System for extracting helium from natural gas by cryogenic separation method

Abstract

The utility model relates to the technical field of cryogenic helium extraction, and provides a cryogenic separation method natural gas helium extraction system which comprises a main heat exchanger and a concentration tower, the concentration tower comprises a reboiler arranged at the bottom of the concentration tower and a condenser arranged at the top of the concentration tower, and a liquid phase outlet at the bottom of the concentration tower is throttled and divided into two paths with different pressures; the cooling capacity of backflow liquid at the bottom of the concentration tower is fully utilized, cooling capacity balance is achieved, and energy consumption is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of deep-cold helium extraction, in particular to a natural gas helium extraction system using a deep-cold separation method. Background Art

[0002] At normal temperature and pressure, helium is a colorless, odorless, non-toxic inert gas with very stable chemical properties. Due to its low boiling point and high thermal conductivity, helium is widely used in low-temperature experiments, superconducting magnets, balloons, and gas shielded welding. The content of helium in the air is extremely small and it mainly exists in natural gas. Extracting helium from natural gas is the main industrial source of helium.

[0003] At present, the main natural gas helium extraction processes include cryogenic separation, membrane separation and pressure swing adsorption. Among them, cryogenic separation is the most commonly used. Its principle is to utilize the different boiling points of natural gas components, cool and condense the natural gas, and obtain crude helium through low-temperature distillation. However, the existing technology still has problems such as large equipment investment, high cost, high energy consumption and difficulty in balancing cold capacity. Utility Model Content

[0004] The utility model aims to provide a natural gas helium extraction system using a deep cold separation method, so as to solve the above technical problems, achieve cold capacity balance and reduce energy consumption.

[0005] The embodiment of the utility model is realized by the following technical scheme: a natural gas helium extraction system by deep cold separation method, comprising a main heat exchanger and a concentration tower, the concentration tower comprising a reboiler built in the bottom of the concentration tower and a condenser built in the top of the concentration tower, the inlet end of the precooling section of the main heat exchanger is connected with raw natural gas, the raw natural gas is connected to the reboiler after being precooled by the main heat exchanger, the reboiler is connected to the inlet end of the cooling section of the main heat exchanger, the outlet end of the cooling section of the main heat exchanger is connected to the middle of the concentration tower, the gas phase outlet of the upper part of the concentration tower is connected to the condenser, the condenser is connected to a reflux tank, the gas phase outlet of the reflux tank is connected to the main heat exchanger, the liquid phase outlet of the reflux tank is connected to the upper part of the concentration body, the liquid phase outlet at the bottom of the concentration tower is throttled into two paths with different pressures, and both are connected to the main heat exchanger, and the main heat exchanger is connected to a cold circulation unit that provides cold for the condenser.

[0006] Furthermore, the two routes divided by the liquid phase outlet at the bottom of the concentration tower are both connected with double regulating valves, and the pressures of the two routes are 1.5MPa~1.6MPa and 0.3MPa~0.4MPa respectively.

[0007] Furthermore, the reboiler is an immersed plate-fin heat exchanger, and the condenser is internally immersed in a liquid nitrogen tank.

[0008] Preferably, the reboiler is connected to a bypass line regulating valve, and the liquid nitrogen tank is connected to a nitrogen throttle valve.

[0009] The utility model has at least the following advantages and beneficial effects: by adopting the main heat exchanger, the concentration tower and the reboiler and condenser built in the concentration tower, the cold capacity of the reflux liquid at the bottom of the concentration tower is fully utilized to achieve cold capacity balance and reduce energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the utility model and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying creative work.

[0011] Figure 1 A schematic diagram of a natural gas helium extraction system using a cryogenic separation method provided by the utility model;

[0012] Icons: 1-main heat exchanger, 2-concentration tower, 21-reboiler, 22-condenser, 3-raw natural gas, 4-reflux tank, 5-cold circulation unit, 6-double regulating valve, 7-liquid nitrogen tank, 8-bypass pipeline regulating valve, 9-nitrogen throttle valve. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical scheme and advantages of the embodiments of the utility model clearer, the technical scheme in the embodiments of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiments of the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Generally, the components of the embodiments of the utility model described and shown in the drawings here can be arranged and designed in various different configurations.

[0014] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the present invention to be protected, but merely represents selected embodiments of the present invention. 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.

[0015] Example

[0016] like Figure 1As shown, in this embodiment, a natural gas helium extraction system using a cryogenic separation method is mainly disclosed. The system process is simple, the equipment investment is small, the operation is stable, and the cooling capacity is easy to balance. The system mainly includes a main heat exchanger 1 and a concentration tower 2. The concentration tower 2 includes a reboiler 21 and a condenser 22. The reboiler 21 is built in the bottom of the concentration tower 2 and can be an immersed plate-fin heat exchanger, which is immersed in the saturated liquid of the mixture at the bottom of the concentration tower 2, and the helium content in the liquid is controlled to be ≤5ppm. The condenser 22 is built in the top of the concentration tower 2 and immersed in the liquid nitrogen tank 7.

