A LNG cold energy utilization system based on BOG combustion

Abstract

A LNG cold energy utilization system based on BOG combustion includes an LNG storage tank, a first heat exchanger, a separator, and a second heat exchanger. The LNG storage tank is connected to a burner through a BOG delivery pipeline, the burner is connected to the first heat exchanger, the first heat exchanger is connected to a separator, and the separator is connected to a third heat exchanger through a water flow mixer; the LNG in the LNG storage tank is connected to the second heat exchanger through an LNG delivery pipe, the second heat exchanger is connected to the third heat exchanger, and a delivery branch pipe is provided on the LNG delivery pipe; the separator is connected to a steam turbine through an air flow pipeline, the steam turbine is connected to the second heat exchanger, the second heat exchanger is connected to a compressor, the compressor is connected to the first heat exchanger, and the air flow outlet of the first heat exchanger is connected to the inlet end of the steam turbine. The present invention overcomes the energy waste caused by BOG venting or flaring, and can make full use of LNG cold energy, improve the energy utilization efficiency of the receiving station, improve the ecological environment of the surrounding sea area, and has high economic and environmental benefits.

Description

Technical Field

[0001] The invention relates to the technical field of LNG cold energy utilization, and in particular to an LNG cold energy utilization system based on BOG combustion. Background Art

[0002] As a form of natural gas, atmospheric pressure liquefied natural gas (LNG) has a volume equivalent to only 1 / 625 of the standard volume. LNG receiving stations are an important link in the LNG industry chain. They are not only the receiving terminals for seaborne liquefied natural gas, but also one of the important sources of natural gas supply on land. However, there are currently two major problems with LNG receiving stations:

[0003] (1) The temperature of liquefied natural gas is very low, and the storage tanks and pipelines in the LNG receiving station cannot be completely insulated, so flash gas (BOG) will inevitably be generated. If BOG is not handled in time, it will not only cause the temperature of the tank to rise, but also cause the pressure of the tank to rise. Excessive pressure in the tank will damage the structure of the tank and endanger its maintenance system. At present, the common method of handling BOG is to vent or flare it, which not only causes a huge waste of energy, but also causes serious pollution to the environment.

[0004] (2) Liquefied natural gas (LNG) needs to be vaporized before it is delivered to users. LNG releases a large amount of cold energy when it vaporizes, with a value of about 830-860 kJ / kg. If all the cold energy released by LNG is converted into electrical energy, then the cold energy per ton of LNG is equivalent to 240 kW•h of electrical energy. In the traditional LNG vaporization process, the cold energy carried by LNG is carried away by seawater or air, resulting in an extreme waste of energy and serious pollution and damage to the ecological environment of the surrounding sea areas.

[0005] Therefore, adopting effective means to recycle and utilize BOG and LNG cold energy is of great significance to the full utilization of energy and the alleviation of environmental pollution. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides an LNG cold energy utilization system based on BOG combustion, which overcomes the energy waste caused by BOG venting or flaring, and can fully utilize the cold energy contained in LNG, thereby improving the energy utilization efficiency of the receiving station and improving the ecological environment of the surrounding sea areas, with high economic and environmental benefits.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] An LNG cold energy utilization system based on BOG combustion includes an LNG storage tank, a first heat exchanger, a separator, and a second heat exchanger. The top of the LNG storage tank is connected to the inlet of a burner through a BOG delivery pipeline, the outlet of the burner is connected to the inlet of the first heat exchanger, the outlet of the first heat exchanger is connected to the inlet of the separator, the water outlet below the separator is connected to the inlet of a water flow mixer, and the outlet of the water flow mixer is connected to the outlet of the third heat exchanger through a water flow delivery pump; the LNG in the LNG storage tank is connected to the outlet of the second heat exchanger through the LNG delivery pipe. The first inlet of the second heat exchanger is connected, the first outlet of the second heat exchanger is connected to the third heat exchanger, one end of a delivery branch pipe is fixedly connected to the LNG delivery pipe, and the other end of the delivery branch pipe is connected to the inlet of the burner; the airflow outlet end of the separator is connected to the outlet end of the steam turbine through an airflow pipeline, the outlet end of the steam turbine is connected to the second inlet of the second heat exchanger, the second outlet of the second heat exchanger is connected to the inlet of the compressor, the outlet of the compressor is connected to the airflow inlet of the first heat exchanger, and the airflow outlet of the first heat exchanger is connected to the inlet end of the steam turbine.

