Nitrogen emptying and recycling device for 400-cubic liquid nitrogen storage tank
By employing a separation tank and a double-shell tube heat exchanger in the nitrogen treatment device for venting liquid nitrogen storage tanks, the staged recovery of cooling capacity from liquid droplets and gaseous nitrogen was achieved, solving the problems of resource waste and safety hazards in small and medium-sized chemical plants, and improving resource utilization and economic benefits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- 重庆朝阳气体有限公司
- Filing Date
- 2025-04-24
- Publication Date
- 2026-04-21
AI Technical Summary
The existing methods for handling nitrogen released from liquid nitrogen storage tanks fail to effectively recover the cold energy of the droplets, resulting in resource waste and safety hazards. Furthermore, the existing equipment is complex in structure and costly, making it unsuitable for small and medium-sized chemical plants.
A device comprising a separation tank, a first heat exchanger, and a second heat exchanger was designed. Gas-liquid separation is achieved through baffles inside the separation tank. The cooling capacity of liquid droplets and gaseous nitrogen is recovered separately using a shell-and-tube heat exchanger for cold storage refrigeration and circulating water cooling. A control valve and heat exchange branch pipes are combined to ensure a stable supply of cooling capacity.
It achieves efficient recovery of vented nitrogen and cold energy, saving approximately 60,000 yuan in costs annually, increasing cold energy utilization by 30%, reducing energy consumption in cold storage and cooling systems, avoiding energy waste and safety hazards, and featuring a simple and low-cost structure suitable for small and medium-sized chemical plants.
Smart Images
Figure CN224151231U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the technical field of industrial gas recovery equipment, specifically relating to a nitrogen venting and recovery device for a 400 cubic meter liquid nitrogen storage tank, used to recover the vented nitrogen and its cooling capacity from the liquid nitrogen storage tank, and applied to scenarios such as cold storage refrigeration and circulating water cooling. Background Technology
[0002] Liquid nitrogen storage tanks are crucial equipment for storing liquid nitrogen in industries such as chemical, metallurgy, and pharmaceuticals, and are widely used in cryogenic processes and gas supply. Taking a 400 cubic meter liquid nitrogen storage tank as an example, its moderate design capacity is commonly found in small to medium-sized chemical plants or industrial bases, used to store high-purity liquid nitrogen to support production. However, in actual operation, due to pressure regulation, maintenance, or shutdown, excess nitrogen needs to be released through a vent pipe to maintain safe pressure. Statistics show that a 400 cubic meter liquid nitrogen storage tank vents approximately 100-120 cubic meters of nitrogen daily, resulting in an average annual economic loss of tens of thousands of yuan. More importantly, the liquid droplets (liquid nitrogen) carried in the venting airflow have extremely low temperatures (approximately -195°C), and their cooling capacity is not effectively utilized; direct release into the atmosphere causes significant energy waste.
[0003] In existing technologies, the handling of vented nitrogen from liquid nitrogen storage tanks is relatively rudimentary, mainly including direct discharge or simple recycling. Direct discharge is the most common method, with nitrogen being released into the atmosphere through a vent pipe, which not only wastes resources but may also pose safety hazards due to the diffusion of low-temperature gases. To reduce losses, some devices attempt to recover vented nitrogen. For example, a common method is to introduce nitrogen into a single vaporizer, reheat it with ambient air or an external heat source, and then use it in production processes, such as main tower pressure maintenance, tank truck replacement, or equipment sealing. However, this method has several shortcomings. First, vaporizers typically only focus on reheating nitrogen, neglecting the recovery of the cold energy from droplets in the vented airflow. Because the droplets are not effectively separated, they directly enter the vaporizer with the airflow, leading to cold energy loss or decreased heat exchange efficiency. Second, existing vaporizers are mostly single-channel designs, with gaseous nitrogen and droplets not treated in stages, and the cold energy utilization is singular (e.g., only for reheating), failing to meet the common cold storage refrigeration or circulating water cooling needs of chemical plants, resulting in low resource utilization.
