LNG cold energy air separation device and method for increasing liquid nitrogen production capacity

Abstract

The present invention provides an LNG cold energy air separation device and method for improving liquid nitrogen production capacity. The device liquefies, separates and purifies oxygen and nitrogen from air by arranging an LNG cold box, a main heat exchanger cold box, a main tower cold box, a low-pressure nitrogen compressor and a circulating nitrogen compressor. The device can supplement low-pressure nitrogen into circulating nitrogen during the air separation process, thereby ensuring the extraction rate of oxygen and argon and improving the output of liquid nitrogen. At the same time, the unit energy consumption of air separation operation can be reduced. The device is particularly suitable for areas with low oxygen demand and high nitrogen demand. In addition, the LNG cold energy air separation device and method also reduce the influence on the temperature of liquid air and liquid nitrogen in the upper tower by independently arranging a liquid nitrogen product supercooler, thereby reducing the influence on the distillation of the upper tower, and also increase the raw material for producing liquid nitrogen by recycling low-pressure nitrogen, thereby achieving the effects of high oxygen extraction rate, large nitrogen-oxygen output ratio, flexible product adjustment and low energy consumption of LNG cold energy air separation.

Description

Technical Field

[0001] The invention relates to the technical field of air separation technology, and in particular to an LNG cold energy air separation device and a method for improving liquid nitrogen production capacity. Background Art

[0002] At present, LNG cold energy air separation has been widely promoted and applied as a way to utilize LNG cold energy. Due to its low energy consumption and high returns, it has become the preferred cold energy utilization project for LNG receiving stations. With the increase in the number of LNG receiving stations and the demand for cold energy utilization projects, LNG cold energy air separation technology will be further promoted.

[0003] The main products of LNG cold energy air separation include liquid oxygen, liquid nitrogen and liquid argon, and its production scale and product structure are affected by the surrounding liquid market. Generally speaking, heavy industrial areas have a higher demand for liquid oxygen and a lower demand for liquid nitrogen, while light industrial areas have a lower demand for liquid oxygen and a higher demand for liquid nitrogen. The current LNG cold energy air separation unit has a higher oxygen extraction rate and a lower nitrogen extraction rate, which can meet the needs of heavy industrial areas, but cannot meet the needs of light industrial areas. It can be seen that there is an urgent need for an LNG cold energy air separation unit and method with a high oxygen extraction rate, a large nitrogen-oxygen output ratio, flexible product adjustment and low energy consumption. Summary of the invention

[0004] In view of the defects of the above-mentioned prior art, the present invention provides an LNG cold energy air separation device and method for improving the liquid nitrogen production capacity. The LNG cold energy air separation device and method liquefy, separate and purify oxygen and nitrogen from air by setting an LNG cold box, a main heat exchanger cold box, a main tower cold box, a low-pressure nitrogen compressor and a circulating nitrogen compressor. The low-pressure nitrogen can be added to the circulating nitrogen during the air separation process to ensure the extraction rate of oxygen and argon and increase the output of liquid nitrogen. At the same time, the unit energy consumption of air separation operation can be reduced. It is particularly suitable for areas with low oxygen demand and high nitrogen demand. In addition, the LNG cold energy air separation device and method reduce the impact on the upper tower liquid air and liquid nitrogen temperature by independently setting a liquid nitrogen product supercooler, thereby reducing the impact on the upper tower distillation, and also increase the raw material for producing liquid nitrogen by recovering low-pressure nitrogen, thereby achieving the effects of high oxygen extraction rate, large nitrogen-oxygen output ratio, flexible product adjustment and low energy consumption of LNG cold energy air separation.

[0005] The present invention provides an LNG cold energy air separation device for improving liquid nitrogen production capacity, and the overall inventive concept is as follows:

[0006] The LNG cold energy air separation unit for increasing liquid nitrogen production capacity comprises an LNG cold box, a main heat exchanger cold box, a main tower cold box, a low-pressure nitrogen compressor (NC01) and a circulating nitrogen compressor (NC02); wherein,

[0007] The LNG cold box is connected to the main tower cold box through a circulating liquid nitrogen pipeline;

[0008] The main tower cold box is connected to the main heat exchanger cold box through a purified air pipeline, a circulating nitrogen pipeline, a low-pressure nitrogen pipeline and a dirty nitrogen pipeline;

[0009] The main heat exchanger cold box is connected to the LNG cold box through the circulating nitrogen pipeline;

[0010] The low-pressure nitrogen compressor (NC01) is connected to the main heat exchanger cold box and the LNG cold box respectively through the low-pressure nitrogen pipeline;

