Natural gas liquefaction process using supersonic velocity spray pipe for precooling

Abstract

The invention relates to a natural gas liquefaction process using supersonic velocity spray pipe precooling. The system comprises a pre-cooling unit, a deep cooling unit, a heat exchange unit and a natural gas liquefaction unit. The pre-cooling unit comprises a supersonic spray pipe and a throttle valve; the cryogenic unit comprises a throttle valve, a compressor, a cooler, a component distributor and a mixer; the heat exchange unit comprises a heat exchanger; the natural gas liquefaction unit comprises a throttle valve and a separator. According to the production process, the technical scheme of supersonic spray pipe precooling and mixed refrigerant circulating cryogenic cooling is adopted. Compared with other processes, the process has the advantages of low refrigerant consumption, low energy consumption, high natural gas liquefaction rate, low process complexity, low equipment investment, good environmental protection benefit and the like under the same condition, and can efficiently recover the natural gas condensate (NGL) while precooling.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical separation, relates to natural gas liquefaction and NGL recovery, and particularly relates to a natural gas liquefaction process using a supersonic nozzle for precooling. Background Art

[0002] LNG is a clean energy formed by liquefying natural gas at ultra-low temperature (-162°C). Its main component is methane, which has the characteristics of being colorless, odorless, non-toxic, and having a high energy density. Its volume is only 1 / 600 of the gaseous state, greatly improving the storage and transportation efficiency. As one of the core energy sources for low-carbon transformation, LNG is widely used in power generation, industrial fuel, city gas, and transportation fields. Especially represented by LNG ships and heavy trucks, it can replace traditional fossil fuels, reduce sulfur oxide and particulate emissions, and improve air quality. At the same time, its flexible peak shaving ability ensures the stability of energy supply. In terms of strategic value, the carbon emissions from LNG combustion are reduced by more than 50% compared to coal, becoming a key path to achieve the "dual carbon" goal; its global trade network not only strengthens energy security but also promotes the coordinated development of regional economies, and is an important pillar for building a sustainable energy system.

[0003] As a clean and low-carbon fossil energy, natural gas plays a key role in the global energy structure transformation. However, its gaseous characteristics lead to high storage and transportation costs. Therefore, natural gas liquefaction technology is usually used to convert gaseous methane into liquid (LNG) through cryogenic refrigeration processes, with the volume reduced to 1 / 600 of the gaseous state, significantly improving the storage and transportation efficiency, and becoming the core technology connecting the resource side and the market side. In recent years, with the development of unconventional resources such as Arctic gas fields and deep-sea gas fields, as well as the application expansion of LNG in fields such as power peak shaving and ship fuel, the research demand for natural gas liquefaction technology has been continuously increasing. Current research focuses on optimizing process energy consumption, developing modular liquefaction devices, and recycling cold energy during the liquefaction process to reduce carbon emission intensity and economic costs.

[0004] Simply using the dual-cycle refrigerant liquefaction process (DMR) requires a large amount of mixed refrigerant and has a complex refrigerant ratio. During the refrigeration process, an additional separation step is required to recover NGL. This increases the equipment investment, complexity, and energy consumption of the liquefaction process; the supersonic nozzle precooling + refrigerant cryogenic natural gas liquefaction process uses a supersonic nozzle to precool natural gas instead of a mixed refrigerant, which can efficiently recover NGL while precooling natural gas, and has the advantages of less refrigerant consumption, low energy consumption, high natural gas liquefaction rate, low process complexity, less equipment investment, and good environmental benefits. Therefore, a natural gas liquefaction process using a supersonic nozzle for precooling is established. Summary of the Invention

[0005] Aiming at the problems of large investment, high operating cost, high energy consumption, etc. existing in the existing natural gas liquefaction technology, the object of the present invention is to provide a natural gas liquefaction process using a supersonic nozzle for precooling. This process adopts a combined technical solution of supersonic nozzle precooling and mixed refrigerant cryogenic cooling, and can simultaneously perform precooling and recover NGL. Compared with other processes under the same conditions, this process has the advantages of less refrigerant consumption, low energy consumption, low process complexity, less equipment investment, good environmental protection benefits, etc., and can recover NGL while precooling.

