top of the lower tower, the outlet end of the third liquid nitrogen delivery branch pipe is connected to the top of the upper tower, and the cold source channel of the second main condensing heat exchanger is connected to the cold source channel of the first main condensing heat exchanger through the first oxygen-rich liquid air delivery pipe.
[0007] Preferably, the upper tower and the lower tower are connected through a second oxygen-enriched liquid air delivery pipe, and a fourth regulating valve is respectively provided on the first oxygen-enriched liquid air delivery pipe, the second oxygen-enriched liquid air delivery pipe, the first liquid nitrogen delivery branch pipe, the second liquid nitrogen delivery branch pipe and the third liquid nitrogen delivery branch pipe.
[0008] Preferably, it also includes a main heat exchanger, the main heat exchanger and the lower tower are provided with a raw air delivery pipe, part of the finished nitrogen delivery pipe is installed on the main heat exchanger, the finished nitrogen delivery pipe is connected to the main heat exchanger, the second main condensing heat exchanger cold source channel and the main heat exchanger are provided with a first dirty nitrogen delivery pipe, the liquid nitrogen delivery main pipe between the second liquid nitrogen delivery branch pipe and the third liquid nitrogen delivery branch pipe, the second oxygen-enriched liquid air delivery pipe, the first dirty nitrogen delivery pipe between the main heat exchanger and the second main condensing heat exchanger, and the finished nitrogen delivery pipe between the main heat exchanger and the upper tower are provided with a subcooler.
[0009] Preferably, a turbine expander is provided on the outlet end of the first dirty nitrogen gas conveying pipe, and the number of turbine expanders is at least two. The inlet of the expansion end of each turbine expander and the outlet end of the first dirty nitrogen gas conveying pipe are respectively connected through the second dirty nitrogen gas conveying pipe, and each second dirty nitrogen gas conveying pipe is respectively provided with a fifth regulating valve. The main heat exchanger is provided with a third dirty nitrogen gas conveying pipe, and the outlet of each turbine expander expansion end is respectively connected to the inlet end of the third dirty nitrogen gas conveying pipe.
[0010] Preferably, a boosting delivery branch pipe is respectively provided on the boosting end of each of the turboexpanders, the inlet end of each boosting delivery branch pipe is connected to the outlet end of the finished nitrogen delivery pipe, a plurality of boosting delivery branch pipes are provided with a boosting nitrogen delivery pipe on their outlet ends, each boosting delivery branch pipe is respectively provided with a stop valve and a check valve in sequence along the direction from the finished nitrogen delivery pipe to the boosting nitrogen delivery pipe, the number of the boosting delivery branch pipes corresponds to the number of the boosting ends of the turboexpander, and the boosting end of the turboexpander on each boosting delivery branch pipe is located between the corresponding stop valve and the corresponding check valve.
[0011] Preferably, liquid level sensors are respectively provided at the bottom of the upper tower, the cold source channel of the first main condensing heat exchanger, and the cold source channel of the second main condensing heat exchanger.
[0012] Preferably, a pressure sensor is provided on the finished nitrogen delivery pipe between the first regulating valve and the upper tower.
[0013] The utility model has the following beneficial effects: firstly, the utility model utilizes the main distillation tower of the traditional full distillation cryogenic distillation process as the main distillation component of the product, utilizes part of the liquid nitrogen after cooling transported from the liquid nitrogen transport main pipe as the reflux liquid and continuously transported to the heat source channel of the first main condensing heat exchanger to form a heat source structure to perform a second distillation on the first oxygen-rich liquid air transported from the lower tower to the upper tower, and further extracts the nitrogen component in the first oxygen-rich liquid air, so that the extraction rate of the nitrogen component in the purified compressed air transported by the raw material air transport pipe as the raw material in the whole distillation system is improved compared with the single-tower single-process, and the oxygen-rich liquid air from which the nitrogen component is further extracted is continuously transported from the cold source channel of the first main condensing heat exchanger to the cold source channel of the second main condensing heat exchanger for evaporation to form oxygen-rich polluted nitrogen with higher oxygen content than the single-tower single-process, and has a higher taste as an oxygen-rich source. Although this product is more complex in structure than the single-tower nitrogen production process, the extraction rate of nitrogen content in unit volume of compressed air is increased, thereby reducing the cost of nitrogen use for float glass manufacturers and providing oxygen-enriched polluted nitrogen with a higher oxygen content.
