Process and method for producing liquefied natural gas

Abstract

The invention relates to the field of liquefied natural gas, and relates to a process and a method for producing liquefied natural gas. The method comprises the following steps: S1, primary compression of natural gas; the method comprises the following steps: performing primary compression on natural gas extracted from a natural gas field, and if the initial pressure of the natural gas is less than 4.6 MPa, increasing the pressure to 4.6 MPa; the temperature is controlled to be 20-50 DEG C, the flow is controlled to be 3-10 m / h, and the natural gas is subjected to primary compression; s2, flash evaporation; the pressure reduction rate of a flash evaporator is controlled to be 1-10 MPa / s, the minimum pressure value is larger than 4.6 MPa, the temperature is-30 DEG C to-40 DEG C, the primarily compressed natural gas is introduced into the flash evaporator, and the flash evaporation time is 20-40 s; s3, condensing; the cooled natural gas enters a condenser, the temperature in the condenser ranges from-100 DEG C to-160 DEG C, the condensation time ranges from 30 s to 2 min, and the natural gas is condensed to be in a liquid state; s4, storing; and storing the condensed liquefied natural gas. According to the invention, a complex refrigerant fluid circulating system and a control process are omitted, the equipment cost and the maintenance difficulty are reduced, and the method has the advantages of being suitable for large-scale production, simple in process and environment-friendly.

Description

Technical Field

[0001] The present invention relates to the field of liquefied natural gas, and more particularly, to a process and method for producing liquefied natural gas. Background Art

[0002] Natural gas is a naturally occurring mixed gas, mainly composed of methane (CH4), but also contains small amounts of hydrocarbons such as ethane, propane, butane, as well as nitrogen, carbon dioxide and other components. It usually exists in natural underground gas fields.

[0003] Natural gas is a highly efficient fuel that generates high energy when burned. It can be widely used in power generation, heating, industrial production and other fields. Compared with coal and oil, natural gas produces less pollution when burned and is a relatively clean energy source. At the same time, natural gas also has the advantages of abundant reserves and convenient transportation, and has gradually become an important fuel worldwide.

[0004] In order to make storage and transportation more convenient, natural gas is generally converted into liquid form through special processes. The existing natural gas liquefaction processing methods include the following two: 1. Cooling-compression cycle method: This method compresses natural gas and then cools it through a multi-stage cooler to reach liquefaction temperature and liquefy the natural gas. This method is relatively mature and suitable for small and medium-sized production facilities. However, it has high energy consumption and requires a large amount of cooling medium and corresponding cooling equipment, making it unsuitable for large-scale production and having a significant impact on the environment.

[0005] 2. Refrigeration fluid circulation method: This method first compresses natural gas and then circulates it through a refrigerant. The cycle involves compression, condensation, and expansion of the refrigerant, thereby cooling and liquefying the natural gas. This method offers high liquefaction efficiency and relatively low energy consumption, making it suitable for large-scale production facilities. However, the circulation system and control process used in this method are relatively complex, resulting in high equipment costs.

[0006] Therefore, the present application aims to provide a simpler method for producing liquefied natural gas with lower costs. Summary of the Invention

[0007] In order to improve the problems of high cost and complex process of liquefied natural gas in related technologies, the present application provides a process and method for producing liquefied natural gas.

[0008] The present application provides a process and method for producing liquefied natural gas, which adopts the following technical solutions: A process and method for producing liquefied natural gas, comprising the following steps: S1, natural gas primary compression The natural gas extracted from the natural gas field is subjected to primary compression. If the initial pressure of the natural gas is less than 4.6 MPa, the pressure is increased to 4.6 MPa. The temperature is controlled at 20-50°C and the flow rate is 3-10 m³ / h to perform primary compression on the natural gas. S2, flash evaporation The pressure drop rate of the flash evaporator is controlled to be 1-10 MPa / s, the minimum pressure is greater than 4.6 MPa, the temperature is -30--40°C, and the primary compressed natural gas is passed into the flash evaporator with a flash time of 20-40 seconds. S3, condensation The cooled natural gas enters the condenser, where the temperature is -100~-160℃ and the condensation time is 30s~2min, condensing the natural gas into liquid form. S4. Storage The condensed liquefied natural gas is stored.

