Nitrogen liquefaction device liquid nitrogen storage tank venting nitrogen recovery system

Abstract

The utility model discloses a nitrogen gas liquefaction device liquid nitrogen storage tank emptying nitrogen gas recovery system relates to nitrogen gas liquefaction technical field, including liquid nitrogen storage tank, residual liquid evaporator, nitrogen gas liquefaction cold box, with the first emptying pipeline of emptying port connection of liquid nitrogen storage tank, set up in the first emptying pipeline end first valve and the recovery pipeline on the first emptying pipeline of first valve front end, the end of recovery pipeline is connected on the low temperature nitrogen gas main pipe of nitrogen gas liquefaction cold box front end, the medium import intercommunication of residual liquid evaporator is provided with first recovery branch pipeline in the middle part of recovery pipeline, and the medium export of residual liquid evaporator is connected with the second recovery branch pipeline of expansion machine seal gas pipeline intercommunication, and expansion machine seal gas pipeline communicates with normal temperature nitrogen gas busbar. The utility model discloses after the parking of liquefaction device, liquid nitrogen storage tank discharges low temperature nitrogen gas and recovers to expansion machine seal gas pipeline and with normal temperature nitrogen gas busbar in series, reduces the waste caused by the nitrogen gas discharge of liquid nitrogen storage tank and discharges into the atmosphere.

Description

Technical Field

[0001] This utility model relates to the field of nitrogen liquefaction technology, and more specifically to the field of nitrogen recovery system for venting liquid nitrogen storage tanks in a nitrogen liquefaction device. Background Technology

[0002] A nitrogen liquefaction unit is an industrial device that uses deep freezing technology to cool gaseous nitrogen and convert it into liquid nitrogen (boiling point at atmospheric pressure -196°C). Liquid nitrogen is an efficient and convenient form of nitrogen storage and transportation, and its high density (1 cubic meter of liquid nitrogen can be vaporized into approximately 696 cubic meters of gaseous nitrogen) makes it indispensable in many fields.

[0003] The core of nitrogen liquefaction is the principle of thermodynamics, which involves removing heat from the nitrogen gas through external work, lowering its temperature below its boiling point, and thus causing a phase change from a gaseous state to a liquid state. The entire process mainly revolves around the throttling effect and isentropic expansion of the gas.

[0004] After liquefaction, nitrogen is stored in liquid nitrogen storage tanks (Dewar tanks or large vertical tanks). These tanks are vacuum-insulated with powder, but 100% insulation is impossible. Therefore, external heat slowly enters the tank, causing some of the liquid nitrogen to absorb heat and evaporate. This vapor is called "evaporation gas" or "flash vapor".

[0005] As BOG (Boiled Oxygen Gas) is continuously generated, the pressure inside the storage tank will continue to rise. To ensure the safety of the storage tank (preventing overpressure explosion), this excess gas must be vented. This is the phenomenon of nitrogen "venting." In small or older installations, this nitrogen is directly released into the atmosphere, resulting in significant waste. Furthermore, although nitrogen itself is non-toxic and harmless, its production process has a carbon footprint. Recycling reduces unnecessary energy waste and indirectly lowers carbon emissions.

[0006] The core idea of ​​nitrogen recovery is to reintroduce the vented low-pressure nitrogen into the front end of the liquefaction system, where it is compressed and purified before being liquefied again.

[0007] The existing method for recovering nitrogen from liquid nitrogen storage tanks involves recovering the vented nitrogen to the cryogenic nitrogen pipeline before it enters the liquefied cold box. When the unit is shut down, the cryogenic nitrogen vented from the liquid nitrogen storage tank cannot enter the liquefied cold box due to its low temperature and can only be released into the air. This release of nitrogen from the liquid nitrogen storage tank into the atmosphere results in a waste of nitrogen. Utility Model Content

[0008] The purpose of this utility model is to solve the above-mentioned technical problems by providing a nitrogen recovery system for venting liquid nitrogen storage tanks in a nitrogen liquefaction device.

