Short-Cut Analysis of Pressure Control In Steam Headers

Almost all chemical/petrochemical plants have steam networks to supply power and heating requirements. Good control of steam systems can have important economic implications. In this paper control of pressure in the high pressure header is analyzed. A simple short-cut model is used. The steam system is represented by a third order transfer function with widely separated time constants. This model compares very well with a detailed non-linear simulation and requires only readily available process information. The question of tuning PI controllers for the integrating pressure loop is treated in detail. A root locus analysis is used to develop tuning rules. Typical upsets such as boiler and turbine trips are evaluated for various steam systems. In each case the tuning rules provide very satisfactory control performance.