Coke formation— thermal cracking effect

COMBUSTOR OVER-ALL FUEL-AIR RATIO. In general, coke and smoke both increase with increasing fuel-air ratio, although some investigations have shown that smoke can attain a peak point beyond which it decreases. However, the location of this peak value was variable and dependent on other factors. These fuel-air ratio effects can be attributed to more fuel wash on surfaces, richer local fuel-air ratios, and increased thermal cracking of the fuel. Increased burning and erosion might lower coke and smoke formation, however. 

Figure 7.13 presents a simplified flowsheet, which concentrates the essential features the balanced VCM technology, as conceptually developed in the previous sections, but this time with the three plants and recycles in place chlorination of ethylene (Rl), thermal cracking of EDC (R2) and oxyclorinahon of ethylene (R3). As mentioned in Section 7.3, from plantwide control three impurities are of particular interest (I]) chloroprene (nbp 332.5 K), (12) trichloroethylene (nbp 359.9K), and (13) tetrachloromethane (nbp 349.8). I, and 12 are bad , since the first can polymerize and plug the equipment, while the second favors the coke formation by EDC pyrolysis. On the contrary, I3 has a catalytic effect on the VCM formation, in some patents being introduced deliberately. 

The thermal chemistry of heavy oils and bitumen is extremely complicated because of wide variations in chemical compositions. The most refractory components in petroleum feedstocks are asphaltenes, which contribute the most to coke formation dining thermal cracking. Next to asphaltenes, resins and large aromatics also contribute to coke. To investigate the effect of these three heavy oil components on the mesophase induction period, Athabasca bitumen fractions containing varying amounts of asphaltenes (obtained by supercritical fluid extraction) and Venezuelan heavy... 

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