A numerical simulation of hazardous waste destruction in a three-dimensional dump incinerator

A predictive model of carbon tetrachloride (CC1₄) incineration in a dump incinerator is described. An empirical model that incorporates the chemical kinetic aspects of CCl₄ destruction is developed to describe the flame inhibition characteristics of CC1₄, which is halogen compounds. Quantitative agreement is found between the predictions of the model and the measured values. Cavity hydrodynamics and flame structure studies are made in a dump incinerator proposed in this study. For the effective destruction of hazardous waste, the waste must injected in the recirculation region of high temperature with the condition of not disturbing the combustion cavity. The core flame has a significant impact on the structure of the recirculation region, in some cases completely changing the nature of the flow within the cavity. The dump incinerator has good characteristics for the destruction of hazardous waste. These characteristics should lead to a very compact device, one which is potentially transportable or usable in a dedicated manner by a small generator.     

Prediction of gaseous pollutants and heavy metals during fluidized bed incineration of dye sludge

This research provides an equilibrium model for predicting both the emission of gaseous pollutants and the fate of heavy metals during incineration of biologically treated dye sludge in a bench-scale fluidized bed incinerator. Major gaseous pollutants and hazardous trace heavy metals have been also measured under various operating conditions. The predicted values, which were derived by using a thermodynamic equilibrium model, can be used to determine the optimum operating parameters and the risk associated with hazardous waste incineration by means of verifying experimental data. However, prediction of NO_x emission using a thermodynamic equilibrium model during incineration of waste was not simple. The reason is that the variation of NO_x emission during incineration of waste was affected by the various operating parameters, such as air-fuel ratio(λ _T ), primary air factor(λ ₁ /λ _T ), combustor geometry, method of heat release, and preheating of combustion air. According to the distributions of Cr and Pb simulated by the equilibrium model, all of the Cr in the feed was retained in the ash as the solid phase of Cr₂CO₃. However, most Pb was retained in the ash during incineration as the solid phase of PbSO₄, or heterogeneously deposited onto the fly ash as PbO(g) when the combustion gas becomes cool. Presented at the Int’/Sym. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Large-eddy-simulation-based multiscale modeling of TiO2 nanoparticle synthesis in a turbulent flame reactor using detailed nucleation chemistry

In this work, we present a multiscale computational model for flame synthesis of TiO₂ nanoparticles in a turbulent flame reactor. The model is based on large-eddy simulation (LES) methodology in conjunction with detailed gas-phase chemical kinetics to accurately model the highly complicated combustion and nucleation processes in a turbulent flame. A flamelet-based model is used to model turbulence–chemistry interactions. In particular, the transformation of TiCl₄ to the solid primary nucleating TiO₂ nanoparticles is represented using an unsteady kinetic model considering 30 species and 69 reactions in order to accurately describe the important event of nanoparticle formation. The evolution of the TiO₂ number density function is tracked using the quadrature method of moments (QMOM). For validation purposes, the detailed computational model is compared against experimental data and reasonable agreement is obtained.     

Predictions of CO and NOx emissions from steam cracking furnaces using GRI2.11 detailed reaction mechanism – A CFD investigation

This investigation develops a three-dimensional Computational Fluid Dynamics (CFD) model to simulate the turbulent diffusion flame on the fire-side of the radiation section of a thermal cracking test furnace coupled with a non-premixed low NO_x floor burner. When this type of burners which uses the internal Flue Gas Recirculation (FGR) technique is coupled with large scale furnaces, both the turbulent mixing and chemical reaction rates are comparable and hence this should be considered in the model. Different combustion models are used to simulate the turbulence–chemistry interactions for this flame. The CFD model, based on the Eddy Dissipation Concept (EDC) combustion model coupled with the detailed GRI2.11 reaction mechanism, gives the most reasonable predictions compared with the available experimental data or empirical correlations for the diffusion flame in the thermal cracking test furnace, especially for the flame length and the CO and NO_x emissions.     

Effect of trimethylphosphate additives on the flammability concentration limits of premixed methane-air mixtures

The effect of small additives of trimethylphosphate (TMP) on the lean and rich flammability concentration limits of CH₄/air gas mixtures were studied using an opposed-flow burner and numerical modeling based on detailed kinetic mechanisms. TMP was found to narrow the flammability concentration limits of premixed CH₄/air mixtures. Modeling using a previously developed model for flame inhibition by phosphorus compounds showed that the model provides a satisfactory fit to experimental results on the effect of TMP additives on the lean concentration limit. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 12–21, January–February, 2008.     