[0009] In a specific embodiment, step S1 is performed in a screw compressor.

[0010] In a specific embodiment, the flash evaporator selected in step S2 is a TD42 flash evaporator.

[0011] In a specific embodiment, the condenser in step S3 is a shell and tube condenser.

[0012] In a specific embodiment, in step S3, the condensation medium is liquid nitrogen.

[0013] In a specific possible implementation scheme, in step S4, double-walled steel storage tanks are selected to store liquefied natural gas.

[0014] This application has the following beneficial effects: 1. This application utilizes a combination of primary compression and flash evaporation, which reduces energy consumption compared to cooling compression cycles and refrigerant circulation methods. The primary compression process results in relatively little energy loss, while the flash evaporation process produces a strong cooling effect through rapid expansion, reducing the need for large amounts of cooling medium.

[0015] 2. Compared with the refrigeration liquid circulation method, the process of this application is simpler. This application omits the complex refrigeration liquid circulation system and control process, reducing equipment costs and maintenance difficulties.

[0016] 3. This application is suitable for small and medium-sized production facilities, but can also be expanded to large production facilities. By controlling the pressure reduction rate of the flash evaporator and the temperature and time of the condenser, the liquefaction process can be flexibly adjusted to meet the production needs of different scales.

[0017] 4. Compared to the cooling compression cycle method, this application reduces the use of a large amount of cooling medium, thereby reducing the impact on the environment. At the same time, this application does not require a complex refrigerant circulation system, reducing potential refrigerant leakage and damage to the ozone layer. Implementation Method

[0018] The present application is further described in detail below with reference to the embodiments. Example Example

[0019] This embodiment provides a process and method for producing liquefied natural gas, comprising the following steps: S1, natural gas primary compression The natural gas extracted from the natural gas field is subjected to primary compression. If the initial pressure of the natural gas is less than 4.6 MPa, the pressure is increased to 4.6 MPa. The temperature is controlled at 20°C and the flow rate is 3 m³ / h for primary compression of the natural gas. S2, flash evaporation The pressure drop rate of the flash evaporator is controlled to be 1 MPa / s, the minimum pressure is 4.6 MPa, the temperature is -40°C, and the primary compressed natural gas is passed into the flash evaporator for a flash time of 20 seconds. S3, condensation The cooled natural gas enters the condenser, where the temperature is -100°C and the condensation time is 30 seconds, condensing the natural gas into liquid form. S4. Storage The condensed liquefied natural gas is stored.

[0020] In step S1, a screw compressor of model MCL805 is used to perform preliminary compression on the natural gas; in step S2, a flash evaporator of model TD42 is used to perform flash evaporation on the natural gas; in step S3, a shell and tube condenser is used to condense the natural gas, and the condensing agent is liquid nitrogen; in step S4, a double-walled steel storage tank is used to store the liquefied natural gas. Example

[0021] S1, natural gas primary compression The natural gas extracted from the natural gas field is subjected to primary compression. If the initial pressure of the natural gas is less than 4.6 MPa, the pressure is increased to 4.6 MPa. The temperature is controlled at 30°C and the flow rate is 5 m³ / h for primary compression of the natural gas. S2, flash evaporation The pressure drop rate of the flash evaporator is controlled to be 3 MPa / s, the minimum pressure is 5 MPa, the temperature is -32°C, and the natural gas after primary compression is passed into the flash evaporator with a flash time of 25 seconds. S3, condensation The cooled natural gas enters the condenser, where the temperature is -150°C and the condensation time is 50 seconds, condensing the natural gas into liquid form. S4. Storage The condensed liquefied natural gas is stored.

