In the past Eliseo Ranzi has collaborated on articles with Michele Corbetta and Alessandra Beretta. One of their most recent publications is Low-temperature combustion: Automatic generation of primary oxidation reactions and lumping procedures☆. Which was published in journal Combustion and Flame.

More information about Eliseo Ranzi research including statistics on their citations can be found on their Copernicus Academic profile page.

Eliseo Ranzi's Articles: (15)

Low-temperature combustion: Automatic generation of primary oxidation reactions and lumping procedures☆

AbstractThe aim of this paper is to present some general rules for the automatic generation of primary oxidation reactions of large hydrocarbon fuels. The proposed approach is applied to n-paraffins for reason of simplicity. Nevertheless, the final goal is to feed the tested rules and kinetic parameters into a more general and effective expert system for the generation of primary mechanisms of real mixtures containing heavier branched hydrocarbons.The first step is the classification of the primary reactions involved in low-temperature oxidation, together with the definition of a limited set of their intrinsic kinetic parameters. These independent rate constants are validated on the basis of primary experimental measurements of pyrolysis and oxidation. In addition to this, the paper analyzes some useful simplications for the kinetic modeling of secondary combustion processes. As the carbon number of the hydrocarbon fuel rises, the detailed reaction schemes become very complex. The number of isomers of the same homologous class of molecules and radicals increases and the number of reactions increases simultaneously. In these cases, the automatic generation of the primary oxidation useful. These lumped mechanisms of heavy species consist of a limited number of equivalent reactions. Then, this small subset of equivalent reactions has to be coupled with a very detailed scheme for the oxidation of C1–C4 species. The final result is still a very large number of reactions, which makes it incompatible with c.f.d. calculations, but whose extension to heavier species becomes easier to handle.A few comparisons of experimental and predicted results for the low-temperature oxidation of n-butane and n-pentane illustrate the applicability of this approach.

Mathematical Modelling of Coal and Biomass Gasification: Comparison on the Syngas H2/CO Ratio under Different Operating Conditions

AbstractGasification is a thermo-chemical process aiming at the production of high heating value syngas, starting from a solid fuel such as biomass or coal. From a chemical point of view the process results in a partial oxidation by means of sub-stoichiometric air or oxygen and/or steam. According to the solid fuel used as a feedstock and to the operating parameters of the process, the quality and the chemical composition of the produced syngas is differently affected. This gas is mainly composed by carbon monoxide and hydrogen, while carbon dioxide, water, methane and small hydrocarbons are minor components. The final applications of syngas include the power generation and the production of chemicals, with special reference to methanol synthesis and Gas-to-Liquid technologies. For these last catalytic processes it is necessary to provide syngas with a specific H2/CO ratio, and for this reason in the present work we apply our comprehensive mechanistic approach to the description of the gasification process, highlighting the sensitivity of the key operating parameters on syngas quality. Moreover a comparison between coal and biomass gasification is proposed, as well as the validation of the kinetic model with some experimental data.

Oxidative dehydrogenation of light paraffins in novel short contact time reactors. Experimental and theoretical investigation

AbstractA previous study on the selective oxidation of propane over a commercial Pt/Al2O3 catalyst is herein extended to the oxidative dehydrogenation (ODH) of ethane. ODH tests were performed in an annular reactor, wherein catalytic experiments could be performed at varying temperatures on a wider operating field than that characteristic of autothermal reactors; besides, gas-phase experiments were performed for comparison. Together with the results of a theoretical analysis on homogeneous ethane oxidative pyrolysis, the bulk of data indicated that the high-temperature production of ethylene observed in the presence of the catalyst could be well explained by the single contribution of gas-phase radical reactions. The catalyst was proved to be active, instead, in the non-selective oxidation of paraffins to COx. Further tests in an insulated millisecond contact time reactor demonstrated that the catalytic combustion reactions could be exploited to ignite the gas-phase reactions; comparison with the simulations of a purely homogeneous adiabatic reactor showed that at the highest temperatures the observed ethylene yields were close to the maximum obtainable values.

Oxidation and combustion of the n-hexene isomers: A wide range kinetic modeling study

AbstractA detailed chemical kinetic mechanism has been developed to study the oxidation of the straight-chain isomers of hexene over a wide range of operating conditions. The main features of this detailed kinetic mechanism, which includes both high and low temperature reaction pathways, are presented and discussed with special emphasis on the main classes of reactions involved in alkene oxidation. Simulation results have been compared with experimental data over a wide range of operating conditions including shock tube, jet stirred reactor and rapid compression machine. The different reactivities of the three isomers have been successfully predicted by the model. Isomerization reactions of the hexenyl radicals were found to play a significant role in the chemistry and interactions of the three n-hexene isomers. A comparative reaction flux analysis is used to verify and discuss the fundamental role of the double bond position in the isomerization reactions of alkenyl radicals, as well as the impact of the allylic site in the low and high temperature mechanism of fuel oxidation.

