LNG is liquefied natural gas, used as fuel that cleaner than oil fuel. Natural gas is processed and liquefied to be liquid. Why must it change to liquid? Because gas distribution using pipeline is restricted by distance.
Many gas sources are located far from users. To reach far users, LNG is sent by tanker. Beside that, gas volume in liquid phase is 600 times less than gas volume in vapor state. So liquid phase can reduce space for LNG distribution.
Liquefaction is a cryogenic system, due to natural gas cooling to below boiling point which is about -160 degree Celcius. LNG is stored at atmospheric pressure in a tank that has double wall and insulated to prevent boil off gas. Before sent to customer, LNG is reheated so can back to vapor phase.
Process steps to change natural gas to LNG are:
Acid Gas Removal, to remove acid components such as Carbon Dioxide and Sulfur that corrosive to the material and will also freeze while liquefaction process. Usually, Amine Treating Unit is used to remove this acid component.
Dehydration, to remove water that also corrosive and freeze while liquefaction process. Usually, industry uses molecular sieve to remove water.
Mercury Removal, to remove mercury component that can damage alumunium material. Usually aluminium is used as cryogenic heat exchanger material. To remove mercury, a bed that sulfur impregnated, carbon activated, and non-regenerative is used in industry.
Heavier components removal, to prevent solidification of this component by using condensation and distillation process.
Liquefaction, to cool gas to below its boiling points by using heat exchanger. Usually use propane and mixed refrigerants (N2, CH4, C2H6, and C3H8) as cooling medium. Refrigeration cycle is used in this liquefaction process.
N2 rejection, to remove N2 component from LNG because N2 is still in gas phase at the natural gas boiling point (not change to liquid phase).
Storage in LNG tanks and loading to tanker.
Below is a simple diagram of LNG Process:
- LNG Handout Slide by Aday Wakhid Nurhidayat & Irfa Nauli - Tripatra
- DMAN-TPE-ENGPRO-006 LNG Plant Manual
- Project Description: LNG Plant by Arrow LNG Plant
credits: Nika Yunitri