(147c) Steam System Control and Optimization

Control of the overall steam system in a refinery or a large petrochemical plant can be one of the most difficult automation challenges, yet one of the most important.  In many plants the steam usage will be 40% or more of the total energy use at the site.  There will normally be multiple steam headers at different pressure levels, each with multiple users and suppliers.  Demand at each level is changing and changes in one header can induce disturbances in the others.  The many users and producers distributed widely around the site with local controls further complicating coordination.  There are also multiple control objectives for the steam system with differing priorities.  Older plants frequently have steam systems that have been enlarged and modified frequently with limited overall planning leading to many opportunities for improvement. Some required measurements and controllers to implement improvements are commonly either missing or underperforming.  Significant steam can be wasted through uncoordinated operation and the response to large disturbances such as equipment trips is often unsatisfactory. Complicating the operation further are the strong interactions among the steam, power, fuel and hydrogen systems – disturbances in one often propagate to the others.  Current and pending environmental emission regulations place additional constraints on the flexibility required to respond to disturbances. Improved automation and optimization can provide significant benefits and an improved capability to balance the competing demands of energy reduction, meeting environmental constraints, and satisfying operational needs.