An experimental and kinetic modeling study of combustion of isomers of butanol

AbstractA kinetic model is developed to describe combustion of isomers of butanol—n-butanol (n-C4H9OH), sec-butanol (sec-C4H9OH), iso-butanol (iso-C4H9OH), and tert-butanol (tert-C4H9OH). A hierarchical approach is employed here. This approach was previously found to be useful for developing detailed and semi-detailed mechanism of oxidation of various hydrocarbon fuels. This method starts from lower molecular weight compounds of a family of species and proceeds to higher molecular weight compounds. The pyrolysis and oxidation mechanisms of butanol isomers are similar to those for hydrocarbon fuels. Here, the development of the complete set of the primary propagation reactions for butanol isomers proceeds from the extension of the kinetic parameters for similar reactions already studied and recently revised for ethanol, n-propanol and iso-propanol. A detailed description leading to evaluation of rate constants for initiation reactions, metathesis reactions, decomposition reactions of alkoxy radicals, isomerization reactions, and four-center molecular dehydration reactions are given. Decomposition and oxidation of primary intermediate products are described using a previously developed semi-detailed kinetic model for hydrocarbon fuels. The kinetic mechanism is made up of more than 7000 reactions among 300 species. The model is validated by comparing predictions made using this kinetic model with previous and new experimental data on counterflow non-premixed flames of n-butanol and iso-butanol. The structures of these flames were measured by removing gas samples from the flame and analyzing them using a gas chromatograph. Temperature profiles were measured using coated thermocouples. The flame structures were measured under similar conditions for both fuels to elucidate the similarities and differences in combustion characteristics of the two isomers. The profiles measured include those of butanol, oxygen, carbon dioxide, water vapor, carbon monoxide, hydrogen, formaldehyde, acetaldehyde, and a number of C1–C4 hydrocarbon compounds. The predictions of the kinetic model of flame structures of the two isomers were satisfactory. Validation of the kinetic model was also performed by comparing predictions with experimental data reported in the literature. These data were obtained in batch reactors, flow reactors, jet-stirred reactors, and shock tubes. In these configurations, combustion is not influenced by molecular transport. The agreement between the kinetic model and experimental data was satisfactory.

A wide range kinetic modeling study of pyrolysis and oxidation of benzene

AbstractThe aim of this work is to collect and review the vast amount of experimental data reported in recent years on benzene pyrolysis and oxidation and to analyze them by using and refining a detailed kinetic mechanism, thereby identifying a sensitive and crucial portion of the mechanism itself. Benzene is the first aromatic compound, a relevant intermediate of several combustion processes and also a key precursor to soot formation. The emphasis here is on high pressure pyrolysis experiments, ignition delay times in shock tubes, premixed flames as well as low temperature reactions with recombination and propagation reactions of cyclopentadienyl and phenoxy radicals playing a significant role. This is the first time the same kinetic model of benzene pyrolysis and oxidation has been compared with such a wide collection of experimental measurements.

Experimental and modeling study of single coal particle combustion in O2/N2 and Oxy-fuel (O2/CO2) atmospheres

AbstractCoal particle combustion experiments were performed in a drop tube furnace (DTF) with oxygen concentration from 21% to 100%, in N2 and CO2 mixtures, under quiescent flow conditions. Small particles (75–90 μm) of a high-volatile bituminous coal (PSOC-1451) and a lignite coal (DECS-11) are analyzed with particular attention to the particle burnout times and the particle surface temperatures. These experimental measurements are compared with the predictions of a comprehensive model of coal combustion. Combustion of coal particles is a multi-scale process where both chemical and physical phenomena are involved, thus it requires a coupled and accurate description of the kinetics as well as of the heat and mass transport phenomena. Important features of the model are a multistep kinetic scheme of coal volatilization and detailed kinetics of the successive gas-phase reactions and of the heterogeneous reactions of both char oxidation and gasification. The achieved overall agreement between the experimental data and the numerical predictions, in terms of particle temperature and burnout times, highlights the capability of the model to simulate the effect of different operating conditions in the coal combustion processes.