[0009] Preferably, a BOG control switch and a BOG delivery pump are fixedly installed on the BOG delivery pipeline.

[0010] Preferably, a water flow control switch is installed on the pipeline connecting the separator and the water flow mixer.

[0011] Preferably, a first LNG delivery pump is fixedly installed on the LNG delivery pipe, and a branch flow control switch and a second LNG delivery pump are installed on the delivery branch pipe.

[0012] Preferably, the end of the airflow duct is also connected to the airflow inlet end of the third heat exchanger, a first airflow control switch is installed on the airflow inlet end of the airflow duct close to the third heat exchanger, and a second airflow control switch is installed on the outlet end of the airflow duct close to the turbine.

[0013] Preferably, the reheated flue gas in the separator is connected to the burner through a flue gas channel.

[0014] The present invention provides an LNG cold energy utilization system based on BOG combustion. It has the following beneficial effects: using CO2 as the working fluid to realize supercritical circulation, not only ensures that the heat energy after BOG combustion is fully utilized, but also fully utilizes the cold energy contained in LNG, thereby improving the overall energy utilization rate of the receiving station. Compared with the traditional BOG treatment process and LNG cold energy utilization method, it reduces the energy waste caused by BOG emptying or flare combustion, alleviates the pollution of seawater to the ecological environment in LNG cold energy utilization, and has great advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the present invention or the technical solutions in the prior art, the drawings required for describing the prior art are briefly introduced below.

[0016] Figure 1 A schematic diagram of the structure of the present invention;

[0017] Description of the numbers in the figure:

[0018] 1. LNG storage tank; 2. First heat exchanger; 3. Separator; 4. Second heat exchanger; 5. BOG delivery pipeline; 6. Burner; 7. Water flow mixer; 8. Water flow delivery pump; 9. Third heat exchanger; 10. LNG delivery pipe; 11. Delivery branch pipe; 12. Steam turbine; 13. Compressor; 14. BOG control switch; 15. BOG delivery pump; 16. Water flow control switch; 17. First LNG delivery pump; 18. Branch flow control switch; 19. Second LNG delivery pump; 20. Second air flow control switch; 21. First air flow control switch; 22. Smoke channel. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

[0020] Embodiment 1, as Figure 1 As shown, a LNG cold energy utilization system based on BOG combustion includes an LNG storage tank 1, a first heat exchanger 2, a separator 3 and a second heat exchanger 4. The top of the LNG storage tank 1 is connected to the inlet of a burner 6 through a BOG delivery pipeline 5, the outlet of the burner 6 is connected to the inlet of the first heat exchanger 2, the outlet of the first heat exchanger 2 is connected to the inlet of the separator 3, the water outlet below the separator 3 is connected to the inlet of a water flow mixer 7, and the outlet of the water flow mixer 7 is connected to the third heat exchanger 9 through a water flow delivery pump 8; the LNG in the LNG storage tank 1 is connected to the first inlet of the second heat exchanger 4 through an LNG delivery pipe 10, and the second heat exchanger 4 is connected to the third heat exchanger 9 through a water flow delivery pump 8; The first outlet of the heat exchanger 4 is connected to the third heat exchanger 9, and one end of the delivery branch pipe 11 is fixedly connected to the LNG delivery pipe 10, and the other end of the delivery branch pipe 11 is connected to the inlet of the burner 6; the air flow outlet end of the separator 3 is connected to the outlet end of the steam turbine 12 through the air flow pipeline, and the end of the air flow pipeline is also connected to the air flow inlet end of the third heat exchanger 9, the outlet end of the steam turbine 12 is connected to the second inlet of the second heat exchanger 4, the second outlet of the second heat exchanger 4 is connected to the inlet of the compressor 13, the outlet of the compressor 13 is connected to the air flow inlet of the first heat exchanger 2, and the air flow outlet of the first heat exchanger 2 is connected to the inlet end of the steam turbine 12.

