Extension of the Model for Fast and Slow Coke

The explicit model can be used to determine the behavior of the TCC kiln when the initial temperature T is varied. A good index of the kiln performance is the distance down the kiln at which 99% of the carbon has been removed. This distance Zb is an important indicator of the extent to 

It was found that for a large spectrum of commercial operations, the kiln behaved as if Ty was approximately 920°F (494°C) regardless of reactor outlet temperature. This observation allowed the explicit model to be extensively used to explore the effects of some of the variables such as catalyst diSiisivity and air inlet location on kiln performance. However, the absence of fast coke in the model limited its usefulness, here leading us to develop a model which included the plume burner and fast coke. This next stage of advance was not possible without numerical integration. 

As with slow coke, the fast coke was shown to bum at a rate that is first order in coke and approximately first order in oxygen. However, the activation energy is approximately half that of the slow coke and the frequency factor is 1.0 x 10 sec in contrast to 3.7 x 10 sec for slow coke. At 950°F (783 K), the fast coke bums 17 times as fast as the slow coke. 

A major part of the fast coke is probably desorbed from the catalyst bed and burned in the gas phase. Even if none of the fast coke was desorbed, a calculation of the Thiele modulus tj for conditions in the plume burner and the top of the first zone of the kiln shows that rj is in the range 0.92-0.99. Thus, the fast coke can be assumed to bum without significant diffusion limitation. 

The effect of catalyst inlet temperature T on the 90% burn-off distance Xt, for the kiln simulated in Fig. 13. 

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