How to safely store and transport LNG?

Liquefied natural gas (LNG) is a liquid that purifies and liquefies natural gas. When natural gas is in a liquid state, its density is 625 times that of standard methane. In other words, 1 cubic liquefied natural gas is equivalent to 625 cubic meters of natural gas. Therefore, liquefied natural gas is more convenient for transportation and storage than the gaseous form of natural gas. In the LNG industrial chain, storage and transportation are two important links. Natural gas is a flammable and explosive fuel with a low storage temperature, so its storage equipment and transportation tools must be safe and reliable.

Liquefied natural gas storage facility

At normal pressure, the boiling point of liquefied natural gas is about -162 ° C. The storage method is normal pressure and low temperature storage. It is mainly stored in atmospheric pressure vault cryogenic storage tanks. It can be divided into above ground tanks, semi-base tanks and underground tanks according to the setting method. .

The most common type of above-ground tank is a double-layer metal can, that is, the outer layer is a carbon steel outer casing, the inner layer is a nickel-containing steel plate of 9%, and the inner and outer ring-shaped design is filled with a nitrogen-filled perlite heat insulating layer. A semi-underground tank refers to a tank between the ground and the ground. This type of storage tank does not require the construction of a berm around it, and it has the advantages of both above-ground and underground storage tanks. Part of the semi-underground tank adopts the inner tank as the steel plate containing 9% nickel and the concrete construction of the outer tank. Underground tanks are usually filled with high-strength concrete, the steel roof is prefabricated and the inner wall is made of stainless steel. Tanks can also be categorized by capacity, insulation, shape and material of the tank. The storage capacity of small storage tanks is 5~50m3, which is often used in gas liquefaction stations, LNG vehicle filling stations, etc. Medium-sized storage tanks have a capacity of 50-100m3, which are often used in satellite liquefaction plants, industrial gasification stations, etc.; ~1000m3, commonly used in small liquefied natural gas production facilities; large storage tank capacity of 10,000 ~ 40000m3, commonly used in basic load and peaking type liquefaction plant; extra large storage tank capacity of 40,000 ~ 200,000 m3, commonly used in LNG receiving stations.

Road safe transportation of LNG

Liquefied natural gas transportation cannot be borne by individuals. It must be a cargo company with certain safety transportation qualifications to undertake the responsibility of transporting LNG. The transportation company must have the safety transportation license approved by the relevant department for the transportation of LNG. Only on the road can be transported.

The road transportation mode of liquefied natural gas is currently the most common mode of transportation of liquefied natural gas. This mode of transportation has relatively low technical requirements and transportation costs are not particularly high, but the requirements for safe transportation are high. The carrier should conduct an early investigation of the route taken by the LNG transport tanker, and try to avoid the environment of many prosperous people such as urban areas and schools. Conduct safety assessment of the roads taken by LNG transport tankers and formulate corresponding emergency accident handling plans. The transportation center of the carrier shall conduct full monitoring of the transportation process of the LNG transportation tanker.

The tanker used for LNG transportation must be a vehicle produced by a regular manufacturer and has a safe transportation mark. The safety inspection of the vehicle should be carried out before each LNG transport tanker, especially the key parts such as tanks and valves. After the item is checked, the vehicle can be allowed to go on the road, and the whole process is tracked during the transportation process, and the driver is scheduled to report the safe running condition regularly.

Carriers should employ drivers with qualified and safe driving experience to conduct transportation and provide safety accident training to drivers in advance, requiring drivers to be familiar with the nature of LNG and the measures to be taken after an accident. In the event of liquefied natural gas leakage or spontaneous combustion, the fire-fighting equipment shall be used for the first time, and the company's management personnel and the local public security organs shall be promptly filed, and the police shall promptly report the accident and properly handle the accident to prevent the situation from expanding to the out-of-control scope.

Pipeline safe transportation of LNG

Liquefied natural gas pipeline transportation is a relatively complicated system involving safety, corrosion prevention, quality control and many other aspects. Compared with the gas pipeline, the same volume of natural gas is transported. The diameter of the LNG pipeline is much smaller, and the pipeline must be made of low-temperature insulation material with good performance.

Liquefied natural gas is used as a liquid product for long-distance pipeline transportation. Its transportation technology is similar to that of crude oil heating and transportation. It is necessary to build a liquefied natural gas pressurized pumping station and cooling station along the pipeline. The pipeline entering the pipeline is a saturated liquefied natural gas liquid. Due to the influence of the temperature along the pipeline, the liquefied natural gas is easily heated, and some of it will be vaporized, resulting in two-phase flow in the pipeline, which not only increases the resistance along the line, but also generates gas segments. Plug flow phenomenon, seriously affecting the pipeline's conveying capacity and safe operation. Therefore, for cryogenic liquid delivery pipelines, especially long-distance pipelines, to prevent liquid vaporization, liquid single-phase flow must be achieved. The method for preventing gasification of liquefied natural gas requires a dense phase transport process, that is, the operating pressure of the pipeline is controlled above the critical condensing pressure, and the fluid temperature in the pipeline is controlled below the critical condensing temperature, so that the pipeline operating condition is in the dense phase of the liquid phase. Area.

In addition, in order to reduce the temperature rise of LNG caused by flow friction and over-pump shear, in addition to the construction of the pressurization station, the long-distance LNG pipeline needs to be provided with a cooling station at a certain distance, and the pressurization station and Cooling stations are built together, so-called cold pumping stations, for construction and management.

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