LNG ship, referred to as "LNG ship". Refers to the "ship" specialized in transporting liquefied natural gas.
Brief introduction of LNG carrier:
LNG Carrier, or LNG carrier, is a kind of liquid carrier specially designed for transporting LNG. It is known as the "crown jewel" of world shipbuilding, and only 13 shipyards in the United States, China, Japan, South Korea and a few European countries can build it. With the growth of LNG market, the number of LNG carriers has also increased rapidly.
Typical freight cycle:
A typical freight cycle begins with "no natural gas" and the cargo hold is filled with air, so the cargo hold and pump can be maintained. Natural gas cannot be directly loaded into the cargo hold, because the existence of oxygen makes the cargo hold explosive. In addition, a sharp drop in temperature will damage the cargo hold.
First, the cargo hold must be inerted with inert gas. At this time, the oxygen in the air is consumed by diesel combustion and replaced by carbon dioxide (CO2), and carbon dioxide is blown into the container until the oxygen is less than 4% and it is in a dry gas environment. This avoids the danger of explosive gas in the container.
Secondly, the ship enters the port for gasification ("refueling") and cooling ("cooling"), but it still cannot be directly loaded into the cargo hold: CO2 will freeze the pump and cold shock will damage the pump column of the container.
After loading on the ship, LNG is sent to the main evaporator along the spray line, where it is gasified, heated to about 20 C (68 F) in the heater, and then blown into the container to replace the inert gas. Until all CO2 gas in the container is replaced and released into the atmosphere. Once the hydrocarbon composition reaches 5% (the lower limit of methane combustion), inert gas is guided to the shore for combustion through pipelines and high-power compressors, so as to avoid the accumulation of a large amount of hydrocarbon gas with explosion danger around the ship when it is directly discharged into the atmosphere.
The cargo hold of the ship is filled with gas (mainly methane) and is at room temperature.
The next step is cooling. Liquid natural gas is injected into the cargo hold through the nozzle, and then gasified while cooling the cargo hold. These excess gases are also brought ashore for re-liquefaction or burned in the Flame Towers. When the container cools to about. At140 c, a large amount of LNG can be loaded.
A large amount of liquefied natural gas is pumped into the cargo hold of the ship from the onshore storage tank. The replaced gas is led to the storage tank on the shore by a high-power pump. Until it is filled to 98.5% of the volume (to avoid thermal expansion and gasification of the cargo hold).
The ship sailed for the unloading port. Various gasification management strategies can be adopted in navigation. The gasified gas can be used for boiler combustion of ship steam turbine, and can also be re-gasified and injected into cargo hold. It depends on the design of the ship.
At the unloading port, LNG is pumped into onshore storage tanks. When the cargo hold is empty, it is full of gas injected from the shore or gasified on the LNG evaporator on board. Some ships can pump out as much liquefied natural gas as possible, and some ships are designed to leave a little heel.
When all the goods are pumped ashore, the cargo hold will be heated to ambient temperature and filled with natural gas at normal temperature.
If a ship needs to enter a natural gas-free state, it must first heat the cargo hold to normal temperature with gaseous natural gas, and then replace the natural gas in the cargo hold with inert gas. When there is no methane in the cargo hold, dry air is used to replace inert gas until it becomes a condition for people to enter work.