[0006] To achieve the above object, the present invention provides a natural gas liquefaction process using a supersonic nozzle for precooling, which includes a precooling unit, a cryogenic cooling unit, a heat exchange unit and a natural gas liquefaction unit;

[0007] The precooling unit includes a supersonic nozzle N-1 and a throttle valve V-1; the cryogenic cooling unit includes a throttle valve V-2, a compressor K-1, a cooler E-1, a component distributor X-1, a mixer M-1, and a cooler E-2; the heat exchange unit includes a heat exchanger HX-1; the natural gas liquefaction unit includes a throttle valve V-3 and a separator S-1;

[0008] In the precooling unit, the raw gas inlet pipeline is connected to the supersonic nozzle N-1, and the supersonic nozzle N-1 and the throttle valve V-1 are connected in sequence; the precooled natural gas flows out through the supersonic nozzle N-1;

[0009] In the cryogenic cooling unit, the outlet of the mixer M-1, the cooler E-2, the heat exchanger HX-1, the throttle valve V-2, the heat exchanger HX-1, the compressor K-1, the cooler E-1, the component distributor X-1, and the inlet of the mixer M-1 are connected in sequence and circulate like this;

[0010] In the natural gas liquefaction unit, the outlet of the throttle valve V-1, the heat exchanger HX-1, the throttle valve V-3, and the separator S-1 are connected in sequence; fuel gas is produced at the top of the separator S-1, and LNG is produced at the bottom of the separator S-2.

[0011] For the above natural gas liquefaction process using a supersonic nozzle for precooling, the raw gas can be natural gas at normal temperature and any pressure, and the applicable range of raw gas conditions is relatively wide.

[0012] For the above natural gas liquefaction process using a supersonic nozzle for precooling, the main function of the supersonic nozzle N-1 is to realize the processes of isentropic expansion (temperature and pressure reduction), heavy component condensation (non-equilibrium phase change) and gas-liquid separation of the gas in this device. In the present invention, an inlet swirl section, a supersonic expansion section, a nucleation condensation section and a gas-liquid separation section are provided in the supersonic nozzle N-1;

[0013] The inlet swirl section is equipped with spiral guide vanes (angle 20°~40°), which force the natural gas to form a high-speed swirl. The diameter of the swirl cavity gradually decreases, and the subsequent nozzle throat smoothly transitions to avoid flow separation. The swirl generates a strong centrifugal force field to pre-separate some liquid impurities (such as free water and heavy hydrocarbon droplets), while providing a uniform flow field for the subsequent expansion section;

[0014] The supersonic expansion section is equipped with a Laval nozzle. The contraction section accelerates the airflow to the throat speed of sound, and the expansion section further accelerates it to supersonic speed. Through adiabatic expansion, the airflow temperature drops to -70℃~-100℃, and the pressure drops to 0.5~2bar, creating a low temperature and low pressure environment for the condensation of heavy components.

[0015] The nucleation and condensation section is provided with a non-equilibrium condensation zone, in which the heavy hydrocarbon components are rapidly supersaturated at low temperatures due to the high dew point temperature, and preferentially nucleate and grow into droplets on the wall surface;

[0016] The gas-liquid separation section is provided with an annular liquid collecting chamber, which is isolated from the central gas channel. The heavy component liquid that is condensed first is discharged through the discharge port due to centrifugal force; the liquid droplets are thrown to the wall by centrifugal force and discharged through the liquid collecting chamber; the purified light components (mainly methane) are output from the central channel.

