Natural gas liquefaction is a process that converts natural gas from a gaseous state to a liquid state for easier storage and transportation. The volume of liquefied natural gas (LNG) is only 1/600 of gaseous natural gas, so it can greatly save space and cost. Liquefied natural gas has incomparable advantages over pipeline natural gas in terms of ocean transportation, utilization of gas from remote gas fields, and peak shaving of urban natural gas.
In recent years, my country's science and technology has developed rapidly. Many advanced technologies and equipment have been put into use in the natural gas liquefaction production process. Through the effective application of modern technology, it has played a very positive role in improving the efficiency of natural gas liquefaction. Therefore, based on the actual production and operation of natural gas liquefaction units at home and abroad, an overview of the plant types of liquefied natural gas is given. At the same time, the new natural gas liquefaction process is elaborated in detail, and the characteristics of the equipment are analyzed in depth.
The main types of LNG plants are as follows:
Large land plants: These plants are generally built in areas rich in natural gas resources and can produce large amounts of liquefied natural gas to supply long-distance markets. The scale of this kind of factory is generally more than 1 million tons/year, and it uses multi-stage compression refrigeration cycles, such as mixed refrigerant cycle (MRC), pre-cooled mixed refrigerant cycle (PMC), waterfall cycle (CASCADE), etc. The advantages of this kind of plant are high production efficiency and stable operation. The disadvantages are high investment cost, long construction period and high quality requirements for raw gas.
Small and medium-sized onshore plants: Such plants are generally built in areas where natural gas demand is small or scattered, and can meet local market demand. The scale of this kind of plant is generally between 100,000 tons/year and 1 million tons/year, using single-stage or two-stage compression refrigeration cycles, such as self-expansion cycle (EXPANDER), self-expansion-mixed refrigerant cycle (EXPANDER-MRC) )wait. The advantages of this kind of plant are low investment cost, short construction period, and low quality requirements for raw gas. The disadvantages are low production efficiency, high operating costs, and high energy consumption.
Floating plant: This kind of plant is generally built in an offshore natural gas field. It can directly liquefy the natural gas on the seabed and load it onto ships for transportation to the market. The scale of this kind of plant is generally between 1 million tons/year and 5 million tons/year. It adopts single-stage or two-stage compression refrigeration cycle, such as self-expansion cycle (EXPANDER), self-expansion-mixed refrigerant cycle (EXPANDER-MRC). )wait. The advantage of this kind of plant is that it can develop remote offshore gas fields and reduce the construction of pipelines. The disadvantages are complex technology, high safety risks, and difficult maintenance.
The new natural gas liquefaction process mainly includes the following types:
Nitrogen cycle: This process uses nitrogen as a refrigerant to liquefy natural gas through compression, expansion and heat exchange. The advantage of this process is that it is simple, safe, and reliable. The disadvantage is that it consumes high energy and is suitable for small natural gas liquefaction devices.
Carbon dioxide cycle: This process uses carbon dioxide as a refrigerant to liquefy natural gas through compression, expansion and heat exchange. The advantages of this process are low energy consumption and low refrigeration temperature. The disadvantage is that it is technically difficult and requires high-pressure and low-temperature equipment. It is suitable for small and medium-sized natural gas liquefaction plants.
Magnetic refrigeration: This process uses magnetic materials as refrigerants to liquefy natural gas by changing the magnetic field. The advantages of this process are no noise, no pollution, and no energy consumption. The disadvantages are low technological maturity and low refrigeration efficiency, and it is suitable for micro natural gas liquefaction devices.
The equipment characteristics of natural gas liquefaction plants mainly include the following points:
Compressor: The compressor is the core equipment of the natural gas liquefaction device. It is used to increase the pressure of natural gas and refrigerant to provide power for the refrigeration cycle. Compressor types include reciprocating, centrifugal, axial flow, etc. Choose the appropriate compressor according to process requirements.
Heat exchanger: The heat exchanger is an important equipment in the natural gas liquefaction device. It is used to realize heat exchange between natural gas and refrigerant, reduce the temperature of natural gas, and achieve liquefaction conditions. The types of heat exchangers include plate type, shell and tube type, plate fin type, etc. Choose the appropriate heat exchanger according to the process requirements.
Expander: The expander is the key equipment of the natural gas liquefaction device. It is used to reduce the pressure and temperature of the refrigerant and provide refrigeration effect. The types of expanders include turbine type, screw type, piston type, etc. Choose the appropriate expander according to the process requirements.
Storage tank: Storage tank is a necessary equipment for natural gas liquefaction equipment. It is used to store liquefied natural gas and ensure the stability of supply. The types of storage tanks include spherical, horizontal, vertical, etc. Choose the appropriate storage tank according to the process requirements.
During the production and operation of natural gas liquefaction units, the source and composition of raw natural gas, market demand, and the reasonable selection and optimization of unit types should be fully considered to select the most appropriate natural gas liquefaction process and better promote my country's natural gas liquefaction unit industry. development.
