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Combustion Systems (combustion + system)
Selected AbstractsAn oven explosion: Lessons learned on PSM applicationsPROCESS SAFETY PROGRESS, Issue 1 2010Michael D. Cazabon Abstract An explosion occurred at one of our customer's locations in late 1998 involving unburned and partially burned natural gas while the unit was in high fire mode. Investigation of the incident led to many contributing causes, most of which can be categorized broadly as lack of process safety information, failure of a fuel combustion control system, contractor control and lack of management of change. Combustion systems are found throughout all industries and homes. Code-based safeguards are thoroughly and adequately described in NFPA. But is the spirit and intent of the code always applied and interpreted safely? Instrumentation application and installation are similarly well described in manufacturer's literature and the ISA standards. But are these systems installed and arranged properly? Is it important to manage change in something as mundane as fuel fired equipment? Is explosion venting on industrial ovens a sound way to limit damage? Is it even possible in all instances? Are there alternatives? This article highlights the investigation activities, answers these questions, presents conclusions and suggests remedies while showing the applicability of PSM concepts to industries other than the CPI. This article will describe, in general terms: the process, critical changes in design, key components involved, applicable codes, discoveries during the investigation and solutions deployed during the rebuild to address these issues. © 2009 American Institute of Chemical Engineers Process Saf Prog 2010 [source] Effects of exhaust gas recirculation on exergy destruction due to isobaric combustion for a range of conditions and fuelsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2008Hari Shanker Sivadas Abstract This study was directed at examining the effects of exhaust gas recirculation (EGR) on the exergy destroyed due to combustion in a simple constant pressure combustion system. Both cooled and adiabatic cases of EGR were studied. Higher ,cooled EGR' fractions lead to higher exergy destruction for reactant temperatures less than 2000,K. For the base case, the percentage of the reactant exergy destroyed for 0,,20, and 40% EGR at 300,K was found to be 28,,32, and 36%, respectively. Neglecting the chemical exergy in the products, the equivalence ratio and reactant temperature that corresponded to the lowest exergy destruction varied from 0.9 to 1.0 and 800,1300,K, respectively, depending on the EGR fraction. The fraction of the reactant exergy destroyed increased with increase in the molecular mass of the fuel for the alkanes examined. The exergy destroyed due to combustion was the least for acetylene and the highest for the alcohols. The trends stayed the same for the different EGR fractions for the eight fuels that were analyzed. For the ,adiabatic EGR' case, the percentage destruction of exergy decreased with increase in the EGR fraction with a 40% ,adiabatic EGR' fraction corresponding to a destruction of exergy of 14%. Copyright © 2008 John Wiley & Sons, Ltd. [source] Comparative study of flame structures and NOx emission characteristics in fuel injection recirculation and fuel gas recirculation combustion systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2004Jeong Park Abstract A numerical study with momentum-balanced boundary conditions has been conducted to grasp the chemical effects of added CO2 to fuel- and oxidizer-sides on flame structure and NO emission behaviour in H2,O2 diffusion flames with varying flame location. A reaction mechanism is proposed to show better agreements with experimental results in CO2 -added hydrogen flames. Oxidizer-side dilution results in significantly higher flame temperatures and NO emission. Flame location is dramatically changed due to high diffusivity of hydrogen according to variation of the composition of fuel- and oxidizer-sides. This affects flame structure and NO emission considerably especially the chemical effects of added CO2. The present work also displays separately thermal contribution and prompt NO emission due to the chemical effects caused by thermal dissociation of added CO2 in NO emission behaviour. It is found that flame temperature and the flame location affect the contribution of thermal and prompt NO due to chemical effects considerably in NO emission behaviour. Copyright © 2004 John Wiley & Sons, Ltd. [source] Numerical study on flame structure in H2,O2/CO2 laminar flamesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2003Jeong Park Abstract Numerical study, aimed at the understanding of the flame structure in O2/CO2 recycling combustion system, has been conducted with detailed chemistry. Special concern is focused on addition effect of carbon dioxide on flame structure in H2,O2 counterflow diffusion flame as a simulating configuration. To clarify chemical and thermal effects on flame structure, the comparison between predicted results with a virtual species X to displace the real carbon dioxide and with added carbon dioxide in oxidizer stream is made according to strain rate and the concentration of added CO2. From the systematical comparison of a dominant radical producing reaction with a chain termination reaction the effects of strain rate and composition control of oxidizer stream on flame structure are estimated. It is found that the behaviours of C1 - and C2 -branch species are a direct outcome of that of produced CO due to the breakdown of added CO2. There exists a temperature dependency in the behaviour of produced CO and this competes for the behaviour of the produced CO with chemical effects due to the backward reaction of CO+OH=CO2+H. Copyright © 2003 John Wiley & Sons, Ltd. [source] Effects of Transition-Metal Substitution on the Catalytic Properties of Barium HexaaluminogallateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Toshiaki Yamaguchi The effects of the substitution of transition-metal ions and/or reductant gases on the catalytic properties of barium hexaaluminogallate were investigated. Transition-metal-substituted hexaaluminogallates (BaM(Al,Ga)11O19, M = transition