[0021] The BOG flash gas released from the top of the LNG storage tank 1 passes through the BOG delivery pipeline 5 and is mixed with the LNG transported in the delivery branch pipe 11, and then enters the burner 6 for full combustion. The generated high-temperature flue gas is fully heat-exchanged with the low-temperature and high-pressure CO2 in the supercritical CO2 circulation process in the first heat exchanger 2. The low-temperature flue gas after heat exchange enters the separator 3, and after separation, it generates heat-recovered flue gas, CO2 airflow, water flow and other working fluids; the water flow enters the water flow mixer 7 through the water outlet and is fully mixed with the seawater from the environment, and then enters the third heat exchanger 9, and the CO2 airflow passes through the airflow pipeline at the airflow outlet end of the separator 3 to mix with the high-temperature and low-pressure CO2 at the outlet end of the turbine 12, and the other way enters the third heat exchanger 9 to absorb the cold energy of LNG; and other working fluids are discharged through the discharge port on the separator 3;

[0022] The LNG stored in the LNG storage tank 1 is divided into two paths through the LNG delivery pipe 10, one of which is mixed with the BOG flash gas in the BOG delivery pipeline 5 through the delivery branch pipe 11 and enters the burner 6 for combustion, and the other is entered into the second heat exchanger 4 through the LNG delivery pipe 10 to condense the high-temperature and low-pressure CO2 of the supercritical CO2 cycle into low-pressure and low-temperature CO2. The LNG after releasing the cold energy enters the third heat exchanger 9 to fully exchange heat with the mixed water flow and CO2 air flow output by the water flow mixer 7. The LNG after releasing the cold energy becomes user natural gas and is delivered out; and after the CO2 air flow absorbs the LNG cold energy in the third heat exchanger 9, the low-temperature CO2 generated can be delivered to the dry ice manufacturing site, and the mixed water flow can be output to the wastewater treatment facility for treatment after absorbing the LNG cold energy;

[0023] Another CO2 gas flow from the separator 3 enters the supercritical CO2 cycle through the gas flow pipeline, and after mixing with the high-temperature, low-pressure CO2 at the outlet end of the turbine 12, enters the second heat exchanger 4 to absorb the cold energy released by LNG, and becomes low-temperature, low-pressure CO2 and then enters the compressor 13. After compression, it becomes low-temperature, high-pressure CO2, and then fully exchanges heat with the high-temperature flue gas in the first heat exchanger 2 to become high-temperature, high-pressure CO2. The high-temperature, high-pressure CO2 is then converted into high-temperature, low-pressure CO2 after expansion work in the turbine 12, completing a complete Brayton cycle. The electrical energy generated by the expansion work can be output by the generator 23.

[0024] This application uses CO2 as the working fluid to realize supercritical circulation, which not only ensures that the heat energy after BOG combustion is fully utilized, but also fully utilizes the cold energy contained in LNG, thereby improving the overall energy utilization rate of the receiving station. Compared with the traditional BOG treatment process and LNG cold energy utilization method, it reduces the energy waste caused by BOG emptying or flare combustion, and alleviates the pollution of seawater to the ecological environment in the utilization of LNG cold energy.

