Experimental and kinetic investigation of the pyrolysis,combustion, and gasification of deoiled asphalt

The pyrolysis, combustion, and gasification behaviors of deoiled asphalt were studied by a thermogravimetric analyzer and the kinetics were also analyzed using a multi-stage first-order integral model. All the experiments were conducted at non-isothermal conditions with heating rates range of 10–40 K min^?1 under N₂ (pyrolysis), air (combustion), or CO₂ (gasification) atmosphere, respectively. The results showed that, for pyrolysis, the reaction mainly occurred between 498 and 798 K and could be divided into two stages: the first was caused by the volatilization of small molecules and the second probably due to the cracking reactions. For combustion, the mass loss process could be divided into three stages: the devolatilization and oxidation first, the ignition and combustion of the volatiles second, and finally the combustion of the formed char. Under CO₂ atmosphere, the mass loss behavior was similar with that of the N₂ atmosphere at lower temperatures, but when the temperature was higher than 1,233 K, the gasification reaction obviously happened. The results of kinetic investigation showed that the multi-stage first-order integral method agreed well with the above experiments.     

A simple reactive gasdynamic model for the computation of gas temperature and species concentrations behind reflected shock waves

A simple gasdynamic model, called CHEMSHOCK, has been developed to predict the temporal evolution of combustion gas temperature and species concentrations behind reflected shock waves with significant energy release. CHEMSHOCK provides a convenient simulation method to study various sized combustion mechanisms over a wide range of conditions. The model consists of two successive suboperations that are performed on a control mass during each infinitesimal time step: (1) first the gas mixture is allowed to combust at constant internal energy and volume; (2) then the gas is isentropically expanded (or compressed) at frozen composition to the measured pressure. The CHEMSHOCK model is first validated against results from a one‐dimensional reacting computational fluid dynamics (CFD) code for a representative case of heptane/O₂/Ar mixture using a reduced mechanism. CHEMSHOCK is found to accurately reproduce the results of the CFD calculation with significantly reduced computational time. The CHEMSHOCK simulation results are then compared to experimental results, for gas temperature and water vapor concentration, obtained using a novel laser sensor based on fixed‐wavelength absorption of two H₂O rovibrational transitions near 1.4 μm. Excellent agreement is found between CHEMSHOCK simulations and measurements in a progression of shock wave tests: (1) in H₂O/Ar, with no energy release; (2) in H₂/O₂/Ar, with relatively small energy release; and (3) in heptane/O₂/Ar, with large energy release. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 189–198, 2008     

The kinetics of gasification of char derived from sewage sludge

Gasification of char derived from sewage sludge was studied under different oxidizing atmospheres containing CO₂, O₂ or H₂O. The gasification tests were carried out in thermobalance at different temperatures and oxidizing reagent concentrations. The most efficient were the gaseous mixtures containing oxygen. The reaction took place at temperature 400–500 °C, whilst in the case of CO₂ and steam much higher temperatures (700–900 °C) were necessary to complete the conversion. Two rate models for gas–solid reaction were applied to describe the effect of char conversion on reaction rate. The shrinking core model for reaction-controlled regime was found to be the best for predicting the rate of char gasification in CO₂ and O₂ atmosphere. The experimental data for steam gasification of the char were fitted best by the first-order kinetics. The kinetic parameters estimated from the experimental data are in accordance with the literature for lignocellulosic char gasification and are the first published for sewage sludge char gasification.     

Modelling the effect of operating conditions on hydrodynamics and mass transfer in a Pd–Ag membrane module for H2 purification

In this work a novel modelling approach based on Computational Fluid Dynamics (CFD) for the prediction of the gas separation process in a Pd–Ag membrane module for H₂ purification is presented. With this approach, the pressure and velocity flow fields of the gas mixture and the species concentration distribution in the selected three-dimensional domain are simultaneously and numerically computed by solving the continuity, momentum and species transport equations, including a gas-through-gas diffusion term derived from the Stefan–Maxwell formulation. As a result, the H₂ permeation calculations depend on the local determination of the mass transfer resistances offered by the gas phase and by the membrane, which is modelled as a permeable surface of known characteristics. The applicability of the model to properly predict the separation process under a wide range of pressure, feed flow rate, temperature and gas mixtures composition is assessed through a strict comparison with experimental data. The influence of inhibitor species on the module performance, that is obtained by implementing in the CFD model a suitable literature correlation, is also discussed.     