metal, Al/Ga = 9/3) were synthesized from aqueous metal nitrates and ammonium carbonate by the coprecipitation followed by crystallization at 1100°C. The direct NOx reduction was observed over BaM(Al,Ga)11O19 to be around 10%. The NOx removal activity of BaM(Al,Ga)11O19 powders was improved by addition of C3H6 as a reductant gas. Co-, Ni- and Cu-substituted BaM(Al,Ga)11O19 catalysts exhibited about 40% NOx reduction with C3H6 in excess oxygen at a high space velocity of 10 000 h,1. The NOx reduction on Mn- and Fe-substituted BaM(Al,Ga)11O19 catalysts was less than 10% even in the presence of C3H6. The temperature of the effective NOx reduction on BaM(Al,Ga)11O19 catalysts could be adjusted from 350° to 500°C by the selection of the transition-metal substitution in the catalysts. The catalysts hold high activities for NOx reduction even at 500°C in water vapor produced in the combustion system of reductant gases. [source] Effects of bias combustion on volatile nitrogen transformationASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010Xiaohui Zhang Abstract Nitrogen oxides (NOx) are among the principal pollutants from coal combustion, which have caused serious environmental issues around the world. Many advanced combustion systems have been developed to reduce NOx emissions. Technologies that combine low NOx burners (LNB) and air staging systems have been widely used as they can control the formation of volatile NOx effectively. In this paper, the process of volatile nitrogen release was simulated using the FG,DVC pyrolysis model, in order to provide reliable reference for designing LNBs and air staging combustion systems. The mechanism of NOx emission from volatile N in a combustion system was studied with CHEMKIN 4.1 package, which demonstrated that noticeable reduction of NOx could be obtained at an equivalence ratio (ER) of 1.22, which was 3,4% and 10,15% higher than that at an ER of 0.77 and 0.39, respectively. Sensitivity study of all basic reactions indicated that NH2 and HCNO radicals are the major inter-compounds which can reduce NO at bias combustion conditions. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Mechanisms of Submicron and Residual Ash Particle Formation during Pulverised Coal Combustion: A Comprehensive ReviewASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2005D. Yu Coal fly ash has been a traditional concern of utilities since coal was used to generate electricity because it may bring about a number of technical and economic problems such as slagging, fouling, corrosion, erosion, waste disposal and overall boiler efficiency reduction. Moreover, fine particulates that escape the combustion system are recognized to have a negative impact on health and the environment due to the enrichment of the toxic trace elements and being readily inhaled. This work gives a brief review of the studies carried out in the past decades and tries to elucidate those processes that contribute to ash formation. They include the mechanisms that control submicron ash formation and those that are related to residual ash formation. The mechanism of vaporization and condensation is believed to be the major source of submicron ash particles and is discussed in detail in this review. Residual ash formation is the consequence of the competition between ash coalescence and char fragmentation. Moreover, fragmentation of excluded minerals and rotationally induced shedding may also contribute to the residual ash formation. Our literature review has provided a number of experimental and theoretical results describing how the submicron ash and residual ash are formed, Finally we present some recommendations for possible future research topics, including sampling techniques, measurement techniques, experimental studies and modelling efforts. [source] Validation of simplified PN models for radiative transfer in combustion systemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2008E. Schneider Abstract This paper illustrates the use of simplified PN approximations as a tools of achieving verification of codes and simulations of radiative transfer in combustion systems. The main advantage of considering these models is the fact that the integro-differential equation for radiative transfer can be replaced by a set of differential equations which are independent of angle variable, compatible to the partial differential equations of flow and combustion, and easy to solve using standard numerical discretizations. Validation of these models is then performed by comparing predictions to measurements for a three-dimensional diffusion flame. The good agreement between measurements and predictions indicates that the simplified PN models can be used to incorporate radiation transfer in combustion systems at very low computational cost without relying on discrete ordinates or Monte Carlo methods. Copyright © 2006 John Wiley & Sons, Ltd. [source] The role of chlorine atoms and hydroxyl radicals in the formation of PCDDs from the oxidative pyrolysis of 2,4,6-trichlorophenolINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2010Lavrent Khachatryan A 132-step gas-phase reaction kinetic model has been combined with a four-step surface model for the formation of 1,3,6,8-tetrachlorodibenzo- p -dioxin (1,3,6,8-TCDD) from the oxidation of 2,4,6-trichlorophenol (2,4,6-TCP) in the presence of hexane. The revised model is based on a simpler model previously published in the literature and modified by adding Cl-releasing and the surface submodels, recalculating polynomial functions for thermodynamic parameters, and updating gas-phase submodels for (i) 1,3,6,8-TCDD formation, (ii) hydrogen oxidation, and (iii) hexane oxidation. The roles of the potential chain carriers, OH and Cl, in the formation of 1,3,6,8-TCDD were specifically addressed. In spite of the reported high reactivity of Cl, it was found that OH:Cl , 1, and OH is the dominant chain carrier from the apparent onset of purely gas-phase reactions at 750 K to 99% conversion of 2,4,6-TCP and hexane at 1075 K. This suggests that oxidation reactions are always dominant in realistic combustion systems, even where there are high concentrations of chlorine and relatively rich burning conditions. The update of the three gas-phase submodels as well as incorporation of Cl-releasing and the surface submodels resulted in improved agreement between calculated and experimental yields of 1,3,6,8-TCDD yields at temperatures as low as 800 K. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 90,97, 2010 [source] Investigation of the correlation of sensitivity vectors of hydrogen combustion modelsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2004Judit Zádor A well-established method for the analysis of large reaction mechanisms is the calculation and interpretation of the sensitivity of the kinetic model output Yi to parameter changes. Comparison of the sensitivity vectors si = {, Yi/,p} belonging to different model outputs is a new tool for kinetic analysis. The relationship of the sensitivity vectors was investigated in homogeneous explosions, freely propagating and burner-stabilized laminar flames of hydrogen,air mixtures, using either calculated adiabatic or constrained temperature profiles, for fuel-to-air ratios , = 0.5,4.0. Sensitivity vectors are called locally similar, if the relationship si = ,ijsj is valid, where ,ij is a scalar. In many systems, only approximate local similarity of the sensitivity vectors exists and the extent of it can be quantified by using an appropriate correlation function. In the cases of adiabatic explosions and burner-stabilized flames, accurate local similarity was present in wide ranges of the independent variable (time or distance), and the correlation function indicated that the local similarity was not valid near the concentration extremes of the corresponding species. The regions of poor similarity were studied further by cobweb plots. The correlation relationships found could be interpreted by the various kinetic processes in the hydrogen combustion systems. The sensitivity vector of the laminar flame velocity is usually considered to be characteristic for the whole combustion process. Our investigations showed that the flame velocity sensitivity vector has good correlation with the H and H2O concentration sensitivities at the front of the adiabatic flames, but there is poor correlation with the sensitivity vectors of all concentrations in homogeneous explosions. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 238,252 2004 [source] Steady-state multiplicity, flashback, and control issues in CH4 radiant burnersAICHE JOURNAL, Issue 9 2004M. Bizzi Abstract Methane is widely employed as a source of energy in combustion systems. Among the currently available technologies, radiant heaters offer high thermal efficiency and low environmental impact in comparison with atmospheric burners. The present work deals with the modeling of methane combustion in a noncatalytic metal fiber burner, represented by means of one-dimensional transient equations. The model accounts for a detailed reaction mechanism, radiation within the porous medium, longitudinal heat and mass transfer. After its validation, the model was employed to analyze a typical stability problem that affects these systems: under given operating conditions (low specific power inputs and excess of air) the occurrence of flashback may in fact preclude the safe operation of the system. As a consequence of energy radiation in the upstream direction, the burner upstream surface and the plenum chamber might become hot enough to heat in turn the gas feedstock, thus eventually determining flashback. In this paper, the mechanism of flashback is numerically investigated as a function of the burner structure and operating conditions by means of a model analysis so as to single out regions of flashback occurrence and a criterion for safe operation. Finally, some guidelines are outlined for a cheap and effective control of the system, paving the way for possible improvement of currently adopted control systems. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2276,2286, 2004 [source] Effects of bias combustion on volatile nitrogen transformationASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010Xiaohui Zhang Abstract Nitrogen oxides (NOx) are among the principal pollutants from coal combustion, which have caused serious environmental issues around the world. Many advanced combustion systems have been developed to reduce NOx emissions. Technologies that combine low NOx burners (LNB) and air staging systems have been widely used as they can control the formation of volatile NOx effectively. In this paper, the process of volatile nitrogen release was simulated using the FG,DVC pyrolysis model, in order to provide reliable reference for designing LNBs and air staging combustion systems. The mechanism of NOx emission from volatile N in a combustion system was studied with CHEMKIN 4.1 package, which demonstrated that noticeable reduction of NOx could be obtained at an equivalence ratio (ER) of 1.22, which was 3,4% and 10,15% higher than that at an ER of 0.77 and 0.39, respectively. Sensitivity study of all basic reactions indicated that NH2 and HCNO radicals are the major inter-compounds which can reduce NO at bias combustion conditions. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] The Oxidation Kinetics of Mercury in Hg/O/H/Cl SystemASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2005Y. Qiao The potential for regulation of mercury emission from coal-fired boilers is a concern for the electric utility industry. Field data show a wide variation in the fraction of mercury that is emitted as a vapor versus that retained in the solid products. The reason for this variation is not well understood. Near the end of the flue gas path, mercury exists as a combination of elemental vapor and HgCl2 vapor. The data show that HCl2 is more likely to be removed form the flue gas. The need to describe accurately mercury reaction products and their concentration-time correlation prompted investigation of mercury chemical kinetic mechanisms and their application to real combustion systems. This paper uses chemical equilibrium analysis to study the speciation of mercury in flue gases during coal combustion and gasification. The paper presents a simple kinetic model of mercury oxidation in the Hg/O/H/Cl system. The results porn the model calculation are in reasonable agreement with the Mamani-Paco and Heleble [1] experimental data [source] | |||||||||||||