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H Spliethoff - One of the best experts on this subject based on the ideXlab platform.
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gasification kinetics during entrained flow gasification part i Devolatilisation and char deactivation
Fuel, 2013Co-Authors: A Tremel, H SpliethoffAbstract:Abstract The Devolatilisation behaviour of solid fuels and the reactivity of the resulting char are important design parameters for entrained flow gasifiers. The volatile yield and Devolatilisation rate of two coals are measured in a pressurised high temperature entrained flow reactor at up to 1600 °C and 4.0 MPa and in a wire mesh reactor. A pyrolysis model is derived that describes the influences of temperature, pressure, and residence time on Devolatilisation. During the entrained flow pyrolysis experiments char samples are collected from the hot reaction zone and their reactivity and surface area are measured. A significant char deactivation is observed when the chars are exposed to a high temperature for a longer time during pyrolysis. This loss of reactivity is caused by a loss of specific surface area, but also by a decrease in intrinsic reactivity. Based on the experimental data set, a char deactivation model is derived that describes the loss of active sites by the continuous transformation of fresh reaction sites to deactivated sites. The experimental data and the models indicate that the Devolatilisation rate is significantly faster than the char deactivation rate. Therefore char deactivation also occurs during the heterogeneous char reactions and should be considered in a char conversion model for entrained flow gasification.
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sensitivity analysis of different Devolatilisation models on predicting ignition point position during pulverized coal combustion in o2 n2 and o2 co2 atmospheres
Fuel, 2012Co-Authors: Rastko Jovanovic, Aleksandra Milewska, Bartosz Swiatkowski, Adrian Goanta, H SpliethoffAbstract: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. However, 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-CO2 conditions were compared with experimental data from the laboratory ignition test facility. Obtained results pointed out that network Devolatilisation models (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. (C) 2011 Elsevier Ltd. All rights reserved.
Juan Adanez - One of the best experts on this subject based on the ideXlab platform.
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coupled drying and Devolatilisation of non spherical wet pine wood particles in fluidised beds
Journal of Analytical and Applied Pyrolysis, 2002Co-Authors: L F De Diego, F Garcialabiano, Alberto Abad, P Gayan, Juan AdanezAbstract:Release of volatiles of non-spherical pine wood particles was analysed by means of continuous measurements of the CO2 and O2 concentrations obtained after the complete combustion of the volatiles and from flame extinction times. The effect of the atmosphere used for Devolatilisation was tested. The volatiles' evolution was nearly identical using air or N2 as fluidising gas. The Devolatilisation times increased with increasing the equivalent particle diameter, but there was an important scattering in the results. The data dispersion greatly decreased when the shape factor of the wood particles was considered. The Devolatilisation times were fitted to a power-law relation replacing the particle diameter by the equivalent particle diameter multiplied by the shape factor. The effect of the moisture content was studied by analysis of the Devolatilisation process of pine wood particles of the same size and different moisture contents (0–50%). As the moisture content of the wood particles increased the Devolatilisation rate of combustible volatiles decreased and was more uniform along the Devolatilisation time.
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modeling of the devolatilization of nonspherical wet pine wood particles in fluidized beds
Industrial & Engineering Chemistry Research, 2002Co-Authors: L F De Diego, F Garcialabiano, Alberto Abad, And Pilar Gayan, Juan AdanezAbstract:The release of volatiles of pine wood particles was analyzed by means of continuous measurements of the CO2 and O2 concentrations obtained after the complete combustion of the volatiles and from flame extinction times. A relatively simple mathematical model was used to predict the O2 consumed, as a function of time, during the devolatilization and further volatiles combustion of wood chips in fluidized beds. In this model, the drying and pyrolysis of wood particles is considered as a coupled process controlled by the kinetics of devolatilization as well as heat transfer to and through the particles. A distributed activation energy model is adopted for the kinetics of devolatilization of the wood particles. The wood chips are characterized by an equivalent particle diameter and a shape factor and transformed into spherical shape. The model was in satisfactory agreement with experimental data over a wide range of operating conditions, particle sizes and shapes, and particle moisture contents of practical im...
Leonardo Tognotti - One of the best experts on this subject based on the ideXlab platform.
