System for mutually utilizing liquid nitrogen cold energy and BOG heat energy

Abstract

The utility model relates to the technical field of liquefied natural gas (LNG) receiving stations, in particular to a system for mutually utilizing liquid nitrogen cold energy and boil-off gas (BOG) heat energy, which comprises a BOG direct output system, a BOG recondensation system and a liquid nitrogen system, the BOG direct output system comprises an LNG storage tank, the LNG storage tank is sequentially connected with a first BOG compressor and a first heat exchanger for providing a cold source by the liquid nitrogen system through a BOG pipeline, and the first heat exchanger is connected with a second BOG compressor through a BOG pipeline. The BOG outlet end of the first heat exchanger is communicated with a natural gas pipe network; the BOG recondensation system comprises a second BOG compressor, a second heat exchanger, a recondenser, a high-pressure pump and a first gasifier which are sequentially connected with the LNG storage tank through a BOG pipeline, the liquid nitrogen system provides a cold source through the second heat exchanger, the recondenser, the high-pressure pump and the first gasifier, and the outlet end of the first gasifier is communicated with a natural gas pipe network; and the in-tank low-pressure pump is connected with the re-condenser through a low-pressure output pipeline. The system is safe and reliable, energy stored by media of the system is mutually utilized, electricity charge is saved, noise is reduced, efficiency is improved, and compared with the prior art, the system has obvious advantages.

Description

Technical Field

[0001] The utility model relates to the technical field of LNG receiving stations, in particular to a system for mutual utilization of liquid nitrogen cold energy and BOG heat energy. Background Art

[0002] During the operation of the LNG receiving station, LNG (Liquefied Natural Gas, LNG for short) will evaporate into BOG (Boil Of Gas, BOG for short) due to absorbing heat. Since the LNG storage tank is a normal pressure storage tank, the evaporated BOG needs to be processed. The BOG processing process usually includes direct external transmission process and recondensation process.

[0003] The direct transmission process is to directly pressurize BOG to 5-7Mpa through a high-pressure compressor, and then use an air cooler to cool the natural gas from 120°C to room temperature before entering the natural gas pipeline network. The air cooler is noisy and energy-consuming during operation.

[0004] The recondensation process is to pressurize BOG to 0.4-0.6Mpa through a low-pressure compressor and then directly enter the recondenser and mix with LNG. After LNG cools the BOG, it is pressurized by a high-pressure pump and sent to the gasifier for gasification and then enters the natural gas pipeline network, and the other way is sent to the cold energy air separation project. Because the maximum temperature of the BOG compressor outlet can reach 40°C, when only one high-pressure pump is running, the temperature of the LNG after recondensation entering the high-pressure pump is only about -130°C. On the one hand, there may be a risk of cavitation of the high-pressure pump, and on the other hand, it has a great impact on the output of the cold energy air separation project. At present, various LNG receiving stations are constantly expanding, and the demand for recondenser volume is also increasing. There may be a problem of insufficient reserved land for BOG plant and recondenser. In the actual operation of the LNG receiving station, from the perspective of energy saving and consumption reduction, the recondensation process is preferred. When there is no gaseous external transmission production line or the recondenser process processing capacity is insufficient, the direct external transmission process is adopted to treat BOG.

[0005] In the LNG receiving station, a liquid nitrogen system is set up and the liquid nitrogen is gasified into nitrogen for equipment sealing, pipeline and equipment purging and replacement. The usage is 0.1 tons to 1.2 tons per hour. In the process of liquid nitrogen being gasified into nitrogen, the cold energy stored in the liquid nitrogen is wasted.

[0006] Therefore, how to use the cold energy stored in liquid nitrogen to reduce the outlet temperature of the high-pressure compressor and BOG compressor is one of the important measures to achieve energy saving and consumption reduction in LNG receiving stations. Utility Model Content

[0007] The utility model aims to provide a system for mutually utilizing liquid nitrogen cold energy and BOG heat energy, which can solve the above technical problems.

[0008] The utility model provides a system for mutual utilization of liquid nitrogen cold energy and BOG heat energy, comprising a BOG direct external transmission system, a BOG recondensation system and a liquid nitrogen system.