[0004] In recent years, liquefied natural gas (LNG) cold energy utilization technology has provided a reference for liquid nitrogen cold energy recovery. LNG cold energy recovery units utilize multi-stage heat exchange to apply low-temperature cold energy for cold storage refrigeration, circulating water cooling, process gas precooling, and even power generation. For example, LNG cold storage refrigeration can cool the circulating medium to -20°C, significantly reducing cold storage energy consumption; circulating water cooling can lower the water temperature to 15-20°C for cooling tower or equipment heat dissipation, saving refrigeration unit power consumption. However, LNG units are typically designed for large-scale cold capacity (processing thousands of cubic meters per day), with complex structures including multi-stage heat exchangers, condensers, and control systems, resulting in high costs. In contrast, the venting capacity of a 400 cubic meter liquid nitrogen storage tank is relatively small (approximately 120 m³). 3 The cooling capacity is limited (per day), and the complex structure of LNG plants makes direct application difficult. In addition, existing liquid nitrogen recovery devices lack specificity in cooling capacity utilization, often mixing the cooling capacity of liquid droplets and gaseous nitrogen, resulting in low heat exchange efficiency. Furthermore, the devices have numerous internal pipes with complex connections, leading to high installation and maintenance costs. Utility Model Content
[0005] In view of this, the purpose of this utility model is to solve the above problems and provide a 400 cubic meter liquid nitrogen storage tank nitrogen venting and recovery device. Combining a separation and dual heat exchanger structure, it realizes the separate recovery of gaseous nitrogen and liquid droplet cooling capacity. The liquid droplet cooling capacity is used for cold storage refrigeration, the combined nitrogen cooling capacity is used for cooling circulating water, and the collected nitrogen is transported to the outside, thereby improving resource utilization efficiency.
[0006] To achieve the above objectives, this utility model provides the following technical solution:
[0007] A nitrogen venting and recovery device for a 400 cubic meter liquid nitrogen storage tank includes a separation tank, a first heat exchanger, a second heat exchanger, and a manifold.
[0008] The top of the separator is connected to the vent pipe of a 400 cubic meter liquid nitrogen storage tank via a flange. An inclined baffle is fixed inside the separator. After the vented nitrogen enters, the liquid nitrogen sinks to the bottom of the tank due to gravity and the obstruction of the baffle.
[0009] The first heat exchanger is externally connected to a cold storage refrigeration circuit, and the bottom of the separation tank is connected to the first heat exchanger through a first heat exchange tube, and the cold energy is transferred to the cold storage refrigeration circuit through the first heat exchanger.
[0010] The second heat exchanger is connected to an external circulating water cooling circuit. The side of the separation tank is connected to the second heat exchanger through a second heat exchange tube, and the cooling capacity is transferred to the circulating water cooling circuit through the second heat exchanger.
[0011] The first heat exchanger and the second heat exchanger are connected by a manifold, so that the first heat exchange tube and the second heat exchange tube are connected through the manifold; the liquid nitrogen separated from the separator is vaporized by heat exchange in the first heat exchanger, and then merges with the nitrogen in the second heat exchange tube through the manifold, and undergoes heat exchange again in the second heat exchanger, transferring the cooling capacity to the circulating water cooling circuit.
[0012] Furthermore, both the first heat exchange tube and the second heat exchange tube are equipped with control valves to control the opening and closing of the pipeline.
[0013] Furthermore, a heat exchange branch pipe is provided between the first heat exchange tube and the second heat exchange tube. One end of the heat exchange branch pipe is connected to the first heat exchange tube, and the other end is connected to the second heat exchange tube. A control valve is also provided on the heat exchange branch pipe. When the separated liquid nitrogen is insufficient, the control valves on the first heat exchange tube, the second heat exchange tube, and the third heat exchange tube are switched so that the nitrogen in the first heat exchange tube can enter the second heat exchanger through the heat exchange branch pipe for heat exchange.
[0014] Furthermore, at least two control valves are provided on the first heat exchange pipeline, and the heat exchange branch pipe is connected between the two control valves.
[0015] Furthermore, the baffle is fixed to the inner wall of the separation tank and is inclined at 45°.
[0016] Furthermore, the first and second heat exchangers are shell-and-tube heat exchangers, both fixed to the outer wall of the liquid nitrogen storage tank.
[0017] Furthermore, both the first heat exchange tube and the second heat exchange tube are fitted with an insulation layer on their outer walls.
[0018] The beneficial effects of this utility model are as follows:
[0019] 1. Outstanding economic benefits
[0020] The device efficiently recovers vented nitrogen and cooling capacity, recovering approximately 120 cubic meters of nitrogen daily, or about 40,000 cubic meters annually. At a market price of 1.5 yuan per cubic meter, this translates to annual cost savings of approximately 60,000 yuan. The droplet cooling capacity is used for cold storage refrigeration (ethylene glycol medium is reduced to -20°C), saving 10%-15% of cold storage energy consumption. Combined with nitrogen cooling capacity to cool circulating water (water temperature reduced to 15-20°C), it reduces cooling tower energy consumption by approximately 10%. Including both energy savings and nitrogen recovery, the device saves tens of thousands of yuan annually, with a short investment payback period and significant economic benefits.