[0017] In the above-mentioned natural gas liquefaction process using supersonic nozzle precooling, the heat exchanger includes a heat exchanger HX-1, which is mainly used to realize heat exchange and transfer in the production of the device and is a conventional device in the field. In the present invention, the heat exchanger HX-1 is provided with a first heat exchange channel and a second heat exchange channel;

[0018] The end of the first heat exchange channel is connected to the throttle valve V-1 through a pipeline, and the head end of the first heat exchange channel is connected to the throttle valve V-3 through a pipeline; the head end of the second heat exchange channel is connected to the throttle valve V-2 through a pipeline, and the end of the second heat exchange channel is connected to the cooler E-2 through a pipeline; the head end of the third heat exchange channel is connected to the compressor K-1 through a pipeline, and the end of the third heat exchange channel is connected to the throttle valve V-2 through a pipeline.

[0019] The above-mentioned natural gas liquefaction process using supersonic nozzle precooling is composed of a supersonic nozzle N-1, a throttle valve V-1, a first heat exchange channel of a heat exchanger HX-1, a throttle valve V-3, a separator S-1 and connecting pipes between adjacent components to form an LNG production circuit.

[0020] The above-mentioned natural gas liquefaction process using supersonic nozzle pre-cooling and the cryogenic system usually use a mixed refrigerant consisting of methane, ethane, propane and nitrogen as a circulating refrigerant. By virtue of the different condensing temperatures of different components, throttling and gasification are performed successively to condense the corresponding components in the natural gas, thereby achieving the purpose of refrigeration.

[0021] The above natural gas liquefaction process using a supersonic nozzle for precooling directly provides cooling capacity for natural gas by the precooling system; the cryogenic system provides cooling capacity for the heat exchanger, and a mixed refrigerant composed of methane, ethane, propane, and nitrogen is used as the circulating refrigerant.

[0022] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0023] (1) The natural gas liquefaction process applicable to NGL recovery provided by the present invention precools and cryogenically cools natural gas through a supersonic nozzle and a heat exchanger respectively. Based on the traditional natural gas liquefaction process, the present invention enables the simultaneous precooling of natural gas and NGL recovery. The combination of the two processes reduces the investment in equipment and refrigerants. While precooling natural gas, it can efficiently recover NGL, achieving a reduction in energy consumption and a multi-level utilization of energy.

[0024] (2) The natural gas liquefaction process applicable to NGL recovery provided by the present invention adopts a mixed refrigerant refrigeration process in the cryogenic unit, with low comprehensive energy consumption of the device, low device complexity, high NGL recovery efficiency, high LNG liquefaction rate, and low equipment investment. Description of the Drawings

[0025] Figure 1 is the process flow diagram of the natural gas liquefaction process using a supersonic nozzle for precooling according to the present invention;

[0026] Figure 2 is the schematic diagram of the natural gas liquefaction process using a supersonic nozzle for precooling according to the present invention;

[0027] Description of the reference numerals: N-1 - supersonic nozzle; V-1 - throttle valve; V-2 - throttle valve; K-1 - compressor; E-1 - cooler; X-1 - component distributor; M-1 - mixer; E-2 - cooler; HX-1 - heat exchanger; V-3 - throttle valve; S-1 - separator. Detailed Embodiments

[0028] The following will combine with the attached Figure 1 to clearly and completely describe the technical solution of the natural gas liquefaction process using a supersonic nozzle for precooling provided by the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention.

[0029] A natural gas liquefaction process using a supersonic nozzle for precooling provided by this embodiment, as Figure 1 shown, includes a precooling unit, a heat exchange unit, a cryogenic unit, and a natural gas liquefaction unit connected by pipelines.

[0030] The natural gas liquefaction unit includes a separator S-1.

[0031] The heat exchange unit includes a heat exchanger HX-1. Inside the heat exchanger HX-1, a first heat exchange channel, a second heat exchange channel, and a third heat exchange channel are provided.