[0009] To achieve the above objectives, this utility model specifically adopts the following technical solution: This utility model provides a nitrogen recovery system for the venting of a liquid nitrogen storage tank in a nitrogen liquefaction device, including a liquid nitrogen storage tank, a residual liquid evaporator, a nitrogen liquefaction cold box, a first venting pipe connected to the vent of the liquid nitrogen storage tank, a first valve installed at the end of the first venting pipe, and a recovery pipe connected to the first venting pipe at the front end of the first valve; the end of the recovery pipe is connected to a low-temperature nitrogen main pipe at the front end of the nitrogen liquefaction cold box. The middle of the recovery pipeline is equipped with a first recovery branch pipeline that is connected to the medium inlet of the residual liquid evaporator. The medium outlet of the residual liquid evaporator is connected to a second recovery branch pipeline that is connected to the expansion machine sealing gas pipeline. The expansion machine sealing gas pipeline is connected to the ambient temperature nitrogen busbar.

[0010] Specifically, this solution allows the cryogenic nitrogen discharged from the liquid nitrogen storage tank to be recovered into the expander sealing gas pipeline after the liquefaction unit is shut down, and connected in series with the ambient temperature nitrogen busbar, thereby reducing the waste caused by the nitrogen discharged from the liquid nitrogen storage tank into the atmosphere.

[0011] In one embodiment, a fourth valve is provided on the recycling pipe located at the front end of the first recycling branch pipe, and a second valve is provided on the recycling pipe located at the rear end of the first recycling branch pipe.

[0012] In one embodiment, a second vent pipe is provided on the recovery pipe located between the second valve and the first recovery branch pipe, and the second vent pipe is provided with a third valve.

[0013] In one embodiment, a third vent pipe is connected to the second recovery branch pipe, and a seventh valve is installed on the third vent pipe.

[0014] In one embodiment, a fifth valve is provided on the first recovery branch pipe, and a sixth valve is provided on the second recovery branch pipe located at the rear end of the third vent pipe.

[0015] In one embodiment, a residual liquid discharge pipe is connected to the first recovery branch pipe at the rear end of the fifth valve, and an eighth valve is installed on the residual liquid discharge pipe.

[0016] In one embodiment, a tenth valve is provided on the cryogenic nitrogen header located at the front end of the recovery pipeline.

[0017] In one embodiment, a ninth valve is provided on the expander sealing gas pipeline located at the front end of the second recovery branch pipeline.

[0018] In one embodiment, one end of the expander sealing gas pipeline is connected to the ambient temperature nitrogen busbar, and the other end is connected to the expander.

[0019] The method for recovering vented nitrogen from a liquid nitrogen storage tank venting system in a nitrogen liquefaction device includes the following steps: Step 1: When the liquefaction unit is starting up or stopping, close the second, third, fourth, fifth, and sixth valves, and open the first and seventh valves to vent the nitrogen from the liquid nitrogen storage tank for a short period of time.

[0020] Step 2: When the liquefaction unit is operating normally, close the first valve, the third valve, the fifth valve, and the sixth valve, and open the fourth valve, the second valve, and the seventh valve. The nitrogen gas from the liquid nitrogen storage tank is released into the low-temperature nitrogen main pipe before the liquefaction cold box.

[0021] Step 3: After the liquefaction unit stops operating, close the first, second, third, and seventh valves, and open the fourth, fifth, and sixth valves. Release the nitrogen gas from the liquid nitrogen storage tank into the expander's sealing gas pipeline (e.g., Figure 1 ).

[0022] Specifically, this scheme connects the first recovery branch pipe (with a fifth valve) between the fourth valve and the second valve to the medium inlet of the residual liquid evaporator. One path from the medium outlet of the residual liquid evaporator is connected to the second recovery branch pipe (with a sixth valve) and connected to the expander sealing gas pipe. The other path is connected to the third vent pipe (with a seventh valve) for venting after the residual liquid is vaporized.

[0023] The beneficial effects of this utility model are as follows: 1. This utility model is reasonably designed. After the liquefaction unit is shut down, the low-temperature nitrogen gas discharged from the liquid nitrogen storage tank is recovered to the expansion machine sealing gas pipeline and connected in series with the normal temperature nitrogen bus, thereby reducing the waste caused by the nitrogen gas discharged from the liquid nitrogen storage tank into the atmosphere.