[0021] 2. Energy-saving, environmentally friendly and efficient
[0022] The dual heat exchangers recover the cooling capacity of liquid droplets (-195℃) and gaseous nitrogen in stages, which are used for cold storage refrigeration and circulating water cooling, respectively, improving the utilization rate of cooling capacity by about 30%. Compared with direct emission, the device reduces energy waste, lowers the power consumption of cold storage and cooling systems, avoids thermal pollution and safety hazards caused by low-temperature nitrogen venting, and meets the requirements of green manufacturing and energy conservation and emission reduction.
[0023] 3. Simple structure and low cost
[0024] A single baffle achieves gas-liquid separation, and the double-shell-tube heat exchanger is fixed to the outer wall of the storage tank, resulting in a compact structure and small footprint. The first and second heat exchange tubes are insulated to reduce cooling loss, and threaded and flanged connections facilitate installation. The heat exchange branch pipes and control valves simplify maintenance, and the manufacturing and operating costs are low, making it suitable for small and medium-sized chemical plants.
[0025] 4. Flexible and stable operation
[0026] Control valves (two on the first heat exchanger tube, one each on the second heat exchanger tube and the branch pipe) regulate airflow. The heat exchange branch pipes are used to handle scenarios with insufficient droplets, ensuring a stable cooling supply. Operation is simple and adaptable to fluctuations in venting volume (100-150m³). 3 / day), improving operational reliability.
[0027] Other advantages, objectives, and features of this invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination and study, or may be learned from practice of this invention. The objectives and other advantages of this invention can be realized and obtained through the following description. Attached Figure Description
[0028] To make the objectives, technical solutions, and advantages of this utility model clearer, the preferred embodiments of this utility model will be described in detail below with reference to the accompanying drawings, wherein:
[0029] Figure 1 This is a schematic diagram of the nitrogen venting and recovery device for a 400 cubic meter liquid nitrogen storage tank in this utility model.
[0030] Attached reference numerals: 1-Separation tank; 2-Vent pipe; 3-Second heat exchange pipe; 4-First heat exchange pipe; 5-First heat exchanger; 6-Second heat exchanger; 7-Cold storage refrigeration circuit; 8-Circulating water cooling circuit; 9-Manifold; 10-Heat exchange branch pipe. Detailed Implementation
[0031] The following specific examples illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this utility model. Unless otherwise specified, the following embodiments and features can be combined with each other.
[0032] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the present invention. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.
[0033] In the accompanying drawings of this utility model, the same or similar reference numerals correspond to the same or similar components. In the description of this utility model, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this utility model. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.
[0034] Example 1
[0035] In a 4000 kW unit of a chemical plant, a nitrogen venting and recovery device of this invention is deployed for a 400 cubic meter liquid nitrogen storage tank. This device is used to recover vented nitrogen and its cooling capacity, and is applied to cold storage refrigeration, circulating water cooling, and main tower pressure maintenance. The device includes the following components: a separation tank 1, a venting pipe 2, a second heat exchange pipe 3, a first heat exchange pipe 4, a first heat exchanger 5, a second heat exchanger 6, a cold storage refrigeration circuit 7, a circulating water cooling circuit 8, a manifold 9, and a heat exchange branch pipe 10.
[0036] The top of the separator 1 is connected to the vent pipe 2 via a flange, and a 45° inclined baffle is welded inside and fixed to the inner wall of the tank. One end of the first heat exchange pipe 4 is threaded to the bottom of the separator 1, and the other end is threaded to the first heat exchanger 5. An insulation layer is fitted over the pipe, and two control valves are installed on the pipeline. One end of the second heat exchange pipe 3 is threaded to the side outlet of the separator 1, and the other end is threaded to the second heat exchanger 6. An insulation layer is fitted over the pipe, and one control valve is installed on the pipeline. One end of the heat exchange branch pipe 10 is connected to the first heat exchange pipe 4 (located between the two control valves), and the other end is connected to the second heat exchange pipe 3. One control valve is installed on the branch pipe. The first heat exchanger 5 is a shell-and-tube type, fixed to the outer wall of the liquid nitrogen storage tank with clamps, and connected to the cold storage refrigeration circuit 7. The second heat exchanger 6 is a shell-and-tube type, fixed side-by-side with the first heat exchanger 5 to the outer wall of the storage tank, and connected to the circulating water cooling circuit 8. The manifold 9 is a straight pipe, with one end threaded to the outlet of the first heat exchanger 5 and the other end threaded to the inlet of the second heat exchanger 6. The outlet is connected to the output pipe through a flange, leading to the nitrogen pipeline network.
