Principle of liquefaction process
The main component of natural gas is methane, which is in gaseous state at normal temperature and pressure. Liquefied natural gas (LNG) is produced by pre-treating natural gas (removing impurities, carbon dioxide, hydrogen sulfide, etc.) and then deep cooling it using a refrigeration cycle system. Generally, a cascade refrigeration cycle or a mixed refrigerant refrigeration cycle is used to cool the natural gas to about -162°C. At this low temperature, natural gas changes from gas to liquid, and its volume is greatly reduced to about 1/600 of its original gaseous volume. This allows natural gas to be stored and transported more efficiently.
Storage principle
Tank storage: There is a liner inside the LNG cylinder, which is usually made of low-temperature resistant materials (such as stainless steel or aluminum alloy). The liquefied natural gas is stored in this liner. The liner design must ensure that it can withstand the low temperature of LNG and has good sealing to prevent natural gas leakage.
Insulation: There is a vacuum insulation layer between the inner liner and the outer shell of the gas cylinder. This is because heat will vaporize the liquefied natural gas. In order to reduce the heat transfer from the outside to the inner liner, the vacuum insulation layer takes advantage of the fact that vacuum is not easy to conduct heat, effectively preventing heat transfer. In addition, some insulation layers will also contain some high-performance insulation materials (such as pearlite insulation materials) to further reduce the conduction of heat, allowing liquefied natural gas to be stored in a relatively stable low-temperature state. Only a small amount of heat will slowly transfer to the inner liner through the insulation layer, causing the liquefied natural gas to vaporize to a certain extent, and the resulting gaseous natural gas will accumulate in the upper space of the gas cylinder.
Output principle
Liquid phase output: When liquefied natural gas is needed, if the terminal equipment (such as industrial furnaces, LNG vehicle engines, etc.) has the ability to convert liquefied natural gas into gas and use it efficiently, liquefied natural gas can be output through the liquid phase valve on the gas cylinder. For example, in LNG vehicles, liquefied natural gas is transported to the vaporizer near the engine, where it absorbs heat and quickly vaporizes, and then enters the engine for combustion.
Gas phase output: If the terminal equipment can only use gaseous natural gas, then the gaseous natural gas accumulated in the upper space of the gas cylinder is output through the gas phase valve. This method is more convenient in some small application scenarios (such as household gas appliances). When the pressure in the gas cylinder decreases due to the output of natural gas, the vaporization process will be accelerated because the pressure reduction is conducive to the vaporization of liquefied natural gas, thereby ensuring the continuous supply of natural gas until the liquefied natural gas in the gas cylinder is completely vaporized or needs to be refilled.
Pressure control principle
A pressure sensor and a safety valve are installed in the gas cylinder. Under normal working conditions, the pressure sensor monitors the pressure in the gas cylinder. When the pressure increases due to factors such as temperature rise (such as ambient temperature rise or direct sunlight) or liquefied natural gas vaporization, the data is transmitted to the control system. If the pressure is close to the opening pressure of the safety valve, the control system will sound an alarm. Once the pressure exceeds the set value of the safety valve, the safety valve automatically opens, releasing part of the gas to reduce the pressure in the gas cylinder, preventing the gas cylinder from rupturing or other safety accidents due to excessive pressure. When the pressure returns to a safe range, the safety valve automatically closes.
In short, liquefied natural gas cylinders are like a magical energy treasure house. Although its working principle involves complex physical and chemical changes, it stores and delivers clean energy for us in an efficient and safe way. If you want to know the working principle of liquefied natural gas cylinders, you are welcome to follow www.qinengwelding.com !
