Oil-free gas liquefaction system with closed cooling system and liquefaction method of oil-free gas liquefaction system

Abstract

The invention discloses an oil-free gas liquefaction system with a closed cooling system and a liquefaction method of the oil-free gas liquefaction system. The oil-free gas liquefaction system comprises a compression system, a gas source system, a pre-cooling system, a re-liquefaction system and a liquid storage system, the compression system comprises a first compressor, a buffer tank, a high-pressure unloading valve, a high-pressure loading valve and a low-pressure control valve, and is used for adjusting the pressure of a refrigerant and providing a pre-cooling stage air source; the gas source system comprises a pressure reducing valve, a regulating valve, a flow meter and a gas pretreatment unit.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of low-temperature refrigeration, more specifically, relates to an oil-free gas liquefaction system with a closed cooling system and a liquefaction method thereof. BACKGROUND

[0002] China is promoting the transformation of the energy system to clean and low-carbon. Hydrogen energy, as a clean energy, requires efficient storage and transportation of liquid hydrogen (the density of liquid hydrogen is about 800 times that of gaseous hydrogen, which can significantly reduce storage and transportation costs) for its large-scale application. However, current domestic liquid hydrogen production relies on imported equipment.

[0003] In traditional hydrogen-helium liquefaction systems, the pre-cooling stage usually uses a liquid nitrogen open system (such as a 5-ton / day hydrogen liquefier consuming about 2000 liters of liquid nitrogen per hour), but the transportation cost of liquid nitrogen in remote areas is high, and the installation of large-capacity storage tanks is limited, which becomes a key problem restricting the self-development of liquid hydrogen. Therefore, it is urgent to develop a closed pre-cooling system that does not require liquid nitrogen consumption, has a compact structure, and is safe. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides an oil-free gas liquefaction system with a closed cooling system and a liquefaction method thereof to solve the problems raised in the background art.

[0005] To achieve the above purpose, the present application is implemented by the following technical scheme: an oil-free gas liquefaction system with a closed cooling system, comprising a compression system, a gas source system, a pre-cooling system, a reliquefaction system, and a liquid storage system; The compression system includes a first compressor, a buffer tank, a high-pressure unloading valve, a high-pressure loading valve, and a low-pressure control valve for adjusting the refrigerant pressure and providing a pre-cooling stage gas source; The gas source system includes a pressure reducing valve, a regulating valve, a flowmeter, and a gas pretreatment unit to provide stable gas to be liquefied for the entire liquefaction system; The pre-cooling system includes a compression-expansion integrated machine, which integrates a second compressor, an expander, a motor, a cooler, and a second heat exchanger. The second compressor and the expander are driven by the motor to operate coaxially. The compressed gas is expanded by the expander to generate cold energy after being cooled; The reliquefaction system includes a third heat exchanger, a fourth heat exchanger, a fifth heat exchanger, a main adsorber, a first adsorber, a second adsorber, a turbo expander, and a throttle valve for gradually cooling the pre-cooled gas to a liquid phase; The second heat exchanger, the third heat exchanger, the fourth heat exchanger, and the fifth heat exchanger form a multi-stage heat exchanger; The liquid storage system includes a storage tank for storing liquefied gas.

[0006] Preferably, the first adsorber and the second adsorber of the reliquefaction system are in parallel one-for-one structure and are respectively controlled by a first switch valve and a second switch valve to control the gas passage.

[0007] Preferably, the multi-stage heat exchanger of the precooling system works with the heat exchanger of the compression system to recover the cold energy of the refrigerant.

[0008] Preferably, the compression-expansion integrated machine is connected in series with the second compressor, the expander and the motor through a single main shaft to realize integrated operation of compression and expansion.

[0009] Preferably, the precooling system is a closed cycle without liquid nitrogen consumption, and the compression-expansion integrated machine is a centrifugal oil-free design.

[0010] Preferably, the first compressor of the compression system adopts magnetic suspension or dry sealing technology to avoid lubricating oil pollution of the refrigerant.

[0011] The application provides an oil-free gas liquefaction method with a closed cooling system, comprising the following steps: Precooling step: the refrigerant is pressurized by the first compressor and is compressed-cooled-expanded by the compression-expansion integrated machine of the precooling system to generate cold energy; Liquefaction step: the gas source gas is pre-cooled, impurity-removed by the main adsorber, gradually cooled by the multi-stage heat exchanger and finally liquefied by the throttling valve; Circulation step: the refrigerant is recycled by the closed loop to maintain continuous operation of the system.

[0012] Preferably, in the precooling step, the outlet temperature of the expander is-120℃ to-180℃.