[0024] 2. In this utility model, a first recovery branch pipe (with a fifth valve installed on it) is connected between the fourth valve and the second valve to the medium inlet of the residual liquid evaporator. One path from the medium outlet of the residual liquid evaporator is connected to the second recovery branch pipe (with a sixth valve installed on it) and connected to the expansion machine sealing gas pipe. The other path is connected to the third vent pipe (with a seventh valve installed on it) for venting after the residual liquid is vaporized. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this utility model and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of this utility model.

[0027] Reference numerals: F1, first valve; F2, second valve; F3, third valve; F4, fourth valve; F5, fifth valve; F6, sixth valve; F7, seventh valve; F8, eighth valve; F9, ninth valve; F10, tenth valve. Detailed Implementation

[0028] To make the technical problems, technical solutions, and technical effects of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this utility model. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0030] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0031] In the description of the embodiments of this utility model, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the utility model product is usually placed when in use. 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, they should not be construed as limitations on this utility model.

[0032] Example 1 like Figure 1 As shown, this embodiment provides a nitrogen recovery system for the venting of a liquid nitrogen storage tank in a nitrogen liquefaction device, including a liquid nitrogen storage tank, a residual liquid evaporator, a nitrogen liquefaction cold box, a first venting pipe connected to the vent of the liquid nitrogen storage tank, a first valve F1 installed at the end of the first venting pipe, and a recovery pipe connected to the first venting pipe at the front end of the first valve F1; the end of the recovery pipe is connected to a cryogenic nitrogen header at the front end of the nitrogen liquefaction cold box. The middle of the recovery pipeline is equipped with a first recovery branch pipeline that is connected to the medium inlet of the residual liquid evaporator. The medium outlet of the residual liquid evaporator is connected to a second recovery branch pipeline that is connected to the expansion machine sealing gas pipeline. The expansion machine sealing gas pipeline is connected to the ambient temperature nitrogen busbar.

[0033] A fourth valve F4 is installed on the recycling pipe located at the front end of the first recycling branch pipe, and a second valve F2 is installed on the recycling pipe located at the rear end of the first recycling branch pipe.

[0034] A second vent pipe is installed on the recovery pipe located between the second valve F2 and the first recovery branch pipe, and a third valve F3 is installed on the second vent pipe.

[0035] The second recovery branch pipe is connected to the third vent pipe, and the third vent pipe is equipped with the seventh valve F7.

[0036] The first recovery branch pipe is equipped with a fifth valve F5, and the second recovery branch pipe, located at the rear end of the third vent pipe, is equipped with a sixth valve F6.

[0037] A residual liquid discharge pipe is connected to the first recovery branch pipe at the rear end of the fifth valve F5, and an eighth valve F8 is installed on the residual liquid discharge pipe.

[0038] The tenth valve, F10, is installed on the cryogenic nitrogen main pipe located at the front end of the recovery pipeline.

[0039] A ninth valve, F9, is installed on the expander sealing gas pipeline located at the front end of the second recovery branch pipeline.

[0040] One end of the expander sealing gas pipeline is connected to the ambient temperature nitrogen busbar, and the other end is connected to the expander.

[0041] Specifically, this solution allows the cryogenic nitrogen discharged from the liquid nitrogen storage tank to be recovered into the expander sealing gas pipeline after the liquefaction unit is shut down, and connected in series with the ambient temperature nitrogen busbar, thereby reducing the waste caused by the nitrogen discharged from the liquid nitrogen storage tank into the atmosphere.

[0042] Example 2 like Figure 1 As shown, this embodiment provides a method for recovering nitrogen from the venting of a liquid nitrogen storage tank in a nitrogen liquefaction device. Using the nitrogen recovery system for the venting of a liquid nitrogen storage tank in a nitrogen liquefaction device described in Embodiment 1, the method includes the following steps: Step 1: When the liquefaction unit is starting up or stopping, close the second valve F2, the third valve F3, the fourth valve F4, the fifth valve F5, and the sixth valve F6, and open the first valve F1 and the seventh valve F7 to vent the nitrogen in the liquid nitrogen storage tank for a short time.