An experimental and kinetic modeling study of cyclopentadiene pyrolysis: First growth of polycyclic aromatic hydrocarbons

AbstractThe importance of 1,3-cyclopentadiene (CPD) and cyclopentadienyl (CPDyl) moieties in the growth of polycyclic aromatic hydrocarbons (PAHs) was studied using new experimental data and ab initio calculations. The experimental investigation was performed in a tubular continuous flow pyrolysis reactor under both high (24molN2/molCPD) and low (5molN2/molCPD) nitrogen dilutions, covering a temperature range of 873–1123 K, at a fixed pressure of 1.7 bara. At the most severe conditions up to 84% of CPD is converted, and the amount of PAHs is more than 65 wt%. Major products observed during CPD pyrolysis were benzene, indene, methyl-indenes and naphthalene, in line with previous studies. On-line GC × GC-FID/(TOF-MS) also allowed to quantify minor species (methane, toluene, styrene, phenanthrene, anthracene, etc.), never reported before at this level of accuracy. The new experimental data have been used to further analyze the role of the successive interactions of CPD, indene, and naphthalene as well as the recombination and addition reactions of their resonantly stabilized radicals and refine their kinetics. The results of the modeling study are in good agreement with existing and new experimental observations.

New reaction classes in the kinetic modeling of low temperature oxidation of n-alkanes

AbstractDue to the rapid advance in analytical methods, a large detail of intermediate products from the low temperature oxidation of hydrocarbon fuels in jet stirred reactors became recently available in the literature. This new comprehensive information allowed to highlight systematic deviations between model predictions and experimental measurements, both in some oxygenated species and in fuel conversion at very low temperatures (550–650 K). These discrepancies are largely reduced by including new reaction classes in the oxidation mechanism. Successive H-abstraction and molecular reactions of hydroperoxide species are proved to play a relevant role at very low temperatures, in competition with the chain branching decomposition reactions. Several recombination and disproportionation reactions of peroxy radicals are also of interest in explaining some intermediate oxygenated components. The aim of this paper is to discuss and analyze the ability of these new reaction classes to explain the formation of oxygenated species, such as organic acids and dicarbonyl species. Rate constants were determined using similarity and analogy rules for consolidated reactions, while theoretical calculations were performed to determine preliminary estimates for reaction channels lacking a reference reaction. Detailed comparisons with several experimental data of propane and n-butane oxidation at low temperatures support these assumptions. This kinetic study points out the need of further research activities in the investigation of successive reactions of hydroperoxide species.

Kinetic modeling of particle size distribution of soot in a premixed burner-stabilized stagnation ethylene flame

AbstractA detailed model of soot formation is proposed, which consists of a gas-phase kinetic model for the pyrolysis and oxidation of selected hydrocarbon fuels and a kinetic mechanism of soot nucleation and mass/size growth through coagulation and surface reactions. The gas-phase model (Ranzi et al., 2012) was expanded to include the chemistry of Polycyclic Aromatic Hydrocarbons (PAHs) up to four-to-five ring PAHs, with a modular and hierarchical approach. The discrete sectional method was employed to solve the size evolution of the particle size distribution function (PSDF). Analogy and similarity rules were employed to describe heterogeneous reaction kinetics of soot surface reactions. A variable collision efficiency was assumed for the coalescence of small soot particles. Larger particles were assumed to undergo aggregation. The predicted PSDFs are found to be in reasonably good agreement with the experimental data for nascent soot measured in an atmospheric-pressure premixed ethylene–oxygen–argon flame in the burner-stabilized stagnation flame configuration. Sensitivity analyses of the PSDF, number density, and volume fraction were carried out with respect to the rate parameters of addition reactions of acetylene, PAHs, resonantly stabilized radical reactions, and coalescence and aggregation. The results show that the reaction of PAHs and acetylene with soot surfaces and the kinetics of coalescence and aggregation exhibit dominant effects on the detailed and global soot properties for the flame studied, in agreement with conclusions of a large range of previous modeling studies.

Experimental and modeling investigation of the effect of the unsaturation degree on the gas-phase oxidation of fatty acid methyl esters found in biodiesel fuels

AbstractThe oxidation of three C19 fatty acid methyl esters present in biodiesel fuel was experimentally investigated using a jet-stirred reactor in order to highlight the effect of double bonds on the reactivity and product distribution. Fuel candidates were methyl-stearate, methyl oleate and methyl linoleate with no, one and two double bonds, respectively. Experiments were carried out over a wide temperature range (500–1050 K), at a pressure of 1.067 bar, at a residence time of 2 s. Methyl esters were diluted with benzene to avoid their condensation as much as possible. Inlet mole fractions of methyl ester, benzene and oxygen were 4 × 10−4, 5 × 10−3 and 4.5 × 10−2, respectively (with dilution in helium). However, as previously demonstrated for alkanes, the presence of benzene does not notably influence the mixture reactivity below 850 K. Many reaction intermediate products have been quantified, including species which can be formed through Waddington reaction for unsaturated reactants. The present experiments are the first ones allowing the actual measurement of large ester intrinsic reactivity in a jet-stirred reactor. They further contribute to an extensive validation of the POLIMI lumped kinetic scheme of pyrolysis and oxidation of biodiesel fuels. Two reaction classes have been added to better account for the oxidation of species with double bonds: the Waddington mechanism and the concerted decomposition reactions through cyclic transition states. The new model contains 18,217 reactions involving 461 species. Overall, a correct agreement was obtained for the reactivity of the three fuels. The model well reproduces mole fraction profiles of many reaction products. The kinetic analysis performed at low-temperature (650 K) confirmed the significant inhibitive effect of H-atom abstractions forming non-propagating allyl type radicals in this temperature region. It also showed that the inhibitive effect of these reactions increases from methyl oleate to methyl linoleate, which explains the large difference observed in the reactivity.