[0009] The BOG direct export system comprises an LNG storage tank, which is sequentially connected to a first BOG compressor and a first heat exchanger provided with a cold source by a liquid nitrogen system through a BOG pipeline, and the BOG outlet end of the first heat exchanger is connected to a natural gas pipeline network.

[0010] The BOG recondensing system includes a second BOG compressor connected to the LNG storage tank in sequence through a BOG pipeline, a second heat exchanger provided with a cold source by a liquid nitrogen system, a recondenser, a high-pressure pump and a first vaporizer, wherein the outlet end of the first vaporizer is connected to a natural gas pipeline network, and further includes an in-tank low-pressure pump, which is connected to the recondenser through a low-pressure external transmission pipeline.

[0011] Furthermore, the liquid nitrogen system includes a liquid nitrogen storage tank and a second vaporizer, the outlet of the liquid nitrogen storage tank is respectively connected to a first liquid nitrogen pipeline, a second liquid nitrogen pipeline, and a third liquid nitrogen pipeline, the first liquid nitrogen pipeline is connected to the first heat exchanger and then merged into the third liquid nitrogen pipeline, the second liquid nitrogen pipeline is connected to the second heat exchanger and then merged into the third liquid nitrogen pipeline, the third liquid nitrogen pipeline is directly connected to the second vaporizer, and the outlet end of the second vaporizer is connected to the nitrogen pipeline network through a nitrogen pipeline.

[0012] Furthermore, a first control valve is provided on the first liquid nitrogen pipeline between the liquid nitrogen storage tank and the first heat exchanger.

[0013] Furthermore, a second control valve is provided on the second liquid nitrogen pipeline between the liquid nitrogen storage tank and the second heat exchanger.

[0014] Furthermore, a third control valve is provided on the third liquid nitrogen pipeline between the liquid nitrogen storage tank and the second vaporizer.

[0015] Furthermore, the first BOG compressor is a high-pressure BOG compressor, which increases the pressure of BOG to 5-7 MPa.

[0016] Furthermore, the second BOG compressor is a low-pressure BOG compressor, which increases the BOG pressure to 0.4-0.6 MPa.

[0017] Furthermore, a nitrogen buffer tank is provided on the nitrogen pipeline between the second gasifier and the nitrogen pipeline network.

[0018] Furthermore, a first temperature detection device is provided on the BOG pipeline between the first heat exchanger and the natural gas pipeline network, and a second temperature detection device is provided on the BOG pipeline between the second heat exchanger and the recondenser.

[0019] Furthermore, a pressure detection device is provided on the nitrogen pipeline between the nitrogen buffer tank and the nitrogen pipeline network.

[0020] Beneficial effects:

[0021] 1) Use the cooling capacity of liquid nitrogen to reduce the temperature of natural gas pressurized by the high-pressure compressor to room temperature, reduce the operating time of the air cooler at the outlet of the high-pressure compressor, save electricity costs and reduce noise;

[0022] 2) The refrigeration capacity of liquid nitrogen is used to reduce the temperature of BOG after being pressurized by the BOG compressor, thereby improving the processing capacity of the recondenser and reducing the floor space of the recondenser in the expansion project;

[0023] 3) Use the coldness of liquid nitrogen to lower the temperature of BOG after being pressurized by the BOG compressor, thereby lowering the temperature of LNG at the outlet of the recondenser, avoiding cavitation of the high-pressure pump, and increasing the output of the cold energy air separation project;

[0024] 4) Using the heat of the natural gas exported by the high-pressure compressor and BOG compressor to gasify liquid nitrogen into nitrogen can improve the gasification production capacity of the liquid nitrogen system, which is particularly effective in winter.

[0025] The system is safe and reliable, and utilizes the energy stored in its medium to save electricity costs, reduce noise, and improve efficiency. It has obvious advantages over existing technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a schematic diagram of the system structure of the utility model for mutual utilization of liquid nitrogen cold energy and BOG heat energy.