Influence of organophosphorus inhibitors on the structure of atmospheric lean and rich methane-oxygen flames

The inhibition of atmospheric laminar methane-oxygen flames of various compositions by trimethyl phosphate was studied experimentally and by numerical modeling using mechanisms based on detailed kinetics. The H and OH concentration profiles in flames with and without the addition of trimethyl phosphate were measured and calculated. It was shown that the addition of the inhibitor reduced the maximum (in the reaction zone) concentrations of H and OH in lean and rich flames. The concentration reduction was higher in rich flames than in lean flames. The concentration profiles of the phosphorus-containing products PO, PO₂, HOPO, HOPO₂, and (HO)₃PO in lean and rich flames stabilized on a flat burner were measured and calculated. Tests of the previously developed model of flame inhibition by phosphorus compounds showed that the model provides adequate predictions of many experimental results. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 23–31, March–April, 2007.     

Chemical processes in the HNF flame

Results of modeling the HNF flame structure are presented. From an analysis of literature data on the thermal decomposition and combustion of HNF, it is concluded that the dissociative vaporization of HNF proceeds via the route HNF_liq → (N₂H₄)_g + (HC(NO₂)₃)_g. The flame structure is modeled using a detailed kinetic mechanism consisting of 47 species and 283 elementary reactions. Its constituents are the decomposition mechanisms of hydrazine (N₂H₄)_g and trinitromethane (HC(NO₂)₃)_g (nitroform, NF_g). The latter come from the burning surface by dissociative vaporization. The modeling was performed for different routes of NF_g decomposition involving HC(NO₂)₂, HCNO₂, and HC(O)NO₂ radicals. The HNF flame structure was calculated for pressures of 0.4, 1, and 5 atm using data on the product composition on the burning surface that correspond to the developed reaction in the condensed phase and are consistent with the chemical composition and enthalpy of formation of HNF. As follows from the calculations, the heat release in the gas-phase reaction of nitroform with hydrazine (and partially with ammonia) leads to a temperature increase in the flame zone adjacent to the burning surface from its value on the surface to ≈1300 K. A further increase in the flame temperature is related to the reaction in the H₂O/N₂/N₂O/NH₃/NO/NO₂/HNO₂/CO/CO₂/HCNO/HCN mixture. The calculation results are compared with experimental data on the thermal and chemical structure of the HNF flame. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 20–31, September–October, 2006.     

NO reduction over La2O3 using methanol

Nitric oxide (NO) reduction by methanol was studied over La₂O₃ in the presence and absence of oxygen. In the absence of O₂, CH₃OH reduced NO to both N₂O and N₂, with selectivity to dinitrogen formation decreasing from around 85% at 623 K to 50–70% at 723 K. With 1% O₂ in the feed, rates were 4–8 times higher, but the selectivity to N₂ dropped from 50% at 623 K to 10% at 723 K. The specific activities with La₂O₃ for this reaction were higher than those for other reductants; for example, at 773 K with hydrogen a specific activity of 35 _μmol NO/s m² was obtained whereas that for methanol was 600 μmol NO/s m². The Arrhenius plots were linear under differential reaction conditions, and the apparent activation energy was consistently near 14 kcal/mol with CH₃OH. Linear partial pressure dependencies based on a power rate law were obtained and showed a near‐zero order in CH₃OH and a near‐first order in H₂. In the absence of O₂, a Langmuir–Hinshelwood type model assuming a surface reaction between adsorbed CH₃OH and adsorbed NO as the slow step satisfactorily fitted the data, and the model invoking two types of sites provided the best fit and gave thermodynamically consistent rate constants. In the presence of O₂ a homogeneous gas‐phase reaction between O₂, NO, and CH₃OH occurred to yield methyl nitrite. This reaction converted more than 30% of the methanol at 300 K and continued to occur up to temperatures where methanol was fully oxidized. Quantitative kinetic studies of the heterogeneous reaction with O₂ present were significantly complicated by this homogeneous reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of Taguchi method in the optimization of dissolution of ulexite in NH4Cl Solutions

The Taguchi method was used to determine optimum conditions for the dissolution of ulexite in NH₄Cl solutions. The ranges of experimental parameters were between 50–87 ‡C for reaction temperature, 0.05-0.20 gmL^-1 for solid-to-liquid ratio, 1–4 M for NH₄Cl concentration, 5–25 min for reaction time, and (-850+600)-(-90) Μm for particle size. The optimum conditions for these parameters were found to be 87 ‡C, 0.05 gmL^-1, 4M, (-300+212) Μm, and 18 minutes, respectively. Under these conditions, the dissolution percentage of ulexite in NH₄Cl solution was 98.37. Reaction products were found to be boric acid, ammonium tetraborates, sodium tetraborate decahydrate, calcium chloride, and sodium chloride.     

