Devolatilization rate equation

For reactor design calculations it is necessary to know the total devolatilization rate as well as the species production rates. Therefore, one needs to include in the reactor model all the reaction rates that are available for the devolatilization of the particular coal. Kayihan and Reklaitis (8) show that the kinetic data provided by Howard, et al. (5,6) can be easily incorporated in the design calculations for fluidized beds where the coal residence times are long. However, if the residence time of pulverized coal in the reactor is short as it is in entrained bed reactors, then the handling of ordinary differential equations arising from the reaction kinetics require excessive machine computation time. This is due to the stiffness of the differential equations. It is found that the model equations cannot be solved... 

The centerline gas velocity was approximated by doubling the bulk gas velocity. The bulk gas velocity was calculated as the volumetric gas flow rate divided by the cross sectional area of the tube inside the drop tube furnace. Stokes law was used to calculate the terminal velocity. At a temperature of 1700 C (3092°F). the calculated residence time for the coal particles was 186ms. The resulting devolatilization kinetics for petroleum coke are shown in Hgure 2.2. The devolatilization reactivity equations among various petroleum cokes will be reasonably consistent rather, the significant variability will come fi om the maximum volatile yield. 

Each surface film of area S (per unit length of devolatilizer) has a specific exposure time, or regeneration rate, and hence is associated with a specific Equation 2. For any number, 1,2,3,.. . n separate films, therefore, the effective product of the diffusion film coefficient and surface area is given by the summation ... 

Replacing the product of k cxp(-EIRT) in Equation 11.48 by Equation 11.50, we have the overall reaction rate that would be observed at temperature T, to which the coal is assumed to be heated at constant rate m from the initial temperature T0. For devolatilization of Montana lignite, k0 = 1.07 x 1010 s-1, E0 = 48.72 kcal/mol, and o = 9.38 kcal/mol. 

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