Investigation of effective dimensionless numbers on initiation of instability in combustion of moisty organic dust

In this work,the effect of various effective dimensionless numbers and moisture contents on initiation of instability in combustion of moisty organic dust is calculated.To have reliable model,effect of thermal radiation is taken into account.One- dimensional flame structure is divided into three zones: preheat zone,reaction zone and post-flame zone.To investigate pulsating characteristics of flame,governing equations are rewritten in dimensionless space-time(ξ,η,τ) coordinates.By solving these newly achieved governing equations and combining them,which is completely discussed in body of article,a new expression is obtained.By solving this equation,it is possible to predict initiation of instability in organic dust flame.According to the obtained results by increasing Lewis number,threshold of instability happens sooner.On the other hand,pulsating is postponed by increasing Damk?hler number,pyrolysis temperature or moisture content.Also,by considering thermal radiation effect,burning velocity predicted by our model is closer to experimental results.

Micro-organic dust combustion considering particles thermal resistance

Organic dust flames deal with a field of science in which many complicated phenomena like pyrolysis or devolatization of solid particles and combustion of volatile particles take place. One-dimensional flame propagation in cloud of fuel mixture is analyzed in which flame structure is divided into three zones. The first zone is preheat zone in which rate of the chemical reaction is small and transfer phenomena play significant role in temperature and mass distributions. In this model, it is assumed that particles pyrolyze first to yield a gaseous fuel mixture. The second zone is reaction zone where convection and vaporization rates of the particles are small. The third zone is convection zone where diffusive terms are negligible in comparison of other terms. Non-zero Biot number is used in order to study effect of particles thermal resistance on flame characteristics. Also, effect of particle size on combustion of micro organic dust is investigated. According to obtained results, it is understood that both flame temperature and burning velocity decrease with rise in the Biot number and particle size.

Pyrolysis and combustion kinetics of lycopodium particles in thermogravimetric analysis

Biomass is a kind of renewable energy which is used increasingly in different types of combustion systems or in the production of fuels like bio-oil. Lycopodium is a cellulosic particle, with good combustion properties, of which microscopic images show that these particles have spherical shapes with identical diameters of 31 μm. The measured density of these particles is 1.0779 g/cm2. Lycopodium particles contain 64.06% carbon, 25.56% oxygen, 8.55% hydrogen and 1.83% nitrogen, and no sulfur. Thermogravimetric analysis in the nitrogen environment indicates that the maximum of particle mass reduction occurs in the temperature range of 250-550 °C where the maximum mass reduction in the DTG diagrams also occurs in. In the oxygen environment, an additional peak can also be observed in the temperature range of 500-600 °C, which points to solid phase combustion and ignition temperature of lycopodium particles. The kinetics of reactions is determined by curve fitting and minimization of error.

NUMERICAL MODELING OF 3-D TURBULENT TWO-PHASE FLOW AND COAL COMBUSTION IN A PULVERIZED-COAL COMBUSTOR

In the present paper, a multifluid model of two-phase flows with pulverized-coal combustion, based on a continuum-trajectory model with reacting particle phase, is developed and employed to simulate the 3-D turbulent two-phase hows and combustion in a new type of pulverized-coal combustor with one primary-air jet placed along the wall of the combustor. The results show that: (1) this continuum-trajectory model with reacting particle phase can be used in practical engineering to qualitatively predict the flame stability, concentrations of gas species, possibilities of slag formation and soot deposition, etc.; (2) large recirculation zones can be created in the combustor, which is favorable to the ignition and flame stabilization.

Effect of wall temperature and random distribution of micro organic dust particles on their combustion parameters

The effect of wall temperature on the characteristics of random combustion of micro organic particles with recirculation was investigated. The effect of recirculating in micro-combustors is noticeable, hence it is necessary to present a model to describe the combustion process in these technologies. Recirculation phenomenon is evaluated by entering the exhausted heat from the post flam zone into the preheat zone. In this work, for modeling of random situation at the flame front, the source term in the equation of energy was modeled considering random situation for volatizing of particles in preheat zone. The comparison of obtained results from the proposed model by experimental data regards that the random model has a better agreement with experimental data than non-random model. Also, according to the results obtained by this model, wall temperature affects the amount of heat recirculation directly and higher values of wall temperature will lead to higher amounts of burning velocity and flame temperature.

