When it comes to natural gas liquefaction, selecting the right machinery to drive refrigeration compressors is critical. There are generally four types of drivers LNG operators can choose from, each of which possesses unique characteristics that make it more or less appropriate depending on the application. They are:
Gas Turbines – Over the past two decades, large gas turbines have been the driver of choice for liquefaction operations. They possess high thermal efficiency (up to 39%) and are available in a broad range of sizes, which makes them suitable for virtually any train capacity. One drawback of industrial gas turbines is that they cannot be started from settle-out condition and in some cases may require the use of starter motors. With high fuel consumption, they often are associated with high emissions.
Aeroderivative Gas Turbines – Aeroderivative gas turbines (or AGDTs) offer a higher thermal efficiency than industrial gas turbines. This leads to less fuel consumption and fewer emissions. They are also smaller and lighter, making them a particularly popular solution for offshore LNG applications. Multiple aeroderivative turbines have to be run in parallel to achieve the same power output as industrial units, and for this reason they may not be the best option for high-capacity trains.
Electric Motors – Electric motors have become an increasingly popular option for natural gas liquefaction in recent years. In addition to eliminating issues associated with air temperature variation, which can be a particular concern with gas turbines, electric motors offer high reliability and are environmentally friendly. This is especially important due to the possibility of a carbon tax in the coming years. One key drawback of electric motors, however, is that they often are associated with a higher CAPEX than gas turbines.
Steam Turbines – Although steam turbines offer high reliability, their low efficiency and substantial requirements with regards to weight and footprint have made them virtually obsolete since the 1990s.