[0014] Secondly, an online chromatograph is arranged on the third contaminated nitrogen delivery pipe of the utility model, and the installation of the online chromatograph is convenient for feedback of component parameters.
[0015] The utility model has the advantages of simple structure, convenient operation, ingenious design, greatly improved work efficiency, good social and economic benefits, and is a product that is easy to promote and use. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 It is a structural schematic diagram of the utility model. DETAILED DESCRIPTION
[0017] like Figure 1 As shown, a nitrogen production system using double towers and double condensing heat exchangers for distillation includes a main distillation tower, the main distillation tower includes an upper tower 1, a first main condensing heat exchanger 2 and a lower tower 3 from top to bottom, a finished nitrogen gas delivery pipe 4 is arranged on the upper tower 1, a second main condensing heat exchanger 5 is arranged on the outer side of the main distillation tower, a first regulating valve 6 is arranged on the finished nitrogen gas delivery pipe 4, an inlet end of the heat source channel of the first main condensing heat exchanger 2 and an inlet end of the heat source channel of the second main condensing heat exchanger 5 are respectively connected to the top of the lower tower 3, and an outlet end of the heat source channel of the first main condensing heat exchanger 2 is provided with a liquid nitrogen delivery main pipe 7, and the liquid nitrogen delivery main pipe 7 is arranged along the first main condensing heat exchanger 2 near the first main condensing heat exchanger 2. The heat exchanger 2 is provided with a second regulating valve 8, an outlet end of a first liquid nitrogen delivery branch pipe 9, an inlet end of a second liquid nitrogen delivery branch pipe 10, an inlet end of a third liquid nitrogen delivery branch pipe 11 and a third regulating valve 12 in sequence in the direction away from the first main condensing heat exchanger 2. The inlet end of the first liquid nitrogen delivery branch pipe 9 is connected to the outlet end of the heat source channel of the second main condensing heat exchanger 5, the outlet end of the second liquid nitrogen delivery branch pipe 10 is connected to the top of the lower tower 3, the outlet end of the third liquid nitrogen delivery branch pipe 11 is connected to the top of the upper tower 1, and the cold source channel of the second main condensing heat exchanger 5 is connected to the cold source channel of the first main condensing heat exchanger 2 through the first oxygen-rich liquid air delivery pipe 13. The upper tower 1 and the lower tower 3 are connected through the second oxygen-rich liquid air delivery pipe 14, and the first oxygen-rich liquid air delivery pipe 13, the second oxygen-rich liquid air delivery pipe 14, the first liquid nitrogen delivery branch pipe 9, the second liquid nitrogen delivery branch pipe 10 and the third liquid nitrogen delivery branch pipe 11 are respectively provided with a fourth regulating valve 15.
