LNG (Liquefied Natural Gas) flash steam helium recovery system

Abstract

The utility model relates to the technical field of gas separation, in particular to an LNG flash steam helium recovery system which comprises a compressor, and a dehydrogenation drying system, a roughing system and a low-temperature system which are connected with one another are connected to the compressor. The dehydrogenation drying system comprises a dehydrogenation heat regenerator connected with a compressor, the dehydrogenation heat regenerator is connected with a dehydrogenation electric heater, a dehydrogenation reactor and a dehydrogenation post-cooling separator, and the dehydrogenation electric heater is communicated with an oxygen inlet pipeline for supplying oxygen and then is connected with the dehydrogenation reactor; the after-dehydrogenation cooling separator is connected with the roughing system through a dryer; the utility model has the characteristics of advanced process, mature technology, reliable operation, convenience in operation, low energy consumption, good safety, easiness in control, strong adaptability and economic and reasonable unit configuration.

Description

Technical Field

[0001] The utility model relates to the technical field of gas separation, in particular to an LNG flash vapor helium recovery system. Background Art

[0002] Helium is widely used in aerospace, cutting-edge infrastructure for large scientific projects, medical nuclear magnetic resonance imaging, semiconductors / optical fibers and other high-end equipment manufacturing fields due to its unique physical and chemical properties such as low density, low boiling point, good thermal conductivity and stable chemical properties.

[0003] Currently, there are four main methods for extracting helium from helium-containing natural gas, namely cryogenic separation, membrane separation, pressure swing adsorption, and hydrate method. However, the existing helium extraction process has problems such as complex procedures, high energy consumption, low economic efficiency, and low raw gas utilization rate.

[0004] This device obtains hydrogen-containing crude helium through cryogenic distillation, dehydrogenates it through catalytic reaction with oxygen addition, and removes water generated by the catalytic dehydrogenation through molecular sieve adsorption to obtain dry crude helium. The dry crude helium is subjected to high-pressure and low-temperature condensation, low-temperature adsorption, and ultra-low-temperature removal of impurities such as nitrogen and neon to obtain high-purity helium products.

[0005] This device has the characteristics of advanced process, mature technology, reliable operation, convenient operation, low energy consumption, good safety, easy control, strong adaptability and economical and reasonable unit configuration. Utility Model Content

[0006] In order to solve the above problems, the utility model provides an LNG flash vapor helium recovery system with reliable operation, convenient operation, low energy consumption, good safety, easy control and strong adaptability.

[0007] The utility model discloses an LNG flash vapor helium recovery system, comprising a compressor, to which a dehydrogenation drying system, a crude system, and a cryogenic system are connected;

[0008] The dehydrogenation drying system includes a dehydrogenation regenerator connected to a compressor, the dehydrogenation regenerator is connected to a dehydrogenation electric heater, a dehydrogenation reactor and a post-dehydrogenation cooling separator, the dehydrogenation electric heater is connected to an oxygen inlet pipeline for oxygen supply and then connected to the dehydrogenation reactor;

[0009] The post-dehydrogenation cooling separator is connected to the crude system via a dryer;

[0010] The crude system includes a cold box main heat exchanger connected to the dryer, the cold box main heat exchanger is connected to a first-stage separator, the first-stage separator is provided with a first liquid phase outlet and a first gas phase outlet, the first gas phase outlet is connected to a second-stage separator through a crude helium condenser, the second-stage separator is provided with a second liquid phase outlet and a second gas phase outlet, the second gas phase outlet is connected to a third-stage separator through a normal pressure liquid nitrogen condenser, the third-stage separator is provided with a third liquid phase outlet and a third gas phase outlet, the third gas phase outlet is connected to a fourth-stage separator through a negative pressure liquid nitrogen condenser, the fourth-stage separator is provided with a fourth liquid phase outlet and a fourth gas phase outlet, and the fourth gas phase outlet is connected to the low-temperature system;

