Sensitivity analysis of different devolatilisation models on predicting ignition point position during pulverized coal combustion in O 2 /N 2 and O 2 /CO 2 atmospheres Rastko Jovanovic a,⇑ , Aleksandra Milewska a , Bartosz Swiatkowski a , Adrian Goanta b , Hartmut Spliethoff b a Institute of Power Engineering, Thermal Processes Department, Augustowka 36, Warsaw, Poland b Technische Universität München, Fakultät für Maschinenwesen Gebäudeteil 7, Boltzmannstraße 15D-85748, Garching bei München, Germany article info Article history: Received 1 October 2010 Received in revised form 16 February 2011 Accepted 17 February 2011 Available online 3 March 2011 Keywords: Pulverized coal Devolatilisation Oxy-fuel CFD modelling Oxy-combustion abstract Oxy-fuel combustion is considered as a promising solution to reduce greenhouse-gases and pollutant emissions. The main advantage of oxy-fuel combustion over other technologies for pollution reduction from pulverized coal combustion is that it can be applied to the existing coal-fired power plants. How- ever, switching from conventional to oxy-fired coal combustion brings significant challenges. One of the most important is change of pulverized coal ignition characteristics. This paper presents the results of experimental and numerical analysis of ignition phenomena under oxy-fuel conditions. The main focus of the presented paper is to evaluate the effectiveness of the mathematical devolatilisation sub-model, in predicting the ignition point of pulverized coal flames under oxy-firing conditions. Regarding this, the performance of several devolatilisation models, from simple to more complex ones, in predicting ignition point position have been investigated. Numerically determined values of the ignition point position, and ignition temperature for various O 2 –N 2 and O 2 –CO 2 conditions were compared with experimental data from the laboratory ignition test facility. Obtained results pointed out that network devolatilisation mod- els (CPD and FG) give more accurate results in comparison with standard devolatilisation models (single rate and two competing rates). The best performance is achieved using FG devolatilisation model. Thus, newly implemented FG model will be used for future numerical simulations of oxy-fuel pulverized coal combustion on 0.5 MW pilot plant facility. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Oxy-fuel combustion technology and ongoing research Pulverized coal oxy-fuel combustion with CO 2 capture from flue gas is considered as a possible solution to reduce greenhouse-gases and pollutant emissions which can be used in both new and exist- ing coal-fired power plants. During oxy-fuel combustion, pulver- ized fuel is burnt in a mixture of re-circulated flue gas and pure oxygen to produce a flue gas stream with a high concentration of CO 2 which can be sequestrated without costly flue gas separation. However, switching from conventional to oxy-fuel pulverized coal combustion technology brings a number of technical challenges. Different heat capacity and densities of main gases, i.e., N 2 and CO 2 , will change mass flows and velocities of primary and second- ary oxidants (to attain a similar adiabatic flame temperature to the conventional pulverized coal combustion mode) thus affecting burner aerodynamics. This will result in different fuel ignition properties, flame propagation, flame shape, and residence time [1]. Here should be explained that authors in this work will use term primary/secondary oxidant instead of primary/secondary air. This term is introduced because, strictly speaking, term air means mixture of 21% of O 2 and 79% of N 2 on volumetric basis. Since in presented paper instead of air (commonly used in conven- tional pulverized coal ignition) different compositions of O 2 /N 2 and O 2 /CO 2 are used, it is authors’ opinion that is more accurate to use term oxidant instead of air. Numerous studies of pulverized coal flame properties, in partic- ular the ignition position, ignition temperature, flame shape and stability, during oxy-fuel combustion have been undertaken. Toporov et al. [2] performed an experimental and numerical study of a stable oxy-fired pulverized coal swirl flame in a vertical pilot- scale furnace (100 kWth) focusing on underlying mechanisms as well as on the aerodynamics of the oxy-coal flame. Bajerano and Levendis [3] investigated combustion of single particles of bitumi- nous and lignite coals in a laminar-flow drop-tube furnace at increasing O 2 mole fractions in either N 2 or CO 2 balance gases. The main aim of their work was to determine basic knowledge, such as the luminous temperature – time histories, of burning sin- gle coal particles. In their work, Qiao et al. [4] evaluate the influ- ences of reactions involving char (including the char structure) 0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2011.02.024 ⇑ Corresponding author. Present address: Institute of Nuclear Sciences Vinca, Laboratory for Thermal Engineering and Energy, Mike Alasa 12-14, 11001 Belgrade, Serbia. Tel.: +381 641969597; fax: +381 112453670. E-mail address: virrast@vinca.rs (R. Jovanovic). Fuel 101 (2012) 23–37 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel