Operation of a differential fixed bed reactor for investigations on micro-kinetics of heterogeneous gasification reactions

A pressurized differential fixed bed reactor (dFBR) developed for the investigation of micro-kinetics of heterogeneous
reactions is presented in this work. The operability of the dFBR is assessed by the example of gasification
experiments with biogenic char and steam. Two main challenges are addressed: the definition and verification of
differential operation and the influence of the system response behavior on the derived reaction kinetics. Based
on the first Damk¨ohler number, a threshold value of the ratio between the reaction gas concentration ci,H leaving
the differential fixed bed and the concentration ci,0 entering was derived as a new criterion for differential
operation. For a ratio of ci,H/ci,0 ≥ 0.9, the fixed bed reactor is operated differentially. To determine the influence
of the system response behavior on the reaction kinetics, system responses were investigated for a set of different
reactor temperatures, total pressures and reaction gas compositions. Then, the system-specific response behavior
was described based on the axial dispersion model. The description was integrated into the experimental data
evaluation routine. ... mehrSubsequently, the influence of the system response behavior on the derived kinetics was
assessed by means of the ratio between the reciprocal value of the reactivity 1/RUCM-C to the spread of the
residence time distribution E(t). It was found that for ratios of six or lower, the system response behavior
relevantly affected the experimental results.