Dust Cloud Combustion Research Articles

Modeling Counterflow Combustion of Dust Particle Cloud in Heterogeneous Media

AbstractThis study investigates the counterflow combustion of an aluminum dust cloud in a heterogeneous system of discrete heat sources. A numerical thermal model was developed to estimate the burning velocity at different concentrations of the dust cloud and oxidizer. The proposed model considers the effects of heat transfer mechanisms, and the calculation of the flame speed is based on a point-source approach. The model equations were derived and solved first to study the single-particle combustion. Later, to investigate the dust cloud combustion, the superposition principle was applied to include the effects of particles. The burning velocity and flame stabilization point were studied at different particle diameters, and the effect of counterflow strain rate was analyzed as well. Moreover, the minimum ignition energy was obtained as a function of dust cloud concentration. The predicted results for the burning velocity were in reasonable agreement with experimental data from the literature.

A comparative study of different burning time models for the combustion of aluminum dust particles

In the present paper combustion of micron-sized aluminum dust cloud has been studied in a quiescent reaction medium with spatially discrete sources. A new thermal model is generated to estimate the flame front speed in a lean reaction environment in different oxidizer concentrations. Different burning time models for aluminum are utilized in the generated thermal model to compare their applicability by using the existing experimental data. The model is based on conduction and radiative heat transfer mechanisms using the heat point source method. The combustion of single-particle was first studied and the solution is presented. Then the dust combustion was investigated using the superposition principle to include the effects of inter-particles. The flame propagation speed as a function of aluminum dust concentration for various particle diameters is studied and the effects of radiation heat transfer are taken into account in the governing equations. In addition, flame speed in different types of oxidizers such as air, carbon dioxide, and water vapor is investigated and nitrogen is considered as the inert gas. A reasonable agreement between the results of the numerical solution of combustion of an aluminum dust cloud and the experimental data was obtained in terms of flame propagation speed. It is found that the value of flame speed of combustion of aluminum dust particles in carbon dioxide reaction medium in a considered dust concentration and particle size, is the lowest compared to the other oxidizers.

Mathematical modeling of premixed counterflow combustion of organic dust cloud

In the present study, a mathematical approach is utilized so as to modeling the flame structure of organic dust particle and air through a two-phase mixture consisting in a counterflow configuration where heat loss is taken into account. Lycopodium is considered as the organic fuel in our research. In order to simulate combustion of organic dust particles, a three-zone flame structure has been considered; preheat-vaporization zone, reaction and post flame zones. The variations of the gaseous phase mass fraction and fuel particle mass fraction as a function of the distance from the stagnation plate are obtained. Subsequently, flame temperature and flame velocity in terms of strain rate are studied. Finally, the effect of heat loss on the non-dimensionalized temperature at different heat loss coefficients is investigated.

Analysis of Aluminum Dust Cloud Combustion Using Flame Emission Spectroscopy.

In this study, aluminum flame analysis was researched in order to develop a measurement method for high-energy-density metal aluminum dust cloud combustion, and the flame temperature and UV-VIS-IR emission spectra were precisely measured using a spectrometer. Because the micron-sized aluminum flame temperature was higher than 2400 K, Flame temperature was measured by a non-contact optical technique, namely, a modified two-color method using 520 and 640 nm light, as well as by a polychromatic fitting method. These methods were applied experimentally after accurate calibration. The flame temperature was identified to be higher than 2400 K using both methods. By analyzing the emission spectra, we could identify AlO radicals, which occur dominantly in aluminum combustion. This study paves the way for realization of a measurement technique for aluminum dust cloud combustion flames, and it will be applied in the aluminum combustors that are in development for military purposes.

Flame propagation in hybrid “coal-methane-air” aerosuspensions

Results of laminar flame propagation experimental studies on hybrid aerosuspensions «methane-coal-air» are presented. Combustion of fine coal dust clouds (r0 = 8 microns, volume 4 · 10-3m3) and iron oxide clouds (r0 = 5 microns, volume 4 · 10-3m3) is investigated in isobaric conditions. Volumetric methane concentration was 6%. Comparison of visible and normal flame propagation velocities of mixtures "methane - air", "methane - coal - air" and "methane - inert component - air" testifies that fine coal particles increase flame propagation rate.