[0011] The first liquid phase outlet is connected to a high-pressure flash tank via a throttle valve, the high-pressure flash tank is connected to a low-pressure flash tank via a pressure control valve, and the high-pressure flash tank is also connected to the cold box main heat exchanger via a reflux pipe;

[0012] The second liquid phase outlet, the third liquid phase outlet and the fourth liquid phase outlet are respectively connected to the low-pressure flash tank through liquid level control valves;

[0013] The cold box main heat exchanger is connected to the dryer;

[0014] The low temperature system includes a connected low temperature adsorption dewar and an ultra-low temperature cold box. The low temperature adsorption dewar is connected to the fourth gas phase outlet, and the ultra-low temperature cold box is directly connected to a helium storage tank.

[0015] Preferably, two dryers are provided, namely an adsorption dryer and a regeneration dryer, the inlets of the adsorption dryer and the regeneration dryer are respectively connected to the post-dehydrogenation cooling separator through switching valves, and the outlets of the adsorption dryer and the regeneration dryer are respectively connected to the main heat exchanger through switching valves;

[0016] The adsorption dryer and the regeneration dryer are respectively connected to a regeneration gas electric heater and a regeneration gas cooler through valves, and the regeneration gas electric heater is connected to a regeneration gas supply pipeline;

[0017] The regeneration gas cooler is connected to a regeneration gas-water separator.

[0018] Preferably, a shut-off valve interlocked with the temperature inside the dehydrogenation reactor is provided at the inlet of the dehydrogenation reactor.

[0019] Preferably, an analyzer for analyzing the hydrogen, helium and nitrogen contents in the intake air is provided between the compressor and the dehydrogenation regenerator;

[0020] A device for analyzing the content of hydrogen, water and oxygen in the crude helium after dehydrogenation is also provided between the dryer and the cold box main heat exchanger.

[0021] Preferably, a fuel gas compressor is further connected to the cold box main heat exchanger, and the fuel gas compressor is connected to the regeneration gas supply pipeline.

[0022] Preferably, the hydrogen content in the gas entering the cold box main heat exchanger is ≤1 ppm, and the water content is ≤1 ppm.

[0023] The utility model utilizes a dehydrogenation drying system to reduce hydrogen content, so the reaction temperature is low and easier to control. The temperature of the catalytic reaction is controlled during operation to avoid methane reaction to generate CO2. Even if a trace amount of CO2 is generated, the content will not cause freezing and blocking of the cold box.

[0024] The utility model is provided with two dryers, and a molecular sieve is provided in the dryer. The molecular sieve adopts 13X, which can absorb part of CO2. The regenerated gas comes from the outlet of the fuel gas compressor, and the regenerated gas is removed from the fuel gas of the original device to avoid the circulation and accumulation of CO2 in the utility model.

[0025] The utility model adopts low-temperature condensation separation to return the helium directly to the BOG pipeline coming out of the LNG storage tank for recovery. In addition, the condensate separated at -190℃ and -205℃ is recovered to reduce the loss of helium. Multiple condensation separations are performed to achieve helium recovery.

[0026] The utility model utilizes a primary separator, a secondary separator, a tertiary separator and a quaternary separator to be sequentially connected to the main heat exchanger of the cold box to realize multi-stage condensation and extraction of crude helium. The cold source comes from liquid nitrogen instead of a nitrogen compressor (, thus eliminating multiple diaphragm compressors and significantly reducing power consumption).

[0027] The utility model obtains dry raw gas through a dehydrogenation drying system, obtains hydrogen-containing crude helium gas through rectification in a crude system, and obtains high-purity helium product through high-pressure and low-temperature condensation, low-temperature adsorption and ultra-low-temperature removal of impurities such as nitrogen and neon in a low-temperature system.