[0032] The precooling unit includes a supersonic nozzle N-1 and a throttle valve V-1.

[0033] The cryogenic unit includes a throttle valve V-2, a compressor K-1, a cooler E-1, a component distributor X-1, a mixer M-1, and a cooler E-2.

[0034] The end of the first heat exchange channel is connected to the throttle valve V-1 through a pipeline, and the head of the first heat exchange channel is connected to the throttle valve V-3 through a pipeline; the head of the second heat exchange channel is connected to the throttle valve V-2 through a pipeline, and the end of the second heat exchange channel is connected to the cooler E-2 through a pipeline; the head of the third heat exchange channel is connected to the compressor K-1 through a pipeline, and the end of the third heat exchange channel is connected to the throttle valve V-2 through a pipeline.

[0035] The above natural gas liquefaction process using a supersonic nozzle for precooling consists of a supersonic nozzle N-1, a throttle valve V-1, the first heat exchange channel of the heat exchanger HX-1, a throttle valve V-3, a separator S-1, and the connecting pipelines between adjacent components to jointly form an LNG production loop.

[0036] In the above natural gas liquefaction process using a supersonic nozzle for precooling, the cryogenic system usually uses a mixed refrigerant composed of methane, ethane, propane, and nitrogen as the circulating refrigerant.

[0036] In the above natural gas liquefaction process using a supersonic nozzle for precooling, the feed gas can be natural gas at normal temperature and any pressure, and the applicable range of feed gas conditions is relatively wide.

[0037] A precooling method using a supersonic nozzle provided in this embodiment, as Figure 2 shown, includes an inlet swirl section, a supersonic expansion section, a nucleation condensation section, and a gas-liquid swirl separation section.

[0038] In the above natural gas liquefaction process using a supersonic nozzle for precooling, the main function of the supersonic nozzle N-1 is to achieve the isentropic expansion (temperature and pressure reduction), recombination condensation (non-equilibrium phase change), and gas-liquid separation processes of the gas in this device. In the present invention, an inlet swirl section, a supersonic expansion section, a nucleation condensation section, and a gas-liquid separation section are provided inside the supersonic nozzle N-1;

[0039] The inlet swirl section is provided with spiral guide vanes (angle 20° - 40°), which force the natural gas to form a high-speed swirl. The diameter of the swirl chamber gradually decreases and smoothly transitions to the throat of the subsequent nozzle to avoid flow separation. A strong centrifugal force field is generated through the swirl to pre-separate some liquid impurities (such as free water and heavy hydrocarbon droplets), and at the same time provide a uniform flow field for the subsequent expansion section;

[0040] The supersonic expansion section is provided with a Laval nozzle. The converging section accelerates the airflow to the sonic speed at the throat, and the diverging section further accelerates it to supersonic speed. The temperature of the airflow drops sharply to -70°C to -100°C through adiabatic expansion, and the pressure drops to 0.5 to 2 bar, creating a low-temperature and low-pressure environment for the condensation of heavy components.

[0041] The nucleation and condensation section is provided with a non-equilibrium condensation zone. In this zone, heavy-component hydrocarbons have a higher dew point temperature and become rapidly supersaturated at low temperatures, preferentially nucleating and growing into droplets on the wall surface.

[0042] The gas-liquid separation section is provided with an annular liquid collection chamber, which is isolated from the central gas channel. The preferentially condensed heavy-component liquid is discharged as a liquid heavy component through the drain port due to the centrifugal force. The liquid droplets are thrown towards the wall surface by the centrifugal force and discharged through the liquid collection chamber. The purified light components (mainly methane) are output from the central channel.

[0043] The above is to help the reader understand the principle of the present invention. The protection scope of the present invention is not limited to such specific statements and embodiments. For those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several combinations and improvements can be made, and these combinations and improvements are also within the protection scope of the present invention.

