N
atural gas of fossil origin is a mix of gases where the main component is methane, which comprises between 75% - 95% of the mixture volume. The rest of the gases are ethane, propane, butane, pentanes, as well as traces of water, carbon dioxide, nitrogen, hydrogen sulfide, mercury, and others. At the moment, natural gas is the least polluting fossil fuel, and this translates into a lower environmental impact as a result of its high hydrogencarbon ratio in its composition. This means that natural gas has a very important role in the medium- and long-term as the main energy raw material since it will allow the significant reduction of pollutant emissions.
LNG market evolution
Although in 1818 Michael Faraday managed to cool a gas resulting in the gas liquefaction procedure, it was not until the middle of the last century that liquefaction plants began to be developed at an industrial level. The natural gas market has suffered several corrections during the last 50 years, mainly due to the low price of other fuels, but the LNG market remained constant although at a low level in regions such as North America, Asia-Pacific, and the Middle East. In recent years, the LNG trade has significantly grown caused by the reduction in transport and distribution costs and, above all, due to its use for transport itself against dominant fuels in the sector such as gasoline and diesel. The prospects regarding the gas market indicate that the demand might increase by up to 50% by 2035.
Small/mid liquefaction plants
The liquefaction process consists of lowering the gas temperature down to -160˚C, resulting in a phase change from gas to liquid. With this change of state, its volume is reduced by approximately 600 times, making it much more efficient to store and transport. Both for large and smaller liquefaction plants, gas pretreatment is required before the liquefaction process. The objective of this pretreatment is to remove those impurities that could have an impact on the LNG characteristics or could solidify causing significant damage to the equipment making up the liquefaction plant. Specifically, the main impurities that must be removed are the following: � H2O, CO2, and H2S: Cryogenic processes work at much lower temperatures. The water in these conditions either freezes solid or forms methane hydrates (H2O + methane and/or ethane). The CO2 and H2S, along with
Figure 1. FNX liquefaction plant – NBC 2000.
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