[0037] Operation process:
[0038] Nitrogen gas is released through vent pipe 2 into separator 1. Droplets, blocked by gravity and a 45° baffle, settle to the bottom of the tank. Gaseous nitrogen flows into the second heat exchange pipe 3 from the side outlet. Droplets then enter the first heat exchanger 5 through the first heat exchange pipe 4. The droplet's cooling capacity of -195°C is transferred through the pipe wall to the cold storage refrigeration circuit 7, lowering the ethylene glycol medium to -20°C and maintaining the cold storage temperature from 0 to -18°C. The droplets vaporize into nitrogen at approximately -50°C and flow into manifold 9. Gaseous nitrogen then enters the second heat exchanger 6 through the second heat exchange pipe 3, merging with the vaporized nitrogen in manifold 9. The combined nitrogen's cooling capacity is transferred through the pipe wall to the circulating water cooling circuit 8, lowering the water temperature from 25°C to 15-20°C for cooling tower heat dissipation. The nitrogen is reheated to 20°C. When droplet volume is insufficient, the control valve of heat exchange branch pipe 10 opens, allowing gaseous nitrogen from the first heat exchange pipe 4 to enter the second heat exchanger 6, maintaining the cooling supply. The reheated nitrogen is collected through manifold 9, transported to the nitrogen pipeline network via the output pipeline, and distributed to the main tower for pressure maintenance.
[0039] In this embodiment, the device recovers approximately 120 cubic meters of nitrogen per day, saving about 60,000 yuan annually. The cold storage refrigeration circuit 7 saves 10%-15% of energy, and the circulating water cooling circuit 8 saves 10% of energy. The control valves and heat exchange branch pipes 10 ensure stable operation, maintain the main tower pressure within the process requirements range, and the device is easy to operate and has low maintenance costs.
[0040] Example 2
[0041] At a liquid nitrogen storage facility of a metallurgical enterprise, this utility model's nitrogen venting and recovery device was deployed on a 400-cubic-meter liquid nitrogen storage tank to recover vented nitrogen and its cooling capacity for use in cold storage refrigeration, circulating water cooling, and tank truck replacement. The device includes the following components: a separation tank 1, a venting pipe 2, a second heat exchange pipe 3, a first heat exchange pipe 4, a first heat exchanger 5, a second heat exchanger 6, a cold storage refrigeration circuit 7, a circulating water cooling circuit 8, a manifold 9, and a heat exchange branch pipe 10.
[0042] The top of the separator 1 is connected to the vent pipe 2 via a flange. A 45° inclined baffle is fixed inside and welded to the inner wall of the separator. One end of the first heat exchange pipe 4 is threaded to the bottom of the separator 1, and the other end is threaded to the first heat exchanger 5. An insulation layer is fitted over the pipe, and two control valves are installed on the pipeline. One end of the second heat exchange pipe 3 is threaded to the side outlet of the separator 1, and the other end is threaded to the second heat exchanger 6. An insulation layer is fitted over the pipe, and one control valve is installed on the pipeline. One end of the heat exchange branch pipe 10 is connected to the first heat exchange pipe 4 (located between the two control valves), and the other end is connected to the second heat exchange pipe 3. One control valve is installed on the branch pipe. The first heat exchanger 5 is a shell-and-tube type, clamped to the outer wall of the liquid nitrogen storage tank, and connected to the external cold storage refrigeration circuit 7. The second heat exchanger 6 is a shell-and-tube type, fixed side-by-side with the first heat exchanger 5, and connected to the external circulating water cooling circuit 8. The manifold 9 is a straight pipe, with one end threaded to the outlet of the first heat exchanger 5 and the other end threaded to the inlet of the second heat exchanger 6. The outlet is connected to the output pipe through a flange, leading to the nitrogen pipeline network.