[0028] The utility model has the characteristics of advanced process, mature technology, reliable operation, convenient operation, low energy consumption, good safety, easy control, strong adaptability and economical and reasonable unit configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the utility model system. DETAILED DESCRIPTION

[0030] The utility model discloses an LNG flash vapor helium recovery system, comprising a compressor, to which a dehydrogenation drying system, a crude system, and a cryogenic system are connected;

[0031] The dehydrogenation drying system includes a dehydrogenation regenerator connected to a compressor, the dehydrogenation regenerator is connected to a dehydrogenation electric heater, a dehydrogenation reactor and a post-dehydrogenation cooling separator, the dehydrogenation electric heater is connected to an oxygen inlet pipeline for oxygen supply and then connected to the dehydrogenation reactor;

[0032] The post-dehydrogenation cooling separator is connected to the crude system via a dryer;

[0033] The crude system includes a cold box main heat exchanger connected to the dryer, the cold box main heat exchanger is connected to a first-stage separator, the first-stage separator is provided with a first liquid phase outlet and a first gas phase outlet, the first gas phase outlet is connected to a second-stage separator through a crude helium condenser, the second-stage separator is provided with a second liquid phase outlet and a second gas phase outlet, the second gas phase outlet is connected to a third-stage separator through a normal pressure liquid nitrogen condenser, the third-stage separator is provided with a third liquid phase outlet and a third gas phase outlet, the third gas phase outlet is connected to a fourth-stage separator through a negative pressure liquid nitrogen condenser, the fourth-stage separator is provided with a fourth liquid phase outlet and a fourth gas phase outlet, and the fourth gas phase outlet is connected to the low-temperature system;

[0034] The first liquid phase outlet is connected to a high-pressure flash tank via a throttle valve, the high-pressure flash tank is connected to a low-pressure flash tank via a pressure control valve, and the high-pressure flash tank is also connected to the cold box main heat exchanger via a reflux pipe;

[0035] The second liquid phase outlet, the third liquid phase outlet and the fourth liquid phase outlet are respectively connected to the low-pressure flash tank through liquid level control valves;

[0036] The cold box main heat exchanger is connected to the dryer;

[0037] The low temperature system includes a connected low temperature adsorption dewar and an ultra-low temperature cold box. The low temperature adsorption dewar is connected to the fourth gas phase outlet, and the ultra-low temperature cold box is connected to a helium storage tank.

[0038] Two dryers are provided, namely an adsorption dryer and a regeneration dryer. The inlets of the adsorption dryer and the regeneration dryer are respectively connected to the post-dehydrogenation cooling separator through switching valves, and the outlets of the adsorption dryer and the regeneration dryer are respectively connected to the main heat exchanger through switching valves;

[0039] The adsorption dryer and the regeneration dryer are respectively connected to a regeneration gas electric heater and a regeneration gas cooler through valves, and the regeneration gas electric heater is connected to a regeneration gas supply pipeline;

[0040] The regeneration gas cooler is connected to a regeneration gas-water separator.

[0041] A shut-off valve interlocked with the temperature inside the dehydrogenation reactor is provided at the inlet of the dehydrogenation reactor.

[0042] An analyzer for analyzing the hydrogen, helium and nitrogen content in the intake air is provided between the compressor and the dehydrogenation regenerator;

[0043] A device is also provided between the dryer and the cold box main heat exchanger to analyze the contents of hydrogen, water and oxygen in the crude helium after dehydrogenation.

[0044] The cold box main heat exchanger is also connected to a fuel gas compressor, which is communicated with a regeneration gas supply pipeline.

[0045] The hydrogen content in the gas entering the cold box main heat exchanger is ≤1ppm, and the water content is ≤1ppm.

[0046] When in use, the BOG compressed to 2.0MPa from the LNG device is measured (1500Nm 3 / h) enters the dehydrogenation and drying system. The dehydrogenation and drying system removes hydrogen from the feed gas through a catalytic reaction with oxygen. The water generated by the dehydrogenation reaction is cooled to remove some free water, and then adsorbed to remove trace water from the feed gas. After the feed gas passes through the dehydrogenation and drying system, the hydrogen content is ≤1ppm, and the water content is ≤1ppm.

