Ignition characteristics of co-fired mixtures of petroleum coke and bituminous coal in a pilot-scale furnace B.R. Clements a,⇑ , Q. Zhuang a , R. Pomalis a , J. Wong a , D. Campbell b a CanmetENERGY, Natural Resources Canada, 1 Haanel Dr., Ottawa, Ontario, Canada K1A 1M1 b Nova Scotia Power Inc., P.O. Box 910, Halifax, Nova Scotia, Canada B3J 2W5 article info Article history: Received 17 June 2011 Received in revised form 4 January 2012 Accepted 6 January 2012 Available online 21 February 2012 Keywords: Combustion Co-firing Coal Fuel blending Devolatilization abstract 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 pro- posed to determine lean ignition limits and experimental results are presented. Experimental data is pre- sented 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 proce- dure 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 con- ditions that may be experienced during operational upset conditions. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Petroleum coke use at Nova Scotia Power Incorporated (NSPI) There is a significant financial incentive for power generation utilities that have the capacity to co-fire petroleum coke with coal to maximize the fraction of coke in the mixture; however, there are operational concerns associated with ignition stability of the burn- ers at high petroleum coke fractions. In addition to ignition prob- lems that will be discussed here, other issues are associated with petroleum coke co-firing, the most troublesome being carbon burnout and elevated sulphur levels. Petroleum coke has very little volatile matter; therefore, a point is reached during co-firing where insufficient volatile matter is present to ensure stable ignition. To address concerns about the upper limits of petroleum coke usage, a pilot-scale test matrix was designed and tests were conducted at CanmetENERGY’s test facility. These data were used by NSPI to establish safe operating guidelines for co-firing petroleum coke at its pulverized coal-fired power plants. In 2001 most local coal mines in Nova Scotia were closed and as a result, NSPI had to begin importing high volatile bituminous coals from around the world to burn in its three pulverized coal- fired power generating stations. In 2002, to improve the economics of using imported bituminous coal, NSPI began co-firing delayed petroleum coke. At the time of this study, NSPI had successfully operated with up to 20% petroleum coke co-fired with various international bituminous coals in its pulverized coal units and there was a desire to increase this fraction. To address these ignition stability concerns associated with the use of petroleum coke beyond the 20% limit NSPI initiated stability testing of various blends in a laboratory-scale furnace located at the CanmetENERGY site in Ottawa, Ontario. 1.2. Petroleum coke A limited amount of research has been done on the ignition char- acteristics of petroleum coke in larger pilot-scale furnaces. Bryer defined many of the hurdles of petroleum coke usage. Delayed petroleum coke is produced from the heating of crude oil in a batch furnace at specific temperatures and pressures in the presence of steam. The products of such a coking process are gas, gasoline, gas oil and coke. Petroleum coke, unlike coal, is low in volatiles and contains substantial concentrations of vanadium, nickel and sulphur. Volatile matter in petroleum coke is typically in the range of 1.25–8.5% but can be as high as 16%. Consequently, it can be 0016-2361/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2012.01.009 ⇑ Corresponding author. E-mail address: clements@nrcan.gc.ca (B.R. Clements). Fuel 97 (2012) 315–320 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel