Reasons and Steps for Precooling LNG Loading Arms
LNG is a low-temperature, flammable, and explosive medium, and precooling is a critical step before an LNG station enters operation. Before use, low-temperature facilities in the station must undergo various inspections and tests to identify and resolve potential hazards in advance, ensuring safe commissioning. Let's explore the reasons and steps for precooling LNG loading arms.
Ⅰ. Main Reasons for Precooling LNG Loading Arms
Volume Reduction
LNG is liquid at normal temperature but has a relatively large volume. Precooling LNG to near its boiling point (approximately -162°C) can significantly reduce its volume to about 1/600 of that of compressed natural gas (CNG). This volume reduction is highly beneficial for storage and transportation, saving space and reducing transportation costs.
Heat Loss Minimization
The temperature difference between LNG at normal temperature and the surrounding environment is significant, leading to heat transfer and loss. Precooling LNG to near its boiling point reduces this heat loss, improving the efficiency of storage and transportation.
Gasification Prevention
LNG partially gasifies at normal temperature, forming vapor-phase LNG. This not only increases system pressure but also causes losses. The precooling process maintains LNG in a liquid state, reducing gasification and avoiding excessive system pressure and losses.
Ⅱ. Specific Steps for Precooling LNG Loading Arms
Preparation Phase
Inspect the integrity of the loading arm and related equipment to ensure no leaks or damage.
Pressure Reduction and Filtration
Before entering the loading arm system, LNG passes through a pressure relief valve to reduce its pressure and undergoes coarse filtration and desulfurization to remove impurities and sulfides.
Heat Exchange
After entering the precooling loading arm, LNG gradually reduces its temperature through heat exchange with a coolant (such as liquid nitrogen). The coolant circulates through internal heat exchangers to exchange heat with LNG.
Monitoring and Adjustment
During precooling, closely monitor the temperature and pressure of LNG to keep them within safe ranges. Adjust the flow rate and temperature of the coolant as needed to achieve the desired precooling effect.
Conclusion
Through precooling, LNG achieves significant volume reduction, minimized heat loss, prevented gasification, and stable supply. This process is essential for ensuring the safety and efficiency of LNG storage and transportation operations.
