ic a oces r, Ed

Keywords:

Char conversion thr t O coupled with the energy and species conservation equations, a finite volume solver was applied. In addition to the solid carbon the model incorporates six gaseous chemical species (O , CO, CO , H , H O, and busto chara by Edge et al. [1]. An analysis of this review shows that most computer-based simulations of combustors, which utilize software for computational fluid dynamics (CFD), use surface-based or shrinking core models. Thus, the carbon consumption is only correlated to the outer surface of the particle. The popular Baum and Street model [2], which was developed 40 years ago, represents this class of models. However, it is a well-known fact that coal particles literature about mbient gas flow, actions ar

Nowadays CFD-based simulation models have become established tools for understanding high-temperature con processes on a particulate level, e.g. see the works [6–10]. In ular, numerical simulations of single reacting particles can highlight different physical phenomena and correlations and can therefore help better understand the complex conversion physics.

An example of such an approach is given by Lee et al. [6]. The authors carried out a numerical investigation into single particle combustion in hot air. In this work they focused on transient phenomena and considered different Reynolds numbers. The authors ⇑ Corresponding author.

E-mail address: a.richter@vtc.tu-freiberg.de (A. Richter).

International Journal of Heat and Mass Transfer 83 (2015) 244–258

Contents lists availab

H .ereveals that e.g. the influence of the ambient gas flow on the overall carbon consumption and surface-averaged temperature of porous particles is not well understood. A comprehensive overview of the common char conversion sub-models can be found in the paper

However, there has been little discussion in the coal-char conversion under the influence of an a where many heterogeneous and homogeneous re into account.http://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.11.090 0017-9310/ 2014 Elsevier Ltd. All rights reserved.e taken wellversion partic-physics. For that reason the numerical simulation of such systems requires the application of so-called sub-models that describe the interaction between solid particles and the gas phase. The quality of numerical simulations depends directly on the adequate modeling of char oxidation and gasification. However, an analysis of existing computational combustion and gasification sub-models dation of char. As an example, the work by Everson et al. [4] takes into account intra-particle diffusion, intrinsic reactivity and the change in particle porosity during gasification. An alternative is the use of surface-based models utilizing the effectiveness factor and the Thiele modulus, which are obtained from an analytical solution of the species intra-particle diffusion equation [5].Porous carbon particle

Particle agglomerate

Partial oxidation

Oxy-fuel

Stefan flow

Combustion 1. Introduction

The technological processes of com on solid carbonaceous materials are2 2 2 2

N2). The reaction mechanism includes semi-global carbon monoxide oxidation, the forward and backward water–gas-shift reaction, and four heterogeneous reactions. The ambient medium was assumed to be nearly dry. The main objective of this work was to understand the char conversion processes inside a porous carbon particle. In particular, the change of regimes depending on the ambient gas temperature and the influence of the flow velocity on the processes inside the porous particle were studied in detail.

As a reference case the oxidation of a solid non-permeable sphere moving in a hot O2/CO2 gas was considered, and the results for the porous particle are discussed and compared against the reference case. 2014 Elsevier Ltd. All rights reserved. rs and gasifiers working cterized by multi-scale become porous after devolatilization [3]. Thus, depending on the ambient temperature heterogeneous reactions can occur inside the particle, namely in pores. Existing sub-models, e.g. the shrinking reacted core model, consider only the diffusion-controlled oxi-Accepted 29 November 2014 monodisperse spherical particles distributed inside a sphere. The ambient temperature was systematically varied in a range between 1200 and 2500 K. To solve the Navier–Stokes equations for the flow fieldThree-dimensional calculation of a chem moving in a hot O2/CO2 atmosphere

Andreas Richter a,⇑, Petr A. Nikrityuk b, Bernd Meyer a Technische Universität Bergakademie Freiberg, CIC Virtuhcon and Institute of Energy Pr bDepartment of Chemical and Materials Engineering, University of Alberta, 9107-116 St a r t i c l e i n f o

Article history:

Received 2 May 2014

Received in revised form 21 November 2014 a b s t r a c t

This work is devoted to the bon particle moving in a ho

International Journal of journal homepage: wwwally reacting porous particle s Engineering and Chemical Engineering, Fuchsmühlenweg 9, 09599 Freiberg, Germany monton T6G 2V4, Canada ee-dimensional numerical investigation of a chemical reacting porous car2/CO2 gas. The porous particle was represented by an agglomerate of small le at ScienceDirect eat and Mass Transfer l sevier .com/locate / i jhmt

HeaNomenclature

Roman symbols

A pre-exponential factor c concentration cd drag coefficient

C polynomial coefficient da agglomerate diameter

D mass diffusion coefficient

Da Damköhler number

E activation energy

G incident radiation term h enthalpy h0 enthalpy of formation

I identity matrix k forward rate constant

L domain parameter _m mass flow rate _m0C carbon net mass flux between surface and gas

M molecular weight ~n normal vector n temperature exponent

A. Richter et al. / International Journal ofconfirmed that the particle’s burning mode is sensitive to the Reynolds number. Higuera [7] carried out a numerical study into the influence of particle size, velocity, temperature and gas composition on burning rates, using simple chemistry. Recently, Kestel et al. [8] examined the influence of water vapor on the carbon consumption rate and the surface temperature of a single particle moving in hot air. Richter et al. [10] conducted a numerical investigation into single non-porous particle burnout in different O2/CO2 atmospheres and for different gas velocities.