Gasification in Fixed Bed Reactors

Multi agricultural fueled staged gasifier with dry gas cleaning
Partner in the European Community project LIFTOFF (CIRAD, Montpellier, France)

Modeling of char fixed bed gasification in a continuous reactor
Post-doctoral work of Fabrice Golfier

PhD work of Floriane Mermoud at CIRAD Montpellier - CIRAD/EMAC
Gazéification de charbon de bois à la vapeur d'eau : de la particule isolée au lit fixe continu
Institut National Polytechnique de Toulouse, June the 2nd 2006
Abstract: From the last decades, the continuous increase of the world energy demand and the problem of the increase in the greenhouse effect made the renewable energies more attractive. In this context, the biomass presents an interesting potential, and the emergence of efficient technologies, such as gasification, encourages the development of this route. An experimental study on the steam gasification of an isolated wood char particle was performed on a "macro-TG" apparatus. The evolution of the particle mass during gasification under precisely controlled operating conditions was recorded. Typically, at a temperature of 930°C and under a steam partial pressure of 0,2 atm, the time for complete gasification of a 7 mm diameter wood char particle was 32 min. The parametric study enabled to identify the temperature and the heating rate during pyrolysis as strongly influent parameters on the gasification rate. Moreover, the investigation of a good indicator for the char reactive surface was carried out. A numerical model of the gasification of a wood char particle was developed. The confrontation with the experimental results from the parametric study enabled to determine the kinetics constants of the steam gasification reaction. The results showed that in industrial conditions, the gasification process of a charcoal particle follows neither a shrinking core, nor a homogeneous model. The model enabled to better understand the coupling between reaction kinetics and heat/mass transfers inside the particle.Finally, an experimental reactor for the gasification of a fixed bed of char particles was especially designed a nd built; it precisely replicates the operating conditions of an industrial reactor. The first tests in steady state exhibited very satisfactory mass balance closures.

Gazéification du charbon de plaquettes forestières : particule isolée et lit fixe continue
PhD work of Jean-Philippe Tagutchou at CIRAD Montpellier - CIRAD/EMAC
Institut National Polytechnique de Toulouse, December the 8th 2008

Abstract: Biomass gasification is considered today as a promising route for energy production, such as electricity, natural gas or synthetic biofuels. Mechanisms involved in such processes are very complex and need further understanding. In staged processes, the zone of gasification of carbon residue impacts significantly the energy efficiency and the quality of gas produced. This thesis improves the understanding of this reaction zone in order to optimize the design and the operation of reactors. The gasification of char from forestry woodchips has been precisely characterised in the case of both a single particle and a continuous fixed bed. We have measured the gasification kinetic of particles of different sizes and in various atmospheres using a "macro-ATG" type reactor. We noticed that between 800 and 1000 °C, the thickness of the particle is the characteristic dimension; the reaction of gasification is about three times faster in the presence of steam than it is with carbon dioxide. The results of the parametric study confronted with those of our numerical model, enabled us to identify the intrinsic kinetic constants of chemical reactions. In parallel, we modified our numerical model to take into account the complex evolution of carbon reactivity. Thus, we added the concept of "structural factor" relative to active sites. This allowed us to propose a new kinetic model in the case of a mixed atmosphere of CO2 and H2O. Furthermore, we studied the gasification of a continuous fixed bed experimentally using an original reactor, the CFiBR (Continuous Fixed Bed Reactor). Superheated steam has been injected, and a more elaborated instrumentation enabled us to determine profiles of temperature, concentration of gaseous species, char conversion, pressure and porosity of the bed. We have identified reactions zones within the bed and determined the relative importance of different reactions on the conversion of carbon, the production of synthesis gas and energy consumption.

Gazéification de charbon de granulé de bois : comportement thermochimique et mécanique du lit fixe continu
PhD work of Gabriel Teixeira CIRAD Montpellier - CIRAD/EMAC
Institut National Polytechnique de Toulouse, March the16th 2012