Reductive and oxidative combustion of polyethylene bags: Characterization of carbonaceous and nitrogenous species

This study aims to experimentally characterize the gaseous carbonaceous and nitrogenous species from the reductive and oxidant combustion of polyethylene plastic bags. The experimental device used is the tubular furnace, coupled to two gas analyzers: a Fourier transform infrared analyzer (FTIR) and a non dispersive infrared analyzer (NDIR). The gaseous products analyzed are: CO, CO₂, CH₄, C₃H₈, C₂H₄, C₂H₂, C₆H₆, HCN, N₂O, NO, NO₂ and NH₃. The experiments were conducted at temperatures ranging from 800 to 1000 °C. The results obtained allow us to note that carbonaceous compounds are mainly emitted as carbon oxides (CO and CO₂) whether you are reductive combustion or oxidative combustion.In addition:

• -Under reductive conditions, combustion is controlled by oxygen. The hydrocarbon most active in the formation of carbon monoxide is ethylene (C₂H₄) and to a lesser extent, from 900 °C, acetylene (C₂H₂). The extents we have made show that ammonia seem to be emitted during combustion with 10% of oxygen.
• -In an oxidative environment, there is production of C₆H₆ in substantial quantities, which partly explains the presence of soot and tar in the smoke exhaust ducts. The C₂H₄, CH₄ and C₂H₂ are hydrocarbons most active in the formation of CO and CO₂. Increasing of concentration of local oxygen from 10 to 21% for the combustion of plastic bags, favors an increase in efficiency of carbon conversion about 30%. About 99% of the carbon of the fuel is found to be converted to carbon oxides or hydrocarbons. Nitrogen monoxide (NO) is the major component among the gases measured with a conversion rate of nitrogen about 20%, three times larger than that obtained during the reductive combustion of plastic bags with 10% oxygen.

     

Thermal degradation and evolved gas analysis of thiourea-formaldehyde resin (TFR) during pyrolysis and combustion

Thiourea formaldehyde resin (TFR) has been synthesized by condensation of thiourea and formaldehyde in acidic medium and its thermal degradation has been investigated using TG-FTIR-MS technique during pyrolysis and combustion. The results revealed that the thermal decomposition of TFR occurs in three steps assigned to drying of the sample, fast thermal decomposition of polymers, and further cracking. The similar TG and DTG characteristics were found for the first two stages during pyrolysis and combustion. The combustion process was almost finished at 680?°C, while during pyrolysis a total mass loss of 93 wt% is found at 950?°C. The release of volatile products during pyrolysis are NH₃, CS₂, CO, HCN, HNCS, and NH₂CN. The main products in the second stage are NH₃ CO₂, CS₂, SO₂, and H₂O during combustion. In the next stage, the combustion products mentioned above keep on increasing, but some new volatiles such as HCN, COS etc., are identified. Among the above volatiles, CO₂ is the dominant gaseous product in the whole combustion process. It is found that the thermal degradation during pyrolysis of TFR produced more hazardous gases like HCN, NH₃, and CO when compared with combustion in similar conditions.     

空气污染各组分对甲烷超声速燃烧性能的影响

在与甲烷详细化学反应机理对比验证基础上,采用18组分24步简化反应机理模拟甲烷超声速燃烧过程,从化学动力学和热力学角度用数值方法研究了乙醇燃烧加热空气中的七种主要污染组分(H2O,CO2,O,OH,CO,H,H2)对甲烷超声速燃烧性能的影响.分析结果表明:在一定条件下,进口空气中污染组分H2O的增加造成平均比热容增加,总温降低,并作为第三体抑制甲烷的燃烧过程,使超燃室的性能下降;CO2因大分子量特性使燃气平均分子量增大,降低超燃室做功能力,H2O和CO2两组分对甲烷超燃性能都起消极作用;污染组分自由基H、O、OH和燃烧中间产物CO、H2使燃烧室燃烧效率上升,对甲烷超燃性能起积极作用.     

