Natural gas liquefaction method and device

Abstract

According to the natural gas liquefaction method and device, the heat exchange pipes are distributed in the heat exchange tank in an S shape, the stability of a heat exchanger can be effectively guaranteed, the flow direction is changed through a bent curve, heating is accelerated, the heat exchange efficiency is improved, then the energy utilization rate of the whole natural gas liquefaction process is increased, and energy consumption is reduced; the heat exchange tank is wrapped by cold water, and copper is adopted as the material of the heat exchange tank, so that the heat exchange efficiency of the heat exchange tank is greatly improved, natural gas can be fully cooled and liquefied, and the natural gas liquefaction efficiency is improved; the device provided by the invention is simple in steps, simple in structure and easy to operate, and can quickly and effectively perform the liquefaction process of the natural gas.

Description

Technical Field

[0001] The present invention relates to the technical field of liquefied natural gas preparation devices, and in particular, to a natural gas liquefaction method and device. Background Art

[0002] With the emergence of global energy and environmental problems, people's demand for clean energy has been increasing continuously. Among them, natural gas has become one of the current main energy sources with its characteristics of high efficiency and cleanness, and its consumption shows an increasing trend.

[0003] In order to meet various requirements including the demand for high efficiency and larger capacity, a thermodynamic process for liquefying natural gas to produce liquefied natural gas has been developed since the 1970s. Natural gas liquefaction technology is relatively complex and involves a wide range of specialties. It is a combination of natural gas pretreatment, gas separation, cryogenic technology, and the design and process of large cryogenic containers, etc.

[0004] Although natural gas liquefaction technology has developed rapidly, there are still some problems in existing natural gas liquefaction devices. The essence of the natural gas liquefaction process is a process of continuously removing the heat of natural gas through low-temperature heat exchange. Therefore, the heat exchanger is a key component in the natural gas liquefaction process. According to literature analysis, in the existing technology, the energy consumption and losses in the entire natural gas liquefaction process are mainly concentrated in the compressor and the heat exchanger. Therefore, improving the heat exchange efficiency of the low-temperature heat exchanger is of great significance for reducing the energy loss in the natural gas liquefaction process and is also very important for improving the performance of the entire natural gas liquefaction device. Summary of the Invention

[0005] The purpose of the present invention is to provide a natural gas liquefaction method and device. Through the heat exchange tubes with an S-shaped structure in the heat exchange device, the stability of the heat exchanger can be effectively ensured. And through the curved line, the flow direction is changed, the heating is accelerated, and the heat exchange efficiency is improved. Furthermore, the energy utilization rate of the entire natural gas liquefaction process is improved, and the energy consumption is reduced. By using cold water to wrap the heat exchange tank outside the heat exchange tank and using copper as the material of the heat exchange tank, the heat exchange efficiency of the heat exchange tank is greatly improved, enabling the natural gas to be fully cooled and liquefied, and improving the efficiency of natural gas liquefaction. The present invention provides simple steps and a device with a simple structure and easy operation, which can quickly and effectively carry out the liquefaction process of natural gas.

[0006] A natural gas liquefaction method includes the following steps: Step S1, pre-compressing the raw natural gas through a suction device until some natural gas is liquefied; Step S2, sequentially passing the pre-compressed natural gas and the refrigerant through a heat exchange device for heat exchange, and after the natural gas is cooled, a mixed liquid is obtained; Step S3: Separate the mixed liquid obtained after heat exchange in a gas-liquid separator to obtain liquefied natural gas and unliquefied natural gas. Step S4: Transport the separated liquefied natural gas to a liquefied natural gas storage tank for storage, discharge the unliquefied natural gas to a suction device for recompression, and then discharge it back into the heat exchange device to repeat the above steps.

[0007] Furthermore, before the raw natural gas undergoes compression pretreatment, there is also a step of purifying the raw natural gas.

[0008] Furthermore, the step of purifying the raw natural gas includes filtration, adsorption, and separation.

