Modeling and Optimal Design of Natural Gas Liquefaction and Regasification Processes

Abstract

Natural gas is the worlds fastest-growing fossil fuel, favored for electric power and industrial sectors because of its low carbon intensity and reduced emissions. International natural gas trade is expected to double from 1 trillion cubic meter (tcm) in 2010 to 2 tcm in 2030. Liquefied natural gas (LNG) accounts for a growing share of world natural gas. The core of LNG value chain is the phase change of natural gas that makes it feasible for ship transportation to remote regions. This thesis addresses modeling and optimal design for LNG value chain and it contains two main processes: one is the liquefaction process in the production plant and the other is the regasification process in LNG receiving terminal. These two processes occupy the main parts in the whole in LNG value chain and are worth to be studied in depth. This thesis has five main parts. First, modeling and simulation of a liquefaction plant is conducted. Second part proposes a simulation-based optimization methodology, taking full advantage of commercial simulator in process design step. The methodology is applied to a case study of double-expander process optimization to prove its performance. A novel process design of natural gas liquefaction using nonflammable refrigerants is developed in the third part. Safety issue for floating LNG drives interest in minimization of hydrocarbon refrigerants. A new N2O-N2O-N2 cascade liquefaction process with nitrous oxide for the pre-cooling and condensation section and nitrogen gas for the sub-cooling section is proposed. Lastly, retrofit design scheme is introduced for boil-off gas handling process in LNG receiving terminal.