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a generalized correlation for coal devolatilization kinetics at high temperature
Fuel Processing Technology, 2014Co-Authors: Enrico Biagini, Leonardo TognottiAbstract:Abstract The optimization of thermochemical (combustion, gasification, pyrolysis, oxyfiring) systems requires a comprehensive model, able to simulate conventional and innovative plants, for achieving the high levels of efficiency and low pollutant emissions required by the current applications. A devolatilization model is the basis of these processes and should be sufficiently simple and accurate to be implemented in commercial codes for simulating large scale plants. Kinetic parameters should be validated in qualified tests under severe thermal conditions and for coals of different ranks. In this work the experimental data from the isothermal plug flow reactor of IFRF (with temperatures up to 1673 K and heating rates on the order of 10 4 K/s), previously uniformed and organized in the solid fuel database SFDB, are elaborated to obtain the kinetic parameters according to a modified version of the single first order reaction model. The effective thermal history of the particles is estimated by simulating the devolatilization tests with a CFD model. A generalized correlation is obtained between the kinetic parameters and coal properties, preferably among those routinely reported in standard analyses. Finally, a practical and useful predictive tool is provided for studying the devolatilization of pulverized coal.
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effect of the heating rate on the devolatilization of biomass residues
Thermochimica Acta, 2008Co-Authors: Enrico Biagini, A Fantei, Leonardo TognottiAbstract:Abstract The devolatilization is the basic step of thermochemical processes and requires a fundamental characterization. Three biomass residues (rice husks, olive cake, cacao shells) are studied here in a thermogravimetric (TG) balance. The effect of the heating rate (HR) is evaluated in the range 5–100 K/min providing significant parameters for the fingerprinting of the fuels. Kinetics are obtained by applying traditional isoconversional methods. The activation energy as function of the conversion reveals the multi-step nature of the biomass devolatilization. Although average values allow the reactivity of different fuels to be compared, a first order reaction model can hardly predict the biomass devolatilization. A VEB (Variable activation Energy model for Biomass devolatilization) model is developed, basing on the results of the kinetic analysis. A good agreement is obtained for the biomass residues in all HR runs in the entire range of temperatures. Similarities in the optimized E VEB curves for the three fuels of this work suggest to pursue a generalization in the approach, enlarging the number and variety of fuels studied.
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characterization of a lab scale platinum filament pyrolyzer for studying the fast devolatilization of solid fuels
Fuel, 2006Co-Authors: Enrico Biagini, Federica Lippi, Leonardo TognottiAbstract:Platinum filament pyrolyzers achieve very high temperature and heating rate and can provide useful parameters for practical applications in combustion, pyrolysis and gasification processes. The critical use of an experimental instrument is necessary to provide reliable data. In this work, a commercial pyrolyzer (CDS Pyroprobe 2000) is characterized to obtain a correspondence between the nominal and the effective operating conditions. This is the basis for the modeling estimation of the effective thermal history of the sample during each experimental run. The experimental results obtained performing the devolatilization of coals, biomass and waste fuels using the pyrolyzer are compared with those obtained in a conventional thermogravimetric balance, to evaluate the effects of extremely different operating conditions. The amount of volatile released programming the most severe thermal conditions using the pyrolyzer (thus in conditions more similar to large-scale plants) differs significantly from that of thermogravimetric runs. Global kinetics are obtained fitting the experimental results and using the thermal history of the sample from the model results. They depend strongly on the conditions used for the devolatilization. Global kinetics obtained in the thermogravimetric balance runs (low heating rate) overestimate the rate of devolatilization in the pyrolyzer (high heating rate).
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devolatilization of biomass fuels and biomass components studied by tg ftir technique
Industrial & Engineering Chemistry Research, 2006Co-Authors: Enrico Biagini, Federica Barontini, Leonardo TognottiAbstract:Biomass fuels represent a renewable energy source, they are CO2 neutral fuels, and their use reduces the consumption of fossil fuels and limits the emissions of SOx, NOx, and heavy metals. They are used in pyrolysis, gasification, combustion, and co-combustion. The devolatilization is a fundamental mechanism in all these processes, especially for high volatile matter fuels. In this work, the devolatilization of biomass fuels (of different origin, properties, and composition) and biomass components is studied coupling thermogravimetric (TG) analysis with infrared spectroscopy. The characteristic temperatures are determined for the main devolatilization steps and compared for all fuels. A bituminous coal and a paper sludge are also studied for comparison. Light gases released (CO, CO2, H2O, CH4, CH3OH, HCOOH) are detected, whereas more complex organic (hydrocarbon and oxygenated) compounds are grouped because of the large variety of volatile species released in a narrow range of temperature. The weight loss...
