The measurement of transport coefficients in gas-solid heterogeneous reactions

Abstract

If reasonably uniformly sized spherical pellets are packed in a tube only slightly larger in size, so that the tube/pellet dia ratio is from 1·1 to 1·4, and the tube contains 50 or more pellets, then the flow behaviour is very similar to that of a conventional packed bed. Pressure drop results and axial dispersion values obtained for non-porous pellets using pulse techniques can be predicted from existing packed bed correlations. Magnetite pellets of different porosities were used as porous packing, also, and, by Fourier analysis of outlet tracer pulse dispersion, external mass transfer and effective diffusion coefficients were obtained, assuming the validity of the Kubin-Kucera model. The use of this ‘single pellet string reactor’ (SPSR) appears to give a convenient laboratory simulation of a packed bed reactor, which would be particularly useful for larger solid particles such as pelletized ores. It also offers a convenient laboratory method for obtaining average effective diffusion coefficients over a range of temperatures and pressures for a representative sample of large porous particles.