[0013] Preferably, in the liquefaction step, after the gas is impurity-removed by the main adsorber, the gas is filled with positive-secondary hydrogen catalytic conversion agent by the multi-stage heat exchanger to ensure that the content of secondary hydrogen in the liquid hydrogen is greater than or equal to 95%.

[0014] The application provides an oil-free gas liquefaction system with a closed cooling system and a liquefaction method thereof, which has the following beneficial effects: 1. Energy saving and consumption reduction: the closed precooling has no liquid nitrogen consumption, solves the transportation and storage tank problem and reduces the operation cost; 2. Compact structure: the centrifugal oil-free compression-expansion integrated machine has a small volume and reduces the land occupation area by more than 30%; 3. Simple operation: the oil-free system eliminates the subsequent oil removal / adsorption process and prolongs the maintenance cycle by 50%. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a system structure schematic diagram of the application.

[0016] In the figure, S1, compression system; C0, first compressor; B1, buffer tank; CV1, high pressure unloading valve; CV2, high pressure loading valve; CV3, low pressure control valve; S2, pre-cooling system; HEX1, multi-stage heat exchanger; C1, second compressor; E1, expander; M1, motor; S3, reliquefaction system; HEX2, second heat exchanger; HEX3, third heat exchanger; HEX4, fourth heat exchanger; HEX5, fifth heat exchanger; A1, main adsorber; A21, first adsorber; A22, second adsorber; CV, throttle valve; S4, gas source system; S5, liquid storage system; Tank, storage tank. DETAILED DESCRIPTION

[0017] The embodiments of the present application will be further described below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0018] In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more; the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the purpose of facilitating the description of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0019] In the description of the present application, it should be noted that, unless otherwise specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0020] Please refer to Figure 1 The present application provides a technical solution: an oil-free gas liquefaction system with a closed cooling system and a liquefaction method thereof, which includes five core modules of compression system S1, gas source system S4, pre-cooling system S2, reliquefaction system S3 and liquid storage system S5, and the specific structure is as follows: The compression system S1 includes a first compressor C0, a buffer tank B1, and pressure control valves (a high-pressure unloading valve CV1, a high-pressure loading valve CV2, and a low-pressure control valve CV3) for adjusting the refrigerant pressure and providing a pre-cooling stage gas source. The refrigerant (such as helium) is pressurized by the first compressor C0 and then enters the buffer tank B1 through water cooling. The buffer tank B1 maintains stable system pressure (such as maintaining the pressure within the range of 1.8-2.2 MPa) through the high-pressure unloading valve CV1 (returning gas to the inlet of the first compressor C0 when the pressure is too high), the high-pressure loading valve CV2 (supplementing gas to the buffer tank when the pressure is too low), and the low-pressure control valve CV3 (adjusting the air supply when the low pressure is insufficient), ensuring reliable pre-cooling stage gas source.

[0021] The gas source system S4 provides stable liquefiable gas (such as hydrogen, helium, etc.) for the entire liquefaction system, including a pressure reducing valve, a regulating valve, a flow meter, and a gas pretreatment unit. The main functions of the gas source system include: Pressure reduction: reducing the high-pressure gas (such as 10-20 MPa high-pressure gas output by a hydrogen storage tank) input from the outside to a suitable pressure range (such as 1.0-2.0 MPa) for the pre-cooling system to process; Flow regulation: accurately controlling the gas flow (such as setting 300 Nm³ / h) through the regulating valve (such as a pneumatic regulating valve) according to the liquefaction demand, and monitoring the flow data in real time through the flow meter and feeding back to the control system; Pretreatment: removing solid particles (such as dust), moisture, and acidic impurities (such as CO2) in the gas through the gas pretreatment unit (including a dust filter, a molecular sieve adsorber, and a CO2 adsorption bed), ensuring that the gas entering the pre-cooling system has a purity of ≥99.999%, and avoiding pollution of subsequent equipment.

[0022] The pre-cooling system S2 is the core innovative module, including a compression-expansion integrated machine, which integrates the second compressor C1, the expander E1, the motor M1, the cooler CL1, and the second heat exchanger HEX2 in the multi-stage heat exchanger HEX1. The second compressor C1 and the expander E1 are coaxially operated by the motor M1 (through a single main shaft in series, realizing integrated operation of compression and expansion): the second compressor C1 compresses the gas (refrigerant or liquefiable gas circulating medium) to the rated pressure (such as 0.2 MPa), and then cools it to room temperature (such as 30-40°C) through the cooler CL1; the compressed high-pressure gas enters the expander E1 to expand and reduce pressure (such as to 0.1 MPa), generating low-temperature cold energy (outlet temperature ≤-150°C) through the adiabatic expansion effect. The pre-cooling system is a closed cycle (refrigerant flows internally without consuming working medium such as liquid nitrogen), and the compression-expansion integrated machine adopts a centrifugal oil-free design (without lubricating oil pollution, eliminating the need for traditional oil separation and adsorption systems).

