Ignition Temperature Of Dust Cloud Research Articles

A numerical model for the prediction of the minimum ignition temperature of dust clouds

This paper presents a numerical model for the prediction of the minimum ignition temperature (MIT) of dust clouds. First, a physical model is developed for the dust cloud ignition in the Godbert-Greenwald furnace. A numerical approach is then applied for the MIT prediction based on the physical model. The model considers heat transfer between the air and dust particles, the dust particle reaction kinetics, and the residence times of dust clouds in the furnace. In general, for the 13 dusts studied, the calculated MIT data are in agreement with the experimental values. There is also great accordance between the experimental and numerical MIT variation trends against particle size. Two different ignition modes are discovered. The first one consists in ignition near the furnace wall for bigger particles characterized by rather short residence times. In the second mode, the ignition starts from the center of the furnace by self-heating of the dust cloud for smaller particles with longer residence times. For magnesium, as dust concentration increases, the lowest ignition temperature of the dust cloud IT(conc) decreases first, then transits to increase at a certain point. The transition happens at different dust concentrations for different particle sizes. Moreover, the MIT of the magnesium dust cloud generally increases as particle size increases, but the increasing trend stagnates within a certain medium particle size range.

Characterization of the explosiveness of wood dust

Factors that influence the explosiveness of wood dust, like particle size distribution, moisture content and microscopic structure, have been characterised. Sawdust flammability has been tested in a Hartmann tube. The Minimum Explosive Concentration and Minimum Ignition Temperature of dust clouds and layers have also been measured. Dust granulometry linked to the regularity of its structure and moisture are the essential parameters to generate or not an explosive atmosphere. Smaller particle size dust with a lower moisture content is much more likely to create an ignition and/or explosion risk. The samples have been classified into two groups, those collected from cutting processes and those found in the ventilation ducts or deposited in the facilities. The most dangerous samples are those from Group 2. In some cases, dust samples up to 35 % moisture or with particle size greater than 500 µm at maximum dryness are able to produce an explosion.

Comparison between a numerical model and the classic thermal explosion theories for the calculation of the minimum ignition temperature of dust clouds

A numerical model for the calculation of the minimum ignition temperature (MIT) of dust clouds is compared with the classic Semenov and Frank-Kamenetskii thermal explosion theories. The numerical model is developed based on the MIT testing equipment: Godbert-Greenwald furnace. The Semenov theory for uniform temperature system is exploited for the MIT calculation of a single dust particle (MITP). The Frank-Kamenetskii theory for a uniform system with temperature gradient is modified for the MIT calculation of a dust cloud (MITC). At stoichiometric dust concentration with infinite dust cloud residence time, two horizontal asymptotes are discovered along with the variation trend of the numerical ignition temperature against ignition delay time. The higher asymptotic temperature is only discovered for metal dusts. This temperature is almost identical to the MITP value with the Semenov theory. On the other hand, the lower asymptotic temperature for both metal and organic dusts almost equals the calculated MITC value with the Frank-Kamenetskii theory. Thus, there is good agreement between the numerical model and the classic thermal explosion theories. This study can provide reference for the theoretical prediction of the MIT of dust clouds.

Study on the characteristics and influencing factors of micron/nano carbon material dust explosions

