Fundamental Mechanisms Governing Transients From the Batch Incineration of Liquid Wastes in Rotary Kilns

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The first, "surface renewal" model was not s uccessful , b ecause the pse udo stationary state assumption used i n calculating t e mporal l y var y ing hea t and mass transfer coeffic i ents i s i nv alid. With that a ssumption , low s urface renewal veloci ties ( low kiln rotation speeds) led to deeper penetration of h eat into the s orbent film, and thus to increased local vaporization rates and higher mas s ev olution rates, compared to the case for high surface renewal rates . This is contrary to experimental observations (see Figures 3 and 4 ), and the assumption of a pseudo stationary state is fundamentally incorrect, since the time taken to achieve it is greater than the time interval over which it is applied. Therefore this model was discarded and is not discussed further here . The second, transient transport/fragmentation , model led to very reasonable results and is described in detail below. The model consists of two parts : the first comprises the prototype problem of transient simultaneous heat and mass transfer in a sorbent aggregate layer, coupled with lo.., cal vapo.r ization rates depending on local vapor pressure and local composition; the second comprises the aggregate size dependent fragmentation model , which also depends on kiln rotation speed. 3 . 2 Transient Transport Model Consider time dependent , simultaneous heat and mass transfer in a sorbent aggregate , as shown on Figure 5 (Upper Portion) . The sorbent aggregate is composed of individual sorbent particles, each of which locally releases vapor into the interstitial gas volume at a rate determined by the local "particle drying rate . The gas evolved diffuses through the voids to the surface , and is 11