[0047] The BOG after dehydrogenation and drying enters the main heat exchanger of the cold box for condensation and then enters the first-stage separator. The separated gas phase enters the crude helium condenser and then the second-stage separator. The separated gas phase enters the atmospheric pressure liquid nitrogen condenser for condensation and then enters the third-stage separator. The separated gas phase enters the negative pressure liquid nitrogen condenser for condensation and then enters the fourth-stage separator. The separated gas phase crude helium enters the subsequent low-temperature system to remove the remaining impurities.

[0048] The cryogenic system removes nitrogen impurities from crude helium through cryogenic adsorption. The denitrified helium then enters an ultra-low-temperature system to remove neon impurities. Two cryogenic adsorption dewars are installed, switched between them, and ultra-low-temperature adsorption is used in conjunction with cryogenic adsorption. Crude helium from the crude system enters the cryogenic adsorption dewar. During the initial adsorption cycle, all trace impurities are removed, resulting in low-temperature, high-purity helium. This low-temperature, high-purity helium then returns to the ultra-low-temperature cold box through the helium bypass valve, where it is reheated to room temperature before entering the storage and filling system. During the final adsorption cycle, the neon impurities and helium exit the cryogenic adsorber and enter the ultra-low-temperature cold box. After the neon impurities are removed, the helium returns to the cold box, where it is reheated to room temperature before entering the storage and filling system.

[0049] The overall process flow of this utility model is as follows: the raw BOG gas is pressurized by a BOG compressor and then enters the dehydrogenation and drying system. Hydrogen is removed from the BOG through catalytic oxygenation. Water produced by the reaction is then removed through adsorption. The dried gas then enters the crude helium system, where it undergoes cryogenic distillation to produce crude helium. The crude helium then enters the cryogenic system, where impurities such as oxygen, nitrogen, and neon are removed to produce high-purity helium, which is then delivered to a helium storage tank. The technology also produces two products of varying specifications: BOG gas returned from the crude unit. A portion of this gas is returned to the original liquefaction station's fuel gas system, while a portion, containing a high helium content, is returned to the original liquefaction unit for re-liquefaction.

[0050] BOG from the liquefaction unit is pressurized by the BOG compressor, then heated to approximately 110°C in the dehydrogenation regenerator and dehydrogenation electric heater. After mixing with oxygen from the oxygen regenerator, it enters the dehydrogenation reactor to remove hydrogen and oxygen from the feed gas. The high-temperature gas after the reaction enters the dehydrogenation regenerator to recover some heat while being cooled. After cooling in the dehydrogenation post-cooler, it enters the dehydrogenation post-water separator to separate free water. It then enters two dryers that are switched for dehydration before entering the crude system to further remove methane and most of the nitrogen.

[0051] Two dryers are used alternately, with pressure reduction and regeneration. The adsorption cycle is 8 hours, with one dryer performing adsorption while the other performs regeneration and cold purge. The regeneration gas comes from the BOG compressed by the crude helium system's fuel gas compressor. The regeneration gas is heated in an electric regeneration heater before being sent to the dryer for regeneration. After removing moisture from the dryer, it is cooled in a regeneration gas cooler and then sent to a regeneration gas water separator. After free water is separated, it exits the boundary area and is sent to the fuel gas system of the liquefaction unit. When dryer regeneration is complete and cold purge begins, the electric heater is turned off. A shut-off valve is installed at the inlet of the dehydrogenation reactor, interlocked with the reactor's temperature. The dehydrogenation reactor is also equipped with a bursting disc. Analyzers are used to analyze hydrogen, helium, and nitrogen in the crude helium before dehydrogenation, and to analyze H2, H2O, and oxygen after dehydrogenation.

