Experiments were conducted in a moving and stirred bed vacuum pyrolysis reactor handling polydispersed softwood bark feedstock to study flow characteristics as functions of feed throughput, agitation speed, particle size and shape. A new idea of polydispersed fluorescent tracers was employed for the first time to investigate the residence time distribution (RTD), mean residence time and reactor hold-up. A single parameter dispersed plug flow model and an identical CSTRs-in-series model have been successfully used to fit the experimental data. Correlations are proposed for mean residence time, reactor hold-up, vessel dispersion number and number of identical CSTRs-in-series in terms of operating variable, for example feed throughput and agitation speed in the range of 20-70 kg hr(-1) and 10-30 cm s(-1) respectively.