4. a) Compare and contrast the Progressive-Conversion Model and Shrinking -Core Model describing fluid-particle reactions. 171 b) Spherical particles of zine blend of size R=1 mm are roasted in an 8% oxygen stream at 900C and 1 atm. The reaction is ZnS + 02 -- ZnO + SO, Assuming that reaction proceeds by the shrinking-core model calculate: (0) The time needed for complete conversion of a particle 181 (ii) The relative resistance of ash layer diffusion during this operation 151 Page 3 of 7 TCE 3102 Copyright: National University of Science and Technology, 2019 Data Density of solid, pe = 4.13 gm/cm3 = 0,0425 mol/cm Reaction rate constant, k"=2 cm/sec For gases in the ZnO layer, 6)=0.08 cm /sec Note that film resistance can safely be neglected as long as a growing ash layer is present. c) Solids of unchanging size, R = 0,3 mm, are reacted with gas in a steady flow bench scale fluidized reactor with the following result. F. = 10 gm/sec, W - 1000 gm, I, = 0.75 Also, the conversion is strongly temperature-sensitive suggesting that the reaction step is rate-controlling Design a commercial sized fluidized bed reactor (find W) to treat 4 metric tons /hr of solid feed of size R = 0.3mm to 98% conversion [10]