Hydrogen‐Abstraction/Acetylene‐Addition Exposed

Polycyclic aromatic hydrocarbons (PAHs) are omnipresent in the interstellar medium (ISM) and also in carbonaceous meteorites (CM) such as Murchison. However, the basic reaction routes leading to the formation of even the simplest PAH—naphthalene (C₁₀H₈)—via the hydrogen‐abstraction/acetylene‐addition (HACA) mechanism still remain ambiguous. Here, by revealing the uncharted fundamental chemistry of the styrenyl (C₈H₇) and the ortho‐vinylphenyl radicals (C₈H₇)—key transient species of the HACA mechanism—with acetylene (C₂H₂), we provide the first solid experimental evidence on the facile formation of naphthalene in a simulated combustion environment validating the previously postulated HACA mechanism for these two radicals. This study highlights, at the molecular level spanning combustion and astrochemistry, the importance of the HACA mechanism to the formation of the prototype PAH naphthalene.     

Enthalpy of formation and bond energies on unsaturated oxygenated hydrocarbons using G3MP2B3 calculation methods

Enthalpies of unsaturated oxygenated hydrocarbons and radicals corresponding to the loss of hydrogen atoms from the parent molecules are intermediates and decomposition products in the oxidation and combustion of aromatic and polyaromatic species. Enthalpies (Δ_fH⁰₂₉₈) are calculated for a set of 27 oxygenated and nonoxygenated, unsaturated hydrocarbons and 12 radicals at the G3MP2B3 level of theory and with the commonly used B3LYP/6‐311g(d,p) density functional theory (DFT) method. Standard enthalpies of formation (Δ_fH⁰₂₉₈) are determined from the calculated enthalpy of reaction (ΔH⁰_rxn,298) using isodesmic work reactions with reference species that have accurately known Δ_fH⁰₂₉₈ values. The deviation between G3MP2B3 and B3LYP methods is under ±0.5 kcal mol^?1 for 9 species, 18 other species differs by less than ±1 kcal mol^?1 , and 11 species differ by about 1.5 kcal mol^?1. Under them are 11 radicals derived from the above‐oxygenated hydrocarbons that show good agreement between G3MP2B3 and B3LYP methods. G3 calculations have been performed to further validate enthalpy values, where a discrepancy of more than 2.5 kcal mol^?1 exists between the G3MP3B3 and density functional results. Surprisingly the G3 calculations support the density functional calculations in these several nonagreement cases. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 633–648, 2005     

烟煤焦在H2O和CO2气氛下的结构演变与气化反应性关联

本研究以烟煤在1000 ℃热解所制得的焦样为研究对象,考察了其在H₂O、CO₂及两者混合气氛下的结构演变,以及气化反应性的影响。为了探究焦样在气化过程中的结构演变,利用氮吸附、SEM和拉曼光谱等表征手段分析不同碳转化率下的焦样结构。结果表明,H₂O气氛对焦样结构的演变明显不同于CO₂气氛,揭示了焦样在两种气氛下的反应路径不同。因结构演变的不同,随碳转化率的增加,焦样在两种气氛下表现出不同的气化反应性能。在CO₂气氛下,焦样的气化反应速率随碳转化率的增加而逐渐降低,与H₂O气氛存在下变化趋势相反。在H₂O和CO₂共气化条件下,煤焦在H₂O和CO₂混合气氛下的反应速率高于单气氛下的反应速率的计算值,表现出一定的协同作用。这是因为焦样与H₂O反应能够产生较大的比表面积,为焦样与CO₂反应提供更多的反应场所,促进了焦样与CO₂的反应。     

A parametric study on coal gasification for the production of syngas

In this parametric study, the effects of coal and oxidiser type, air-to-fuel ratio, steam-to-fuel ratio, reactor temperature, and pressure on H₂ and CO amounts at the gasifier output, H₂/CO, and higher heating value of the syngas produced have been calculated using a coal gasification model. Model simulations have been performed to identify the optimum values which are assumed to be 100 % for both cold gas efficiency and carbon conversion efficiency in the gasification process. From this study, it may be observed that the moisture content of the coal type is of crucial importance for the air gasification process; the O₂ content of similar coals (taking into consideration the moisture and H₂ content) is of significant importance for the air gasification process. When compared with air gasification, air-steam gasification becomes a more effective coal gasification method. The optimum working condition for air-steam gasification is to carry out the process at one atmosphere. High gasifier temperatures are not needed for the air-steam gasification of coal.     