[0028] Explanation of the reference numerals: 1-LNG storage tank, 2-BOG pipeline, 3-first BOG compressor, 4-first heat exchanger, 5-first temperature detection device, 6-second BOG compressor, 7-second heat exchanger, 8-second temperature detection device, 9-recondenser, 10-high-pressure pump, 11-first vaporizer, 21-liquid nitrogen storage tank, 22-liquid nitrogen pipeline, 221-first liquid nitrogen pipeline, 222-second liquid nitrogen pipeline, 223-third liquid nitrogen pipeline, 23-second control valve, 24-third control valve, 25-first control valve, 26-second vaporizer, 27-nitrogen pipeline, 28-nitrogen buffer tank, 29-pressure detection device, 31-low-pressure pump in the tank, 32-low-pressure external transmission pipeline. DETAILED DESCRIPTION

[0029] The technical solution of the utility model will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0030] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0031] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0032] Example 1

[0033] like Figure 1 The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy comprises a BOG direct external transmission system, a BOG recondensation system, and a liquid nitrogen system;

[0034] The BOG direct external transmission system includes an LNG storage tank 1, a first BOG compressor 3, a first heat exchanger 4, a first temperature detection device 5, and a BOG pipeline 2 connecting the components. A BOG pipeline 2 is arranged on the top of the LNG storage tank 1. One path is pressurized by the first BOG compressor 3 and then transported to the first heat exchanger 4 and then heat exchanged with liquid nitrogen and then directly transported to the natural gas network. The other path enters the BOG recondensation system.

[0035] The BOG recondensation system includes a second BOG compressor 6, a second heat exchanger 7, a second temperature detection device 8, a recondenser 9, a high-pressure pump 10, a first vaporizer 11, a BOG pipeline 2 connected to each component, a low-pressure pump 31 in the tank, and a low-pressure external transmission pipeline 32. BOG comes from the top of the LNG storage tank 1, passes through the BOG pipeline 2, is pressurized by the second compressor 6 and then transported to the second heat exchanger 7, and the BOG after heat exchange with liquid nitrogen enters the recondenser 9, is mixed with the LNG pressurized by the low-pressure pump 31 in the tank in the recondenser 9, and is condensed into LNG and transported to the high-pressure pump 10 together, and is pressurized by the high-pressure pump 10 and then transported to the first vaporizer 11, and then enters the natural gas pipeline network after being gasified;

[0036] The liquid nitrogen system includes a liquid nitrogen storage tank 21, a first control valve 25, a second control valve 23, a third control valve 24, a second vaporizer 26, a nitrogen pipeline 27, a nitrogen buffer tank 28 and a pressure detection device 29. The outlet of the liquid nitrogen storage tank 21 is connected to the liquid nitrogen pipeline 22 and is divided into three routes (divided into a first route liquid nitrogen pipeline 221, a second route liquid nitrogen pipeline 222, and a third route liquid nitrogen pipeline 223). The first route is connected to the first control valve 25 and then transported to the first heat exchanger 4, and output to the inlet of the second vaporizer 26 after heat exchange; the second route is connected to the second control valve 23 and then transported to the second heat exchanger 7, and output to the inlet of the second vaporizer 26 after heat exchange; the third route is connected to the third control valve 24 and then directly output to the inlet of the second vaporizer 26. After the three routes are merged, the liquid nitrogen or nitrogen is gasified in the second vaporizer 26 and then transported to the nitrogen buffer tank 28 through the nitrogen pipeline 27 and then enters the nitrogen pipeline network.

[0037] The first BOG compressor 3 is a high-pressure BOG compressor that can increase the pressure of BOG to 6.5 MPa;

[0038] The second BOG compressor 6 is a low-pressure BOG compressor that can increase the BOG pressure to 0.5 MPa;

[0039] The first temperature detection device 5 is logically interlocked with the first control valve 25, and the second temperature detection device 8 is logically interlocked with the second control valve 23; the pressure detection device 29 is logically interlocked with the third control valve 24, wherein the first control valve, the second control valve and the third control valve are all remote electric control valves with automatic control function. The above are all existing technologies and will not be elaborated here.