Modeling combustion of aluminum dust cloud in media with spatially discrete sources

In the present work, combustion of aluminum dust cloud has been studied in media with spatially discrete sources by means of numerical approach. A thermal model has been generated to estimate the flame propagation speed in various oxidizer concentrations. The model is based on conduction and radiation heat transfer mechanisms and using the heat point source method. First combustion of single-particle is studied and the solution is presented. Then the dust combustion is investigated using the superposition principle to include the effects of particles. Oxygen and Nitrogen have been considered as the main oxidizer and the inert gas, respectively. Flame speed as a function of particle diameter has been studied and the effects of radiation heat transfer have been taken to account. Furthermore, Minimum ignition energy as a function of dust concentration for different particle diameters has been investigated. Reasonable agreement between the results of numerical solution of aluminum dust cloud combustion and experimental data is obtained in terms of flame propagation speed and minimum ignition energy.

Dust cloud combustion characterization of a mixture of LiBH4 destabilized with MgH2 for reversible H2 storage in mobile applications

This study discusses results of an experimental program to determine dust cloud combustion characteristics of 2LiBH4 + MgH2 binary system in air. The determined parameters of hydrided and partially-dehydrided states of this system include: maximum deflagration pressure rise (PMAX), maximum rate of pressure rise (dP/dt)MAX, minimum ignition temperature (TC), minimum explosible concentration (MEC), minimum ignition energy (MIE), and explosion severity index (KSt). Impact of dust particle size on the measured parameters is evaluated for the partially-dehydrided state. For dust of same mean particle size, results show the hydrided state to be more explosible in air compared to its partially-dehydrided state. Moreover, MIE of the partially-dehydrided mixture is identified in the test with lowest ignition delay time (IDT) and highest dust cloud concentration (DC). Taguchi's mixed-levels design of experiments (DoE) methodology is employed to calculate dust's MIE response surface as a function of DC and IDT. The one-at-a-time effect and interaction effect between DC and IDT on dust MIE are determined. The core insights of this contribution are useful for quantifying risks in mobile and stationary H2 storage applications, informing H2 safety standards, and augmenting property databases of H2 storage materials.

Flame propagation of boron dust particles in heterogeneous media

In this paper the combustion of boron dust clouds has been studied numerically in an environment with spatially discrete sources. A thermal model has been generated to estimate the flame propagation speed in various dust concentrations. Furthermore, flame speed as a function of particle diameter has been studied. The results show a very good agreement with the theoretical and experimental data. Also, in this case, a comparison between dust cloud combustion models has been made. Flame front propagation as a function of oxygen mole factor and pressure for certain particle sizes has been studied.

The discrete heat source approach to dust cloud combustion

In the present paper, combustion of dust clouds from the discrete point heat source method has been addressed. Time-place temperature profile generated by single particle burning has been obtained to study the dust combustion. The summation of the temperature profiles of burned and burning particles predict the temperature in the preheating zone so that the ignition time of layer in flame front can be determined. Consequently the flame propagating speed was obtained based on the dust concentration corresponding to particles spacing and particle diameter. This method has been validated with aluminum dust cloud combustion. Decrease in the dust concentration leads to the lean limit of dust combustion. Increase in particles diameter or reduction in the dust concentration causes higher lean limit and also reduction in the flame propagating speed. Adding the ignition energy as igniter to this system, provides the path to study the effects of ignition energy in the dust combustion.

알루미늄 군입자 화염특성 분석을 위한 광학기법 연구

본 연구에서는 고에너지 금속 알루미늄 군입자 연소 화염 분석을 위한 측정기법 개발 연구로서 스펙트로메터를 사용하여 화염 온도와 자발광 스펙트럼을 측정하였다. 마이크로 크기의 알루미늄 군입자 연소 반응시 발생하는 화염온도는 약 2400 K 이상의 초고온이므로 비접촉식 광학 계측 방법을 사용하였으며, 측정을 위해 개발된 기법은 520 nm, 640 nm를 사용하는 이색법을 응용한 방법과 광대역 파장 비교법으로서 각각의 방법은 정밀하게 검증 후 실험에 적용되었다. 연소실 하단에서 화염온도 측정결과 두 방법 모두 2400 K 이상의 화염온도를 확인할 수 있었으며 자발광 측정 결과 알루미늄 연소 반응시 가장 지배적으로 발생하는 화학종인 AlO를 확인할 수 있었다. In this study, In order to develop the measurement method of high energy density metal aluminum dust cloud combustion, flame temperature and emission spectrum was measured using spectrometer. Because of the ultra high <TEX>${\mu}m$</TEX>-sized aluminum flame temperature more than 2400 K, it was measured by non-contact optical technique which is the modified two wavelength pyrometry with 520, 640 nm and spectrum comparison method. These methods were applied to experiment after accurate verification. As a result, we could identify that flame temperature is more than 2400 K in bottom of combustor in both methods. And on the emission spectrum analysis, we could measure AlO radical which is occurred dominantly in aluminum combustion.