[0025] Embodiment 2, as a preferred solution of embodiment 1, a BOG control switch 14 and a BOG delivery pump 15 are fixedly installed on the BOG delivery pipeline 5. A first LNG delivery pump 17 is fixedly installed on the LNG delivery pipe 10, and a branch flow control switch 18 and a second LNG delivery pump 19 are installed on the delivery branch pipe 11. The BOG flash gas in the LNG storage tank 1 is delivered by the BOG delivery pump 15, and the LNG in the LNG storage tank 1 is delivered by the first LNG delivery pump 17 and the second LNG delivery pump 19, wherein the quality ratio can be appropriately adjusted according to the gasification rate of the BOG flash gas and the demand for natural gas by downstream users by controlling the BOG control switch 14 and the branch flow control switch 18.

[0026] Embodiment 3, as a preferred solution of embodiment 1, a water flow control switch 16 is installed on the pipe connecting the separator 3 and the water flow mixer 7. The water flow control switch 16 is used to properly adjust the water flow rate of the water outlet of the separator 3.

[0027] Embodiment 4, as a preferred solution of embodiment 1, a first airflow control switch 21 is installed on the airflow inlet end of the airflow pipeline close to the third heat exchanger 9, and a second airflow control switch 20 is installed on the outlet end of the airflow pipeline close to the steam turbine 12. Thus, the sizes of the first airflow control switch 21 and the second airflow control switch 20 can be appropriately adjusted according to the demand for the working medium of the supercritical CO2 cycle.

[0028] Embodiment 5, as a preferred solution of embodiment 1, the reheated flue gas in the separator 3 is connected to the burner 6 through the flue gas channel 22. By delivering a proper amount of reheated flue gas in the separator 3 to the burner 6, it helps to improve the BOG combustion efficiency.

[0029] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An LNG cold energy utilization system based on BOG combustion, characterized in that: The invention comprises an LNG storage tank (1), a first heat exchanger (2), a separator (3) and a second heat exchanger (4); the upper part of the LNG storage tank (1) is connected to the inlet of a burner (6) via a BOG delivery pipeline (5); the outlet of the burner (6) is connected to the inlet of the first heat exchanger (2); the outlet of the first heat exchanger (2) is connected to the inlet of the separator (3); the water outlet below the separator (3) is connected to the inlet of a water flow mixer (7); and the outlet of the water flow mixer (7) is connected to a third heat exchanger (9) via a water flow delivery pump (8); The LNG in the LNG storage tank (1) is connected to a first inlet of the second heat exchanger (4) through an LNG delivery pipe (10); the first outlet of the second heat exchanger (4) is connected to a third heat exchanger (9); one end of a delivery branch pipe (11) is fixedly connected to the LNG delivery pipe (10); the other end of the delivery branch pipe (11) is connected to an inlet of the burner (6); The air flow outlet end of the separator (3) is connected to the outlet end of the steam turbine (12) through an air flow pipeline, the outlet end of the steam turbine (12) is connected to the second inlet of the second heat exchanger (4), the second outlet of the second heat exchanger (4) is connected to the inlet of the compressor (13), the outlet of the compressor (13) is connected to the air flow inlet of the first heat exchanger (2), and the air flow outlet of the first heat exchanger (2) is connected to the inlet end of the steam turbine (12); A BOG control switch (14) and a BOG delivery pump (15) are fixedly installed on the BOG delivery pipeline (5); A water flow control switch (16) is installed on the pipeline connecting the separator (3) and the water flow mixer (7).

2. The LNG cold energy utilization system based on BOG combustion according to claim 1, characterized in that: A first LNG delivery pump (17) is fixedly mounted on the LNG delivery pipe (10), and a branch flow control switch (18) and a second LNG delivery pump (19) are mounted on the delivery branch pipe (11).

3. The LNG cold energy utilization system based on BOG combustion according to claim 1, characterized in that: The end of the airflow duct is also connected to the airflow inlet end of the third heat exchanger (9), and a first airflow control switch (21) is installed on the airflow inlet end of the airflow duct close to the third heat exchanger (9), and a second airflow control switch (20) is installed on the outlet end of the airflow duct close to the turbine (12).

4. The LNG cold energy utilization system based on BOG combustion according to claim 1, characterized in that: The reheated flue gas in the separator (3) is connected to the burner (6) through the flue gas channel (22).

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