Char, proportion occurring

Figurc 9. The proportion of char occurring as cenospheres and the O/C atomic ratios for the oxidised coals (373 K).

In the pyrolysis processes, a thermal degradation occurs between 400 and 600°C in the complete absence of oxygen. These processes are characterized by the indirect heating of the material through the furnace wall (or pipes). The pyrolitic products, the solid (mix of char metals and mineral matter) and the hot gases (condensable and noncondensable mixture), are collected. Their relative proportions depend on the nature of the material, the applied technology and the pyrolysis conditions, i.e. temperature, pressure, heating rate, etc. The reductive atmosphere of the furnace is mainly a function of the pyrolitic gas composition. 

Heterogeneous tar cracking. If the tar cracking rate is proportional to the solids hold-up (char) more cracking occurs near the wall. 

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