General combined model for the hydrodynamic behaviour of fixed and fluidised granular beds

This work describes the derivation of a general mathematical model applicable to both fixed and fluidised granular beds, operating within the full hydrodynamic spectrum from viscous to inertial flows. The fundamental insight for the derivation of the model is that practical fluidised beds and fixed beds have similar hydrodynamic properties. The validity of the general model is demonstrated for fluid fractions up to 0.90. A crucial development in the general model is the replacement of hydraulic diameter, which has served as the size descriptor of flow paths in most fixed-bed models derived since the advent of the classic Blake-Kozeny equation. The new, replacement expression is based on the physical structure of the cross section of random porous beds. In addition, the general model contains a tortuosity factor, derived from the results of previous works involving computational fluid dynamics, to correct flow path length and fluid velocity. The model is constructed using regression analysis of experimental data from six previous major works and tested against previous models.

Fluid bed gasification--plasma converter process generating energy from solid waste: experimental assessment of sulphur species

Often perceived as a Cinderella material, there is growing appreciation for solid waste as a renewable content thermal process feed. Nonetheless, research on solid waste gasification and sulphur mechanisms in particular is lacking. This paper presents results from two related experiments on a novel two stage gasification process, at demonstration scale, using a sulphur-enriched wood pellet feed. Notable SO2 and relatively low COS levels (before gas cleaning) were interesting features of the trials, and not normally expected under reducing gasification conditions. Analysis suggests that localised oxygen rich regions within the fluid bed played a role in SO2's generation. The response of COS to sulphur in the feed was quite prompt, whereas SO2 was more delayed. It is proposed that the bed material sequestered sulphur from the feed, later aiding SO2 generation. The more reducing gas phase regions above the bed would have facilitated COS--hence its faster response. These results provide a useful insight, with further analysis on a suite of performed experiments underway, along with thermodynamic modelling.