Modeling multi regional counter flow combustion of lycopodium dust cloud with considering radiative heat loss

In this work, an analytical model is presented to simulate the combustion process of organic dust with considering radiative heat loss effect in counterflow configuration. A thermal model has been generated to estimate the flame propagation speed in various dust concentrations. The structure of premixed flame in a symmetric configuration, containing uniformly distributed volatile fuel particles, with nonunity Lewis number is examined with strain rate issue. The flame structure is divided into six zones: first heating, drying, second heating, volatile evaporation, reaction and post-flame zones. At first, the governing equations of lycopodium combustion dust particles are written for each zone. Finally, boundary conditions and matching conditions are applied for each zone in order to solve the differential equations. The purpose of this article is to analyze radiation heat transfer on lycopodium flame propagation dust particles and characteristics to check the effect of parameters on combustion.

燃煤流化床中氯对碳钢腐蚀的影响机制

在小规模流化床 (FBC)中燃烧一种低S高Cl煤 10 0 0h后 ,对放置于接近沸腾床位置的A2 10 -C碳钢管腐蚀情况进行分析 .发现在碳钢管表面温度为 4 70℃～ 5 6 0℃的区域腐蚀产物 (主要为Fe2 O3 )严重剥落 .剥落的腐蚀产物表面覆盖一层沉积盐 ,部分区域发现有 (K ,Na)Cl.对残留在钢管表面的腐蚀层进行分析 ,发现在腐蚀层 -碳钢界面或其附近的基体中出现局部氯化 ,导致形成FeCl2 层 ;局部快速腐蚀 ,形成向基体一侧的腐蚀突体 ;形成内部空洞这三种腐蚀形态 .并对此现象的产生及Cl2 的影响机制进行了详细探讨 .

Reconstruction model for temperature and concentration profiles of soot and metal-oxide nanoparticles in a nanofluid fuel flame by using a CCD camera

This paper presents a numerical study on the simultaneous reconstruction of temperature and volume fraction fields of soot and metal-oxide nanoparticles in an axisymmetric nanofluid fuel sooting flame based on the radiative energy images captured by a charge-coupled device（CCD） camera. The least squares QR decomposition method was introduced to deal with the reconstruction inverse problem. The effects of ray numbers and measurement errors on the reconstruction accuracy were investigated. It was found that the reconstruction accuracies for volume fraction fields of soot and metaloxide nanoparticles were easily affected by the measurement errors for radiation intensity, whereas only the metal-oxide volume fraction field reconstruction was more sensitive to the measurement error for the volume fraction ratio of metaloxide nanoparticles to soot. The results show that the temperature, soot volume fraction, and metal-oxide nanoparticles volume fraction fields can be simultaneously and accurately retrieved for exact and noisy data using a single CCD camera.

An analytical model for pyrolysis of a single biomass particle

Decreasing in emissions of greenhouse gases to confront the global warming needs to replace fossil fuels as the main doer of the world climate changes by renewable and clean fuels produced from biomass like wood waste which is neutral on the amount of CO2. An analytical and engineering model for pyrolysis process of a single biomass particle has been presented. Using a two-stage semi global kinetic model which includes both primary and secondary reactions, the effects of parameters like shape and size of particle as well as porosity on the particle temperature profile and product yields have been investigated. Comparison of the obtained results with experimental data shows that our results are in a reasonable agreement with previous researchers' works. Finally, a sensitivity analysis is done to determine the importance of each parameter on pyrolysis of a single biomass particle which is affected by many constant parameters.

Analytical Model for Predicting the Heat Loss Effect on the Pyrolysis of Biomass Particles

This paper presents the combined influence of heat-loss and radiation on the pyrolysis of biomass particles by considering the structure of one-dimensional, laminar and steady state flame propagation in uniformly premixed wood particles. The assumed flame structure consists of a broad preheat-vaporization zone where the rate of gas-phase chemical reaction is small, a thin reaction zone composed of three regions: gas, tar and char combustion where convection and the vaporization rate of the fuel particles are small, and a broad convection zone. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity(i.e.u≥1). The principal attention is made on the determination of a non-linear burning velocity correlation. Consequently, the impacts of radiation, heat loss and particle size as the determining factors on the flame temperature and burning velocity of biomass particles are declared in this research.

