The monitoring of fluidized bed processes is valuable for the optimization of operational efficiency and avoiding unscheduled shut-downs in industrial practice. We here focus on two important applications for the industrially widely applied circulating fluidized beds (CFBs): the detection of small, gradual changes in particle size and the early detection of agglomeration. Based on high-frequency (200 Hz) pressure fluctuation measurements we have applied the attractor comparison method in different CFBs to investigate its suitability as a monitoring tool for the two proposed applications. Attractor comparison has shown to be generally sensitive to small, gradual particle size changes in a lab-scale CFB. The sensitivity normally depends on the measurement location (downcomer, return system, riser) and is often larger in the downcomer section. From the results, detection limits for the particle size have been identified. In an industrial installation the sensitivity and applicability of the method for measurements in the riser has been confirmed. With the help of model agglomerates it has been shown that attractor comparison can also detect the presence of small shares of agglomerates on lab-scale; here, filtering the pressure fluctuation data before the analysis has shown to improve the method. The suitability of the method for agglomeration detection has been confirmed with an agglomeration incident in a hot lab-scale facility; in this case the approaching defluidization has been detected with an early time of about 30 min based on measurements in horizontal return-leg and lower riser. (C) 2010 Elsevier B.V. All rights reserved.