[0011] The circulating nitrogen compressor (NC02) is connected to the LNG cold box through the circulating nitrogen pipeline;

[0012] In one embodiment disclosed in the present application, the LNG cold box includes an LNG heat exchanger (E01) and a first liquid nitrogen subcooler (E02); wherein,

[0013] The LNG heat exchanger (E01) is connected to the main heat exchanger cold box and the circulating nitrogen compressor (NC02) respectively through the circulating nitrogen pipeline, and is used to cool the circulating nitrogen;

[0014] The first liquid nitrogen subcooler (E02) is connected to the main tower cold box through the circulating nitrogen pipeline and is connected to the LNG heat exchanger (E01), and is used for subcooling circulating liquid nitrogen;

[0015] In one embodiment disclosed in the present application, the main heat exchanger cold box comprises a main heat exchanger (E03); wherein,

[0016] The main heat exchanger (E03) is connected to the LNG cold box through the circulating nitrogen pipeline, and is connected to the low-pressure nitrogen compressor (NC01) through the low-pressure nitrogen pipeline;

[0017] The main heat exchanger (E03) is used to reheat the circulating nitrogen from the LNG cold box;

[0018] In one embodiment disclosed in the present application, the main tower cold box includes a liquid nitrogen-nitrogen heat exchanger (E04), a second liquid nitrogen subcooler (E05), a liquid air liquid nitrogen subcooler (E06), a lower tower (C01), an upper tower (C02), a main condenser evaporator (K01) and a liquid nitrogen separation tank (V01); wherein,

[0019] The lower tower (C01) is connected to the main condenser evaporator (K01), the liquid nitrogen-nitrogen heat exchanger (E04), and the liquid air-liquid nitrogen subcooler (E06) through pipelines respectively;

[0020] The upper tower (C02) is connected to the second liquid nitrogen subcooler (E05) and the liquid air liquid nitrogen subcooler (E06) through pipelines respectively;

[0021] The liquid nitrogen separation tank (V01) is connected to the second liquid nitrogen supercooler (E05) and the liquid air liquid nitrogen supercooler (E06) through pipelines respectively;

[0022] In one embodiment disclosed in the present application, the low-pressure nitrogen compressor (NC01) is used to pressurize the low-pressure nitrogen from the upper tower (C02) of the main tower cold box, and then transport the pressurized low-pressure nitrogen to the circulating nitrogen pipeline;

[0023] The circulating nitrogen compressor (NC02) is used to pressurize the nitrogen from the circulating nitrogen pipeline.

[0024] Based on the same inventive concept, the present invention also provides an LNG cold energy air separation method for increasing liquid nitrogen production capacity, the LNG cold energy air separation method comprising:

[0025] The LNG cold box provides the cold box of the main heat exchanger and the lower tower (C01) with cold energy generated by LNG vaporization, so as to realize liquefied cooling of air or nitrogen;

[0026] The main heat exchanger cold box cools the purified air and transmits the air to the lower tower (C01);

[0027] The lower tower (C01) performs distillation, purification and condensation on the cooling air from the cold box of the main heat exchanger to form liquid nitrogen;

[0028] The liquid nitrogen is circulated and transmitted between the LNG cold box, the main heat exchanger cold box and the liquid nitrogen-nitrogen heat exchanger (E04), so as to transfer the cold energy of LNG vaporization and obtain part of the liquid nitrogen product;

[0029] In one embodiment of the air separation method, the LNG cold energy air separation method further comprises: after the purified air is cooled by the main heat exchanger (E03), it is sent to the lower tower (C01) for distillation, the lower tower (C01) separates the nitrogen into a first stream and a second stream, wherein the first stream of nitrogen enters the main condenser evaporator (K01) and is liquefied by the main condenser evaporator (K01), wherein a part of the liquefied nitrogen is refluxed to the lower tower (C01) as a reflux liquid, and the other part of the liquefied nitrogen is sent to the liquid air liquid nitrogen subcooler (E03). 06) and a part of it is refluxed to the upper tower (C02) as reflux liquid, and the remaining part of it is sent to the liquid nitrogen storage tank for storage as liquid nitrogen product, the second stream of nitrogen is sent to the liquid nitrogen-nitrogen heat exchanger (E04) to be liquefied and then merged into the main condenser evaporator (K01) and then refluxed to the lower tower (C01), thereby providing cooling capacity and reflux liquid for the lower tower (C01), and the oxygen-rich liquid air at the bottom of the lower tower (C01) is sent to the liquid air and liquid nitrogen subcooler (E06), and after being cooled, it is sent to the upper tower (C02) to participate in distillation;