[0052] After dehydrogenation and drying, the BOG enters the main heat exchanger of the cold box for condensation and then enters the first-stage separator. The separated gas phase enters the crude helium condenser and then the second-stage separator. The separated gas phase enters the atmospheric pressure liquid nitrogen condenser for condensation and then enters the third-stage separator. The separated gas phase enters the negative pressure liquid nitrogen condenser for condensation and then enters the fourth-stage separator. The separated gas phase crude helium enters the subsequent low-temperature system to remove the remaining impurities.

[0053] Separator liquid phase flow path: the liquid phase separated by the first-stage separator enters the high-pressure flash tank after throttling, and the flashed gas phase is collected into the low-pressure flash tank through the pressure control valve; part of the liquid phase returns to the main heat exchanger, and returns to the liquefaction device after reheating, and the other part goes to the low-pressure flash tank after throttling. The flashed gas phase returns to the main heat exchanger for reheating and then returns to the liquefaction device. After the liquid phase returns to the main heat exchanger for reheating, it is pressurized by the fuel gas compressor and sent to the dehydrogenation drying system as the regeneration gas for the dryer. The low-pressure flash tank is equipped with a liquid level control valve and a pressure control valve to control its liquid level and temperature.

[0054] The liquid phases separated by the secondary separator, tertiary separator and quaternary separator are throttled by the liquid level control valve and then collected and returned to the low-pressure flash tank.

[0055] Nitrogen flow path: The liquid nitrogen from the liquid nitrogen storage tank is divided into three streams: the first stream of liquid nitrogen enters the crude helium condenser after throttling, and then enters the main heat exchanger to provide cooling capacity after vaporization, and is then discharged on site; the second stream of liquid nitrogen enters the atmospheric pressure liquid nitrogen condenser after throttling, and the vaporized nitrogen enters the crude helium condenser, provides part of the cooling capacity, and then merges with the vaporized nitrogen of the first stream of liquid nitrogen into the main heat exchanger, and is discharged on site after returning to room temperature; the third stream of liquid nitrogen enters the negative pressure liquid nitrogen condenser after throttling, and the negative pressure is achieved by continuous vacuum pumping of the nitrogen vacuum pump. The evaporated nitrogen in the negative pressure liquid nitrogen condenser exits the cold box, is heated to room temperature by the negative pressure nitrogen reheater and the negative pressure nitrogen electric heater, and then enters the nitrogen vacuum pump and is discharged on site.

[0056] Helium flow path: The helium coming from the ultra-low temperature cold box enters the main heat exchanger for reheating and then exits the cold box. After exiting the cold box, one stream of helium goes to the low-temperature Dewar as regeneration gas for Dewar regeneration, and the other stream is equipped with an online chromatograph. If the helium purity is qualified, it enters the storage and filling system. If the helium purity is unqualified, it returns to the liquefaction device as recycled gas.

[0057] The cryogenic system removes nitrogen impurities from crude helium through cryogenic adsorption. The denitrified helium then enters an ultra-low-temperature system to remove neon impurities. Two cryogenic adsorption dewars are used alternately. The brief process is as follows: Crude helium from the crude system enters the cryogenic adsorption dewar. During the initial adsorption cycle, all trace impurities are removed, resulting in cryogenic, high-purity helium. This low-purity helium then returns to the ultra-low-temperature cold box through the helium bypass valve, where it is reheated to ambient temperature before entering the storage and filling system. During the final adsorption cycle, neon impurities and helium exit the cryogenic adsorber and enter the ultra-low-temperature cold box. After neon impurities are removed in the ultra-low-temperature cold box, the helium returns to the cold box, where it is reheated to ambient temperature before entering the storage and filling system. Two low-temperature adsorption Dewars are switched for use. Low-temperature adsorption regeneration adopts decompression and heating regeneration. The regeneration heat is provided by the regeneration electric heater. The cooling capacity in the regeneration cooling process and the low-temperature adsorption process is provided by liquid nitrogen. The regeneration of ultra-low temperature adsorption is completed in the early stage of the low-temperature adsorption cycle. Ultra-low temperature adsorption regeneration adopts decompression and heating regeneration. The regeneration heat is provided by the ultra-low temperature regeneration electric heater and room temperature helium. The cooling capacity in the regeneration cooling process is provided by liquid nitrogen and GM refrigerator. The cooling capacity in the ultra-low temperature adsorption process is provided by GM refrigerator.

