Authors: Richard Adamson and Mark J. Willis
Multiple air separation units feed a compression network which supplies a major steelmaker with oxygen gas at two pressures. The project aim was to minimize the network running costs whilst reducing product spill and liquid backup usage during steady state and whilst reconfiguring the network. Previous work has modeled the supply network and minimized power consumption using a mixed integer nonlinear programming (MINLP) approach. This paper develops an MILP framework for improved solution speed and further application. Losses during transition between network configurations, such as liquid vaporization and product spill, were reduced by developing a multi-period optimizer and improving site control. The optimizer, when positioned within a production controller, will communicate set points to linear model predictive control interfaces and monitor flows to prompt operators when to alter the network. Coupled further with a scheduler for automated ramping of production units and load management of product liquefiers subject to power price variation, this paper suggests a control hierarchy where profit optimization is possible.
Keywords: Boolean, Compressors, Constraints, Minimization, Network, Nonlinear, Optimization, Power, Scheduling