Resolved flow simulation of pulverized coal particle devolatilization and ignition in air- and O2/CO2-atmospheres

Significance Statement

Production of electrical base load power highly utilizes pulverized coal combustion. The knowledge of coal ignition and combustion is fundamental for improving modern pulverized coal burners. This dictates that knowledge of the underlying physio-chemical processes is necessary so as to predict the pulverized coal combustion performance. The flame characteristics such as pollutant formation, stability and possible extinction are influenced by devolatilization and ignition phenomena. Experiments, which can provide crucial data on the pulverized coal combustion process, have intricate uncertainties and are hence difficult to conduct. Large eddy simulation (LES) has been increasingly used to study pulverized coal combustion since it has the potential to offer more insight as compared to the classical RANS approaches. However, the detailed near-particle processes remain unresolved in LES. Therefore the focus is channeled towards resolved laminar flow simulations of fuel oxidizer mixing, ignition and devolatilization in the immediate vicinity of the particle surface, which provides detailed sub-grid information for LES.

In a recent paper published in Fuel G.L. Tufano and colleagues investigated the effects of enhanced oxygen levels and balance gas atmosphere on single coal particle ignition and compared their numerical data against measured results in well-defined conditions.

The heating rate history of the particle was obtained by solving for the intraparticle heat transfer and heat exchange between the particle and its surroundings. The authors captured the time evolution of volatile release by using the particle mean temperature to compute the devolatilization rate. The research team assumed volatile compositions which included both light gases and larger hydrocarbons to represent the tar. To accurately describe the homogeneous chemistry, a skeletal kinetic mechanism for pyrolysis and oxidation of hydrocarbons and oxygenated fuels was used. Ignition, pyrolysis, particle heat-up and envelope flame stabilization were characterized in four gas atmospheres differing in oxygen content and the use of either nitrogen or carbon dioxide as balance gas.

The authors were able to observe that enhanced oxygen levels shortened the ignition delay time, therefore resulting in a higher intensity of the combustion process according to temperature and radical production peaks for the studied mixtures. They also found that the presence of the carbon dioxide in place of the nitrogen gas delayed the ignition. It is evident that the observed behavior is coherent with the varying thermo-physical properties of the gas mixtures despite the complex uncertainties in both coal simulations and experiments. It is also observed that absolute values of predicted ignition delay time are functions of potential particle preheating, particle Reynolds number and the criterion employed for extraction of ignition delay, but the relative trends for different gas phase environments stand correct.

Resolved flow simulation of pulverized coal particle devolatilization and ignition in air- and O2CO2-atmospheres - advances in engineering

About The Author

G.L. Tufano is a PhD candidate at the Institute for Combustion Technology (ITV) Stuttgart. He obtained his B.Sc. in Aerospace Engineering and M.Sc. in Aerospace and Astronautics Engineering from “Federico II” University in Naples, Italy. During his MSc he performed experimental studies on turbulent combustion at the University of Connecticut (USA). His PhD research concerns the direct numerical simulation (DNS) of pulverized coal combustion in the context of flamelet modeling.

About The Author

O.T. Stein is a senior researcher and lecturer at ITV Stuttgart Germany, where he is heading the group’s research activities on solid fuel combustion modeling by means of LES and DNS. He obtained his Diplom in Mechanical Engineering from Darmstadt University in 2004 and his PhD from Imperial College London in 2009. He is a reviewer for more than 10 scientific journals and a co-organizer of the international CBC workshop series.

About The Author

A. Kronenburg is Professor of combustion at the University of Stuttgart. He graduated in 1994 from RWTH Aachen and received his PhD from the University of Sydney in 1999. After working for DaimlerChrysler until the end of 2000, he moved to Imperial College London where he was first appointed to a Governor’s lectureship and later promoted to Reader of Combustion.

In 2009, he became director of ITV Stuttgart. His research interests include turbulent, multiphase reacting flows, aerosol dynamics, nanoparticle flame synthesis and fluid flow under extreme conditions.

About The Author

A. Frassoldati is an Associate Professor of combustion and chemical plants at CMIC Department of Politecnico di Milano, where he graduated in Chemical Engineering in 1999 and obtained his PhD in 2004. He is the head of the PhD Board at Politecnico di Milano for the PhD programme in Industrial Chemistry and Chemical Engineering. He conducts research in the areas of detailed kinetic modeling of combustion of hydrocarbons and biofuels, solid fuels pyrolysis and gasification, CFD modeling of burners, combustors and industrial furnaces.

