• Energy Research

Abstract Pyrolysis of glycerol, a by-product of the biodiesel industry, is an important potential source of hydrogen. The obtained high calorific value gas can be used either as a fuel for combined heat and power (CHP) generation or as a transportation fuel (for example hydrogen to be used in fuel cells). Optimal process conditions can improve glycerol pyrolysis by increasing gas yield and hydrogen concentration. A detailed kinetic mechanism of glycerol pyrolysis, which involves 137 species and more than 4500 reactions, was drastically simplified and reduced to a new skeletal kinetic scheme of 44 species, involved in 452 reactions. An experimental campaign with a batch pyrolysis reactor was properly designed to further validate the original and the skeletal mechanisms. The comparisons between model predictions and experimental data strongly suggest the presence of a catalytic process promoting steam reforming of methane. High pyrolysis temperatures (750–800 °C) improve process performances and non-condensable gas yields of 70%w can be achieved. Hydrogen mole fraction in pyrolysis gas is about 44–48%v. The skeletal mechanism developed can be easily used in Computational Fluid Dynamic software, reducing the simulation time.

This work presents a comprehensive mathematical model of a fixed bed gasifier, where heat and mass transport resistances and chemical kinetics are accounted for both at the reactor and the particle scale. A multistep kinetic model of devolatilization of solid fuels, such as coals, plastics, biomasses and wastes has been employed and validated. The kinetic model of refuse derived fuels (RDF) and wastes is simply based on a linear combination of the devolatilization models of its main constituents. Ligno-cellulosic and plastic materials, together with ash and moisture, allow to account for the high heterogeneity of RDF. Successive gas phase reactions of the released species are described with a detailed kinetic scheme. Furthermore, an accurate description of heat and mass transport between gas and solid phases allows the proper characterization of combustion and gasification of the solid fuel at the particle and reactor scale. The mathematical model of a counterflow fixed bed reactor is then applied first to discuss the importance of heat transfer resistances at the particle scale, then to describe coal and biomass gasification. This work summarizes several facets of this problem with validations and examples and it allows to evaluate feasibility and limitations of the proposed approach.

In recent years, significant improvements have been reached both in the technology of hydrocarbons pyrolysis for olefines production and in the modeling of the kinetic schemes involved. Some of the reasons for these improvements are: • New sophisticated instrumentation for continuous analysis of effluents from commercial units. • Economic interest for non-conventional feedstocks, e.g. vacuum gasoils, hydrotreated heavy gasoils, recycle fractions, reformed naphthas and/or other refinery streams. • Improvements in computer, technology, hardware and software, which allow handling , in real time, complex systems of kinetic equations. • New strategies for on-line plant control and optimization. The rising needs of accuracy in predicting the reactor effluents under a wider range of feedstocks and different reactor coils demand models even more flexible and more detailed than the best ones actually available. In this paper the criteria for the development of complex and non-regular kinetic schemes (up to thousands of reactions involved) are presented and discussed. The automatic generation of the elementary reaction stoichiometries and the non-Arrhenius behaviour of the kinetic constants are also considered. Some effort has also been devoted to the optimization and data reconciliation of the reactors effluents within the framework of the entire olefins plant.

Abstract The aim of this work is to discuss a lumped approach to the kinetic modeling of the pyrolysis and oxidation of biodiesel fuels, i.e. rapeseed and soybean methyl esters. The lumped model is the natural extension of the kinetic scheme of methyl butanoate and methyl decanoate and takes also a great advantage from the detailed kinetic scheme of biodiesel fuels [Westbrook et al. Combustion and Flame 158 (2011) 742–755]. The combustion of methyl palmitate and methyl stearate is very similar to the one of methyl decanoate, while large unsaturated methyl esters are significantly less reactive at low and intermediate temperatures. The formation of resonantly stabilized allylic radicals from unsaturated methyl esters constitutes a critical element very useful to characterize the reactivity of the different fuels. The extension of the previous kinetic model of hydrocarbon and oxygenated fuel combustion to the methyl esters required the introduction of ∼60 lumped species and ∼2000 reactions. The dimension of the overall kinetic scheme (∼420 species involved in ∼13,000 reactions) allows a more flexible and direct application of the model without the need of kinetic reductions. The comparison of model predictions and different sets of experimental data from one side allows to verify the reliability of the proposed model, from the other side calls for further experimental and theoretical work on this subject.