[0030] The liquid oxygen at the bottom of the upper tower (C02) is evaporated and purified by the main condenser evaporator (K01), and then transferred to the liquid air and liquid nitrogen subcooler (E06) as a liquid oxygen product for subcooling, and then transferred to the liquid oxygen storage tank of the main tower cold box for storage; the low-pressure nitrogen at the top of the upper tower (C02) is successively reheated by the liquid air and liquid nitrogen subcooler (E06) and the main heat exchanger (E03), and then transferred to the low-pressure nitrogen compressor (NC01) for pressurization, and then transferred to the circulating nitrogen channel; the dirty nitrogen at the top of the upper tower (C02) is successively reheated by the liquid air and liquid nitrogen subcooler (E06) and the main heat exchanger (E03) as a regeneration gas;

[0031] In one embodiment of the air separation method, circulating liquid nitrogen from an LNG cold box enters a liquid nitrogen separation tank (V01) after throttling, and is liquid-phase-divided into a first stream and a second stream; wherein the first stream is transmitted to a liquid nitrogen-nitrogen heat exchanger (E04), and is heat-exchanged with nitrogen from a lower tower (C01) to be vaporized, and the vaporized first stream is merged to the top of the liquid nitrogen separation tank (V01) and enters a main heat exchanger (E03) in the form of a gas phase, and then is reheated in the main heat exchanger (E03) and returns to the LNG cold box as circulating nitrogen; the second stream is subcooled by a second liquid nitrogen subcooler (E05) and is divided into a first part and a second part, the first part is transmitted to a liquid nitrogen storage tank as a liquid nitrogen product for storage, the second part is throttled and returned to the second liquid nitrogen subcooler (E05), and is reheated by the second liquid nitrogen subcooler (E05) and then merged into a low-pressure nitrogen pipeline, and then transmitted to the main heat exchanger (E03) for reheating;

[0032] In one embodiment of the air separation method, the circulating nitrogen from the cold box of the main heat exchanger is transmitted to the LNG heat exchanger (E01), cooled to a predetermined temperature, and then enters the first section of the circulating nitrogen compressor (NC02) for pressurization, and then enters the LNG heat exchanger (E01) again to be cooled to a predetermined temperature and then enters the second section of the circulating nitrogen compressor (NC02) for pressurization, and then enters the LNG heat exchanger (E01) to be cooled and liquefied, and then enters the first liquid nitrogen subcooler (E02) and is divided into a first stream, a second stream and a third stream, and the first stream is transmitted to the circulating liquid nitrogen as the circulating liquid nitrogen. The main tower cold box provides cooling capacity for the main tower cold box. The second stream meets the predetermined pressure after throttling and returns to the first liquid nitrogen subcooler (E02) and is reheated. Then, it enters the LNG heat exchanger (E01) and is reheated to a predetermined temperature before being merged into the circulating nitrogen and then enters the circulating nitrogen compressor (NC02). The third stream meets another predetermined pressure after throttling and returns to the first liquid nitrogen subcooler (E02) and is reheated. Then, it enters the LNG heat exchanger (E01) and is reheated to a predetermined temperature before being merged into the circulating nitrogen and then enters the circulating nitrogen compressor (NC02).

[0033] In one embodiment of the air separation method, after the LNG from the LNG receiving station enters the LNG heat exchanger (E01) and is reheated to a predetermined temperature by nitrogen, a portion of it is transmitted to the LNG-ethylene glycol heat exchanger to provide cooling capacity for the ethylene glycol solution, and then is reheated by the LNG-ethylene glycol heat exchanger and returned to the LNG receiving station, and the remaining portion is further reheated by the LNG heat exchanger (E01) to a predetermined temperature and then directly returned to the LNG receiving station.

[0034] Compared with the prior art, the LNG cold energy air separation device and method for improving liquid nitrogen production capacity of the present invention, the LNG cold energy air separation device and method liquefy, separate and purify oxygen and nitrogen from air by arranging an LNG cold box, a main heat exchanger cold box, a main tower cold box, a low-pressure nitrogen compressor and a circulating nitrogen compressor, and can supplement low-pressure nitrogen to the circulating nitrogen during the air separation process, thereby ensuring the extraction rate of oxygen and argon and increasing the output of liquid nitrogen, and at the same time reducing the unit energy consumption of air separation operation, which is particularly suitable for areas with low oxygen demand and high nitrogen demand. In addition, the LNG cold energy air separation device and method reduce the impact on the upper tower liquid air and liquid nitrogen temperature by independently arranging a liquid nitrogen product supercooler, thereby reducing the impact on the upper tower distillation, and also increase the raw material for producing liquid nitrogen by recovering low-pressure nitrogen, thereby achieving the effects of high oxygen extraction rate, large nitrogen-oxygen output ratio, flexible product adjustment and low energy consumption of LNG cold energy air separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 A schematic structural diagram of an LNG cold energy air separation unit for increasing liquid nitrogen production capacity provided by the present invention.

