Whisker carbon in tubular reformer

The higher hydrocarbons may lead to carbon formation by all three mechanisms (Table 5.1). Thermod5mamics will predict carbon formation as long as the higher hydrocarbons are present. Carbon may be stable in a steady state in spite of the principle of equilibrated gas (refer to Section 5.2.4). 

The risk of carbon formation may be assessed by the critical steam-to-hydrocarbon ratio [384] [389]. This decreases with temperature and depends on the t5q)e of hydrocarbon and the type of catalyst. 

The critical ratio increases with temperature (Equation 5.11) and depends on the type of catalyst. The actual ratio increases as the hydrocarbons are being converted. As for the principle of actual gas, the comparison of actual and critical ratios should be carried out for any 

Equation (5.12) shows that the risk of carbon is increased by high adsorption rate (kA) as for alkenes and low hydrocracking rate as for aromatics. The other constants are related to the catalyst properties. Carbon formation is depressed by a strong adsorption of steam (high Kw) reflected by negative orders with respect to steam, kc may be decreased by blocking the nucleation sites for carbon as discussed in Sections 5.3.2 and 5.5. 

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