Claims

1. An LNG flash gas helium recovery system, comprising a compressor, to which are connected a dehydrogenation drying system, a crude system, and a cryogenic system; It is characterized by: The dehydrogenation drying system includes a dehydrogenation regenerator connected to a compressor, the dehydrogenation regenerator is connected to a dehydrogenation electric heater, a dehydrogenation reactor and a post-dehydrogenation cooling separator, the dehydrogenation electric heater is connected to an oxygen inlet pipeline for oxygen supply and then connected to the dehydrogenation reactor; The post-dehydrogenation cooling separator is connected to the crude system via a dryer; The crude system includes a cold box main heat exchanger connected to the dryer, the cold box main heat exchanger is connected to a first-stage separator, the first-stage separator is provided with a first liquid phase outlet and a first gas phase outlet, the first gas phase outlet is connected to a second-stage separator through a crude helium condenser, the second-stage separator is provided with a second liquid phase outlet and a second gas phase outlet, the second gas phase outlet is connected to a third-stage separator through a normal pressure liquid nitrogen condenser, the third-stage separator is provided with a third liquid phase outlet and a third gas phase outlet, the third gas phase outlet is connected to a fourth-stage separator through a negative pressure liquid nitrogen condenser, the fourth-stage separator is provided with a fourth liquid phase outlet and a fourth gas phase outlet, and the fourth gas phase outlet is connected to the low-temperature system; The first liquid phase outlet is connected to a high-pressure flash tank via a throttle valve, the high-pressure flash tank is connected to a low-pressure flash tank via a pressure control valve, and the high-pressure flash tank is also connected to the cold box main heat exchanger via a reflux pipe; The second liquid phase outlet, the third liquid phase outlet and the fourth liquid phase outlet are respectively connected to the low-pressure flash tank through liquid level control valves; The cold box main heat exchanger is connected to the dryer; The low temperature system includes a connected low temperature adsorption dewar and an ultra-low temperature cold box. The low temperature adsorption dewar is connected to the fourth gas phase outlet, and the ultra-low temperature cold box is connected to a helium storage tank.

2. The LNG flash gas helium recovery system according to claim 1, characterized in that: The dryers are provided in two units, namely an adsorption dryer and a regeneration dryer. The inlets of the adsorption dryer and the regeneration dryer are respectively connected to the post-dehydrogenation cooling separator via switching valves, and the outlets of the adsorption dryer and the regeneration dryer are respectively connected to the main heat exchanger via switching valves. The adsorption dryer and the regeneration dryer are respectively connected to a regeneration gas electric heater and a regeneration gas cooler through valves, and the regeneration gas electric heater is connected to a regeneration gas supply pipeline; The regeneration gas cooler is connected to a regeneration gas-water separator.

3. The LNG flash gas helium recovery system according to claim 2, characterized in that: A shut-off valve interlocked with the temperature inside the dehydrogenation reactor is provided at the inlet of the dehydrogenation reactor.

4. The LNG flash gas helium recovery system according to claim 1, characterized in that: An analyzer for analyzing the hydrogen, helium and nitrogen contents in the intake air is provided between the compressor and the dehydrogenation regenerator; A device is also provided between the dryer and the cold box main heat exchanger to analyze the contents of hydrogen, water and oxygen in the crude helium after dehydrogenation.

5. The LNG flash gas helium recovery system according to claim 1, characterized in that: The cold box main heat exchanger is also connected to a fuel gas compressor, and the fuel gas compressor is connected to the regeneration gas supply pipeline.

6. The LNG flash gas helium recovery system according to claim 1, characterized in that: The hydrogen content in the gas entering the cold box main heat exchanger is ≤1ppm, and the water content is ≤1ppm.

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