[0037] Figure 2 The present invention provides a flow chart of an LNG cold energy air separation method for increasing liquid nitrogen production capacity.

[0038] Figure 3 A comparison chart of production capacity parameters of an LNG cold energy air separation unit for increasing liquid nitrogen production capacity provided by the present invention.

[0039] Figure 4 A comparison chart of equipment parameters of an LNG cold energy air separation unit for increasing liquid nitrogen production capacity provided by the present invention.

[0040] Figure numerals: 1. LNG cold box; 2. Main heat exchanger cold box; 3. Main tower cold box. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] See also Figure 1 , which is a schematic diagram of the structure of the LNG cold energy air separation device and method for increasing the liquid nitrogen production capacity provided by the present invention. The LNG cold energy air separation device for increasing the liquid nitrogen production capacity comprises an LNG cold box 1, a main heat exchanger cold box 2, a main tower cold box 3, a low-pressure nitrogen compressor NC01 and a circulating nitrogen compressor NC02; wherein,

[0043] The LNG cold box 1 is connected to the main tower cold box 3 via a circulating liquid nitrogen pipeline;

[0044] The main tower cold box 3 is connected to the main heat exchanger cold box 2 through a purified air pipeline, a circulating nitrogen pipeline, a low-pressure nitrogen pipeline and a dirty nitrogen pipeline;

[0045] The main heat exchanger cold box 2 is connected to the LNG cold box 1 through the circulating nitrogen pipeline;

[0046] The low-pressure nitrogen compressor NC01 is connected to the main heat exchanger cold box 2 and the LNG cold box 1 respectively through the low-pressure nitrogen pipeline;

[0047] The circulating nitrogen compressor NC02 is connected to the LNG cold box 1 through the circulating nitrogen pipeline.

[0048] Preferably, in one embodiment disclosed in the present application, the LNG cold box 1 includes an LNG heat exchanger E01 and a first liquid nitrogen subcooler E02; wherein,

[0049] The LNG heat exchanger E01 is connected to the main heat exchanger cold box 2 and the circulating nitrogen compressor NC02 respectively through the circulating nitrogen pipeline, and is used to cool the circulating nitrogen;

[0050] The first liquid nitrogen subcooler E02 is connected to the main tower cold box 3 through the circulating nitrogen pipeline and is connected to the LNG heat exchanger E01, and is used for subcooling circulating liquid nitrogen.

[0051] Preferably, the main heat exchanger cold box 2 includes a main heat exchanger E03; wherein,

[0052] The main heat exchanger E03 is connected to the LNG cold box 1 through the circulating nitrogen pipeline, and is connected to the low-pressure nitrogen compressor NC01 through the low-pressure nitrogen pipeline;

[0053] The main heat exchanger E03 is used to reheat the circulating nitrogen from the LNG cold box 1.

[0054] Preferably, the main tower cold box 3 includes a liquid nitrogen-nitrogen heat exchanger E04, a second liquid nitrogen subcooler E05, a liquid air liquid nitrogen subcooler E06, a lower tower C01, an upper tower C02, a main condenser evaporator K01 and a liquid nitrogen separation tank V01; wherein,

[0055] The lower tower C01 is connected to the main condenser evaporator K01, the liquid nitrogen-nitrogen heat exchanger E04, and the liquid air-liquid nitrogen subcooler E06 through pipelines;

[0056] The upper tower C02 is connected to the second liquid nitrogen subcooler E05 and the liquid air liquid nitrogen subcooler E06 through pipelines respectively;

[0057] The liquid nitrogen separation tank V01 is connected to the second liquid nitrogen supercooler E05 and the liquid air liquid nitrogen supercooler E06 through pipelines.

[0058] Preferably, the low-pressure nitrogen compressor NC01 is used to pressurize the low-pressure nitrogen from the upper tower CO2 of the main tower cold box 3, and then transport the pressurized low-pressure nitrogen to the circulating nitrogen pipeline;

[0059] The circulating nitrogen compressor NC02 is used to pressurize the nitrogen from the circulating nitrogen pipeline.