[0022] In step S1, a screw compressor of model MCL805 is used to perform preliminary compression on the natural gas; in step S2, a flash evaporator of model TD42 is used to perform flash evaporation on the natural gas; in step S3, a shell and tube condenser is used to condense the natural gas, and the condensing agent is liquid nitrogen; in step S4, a double-walled steel storage tank is used to store the liquefied natural gas. Example

[0023] S1, natural gas primary compression The natural gas extracted from the natural gas field is subjected to primary compression. If the initial pressure of the natural gas is less than 4.6 MPa, the pressure is increased to 4.6 MPa. The temperature is controlled at 30°C and the flow rate is 6 m³ / h for primary compression of the natural gas. S2, flash evaporation The pressure drop rate of the flash evaporator is controlled to be 6 MPa / s, the minimum pressure is 6 MPa, the temperature is -35°C, and the primary compressed natural gas is passed into the flash evaporator for 30 seconds. S3, condensation The cooled natural gas enters the condenser, where the temperature is -130°C and the condensation time is 1 minute, condensing the natural gas into liquid form. S4. Storage The condensed liquefied natural gas is stored.

[0024] In step S1, a screw compressor of model MCL805 is used to perform preliminary compression on the natural gas; in step S2, a flash evaporator of model TD42 is used to perform flash evaporation on the natural gas; in step S3, a shell and tube condenser is used to condense the natural gas, and the condensing agent is liquid nitrogen; in step S4, a double-walled steel storage tank is used to store the liquefied natural gas. Example

[0025] S1, natural gas primary compression The natural gas extracted from the natural gas field is subjected to primary compression. If the initial pressure of the natural gas is less than 4.6 MPa, the pressure is increased to 4.6 MPa. The temperature is controlled at 40°C and the flow rate is 8 m³ / h. The natural gas is subjected to primary compression. S2, flash evaporation The pressure drop rate of the flash evaporator is controlled to be 8 MPa / s, the minimum pressure is 8 MPa, the temperature is -35°C, and the natural gas after primary compression is passed into the flash evaporator with a flash time of 35 seconds; S3, condensation The cooled natural gas enters the condenser, where the temperature is -120°C and the condensation time is 1.5 minutes, condensing the natural gas into liquid form. S4. Storage The condensed liquefied natural gas is stored.

[0026] In step S1, a screw compressor of model MCL805 is used to perform preliminary compression on the natural gas; in step S2, a flash evaporator of model TD42 is used to perform flash evaporation on the natural gas; in step S3, a shell and tube condenser is used to condense the natural gas, and the condensing agent is liquid nitrogen; in step S4, a double-walled steel storage tank is used to store the liquefied natural gas. Example

[0027] S1, natural gas primary compression The natural gas extracted from the natural gas field is subjected to primary compression. If the initial pressure of the natural gas is less than 4.6 MPa, the pressure is increased to 4.6 MPa. The temperature is controlled at 50°C and the flow rate is 10 m³ / h for primary compression of the natural gas. S2, flash evaporation The pressure drop rate of the flash evaporator is controlled to be 10 MPa / s, the minimum pressure is 10 MPa, the temperature is -30°C, and the primary compressed natural gas is passed into the flash evaporator with a flash time of 40 seconds. S3, condensation The cooled natural gas enters the condenser, where the temperature is -100°C and the condensation time is 32 minutes, condensing the natural gas into liquid form. S4. Storage The condensed liquefied natural gas is stored.

[0028] In step S1, a screw compressor of model MCL805 is used to perform preliminary compression on the natural gas; in step S2, a flash evaporator of model TD42 is used to perform flash evaporation on the natural gas; in step S3, a shell and tube condenser is used to condense the natural gas, and the condensing agent is liquid nitrogen; in step S4, a double-walled steel storage tank is used to store the liquefied natural gas.

[0029] The principles of each step of Examples 1 to 5 are described as follows: S1. Natural gas primary compression: Primary natural gas compression is the process of compressing natural gas extracted from natural gas fields. If the initial pressure of the natural gas is less than 4.6 MPa, it must be raised to 4.6 MPa. The temperature is controlled within the range of 20-50°C, and the natural gas is brought to the required pressure through primary compression. This step increases the natural gas pressure in preparation for the subsequent flash evaporation and condensation processes.