[0043] Operation process:
[0044] Nitrogen gas is released through vent pipe 2 into separator 1. Droplets settle to the bottom of the tank due to a 45° baffle and gravity. Gaseous nitrogen flows into the second heat exchange pipe 3 from the side outlet. The droplets then pass through the first heat exchange pipe 4 into the first heat exchanger 5, where the -195°C cooling capacity is transferred to the cold storage refrigeration circuit 7. The ethylene glycol medium cools to -20°C, maintaining the cold storage temperature from 0 to -18°C. The droplets vaporize into nitrogen at approximately -50°C and enter manifold 9. The gaseous nitrogen then passes through the second heat exchange pipe 3 into the second heat exchanger 6, merging with the vaporized nitrogen from manifold 9. The combined nitrogen's cooling capacity is transferred to the circulating water cooling circuit 8, lowering the water temperature from 25°C to 15-20°C for equipment cooling. The nitrogen is then reheated to 20°C. When the droplet volume is low, the control valve on heat exchange branch pipe 10 opens, allowing the gaseous nitrogen from the first heat exchange pipe 4 to enter the second heat exchanger 6, ensuring stable cooling. The reheated nitrogen is collected through manifold 9, transported to the nitrogen pipeline network via the output pipeline, and distributed to the tank truck replacement system.
[0045] In this embodiment, the device recovers approximately 120 cubic meters of nitrogen daily, saving about 60,000 yuan annually. The cold storage refrigeration circuit 7 reduces energy consumption by 10%-15%, and the circulating water cooling circuit 8 saves 10% of energy. Recovered nitrogen is used instead of purchased nitrogen for tank truck replacement, saving approximately 1,500 yuan in transportation costs per trip, resulting in tens of thousands of yuan in annual savings. The heat exchange branch pipe 10 and control valves are flexible in operation, adaptable to fluctuations in venting volume, and the device operates reliably.
[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from the spirit and scope of this technical solution, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.
Claims
1. A 400 cubic meter liquid nitrogen tank nitrogen gas venting recycling device, characterized in that: It includes a separator, a first heat exchanger, a second heat exchanger, and a manifold; The top of the separator is connected to the vent pipe of a 400 cubic meter liquid nitrogen storage tank via a flange. An inclined baffle is fixed inside the separator. After the vented nitrogen enters, the liquid nitrogen sinks to the bottom of the tank due to gravity and the obstruction of the baffle. The first heat exchanger is externally connected to a cold storage refrigeration circuit, and the bottom of the separation tank is connected to the first heat exchanger through a first heat exchange tube, and the cold energy is transferred to the cold storage refrigeration circuit through the first heat exchanger. The second heat exchanger is connected to an external circulating water cooling circuit. The side of the separation tank is connected to the second heat exchanger through a second heat exchange tube, and the cooling capacity is transferred to the circulating water cooling circuit through the second heat exchanger. The first heat exchanger and the second heat exchanger are connected by a manifold, so that the first heat exchange tube and the second heat exchange tube are connected through the manifold; the liquid nitrogen separated from the separator is vaporized by heat exchange in the first heat exchanger, and then merges with the nitrogen in the second heat exchange tube through the manifold, and undergoes heat exchange again in the second heat exchanger, transferring the cooling capacity to the circulating water cooling circuit.
2. The 400 cubic liquid nitrogen tank nitrogen venting recycling device according to claim 1, characterized in that: Both the first heat exchange tube and the second heat exchange tube are equipped with control valves to control the opening and closing of the pipeline.
3. The 400 cubic liquid nitrogen tank nitrogen venting recycling device according to claim 1, characterized in that: A heat exchange branch pipe is provided between the first heat exchange tube and the second heat exchange tube. One end of the heat exchange branch pipe is connected to the first heat exchange tube, and the other end is connected to the second heat exchange tube. A control valve is also provided on the heat exchange branch pipe. When the separated liquid nitrogen is insufficient, the control valves on the first heat exchange tube, the second heat exchange tube, and the third heat exchange tube are switched so that the nitrogen in the first heat exchange tube can enter the second heat exchanger through the heat exchange branch pipe for heat exchange.
4. The 400 cubic liquid nitrogen tank nitrogen venting recycling device according to claim 3, characterized in that: The first heat exchange pipeline is equipped with at least two control valves, and the heat exchange branch pipe is connected between the two control valves.
5. The 400 cubic liquid nitrogen tank nitrogen venting recycling device according to claim 1, characterized in that: The baffle is fixed to the inner wall of the separation tank and is inclined at 45°.
6. The 400 cubic liquid nitrogen tank nitrogen venting recycling device according to claim 1, characterized in that: The first and second heat exchangers are shell-and-tube heat exchangers, both fixed to the outer wall of the liquid nitrogen storage tank.
7. The nitrogen venting and recovery device for a 400 cubic meter liquid nitrogen storage tank according to claim 1, characterized in that: Both the first heat exchange tube and the second heat exchange tube are fitted with an insulation layer on their outer walls.