[0060] See also Figure 2 , which is a flow chart of the LNG cold energy air separation method for increasing liquid nitrogen production capacity provided by the present invention. The LNG cold energy air separation method comprises:

[0061] The LNG cold box 1 provides the cold energy generated by LNG vaporization to the main heat exchanger cold box 2 and the lower tower C01 to achieve liquefied cooling of air or nitrogen;

[0062] The main heat exchanger cold box 2 cools the purified air and transmits the air to the lower tower C01;

[0063] The lower tower C01 performs distillation, purification and condensation on the cooling air from the cold box 2 of the main heat exchanger to form liquid nitrogen;

[0064] The liquid nitrogen is circulated and transmitted between the LNG cold box 1, the main heat exchanger cold box 2 and the liquid nitrogen-nitrogen heat exchanger E04, so as to transfer the cold energy of LNG vaporization and obtain part of the liquid nitrogen product.

[0065] Preferably, the LNG cold energy air separation method further comprises the following steps: after the purified air is cooled by the main heat exchanger E03, it is sent to the lower tower C01 for distillation; the lower tower C01 separates the nitrogen into a first stream and a second stream; wherein the first stream of nitrogen enters the main condenser evaporator K01 and is liquefied by the main condenser evaporator K01; wherein a portion of the liquefied nitrogen is refluxed to the lower tower C01 as reflux liquid; and the other portion of the liquefied nitrogen is sent to the liquid air and liquid nitrogen subcooler E06 and is liquefied by the subcooler. A portion of the cooled gas is refluxed to the upper tower C02 as reflux liquid, and the remaining portion after being supercooled is sent to the liquid nitrogen storage tank for storage as a liquid nitrogen product. The second stream of nitrogen is sent to the liquid nitrogen-nitrogen heat exchanger E04, where it is liquefied and then merged into the main condenser evaporator K01 and then refluxed to the lower tower C01, thereby providing cooling capacity and reflux liquid for the lower tower C01. The oxygen-rich liquid air at the bottom of the lower tower C01 is sent to the liquid air and liquid nitrogen supercooler E06, where it is cooled and sent to the upper tower C02 to participate in distillation.

[0066] The liquid oxygen at the bottom of the upper tower C02 is evaporated and purified by the main condenser evaporator K01, and then transmitted to the liquid air and liquid nitrogen subcooler E06 as a liquid oxygen product for subcooling, and then transmitted to the liquid oxygen storage tank of the main tower cold box 3 for storage; the low-pressure nitrogen at the top of the upper tower C02 is successively reheated by the liquid air and liquid nitrogen subcooler E06 and the main heat exchanger E03, and then transmitted to the low-pressure nitrogen compressor NC01 for pressurization, and then transmitted to the circulating nitrogen channel; the dirty nitrogen at the top of the upper tower C02 is successively reheated by the liquid air and liquid nitrogen subcooler E06 and the main heat exchanger E03 as a regeneration gas.

[0067] Preferably, the circulating liquid nitrogen from the LNG cold box 1 enters the liquid nitrogen separation tank V01 after throttling, and is divided into a first stream and a second stream by the liquid phase; wherein the first stream is transmitted to the liquid nitrogen-nitrogen heat exchanger E04, and is vaporized by heat exchange with the nitrogen from the lower tower C01, and the vaporized first stream is merged to the top of the liquid nitrogen separation tank V01 and enters the main heat exchanger E03 in the form of gas phase, and then returns to the LNG cold box 1 as circulating nitrogen after reheating in the main heat exchanger E03; the second stream is divided into a first part and a second part after being supercooled by the second liquid nitrogen supercooler E05, the first part is transmitted to the liquid nitrogen storage tank for storage as a liquid nitrogen product, and the second part is returned to the second liquid nitrogen supercooler E05 after throttling, and after being reheated in the second liquid nitrogen supercooler E05, it is merged into the low-pressure nitrogen pipeline, and then transmitted to the main heat exchanger E03 for reheating.

