Commercial and in-house simulation software used by industrial practitioners are often of a "black box" type from which derivatives cannot be directly obtained. This paper demonstrates a linkage between available industrial tools and cost reduction opportunity creation through the application of a derivative free optimization technique. An operational liquefier in an air separation unit is used in our study due to the increasing importance of liquid production in the plant's overall operation strategy, and limited evaluation on the operation of such systems under disturbances. Particle swarm optimization is implemented, and optimization results show that when the plant is forced to operate away from its nominal operating/design conditions, it is possible to reduce the unit power consumption by adjusting different operation set-points. A reference map is generated to guide the operation under selected realizations of cooling water temperature, production load and feed conditions. (C) 2016 Elsevier Ltd. All rights reserved.