Deposition of SiO 2 Nanoparticles Produced in a Turbulent H 2 /Om2 Flame

Measurements and simulations of an industrial outside vapor deposition process as used for the manufacture of optical wave guides were performed. Deposition efficiencies, flame temperatures, and gas velocities were measured. The hydrogen flame reaction was modeled by calculating the turbulent flow including a combustion model and using a computational fluid dynamics (CFD) solver to compute flow velocities, turbulence and temperatures in the flame. These results were compared with experimental data and reasonable agreement was found. The produced SiO ₂ particles with predefined size were tracked through the flow field and it was determined whether they hit the surface of the cylindrical target or pass it.

Three flame configurations were investigated and the model could predict well the trends of the deposition efficiencies for the different flames. The differences in flame velocities and turbulence levels for the different configurations assisted the explanation of the performances of the flames. Turbulence levels were different for the three flames and it was concluded that for turbulent deposition processes the thermophoretic force that drives particles towards colder surfaces is less important than for laminar deposition processes.     

Reduction and oxidation properties of Fe2O3/ZrO2 oxygen carrier for hydrogen production

Fe₂O₃ is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH₄, CO and H₂ respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe₂O₃ (20 wt.%)/ZrO₂ was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH₄, CO and H₂, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH₄, but the phenomenon was not remarkable for the reduction by CO and H₂. The reduction rate achieved using CO and H₂ was relatively faster than achieved using CH₄. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe₂O₃ to FeO by CH₄, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH₄. The reduction of Fe₂O₃ to Fe by CO and H₂ can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe₃O₄ by water and FeO to Fe₂O₃ by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems.     

Formations and controls of HCl and PAHs by different additives during waste incineration

This study employed a laboratory-scale fluidized bed incinerator to investigate the formations and controls of hydrogen chloride (HCl) and polycyclic aromatic hydrocarbons (PAHs) by adding different additives in the feedstock during waste incineration. The effects of different organic and inorganic chlorides on the formation and control of HCl and PAHs were also studied. Additionally, the thermodynamic equilibrium modeling was also carried out to interpret and compare with the experimental results.Experimental results showed that the formation of HCl was related to the potential of chlorine released from the combustion of different chlorides. Organic chloride PVC had greater potential to form HCl than inorganic chloride NaCl. The performances of additives were affected by incineration temperature. Increasing temperature decreased the control efficiency of additives because the emission yields of HCl and Cl₂ were increased with temperature. The control efficiencies for HCl and Cl₂ by calcium based additives (Ca(OH)₂, CaO, CaCO₃) were better than that by magnesium based additive (Mg(OH)₂) and CaO was the best additive. The control efficiencies of PAHs by adding CaO in the feedstock were not apparent because the fluidization quality in the fluidized bed incinerator was decreased.     

Heat-release mechanism in ammonium dinitramide flame

To verify the adequacy of various models of heat release in ammonium dinitramide flame to real processes, chemical processes in products of thermal decomposition at a pressure of 10 torr and in ammonium dinitramide [ADN; NH₄N(NO₂)₂] flame at a pressure of 0.4 to 60 atm are numerically simulated. The calculations are performed on the basis of a detailed kinetic mechanism and boundary conditions correlated with experimental data, thermodynamic properties, and chemical composition of ADN. The kinetic mechanism includes submechanisms that describe high-temperature chemical processes in NH₃/N₂O/NO/NO₂/HNO₂/HNO₃ and NH₃/HN(NO₂)₂ mixtures, and the global stages of aerosol decomposition. Based on calculated and experimental data, the role of dinitraminic acid HN(NO₂)₂, aerosols, and ADN vapor in heat release in the ADN flame zone adjacent to the burning surface is estimated. The calculations predict that the main source of heat release in the cold flame zone at p ≥ 3 atm is dinitraminic acid incoming through the channel of dissociative evaporation ADN_liq → NH₃ + HN(NO₂)₂ from the burning surface. In the high-temperature flame zone, heat release is caused by the reaction that occurs in the NH₃/N₂O/NO/NO₂/HNO₂/HNO₃ mixture. At moderate pressures, the high-temperature and low-temperature zones are separated by an induction zone. The stage governing production of the OH radical, which plays an important role in combustion, in the induction zone is the reaction HNO₃ + M → OH + NO₂ + M. Because of a high activation energy of the stage, small temperature perturbations in the induction zone at low pressures lead to a finite change in the stand-off distance between the high-temperature flame zone and the burning surface. Therefore, small temperature perturbations in the induction zone, which are caused by admixtures in the sample or by heat transfer between the reacting gas and the ambient medium, may be responsible for disagreement between various experimental data and between experimental and calculated data on the stand-off distance between the high-temperature flame zone and the burning surface. In numerical calculations, the position of the high-temperature zone is effectively controlled by varying rate constants of elementary stages within admissible limits. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 64–76, September–October, 2007.     

