The utilization and development of natural gas are crucial for optimizing our country's energy structure and advancing ecological civilization. Representatives from the National Development and Reform Commission, the Ministry of Environmental Protection, the Ministry of Finance, and other ministries, as well as from State Grid Corporation and the five major power groups, three major oil companies, gas enterprises, the Development Research Center of the State Council, and various research institutions and professional trade associations, among others, have engaged in discussions to contribute their wisdom to promoting the use and development of natural gas in our country.

One of the advantages of natural gas - safety

The gas density of natural gas is half that of air, with compressed natural gas being lighter than air, highly volatile, and not easily explosive. Methane, ethane, and propane in natural gas are inherently non-toxic. In terms of safety, pipeline gas is superior to bottled gas. This is because pipeline gas employs a centralized storage and supply management method at gasification stations, avoiding the safety risks associated with the dispersed storage of bottled gas, liquefied natural gas tanks, and self-use. The indoor pressure of pipeline gas is only 1/130 of that of tap water and 1/170 of bottled gas pressure. The storage capacity of the gas pipeline itself is very small, approximately 1/3000 of bottled gas when calculating the indoor pipeline length of 12 meters per household. In case of leaks or fires due to other reasons, simply closing the main valve or the unit riser valve indoors can cut off the gas supply and eliminate the danger. In contrast, in similar situations, it is difficult to effectively close or remove the oil liquefied gas cylinder, which can easily lead to explosions.

Second advantage of natural gas - Economic

Economical and cost-effective is one of the advantages of natural gas, which is also a reason for the rapid nationwide popularity of pipeline natural gas. Compared to other fuel prices in the market for the same usage volume (calorific value), using pipeline natural gas can save at least 25% to 35% in monthly costs. This not only eliminates the expenses of purchasing and regularly inspecting steel cylinders but also reduces the costs and hassle associated with transporting and replacing liquefied gas in daily life. The cost of using natural gas is more than 35% cheaper than electricity, and about 25% to 35% cheaper than diesel or heavy oil. The third advantage of natural gas – environmental friendly. Natural gas is composed of 98% methane, which is a simple molecule (CH4) consisting of one carbon atom and four hydrogen atoms.

Natural gas is widely recognized as a clean, environmentally friendly, and safe high-quality energy source. After liquefaction, its volume is reduced by approximately 600 times, which greatly benefits storage. Storage of liquefied natural gas (LNG) is done using atmospheric pressure and low-temperature tanks. Let's discuss the unique features of these LNG storage tanks.

What are the special requirements for LNG low-temperature storage tanks?

1.Low-temperature resistance

At atmospheric pressure, the boiling point of liquefied natural gas (LNG) is -160°C. LNG is stored at low temperatures and atmospheric pressure, lowering the natural gas temperature below its boiling point. This operation maintains the storage tank's pressure slightly above atmospheric, which compared to high-pressure, ambient-temperature storage, significantly reduces the tank wall thickness and enhances safety performance.

Therefore, LNG requires storage tanks with excellent low-temperature resistance and superior insulation properties.

2.High safety requirements

Due to the storage of low-temperature liquids inside the tank, in the event of an accident, the refrigerated liquid would volatilize in large quantities, with the vaporization amount being approximately 300 times that of the refrigerated state, forming explosive gas clouds in the atmosphere.

Therefore, standards such as API and BS require double-walled tank structures, employing containment concepts. In the event of a leak in the first layer, the second layer can completely seal off the leaked liquid and evaporated gases, ensuring storage safety.

3.Special Material

The inner罐wall requires low-temperature resistance, commonly using materials like 9Ni steel or aluminum alloy, while the outer罐wall is pre-stressed reinforced concrete.

4.Thermal insulation measures are strict

The tank must have excellent insulation properties, filled with high-performance insulation material between the inner and outer tanks, to maintain an internal temperature of -160℃. The insulation material at the bottom of the tank must also have sufficient pressure-bearing capacity.

5.Excellent seismic performance

The seismic requirement for general buildings is to crack but not collapse under specified seismic loads. To ensure the safety of storage tanks under accidental loads, they must have good seismic performance. For LNG tanks, it is required that they neither collapse nor crack under the specified seismic loads.

Therefore, the selected construction site generally avoids seismic fault zones, and seismic tests must be conducted on the storage tanks before construction. This is to analyze the structural performance of the tanks under dynamic conditions, ensuring that the tank body remains undamaged under the given seismic intensity.

6.Strict construction requirements

The tank welds must undergo 100% magnetic particle testing (MT) and 100% vacuum leak testing (VBT). Strict selection of insulation materials is required, and the prescribed procedures must be followed during construction. To prevent concrete cracks, post-tensioned prestressed construction is used uniformly, with strict control over the verticality of the tank walls.