CONTRIBUTION TO THE STUDY OF CARBON DEPOSITION IN COKE OVENS

The formation of carbon deposits from coal pyrolysis in a two-stage reactor has been studied for several cracking temperatures from 850 to 1000 degrees C. The weight of the carbon deposit was monitored continuously during pyrolysis by a thermogravimetric balance. Four successive periods of deposition can be distinguished: (1) no weight uptake; (2) a slow increase in weight; (3) a sharp increase in weight; (4) constant weight. From the data, three distinct deposition rates have been calculated at different cracking temperatures: germination rate, growth rate and overall deposition rate. The general tendency is an increase in all three deposition rates with temperature. Scanning electron and polarized light micrographs of these deposits show that they have a laminar structure. There are two (sometimes three) cone layers, the first being formed during the liberation of water contained in the coal charge, indicating that water plays the role of an inhibitor in the formation of carbon deposits. The structure of the deposits is independent of the temperature at which deposition takes place. The mechanism of this carbon formation is discussed.