[0018] In addition, the product also includes a main heat exchanger 16. A raw material air delivery pipe 17 is provided on the main heat exchanger 16 and the lower tower 3. Part of the finished nitrogen delivery pipe 4 is installed on the main heat exchanger 16. The finished nitrogen delivery pipe 4 is connected to the main heat exchanger 16. A first dirty nitrogen delivery pipe 18 is provided on the cold source channel of the second main condensing heat exchanger 5 and the main heat exchanger 16. A subcooler 19 is provided on the liquid nitrogen delivery main pipe 7 between the second liquid nitrogen delivery branch pipe 10 and the third liquid nitrogen delivery branch pipe 11, the second oxygen-enriched liquid air delivery pipe 14, the first dirty nitrogen delivery pipe 18 between the main heat exchanger 16 and the second main condensing heat exchanger 5, and the finished nitrogen delivery pipe 4 between the main heat exchanger 16 and the upper tower 1. A turbine expander 20 is arranged at the outlet end of the first dirty nitrogen gas conveying pipe 18, and the number of turbine expanders 20 is at least two. The inlet of the expansion end of each turbine expander 20 and the outlet end of the first dirty nitrogen gas conveying pipe 18 are respectively connected through a second dirty nitrogen gas conveying pipe 22, and each second dirty nitrogen gas conveying pipe 22 is respectively provided with a fifth regulating valve 23. A third dirty nitrogen gas conveying pipe 24 is arranged on the main heat exchanger 16, and the outlet of each expansion end of the turbine expander 20 is respectively connected to the inlet end of the third dirty nitrogen gas conveying pipe 24. A boosting delivery branch pipe 21 is respectively provided on the boosting end of each of the turboexpanders 20, and the inlet end of each boosting delivery branch pipe 21 is connected to the outlet end of the finished nitrogen delivery pipe 4. A boosting nitrogen delivery pipe 25 is provided on the outlet end of a plurality of boosting delivery branch pipes 21. Each boosting delivery branch pipe 21 is respectively provided with a stop valve 26 and a check valve 27 in sequence along the direction from the finished nitrogen delivery pipe 4 to the boosting nitrogen delivery pipe 25. The number of the boosting delivery branch pipes 21 corresponds to the number of the boosting ends of the turboexpanders 20, and the boosting end of the turboexpander 20 on each boosting delivery branch pipe 21 is located between the corresponding stop valve 26 and the corresponding check valve 27.
[0019] Liquid level sensors 28 are respectively provided at the bottom of the upper tower 1, the cold source channel of the first main condensing heat exchanger 2 and the cold source channel of the second main condensing heat exchanger 5; the installation of the liquid level sensors 28 facilitates the feedback of liquid level parameters.
[0020] A pressure sensor 30 is provided on the finished nitrogen gas delivery pipe 4 between the first regulating valve 6 and the upper tower 1; the pressure sensor 30 is installed to facilitate the feedback of pressure parameters.
[0021] The usage of this product is as follows: Figure 1 As shown, the following steps are included:
[0022] S1, the purified compressed air is delivered to the raw air delivery pipe 17 and then delivered to the lower tower 3 as a distillation raw material after heat exchange through the heat source channel of the main heat exchanger 16 and the cold source continuously delivered to the main heat exchanger 16. After the compressed air enters the lower tower 3, it forms a first ascending airflow and performs countercurrent heat exchange with the first condensate reflux liquid entering the lower tower 3 while continuously ascending along the inner cavity of the lower tower 3. The nitrogen component of the first condensate reflux liquid is vaporized and merged into the first ascending airflow and ascends together, and the oxygen component in the first ascending airflow is liquefied and merged with the first condensate reflux liquid to form a first descending liquid flow during the countercurrent heat exchange with the first condensate reflux liquid. The oxygen content of the first descending liquid flow continues to increase as it continues to descend along the inner cavity of the lower tower 3, and finally forms a first oxygen-rich liquid air enrichment zone at the bottom of the lower tower 3; as the first ascending airflow continues to ascend along the inner cavity of the lower tower 3, the nitrogen component in the first ascending airflow continues to increase, and finally forms a first nitrogen enrichment zone at the top of the lower tower 3.
