Title: Circulation of Sand and Char Particles in a System with Fluidized Bed and Pneumatic Transport - Effects Of Design and Operation Parameters
Citation: Proceedings of the 34th International Conference of the Slovak Society of Chemical Engineering vol. ISBN: 978-80-227-2640-5 p. 013-1, 013-15
Publisher: Slovak Society of Chemical Engineering
Publication Year: 2007
JRC N°: JRC37180
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC37180
Type: Articles in periodicals and books
Abstract: Dual separated fluidized bed (FB) reactor systems or fluidized bed/pneumatic transport systems are convenient for cleaning of gases with regeneration of a solid sorbent or for separation of gasification of solid fuels (e.g. wood) and combustion. Such gasification/combustion systems can produce high calorific value fuel gas practically free of nitrogen by means of air used for combustion and generation of heat necessary for gasification. A laboratory plexi-glass apparatus with a fluidized bed reactor and pneumatic transport (PT) column connected for circulation of solids by orifices in the bottom part and with arrangements for return of solids from the exit of the PT-column to the FB has been used for the experimental study. The experimental study has three main parts: gas leakage in the bottom and upper part of the dual FB-PT circulating system, circulating flow of solids and circulation of bigger char particles. Results of experimental investigations of gas leakage and circulating flow of solids between fluidized bed, pneumatic transport column (ID = 4.4 cm) and return to FB are presented for a range of superficial gas (air) velocities in PT-column, various heights of FB and two lengths of PT-column (1 m and 2 m). Quartz sand, size fraction 0.2 – 0.4 mm, served as the basic solid particulate material for experiments. For comparison a bigger size fraction of sand has been used (0.4 – 0.6 mm). Selected cylindrical wood char particles (diameter about 4 mm, height about 5 mm) have been used to study gas velocity and sand effects on circulation of bigger particles driven by circulating small sand particles. Due to the Plexi-glas (Perspex) material of the experimental set-up all experiments have been carried out at ambient temperature. The effect of diameter of the PT-column has not been measured. Effects of geometrical and scale parameters as for example, height of PT-column, orifice cross sectional area, exit geometric arrangement and distributor design on circulation of solids, pressure drop behaviour and critical states (particularly choking) have been studied. Full functioning of gas distributors in the FB-compartment and FB-siphon for return of particles from PT-column turned out to be a very substantial factor for problem-less circulation of solids. The circulation of bigger char particles depends on operating conditions (gas flow rate in PT-column, height of FB and sand particle size). The smaller sand particles are more efficient in support of up-flow and circulation of bigger char particles.
JRC Directorate:Energy, Transport and Climate

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