Ambient conditions can have a significant impact on the overall operation of an LNG plant — particularly when it comes to liquefaction. Among all environmental factors, air temperature typically has the largest effect due to the fact that as it increases, the efficiency of turbines that drive the liquefaction process will decrease. This results in a corresponding decrease in the available power from the turbine, leading to a drop in overall production.
Industrial gas and aero derivative turbines are especially sensitive to temperature fluctuation — exhibiting anywhere from a 0.7 – 1.2% drop in efficiency per rise in degree Celsius (source: Air Products). In most cases, low ambient temperatures are more advantageous when it comes to LNG production; however, it’s important to note that in extremely cold conditions propane compressors may be forced into partial recycle mode, leading to higher specific energy usage.
Air humidity can also affect LNG plants, especially high capacity operations. In most cases, fluctuations in humidity will not produce any substantial changes in production, however, in the case of liquefaction islands driven by single-shaft turbines, any increase in humidity will lead to reduced power. This is typically not an issue with multi-shaft turbines, as their design is able to offset any changes in air density. Increased humidity also increases the heat transfer (i.e., film) coefficient of air, leading to improved performance of air-based exchangers.
Atmospheric pressure has very little impact on LNG plant operation; however, it is worth noting that as pressure increases so does the efficiency of turbines, leading to more available power to drive liquefaction.