An optimized kinetics model for OH chemiluminescence at high temperatures and atmospheric pressures

Chemiluminescence from the OH(A → X) transition near 307 nm is a commonly used diagnostic in combustion applications such as flame chemistry, shock‐tube experiments, and reacting‐flow visualization. Although absolute measurements of OH(X) concentrations are well defined, there is no elementary relation between emission from the electronically excited state (OH*) and its absolute concentration. Thus, to enable quantitative emission measurements, a kinetics model has been assembled and optimized to predict OH* formation and quenching at combustion conditions. Shock‐tube experiments were conducted in mixtures of H₂/O₂/Ar, CH₄/O₂/Ar, and CH₄/H₂/O₂/Ar with high levels of argon dilution (>98%). Elementary reactions to model OH*, along with initial estimates of their rate coefficients, were taken from the literature. The important formation steps follow: (R0) (R1) Sensitivity analyses were performed to identify experimental conditions under which the shape of the measured OH* profiles and the magnitude of the OH* emission would be sensitive to the formation reactions. A fitting routine was developed to express the formation rate parameters as a function of a single rate, k₁ at the reference temperature (1490 K). With all rates so expressed, H₂/CH₄ mixtures were designed to uniquely determine the value of k₁ at the reference temperature, from which the remaining rate parameters were calculated. Quenching rates were fixed at their literature values. The new model predicts the experimental data over the range of conditions studied and can be used to calibrate the emission diagnostic for other applications, such as measurements in real combustion environments, containing higher order hydrocarbon fuels and lower levels of dilution in air. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 714–724, 2006     

Experimental and kinetic modeling of the reduction of NO by isobutane in a Jsr at 1 atm

A kinetic study of the reduction of nitric oxide (NO) by isobutane in simulated conditions of the reburning zone was carried out in a fused silica jet‐stirred reactor operating at 1 atm, at temperatures ranging from 1100 to 1450 K. In this new series of experiments, the initial mole fraction of NO was 1000 ppm, that of isobutane was 2200 ppm, and the equivalence ratio was varied from 0.75 to 2. It was demonstrated that for a given temperature, the reduction of NO is favored when the temperature is increased and a maximum NO reduction occurs slightly above stoichiometric conditions. The present results generally follow those reported in previous studies of the reduction of NO by C₁ to C₃ hydrocarbons or natural gas as reburn fuel. A detailed chemical kinetic modeling of the present experiments was performed using an updated and improved kinetic scheme (979 reversible reactions and 130 species). An overall reasonable agreement between the present data and the modeling was obtained. Furthermore, the proposed kinetic mechanism can be successfully used to model the reduction of NO by ethylene, ethane, acetylene, a natural gas blend (methane‐ethane 10:1), propene, and HCN. According to this study, the main route to NO reduction by isobutane involves ketenyl radical. The model indicates that the reduction of NO proceeds through the reaction path: iC₄H₁₀ → C₃H₆ → C₂H₄ → C₂H₃ → C₂H₂ → HCCO; HCCO + NO → HCNO + CO and HCN + CO₂; HCNO + H → HCN → NCO → NH; NH + NO → N₂ and NH + H → followed by N + NO → N₂; NH + NO → N₂O followed by N₂O + H → N₂. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 365–377, 2000     

Tunable Diode Laser Diagnostic Studies of H2-Ar-O2 Microwave Plasmas Containing Methane or Methanol

Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and ten stable molecules in H₂-Ar-O₂ microwave plasmas containing up to 7.2% of methane or methanol, under both flowing and static conditions. The degree of dissociation of the hydrocarbons varied between 30 and 90% and the methyl radical concentration was found to be in the range 10 ¹⁰ –10 ¹² molecules cm ^–3 . The methyl radical concentration and the concentrations of the stable C-2 hydrocarbons C ₂ H ₂ , C ₂ H ₄ , and C ₂ H ₆ , produced in the plasma decayed exponentially when increasing amounts of O ₂ were added at fixed methane or methanol partial pressures. In addition to detecting the hydrocarbon species, the major products CO, CO ₂ , and H ₂ O were also monitored. For the first time, formaldehyde, formic acid, and methane were detected in methanol microwave plasmas, formaldehyde was detected in methane microwave plasmas. Chemical modeling with 57 reactions was used to successfully predict the concentrations in methane plasmas in the absence of oxygen and the trends for the major chemical product species as oxygen was added.     

A comprehensive kinetic mechanism for CO,CH2O,and CH3OH combustion

New experimental profiles of stable species concentrations are reported for formaldehyde oxidation in a variable pressure flow reactor at initial temperatures of 850–950 K and at constant pressures ranging from 1.5 to 6.0 atm. These data, along with other data published in the literature and a previous comprehensive chemical kinetic model for methanol oxidation, are used to hierarchically develop an updated mechanism for CO/H₂O/H₂/O₂, CH₂O, and CH₃OH oxidation. Important modifications include recent revisions for the hydrogen–oxygen submechanism (Li et al., Int J Chem Kinet 2004, 36, 565), an updated submechanism for methanol reactions, and kinetic and thermochemical parameter modifications based upon recently published information. New rate constant correlations are recommended for CO + OH = CO₂ + H ( R23 ) and HCO + M = H + CO + M ( R24 ), motivated by a new identification of the temperatures over which these rate constants most affect laminar flame speed predictions (Zhao et al., Int J Chem Kinet 2005, 37, 282). The new weighted least‐squares fit of literature experimental data for ( R23 ) yields k₂₃ = 2.23 × 10⁵T^1.89exp(583/T) cm³/mol/s and reflects significantly lower rate constant values at low and intermediate temperatures in comparison to another recently recommended correlation and theoretical predictions. The weighted least‐squares fit of literature results for ( R24 ) yields k₂₄ = 4.75 × 10¹¹T^0.66exp(?7485/T) cm³/mol/s, which predicts values within uncertainties of both prior and new (Friedrichs et al., Phys Chem Chem Phys 2002, 4, 5778; DeSain et al., Chem Phys Lett 2001, 347, 79) measurements. Use of either of the data correlations reported in Friedrichs et al. (2002) and DeSain et al. (2001) for this reaction significantly degrades laminar flame speed predictions for oxygenated fuels as well as for other hydrocarbons. The present C₁/O₂ mechanism compares favorably against a wide range of experimental conditions for laminar premixed flame speed, shock tube ignition delay, and flow reactor species time history data at each level of hierarchical development. Very good agreement of the model predictions with all of the experimental measurements is demonstrated. © 2007 Wiley Periodicals, Inc. 39: 109–136, 2007     

Concentration Limits of Flame Propagation in H<Subscript>2</Subscript>—C<Subscript>3</Subscript>H<Subscript>8</Subscript>—Air Mixtures at Elevated Pressures

Upper concentration limits of flame propagation in H₂—C₃H₈—air mixtures at elevated initial pressures are determined. It is revealed that the flame propagation area widens substantially with the initial pressure rise. It is found that the presence of hydrogen promotes combustion of rich propane—air mixtures at concentrations of propane that exceed its upper concentration limit. It is concluded that research results can be explained from consideration of features of chain branching reactions, which are responsible for hydrogen and hydrocarbons combustion in air.     

Comparison of pulverized coal combustion in air and in O2/CO2 mixtures by thermo-gravimetric analysis