[0068] Preferably, the circulating nitrogen from the main heat exchanger cold box 2 is transmitted to the LNG heat exchanger E01, cooled to a predetermined temperature, and then enters the first section of the circulating nitrogen compressor NC02 for pressurization, and then enters the LNG heat exchanger E01 again to be cooled to a predetermined temperature and then enters the second section of the circulating nitrogen compressor NC02 for pressurization, and then enters the LNG heat exchanger cold E01 to be liquefied, and then enters the first liquid nitrogen subcooler E02 and is divided into the first stream, the second stream and the third stream, and the first stream is transmitted to the main tower cold box 3 as circulating liquid nitrogen. , so as to provide cooling capacity for the main tower cold box 3. The second stream meets the predetermined pressure after throttling and returns to the first liquid nitrogen supercooler E02 and is reheated. It then enters the LNG heat exchanger E01 and is reheated to a predetermined temperature, then merges with the circulating nitrogen and enters the circulating nitrogen compressor NC02. The third stream meets another predetermined pressure after throttling and returns to the first liquid nitrogen supercooler E02 and is reheated. It then enters the LNG heat exchanger E01 and is reheated to a predetermined temperature, then merges with the circulating nitrogen and enters the circulating nitrogen compressor NC02.

[0069] Preferably, after the LNG from the LNG receiving station enters the LNG heat exchanger E01 and is reheated to a predetermined temperature by nitrogen, a portion of it is transmitted to the LNG-ethylene glycol heat exchanger to provide cooling for the ethylene glycol solution, and then is reheated by the LNG-ethylene glycol heat exchanger and returned to the LNG receiving station, and the remaining portion is further reheated by the LNG heat exchanger E01 to a predetermined temperature and then directly returned to the LNG receiving station.

[0070] By setting a liquid nitrogen subcooler E05 in the main tower cold box 3, it is possible to remove the supercooling of the liquid nitrogen product from the liquid air and liquid nitrogen subcooler E06, thereby reducing the impact on the temperature of the liquid air and liquid nitrogen in the upper tower C02 and reducing the impact on the distillation process of the upper tower C02; in addition, the liquid nitrogen subcooler E05 transmits the refluxed low-pressure nitrogen to the main heat exchanger E03 for reheating and recovery, which effectively improves the nitrogen extraction rate and increases the output of liquid nitrogen; in addition, the low-pressure nitrogen from the upper tower C02 is pressurized by the low-pressure nitrogen compressor NC01 and then transmitted into the circulating nitrogen pipeline, thereby providing a source of raw materials for the preparation of liquid nitrogen products.

[0071] See also Figure 3 and 4 , respectively, are a capacity parameter comparison diagram and an equipment parameter comparison diagram between the LNG cold energy air separation device for increasing liquid nitrogen capacity provided by the present invention and the conventional LNG cold energy air separation device in the prior art. The LNG cold energy air separation device for increasing liquid nitrogen capacity can maximize the liquid nitrogen production. Figure 3-4 It can be seen that the LNG cold energy air separation device of the present invention has higher advantages in terms of production capacity and equipment operation performance compared with conventional LNG cold energy air separation equipment, which are specifically manifested as follows: first, under the same air scale, the LNG cold energy air separation device of the present invention has a large liquid nitrogen production capacity, a large nitrogen-oxygen production ratio and a high extraction rate; second, the LNG cold energy air separation device of the present invention has low unit energy consumption, which is 10% lower than the energy consumption of conventional LNG cold energy air separation equipment; third, the low-pressure nitrogen compressor of the LNG cold energy air separation device of the present invention has high working flexibility, and it can adjust the output of liquid nitrogen in a large range; fourth, the LNG cold energy air separation device of the present invention can perform independent liquid nitrogen product supercooling configuration, which has little impact on the operation of the distillation system during variable load operation.

[0072] It can be seen from the contents of the above embodiments that the LNG cold energy air separation device and method for improving liquid nitrogen production capacity can maximize the liquid nitrogen production. It separates and purifies air by setting an LNG cold box, a main heat exchanger cold box, a main tower cold box, a low-pressure nitrogen compressor and a circulating nitrogen compressor, and produces liquid oxygen, liquid nitrogen and liquid argon. At the same time, it can also supplement low-pressure nitrogen to the circulating nitrogen during the air separation process, thereby ensuring the extraction rate of oxygen and argon and improving the output of liquid nitrogen, and reducing the unit energy consumption of air separation operation. It is particularly suitable for areas with low oxygen demand and high nitrogen demand. In addition, the LNG cold energy air separation device and method also independently set a liquid nitrogen product supercooler to reduce the impact on the temperature of liquid air and liquid nitrogen entering the upper tower, thereby reducing the impact on the distillation of the upper tower, and also recovering low-pressure nitrogen to increase the raw material for producing liquid nitrogen, thereby achieving the effects of high oxygen extraction rate, large nitrogen-oxygen output ratio, flexible product adjustment and low energy consumption of LNG cold energy air separation.

Claims

1. LNG cold energy air separation unit for increasing liquid nitrogen production capacity, characterized by: The LNG cold energy air separation unit for increasing liquid nitrogen production capacity comprises an LNG cold box, a main heat exchanger cold box, a main tower cold box, a low-pressure nitrogen compressor (NC01) and a circulating nitrogen compressor (NC02); wherein, The LNG cold box is connected to the main tower cold box through a circulating liquid nitrogen pipeline; The main tower cold box is connected to the main heat exchanger cold box through a purified air pipeline, a circulating nitrogen pipeline, a low-pressure nitrogen pipeline and a dirty nitrogen pipeline; The main heat exchanger cold box is connected to the LNG cold box through the circulating nitrogen pipeline; The low-pressure nitrogen compressor (NC01) is connected to the main heat exchanger cold box and the LNG cold box respectively through the low-pressure nitrogen pipeline; The circulating nitrogen compressor (NC02) is connected to the LNG cold box through the circulating nitrogen pipeline; The main tower cold box includes a liquid oxygen storage tank; The LNG cold box includes an LNG heat exchanger (E01) and a first liquid nitrogen subcooler (E02); wherein, The LNG heat exchanger (E01) is connected to the main heat exchanger cold box and the circulating nitrogen compressor (NC02) respectively through the circulating nitrogen pipeline, and is used to cool the circulating nitrogen; The first liquid nitrogen subcooler (E02) is connected to the main tower cold box through the circulating nitrogen pipeline and is connected to the LNG heat exchanger (E01), and is used for subcooling circulating liquid nitrogen; The main heat exchanger cold box includes a main heat exchanger (E03); wherein, The main heat exchanger (E03) is connected to the LNG cold box through the circulating nitrogen pipeline, and is connected to the low-pressure nitrogen compressor (NC01) through the low-pressure nitrogen pipeline; The main heat exchanger (E03) is used to reheat the circulating nitrogen from the LNG cold box; The main tower cold box includes a liquid nitrogen-nitrogen heat exchanger (E04), a second liquid nitrogen subcooler (E05), a liquid air liquid nitrogen subcooler (E06), a lower tower (C01), an upper tower (C02), a main condenser evaporator (K01) and a liquid nitrogen separation tank (V01); wherein, The lower tower (C01) is connected to the main condenser evaporator (K01), the liquid nitrogen-nitrogen heat exchanger (E04), and the liquid air-liquid nitrogen subcooler (E06) through pipelines respectively; The upper tower (C02) is connected to the second liquid nitrogen subcooler (E05) and the liquid air liquid nitrogen subcooler (E06) through pipelines respectively; The liquid nitrogen separation tank (V01) is connected to the second liquid nitrogen supercooler (E05) and the liquid air liquid nitrogen supercooler (E06) through pipelines respectively.

2. The LNG cold energy air separation device for increasing liquid nitrogen production capacity according to claim 1, characterized in that: The low-pressure nitrogen compressor (NC01) is used to pressurize the low-pressure nitrogen from the upper tower (C02) of the main tower cold box, and then transport the pressurized low-pressure nitrogen to the circulating nitrogen pipeline; The circulating nitrogen compressor (NC02) is used to pressurize the nitrogen from the circulating nitrogen pipeline.

3. A method for LNG cold energy air separation based on the LNG cold energy air separation unit for improving liquid nitrogen production capacity according to claim 2, characterized in that: The LNG cold energy air separation method comprises: The LNG cold box provides the cold box of the main heat exchanger and the lower tower (C01) with cold energy generated by LNG vaporization, so as to realize liquefied cooling of air or nitrogen; The main heat exchanger cold box cools the purified air and transmits the air to the lower tower (C01); The lower tower (C01) performs distillation, purification and condensation on the cooling air from the cold box of the main heat exchanger to form liquid nitrogen; The liquid nitrogen is circulated and transmitted between the LNG cold box, the main heat exchanger cold box and the liquid nitrogen-nitrogen heat exchanger (E04), thereby transferring the cold energy of LNG vaporization and obtaining part of the liquid nitrogen product.