Modeling flame propagation speed and quenching distance of aluminum dust flame with spatially random distribution of particles

In this research combustion of aluminum dust particles in a quiescent medium with spatially discrete sources distributed in a random way was studied by a numerical approach.A new thermal model was generated to estimate flame propagation speed in a lean/rich reaction medium.Flame speed for different particle diameters and the effects of various oxidizers such as carbon dioxide and oxygen on flame speed were studied.Nitrogen was considered the inert gas.In addition,the quenching distance and the minimum ignition energy(MIE) were studied as a function of dust concentration.Different burning time models for aluminum were employed and their results were compared with each other.The model was based on conduction heat transfer mechanism using the heat point source method.The combustion of single-particle was first studied and the solution was presented.Then the dust combustion was investigated using the superposition principle to include the effects of surrounding particles.It is found that larger particles have higher values of quenching distance in comparison with smaller particles in an assumed dust concentration.With the increase of dust concentration the value of MIE would be decreased for an assumed particle diameter.Considering random discrete heat sources method,the obtained results of random distribution of fuel particles in space provide closer and realistic predictions of the combustion physics of aluminum dust flame as compared with the experimental findings.

Radiation Efficiency of Surface Burning on a Foam Metal Matrix with Ceramic Coating

The modified empirical two-temperature model of surface burning on a foam metal matrix was proposed. The comparative experimental studies of radiation properties of both matrices without and with ceramic coating (alumina) were carried out. Measurement was conducted in different spectral ranges. The experimental results were compared with theoretical calculations. It was shown that the integral radiation efficiency of the matrix with ceramic coating was comparable with radiation efficiency of the matrix without any coating in the wide range of the firing rate and surpassed it on 30% - 40% at firing rate above 50 W/cm2.

The Italian ZECOMIX Platform: CO₂Capture on Calcined Dolomite in Fluidized Bed Carbonator Unit

The Italian Zecomix platform is a gasification pilot-scale plant integrated CCS technology, whose flexibility allows operating each unit alone. For quantitative analysis of the gaseous species an analytical system based on commercially available instruments and sampling lines at various points of plant was properly designed. A Fourier Transform Infrared Spectrometric (FTIR) with portable low resolution and gas chromatographic tools were used. The fluidized bed calciner/ carbonator unit was fed with naturally occurring dolomite (about 300 kg) from quarry of Biella (Italy) and tested for CO2 capture. Carbonation reaction was conducted at around 700°C under simulated reformed synthesis gas containing 30% of CO2. Based on GC and FTIR results a CO2 retention better than 70% was achieved. The application of grain model establishing the carbonation reaction was kinetically controlled within 50 seconds and the reaction rate constant was comparable to that obtained at laboratory-scale level by thermogravimetric analyzer.

Effects of dimethyl ether and ethanol additions on soot transition in ethylene counterflow diffusion flames

This paper investigates the effect of blending dimethyl ether(DME)and ethanol on the soot transition periods in ethylene counterflow diffusion flames by using a novel optical diagnostic method.The soot critical transition point in different conditions is identified experimentally and numerically.Two kinds of flames are carried out to gain the soot critical transition point in counterflow diffusion flames by changing oxygen fraction(Xo)and changing volume flow rates of fuel and oxidizer(Qv).The red-green-blue(RGB)ratio method is used to precisely identify the soot critical transition point,and chemical kinetic simulations are performed to analyze the detailed reaction paths.The results show that compared to the ethylene flame,the soot critical transition point occurs at a higher Xoand a lower Qvwhen DME or ethanol is blended.The addition of DME and ethanol can inhibit soot formation,due to the degree of soot formation reaction being lower than the degree of the oxidation reaction in the blending flames.