[0023] The reliquefaction system S3 comprises a third heat exchanger HEX3, a fourth heat exchanger HEX4, a fifth heat exchanger HEX5, a first adsorber A21, a second adsorber A22 and a throttle valve CV of the multi-stage heat exchanger HEX1. The pre-cooled cryogenic gas (carrying cold energy) first passes through the first adsorber A21 and the second adsorber A22 in parallel, a one-by-one structure, and is controlled to pass through the first switching valve CV4 and the second switching valve CV5 to remove residual impurities such as trace CO2 and moisture; then sequentially passes through the multi-stage heat exchanger HEX1 to gradually reduce the temperature (for example, HEX3 to -100℃, HEX4 to -180℃, and HEX5 to -200℃); and finally, the gas is throttled to the liquid phase (for example, the liquefied hydrogen temperature is ≤-253℃) by the throttle valve (CV) and stored in the tank (Tank) of the liquid storage system (S5).

[0024] The liquid storage system S5 comprises a tank (Tank) for safely storing the liquefied gas (such as liquid hydrogen).

[0025] The working process of the present application is as follows: Step 1: Gas supply and pretreatment The high-pressure hydrogen gas (for example, 15MPa) output from the external hydrogen tank enters the gas source system S4: first, the pressure is reduced to 2MPa (an intermediate pressure suitable for the pre-cooling system) by the pressure reducing valve, and then the flow rate is accurately controlled (for example, set to 300Nm³ / h) by the regulating valve (for example, a pneumatic regulating valve) according to the liquefaction demand; the flow meter monitors the flow data in real time and feeds back to the control system; the gas pretreatment unit (including a dust filter, a molecular sieve adsorber and a CO2 adsorption bed) removes dust particles (filtration accuracy ≤1μm), moisture (dew point ≤-70℃) and acidic gases (such as CO2, concentration ≤1ppm) in the hydrogen gas in sequence, ensuring that the gas entering the pre-cooling system has a purity of ≥99.999%.

[0026] Step 2: Compression and pressure regulation The stable gas treated by the gas source system S4 enters the compression system S1: the refrigerant (such as helium, or the liquefied gas itself as a circulating medium) is pressurized to a high pressure (for example, 2MPa) by the first compressor C0, and after water cooling, enters the buffer tank B1; the buffer tank B1 is maintained at a stable pressure (for example, the pressure in the buffer tank is maintained within the range of 1.8-2.2MPa) by the high-pressure unloading valve CV1 (when the pressure exceeds 2.2MPa, the backflow gas is returned to the inlet of the first compressor), the high-pressure loading valve CV2 (when the pressure is lower than 1.8MPa, the gas is supplemented to the buffer tank) and the low-pressure control valve CV3 (when the pressure is insufficient, the gas is adjusted to supplement), ensuring the reliability of the pre-cooling stage gas source.

[0027] Step 3: Closed pre-cooling (cold energy generation) Stable gas source enters the compression-expansion integrated machine of the pre-cooling system S2: the single main shaft driven by the motor M1 makes the second compressor C1 compress the gas to a higher pressure (such as 3 MPa), and then the gas is cooled to normal temperature (such as 35℃) through the cooler CL1 (water cooling); the compressed high-pressure gas enters the expander (E1) to expand and reduce the pressure (such as reducing to 0.1 MPa), and low-temperature cold energy (outlet temperature ≤-196℃) is generated through the adiabatic expansion effect, providing the required low-temperature environment for subsequent liquefaction. The process is a closed cycle (the refrigerant flows internally, and no working medium such as liquid nitrogen is consumed), and the compression-expansion integrated machine adopts a centrifugal oil-free design (no lubricating oil pollution).

[0028] Step 4: Gas liquefaction The pre-cooled low-temperature gas (carrying cold energy) enters the re-liquefaction system S3: first, impurities are removed through the main adsorber A1, and then residual impurities (such as trace amounts of CO2, moisture, etc.) are removed through the first adsorber A21 or the second adsorber A22 (a one-backup-one-use structure in parallel, the passage is controlled through the first switching valve CV4 or the second switching valve CV5); then, the gas is sequentially cooled through multiple heat exchangers HEX1 (HEX3 to-100℃, HEX4 to-180℃, and HEX5 to-200℃); finally, the gas is throttled and reduced in pressure to the liquid phase (such as hydrogen liquefaction temperature ≤-253℃) through the throttle valve CV, and is stored in the storage tank (Tank).

