(167a) New Method to Cooldown Cryogenic Multi-Stream Heat Exchanger

During the startup of cryogenic plants such as Liquefied natural gas (LNG) plants, it is crucial to precisely control the cooldown rate of heat exchangers within the acceptable limits to avoid any damage of heat exchanger mechanical integrity. A novel method, therefore, is developed to control the cooldown of cryogenic multi-stream heat exchanger based on fundamental solutions of time-dependent heat transfer equations.

A vivid demonstration of this new method is provided via dynamic simulations of LNG plant startup scenarios. This method enables an automated control of a flow rate of a natural gas feed stream through the main cryogenic heat exchanger (MCHE) based on one or more process variables. On the other hand, the flow rate of refrigerant streams through the same heat exchanger is controlled by different process variables and set points, and thereby controlled independently of the flow rate of the natural gas feed stream.