The study proposes the evaluation of the residence-time distribution (RTD)
in-situ in an industrial dryer for the production of recycled polyester
fibers (PES) from colorless polyethylene terephthalate (PET) flakes without
interruption of the production. A disturbance of the pulse type was
employed, in which the tracer (blue PET flakes) had previously been
crystalized and its concentration was obtained according to the time at the
dryer outlet. Additionally, analyses of intrinsic viscosity and
crystallization percentage of the PET flakes (colorless and blue) and PES
intrinsic viscosity and color force were performed. By RTD, the mean
residence time (322.8 min), the variance (1305.4 min2), the standard
deviation (36.1 min) and the relative error (1.5%) were obtained when
compared to the theoretical residence time, indicating the absence of
preferred paths or flake agglomerates in the equipment. Finally, the
characterization demonstrated that there was no alteration in the parameters
of product quality during RTD evaluation, confirming the potential of
application of this methodology for diagnoses of continuous industrial
processes.