Modelling and Advanced Control of Industrial Wood Waste Boilers

This paper describes recent work to develop an improved approach to control of wood-waste fired boilers, and, in particular, bark-fired boilers commonly in operation in the pulp and paper industry. A brief review of the process and control requirements and common control methods currently employed is followed by a discussion of development of a first-principles boiler model suitable for use in development of a robust controller. A simple nonlinear model for the boiler is developed and used for designing a robust controller that offers better performance in terms of tracking the desired reference point in the face of uncertain variations in the system parameters. The objective of the proposed controller is to increase the responsiveness to load changes, reduce the variability of controlled parameters, and improve efficiency of the boiler (reducing fuel consumption). With hundreds of these boilers in operation at large pulp, paper, and paperboard mills in the U.S., potential net energy savings through efficiency improvement and reduced fuel consumption are substantial, with likely side benefits of reduced emissions and possible reapplication of developments to fossil-fired electric utility boilers, waste incinerators, hog fuel, and biomass boilers.