A Comparative Study of Direct Expanders Utilizing Different Mixtures of Natural Gas

Abstract

Natural gas refers to a mixture of the hydrocarbons such as Methane, Ethane, Propane, Butane, and other substances. One of the advantages of this fuel is that it emits relatively low amounts of pollutants; therefore, it appears to be more environmentally friendly than coal or oil. Large amounts of natural gas can be transported via pipelines (as pressurized gas) or alternatively in the liquid phase by tankers (as liquefied natural gas or LNG). A liquefaction of natural gas, which produces LNG at around $-162\ ^{\circ}\mathrm{C}$ from ambient temperature, requires a lot of energy. The LNG needs to be regasified and warmed up to ambient temperature to utilize this fuel. During vaporization, some of the energy used for liquefaction can be restored. One of the ways to do that is the application of a direct expander, where part of this “cold energy” can be recovered (to produce the electricity) from this LNG during regasification. Since the composition of the LNG in selected countries (e.g., Algeria, Australia, Malaysia, Nigeria, Oman, Qatar, Trinidad and Tobago) is different, the gasification process and the energy recovery will differ as well. This work presents a comparative analysis of energy recovery from LNG by direct expander with different gas compositions. Comparing the recoverable energies from the typical LNGs used in the listed countries, the most energy can be recovered from the LNG produced in Trinidad and Tobago (which consists of 96.9% Methane, 2.7% Ethane, 0.3% Propane, and 0.1% Butane).