[0030] S2, flash evaporation: Flash evaporation is a process that rapidly vaporizes high-pressure gas by controlling the rate of pressure reduction. In this step, natural gas, after primary compression, enters the flash evaporator, where the pressure is reduced from a high pressure (greater than 4.6 MPa) to a lower pressure by controlling the rate of pressure reduction. Simultaneously, the temperature is controlled within a range of -30°C to -40°C. This causes a portion of the natural gas to rapidly evaporate, forming a gas phase, while the remaining gas becomes a liquid phase, known as liquefied natural gas.

[0031] Condensation is the process of cooling a gas below its critical temperature, converting it into a liquid. In this step, the flashed natural gas enters the condenser. The temperature in the condenser is controlled within a range of -100°C to -160°C, rapidly cooling the natural gas. Due to the low temperature, water vapor and other impurities in the natural gas are condensed into liquid, and the natural gas itself is also cooled to a liquid state.

[0032] S4. Storage: The condensed liquefied natural gas is stored in storage tanks. Double-walled steel tanks have excellent thermal insulation and sealing properties, making them suitable for efficient storage of liquefied natural gas.

[0033] In summary, the present invention increases the pressure of natural gas through primary compression, then liquefies it through flash evaporation. Subsequently, condensation cools the natural gas and converts it into a liquid state, and finally stores the liquefied natural gas in double-walled steel tanks. Compared to the cooling compression cycle and the refrigerant circulation method, the present invention's method can reduce energy consumption. During the primary compression process, energy loss is relatively small, while the flash evaporation process produces a strong cooling effect through rapid expansion, reducing the need for large amounts of cooling medium. Compared to the refrigerant circulation method, the present invention's process is more simplified. The present invention omits the complex refrigerant circulation system and control process, reducing equipment costs and maintenance difficulties. Furthermore, the present invention is suitable for small and medium-sized production facilities but can also be expanded to large-scale production facilities. By controlling the pressure reduction rate of the flash evaporator and the temperature and time of the condenser, the liquefaction process can be flexibly adjusted to meet the needs of production of different scales. Compared to the cooling compression cycle method, the present invention reduces the use of large amounts of cooling medium, thereby reducing the impact on the environment. Furthermore, the present invention does not require a complex refrigerant circulation system, reducing potential refrigerant leakage and damage to the ozone layer.

[0034] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A process and method for producing liquefied natural gas, characterized in that: The steps include: S1, Natural gas primary compression The natural gas extracted from the natural gas field is subjected to primary compression. If the initial pressure of the natural gas is less than 4.6MPa, the pressure is increased to 4.6MPa. The temperature is controlled at 20~50℃ and the flow rate is 3~10m³ / h to perform primary compression on the natural gas. S2, flash evaporation The pressure drop rate of the flash evaporator is controlled to be 1~10MPa / s, the minimum pressure value is greater than 4.6MPa, the temperature is -30~-40℃, and the primary compressed natural gas is passed into the flash evaporator, and the flash time is 20~40s; S3, Condensation The cooled natural gas enters the condenser, where the temperature is -100~-160℃ and the condensation time is 30s~2min, condensing the natural gas into liquid state; S4. Storage The condensed liquefied natural gas is stored.

2. A process and method for producing liquefied natural gas according to claim 1, characterized in that: Step S1 is performed in a screw compressor.

3. A process and method for producing liquefied natural gas according to claim 1, characterized in that: The flash evaporator selected in step S2 is a TD42 flash evaporator.

4. A process and method for producing liquefied natural gas according to claim 1, characterized in that: The condenser in step S3 is a shell and tube condenser.

5. A process and method for producing liquefied natural gas according to claim 1, characterized in that: In step S3, the condensation medium is liquid nitrogen.

6. A process and method for producing liquefied natural gas according to claim 1, characterized in that: In step S4, double-walled steel storage tanks are used to store liquefied natural gas.