[0009] The present invention also provides a natural gas liquefaction device, including a suction device, a heat exchange device, a gas-liquid separator, and a liquefied natural gas storage tank. The input end of the heat exchange device is connected to the suction device, and the output end is connected to the gas-liquid separator. The liquid outlet of the gas-liquid separator is connected to the liquefied natural gas storage tank through a gas outlet pipe. Among them, the heat exchange device includes a heat exchange tube, a heat exchange tank, and a tank body. The heat exchange tank is placed inside the tank body, the heat exchange tube is arranged inside the heat exchange tank, both ends of the heat exchange tube are a refrigerant inlet and a refrigerant outlet respectively, and the refrigerant inlet and the refrigerant outlet pass through the side wall of the heat exchange tank and the side wall of the tank body and are located outside the tank body.

[0010] Furthermore, it also includes a raw natural gas purification device. The raw natural gas purification device is connected to the suction device through an intake pipe and is also connected to the gas outlet of the gas-liquid separator.

[0011] Furthermore, the heat exchange tube is arranged in an S shape inside the heat exchange tank.

[0012] Furthermore, cold water is injected into the tank body to assist in heat exchange.

[0013] Furthermore, a pressure sensor and a temperature sensor are also arranged inside the heat exchange tank.

[0014] Furthermore, the heat exchange tank is made of copper.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The heat exchange tubes are distributed in an S shape in the heat exchange tank, which can effectively ensure the stability of the heat exchanger. Moreover, through the curved lines, the flow direction is changed, heating is accelerated, the heat exchange efficiency is improved, thereby improving the energy utilization rate of the entire natural gas liquefaction process and reducing energy consumption. Cold water is used to wrap the heat exchange tank outside the heat exchange tank, and copper is used as the material of the heat exchange tank, which greatly improves the heat exchange efficiency of the heat exchange tank, enables the natural gas to be fully cooled and liquefied, and improves the efficiency of natural gas liquefaction. The present invention provides simple steps and a device with a simple structure and easy operation, which can quickly and effectively carry out the liquefaction process of natural gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a schematic flow chart of the natural gas liquefaction method provided by the present invention; Figure 2 It is a schematic structural diagram of the natural gas liquefaction device provided by the present invention.

[0018] Reference numerals: 1, suction device; 2, heat exchange device; 21, heat exchange tube; 22, heat exchange tank; 23, tank body; 3, gas-liquid separator; 4, liquefied natural gas storage tank; 5, raw natural gas purification device; 6, pressure sensor; 7, temperature sensor; 8, intake pipeline; 9, outlet pipeline. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] In the following text, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and the description are considered to be exemplary in nature rather than restrictive.

[0020] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0021] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. This repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0022] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] Refer to Figure 1 , which is a schematic flow chart of the natural gas liquefaction method provided by the embodiment of the present invention. The natural gas liquefaction method includes the following steps: Step S1, compress and preprocess the raw natural gas through a suction device until some natural gas is liquefied; Step S2, sequentially perform heat exchange on the compressed and preprocessed natural gas and the refrigerant through a heat exchange device, and a mixed liquid is obtained after the natural gas is cooled; Step S3, separate the mixed liquid obtained after the heat exchange in a gas-liquid separator to obtain liquefied natural gas and unliquefied natural gas; Step S4, transport the liquefied natural gas obtained after the separation to a liquefied natural gas storage tank for storage, discharge the unliquefied natural gas to the suction device for re-compression, and then discharge it into the heat exchange device again, repeating the above steps.

[0024] In the above technical solution, when some natural gas is liquefied, it means that it is almost approaching the critical point. At this time, by cooling down, the remaining unliquefied natural gas can be quickly liquefied. Compared with direct cooling, it not only has high efficiency but also a relatively fast speed; after heat exchange, some natural gas may not be liquefied. Through the gas-liquid separator, it can ensure that the obtained is pure liquefied natural gas rather than a gas-liquid mixture, improving the purity of the product.