Effect of the addition of triphenylphosphine oxide,hexabromocyclododecane, and ethyl bromide on a CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> flame at atmospheric pressure

The chemical and thermal structure of a Mache-Hebra burner stabilized premixed rich CH₄/O₂/N₂ flame with additives of vapors of triphenylphosphine oxide [(C₆H₅)₃PO], hexabromocyclododecane (C₁₂H₁₈Br₆), and ethyl bromide (C₂H₅Br) was studied experimentally using molecular beam mass spectrometry (MBMS) and a microthermocouple method. The concentration profiles of stable and active species, including atoms and free radicals, and flame temperature pro.les were determined at a pressure of 1 atm. A comparison of the experimental and modeling results on the flame structure shows that MBMS is a suitable method for studying the structure of flames stabilized on a Mache-Hebra burner under near-adiabatic conditions. The relative flame inhibition effectiveness of the added compounds is estimated from changes in the peak concentrations of H and OH radicals in the flame and from changes in the flame propagation velocity. The results of the investigation suggest that place of action of the examined flame retardants is the gas phase. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 12–20, September–October, 2007.     

A two zone model of flame propagation applied to H2 + air flames and HCL inhibited flames

This communication presents a two zone flame model which allows computation of flame propagation velocity and average properties in the radical generation region and fuel attack region of the flame. The approach is computationally simpler than formal flame theory calculations; however, it provides only limited information since detailed structural information is sacrificed for computational simplicity. The zonal approach to flame structure is described and justification is provided for the various approximations which characterize the model. The model is largely a chemical one; however, the balance maintained between the radical molecule attack reaction and diffusional transport of radicals into the reaction region controls the propagation rate. The model was tested on five H₂ + air flames, and the computed propagation velocities compared favorably with experimental values. HCL inhibition of the stoichiometric H₂ + air flame was investigated, and the zonal approach was found suitable for studying flame inhibition.     

HMX flame structure for combustion in air at a pressure of 1 atm

The chemical structure of HMX flame during combustion in air at a pressure of 1 atm was calculated using molecular beam mass spectrometric sampling. HMX vapor was recorded for the first time near the burning surface. A total of 11 species were identified in the HMX flame (H₂, H₂O, HCN, N₂, CO, CH₂O, NO, N₂O, CO₂, NO₂, and HMX vapor), and their concentration profiles were measured. The HMX combustion was unstable. The species concentration profiles exhibit periodic pulsations related to variation in the HMX burning rate. The HMX flame structure at various distances to the burning surface was determined using the average value of the burning rate. Two main zones of chemical reactions in the flame were found. In the first zone ≈0.8 mm wide adjacent to the burning surface, HMX vapor decomposes and NO₂, N₂O, and CH₂O react with each other to form HCN and NO. In the second zone ≈0.8–1.5 mm wide, HCN was oxidized by nitric oxide to form the final combustion products. The composition of the final combustion products was analyzed. The global reaction of HMX gasification at a pressure of 1 atm was established. Heat release values in the condensed phase calculated by the global gasification reaction and by the equation of heat balance on the burning surface (using literature data from microthermocouple measurements) were analyzed and compared. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 26–43, November–December, 2008.     

