Drying 2004 – Proceedings of the 14th International Drying Symposium (IDS 2004) São Paulo, Brazil, 22-25 August 2004, vol. A, pp. 232-238 232 DETERMINATION OF RESIDENCE TIME OF PASTE DURING DRYING OF A PHYTOMEDICINE IN A SPOUTED BED Maria P.G. Peixoto , Anna P. R. Monteiro and Luis A. P. Freitas Faculdade de Ciências Farmacêuticas de Ribeirão Preto Universidade de São Paulo Via do Café s/n, Campus USP, 14040-903, Ribeirão preto, SP, Brazil. Email: lapdfrei@usp.br Key words: stimulus-response, annatto extract, methylene blue, exit age. ABSTRACT Residence time distributions (RTD) of a phytopharmaceutical paste in a conventional spouted bed dryer (CSBD) with inert bodies were determined using a stimulus response technique. Glass beads with different sizes were used as inert bodies in a cylindrical column of 14.0 cm diameter and 80 o conical base. The effects of inert bodies size and air flow rates on residence times were measured for an annatto extract preparation. Methylene blue was used as chemical marker in the stimulus-response technique. The results showed that the technique applied is adequate for those measurements in spouted beds with inert bodies. Also a strong effect of process variables on RTD was observed, e.g., mean residence times decreased with increasing air velocity and particle size. The mean residence time in CSBD showed to vary from 10.32 to 16.81 minutes.. INTRODUCTION Spouted bed dryers with inert bodies have been extensively studied for drying of bio-resources such as foodstuffs and phytopharmaceutical products (Adamiec et al., 1995; Pakowski & Mujumdar, 1995). Recently, spouted beds have been applied for the drying of medicinal extracts of brazilian plants (Freitas et al, 1998; Runha et al., 2001; Shuhama et al., 2003).The drying of biological or biosynthesis products is a delicate process step since most part of those materials are thermo sensitive or thermo labile. For those heat sensitive products, not only the temperature can bring significant active degradation but also the time of exposure to heat (Adamiec et al., 1995). The knowledge of some process features is important to achieve successful drying in CSBD with inert bodies: drying mechanisms and kinetics, system fluid-dynamics with and without paste feed, mechanism of deposition and removal of paste from inert body surface, drying performance and degradation kinetics.