Combining the lumped capacitance method and the simplified distributed activation energy model to describe the pyrolysis of thermally small biomass particles

The pyrolysis process of thermally small biomass particles was modeled combining the Lumped Capacitance Method (LCM) to describe the transient heat transfer and the Distributed Activation Energy Model (DAEM) to account for the chemical kinetics. The inverse exponential temperature increase predicted by the LCM was considered in the mathematical derivation of the DAEM, resulting in an Arrhenius equation valid to describe the evolution of the pyrolysis process under inverse exponential temperature profiles. The Arrhenius equation on which the simple LCM-DAEM model proposed is based was derived for a wide range of pyrolysis reactor temperatures, considering the chemical kinetics data of four lignocellulosic biomass species: pine wood, olive kernel, thistle flower, and corncob. The LCM-DAEM model proposed was validated by comparison to the experimental results of the pyrolysis conversion evolution of biomass samples subjected to various inverse exponential temperature increases in a TGA. To extend the validation, additional biomass samples of Chlorella Vulgaris and sewage sludge were selected due to the different composition of microalgae and sludge compared to lignocellulosic biomass. The deviations obtained between the experimental measurements in TGA and the LCM-DAEM predictions for the evolution of the pyrolysis conversion, regarding the root mean square error of temperature, are below 5 degrees C in all cases. Therefore, the simple LCM-DAEM model proposed can describe-accurately the pyrolysis-process of a thermally small biomass particle, accounting for both the transient heat transfer and the chemical kinetics by solving a simple Arrhenius equation.The authors express their gratitude to the BIOLAB experimental facility and to the “Programa de movilidad de investigadores en centros de investigación extranjeros (Modalidad A)” from the Carlos III University of Madrid (Spain) for the financial support conceded to Antonio Soria-Verdugo for a research stay at the German Aerospace Center DLR (Stuttgart, Germany) during the summer of 2018. Funding by Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR), the German Aerospace Center, is also gratefully acknowledged

On the characteristic heating and pyrolysis time of thermally small biomass particles in a bubbling fluidized bed reactor

Pyrolysis of crushed olive stone particles in a lab scale Bubbling Fluidized Bed (BFB) reactor wasinvestigated. The time evolution of the pyrolysis conversion degree of the olive stone particles, while moving freely in the BFB, was determined from the evolution of the mass of olive stones remaining in thebed, measured by a precision scale holding the whole reactor installation. The experimental measurements of the pyrolysis conversion degree were employed to validate a simple model combining heattransfer and chemical kinetics, which is valid for thermally small particles. The model combines the Lumped Capacitance Method (LCM) and the simplified Distributed Activation Energy Model (DAEM) toaccount for heat transfer and pyrolysis chemical kinetics, respectively. The estimations of the combined LCM-DAEM model for the pyrolysis conversion degree were found to be in good agreement with the experimental measurements for the pyrolysis of olive kernels in a BFB operated at various bed temperatures,fluidizing gas velocities, and biomass particle size ranges. From the combined LCM-DAEM model, the characteristic heating time and the pyrolysis time of the olive stone particles were derived, obtaining a direct relation between these two parameters for constant values of the bed temperature.The authors express their gratitude to the BIOLAB experimentalfacility and to the program "Research Stays for University Academics and Scientists" from the German Academic Exchange Service (DAAD) for the financial support conceded to Antonio Soria-Verdugo for a research stay at the German Aerospace Center(DLR) (Stuttgart, Germany) during the summer of 2019. Funding by Deutsches Zentrum für Luft-und Raumfahrt e. V. (DLR), the German Aerospace Center, and the Helmholtz Association in the research fields energy, fuels and gasification, especially in the Program "Energy Efficiency, Materials and Resources" Topic 4 "Efficient Use of Fuel Resources" is also gratefully acknowledged

Analyzing the pyrolysis kinetics of several microalgae species by various differential and integral isoconversional kinetic methods and the Distributed Activation Energy Model

The pyrolysis kinetics of the microalgae Chlorella vulgaris (CV), Isochrysis galbana (IG), Nannochloropsis gaditana (NG), Nannochloropsis limnetica (NL), Phaeodactylum tricornutum (PT), and Spirulina platensis (SP) were studied by non-isothermal thermogravimetric analysis conducted at nine different constant heating rates. The kinetic parameters of each microalgae species were calculated using several kinetic methods, such as those of Kissinger, Friedman, Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS), Vyazovkin, and the simplified Distributed Activation Energy Model (DAEM). The results show that the kinetic parameters calculated from the integral isoconversional methods OFW, KAS and Vyazovkin are similar to those determined by applying the simplified DAEM. In contrast, application of the differential isoconversional method of Friedman led to moderate deviations in the activation energies and pre-exponential factors computed, whereas the unique values of the kinetic parameters determined by the Kissinger method resulted in the highest deviations.The authors express their gratitude to the BIOLAB experimental facility. Funding by Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR), the German Aerospace Center, is gratefully acknowledged as well as funding by the DLR international collaboration project “Accurate Kinetic Data of Biomass Pyrolysis”.Publicad