Sensitivity analysis of modeling parameters to soot and PAHs prediction in ethylene inverse diffusion flame

The soot formation model based on inverse ethylene diffusion flames was performed to study the sensitivity of the soot formation process to the prediction results.The effects of efficiency parameters such as soot inception,surface growth and coagulation on the simulation results were studied by using the adjustable efficiency model.In addition,the reversible soot model and conjugate heat transfer(CHT)model were also introduced to explore their advantages.Results indicated that,among adjustable efficiency parameters,the nucleation efficiency had the greatest influence on the predicted soot and PAHs distributions,while the Habstraction-C2H2-addition(HACA)process and PAH adsorption surface growth efficiencies impacted little.The adjustable efficiency parameters had a significant effect on the concentration of soot gaseous precursors and soot particles,but their effects on temperature,gas phase molecules,and intermediate species were not obvious.When the nucleation efficiency increased from 2×10^(-6)to 1×10^(-4),the predicted value of the integrated soot was increased by nearly 50%,and the maximum primary particle number density and the number of aggregates were increased by an order of magnitude.The maximum concentration of BAPYR was doubled.However,the peak temperature along the axial direction increased by only 3.5 K.Using the reversible soot model,the approximation results of the adjustable efficiency parameters could be modified,which showed the feasibility of the model.The use of the CHT model promoted pyrolysis of the fuel below the outlet of the fuel tube,with high-temperature zones,soot zones,and PAHs zones moving towards higher flame heights.Besides,when using the reversible model and the CHT model,the maximum soot volume fraction decreased by 39%compared with the basic efficiency parameters,while the concentration of BAPYR increased by 162%,and the concentrations of gas phase species were decreased.

Coupled interactive effects of ammonia and hydrogen additions on ethylene diffusion flames: A detailed kinetic study

In order to create effective combustion technologies and fuels with low or no carbon emissions,the research was conducted to assess the coupled interactive effects of NH_(3) and H_(2) additions on ethylene counterflow diffusion flames from a kinetic perspective.The effects of the NH_(3)/H_(2) combination on flame temperatures,major species,key radicals,important intermediate species,representative oxygenated species and NO_xwere examined.The results of the study utilizing fictitious inert NH_(3) and/or H_(2) revealed the chemical effects of the two components.It was found that the NH_(3)/H_(2) coupled effects had a more effective inhibitory effect on soot precursors than the effects of corresponding sum of single NH_(3) or H_(2) addition.The production of soot precursors was promoted by the coupled chemical effects of NH_(3) and H_(2),but the coupled dilution and thermal effects were observed to have a greater impact,resulting in a decrease of the mole fractions of soot precursors.As for the interaction of NH_(3) and H_(2) effects,the presence of H_(2) decreased the chemical effects of NH_(3) on the augmentation of C_(2)H_(2),A1,A2,and CH_(3)CHO mole fractions.The NH_(3) addition alleviated the H_(2) chemical effects on increasing C_(2)H_(2),C_(3)H_(3),A1 and A2 concentrations.Conversely,the NH_(3)chemical effects on C_(3)H_(3),OH and CH_(3)CHO were enhanced when H_(2) was added.The presence of NH_(3) augmented the chemical effects of H_(2) on the growth of OH mole fraction.Moreover,the H_(2) chemical effects hindered the production of NO and NO_(2) in the presence of NH_(3).

Experimental study on effects of gas flow rate on soot characteristics in diffusion flames coupled with plasma

This study examined the evolution of morphology and nanostructure of soot particles from the plasma-flame interaction for various gas flow rates.The current study used both optical diagnostic and sampling methods to explore the soot production and combustion characteristics.Soot particles were characterized at the same positions downstream from the flame zone by thermophoretic sampling and transmission electron microscopy.Moreover,X-ray diffraction analysis,and thermogravimetric analysis were performed to study the nanostructure and oxidation reactivity of soot.A reduction in soot concentration was found with the plasma addition,which illustrated an inhibition effect of plasma on soot emission.The increased gas flow rate promoted soot concentration since a growing number of carbons participated in the combustion process.Depending on the gas flow rate(carbon content)variation and plasma activation,either liquid-like soot material with irregularly shaped protrusions or chain-like structure,or a mixture of both,were generated from the diffusion flames.The soot produced by plasma-flame interaction also demonstrated a high correlation between nanostructure and reactivity.The soot from lower carbon content with plasma activation had a shorter fringe length and larger fringe tortuosity related to higher oxidation reactivity.On the contrary,soot from the highest carbon content without plasma-flame interaction exhibited prevalent fullerene-like nanostructures with evident large or small shells and also had a higher carbonization degree resulting in lower oxidation reactivity.

