Operational characteristics of propane-mixed refrigerant liquefaction process for application to 30 kg/h-scale LNG plant: Mixed refrigerant supply and its effect on natural gas temperature

Abstract

For stable LNG production, the feasibility study of the LNG liquefaction process control logic and the operational characteristics is to be performed before its implementation in actual plant construction where natural gas is cooled down below–160°C. Therefore, it is imperative to understand how the controlled variables are influenced by the manipulated variables for the best process control strategy. In this study, 30 kg/h-bench scale natural gas liquefaction process was optimized by using Propane pre-cooled mixed refrigerant (C3MR) process. Variation of the temperature in the propane refrigerant, mixed refrigerant and the natural gas was studied in response to refrigerant flow rate to assess the effect of manipulated flow rate of natural gas on the controlled variables. Furthermore, the effects of the three manipulated variables on the controlled variables were examined, with major emphasis on analyzing the effect of the natural gas flow rate on the temperature of refrigerant. Each controlled variable is not independent, but closely related to one another. However, some controlled variables displayed relatively larger sensitivities to variation of certain manipulated variables.