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comparison of devolatilization char oxidation and direct oxidation of solid fuels at low heating rate
Energy & Fuels, 2006Co-Authors: Enrico Biagini, Leonardo TognottiAbstract:Fundamental information can be obtained by comparing the behavior of different classes of solid fuels (low- and high-volatile matter coals, biomass fuels, residues, wastes, and plastics) in oxidizing and inert thermogravimetric runs. Different mechanisms can be recognized and attributed to devolatilization, char oxidation, and direct oxidation. The direct oxidation of the fuel can be favored with respect to the traditional devolatilization/char oxidation scheme depending on the conditions used and the characteristics of the fuel. Oxygen enhances the thermal devolatilization of the fuel and the reactivity of the produced char. The reactivity of all fuels are quantified by defining characteristic temperatures of each mechanism and providing kinetics for all steps. Also, the effect of the operating conditions are evaluated. Results obtained in this work represent a significant set of data on very different solid fuels, useful for modeling purposes, for practical system handling (grate furnaces or fixed-bed combustors, operating in conditions similar to this study), for safety of fuel stockpiles, and for investigations on ignition and char reactivity.
Hartmut Spliethoff - One of the best experts on this subject based on the ideXlab platform.
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sensitivity analysis of different Devolatilisation models on predicting ignition point position during pulverized coal combustion in o2 n2 and o2 co2 atmospheres
Fuel, 2012Co-Authors: Rastko Jovanović, Aleksandra Milewska, Bartosz Swiatkowski, Adrian Goanta, Hartmut SpliethoffAbstract: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. However, 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-CO2 conditions were compared with experimental data from the laboratory ignition test facility. Obtained results pointed out that network Devolatilisation models (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. (C) 2011 Elsevier Ltd. All rights reserved.
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the fate of main gaseous and nitrogen species during fast heating rate devolatilization of coal and secondary fuels using a heated wire mesh reactor
Fuel Processing Technology, 2009Co-Authors: Gary Nola, W De Jong, Hartmut SpliethoffAbstract:Abstract Fast devolatilization experiments of coal and biomass fuels have been carried out using a heated wire mesh setup integrated within an FTIR spectrophotometer for in-situ gas analysis. A bituminous coal and slaughter/poultry biomass residues, currently utilized in the Dutch power sector as secondary fuels in coal-fired utilities, have been studied. The influence of peak temperature (500–1300 °C), heating rate (600–1000 K/s) and hold time at peak temperature on the devolatilization has been investigated. Particular emphasis was given to characterize the fuel-bound nitrogen partitioning of these fuels as a function of the various operating parameters. The results suggest that, for combustion applications, the effectiveness of primary measures for NO x control can be enhanced when biomass fuels are co-fired with coal if a complete devolatilization is ensured in the fuel-rich zone of the furnace.
L F De Diego - One of the best experts on this subject based on the ideXlab platform.
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coupled drying and Devolatilisation of non spherical wet pine wood particles in fluidised beds
Journal of Analytical and Applied Pyrolysis, 2002Co-Authors: L F De Diego, F Garcialabiano, Alberto Abad, P Gayan, Juan AdanezAbstract:Release of volatiles of non-spherical pine wood particles was analysed by means of continuous measurements of the CO2 and O2 concentrations obtained after the complete combustion of the volatiles and from flame extinction times. The effect of the atmosphere used for Devolatilisation was tested. The volatiles' evolution was nearly identical using air or N2 as fluidising gas. The Devolatilisation times increased with increasing the equivalent particle diameter, but there was an important scattering in the results. The data dispersion greatly decreased when the shape factor of the wood particles was considered. The Devolatilisation times were fitted to a power-law relation replacing the particle diameter by the equivalent particle diameter multiplied by the shape factor. The effect of the moisture content was studied by analysis of the Devolatilisation process of pine wood particles of the same size and different moisture contents (0–50%). As the moisture content of the wood particles increased the Devolatilisation rate of combustible volatiles decreased and was more uniform along the Devolatilisation time.
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modeling of the devolatilization of nonspherical wet pine wood particles in fluidized beds
Industrial & Engineering Chemistry Research, 2002Co-Authors: L F De Diego, F Garcialabiano, Alberto Abad, And Pilar Gayan, Juan AdanezAbstract:The release of volatiles of pine wood particles was analyzed by means of continuous measurements of the CO2 and O2 concentrations obtained after the complete combustion of the volatiles and from flame extinction times. A relatively simple mathematical model was used to predict the O2 consumed, as a function of time, during the devolatilization and further volatiles combustion of wood chips in fluidized beds. In this model, the drying and pyrolysis of wood particles is considered as a coupled process controlled by the kinetics of devolatilization as well as heat transfer to and through the particles. A distributed activation energy model is adopted for the kinetics of devolatilization of the wood particles. The wood chips are characterized by an equivalent particle diameter and a shape factor and transformed into spherical shape. The model was in satisfactory agreement with experimental data over a wide range of operating conditions, particle sizes and shapes, and particle moisture contents of practical im...