Time Delay Compensating Control of Flue-Gas Oxygen-Content in FBB

M. Paloranta, I. Benyo, K. Leppäkoski, and U. Kortela (Finland)


energy production, delay-compensation, boilers, control


Flue-gas oxygen-content control is an important way to decrease emissions and increase thermal efficiency in fluidized bed boilers (FBB). Oxygen-content control is also stabilizing the burning process leading to more stable steam and electricity production. The oxygen-content is controlled normally by PI-controller. PI-controller is tuned to have a slow control performance, because of long time delay in the burning process. In this paper, a robust delay compensating controller, filtered Smith-predictor, is used to improve the oxygen-content control performance Delay-compensating controller needs a model of the controlled process. For fluidized bed boilers, an accurate model is impossible to make because of unmeasured variation of fuel properties. The robust stability criterion is used to examine how robust the proposed control system is against modeling errors. Filtered Smith predictor is compared to the PI-controller by simulations.

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