Determination and modelling of the particle size dependent residence time distribution in a pilot plant spray dryer

Abstract

The residence time distribution (RTD) in a pilot plant spray dryer was characterised for two kinds of air distributors (centrifugal and parallel flow) and for different atomizing air pressures. To determine the RTD - and the RTD of different particle size fractions - the particle concentration and size at the dryer outlet was measured continuously using a particle counter. Results were modelled using the Bodenstein number and the CSTR in series model. An increasing nozzle pressure leads to a decrease in mean residence time and a more narrow distribution. The influence of nozzle pressure is more pronounced than of air distributor and particle size fraction. Keywords: Residence time distribution; Particle size; Bodenstein number modelling; Nozzle influence; Mechanism of air distribution

Color formation and Maillard reactions during the spray drying process of skim milk and model systems

“…The non-uniform distribution of particle residence was also reported in other studies (Ruprecht & Kohlus, 2019). A long tail in the particle residence time distribution suggests that most of the spray-dried particles are held back by the wall deposition and re-entrainment process (Francia, Martin, Bayly, & Simmons, 2015), leading to longer thermal exposure times.…”

“…A continuous stirred tank reactor (CSTR) in series model was used to fit the experimental data for particle residence time distribution in MATLAB using the least-squares method. The equation for the particle residence time distribution model is shown in Equation ( 1) (Ruprecht & Kohlus, 2019).…”

The Use of Optimized Restitution Coefficients to Improve Residence Time Prediction in Computational Fluid Dynamics-Discrete Parcel Method Models for Counter-Current Spray Dryers

“…An alternative integral approach to describe RTD in particle processing units, among them co-current spray dryers, is the use of models based on equivalent reactor networks. ,− Here, we report the use of these ideal models to recreate the experimental RTD of counter-current spray dryer. This will help to elucidate if simple reduced networks could properly reproduce the system with a lower computational cost and suggest the best network to be put forward.…”

“…Recently, Ruprecht and Kohlus determined the dispersion in a co-current dryer by using a scattered light technique. The characterized RTD was compared with a combined PFR and CSTR equivalent reactor model showing to reproduce with accuracy the RTD …”

“…The characterized RTD was compared with a combined PFR and CSTR equivalent reactor model showing to reproduce with accuracy the RTD. 19 However, swirl counter-current dryers are more complex and less well known. As noted above, even in a single-phase flow, the scale-up of turbulent vortices with rough walls is not trivial.…”