Modeling of the pyrolysis of biomass under parabolic and exponential temperature increases using the Distributed Activation Energy Model

A modification of the simplified Distributed Activation Energy Model is proposed to simulate the pyrolysis of biomass under parabolic and exponential temperature increases. The pyrolysis of pine wood, olive kernel, thistle flower and corncob was experimentally studied in a TGA Q500 thermogravimetric analyzer. The results of the measurements of nine different parabolic and, exponential temperature increases for each sample were employed to validate the models proposed. The deviation between the experimental TGA measurements and the estimation of the reacted fraction during the pyrolysis of the four samples under parabolic and exponential temperature increases was lower than 5 degrees C for all the cases studied. The models derived in this work to describe the pyrolysis of biomass with parabolic and exponential temperature increases were found to be in good agreement with the experiments conducted in a thermogravimetric analyzer.The authors express their gratitude to the BIOLAB experimental facility and to the "Programa de movilidad de investigadores en centros de investigación extranjeros (Modalidad A)" from the Carlos III University of Madrid (Spain) for the financial support conceded to Antonio Soria for a research stay at the German Aerospace Center DLR (Stuttgart, Germany) during the summer of 2014. The authors also gratefully acknowledge the financial support provided by Fundación Iberdrola under the "VI Programa de Ayudas a la Investigación en Energía y Medioambiente". Funding by the combustion and gas turbine technology program (EVG), of Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR), the German Aerospace Center, is gratefully acknowledged by Elke Goos

Pyrolysis of biofuels of the future: Sewage sludge and microalgae-Thermogravimetric analysis and modelling of the pyrolysis under different temperature conditions

The pyrolysis process of both microalgae and sewage sludge was investigated separately, by means of non-isothermal thermogravimetric analysis. The Distributed Activation Energy Model (DAEM) was employed to obtain the pyrolysis kinetic parameters of the samples, i.e. the activation energy Ea and the pre-exponential factor k0. Nine different pyrolysis tests at different constant heating rates were conducted for each sample in a thermogravimetric analyzer (TGA) to obtain accurate values of the pyrolysis kinetic parameters when applying DAEM. The accurate values of the activation energy and the pre-exponential factor that characterize the pyrolysis reaction of Chlorella vulgaris and sewage sludge were reported, together with their associated uncertainties. The activation energy and pre-exponential factor for the C. vulgaris vary between 150–250 kJ/mol and 1010–1015 s−1 respectively, whereas values ranging from 200 to 400 kJ/mol were obtained for the sewage sludge activation energy, and from 1015 to 1025 s−1 for its pre-exponential factor. These values of Ea and k0 were employed to estimate the evolution of the reacted fraction with temperature during the pyrolysis of the samples under exponential and parabolic temperature increases, more typical for the pyrolysis reaction of fuel particles in industrial reactors. The estimations of the relation between the reacted fraction and the temperature for exponential and parabolic temperature increases were found to be in good agreement with the experimental values measured in the TGA for both the microalgae and the sludge samples. Therefore, the values reported in this work for the activation energy and the pre-exponential factor of the C. vulgaris can be employed as reference values in numerical studies of the pyrolysis process of this biofuel since its chemical composition is quite homogeneous. In the case of sewage sludge, due to the heterogeneity of its composition, the results reported for the kinetic parameters of the pyrolysis process can be employed to describe the pyrolysis of sludge with similar composition.The authors express their gratitude to the BIOLAB experimental facility and to the “Programa de movilidad de investigadores en centros de investigación extranjeros (Modalidad A)” from the Carlos III University of Madrid (Spain) for the financial support conceded to Antonio Soria for a research stay at the German Aerospace Center DLR (Stuttgart, Germany) during the summer of 2016. The authors also gratefully acknowledge the financial support provided by Fundación Iberdrola under the “VI Programa de Ayudas a la Investigación en Energía y Medioambiente”. Funding by the energy, combustion, and gas turbine technology program (EVG) of Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR), the German Aerospace Center, is gratefully acknowledged as well as funding by the DLR international collaboration project “Accurate Kinetic Data of Biomass Pyrolysis”Publicad

The Importance of Detailed Chemical Mechanisms in Gas Turbine Combustion Simulations

This paper – in memory of Jürgen Warnatz – summarizes selected recent papers of the Chemical Kinetics Group at the German Aerospace Center in Stuttgart. It shows the need for detailed chemical reaction mechanisms to understand practical combustion systems. A comprehensive description of combustion processes based on detailed mechanisms is especially important in the design of new gas turbine combustion chambers and in the optimization of existing ones to improve efficiency and to reduce pollutant emissions, with fuel-flexibility and load-flexibility ever becoming more important. Different aspects of combustion processes where detailed reaction mechanisms provide useful insights will be covered in this paper: Fuels (alternative jet fuels, biomass based fuels), pollutants (soot), diagnostics (chemiluminescence), and thermochemistry. Furthermore, the underlying thermodynamics inevitably connected with detailed reaction schemes will be addressed. Exemplified results will be presented clearly demonstrating the predictive capabilities of detailed reaction mechanisms to be explored in computational fluid dynamic simulations to further optimize technical combustion systems

