282488 Drying of Biomass Pellets: Experimental Study and Comparison of the Performance of a Conventional Fluidized Bed and a Rotating Fluidized Bed in a Static Geometry

Thursday, November 1, 2012: 3:40 PM
Conference A (Omni )
Philippe Eliaers and Juray De Wilde, Materials and Process Engineering, UCL, Louvain-la-Neuve, Belgium

The use of dry woody biomass for combustion or gasification improves the process efficiency and reduces net air emissions. Dry biomass is also required for pelletization which often precedes these two processes. Finally, dry biomass facilitates transport and storage because of its reduced biological activity its reduced density.

In this work, the intensification of the drying of biomass particles using rotating fluidized beds in a static geometry [1] was experimentally studied. Experiments in both a 10 cm diameter, 1.5 m tall conventional, that is, gravitational fluidized bed and in a 43 cm diameter, 5 cm length rotating fluidized bed in a static geometry (RFB-SG) were carried out in a range of operating conditions and resulting solids outlet humidity. A schematic representation of the RFB-SG and the rotating bed of biomass particles are shown in Figure 1.

Figure 1. (a) Schematic representation of a Rotating Fluidized Bed in a Static Geometry;

(b) Rotating bed of biomass particles during drying.

The comparison between the specific drying rates (the quantity of water transferred per second and per m3 drying chamber) in the two types of reactor (Figure 2) shows the process intensification that can be achieved. In the range of operating conditions studied, the process intensification factor was between 10 and 13.

The process intensification results from 3 factors: (i) the higher gas-solid slip velocities resulting in improved mass and heat transfer, (ii) the higher particle bed density and (iii) the higher particle bed uniformity. The relative importance of the three contributions is analyzed. The efficiency of the air utilization was also measured and is discussed. Finally, possible improvements of the RFB-SG design to reduce the air consumption are presented.

Figure 2. Comparison of the specific drying rates obtained in the conventional fluidized bed and in the rotating fluidized bed in a static geometry for varying mean biomass outlet humidity. Beech wood particles are shown in the picture.

[1] J. De Wilde and A.de Broqueville: Rotating fluidized beds in a static geometry: Experimental proof of concept. AIChE Journal, 53, p. 793810, 2007.

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