[0025] Specifically, liquid nitrogen can be used as the refrigerant. Compared with other refrigerants, liquid nitrogen is colorless, transparent, slightly lighter than water, highly inert, non-corrosive, and stable to vibration and electric sparks. At one atmosphere, the vaporization temperature of liquid nitrogen is 195.81t, and the latent heat of vaporization is 47.9 kcal / kg. Due to the development of space technology and industries such as steelmaking, a large amount of liquid nitrogen obtained by liquefying the by-product nitrogen from oxygen production has been widely used as a cryogenic cold source in various industrial production and scientific research fields such as medicine, laser, superconductivity, food, and biology.

[0026] Before the raw natural gas is compressed and pre-treated, a step of purifying the raw natural gas is also included to improve the purity of the natural gas.

[0027] Specifically, the step of purifying the raw natural gas includes filtration, adsorption, and separation.

[0028] In the above technical solution, since the natural gas extracted from the formation often contains solid impurities such as sand and rust mixed in, as well as harmful substances such as water, water vapor, sulfides, and carbon dioxide, and dust particles such as sand and rust move with the gas flow, which will wear the components of the pumping and compressing devices, pipelines, and instruments, and even cause damage. Sometimes they will accumulate in certain parts, affecting the normal gas transmission. Therefore, before the raw natural gas is compressed and pre-treated, filtration, adsorption, and separation operations need to be carried out first to remove the solid impurities and harmful substances in the raw natural gas to ensure the smooth progress of the subsequent liquefaction operation, and then liquefied natural gas meeting the standards can be obtained.

[0029] Refer to Figure 2 , which is a schematic structural diagram of the natural gas liquefaction device provided by the embodiment of the present invention. The natural gas liquefaction device includes a suction device 1, a heat exchange device 2, a gas-liquid separator 3, and a liquefied natural gas storage tank 4. The input end of the heat exchange device 2 is connected to the suction device 1, and the output end is connected to the gas-liquid separator 3. The liquid outlet of the gas-liquid separator 3 is connected to the liquefied natural gas storage tank 4 through an air outlet pipe 9. Among them, the heat exchange device 2 includes a heat exchange tube 21, a heat exchange tank 22, and a tank body 23. The heat exchange tank 22 is placed inside the tank body 23, the heat exchange tube 21 is arranged inside the heat exchange tank 22, both ends of the heat exchange tube 21 are a refrigerant inlet and a refrigerant outlet respectively, and the refrigerant inlet and the refrigerant outlet pass through the side wall of the heat exchange tank 22 and the side wall of the tank body 23 and are located outside the tank body 23.

[0030] Specifically, the suction device 1 can be but not limited to a compressor. A compressor is a machine that compresses gas to increase gas pressure or transports gas, and can continue to compress and process the raw natural gas.

[0031] Preferably, a raw natural gas purification device 5 is further included. The raw natural gas purification device 5 is connected to the suction device 1 through an intake pipe 8 and is also connected to the air outlet of the gas-liquid separator 3.

[0032] In the above technical solution, since the natural gas extracted from the formation often contains solid impurities such as sand and mixed rust, as well as harmful substances such as water, water vapor, sulfides, and carbon dioxide, and dust particles such as sand and rust move with the airflow, which will wear the components of the pumping and compressing device, pipelines, and instruments, and even cause damage. Sometimes, they will accumulate in certain parts, affecting the normal gas transmission. Therefore, before the raw natural gas is compressed, it needs to enter the raw natural gas purification device 5 for filtration, adsorption, and separation operations to remove the solid impurities and harmful substances in the raw natural gas, ensure the smooth progress of the subsequent liquefaction operation, and thus obtain liquefied natural gas that meets the standards.