[0023] S2, the pressurized nitrogen transported outward from the first nitrogen-enriched zone is divided into two parts, namely, the first part of the pressurized nitrogen and the second part of the pressurized nitrogen. The first part of the pressurized nitrogen is transported to the heat source channel of the first main condensing heat exchanger 2 and the medium of the cold source channel of the first main condensing heat exchanger 2 to form the first liquid nitrogen after heat exchange and transported to the liquid nitrogen transport main pipe 7. The second part of the pressurized nitrogen is transported to the heat source channel of the second liquid nitrogen transport branch pipe 10 and the medium of the cold source channel of the second liquid nitrogen transport branch pipe 10 to form the second liquid nitrogen after heat exchange and transported to the liquid nitrogen transport main pipe 7 to combine with the first liquid nitrogen to form the third liquid nitrogen. The third liquid nitrogen continues to flow along the liquid nitrogen transport main pipe 7 and is transported to The first heat source channel of the subcooler 19 and the cold source continuously delivered to the subcooler 19 undergo heat exchange to form subcooled liquid nitrogen, which is then divided into two parts, namely, a first part of subcooled liquid nitrogen and a second part of subcooled liquid nitrogen. The first part of subcooled liquid nitrogen is discharged through the outlet end of the liquid nitrogen delivery main pipe 7 and delivered to the liquid nitrogen storage device as a liquid nitrogen product; the second part of subcooled liquid nitrogen is delivered to the top of the upper tower 1 through the third liquid nitrogen delivery branch pipe 11 as the second reflux condensate; the first oxygen-rich liquid air enrichment zone delivers the first oxygen-rich liquid air to the second oxygen-rich liquid air delivery pipe 14 through the second heat source channel of the subcooler 19 and the cold source continuously delivered to the subcooler 19 for heat exchange to form a subcooled liquid nitrogen. The supercooled first oxygen-rich liquid air is then transported to the upper tower 1 as a distillation feedstock. The supercooled first oxygen-rich liquid air enters the upper tower 1 and continues to descend along the upper tower 1 to the cold source channel of the first main condensing heat exchanger 2 and exchanges heat with the heat source medium continuously transported to the heat source channel of the first main condensing heat exchanger 2 to form a second rising airflow. The second rising airflow first encounters the supercooled first oxygen-rich liquid air entering the upper tower 1 during the rising process. The nitrogen component in the supercooled first oxygen-rich liquid air is evaporated and merged into the second rising airflow, and the oxygen component in the second rising airflow is liquefied and merged into the supercooled first oxygen-rich liquid air that is continuously falling to form the second The second ascending gas flow continues to ascend in the upper tower 1 and performs countercurrent heat exchange with the second reflux condensate entering the upper tower 1, the nitrogen component in the second reflux condensate is vaporized and continuously merged into the second ascending gas flow, and the oxygen component in the second ascending gas flow is continuously liquefied and merged into the second descending liquid flow and continues to descend; the second descending liquid flow and the second descending liquid flow are combined to form a third descending liquid flow and are continuously transported to the cold source channel of the first main condensing heat exchanger 2; finally, a second nitrogen enriched zone is formed at the top of the upper tower 1, and a second oxygen-rich liquid air enriched zone is formed in the cold source channel of the first main condensing heat exchanger 2.
[0024] S3, the second oxygen-rich liquid air enrichment zone transports the second oxygen-rich liquid air to the cold source channel of the second main condensing heat exchanger 5 through the first oxygen-rich liquid air delivery pipe 13, the second oxygen-rich liquid air exchanges heat with the medium continuously delivered to the heat source channel of the second main condensing heat exchanger 5, and then is continuously vaporized to form oxygen-rich dirty nitrogen gas and transported to the first dirty nitrogen gas delivery pipe 18, during which it first passes through the first cold source channel of the cooler 19 and the heat source continuously delivered to the subcooler 19 for heat exchange, and then is transported to the first cold source channel of the main heat exchanger 16 and the heat source continuously delivered to the main heat exchanger 16 for heat exchange, and then is discharged from the medium temperature zone of the main heat exchanger 16; the second nitrogen enrichment zone transports the finished nitrogen to the finished nitrogen delivery pipe 4, first passes through the second cold source channel of the cooler 19 and the heat source continuously delivered to the subcooler 19 for heat exchange, and then is transported to the second cold source channel of the main heat exchanger 16 and the heat source continuously delivered to the main heat exchanger 16 for heat exchange, and then is discharged from the high temperature zone of the main heat exchanger 16.