Combustion characteristics and synergy behaviors of biomass and coal blending in oxy-fuel conditions: A single particle co-combustion method

Co-combustion biomass and coal can effectively reduce the emission of CO_2. O_2/H_2O combustion is regarded as the next generation of oxy-fuel combustion technology. By co-combustion biomass and coal under oxy-fuel condition, the emission of CO_2 can be minimized. This work investigates the co-combustion characteristics of single particles from pine sawdust(PS) and bituminous coal(BC) in O_2/N2, O_2/CO_2 and O_2/H_2O atmospheres at different O_2 mole fractions(21%, 30% and 40%). The experiments were carried out in a drop tube furnace(DTF), and a high speed camera was used to record the combustion process of fuel particles. The combustion temperature was measured by a two-color method. The experiments in O_2/N2 atmosphere indicate that the particles from pine sawdust and bituminous coal all ignite homogeneously. After replacing H_2O for N2, the combustion temperature of volatiles of blended fuel particles decreases, while the combustion temperature of char increases. The ignition delay time in O_2/H_2O atmosphere is shorter than that in O_2/N2 or O_2/CO_2 atmosphere. The combustion temperature of volatiles of blended fuel particles increases as the mass fraction of bituminous coal increases, while the combustion temperature of char of blended fuel particles is higher than that of biomass or bituminous coal. The ignition delay time of blended fuel particles increases with the increasing mass fraction of bituminous coal, and the experimental ignition delay time of blend fuel particles is shorter than the theoretical one. These reveal a synergy during co-combustion process of pine sawdust and bituminous coal.

Combustion characteristics of nanofluid fuels in a half-opening slot tube

Combustion characteristics of nanofluid fuels containing aluminum nanoparticles were investigated in half-opening slot tubes from the fundamental view. The effects of particle loading rates(0.25% and 2.5% by weight), type of base fuels(ethanol and butanol),and fuel flow rates(0.2, 0.6, and 1 mL/min) were studied in details. The combustion characteristics of the nanofluid fuels and pure based fuels were also examined to provide a comparison. Flame was unstable with reignition, stable state, nearly extinguishment repeatedly at low flow rate. At medium flow rate, flame height was increased and flame tended to be stable. At high flow rate,flame became unstable and was disturbed by the droplet forming and dripping significantly. Al atoms inside the oxide layer should be melted before the particles combustion, while Al oxide layer should be melted before the particles aggregates combustion. The effects of particles on the combustion characteristics, especially on the evaporation rate of base fuel, were discussed. The reasons for various combustion phenomena of nanofluid fuels were given, which can provide the useful guidance for the experimental research and practical applications of nanofluid fuels.

Inhibition Effects of CH_(4)/CH_(3)OH on Dimethyl Ether Cool Flames

CH_(4)/DME mixtures can be used for engines and gas turbines,and have already been studied for many years.However,DME has a strong cool flame phenomenon,which will greatly influence the ignition and combustion characteristics of following hot flames.Therefore,the cool flame characteristics of CH_(4)/DME mixture are very important for their utilization.Recently,the inhibition effect of CH_(4)on DME cool flames has been discovered,but the mechanisms of the inhibition effects lack further verification and research.In this study,the inhibition effects were investigated via both experiments and simulations.In order to validate the inhibition effects,a comparison fuel of CH_(3)OH/DME was also used in this study.The extinction limits,flame temperatures and combustion products of the cool flames of the CH_(4)/DME and CH_(3)OH/DME mixtures were measured using a counterflow burner,and the reaction paths and heat release rate were derived from the HPMech-v3.3.The results indicate that CH_(4)and CH_(3)OH will both inhibit the cool flame of DME via competing with DME for OH and O radicals,and CH_(3)OH has stronger inhibition effects than CH_(4),because it is more competitive and produces more CH2O,which inhibits the oxidation of DME.The HPMech-v3.3 closely agrees with the experimental data,but still needs to be improved.