[0017] The inlet end of the precooling section of the main heat exchanger 1 is connected to the raw natural gas 3 with a pressure of 2.2MPa to 2.5MPa. The required pressure of the raw natural gas 3 is relatively small, which can effectively reduce energy consumption. The raw natural gas 3 is first purified, dehydrated, deacidified, etc. at the front end, and then enters the main heat exchanger 1 to cool down and precool to -101℃ to -104℃, and then enters the reboiler 21 to act as a heat source. Since the boiling point of helium is -268.9℃ under normal circumstances, the evaporable gas in the saturated liquid at the bottom of the concentration tower 2, such as helium, evaporates and rises due to heat. The reboiler 21 is connected to the main heat exchanger 1. The raw natural gas 3 after heat dissipation returns to the main heat exchanger 1 through the inlet of the cooling section of the main heat exchanger 1 to continue to be supercooled to -142℃~-148℃. The outlet of the cooling section of the main heat exchanger 1 is connected to the middle of the concentration tower 2. The supercooled raw natural gas 3 is throttled by the regulating valve so that its pressure is controlled to 1.8MPa~2.0MPa, and enters the middle of the concentration tower 2 to spray and fall to contact with the rising gas for mass transfer and heat transfer, completing low-temperature distillation separation. The upper gas phase outlet of the concentration tower 2 is connected to the condenser 22, so that the evaporated rising gas is collected into The main heat exchanger 1 is connected to a cold circulation unit 5, which is connected to a liquid nitrogen tank 7 outside the condenser 22 through a pipeline to provide cold for the condenser 22, and the condensation temperature is controlled to be ≤-180°C. The condenser 22 is connected to a reflux tank 4, and the obtained crude helium gas is distributed in the upper part of the reflux tank 4. The gas phase outlet of the reflux tank 4 is connected to the main heat exchanger 1, so that the crude helium gas enters the main heat exchanger 1 for cold recovery and reheating, and then enters the subsequent crude helium refining unit. The mixed liquid is collected at the lower part of the reflux tank 4, and the liquid phase outlet of the reflux tank 4 is connected to the upper part of the concentration tower 2, so that The mixed liquid flows back into the concentration tower 2 for further separation. It should be noted that the separation pressure (1.8MPa-2.0MPa) of the concentration tower 2 is slightly higher than the separation pressure (1.1MPa-1.5MPa) of the conventional concentration tower 2, and the temperature is controlled to be relatively low (≤-180°C). The difference in boiling points of natural gas under different pressures is used to separate and purify helium, so that the unit energy consumption of the separated product is reduced, the crude helium concentration is high, and the helium recovery rate is high. The crude helium concentration obtained by the system can reach 80%-85%, and the helium recovery rate is ≥98%.

[0018] The throttling of the liquid phase outlet at the bottom of the concentration tower 2 is divided into two paths with different pressures, and both are connected to the main heat exchanger 1. Since the bottom of the concentration tower 2 is a high-pressure saturated liquid, the pressure suddenly drops after the high-pressure saturated liquid enters the relatively low-pressure channel through throttling, and flash evaporation will occur. Heat absorption and cooling provide cooling for the main heat exchanger 1, efficiently utilize cooling energy, and obtain cooling balance. After cooling energy is recovered, the separated liquid natural gas can be pressurized and exported to the natural gas pipeline network.

[0019] Furthermore, in the specific implementation, the two routes divided by the liquid phase outlet at the bottom of the above-mentioned concentration tower 2 provided in the embodiment of the utility model are both connected with a double regulating valve 6 to achieve throttling effect, and the pressures of the two routes are 1.5MPa~1.6MPa and 0.3MPa~0.4MPa respectively. The flow and pressure of the two routes can be adjusted in real time according to changes in operating conditions to obtain an overall cooling balance.

[0020] Furthermore, in a specific implementation, the above-mentioned reboiler 21 provided in the embodiment of the utility model is connected with a bypass pipeline regulating valve 8, and the bottom heat source of the concentration tower 2 can be bidirectionally controlled by adjusting the bypass pipeline regulating valve 8 and the liquid immersion height of the lower part of the concentration tower 2; the liquid nitrogen tank 7 is connected with a nitrogen throttle valve 9, and the top cold source of the concentration tower 2 can be bidirectionally controlled by adjusting the nitrogen throttle valve 9 and the liquid nitrogen immersion height of the liquid nitrogen tank 7, which is convenient for starting and adjusting the variable component working conditions, easy to operate, and ensures the stability of the system operation.

[0021] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A natural gas helium extraction system using a cryogenic separation method, characterized in that: It comprises a main heat exchanger and a concentration tower, wherein the concentration tower comprises a reboiler built into the bottom of the concentration tower and a condenser built into the top of the concentration tower; The inlet end of the precooling section of the main heat exchanger (1) is connected to the raw natural gas (3), the raw natural gas (3) is connected to the reboiler (21) after being precooled by the main heat exchanger (1), the reboiler (21) is connected to the inlet end of the cooling section of the main heat exchanger (1), and the outlet end of the cooling section of the main heat exchanger (1) is connected to the middle of the concentration tower (2); The gas phase outlet at the upper part of the concentration tower (2) is connected to the condenser (22), the condenser (22) is connected to a reflux tank (4), the gas phase outlet of the reflux tank (4) is connected to the main heat exchanger (1), and the liquid phase outlet of the reflux tank (4) is connected to the upper part of the concentration tower (2); The liquid phase outlet at the bottom of the concentration tower (2) is throttled into two paths with different pressures, and both are connected to the main heat exchanger (1); The main heat exchanger (1) is connected to a cold circulation unit (5) for providing cold air to the condenser (22).

2. A natural gas helium extraction system using a cryogenic separation method as claimed in claim 1, characterized in that: The two routes divided by the liquid phase outlet at the bottom of the concentration tower (2) are both connected to a double regulating valve (6), and the pressures of the two routes are 1.5MPa-1.6MPa and 0.3MPa-0.4MPa respectively.

3. A natural gas helium extraction system using a cryogenic separation method as claimed in claim 1, characterized in that: The reboiler (21) is an immersed plate-fin heat exchanger, and the condenser (22) is internally immersed in a liquid nitrogen tank (7).

4. A natural gas helium extraction system using a cryogenic separation method as claimed in claim 3, characterized in that: The reboiler (21) is connected to a bypass pipeline regulating valve (8), and the liquid nitrogen tank (7) is connected to a nitrogen throttle valve (9).

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