Radiation heat transfer in transient dust cloud flame propagation

This study investigates the impact of radiation heat transfer and heat conduction on dust cloud combustion. Radiation plays a very important role in the stability of dust cloud flame, and increasing the amount of radiation drastically raises the possibility of instability and explosion in a dust cloud mixture. Flame speed, which is a function of mixture characteristics, can exhibit a fluctuating behavior. By using the discrete heat source method, it would be possible to study the transient propagation of dust flames. Thus, the propagation speed of flame can be obtained, and as time goes by, the transient speed of dust flame will reach its steady state value. By considering the radiation effect, better agreement is observed between the obtained results and experimental data.

Oxy-fuel combustion: Laboratory experiments and pilot scale tests

Our focus is on oxy-fuel combustion and its associated heat transfer properties, especially radiative transport. Spectral intensity measurements have been obtained in a laboratory setting as well as on a pilot scale boiler. The pilot-scale experiments utilize a boiler retrofitted for oxy-fuel that operates at a temperature ranging to over 3000K. Due to such high temperatures, temperature measurements of the flame are not possible with probes and are instead inferred by a process called inverse radiation interpretation. Multiple operating conditions are considered while noting that the temperature profiles indicate peak temperatures ranging from 2400K to 3200K. Laboratory-scale dust cloud combustion studies are also performed that characterize the radiative properties and flame speed while varying the coal type, particle size and oxygen content. Laboratory flame speed and spectral intensity is seen to increase with higher levels of oxygen, higher volatile content in coals, smaller particle sizes and diluents with lower specific heats. Flame speed is seen to range between 0.8m/s and 4.1m/s in these experiments. Lastly, chemical equilibrium calculations are presented. Equilibrium product temperature and species were shown with varying parameters. The maximum temperature for Illinois #6 coal and an Indonesian low sulfur bituminous coal is 2954K and 2959K respectively.

Analytical investigation of temperature distribution and flame speed across the combustion zones propagating through an iron dust cloud utilizing a three-dimensional mathematical modeling

In the analytical model of iron dust cloud combustion presented in this article, by solving the 3D energy equations, the gas temperature distribution in the channel and a new equation for flame speed are obtained. This equation can determine the relationship between flame speed and particle radius and dust concentration. The equations are written in two limiting cases: lean and rich mixtures. Flame structure consists of preheat, reaction, and post-flame zones for the lean mixture and preheat and reaction zones for the rich mixture. Equations in both mixture conditions are solved using the finite Fourier transform method. By solving the energy equations in each zone and matching the temperature and heat flux at the interfacial boundaries, algebraic equations of flame speed are obtained. The obtained gas temperature distribution in different flame zones in the channel and also flame speed changes in terms of particles’ radius, equivalence ratio, and channel width in both lean and rich mixtures are presented in the results section.

Analysis of size distribution and ignition temperature effects on flame speeds in aluminium dust clouds

Reaction rate plays a major role in modelling of aluminium dust cloud combustion. In this article, a new model for the reaction rate is presented as a function of aluminium particle size distributions and ignition temperature of each particle. Moreover, the reaction rate is obtained in proportion to the amount of fuel considered to be constant in the reaction zone of previous models. In comparison with the old models, the new model is closer to the experimental results.

Predictions of laminar flame in aluminium dust clouds with a two-dimensional analytical model

In the present study, with the assumption of a laminar, steady and uniform flow and with the purpose of gaining flame speed, quenching distance, lean flammability limit, and temperature distribution, a two-dimensional (2D) analytical model of micro-sized aluminium dust cloud combustion in a channel is presented. In the previous analytical models, energy conservation equations of laminar flame had been solved one-dimensionally and flame speed and quenching distance had been obtained assuming that heat loss to the wall is linear. This model is developed with the assumption that the particle burning rate in the flame front is controlled by the process of oxygen diffusion, and a channel with constant temperature boundary conditions, similar to those of quenching plates and experimental aluminium dust cloud combustion channels, is assumed as well. In order to examine more precisely the impact from the amount of heat loss originating from the channel wall on combustion parameters including flame speed, energy equations are written in two-dimensions. The equations are written in two limiting cases: lean and rich mixtures. Flame structure consists of preheat, reaction, and post-flame zones for the lean mixture and preheat and reaction zones for the rich mixture. Although equations in the lean mixture are solved using the separation of variables method, Laplace method is used for their solution in the rich mixture. By solving the energy equations in each zone and matching the temperature and heat flux at the interfacial boundaries, algebraic equations of flame speed are obtained. The obtained gas temperature distribution in different flame zones in the channel and also flame speed changes in terms of particles' diameter, equivalence ratio, and channel width in both lean and rich mixtures are presented in the results section. Generally, the results of the study shows that solving equations in 2D models leads to higher agreements between the theoretical and experimental results in flame speed, lean limit, and quenching distance terms.

