Liquefied natural gas (LNG) is a new type of clean energy and has been widely used in China recently, which has promoted the development of LNG in this country. In the development of liquefied natural gas, the storage problem has attracted the attention of all industries. Moreover, China's demand for natural gas is constantly increasing, and some dangerous problems in its storage are gradually emerging. Therefore, it is necessary for relevant personnel to conduct in-depth analysis on the problems existing in the current LNG storage, and formulate corresponding prevention and control strategies based on understanding the risk factors, so as to promote the safe and stable development of LNG.
1. Analysis of basic characteristics of liquefied natural gas
The key component of liquefied natural gas is methane, with a small amount of nitrogen, propane and ethane. The specific composition and content of each component of LNG produced by different factories are different. However, according to the standard regulations of LNG, it can be known that the methane content can not be lower than 76%, but its composition is not pure methane, so it is necessary to analyze its characteristics in specific production and storage, and it can also be processed by computer-related software, so as to realize a further careful understanding of LNG. Liquefied natural gas is usually stored in insulated storage tanks or underground gas storage tanks. The storage of liquefied natural gas will cost a certain amount, and strict safety management is needed in the actual storage process.
2. Analysis of risk factors of LNG in storage
Liquefied natural gas (LNG) is usually stored in double-layer cryogenic storage tanks. LNG is formed by low-temperature liquefaction of natural gas, which has no color, no taste, and is flammable and easy to fry and volatilize.
2.1 The influence of temperature
The temperature will have a great influence on LNG. When the peripheral temperature is relatively high, the pressure inside the tank will rise, which will greatly increase the probability of explosion of liquefied natural gas, and may also lead to leakage of liquefied gas. The leaked natural gas will gasify in a short time, and even combine with air to become an easily explosive gas. Once it encounters a fire source, a serious explosion accident will occur, which will bring casualties and economic losses.
2.2 Impact of storage tanks
In the process of liquefied gas storage, the gas may also be affected by the storage tank. There are the following risk factors related to the storage tank. First, if the grounding device of the storage tank is loose or fails, it will cause static electricity accumulation in the tank, causing the discharge of the tank, which will affect the liquefied natural gas. In case of leakage, even explosions and fires will occur. Second, if the tank wall exceeds the actual service life, it will cause corrosion of the tank wall, which will obviously reduce the thickness, and may also cause damage to a certain part of the tank, with poor anti-corrosion performance, causing more easily leakage. Third, the lack of pressure gauge in the storage tank, or the failure of the pressure gauge, weaken the ability of staff to realize real-time observation of the air pressure in the storage tank, and can not better judge the influence of the outside temperature on the inside tank, nor can they understand the actual situation of the tank that whether there is high pressure or differential pressure inside, and this situation greatly increases the risk.
2.3 Impact of storage area
There is another risk factor in the storage process that will be affected by the storage area. The factors related to the storage area are as follows: First, there are no corresponding protective walls in the storage area. Once there is a natural gas leakage, the fire or explosion can not be effectively alleviated without the protective walls, and the losses caused can not be effectively prevented. Secondly, the basic equipment in the storage tank is inadequate, or the design of the support is not reasonable enough, and there is no corresponding anti-freezing effect, so it is easy to be deformed and damaged during storage. Furthermore, the storage tank will be toppled, thus causing greater losses and increasing the risk factor. Third, the explosion-proof area is a safety line of defense. If the equipment in the explosion-proof area is not complete, and the related design is unreasonable, or the corresponding explosion-proof tools are not equipped, the actual function of the explosion-proof area will be greatly reduced, thus increasing the risk of storage.
3. Safe storage measures of liquefied natural gas
3.1 Strengthen stratified detection of liquefied natural gas in storage tanks. Stratification of natural gas in storage tanks is the main cause of natural gas tumbling. Therefore, in specific operations, it is necessary to focus on reasonable detection of natural gas stratification and take corresponding preventive measures. Usually, the stratification of liquefied natural gas can be detected in the following ways. First of all, set corresponding temperature measuring points according to the specific height of natural gas in the storage tank, and its vertical spacing needs to be less than two meters. Usually, when the temperature difference reaches about 14℃, it is easy to roll over. Secondly, reasonably detect the density difference between the newly poured liquefied natural gas and the natural gas remaining in the tank, or combine the calorific value difference between the two to detect. Once the difference is large, it is easy to roll over.
3.2 Prevent and control the stratification and rolling of LNG in the storage tank.
When liquefied natural gas is injected into the storage tank, during the filling process, liquefied natural gas can be injected directly from the upper nozzle, or it can be injected from the bottom by inserting a pipe from the top. The specific use mode can be determined by combining the different specific gravity of natural gas. Generally, in order to avoid stratification or tumbling of liquefied natural gas in storage tanks, heavy natural gas is injected from above, while light natural gas is injected from below. At the same time, the low-pressure pump of the liquefied natural gas can also be used to circulate the natural gas in the tank in the upper or lower part, which can effectively avoid stratification or tumbling. A ring-mounted nozzle is arranged at the top of the storage tank. Before filling liquefied natural gas, a small amount of liquefied natural gas is used to precool the storage tank. This can prevent the storage tank from experiencing excessive stress or a large amount of evaporation of liquefied natural gas during actual filling. This design has the characteristics of high safety.
3.3 Adopt corresponding safety measures.
Relevant personnel working in storage need to have a deep understanding of the characteristics of liquefied natural gas, as well as a detailed understanding of various risk factors that are easy to occur in it. Besides, they need to store it scientifically and reasonably in combination with specific storage conditions and set the temperature, flow rate and pressure reasonably. In addition, alarm devices for high temperature and high pressure can be added to strengthen the inspection and supervision of the inside of the storage tank, so as to ensure that the equipment and pipelines in the whole storage process are kept in good condition. Check the tanks accordingly to ensure that the instruments, alarm devices, instruments and grounding devices in LNG tanks are well installed, so as to ensure the safe storage of tanks and minimize accidents caused by tank factors.
4. Concluding remarks
There are many safety factors in the process of LNG storage. Therefore, it is necessary to strengthen the analysis of various risk factors, the professionalism and standardization of storage, and minimize the storage risk. Formulate corresponding safety measures to prevent accidents and reduce risks. At the same time, we should enhance our own safety awareness and carry out safety management in order to realize the storage safety of liquefied natural gas.