Rapid tuning of a fuel gas saturator control system using Nyquist and bode diagrams

A multivariable controller is designed and implemented for a saturator in a fuel gas process evaluation facility for coal gasification based power plants. The saturator model developed from first principles is represented by a high-order nonlinear state variable dynamic system. The controller is designed so that the closed-loop frequency response is as close as possible, in a least-squares sense, to a desired response. The design method allows the use of a simple controller structure and minimizes interaction in the critical frequency range where the characteristic gains pass near the critical points. The test results describe the operational performance of the control system and offer a practical approach for coordinated control of heat transfer components in a power plant.