Laminar hydrocarbon flame structure

From the very first experimental studies, based essentially on flame propagation velocity and flame emission measurements, successive improvements in analytical and numerical techniques have contributed to make the analysis of laminar flame structure a powerful tool for extending the knowledge on combustion chemistry, thermodynamics, and transport properties. This better knowledge is very beneficial to design efficient combustion devices with reduced pollutant emission. Overall net species production rates are derived from the experimental determination of the evolution of the gas stream velocity, temperature, and species concentrations in the direction normal to the flame front. For species involved in a limited number of reactions, rate constants can be calculated at the next step. The development, in the early 1980s, of numerical codes for simulating the structure of one-dimensional laminar premixed flames the flame structure data to be directly used for validating detailed reaction mechanisms. Species analyses are still performed with techniques based on local gas sampling by probes, despite flame perturbations, but flame structure analyses have been markedly enriched by the use of non-intrusive spectroscopic techniques. The former allow the analysis of a large variety of species, and they have proven to be very well adapted to the large number of intermediate species formed in rich flames or in flames fed by heavy fuel molecules. The molecular beam mass spectrometry technique has been recently improved by the use of new photoionization sources that allow identification of isomers and extend the knowledge on intermediate species involved in formation of benzene, polycyclic aromatic hydrocarbons, and soot in flames. Amongst various spectroscopic techniques applied to flame structure analyses, laser-induced fluorescence has been largely used to perform accurate quantitative measurements of intermediate radicals that play a key role in the prompt-NO mechanism. In this study, the contribution of flame structure studies to a better knowledge of formation mechanisms of benzene and NO _x is briefly reviewed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 22–42, July–August, 2009.     

Experimental studies of bluff-body stabilized LPG diffusion flames

Bluff-body stabilized turbulent jet diffusion flame has received renewed attention in recent years due to its practical applications. An experimental study is carried out to investigate the effect of coaxial air velocity, U_a, and lip-thickness, δ of the bluff-body on the flame stability limits and emission levels. The stability limits of a typical diffusion flame can be characterized in terms of two parameters namely flame lift-off height and blow-off velocity. It is experimentally observed that lift-off height is not linearly dependent on the fuel exit velocity, U_f, as compared to the simple jet. The flame stability is found to be improved for larger lip-thickness bluff-body because of the presence of lower pressure in the wake region behind the bluff-body. Flame length is observed to be dominated by buoyancy and momentum regimes. The transition from buoyancy to momentum regime is found to be extended with increase in lip-thickness. It is also observed that the blow-off limit is also extended further by 10% as compared to simple jet diffusion flames under similar conditions. The emissions data are reported in terms of mass based emission index, EINO_x (g [NO_x]/kg [fuel]) for a wide range of flow conditions. It is concluded that the addition of coaxial air in the larger lip-thickness bluff-body flames causes a marginal reduction in emission levels relative to smaller lip-thickness bluff-body.     

Study on Selective Dimerization of α-Methylstyrenes Promoted by Ionic Liquids

The catalytic systems composed of ionic liquids containing BF₄⁻ anion and HBF₄ showed high catalytic activity to produce 4-methyl-2,4-diphenyl-1-pentene (MDP-1) or 1,1,3-trimethyl-3-phenylindan (TPI) under different temperature conditions. Up to 90.8% selectivity to MDP-1 with a 98.7% conversion of α-methylstyrene was obtained at 60 °C in the presence of [HexMIm]BF₄–HBF₄, while exclusive TPI was yielded when the reaction temperature increased to 120 °C. Further studies showed that another ionic liquid, [BMIm]Cl · 2AlCl₃, could act as an excellent catalyst and solvent for the dimerization of α-methylstyrene to produce TPI. The dimerization of α-methylstyrene catalyzed by [HexMIm]BF₄–HBF₄ and [BMIm]Cl · 2AlCl₃ performed the same reaction mechanism and the proton was the active species.     

Method of estimating absolute concentrations of C<Subscript>2</Subscript>H<Subscript>5</Subscript> and H radicals in hydrocarbon diffusion flames

A method for estimating absolute concentrations of C₂H₅ and H radicals in hydrocarbon diffusion flames is proposed and substantiated. Concentration profiles of C₂H₅ and H on the flame axis are obtained. In the method proposed, the concentration of C₂H₅ is determined from the equality of two quantities — the rate of loss of n-butane by diffusion and the rate of its formation by recombination of two C₂H₅ radicals. The concentration of H radicals is determined from the relation between the ratio C₂H₅/H and experimental profiles of C₂H₄, C₂H₆, and O₂. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 13–20, November–December, 2007.