Estudo da influência do modo de aeração de uma válvula loop-seal na operação de um leito fluidizado circulante

Abstract

The study of the hydrodynamics behavior inside CFB units either to improve the performance of current processes or to develop new applications still deserves the attention of researchers. In particular, efforts have been devoted to the study of solids recycling devices because of their strong influence on the intensity of the particle circulation, the pressure drop and the distribution of the bed inventory along the fluidization loop. The present study aimed to analyze the effect promoted by the aeration mode of an U-type loop-seal valve on the hydrodynamics behavior of a CFB system. For this, experimental runs under room temperature conditions were performed in a bench-scale CFB unit using vertical chamber aeration in mono and dual modes at the base of the solids recycling valve. By keeping constant both the superficial fluidization velocity at the riser and the bed mass loaded with particles of quartz sand, the study analyzes the influence of the aeration modes applied on the loop-seal valve on the static pressure profile, the bed inventory distribution and the solids circulation rate as a function of the air injection rate used in the supply and/or the recycle chamber. An analysis of variance (ANOVA) is also included in order to verify the significance of the effects caused by the aeration modes used in the loopseal valve under the experimental conditions tested. Under operation in the different aeration modes analyzed, the results indicated increasing solids flow rates in the range of 15 kg/m².s to 46 kg/m2 .s, when the fluidization number in the loop-seal valve ranged from 1.4 to 2.5. It was observed that the aeration mode did not affect the mean GS value at the 95% confidence level. However, significant differences were observed in the pressure drop in the riser, standpipe/supply chamber and recycle chamber components compared to the aeration mode used. In this sense, with the increase of the aeration rate, the first two components described above experienced an increase in the pressure drop, while in the third one there was a decrease due to the increase in the porosity of the bed in the place. The cyclone did not undergo significant variation in the pressure drop in any mode and aeration rate, suggesting the non-dependence of this in relation to the rate of solids circulation promoted in the LFC system.