[0025] S4. The oxygen-enriched contaminated nitrogen gas is transported from the outlet end of the first contaminated nitrogen gas transport pipe 18 to the expansion end of the turbine expander 20 in use for expansion and cooling, and then transported to the third cold source channel of the main heat exchanger 16 and the heat source continuously transported to the main heat exchanger 16 through the third contaminated nitrogen gas transport pipe 24 for heat exchange, and then transported to the target user from the outlet end of the third contaminated nitrogen gas transport pipe 24; the finished nitrogen gas discharged from the high temperature area of the main heat exchanger 16 is transported to the boosting end of the turbine expander 20 in use for boosting, and then transported to the boosting nitrogen gas transport pipe 25 as the pressurized finished nitrogen gas to be transported to the target user.
[0026] Through this embodiment, the product uses the main distillation tower of the traditional full distillation cryogenic distillation process as the main distillation component of the product, and uses the cooled part of the liquid nitrogen transported from the liquid nitrogen transport main pipe 7 as the reflux liquid and the heat source continuously transported to the heat source channel of the first main condensing heat exchanger 2 to form a second distillation of the first oxygen-rich liquid air transported from the lower tower 3 to the upper tower 1, and further extracts the nitrogen component in the first oxygen-rich liquid air, so that the extraction rate of the nitrogen component in the purified compressed air transported by the raw material air transport pipe 17 as the raw material in the entire distillation system is improved compared with the single-tower single-process, and the oxygen-rich liquid air from which the nitrogen component is further extracted is continuously transported from the cold source channel of the first main condensing heat exchanger 2 to the cold source channel of the second main condensing heat exchanger 5 for evaporation to form oxygen-rich polluted nitrogen with a higher oxygen content than the single-tower single-process, and the taste as an oxygen-rich source is higher. Although this product is more complex in structure than the single-tower nitrogen production process, the extraction rate of nitrogen content in unit volume of compressed air is increased, thereby reducing the cost of nitrogen use for float glass manufacturers and providing oxygen-enriched polluted nitrogen with a higher oxygen content.
[0027] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made based on the structures, features and principles described in the patent scope of the present invention should be included in the patent application scope of the present invention.
Claims
1. A nitrogen production system using double towers and double condensing heat exchangers for distillation, comprising a main distillation tower, wherein the main distillation tower comprises, from top to bottom, an upper tower (1), a first main condensing heat exchanger (2) and a lower tower (3), and a finished nitrogen gas delivery pipe (4) is provided on the upper tower (1), characterized in that: A second main condensing heat exchanger (5) is arranged outside the main distillation tower, a first regulating valve (6) is arranged on the finished nitrogen gas delivery pipe (4), the inlet end of the heat source channel of the first main condensing heat exchanger (2) and the inlet end of the heat source channel of the second main condensing heat exchanger (5) are respectively connected to the top of the lower tower (3), a liquid nitrogen delivery main pipe (7) is arranged at the outlet end of the heat source channel of the first main condensing heat exchanger (2), and the liquid nitrogen delivery main pipe (7) is sequentially provided with a second regulating valve (8), a first liquid nitrogen delivery branch pipe (9), and a second regulating valve (10), a first liquid nitrogen delivery branch pipe (11), and a second regulating valve (12), a first liquid nitrogen delivery branch pipe (13), and a second liquid nitrogen delivery branch pipe (14). The outlet end of the first liquid nitrogen delivery branch pipe (9), the inlet end of the second liquid nitrogen delivery branch pipe (10), the inlet end of the third liquid nitrogen delivery branch pipe (11) and the third regulating valve (12); the inlet end of the first liquid nitrogen delivery branch pipe (9) is connected to the outlet end of the heat source channel of the second main condensing heat exchanger (5); the outlet end of the second liquid nitrogen delivery branch pipe (10) is connected to the top of the lower tower (3); the outlet end of the third liquid nitrogen delivery branch pipe (11) is connected to the top of the upper tower (1); and the cold source channel of the second main condensing heat exchanger (5) is connected to the cold source channel of the first main condensing heat exchanger (2) via the first oxygen-rich liquid air delivery pipe (13).