Final Project Report; ESA TDE Activity: High Performance Propellant Development ESA Contract No. 4000130652/20/NL/MG

The global search for green alternatives to the highly toxic monopropellant hydrazine (N2H4) is still ongoing. Different alternatives for hydrazine with different degrees of maturity are currently under investigation. One of these alternatives are mixtures of nitrous oxide and fuels. These propellants offer a high performance (Isp approx. 300 s), low propellant costs and are non-toxic. In the frame of the ESA activity High Performance Propellant Development, DLR investigated a premixed N2O/C2H6 propellant and assessed the safety and performance properties of the mixture. To study the propellant properties DLR built a liquefaction and mixing setup which allows condensation, pressurization and mixing of liquid N2O and C2H6. The produced propellant mixture was used to feed a thermal stability, a material compatibility as well as a priming/water hammer test setup. Furthermore, the gaseous propellant was used to conduct ignition test under vacuum conditions. A last work package included hot runs with liquefied N2O/C2H6 propellant supplied to a monopropellant like setup from a single tank. Despite the premixed nature of the propellant, the thermal stability tests showed no decomposition or combustion of the propellant. The compatibility testing of the propellant with metal alloys Al 2219, Ti64, and stainless steels SS 316 and CRES-15-5 showed no degradation of the material or propellant. In addition, the polymers PTFE (Polytetrafluoroethylene), Kalrez and FEP (Fluorinated ethylene propylene) were tested, here only FEP was incompatible with the propellant. The priming/water hammer tests also showed no decomposition or combustion of the propellant, even for supply pressures of up to 60 bar. The ignition tests under vacuum conditions showed a reproducible, good ignitability of the propellant in a 22 N research thruster. The mixture was ignitable for mass mixture ratios of ROF=4 to 11 while the mass flow was changed in between 4 g/s and 10 g/s. The final task was to conduct a series of hot gas combustion tests with an experimental 22 N thruster. The thruster was fed from a tank with liquified, premixed propellant. During 40 test runs, the propellant showed a reliable ignition and combustion behaviour. The mixture ratio of oxidizer to fuel in the test runs was in between 5.4 and 9.9 and showed very low combustion roughness and high combustion efficiencies (up to 96 %). Due to the positive results of the activity, the next step is the development of higher TRL thrusters and propulsion systems for the N2O/C2H6 propellant

High Performance Propellant Development - Overview of Development Activities Regarding Premixed, Green N2O/C2H6 Monopropellants

The global search for green alternatives to the highly toxic monopropellant hydrazine (N2H4) is still ongoing. Different alternatives for hydrazine with different degrees of maturity are currently under investigation. One of these alternatives are mixtures of nitrous oxide and fuels. These propellants offer a high performance (Isp approx. 300 s), low propellant costs and are non-toxic. In the frame of the ESA activity High Performance Propellant Development, DLR investigates a premixed N2O/C2H6 propellant and assesses the safety and performance properties of the mixture. To study the propellant properties DLR built a liquefaction and mixing setup which allows condensation, pressurization and mixing of liquid N2O and C2H6. The produced propellant mixture was used to feed a thermal stability, a material compatibility as well as a priming/water hammer test setup. Furthermore, the gaseous propellant was used to conduct ignition test under vacuum conditions. A last work package included hot runs with liquefied N2O/C2H6 propellant supplied to a monopropellant like setup from a single tank. Despite the premixed nature of the propellant, the thermal stability tests showed no decomposition or combustion of the propellant. The compatibility testing of the propellant with metal alloys Al 2219, Ti64, and stainless steels SS 316 and CRES-15-5 showed no degradation of the material or propellant. In addition, the polymers PTFE (Polytetrafluoroethylene), Kalrez and FEP (Fluorinated ethylene propylene) were tested, here only FEP was incompatible with the propellant. The priming/water hammer tests also showed no decomposition or combustion of the propellant, even for supply pressures of up to 60 bar. The ignition tests under vacuum conditions showed a reproducible, good ignitability of the propellant in a 22 N research thruster. The mixture was ignitable for mass mixture ratios of ROF=4 to 11 while the mass flow was changed in between 4 g/s and 10 g/s. The final task was to conducted a series of hot gas combustion tests with an experimental 22 N thruster. The thruster was fed from a tank with liquified, premixed propellant. During 40 test runs, the propellant showed a reliable ignition and combustion behaviour. The mixture ratio of oxidizer to fuel in the test runs was in between 5.4 and 9.9 and showed very low combustion roughness and high combustion efficiencies (up to 96 %). Due to the positive results of the activity, the next step is the development of higher TRL thrusters and propulsion systems for the N2O/C2H6 propellant