[0029] Step 5: Cold energy recovery After the completion of pre-cooling, the refrigerant (such as helium) is recovered through the second heat exchanger HEX2 (one of the multiple heat exchangers HEX1) of the pre-cooling system S2 and the heat exchanger of the compression system S1, and the remaining cold energy is recovered (for example, the compressed gas is pre-cooled to a lower temperature), and is returned to the inlet of the first compressor C0 to form a closed cycle, ensuring efficient use of cold energy (cold energy recovery efficiency ≥95%).

[0030] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent replacements or changes to the technical solutions and the inventive concept of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. An oil-free gas liquefaction system with a closed cooling system, characterized by: The system comprises a compression system (S1), a gas source system (S4), a pre-cooling system (S2), a reliquefaction system (S3) and a liquid storage system (S5); The compression system (S1) comprises a first compressor (C0), a buffer tank (B1), a high-pressure unloading valve (CV1), a high-pressure loading valve (CV2) and a low-pressure control valve (CV3) for adjusting the refrigerant pressure and providing a pre-cooling stage gas source; The gas source system (S4) comprises a pressure reducing valve, a regulating valve, a flowmeter and a gas pretreatment unit, which provides stable gas to be liquefied for the whole liquefaction system; The pre-cooling system (S2) comprises a compression-expansion integrated machine, which integrates a second compressor (C1), an expander (E1), a motor (M1), a cooler (CL1) and a second heat exchanger (HEX2). The motor (M1) drives the second compressor (C1) and the expander (E1) to operate coaxially. The compressed gas is cooled and then expanded by the expander (E1) to generate cold energy; The reliquefaction system (S3) comprises a third heat exchanger (HEX3), a fourth heat exchanger (HEX4), a fifth heat exchanger (HEX5), a main adsorber (A1), a first adsorber (A21), a second adsorber (A22), a turbo expander (TB) and a throttle valve (CV), which are used for gradually cooling the pre-cooled gas to the liquid phase; The second heat exchanger (HEX2), the third heat exchanger (HEX3), the fourth heat exchanger (HEX4) and the fifth heat exchanger (HEX5) form a multi-stage heat exchanger (HEX1); The liquid storage system (S5) comprises a storage tank (Tank) for storing the liquefied gas.

2. An oil-free gas liquefaction system with a closed cooling system according to claim 1, characterized in that: The first adsorber (A21) and the second adsorber (A22) of the reliquefaction system (S3) are in parallel one-by-one structure and are respectively controlled by a first switching valve (CV4) and a second switching valve (CV5) to control the gas passage.

3. The oil-free gas liquefaction system with a closed cooling system of claim 1, wherein: The multi-stage heat exchanger (HEX1) of the pre-cooling system (S2) works with the heat exchanger of the compression system (S1) to recover the cold energy of the refrigerant.

4. The oil-free gas liquefaction system with a closed cooling system of claim 1, wherein: The compression-expansion integrated machine connects the second compressor (C1), the expander (E1) and the motor (M1) through a single main shaft to realize integrated operation of compression and expansion.

5. The oil-free gas liquefaction system with a closed cooling system of claim 1, wherein: The pre-cooling system (S2) is a closed cycle without liquid nitrogen consumption, and the compression-expansion integrated machine is a centrifugal oil-free design.

6. The oil-free gas liquefaction system with a closed cooling system of claim 1, wherein: The first compressor (C0) of the compression system (S1) adopts magnetic suspension or dry sealing technology to avoid lubricating oil pollution of the refrigerant.

7. A method of oil-free gas liquefaction with a closed cooling system, characterized by: The method comprises the following steps: A pre-cooling step: the refrigerant is pressurized by the first compressor (C0) and then compressed, cooled and expanded by the compression-expansion integrated machine of the pre-cooling system (S2) to generate cold energy; A liquefaction step: the gas source gas is pre-cooled, impurity-removed by the main adsorber (A1), gradually cooled by the multi-stage heat exchanger (HEX1) and finally liquefied by the throttle valve (CV); A circulation step: the refrigerant recovers cold energy through a closed loop to maintain continuous operation of the system.

8. The method of claim 7, wherein: In the pre-cooling step, the outlet temperature of the expander (E1) is -120℃ to -180℃.

9. The method of claim 8, wherein: In the liquefaction step, after the gas is purified by the main adsorber (A1), the multi-stage heat exchanger (HEX1) is filled with a positive-para hydrogen catalytic conversion agent to ensure that the content of para hydrogen in the liquid hydrogen is ≥ 95%.

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