He is member of the Italian Section of the Combustion Institute and member of the Board. He is the author of about 80 papers in international scientific journals and more than 100 publications in conference proceedings.

About The Author

T. Faravelli is Professor of combustion and transport properties at the Department of Chemistry, Materials and Chemical Engineering of Politecnico di Milano, where he graduated in Chemical Engineering in 1987 and obtained his PhD in 1990. He is the head of the Chemical Engineering Section.

His main scientific activity refers to: numerical fluid dynamics of reactive flows, turbulence/kinetics interactions, chemical reaction engineering of complex systems (pyrolysis, partial oxidation and combustion modeling of gas, liquid and solid fuels) and pollutant formation (NOx, PAH and soot) from combustion processes.

He is Associate Editor of the Proceedings of the Combustion Institute and of Combustion and Flame. He is author of about 180 papers.

About The Author

L. Deng holds a PhD from the University of Duisburg-Essen, where he conducted research on the simulation and analysis of flames and nano-particle synthesis at the chair of Fluid Dynamics. Since March 2017, Dr. Deng works in the joined research department of BASF in Ludwigshafen, simulating polymerization processes by computational fluid dynamics.

About The Author

A.M. Kempf holds the chair of Fluid Dynamics at the University of Duisburg-Essen. He studied Mechanical Engineering at Darmstadt University and graduated with a PhD on the Large-Eddy Simulation of Non-Premixed Combustion in 2003. He then joined Imperial College London as an Assistant and then Associate Professor (Senior Lecturer) to develop new models, methods and programs for the simulation of turbulent reacting flows. In 2011, he joined Duisburg-Essen.

He is part of the editorial boards of three international journals, of compute time allocation panels and is the original developer of the PsiPhi code for Direct Numerical Simulation and Large-Eddy Simulation of multiphase flows with moving boundaries, chemical reaction and radiation, efficiently using over 100,000 thousand cores on a regular basis.

About The Author

M. Vascellari is a post-doctoral researcher at the chair of Numerical Thermo-Fluid Dynamics (NTFD) at Freiberg University of Technology. He received his PhD in Mechanical Design at University of Cagliari in Italy in 2005. He was a post-doctoral researcher at the Department of Mechanical Engineering at University of Cagliari, before joining NTFD Freiberg in 2011.

His main research interests are CFD modeling of coal combustion and gasification. In particular, he focused on the development and integration in CFD codes of advanced models for simulating the thermal conversion of solid feedstock, including pyrolysis and char conversion, and on the development of flamelet-based turbulence chemistry interaction models for coal combustion and gasification.

About The Author

Christian Hasse is a Professor in the Department of Mechanical and Chemical Process Engineering at Freiberg University of Technology. He holds the chair of Numerical Thermo-Fluid Dynamics. He received his diploma in Mechanical Engineering in 1998 and his PhD in 2004 from RWTH Aachen University (supervisor: Norbert Peters). After working in engine development at BMW for 5.5 years, he returned to academia in 2010.

His research topics focus on modeling and simulating reactive and non-reactive flows including flamelet modeling, turbulent mixing dynamics, multi-component sprays and evaporation, engine combustion, pollutant formation, population balance modeling and exhaust gas cleaning. His main fields of application are combustion and chemical process engineering. For these topics, a number of specialized software tools are available, ranging from flexible 1D flame solvers to full 3D DNS codes.

He has published more than 80 papers in peer-reviewed journals. He also is a reviewer for more than 20 scientific journals and several national and international funding agencies.

Reference

G.L. Tufano1, O.T. Stein1, A. Kronenburg1, A. Frassoldati2, T. Faravelli2, L. Deng3, A.M. Kempf3, M. Vascellari4, C. Hasse4. Resolved flow simulation of pulverized coal particle devolatilization and ignition in air- and O2/CO2-atmospheres. Fuel volume 186 (2016) pages 285–292.

Show Affiliations
  1. Institut für Technische Verbrennung, Universität Stuttgart, Herdweg 51, 70174 Stuttgart, Germany
  2. Dipartimento di Chimica, Materiali e Ingegneria Chimica, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy
  3. Institute for Combustion and Gasdynamics (IVG), Chair for Fluid Dynamics, University of Duisburg-Essen, Germany
  4. Chair of Numerical Thermo-Fluid Dynamics, ZIK Virtuhcon, TU Bergakademie Freiberg, Germany

 

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