[0033] To ensure uniform heating, the heat exchange tubes 21 are arranged in an S shape inside the heat exchange tank 22, effectively ensuring the stability of the heat exchanger. Moreover, through the curved line, the flow direction is changed, the heating is accelerated, the efficiency of heat exchange is improved, and thus the energy utilization rate of the entire natural gas liquefaction process is increased, and the energy consumption is reduced.

[0034] Preferably, cold water is injected into the tank body 23 to assist heat exchange.

[0035] Preferably, the heat exchange tank 22 is made of copper.

[0036] In the above technical solution, the heat exchange tank 22 is wrapped with cold water outside the heat exchange tank 22, and copper is used as the material of the heat exchange tank 22, which greatly improves the heat exchange efficiency of the heat exchange tank 22, enables the natural gas to be fully cooled and liquefied, and improves the efficiency of natural gas liquefaction.

[0037] Preferably, a pressure sensor 6 and a temperature sensor 7 are further provided inside the heat exchange tank 22 to monitor the temperature and pressure inside the heat exchange tank 22 respectively during the natural gas liquefaction process.

[0038] In the above technical solution, when the natural gas enters the heat exchange device 2 for heat exchange operation, the pressure sensor 6 and the temperature sensor 7 monitor the temperature and pressure inside the heat exchange tank 22 respectively to ensure the stability and safety of the heat exchange device 2.

[0039] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and its equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A natural gas liquefaction method, characterized in that, It includes the following steps: Step S1: Compress and pre-treat the raw natural gas through a suction device until some natural gas is liquefied; Step S2: Sequentially pass the compressed and pre-treated natural gas and the refrigerant through a heat exchange device for heat exchange. After the natural gas is cooled, a mixed liquid is obtained; Step S3: Separate the mixed liquid obtained after the heat exchange in a gas-liquid separator to obtain liquefied natural gas and unliquefied natural gas; Step S4: Transport the liquefied natural gas obtained from the separation to a liquefied natural gas storage tank for storage. The unliquefied natural gas is discharged to the suction device for re-compression and then discharged into the heat exchange device again. Repeat the above steps.

2. The natural gas liquefaction method according to claim 1, characterized in that: Before the raw natural gas is compressed and pre-treated, it also includes a raw natural gas purification treatment step.

3. The natural gas liquefaction method according to claim 2, characterized in that: The raw natural gas purification treatment step includes filtration, adsorption, and separation.

4. A natural gas liquefaction device, characterized in that: It includes a suction device, a heat exchange device, a gas-liquid separator, and a liquefied natural gas storage tank. The input end of the heat exchange device is connected to the suction device, and the output end is connected to the gas-liquid separator. The liquid outlet of the gas-liquid separator is connected to the liquefied natural gas storage tank through a gas outlet pipe; wherein, the heat exchange device includes a heat exchange tube, a heat exchange tank, and a tank body. The heat exchange tank is placed inside the tank body, and the heat exchange tube is arranged inside the heat exchange tank. The two ends of the heat exchange tube are respectively a refrigerant inlet and a refrigerant outlet, and the refrigerant inlet and the refrigerant outlet respectively pass through the side wall of the heat exchange tank and the side wall of the tank body and are located outside the tank body.

5. The natural gas liquefaction device according to claim 4, wherein, It also includes a raw natural gas purification device. The raw natural gas purification device is connected to the suction device through an intake pipe and is also connected to the gas outlet of the raw natural gas purification device and the gas-liquid separator.

6. The natural gas liquefaction device according to claim 4, characterized in that: The heat exchange tube is arranged in an S shape inside the heat exchange tank.

7. The natural gas liquefaction device according to claim 4, characterized in that: Cold water is injected into the tank body to assist heat exchange.

8. The natural gas liquefaction device according to claim 4, characterized in that: A pressure sensor and a temperature sensor are also arranged inside the heat exchange tank.

9. The natural gas liquefaction device according to claim 4, characterized in that: The heat exchange tank is made of copper.

Images