Claims

1. A natural gas liquefaction process using supersonic nozzle precooling, characterized in that: It includes natural gas liquefaction unit, heat exchange unit, pre-cooling unit and cryogenic unit; The natural gas liquefaction unit includes a throttle valve V-3 and a separator S-1; the heat exchange unit includes a heat exchanger HX-1; the precooling unit includes a supersonic nozzle N-1 and a throttle valve V-1; the cryogenic unit includes a throttle valve V-2, a compressor K-1, a cooler E-1, a component distributor X-1, a mixer M-1, and a cooler E-2; In the natural gas liquefaction unit, the throttle valve V-1 outlet, the heat exchanger HX-1, the throttle valve V-3, and the separator S-1 are connected in sequence; the top of the separator S-1 produces fuel gas, and the bottom of the separator S-2 produces LNG. In the precooling unit, the raw gas inlet pipeline is connected to the supersonic nozzle N-1, and the supersonic nozzle N-1 and the throttle valve V-1 are connected in sequence; the precooled natural gas flows out through the throttle valve V-1; The cryogenic unit, the outlet of the mixer M-1, the cooler E-2, the heat exchanger HX-1, the throttle valve V-2, the heat exchanger HX-1, the compressor K-1, the cooler E-1, the component distributor X-1, and the inlet of the mixer M-1 are connected in sequence, and the cycle continues.

2. A natural gas liquefaction process using supersonic nozzle precooling according to claim 1, characterized in that: The heat exchanger HX-1 is provided with a first heat exchange channel, a second heat exchange channel, and a third heat exchange channel. The end of the first heat exchange channel is connected to the throttle valve V-1 through a pipeline, and the head end of the first heat exchange channel is connected to the throttle valve V-3 through a pipeline; the head end of the second heat exchange channel is connected to the throttle valve V-2 through a pipeline, and the end of the second heat exchange channel is connected to the cooler E-2 through a pipeline; the head end of the third heat exchange channel is connected to the compressor K-1 through a pipeline, and the end of the third heat exchange channel is connected to the throttle valve V-2 through a pipeline.

3. A method for precooling using a supersonic nozzle, characterized in that: It includes an inlet swirl section, a supersonic expansion section, a nucleation condensation section, and a gas-liquid separation section; The inlet swirl section is equipped with spiral guide vanes (angle 20°~40°), which force the natural gas to form a high-speed swirl. The diameter of the swirl cavity gradually decreases, and the subsequent nozzle throat smoothly transitions to avoid flow separation. The swirl generates a strong centrifugal force field to pre-separate some liquid impurities (such as free water and heavy hydrocarbon droplets), while providing a uniform flow field for the subsequent expansion section; The supersonic expansion section is equipped with a Laval nozzle. The contraction section accelerates the airflow to the throat speed of sound, and the expansion section further accelerates it to supersonic speed. Through adiabatic expansion, the airflow temperature drops to -70℃~-100℃, and the pressure drops to 0.5~2bar, creating a low temperature and low pressure environment for the condensation of heavy components. The nucleation and condensation section is provided with a non-equilibrium condensation zone, in which the heavy hydrocarbon components are rapidly supersaturated at low temperatures due to the high dew point temperature, and preferentially nucleate and grow into droplets on the wall surface; The gas-liquid separation section is provided with an annular liquid collecting chamber, which is isolated from the central gas channel. The liquid of the first condensed heavy component is discharged through the liquid discharge port due to the centrifugal force; the liquid droplets are thrown to the wall by the centrifugal force and discharged through the liquid collecting chamber; The purified light components (mainly methane) are output from the central channel.

4. A natural gas liquefaction process using supersonic nozzle precooling according to any one of claims 1 to 3, characterized in that: The precooling system directly provides cooling capacity for the natural gas through a supersonic nozzle; the cryogenic system provides cooling capacity for the heat exchanger, and adopts a mixed refrigerant composed of methane, ethane, propane and nitrogen as a circulating refrigerant.

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