Bubbling Fluid Bed Boiler Emissions Firing Bark and Sludge, 1998 Engineering Conference Proceedings

A Bubbling Bed Boiler in the Pacific northwest has been commissioned and operated for more than two years. The unit fires a combination of mill-generated bark, purchased wood waste, and sludge. The sludge is approximately z/J primary and l/s secondary. The uniqueness of the project is the ability to operate the unit within the strict emissions permit under the jurisdiction of the Oregon Department of Environmental Quality. The combustion related emissions being controlled are CO, SO,, HCI (all under 50 ppm), NO, and Dioxin destruction. Dioxin emissions are assumed destroyed by controlling the combustion process to continuously provide flue gas temperature above 1800F for a minimum of 1 second residence time, which is a continuous measurement and control tripping function.

The paper describes the interplay between the different control strategies for each pollutant. The process is a complex chemical reaction with multivariable control strategies that conflict with each other, necessitating a predictive controller to expand the operating window of the system. Also described are emissions from other bubbling bed sources and fuels.