Abstract This paper presents a semi-detailed kinetic scheme for n -heptane oxidation. Both the low and high temperature primary mechanisms are conveniently reduced to a lumped kinetic model involving only a limited number of intermediate steps. This primary reaction scheme, similar to the Shell model, is flexible enough to predict accurately the intermediate components, the heat release and also ignition delay times. General criteria for the reduction of intermediate species allows efficient coupling of the scheme with a detailed kinetic model of C 1 – C 4 oxidation. Several comparisons with experimental data, obtained under very different operating conditions, from pure pyrolysis to fuel-lean conditions, including shock tube, flow and jet stirred reactors support the applicability of this kinetic model of n -heptane oxidation over a wide range of pressures, both in the low and high temperature regions.

Devolatilization is the first step in coal combustion and gasification, thus an accurate kinetic modeling is relevant for the optimal design of these processes. In this work a relatively simple but flexible kinetic model is used to predict the thermal degradation of different coals in a wide range of operating conditions. The main feature of the model lies in its predictive capability: the elemental composition of the starting coal and the operating conditions are the only information required. Three reference coals are used to characterize the devolatilization process. The pyrolysis of each reference coal is described with a multi-step kinetic mechanism effective both at high and low heating rates. The devolatilization of the actual coal is simply obtained as a linear combination of the thermal degradation of the reference coals. The complete kinetic model refers to ∼30 reactions and lumped species, which makes this scheme suitable for being adopted in fluidynamic computations. A wide collection of comparisons between model prediction and experimental data validates this model both in terms of residual char and in terms of detailed gas and tar composition. The importance of secondary gas-phase reactions, mainly at high pressure, is also discussed and verified on the basis of an existing detailed kinetic scheme of pyrolysis and oxidation of hydrocarbon fuels.

Abstract OpenSMOKE++ is a general framework for numerical simulations of reacting systems with detailed kinetic mechanisms, including thousands of chemical species and reactions. The framework is entirely written in object-oriented C++ and can be easily extended and customized by the user for specific systems, without having to modify the core functionality of the program. The OpenSMOKE++ framework can handle simulations of ideal chemical reactors (plug-flow, batch, and jet stirred reactors), shock-tubes, rapid compression machines, and can be easily incorporated into multi-dimensional CFD codes for the modeling of reacting flows. OpenSMOKE++ provides useful numerical tools such as the sensitivity and rate of production analyses, needed to recognize the main chemical paths and to interpret the numerical results from a kinetic point of view. Since simulations involving large kinetic mechanisms are very time consuming, OpenSMOKE++ adopts advanced numerical techniques able to reduce the computational cost, without sacrificing the accuracy and the robustness of the calculations. In the present paper we give a detailed description of the framework features, the numerical models available, and the implementation of the code. The possibility of coupling the OpenSMOKE++ functionality with existing numerical codes is discussed. The computational performances of the framework are presented, and the capabilities of OpenSMOKE++ in terms of integration of stiff ODE systems are discussed and analyzed with special emphasis. Some examples demonstrating the ability of the OpenSMOKE++ framework to successfully manage large kinetic mechanisms are eventually presented. Program summary Program title: OpenSMOKE++ Catalogue identifier: AEVY_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEVY_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 146353 No. of bytes in distributed program, including test data, etc.: 4890534 Distribution format: tar.gz Programming language: C++. Computer: Any computer that can run a C++ Compiler. Operating system: Tested on Microsoft Windows 7, Ubuntu 14.4. RAM: From a few Mb to several Gb depending on the size of the system being simulated. Classification: 22. External routines: Eigen, Boost C++ Libraries, RapidXML Nature of problem: Evolution of reacting gas mixtures with detailed description of thermodynamic, kinetic and transport data. Solution method: Stiff systems of Ordinary differential Equations, whose solution is obtained using methods based on the Backward Differentiation Formulas (BDF) (LU factorization of dense matrices is required). Additional comments: The code was specifically conceived for managing homogeneous, reacting mixtures including thousands of species and reactions. Running time: Problem-dependent, from seconds (small kinetics) to hours

Abstract This paper presents a general and detailed chemical kinetic scheme developed and validated to investigate the interactions between NO and simple hydrocarbons during thermal oxidation and reburning. In a previous paper [1] the low temperature mechanism was presented. In this work the attention is drawn on the high-temperature conditions, referring typically to the reburning process where the hydrocarbon fragments reduce NO to HCN and N2. The goal is to obtain a better understanding of the interactions between NO and hydrocarbons, through the development of a general detailed kinetic model, which describes accurately the influence of NO in a wide temperature range, for different fuels and stoichiometry conditions. The model has been validated through the comparison with experimental measurements coming from different research groups, referring to several hydrocarbon fuels in different operative conditions. Even though the characteristic mechanisms are quite different from the low temperature conditions, the observed agreement in the whole investigation range confirms the correctness of the kinetic assumptions and extends the reliability of the model.