4. The LNG cold energy air separation method according to claim 3, characterized in that: The LNG cold energy air separation method also includes the following steps: after the purified air is cooled by a main heat exchanger (E03), it is sent to a lower tower (C01) for distillation; the lower tower (C01) separates the nitrogen into a first stream and a second stream; wherein the first stream of nitrogen enters a main condenser evaporator (K01) and is liquefied by the main condenser evaporator (K01); a portion of the liquefied nitrogen is refluxed to the lower tower (C01) as a reflux liquid; and the other portion of the liquefied nitrogen is sent to a liquid air and liquid nitrogen subcooler (E06) and is subcooled. The remaining part after being supercooled is refluxed to the upper tower (C02) as reflux liquid, and the remaining part after being supercooled is sent to the liquid nitrogen storage tank for storage as a liquid nitrogen product. The second stream of nitrogen is sent to the liquid nitrogen-nitrogen heat exchanger (E04) to be liquefied and then merged into the main condenser evaporator (K01) and then refluxed to the lower tower (C01), thereby providing cooling capacity and reflux liquid for the lower tower (C01). The oxygen-rich liquid air at the bottom of the lower tower (C01) is sent to the liquid air and liquid nitrogen supercooler (E06), and after being cooled, it is sent to the upper tower (C02) to participate in distillation; The liquid oxygen at the bottom of the upper tower (C02) is evaporated and purified by the main condenser evaporator (K01), and then transferred to the liquid air and liquid nitrogen subcooler (E06) as a liquid oxygen product for subcooling, and then transferred to the liquid oxygen storage tank of the main tower cold box for storage; the low-pressure nitrogen at the top of the upper tower (C02) is successively reheated by the liquid air and liquid nitrogen subcooler (E06) and the main heat exchanger (E03), and then transferred to the low-pressure nitrogen compressor (NC01) for pressurization, and then transferred to the circulating nitrogen channel; the contaminated nitrogen at the top of the upper tower (C02) is successively reheated by the liquid air and liquid nitrogen subcooler (E06) and the main heat exchanger (E03) as a regeneration gas.

5. The LNG cold energy air separation method according to claim 4, characterized in that: The circulating liquid nitrogen from the LNG cold box enters the liquid nitrogen separation tank (V01) after throttling, and is divided into a first stream and a second stream by the liquid phase; wherein the first stream is transmitted to the liquid nitrogen-nitrogen heat exchanger (E04), and is heat-exchanged with the nitrogen from the lower tower (C01) to be vaporized, and the vaporized first stream is merged to the top of the liquid nitrogen separation tank (V01) and enters the main heat exchanger (E03) in the form of gas phase, and then is reheated in the main heat exchanger (E03) and returns to the LNG cold box as circulating nitrogen; the second stream is subcooled by the second liquid nitrogen subcooler (E05) and is divided into a first part and a second part, the first part is transmitted to the liquid nitrogen storage tank as a liquid nitrogen product for storage, and the second part is returned to the second liquid nitrogen subcooler (E05) after throttling, and after being reheated in the second liquid nitrogen subcooler (E05), it is merged into a low-pressure nitrogen pipeline, and then transmitted to the main heat exchanger (E03) for reheating.

6. The LNG cold energy air separation method according to claim 5, characterized in that: The circulating nitrogen from the main heat exchanger cold box is transmitted to the LNG heat exchanger (E01), cooled to a predetermined temperature, and then enters the first section of the circulating nitrogen compressor (NC02) for pressurization. It then enters the LNG heat exchanger (E01) again to be cooled to a predetermined temperature, and then enters the second section of the circulating nitrogen compressor (NC02) for pressurization. It then enters the LNG heat exchanger (E01) to be cooled and liquefied, and then enters the first liquid nitrogen subcooler (E02) and is divided into the first, second and third streams. The first stream is transmitted to the main tower cold box as circulating liquid nitrogen, so that The cooling capacity is provided to the main tower cold box. The second stream meets the predetermined pressure after throttling and returns to the first liquid nitrogen supercooler (E02) and is reheated. Then, it enters the LNG heat exchanger (E01) and is reheated to a predetermined temperature, then merges with the circulating nitrogen and enters the circulating nitrogen compressor (NC02). The third stream meets another predetermined pressure after throttling and returns to the first liquid nitrogen supercooler (E02) and is reheated. Then, it enters the LNG heat exchanger (E01) and is reheated to a predetermined temperature, then merges with the circulating nitrogen and enters the circulating nitrogen compressor (NC02).

7. The LNG cold energy air separation method according to claim 6, characterized in that: After the LNG from the LNG receiving station enters the LNG heat exchanger (E01) and is reheated to a predetermined temperature by nitrogen, a portion of it is transmitted to the LNG-ethylene glycol heat exchanger to provide cooling for the ethylene glycol solution, and then is reheated by the LNG-ethylene glycol heat exchanger and returned to the LNG receiving station. The remaining portion is further reheated by the LNG heat exchanger (E01) to a predetermined temperature and then directly returned to the LNG receiving station.

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