Owen Potter, Emeritus Professor of Chemical Engineering, Monash University, Australia.
Published IChemE Journal Feb 2013, Volume 91, Issue 2, Pages 244–253.
In this paper heat transfer between gas and relatively fine particles, dp < 350 μm, say, is firstly considered. In this system, particles are injected from the top into a gas stream flowing in a horizontal channel, so that acceleration of the particles to the horizontal velocity of the gas is not required, i.e. the inlet velocity can be resolved into the stream velocity in the horizontal direction and in the vertical direction at or above the terminal velocity. The particles are injected in such a way as to ensure the porosity is .99 or higher. Relatively high Numbers of Transfer Units arise. The calculation method applied can cope with parameter changes during the calculation, e.g. due to temperature changes. Values of NO1 could be enhanced by multi-stage operation where particles from one curtain are lifted to become the feed for the up-stream curtain so that the system is overall counter-current. Heat transfer coefficients increase as particle diameter reduces, and surface area rises (for the same mass of particles). Particles employed are chosen at sizes where the particle resistance to heat transfer is very small. Secondly, two limiting examples of mass transfer and chemical reaction, without heat transfer, are briefly examined: chemical reaction between gas and catalyst particles, and gas absorption of carbon dioxide with chemical reaction. All these cases fall under the description of cross-flow.
"Addendum 1 for the Potter “Crossflow gas particle heat and mass transfer” (2013)”: haematite and magnetite performance data"*
Lambert, T & Potter, O.
*Data presented at Chemeca 2017 – 25 July 17
POTTER 2013 investigated the potential for future utilisation of cross flow contacting of gas and particles as a preferred alternative to fluidization. It was shown theoretically to offer interesting possibilities for processes involving heat and/or mass transfer:
• energy recovery to an outstanding level;
• gas-solid catalyst reaction, possibly of value for fouling catalysts;
• absorption by liquids from gases and therefore distillation also.
The commercial implications include both:
• capital cost savings arising from the opportunity to contact gas and solids in significantly smaller equipment than required for a fluidized bed;
• operating cost savings due to both the outstanding energy recovery; and at least an order of magnitude lower pressure drop in comparison to a fluidized bed.
That theoretical investigation employed a computationally efficient calculation method that corroborated well with earlier work to forecast the performance of single stage systems involving heat transfer between air and both silica and alumina.
Today, with investigations underway focusing on pilot studies in a prototype contactor of 500mm square cross section, increased attention is being directed to opportunities for commercial application, particularly in relation to haematite and magnetite. This paper provides additional information forecasting and analysing the heat transfer performance of a single stage 4000 mm square section contactor operating with 232 t/h air fed at 100oC and 293 t/h haematite (or magnetite) fed at 200oC.