Explosion temperatures and pressures of metals and other elemental dust clouds

The Pittsburgh Research Laboratory of the National Institute for Occupational Safety and Health (NIOSH) conducted a study of the explosibility of various metals and other elemental dusts, with a focus on the experimental explosion temperatures. The data are useful for understanding the basics of dust cloud combustion, as well as for evaluating explosion hazards in the minerals and metals processing industries. The dusts studied included boron, carbon, magnesium, aluminum, silicon, sulfur, titanium, chromium, iron, nickel, copper, zinc, niobium, molybdenum, tin, hafnium, tantalum, tungsten, and lead. The dusts were chosen to cover a wide range of physical properties—from the more volatile materials such as magnesium, aluminum, sulfur, and zinc to the highly “refractory” elements such as carbon, niobium, molybdenum, tantalum, and tungsten. These flammability studies were conducted in a 20-L chamber, using strong pyrotechnic ignitors. A unique multiwavelength infrared pyrometer was used to measure the temperatures. For the elemental dusts studied, all ignited and burned as air-dispersed dust clouds except for nickel, copper, molybdenum, and lead. The measured maximum explosion temperatures ranged from ∼1550 K for tin and tungsten powders to ∼2800 K for aluminum, magnesium, and titanium powders. The measured temperatures are compared to the calculated, adiabatic flame temperatures.

95/04970 Coal dust cloud combustion in a microgravity environment

The successful experience in developing the advanced Foster Wheeler Energia Oy’s (former Ahlstrom Pyropower) Circulating Fluidized Bed combustion system subsequently led to the development of the CFB Gasification Technology in the early 80 s. The driving force for the developing work was the dramatically increase in oil price during the oil crises. The primary advantage of CFB gasification technology is that it enables the substitution of expensive fuels e.g. oil or gas with cheap solid fuels. These cheap fuels are typically different types of waste woods, bark or other biofuels. In the CFB gasifier these solid fuels are converted to gaseous fuel which can be used instead of other expensive fuels. In some cases this also solves a waste disposal problem, providing a secondary economic and environmental benefit. Foster Wheeler Energia Oy has supplied four commercial scale atmospheric CFB gasifiers in the mid 80 s to the pulp and paper industry with capacities from 17–35 MW based on fuel input. These applications utilize waste wood as feedstock and the units are still successfully operational today.Lahden Lämpövoima Oy is a Finnish power company producing power and district heat for the city of Lahti. The company is 50% owned by the city of Lahti and 50% by Imatran Voima Oy, which is the largest utility power company in Finland. Lahden Lämpövoima Oy operates the Kymijärvi power plant locating nearby the city of Lahti in Southern Finland. To keep the energy prices as low as possible, Lahden Lämpövoima is continuously looking for the most economical fuel sources, and simultaneously, trying to improve the environmental acceptability of the energy production. At the moment, about 300 GWh/a different type of biofuels and refuse fuels are available in the Lahti area. On an annual basis, the available amount of biofuels and refuse fuels is enough to substitute for about 15% of the fuels burned in the main boiler equaling max 30% of coal.The aim in this Lahden Lämpövoima Oy’s Kymijärvi power plant gasification project is to demonstrate the direct gasification of wet biofuel and the use of hot, raw and very low-calorific gas directly in the existing coal-fired boiler. The gasification of biofuels and co-combustion of gases in the existing coal-fired boiler offers many advantages such as: recycling of CO2, decreased SO2 and NOx emissions, efficient way to utilize biofuels and recycled refuse fuels, low investment and operation costs, and utilization of the existing power plant capacity. Furthermore, only small modifications are required in the boiler, possible disturbances in the gasifier do not shut down the power plant.

Predictions of laminar flame speeds in boron-oxygen-nitrogen dust clouds

A detailed model of boron-oxygen-nitrogen dust-cloud flames including consideration of the details of boron particle ignition and the effects of oxygen depletion has been developed and used for prediction of flame speeds as functions of numerous parameters. Reasonably good agreement between measured flame speeds for the only two data points available on laminar boron dust cloud combustion and those predicted by this model has been obtained, although uncertainty concerning details of the experimental parameters results in this agreement being somewhat inconclusive. In addition, a simplified closed-form flame speed expression has been developed and the effects on predicted flame speeds of the various assumptions used in its development have been examined. The models have been used to study the effects of initial temperature, pressure, initial oxygen mole fraction, weight fraction particles, initial particle size, initial thickness of the oxide coating on the particles, radiation feedback from the postflame zone, and Nusselt Number. Mechanisms leading to the predicted dependencies are discussed.