Pyrolysis characteristics of oil-field sludge and the comparison of kinetic analysis with two representative methods

The pyrolysis of oil-field sludge (OS) has the appeal of resource recovery for this kind of waste disposal. In this paper, we investigate the pyrolysis kinetics of OS with Coast-Redfern (CR) and Flynn-Wall-Ozawa (FWO) methods in a wide temperature range (305-1223 K). The pyrolysis process of OS mainly includes light organics vaporization (Stage-2), middle and heavy organics and carbonates decomposition (Stage-3), coke reduction and other inorganics decomposition (Stage-4). The kinetic analysis manifests that Stage-2 meets well with the reaction order mechanism, and the reaction order (n) is 2 and in the range of 1.3-1.9 obtained by CR and FWO, respectively. The divergence of the two methods mainly appears in Stage-3, where E-a calculated by FWO method is much higher than that by CR method. CR method gives D-1 model for this stage, while FWO method picks D-3 model to describe this stage. The simulation plots indicate that the results of CR method are more credible. As for Stage-4, both methods select G(alpha) = alpha as the mechanism, but CR method performs better agreement and a smaller discrepancy than FWO method does. Thus, FWO method is considered less accurate for OS analysis.