Improving the design and operation of grate-fired biomass boilers


Grate biomass combustion is used for heating especially in cold countries. Numerous technological improvements have been undertaken to improve their efficiency so as to meet the customer needs as well as the policy regulations requirements. The use of computerized tools for the design, development, and simulation of grate biomass models have increased over the past decade. Bed combustion generally comprises of two zones that is fuel bed zone and freeboard zone which supports heterogeneous reactions and gaseous combustion respectively. Unfortunately, it is difficult to achieve accurate modeling of grate-fired combustion devices due to the complex nature of thermal-chemical conversion of particles found in a fuel bed.

Even though computational fluid dynamics (CFD) have been used to effectively simulate the freeboard zone, no good method has been provided for fuel bed combustion modeling. For instance, various approaches including porous medium, stand-alone bed models and empirically derived models experience numerous limitations thus producing inaccurate results. Therefore, developing a numerical tool for simulating biomass combustion in grate-fired is highly required.

Recently, Dr. Adeline Rezeau and Dr. Maryori Diaz-Ramirez at CIRCE Foundation in collaboration with Dr. Luis Diez and Dr. Javier Royo at the University of Zaragoza in Spain developed a numerical tool for simulating biomass combustion in grate-fired biomass boilers based on a simplified computational fluid dynamics. They achieved sufficient results accuracy and computing demand for enhancing the operation and improvements of the biomass devices. Their research work is currently published in the research journal, Fuel Processing Technology.

Briefly, the team of authors simplified the coupling between the freeboard zone and bed zone by integrating them on the same three-dimensional grid. Consequently, they assumed the combustion bed as a porous medium and utilized the modified laminar rate model to simulate the heterogeneous reactions because it allows simulating drying, pyrolysis and char reactions. The introduced site species effectively reacted on the surface of the porous medium thus producing and consuming the gas species. Furthermore, they carried out an experimental test in a 250 kWth grate boiler to validate the numerical tool. Eventually, they used the computational fluid dynamics-based tool to characterize the flow patterns and temperature in a combustion chamber.

The authors observed the similarities between the experimental results and the numerical results. This confirmed the capability of the developed modeling approach to predict the performance of the boiler. Also, the method was capable of detecting some of the operation and design deficiencies hindering the operation of biomass boilers that could not be detected by other experimental tests. For instance, several dead zones were produced by the secondary air inlets forcing the flames to expand in the direction of the combustion wall chambers thus affecting combustion above the grate.

The authors have successfully developed a new modeling method for enhancing the operation and improving the design of grate-fired biomass boilers. As such, it has created a platform for future research and hence will advance the design, development, and operation of efficient biomass boilers.

grate-fired biomass boilers-Advances in Engineering

About the author

Dr. Adeline Rezeau is currently researcher within the “Fuel and Combustion Technologies” Group (Energy and Environmental Technologies Area) at CIRCE Foundation. Since 2005, she has been involved in several national and European R&D&i projects, mainly dedicated to solid biomass conversion, CFD simulations and agro-residues valorization. She obtained her PhD in Mechanical Engineering from the University of Zaragoza in 2014 and has published more than 20 publications, including 4 book chapters and 4 peer-reviewed articles.

Her research expertise and interests include agro-biomass value chains, optimization of grate-fired boilers design and operation and solids combustion modelling.

Email: [email protected]

About the author

Dr Luis Ignacio Díez currently holds a position of Associate Professor in the Department of Mechanical Engineering of the University of Zaragoza. Moreover, he was acknowledged as eligible for Full Professorship by the Spanish National Agency for Professors Evaluation in the year 2015. Since 2017, he holds the position of Head of the Department of Mechanical Engineering, University of Zaragoza.

His research experience covers a total period of 20 years, working in competitive projects funded by public institutions. The total number of projects has been 15: European funds (9), Spanish funds (5) and regional funds (1). Among them, he has been the main researcher in 4 projects (1 European, 3 Spanish). He has also participated in research contracts funded by private companies (13 projects) and with public Administrations (2 projects). He has been the main researcher in 7 of these contracts. As a result of this activity, he has co-authored 35 papers published in international journals (32 in JCR-indexed journals) and 2 book chapters. Additionally, he has also co-authored 30 contributions to international conferences, participating with oral presentations (21) or posters (9).

His research expertise and interests include oxy-fuel combustion, modelling of thermo-chemical processes, energy storage and co-firing with biomass, among others.

About the author

Dr. Javier Royo is Associate Professor of Energy Technology in the Department of Mechanical Engineering of the University of Zaragoza. He has co-authored more than 20 peer-reviewed papers, 5 book chapters and more than 40 contributions to international conferences. Up to now, he has worked in 25 public research projects (Spanish and European funds) and more than 20 contracts with private companies and other organizations.

His research expertise and interests include biomass resources assessment, their thermochemical transformation (by means of combustion and co-firing technologies), and also the determination of the environmental impact of their use (Life Cycle Assessment).

About the author

Dr. Maryori C. Díaz Ramírez is currently researcher within the Process Integration Group (Energy and Environmental Technologies Area) of CIRCE Foundation. She is Chemical Engineer graduated with honors at University of Carabobo (Venezuela) in 2001. After gaining experience as Process Engineer, she was awarded by the Alban Programme in 2004 to get a Master Degree in Eco-Efficiency, Energy Saving and Renewable Energy Technologies at the Centre of Research for Energy Resources and Consumption (CIRCE)-University of Zaragoza. After this period, Maryori initiated her research career at CIRCE where she has attained more than 10 years of consolidated professional experience by being involved in the execution of several R&D&I projects related to industrial processes optimization, biomass as an energy source and environmental assessments.

She also holds a European Ph. D in Renewable Energy and Energy Efficiency from CIRCE Research Institute of the University of Zaragoza. During this period, she was awarded by the Guest Scholarship Program 2007/08 for Advanced Academic Studies or Research in Sweden and by the Ph.D. European Mention Scholarship Program 2009/2010 of the University of Zaragoza to perform two research fellowships; one at Umeå University (2008-2009) and another one at the Technical University of Denmark, DTU (2010).

She has published in JCR listed journals and participated in several international conferences. Maryori works on developing new technical solutions focused on the achievement of a sustainable development involving national and international networks.


Rezeau, A., Díez, L., Royo, J., & Díaz-Ramírez, M. (2018). Efficient diagnosis of grate-fired biomass boilers by a simplified CFD-based approach. . Fuel Processing Technology, 171, 318-329.

Go To Fuel Processing Technology

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