Abstract: Multi-stage gasification of biomass leads to the production of a clean synthetic gas that can easily be used for electrical and/or thermal energy. However, optimization of these processes in terms of conversion yield and flexibility regarding the type of biomass is a major industrial challenge. To that end, a key stage of the process was specifically studied in this thesis: char gasification in a continuous fixed bed reactor. Granulation is the solution proposed for making use of low density or small particle-size biomasses. The performance of two wood chars - made from wood chips and pellets - was studied at the same time using experimental and numerical tools. Experiments were first conducted in a very highly instrumented pilot reactor, reproducing this zone of the process. The profiles measured, namely temperature, gas composition, bed density and particle velocity formed a unique database revealing reactor performance. A very reactive zone under 5 cm thick was thus located at the top of the bed, or even significant compaction leading to a drop in particle velocity, in a ratio of 8. Granular char gasification led to the same final conversion rates and synthetic gas compositions as for the chars derived from wood chips. A numerical model of the study zone was then developed, based on solving conversion equations combined with reaction kinetics, using COMSOL software. Taking into account bed compaction and the apparent kinetics of the heterogeneous reactions on a particle scale in the reaction source terms were two specificities of the model. It enabled satisfactory reproduction of the profiles of the physical magnitudes measured, for various operating conditions and for the two chars studied. Use of this model is already providing new and complementary experimental information; it will eventually make it possible to optimize the industrial process.

Study of the pyrolysis fixed bed with partial oxidation, and of the downstream volatile matter oxidation.
PhD work of Elias DAOUK, in progress - CIRAD/EMN/EMAC

Influence of pyrolysis heating rate on steam gasification kinetics of process size wood char particles
F. Mermoud, S. Salvador, L. Van de steene, F. Golfier
Fuel, 85 (2006) 1473-1482

Experimental and numerical study of steam gasification of a single charcoal particle
F. Mermoud, F. Golfier, S. Salvador, L. Van de steene, J.L. Dirion
Combustion and Flame, 145 (2006) 59-79

Impact of peripheral fragmentation on the steam gasification of an isolated wood charcoal particle in a diffusion-controlled regime
F. Golfier, L. Van de steene, S. Salvador, F. Mercmoud, C. Oltean M.A. Bues
FUEL 88 (2009) 1498-1503

A new experimental Continuous Fixed Bed Reactor to characterise wood char gasification
L. Van de steene, J-P. Tagutchou, F. Mermoud, E. Martin, S. Salvador
Fuel 89 (2010) 3320-3329

Gasification of Wood Char in Single and Mixed Atmospheres of H2O and CO2
J.P. Tagutchou, L. Van de steene, F.J. Escudero Sanz, S. Salvador
Energy Sources, Part A: Recovery, Utilization, and Environmental Effects. Accepted may 2011

Gasification of woodchip particles: Experimental and numerical study of char-H2O, char-CO2, and char-O2 reactions
L. Van de steene, J.P. Tagutchou, F.J. EscuderoSanz, S. Salvador
Chemical Engineering Science 66 (2011) 4499-4509

Gasification of char from wood pellets and from wood chips: textural properties and thermochemical conversion along a continuous fixed bed
Gabriel Teixeira, Laurent Van de Steene, Eric Martin, Franck Gelix, Sylvain Salvador
FUEL 102, p.514-524, 2012.

G. Teixeira, L. Steene, A. Ponthieux, Sylvain Salvador
Prediction of the gasification kinetics of a single wood char particle from a limited set of parameters
Fuel 123, pp.194-204, 2014.

Steam gasification of char from wood chips fast pyrolysis: Development of a semi-empirical model for a fluidized bed reactor application
S. Septien, Francisco Javier Escudero Sanz, Sylvain Salvador, S. Valin
Biomass and Bioenergy 77, pp.64-74, 2015.

The effects of textural modifications on beech wood-char gasification rate under alternate atmospheres of CO2 and H2O
Chamseddine Guizani, Francisco Javier Escudero Sanz, M. Jeguirim, R. Gadiou, Sylvain Salvador
Fuel Processing Technology 138, pp.687-694, 2015.

Influence of temperature and particle size on the single and mixed atmosphere gasification of biomass char with H2O and CO2
Chamseddine Guizani, Francisco Javier Escudero Sanz, Sylvain Salvador
Fuel Processing Technology, 134, pp.175-188, 2015.

The nature of the deposited carbon at methane cracking over a nickel loaded wood-char
Chamseddine Guizani, Francisco Javier Escudero Sanz, Sylvain Salvador
Comptes Rendus Chimie, Elsevier Masson, 19 (4), pp.423-432, 2016.

Chamseddine Guizani, Mejdi Jeguirim, Sylvie Valin, Lionel Limousy, Sylvain Salvador
Biomass Chars: The Effects of Pyrolysis Conditions on Their Morphology, Structure, Chemical Properties and Reactivity
Energies 10 (6), pp.796, 2017.

The effect of pyrolysis heating rate on the steam gasification reactivity of char from woodchips
Santiago Septien, Francisco Javier Escudero Sanz, Sylvain Salvador, Sylvie Valin
Energy, 142, pp.68-78, 2018.