[0040] Based on the system of the above embodiment, a method for using the system is also proposed, which includes the following steps:

[0041] 1) When the first BOG compressor 3 and the second BOG compressor 6 are running at the receiving station at the same time, the outlet natural gas temperature of the first BOG compressor 3 is preferentially controlled at 2°C-35°C through the first control valve 25; when the pressure detection device 29 detects that the nitrogen pipeline network pressure is still decreasing, the outlet natural gas temperature of the second BOG compressor 6 is controlled at above -80°C through the second control valve 23; when the pressure detection device 29 detects that the nitrogen pipeline network pressure is still decreasing after the first BOG compressor 3 and the second BOG compressor 6 are heat exchanged at the same time, the downstream user demand is ensured by controlling the third control valve 24;

[0042] 2) When only the second BOG compressor 6 is running at the receiving station, the outlet natural gas temperature of the second BOG compressor 6 is preferentially controlled to be above -80°C through the second control valve 23; when the pressure detection device 29 detects that the nitrogen network pressure is still decreasing, the downstream user demand is ensured by controlling the third control valve 24;

[0043] 3) When the first BOG compressor 3 and the second BOG compressor 6 are not in operation at the receiving station, the downstream user demand is ensured by controlling the third control valve 24 .

[0044] By using the above system and method, the energy stored in the medium can be mutually utilized, electricity costs can be saved, noise can be reduced, and efficiency can be improved, which has obvious advantages over the existing technology.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the utility model.

Claims

1. A system for mutual utilization of liquid nitrogen cold energy and BOG heat energy, characterized in that: Including BOG direct external transmission system, BOG recondensation system and liquid nitrogen system; The BOG direct external transmission system comprises an LNG storage tank, which is sequentially connected to a first BOG compressor and a first heat exchanger provided with a cold source by a liquid nitrogen system through a BOG pipeline, and a BOG outlet end of the first heat exchanger is connected to a natural gas pipeline network; The BOG recondensing system includes a second BOG compressor connected to the LNG storage tank in sequence through a BOG pipeline, a second heat exchanger provided with a cold source by a liquid nitrogen system, a recondenser, a high-pressure pump and a first vaporizer, wherein the outlet end of the first vaporizer is connected to a natural gas pipeline network, and further includes an in-tank low-pressure pump, which is connected to the recondenser through a low-pressure external transmission pipeline.

2. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 1, characterized in that: The liquid nitrogen system comprises a liquid nitrogen storage tank and a second vaporizer, wherein the outlet of the liquid nitrogen storage tank is respectively connected to a first liquid nitrogen pipeline, a second liquid nitrogen pipeline, and a third liquid nitrogen pipeline, wherein the first liquid nitrogen pipeline is connected to a first heat exchanger and then merged into the third liquid nitrogen pipeline, wherein the second liquid nitrogen pipeline is connected to a second heat exchanger and then merged into the third liquid nitrogen pipeline, wherein the third liquid nitrogen pipeline is directly connected to the second vaporizer, and the outlet end of the second vaporizer is connected to a nitrogen pipe network through a nitrogen pipe.

3. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 2, characterized in that: A first control valve is provided on the first liquid nitrogen pipeline between the liquid nitrogen storage tank and the first heat exchanger.

4. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 2, characterized in that: A second control valve is provided on the second liquid nitrogen pipeline between the liquid nitrogen storage tank and the second heat exchanger.

5. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 3, characterized in that: A third control valve is provided on the third liquid nitrogen pipeline between the liquid nitrogen storage tank and the second vaporizer.

6. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 1, characterized in that: The first BOG compressor is a high-pressure BOG compressor, which increases the pressure of BOG to 5-7 MPa.

7. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 1, characterized in that: The second BOG compressor is a low-pressure BOG compressor, which increases the BOG pressure to 0.4-0.6 MPa.

8. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 2, characterized in that: A nitrogen buffer tank is also provided on the nitrogen pipeline between the second gasifier and the nitrogen pipeline network.

9. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 1, characterized in that: A first temperature detection device is provided on the BOG pipeline between the first heat exchanger and the natural gas network, and a second temperature detection device is provided on the BOG pipeline between the second heat exchanger and the recondenser.

10. The system for mutual utilization of liquid nitrogen cold energy and BOG heat energy according to claim 8, characterized in that: A pressure detection device is provided on the nitrogen pipeline between the nitrogen buffer tank and the nitrogen pipeline network.

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