(170c) An Automated Main Cryogenic Heat Exchanger Cooldown Technology

During a start-up or a re-start of a natural gas liquefaction plant, the main cryogenic heat exchanger (MCHE) is cooled from ambient or precooling temperature to a temperature as low as -160 ^oC at the cold end. Typically, this is a manual process, involving the manipulation of several process variables. An automated cooldown process has been developed that simplifies such cooldown operations, allowing the MCHE to be cooled automatically with minimal operator intervention. This allows the plant to reach normal operation quicker and smoother, which helps increasing plant availability and reduce wasteful flaring during start-ups.

Tailored to fit various liquefaction cycles, the automated cooldown process can be configured and implemented in existing control systems using conventional controller and interlock logic. This technology has been evaluated in depth for various MCHE cooldown scenarios using Air Products’ advanced dynamic simulation models and tools.

This presentation will describe the theory and control scheme for adjusting the key process variables in order to achieve a quicker and smoother start-ups, reduced off-spec LNG production and flaring, and minimized thermal stress on the liquefaction equipment.