Biomass gasification using low-temperature solar-driven steam supply

Highlights•Biomass gasification can be carried out at relatively low-temperature.•Steam from concentrated solar plant can sustain the gasification process.•Appropriate design of the biomass gasifier is needed.•Cost estimation is provided for oxygen supply and gasifier revamping.

Experimental and kinetic modeling study of combustion of gasoline, its surrogates and components in laminar non-premixed flows

AbstractExperimental and numerical studies are carried out to construct surrogates that can reproduce selected aspects of combustion of gasoline in non premixed flows. Experiments are carried out employing the counterflow configuration. Critical conditions of extinction and autoignition are measured. The fuels tested are n-heptane, iso-octane, methylcyclohexane, toluene, three surrogates made up of these components, called surrogate A, surrogate B, and surrogate C, two commercial gasoline with octane numbers (ON) of 87 and 91, and two mixtures of the primary reference fuels, n-heptane and iso-octane, called PRF 87 and PRF 91. The combustion characteristics of the commercial gasolines, ON 87 and ON 91, are found to be nearly the same. Surrogate A and surrogate C are found to reproduce critical conditions of extinction and autoignition of gasoline: surrogate C is slightly better than surrogate A. Numerical calculations are carried out using a semi-detailed chemical-kinetic mechanism. The calculated values of the critical conditions of extinction and autoignition of the components of the surrogates agree well with experimental data. The octane numbers of the mixtures PRF 87 and PRF 91 are the same as those for the gasoline tested here. Experimental and numerical studies show that the critical conditions of extinction and autoignition for these fuels are not the same as those for gasoline. This confirms the need to include at least aromatic compounds in the surrogate mixtures. The present study shows that the semi-detailed chemical-kinetic mechanism developed here is able to predict key aspects of combustion of gasoline in non premixed flows, although further kinetic work is needed to improve the combustion chemistry of aromatic species, in particular toluene.

Robust and efficient numerical methods for the prediction of pollutants using detailed kinetics and fluid dynamics

AbstractThe design of combustion devices demands the fulfillment of always more stringent limitations concerning pollutant emissions. Turbulent flows are characterized by complex interactions between turbulence and chemistry. However, even with the increase of computer power and speed, it is not currently feasible to directly couple CFD models and large kinetic schemes which are necessary to predict pollutants. A two-step approach can be adopted: CFD results obtained with simple combustion schemes are post-processed using detailed kinetics. The proposed Kinetic Post Processor (KPP) operates by assuming the temperature and flow fields to be those predicted by the CFD code and solves the overall system of balance equations in a complex network of reactors. With proper attention to the numerical procedures, this approach is able to couple and handle CFD and detailed kinetics. A specifically conceived hybrid numerical method, based on a modified Newton and successive substitution methods, was developed to solve such large and extremely non-linear systems [1]. In this paper the attention is focused on new improvements in the numerical method obtained by using the age of the fluid to accelerate the convergence of the iterative solver and by calculating the Jacobian matrix analytically rather than numerically. In the application example, these numerical approaches reduced the computational time by a factor of ∼8.

Low Impact Methanol Production from Sulfur Rich Coal Gasification☆

AbstractIn economy nowadays, methanol is already a key compound widely employed as building block for producing intermediates or synthetic hydrocarbons, solvent, energy storage medium, and fuel. In recent times, methanol has been employed in a number of innovative applications. It is a clean and sustainable energy resource that can be produced starting from different sources traditional or renewable: natural gas, coal, biomass, landfill gas and power plant/industrial emissions. In this work is proposed an innovative low impact process for methanol production starting from coal gasification. The most important features, instead the traditional ones, are the lower emissions of CO2 (about 2.5%) and the surplus production of methanol (about 1.7%) without any addiction of primary sources. Moreover, it is demonstrated that a coal charges with a high sulfur content means a higher reduction of CO2 emissions. The key idea is the application of AG2STM technology that is a completely new effective route of processing acid gases: H2S and CO2 are converted into syngas (CO and H2) by means of a regenerative thermal reactor.

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