Theoretical analysis of tracer method for the measurement of wetting efficiency

This work investigates the tracer technique for the measurement of catalyst wetting efficiency, ff, in trickle-bed reactor.The model of Ramachandran et al. [1986. A new model for assessment of external liquid–solid contacting in trickle-bed reactors from tracer response measurements. Chemical Engineering Science 41(4), 855–860], based on a 2D description of the tracer diffusion, is applied for the full range of wetting efficiency. It is also extended to account for the effects of axial dispersion, liquid–solid mass transfer, pattern of the wetted zone on the pellet, and distribution of the partial wetting along the reactor.The numerical method for parameter optimization implies a frequency domain least-squares procedure. A sensitivity analysis has been performed proving that the wetting efficiency may be derived with convenient accuracy in usual trickle-bed conditions: high Péclet and Biot numbers.For f>0.3f>0.3, it is shown that wetting efficiency can be accurately calculated from apparent particle diffusivities derived in liquid-full conditions (Deapp,LF)Deapp,LF) and in partial wetting regime (Deapp,TB)Deapp,TB) using the following relation: f=Deapp,TB/Deapp,LF.