(265e) Transient Natural Gas Liquefaction Process Comparison- Dynamic Heat Exchanger Under Transient Changes in Flow

Authors: 
Fazlollahi, F., Brigham Young University
Baxter, L. L., Brigham Young University

In this study two methods for transient modeling of natural gas liquefaction model have been done using Aspen HYSYS Dynamics. Traditional heat exchanger design (THED) and dynamic heat exchanger design (DHED) are investigated. In THED, Single mixed refrigerant (SMR) process has been simulated and optimized with Aspen HYSYS Dynamics. For DHED, new types of heat exchanger design and optimization method; Model predicted control theory (MPCT) have been presented and transient responses have been compared with traditional design. SMR model has been modified and two methanol streams are added to system to regulate flow rate and temperature profiles during transitions. Operating conditions, MR compositions and heat exchanger’s sizing are the same for both designs.  Temperatures, pressures and other operating conditions are perfectly controlled. K-values and U values technique are used to make flowrates and temperature of heat exchanger’s streams steady. LNG and NG flowrates variation have been shown in time for all cases. Natural gas (NG) consumption and Liquefied natural gas (LNG) production have been compared to show the optimality of new design. Temperature profiles are compared and Last but not least, the efficiency graph for both methods are given and compared to show the adjustability of heat exchanger with NG flow rate change in transient mode.