This study addresses ignition characteristics encountered when co-firing petroleum coke with coal and provides insight into addressing ignition problems that may occur. A pilot-scale test procedure is proposed to determine lean ignition limits and experimental results are presented. Experimental data is presented for various co-fired mixtures of petroleum coke with coal. Qualitative discussions that relate the lean ignition limit to the volatile matter and aerodynamic conditions are presented. The study extends these results to the development of a full-scale pulverized fuel steam generation unit operating procedure that has been successfully implemented within a power generation utility. The lean ignition limit is reached between 62% and 67% petroleum coke for swirl numbers of 0.35 and 0.40, respectively. Although a burner aerodynamic effect exists, it seems relatively small compared with the influence of the amount of overall volatile matter. The total volatile matter in the co-firing case was between 19.9% and 21.0% at the time of flame extinction for the two different aerodynamic conditions tested. Full-scale operating conditions had been limited to 20% petroleum coke prior to this study. This study confirmed that this level of operation was acceptable and far below where ignition problems are expected during full-scale operation. This conservative approach is well justified because it must account for extreme conditions that may be experienced during operational upset conditions. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.