[0043] Step 2: When the liquefaction unit is operating normally, close the first valve F1, the third valve F3, the fifth valve F5, and the sixth valve F6, and open the fourth valve F4, the second valve F2, and the seventh valve F7. The nitrogen gas from the liquid nitrogen storage tank is released into the low-temperature nitrogen main pipe before the liquefaction cold box.

[0044] Step 3: After the liquefaction unit stops operating, close valves F1, F2, F3, and F7, and open valves F4, F5, and F6. Release the nitrogen gas from the liquid nitrogen storage tank into the expander's sealing gas pipeline (e.g., Figure 1 ).

[0045] Specifically, this scheme connects the first recovery branch pipe (with the fifth valve F5 installed on it) between the fourth valve F4 and the second valve F2 to the medium inlet of the residual liquid evaporator. One path from the medium outlet of the residual liquid evaporator is connected to the second recovery branch pipe (with the sixth valve F6 installed on it) and connected to the expansion machine sealing gas pipe. The other path is connected to the third vent pipe (with the seventh valve F7 installed on it) for venting after the residual liquid is vaporized.

Claims

1. A nitrogen recovery system for venting nitrogen from a liquid nitrogen storage tank in a nitrogen liquefaction device, characterized in that, It includes a liquid nitrogen storage tank, a residual liquid evaporator, a nitrogen liquefaction cold box, a first vent pipe connected to the vent of the liquid nitrogen storage tank, a first valve (F1) installed at the end of the first vent pipe, and a recovery pipe connected to the first vent pipe at the front end of the first valve (F1); the end of the recovery pipe is connected to a cryogenic nitrogen main pipe at the front end of the nitrogen liquefaction cold box. The recovery pipeline is provided with a first recovery branch pipeline in the middle, which is connected to the medium inlet of the residual liquid evaporator. The medium outlet of the residual liquid evaporator is connected to a second recovery branch pipeline, which is connected to the expansion machine sealing gas pipeline. The expansion machine sealing gas pipeline is connected to the ambient temperature nitrogen busbar.

2. The nitrogen recovery system for venting liquid nitrogen storage tanks in a nitrogen liquefaction device according to claim 1, characterized in that, A fourth valve (F4) is installed on the recycling pipe located at the front end of the first recycling branch pipe, and a second valve (F2) is installed on the recycling pipe located at the rear end of the first recycling branch pipe.

3. The nitrogen recovery system for venting liquid nitrogen storage tanks in a nitrogen liquefaction device according to claim 2, characterized in that, A second vent pipe is provided on the recovery pipe located between the second valve (F2) and the first recovery branch pipe, and a third valve (F3) is provided on the second vent pipe.

4. The nitrogen recovery system for venting liquid nitrogen storage tanks in a nitrogen liquefaction device according to claim 1, characterized in that, The second recovery branch pipe is connected to a third vent pipe, and the third vent pipe is equipped with a seventh valve (F7).

5. A nitrogen recovery system for venting nitrogen from a liquid nitrogen storage tank in a nitrogen liquefaction device according to claim 4, characterized in that, A fifth valve (F5) is installed on the first recovery branch pipe, and a sixth valve (F6) is installed on the second recovery branch pipe located at the rear end of the third vent pipe.

6. A nitrogen recovery system for venting liquid nitrogen from a nitrogen liquefaction device's liquid nitrogen storage tank according to claim 5, characterized in that, A residual liquid discharge pipe is connected to the first recovery branch pipe at the rear end of the fifth valve (F5), and an eighth valve (F8) is installed on the residual liquid discharge pipe.

7. A nitrogen recovery system for venting liquid nitrogen from a nitrogen liquefaction device's liquid nitrogen storage tank according to claim 5, characterized in that, A tenth valve (F10) is installed on the cryogenic nitrogen main pipe located at the front end of the recovery pipeline.

8. A nitrogen recovery system for venting liquid nitrogen storage tanks in a nitrogen liquefaction device according to claim 5, characterized in that, A ninth valve (F9) is installed on the expander sealing gas pipeline located at the front end of the second recovery branch pipeline.

9. A nitrogen recovery system for venting liquid nitrogen from a nitrogen liquefaction device's liquid nitrogen storage tank according to claim 8, characterized in that, One end of the expander sealing gas pipeline is connected to the ambient temperature nitrogen busbar, and the other end is connected to the expander.

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