Advantages of LNG

Compared to LPG and CNG, the advantages of LNG as a substitute automotive fuel are as follows:

(1) Clean and environmentally friendly. As a fuel for vehicles, LNG must first be vaporized by a vaporizer, then enter the engine in a gaseous state for complete combustion, resulting in extremely low levels of harmful substances in the exhaust, making it highly clean and eco-friendly.

(2) High calorific value per unit price. Compared to other fuels, LNG offers a lower price and higher calorific value per unit. The low-temperature characteristics of LNG can reduce the temperature of the mixed gas and the combustion temperature, thereby improving the engine's thermal efficiency. Consequently, LNG boasts strong economic and applicability advantages.

(3) High safety. LNG fuel tanks typically operate at a pressure of 1.586 MPa, and automotive LNG storage tanks often use double-layered metal vacuum powder insulation or double-layered metal vacuum spiral insulation structures, which offer high thermal insulation efficiency and can maintain a longer period without releasing gas.

(4) Easy to install. Compared to CNG refueling stations, LNG refueling stations occupy less space, produce no noise, and have lower operating costs. The initial investment for setting up an LNG station is over 30% less than that for a CNG station, and it can reduce daily operation and maintenance costs by more than 50%. As LNG refueling stations are not restricted by natural gas sources and pipelines, they can be designed as fixed stations or skid-mounted units, offering high mobility.

(5) High efficiency in cold energy recovery. LNG is stored and transported at atmospheric pressure and low temperature, releasing a large amount of cold energy during gasification. Currently, the cold energy recovery rate of LNG can reach 50%, with 1 cubic meter of LNG capable of recovering and utilizing 960 to 1095 MJ of cold energy. For instance, a refrigerated truck absorbs an average of 56.16 MJ of heat daily during operation. To absorb this heat, a standard diesel refrigeration system would require about 15 liters of diesel. However, in an LNG vehicle, the cold energy released from the gasification of 143 liters of liquefied natural gas can fully absorb 56.16 MJ of heat, significantly improving economic benefits. Utilizing LNG cold energy for vehicle air conditioning or refrigerated trucks eliminates the need for a dedicated refrigeration system, saving energy and reducing noise pollution caused by mechanical refrigeration.

(6) Wide Range of Application. By adding high-pressure pumps and high-pressure gasifiers to the LNG fueling system, an LNG-to-CNG refueling station can be established, allowing direct conversion from LNG to CNG. This station can fuel both LNG and CNG vehicles, thereby avoiding the need for modifying CNG vehicle fuel systems and eliminating the limitations of CNG stations on natural gas supply and pipelines. The expandability of the LNG fueling system further broadens the applicability of LNG.

Natural gas is widely recognized as a clean, environmentally friendly, and safe high-quality energy source. Once liquefied, the volume of natural gas is reduced by approximately 600 times, which greatly benefits storage. Storage of liquefied natural gas (LNG) is done in atmospheric-pressure, 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

The boiling point of liquefied natural gas (LNG) at atmospheric pressure is -160°C. LNG is stored at low temperatures and atmospheric pressure, lowering the gas temperature below its boiling point. This results in an operational 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 will evaporate in large quantities, with the vaporization amount reaching approximately 300 times that of the original refrigerated state. This can form explosive gas clouds in the atmosphere.

Therefore, standards such as API and BS require double-walled tank structures, utilizing the containment concept. 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 shell requires low-temperature resistance, typically made of 9Ni steel or aluminum alloys, while the outer shell is prestressed reinforced concrete.

4.Thermal insulation measures are stringent

Due to the maximum temperature difference of up to 200℃ between the inside and outside of the tank, the tank must have excellent insulation properties to maintain a temperature of -160℃ inside. High-performance insulation material should be filled between the inner and outer tanks. The insulation material at the bottom of the tank must also possess sufficient pressure-bearing capability.

5.Excellent seismic performance

General building seismic requirements are to crack but not collapse under specified seismic loads. To ensure the safety of storage tanks under accidental loads, they must possess excellent seismic performance. For LNG storage tanks, it is required that they neither collapse nor crack under specified seismic loads.

Therefore, the selected construction site usually avoids seismic fault zones, and seismic tests must be conducted on the storage tanks before construction. This analysis examines the structural performance of the tanks under dynamic conditions, ensuring that the tank does not sustain damage under the given seismic intensity.

6.Strict construction requirements

Tanks must undergo 100% magnetic particle testing (MT) and 100% vacuum leak testing (VBT) for welds. Select insulating materials strictly and follow the prescribed procedures during construction. To prevent concrete cracking, post-tensioned prestressed construction is used uniformly, with strict control over the verticality of the tank walls.