Thermo-gravimetric technique was used to study the combustion characteristics of pulverized coal in different O₂/CO₂ environments. The effects of combustion environment, oxygen concentration, particle size and heating rate were considered and the differences of pulverized coal pyrolysis, combustion and gaseous compounds release under two environments were analyzed. Results show that the coal pyrolysis in CO₂ environment can be divided into three stages: moisture release, devolatilization and char gasification by CO₂ in higher temperature zone. In the lower temperature zone, the mass loss rate of coal pyrolysis in CO₂ environment is lower than that in N₂ environment. The burning process of pulverized coal in O₂/CO₂ environment is delayed compared with that in O₂/N₂ environment for equivalent oxygen concentrations. With the oxygen concentration increase or the coal particle size decrease, the burning rate of coal increases and burnout time is shortened. As the heating rate increases, coal particles are faster heated in a short period of time and burnt in a higher temperature region, but the increase in heating rate has almost no obvious effect on the combustion mechanism of pulverized coal. During the programmed heating process, species in flue gas including H₂O, CO₂, CO, CH₄, SO₂ and NO were determined and analyzed using the Fourier-transform infrared (FTIR) spectrometer. Compared with pulverized coal combustion in O₂/N₂ environment, much more CO is produced in O₂/CO₂ coal combustion process, but the releases of SO₂ and NO are less than those released in O₂/N₂ environment. The present results might have important implications for understanding the intrinsic mechanics of pulverized coal combustion in O₂/CO₂ environment.     

Analytical-numerical solution for turbulent jet diffusion flames of hydrogen

The hydrogen fuel seems to be a good candidate to replace the energy obtained from some fossil fuels. Therefore this work explains the process of obtaining a two-step reduced chemical kinetic mechanism for the hydrogen combustion. The development of a reduced mechanism consists in eliminating reactions that produce negligible influence on the combustion process. Moreover, for this mechanism, we obtain an analytical-numerical solution for a turbulent jet diffusion flame. To quantify the intermediate species, the mixture fraction is decomposed into three parts, each part directly related to the mass fraction of a species. The governing equations are discretized using the second order finite-difference approach and are integrated in time using the second order simplified three-step Runge-Kutta scheme. Obtained results compare favorably with data in the literature for a 50/50 % volume H ₂?N ₂ jet diffusion flame. The main advantage of this strategy is the decrease of the work needed to solve the system of governing equations, by one order of magnitude for the hydrogen.     

Determination of exchangeable protons in natural organic matter using a home-made hydrogen/carbon analyser

A home made hydrogen/carbon analyser was used to determine the portion of exchangeable protons in aquatic humic substances. For this purpose, equal sample amounts were dissolved in H₂O and D₂O, respectively, dried and combusted in a stream of oxygen. The amount of water resulting from combustion was measured by an infrared detector which recorded the OH bending vibration of H₂O. The bands stemming from HOD or D₂O were not registered by the detection unit. Thus, combustion of organic samples containing exchangeable protons dissolved in D₂O resulted in a significantly smaller signal compared to the signal observed for the same sample dissolved in H₂O. The relative intensity loss of the H₂O signal observed after combustion was used to derive the portion of exchangeable protons in a standard reference material, a humic substance isolated by the International Humic Substances Society (Suwannee River fulvic acid). According to this method about 20% of the sample protons could be identified as exchangeable protons. With regard to titration data the portion of protons bound to non acidic hydroxy functions could be estimated. The validity of this procedure was proved by combustion experiments using commercially available deuterated substances as well as organic model compounds dissolved in D₂O and H₂O, respectively. Received: 31 August 2000 / Revised: 11 October 2000 / Accepted: 14 October 2000     

适用于汽油参比燃料TRF的多环芳香烃生成机理

构造了一个包括287种组分和1569个反应的汽油参比燃料TRF(toluene reference fuel)燃烧过程中多环芳香烃(PAHs)生成机理的详细化学反应动力学模型,引入四种PAH生长路径将多环芳香烃的生成机理发展到芘A4(C20H12)水平,并通过对PAH产率的分析,指出乙炔(C2H2)、丙炔(C3H3)、乙烯基乙炔(C4H4)以及含有奇数碳原子的环戊二烯自由基(C5H5)和茚基(C9H7)等物质对PAHs生成和生长起到重要作用.该机理可以较准确计算基础燃料(PRF)和TRF火焰的着火延迟期、燃烧火焰中小分子(PAH前驱体C2H2、C3H4等)和PAHs的物质浓度.通过与实验数据的比较表明,该机理在不同温度、压力、化学计量比下具有较好的性能.由此分析,该机理对碳烟前驱物PAHs的预测性能是可靠的.