Brayton Refrigeration Cycle for Small Scale LNG Plants

Liquefying natural gas is an industrial process of great importance with the current worldwide production capacity of about 300 million tonnes per annum (MTPA).  Natural gas is becoming more popular as a transportation fuel in many locations since it is less costly than gasoline or diesel and, it is environmentally friendlier. For these reasons, in industrialized countries there is an increasing interest in small scale LNG plants producing 0.03 - 0.2 MTPA of LNG. Many successful processes for liquefying natural gas have been developed and widely used in the past. Among these processes, mixed refrigerant (MR) based cycles dominate the large and medium scale LNG plants whereas the Brayton refrigeration cycle is often preferred for small scale LNG plants. MR cycles supply refrigeration by boiling multicomponent mixtures, while Brayton refrigeration cycle supplies refrigeration by expanding vapor and extracting work. This presentation explores, Brayton refrigeration cycles. Topics covered are refrigerant choice (often nitrogen or methane) and cycle options that can significantly improve efficiency.