2. The nitrogen production system using double towers and double condensing heat exchangers for distillation according to claim 1, characterized in that: The upper tower (1) and the lower tower (3) are connected via a second oxygen-enriched liquid air delivery pipe (14), and a fourth regulating valve (15) is provided on each of the first oxygen-enriched liquid air delivery pipe (13), the second oxygen-enriched liquid air delivery pipe (14), the first liquid nitrogen delivery branch pipe (9), the second liquid nitrogen delivery branch pipe (10), and the third liquid nitrogen delivery branch pipe (11).
3. The nitrogen production system using double towers and double condensing heat exchangers for distillation according to claim 2, characterized in that: The invention also comprises a main heat exchanger (16), a raw material air delivery pipe (17) being provided on the main heat exchanger (16) and the lower tower (3), a part of a finished nitrogen delivery pipe (4) being installed on the main heat exchanger (16), the finished nitrogen delivery pipe (4) being connected to the main heat exchanger (16), a first dirty nitrogen delivery pipe (18) being provided on the cold source channel of the second main condensing heat exchanger (5) and the main heat exchanger (16), a liquid nitrogen delivery main pipe (7) between the second liquid nitrogen delivery branch pipe (10) and the third liquid nitrogen delivery branch pipe (11), a second oxygen-enriched liquid air delivery pipe (14), the first dirty nitrogen delivery pipe (18) between the main heat exchanger (16) and the second main condensing heat exchanger (5), and a finished nitrogen delivery pipe (4) between the main heat exchanger (16) and the upper tower (1), and a subcooler (19) being provided on the product nitrogen delivery pipe (4) between the main heat exchanger (16) and the upper tower (1).
4. The nitrogen production system using double towers and double condensing heat exchangers for distillation according to claim 3, characterized in that: A turbine expander (20) is arranged at the outlet end of the first dirty nitrogen gas delivery pipe (18), and the number of the turbine expanders (20) is at least two. The inlet of the expansion end of each turbine expander (20) and the outlet end of the first dirty nitrogen gas delivery pipe (18) are respectively connected through a second dirty nitrogen gas delivery pipe (22), and each second dirty nitrogen gas delivery pipe (22) is respectively provided with a fifth regulating valve (23). A third dirty nitrogen gas delivery pipe (24) is arranged on the main heat exchanger (16), and the outlet of each turbine expander (20) is respectively connected to the inlet end of the third dirty nitrogen gas delivery pipe (24).
5. The nitrogen production system using double towers and double condensing heat exchangers for distillation according to claim 4, characterized in that: A pressurizing delivery branch pipe (21) is provided on the pressurizing end of each of the turboexpanders (20), the inlet end of each of the pressurizing delivery branch pipes (21) is connected to the outlet end of the finished nitrogen delivery pipe (4), and a plurality of pressurizing delivery branch pipes (21) are provided on the outlet ends of the pressurizing nitrogen delivery pipes (25). Each of the pressurizing delivery branch pipes (21) is provided with a stop valve (26) and a check valve (27) in sequence along the direction from the finished nitrogen delivery pipe (4) to the pressurizing nitrogen delivery pipe (25). The number of the pressurizing delivery branch pipes (21) corresponds to the number of the pressurizing ends of the turboexpanders (20), and the pressurizing end of the turboexpander (20) on each of the pressurizing delivery branch pipes (21) is located between the corresponding stop valve (26) and the corresponding check valve (27).
6. The nitrogen production system using double towers and double condensing heat exchangers for distillation according to claim 1, characterized in that: Liquid level sensors (28) are respectively provided at the bottom of the upper tower (1), the cold source channel of the first main condensing heat exchanger (2), and the cold source channel of the second main condensing heat exchanger (5).
7. The nitrogen production system using double towers and double condensing heat exchangers for distillation according to claim 1, characterized in that: A pressure sensor (30) is provided on the finished nitrogen gas delivery pipe (4) between the first regulating valve (6) and the upper tower (1).