Coke Oven Carbon Deposits Growth and Their Burning Off

Abstract

Burning off is the main method of carbon deposit removal from coke oven chambers. Optimisation of this operation is of a great interest both from the point of view of current production loss reduction and of coke oven plant lifetime extension. In this study the deposits originating from different parts of chambers have been characterised by chemical analysis, optical microscopy, XRD, Raman spectroscopy and mercury porosimetry. This investigation has shown that deposits contain two carbonaceous phases: the char from pyrolysed carry over coal particles and the pyrolytic carbon from raw gas cracking. Furthermore, the monitoring method for carbon deposits growth in coke oven chamber is presented. The statistical analysis of the visual inspection data has been a useful tool in the evaluation of the rate of deposit growth in individual coke oven chambers. The combustion kinetics of carbon deposits were studied by thermogravimetry under non-isothermal conditions with natural air draft and under isothermal conditions at controlled air flow rate. It was found that the reactivity of carbon deposits is in-between metallurgical coke and electrographite reactivity. At the temperatures below 700 degrees C, under laboratory conditions, the combustion rate (on the basis of external surface) is controlled by surface reaction at higher temperature and activation energy is around is 170 kJ/mol. At temperature higher than 700 degrees C combustion is controlled by gas film diffusion. Modelling of combustion in thermobalance experiments and in industrial coke oven chamber was carried out on the basis of measurement of kinetics using commercial CFD software.