Because of the wide range of applications of lithium ion batteries, the combustible and explosive carbon material dust of a negative electrode material requires additional attention. Few explosion test data of carbon material dust are available. In this paper, the thermodynamic and explosion parameters of allotropes of carbon dust and the same type of carbon material dust with different particle size distributions were determined. The results showed that the explosion pressure of micron/nano carbon material dust ranged from 0.4 to 0.7 MPa; the maximum deflagration index Kst ranged from 4 to 10 MPa · m/s; and the minimum ignition temperature was approximately 600 °C. The proportion of the small dust particles was an important factor that caused a change in the initial oxidation weight loss temperature and apparent activation energy of the same type of carbon dust. The variation trend among the initial oxidation weight loss temperature, apparent activation energy and particle size distribution of different carbon dust materials was not obvious, and mainly depended on the difference in molecular structures. Different molecular structures resulted in different apparent activation energies of the carbon allotropes. The apparent activation energy played a leading role in the change in the dust deflagration index. The smaller the apparent activation energy was, the smaller the energy required for carbon-carbon chemical bond breaking. The faster the carbon-carbon bond-breaking rate was, the larger the deflagration index. The dust particle size distribution, specific surface area and other characteristics had little influence on the deflagration index. Furthermore, the apparent activation energy had a greater impact on the deflagration index than the explosion pressure. The dust explosion pressure was mainly limited by oxygen in the test equipment, and its maximum value remained relatively constant. The minimum ignition temperature of dust clouds decreased with decreasing activation energy and increasing pre-exponential factor. The lower the initial oxidation weight loss temperature was, the lower the measured dust cloud minimum ignition temperature.

Influence of Volatile Content on the Explosion Characteristics of Coal Dust.

To study the influence of different volatile contents on the explosion characteristics of coal dust, the volatile content in coal dust was controlled under different final temperatures of pyrolysis. The maximum explosion pressure, maximum pressure rising rate, and explosion index were used to characterize the pressure behavior, the pressure ratio to characterize the explosibility, and the minimum ignition temperature of the coal dust cloud to characterize the sensitive characteristics. A 20 L of nearly spherical coal dust explosion parameter measuring device and a dust cloud minimum ignition temperature measuring device were used to study the influence of the explosion characteristics of dust with different volatile contents prepared under different pyrolysis temperature conditions. The results showed that the volatile matter content in lignite dust has little effect on the maximum explosion pressure, with an average change rate of 5.435%. When the volatile content was reduced from 45.4 to 2.45%, the maximum explosion pressure rise rate dropped by 65.976%. The explosion index of the experimental sample was in the range of 0–1.6, with weak explosion characteristics; the lower the volatile content, the weaker the explosion intensity. When the volatile content was only 2.45%, the pressure ratio was still greater than 2, that is, the dust was still explosive. When the volatile content in lignite was reduced from 45.4 to 18.21%, the lowest ignition temperature of the dust cloud was consistently 490 °C. At this stage, the contents of H2, CO, CH4, CO2, and other precipitated dases were low. When the volatile content was reduced from 18.21 to 2.45%, the precipitated volatile gas increased rapidly, the remaining precipitated gas content decreased, and the dust could not be easily ignited. The experimental results lay the foundation for studying the influence mechanism of volatile matter in coal dust on the explosion characteristics.

Experimental and theoretical study on the inhibition effect of CO2/N2 blends on the ignition behavior of carbonaceous dust clouds

Gaseous inhibitors are used in many industries for the explosion prevention of combustible dusts, mitigating the potential hazard to humans, properties and environments. This work experimentally and theoretically studied the inerting effect of gaseous inhibitors on the ignition process of dust clouds in O2/N2/CO2 atmospheres, with an emphasis on the role of the CO2/N2 ratio. 10 different combustible carbonaceous dusts were selected, including grain dust, biomass dust and coal dust. Experimental results showed that the inhibition effect of CO2/N2 is closely related to the ignition mechanism of dust clouds. Specifically, a higher ratio of CO2/N2 yields a stronger inhibition effect on the ignition process of dust samples with relatively low volatile matter contents predominated by heterogeneous ignition. In addition, two novel steady-state ignition mechanism models were developed to interpret the experimental observations. Maxwell-Stefan equations were used to describe the diffusivity in the ternary O2/N2/CO2 gas mixtures. The analytical results were in good agreement with the experimental data of the minimum ignition temperature of dust cloud (MITC) in oxygen-lean atmospheres. The mechanism modelling can be used to estimate the critical ignition temperature of all carbonaceous dust clouds with a wide range of volatile matter content under different inert atmospheres, which will provide a reference for the explosion hazard assessment of dust posed by a hot surface in the process industries.

Inhibiting effects by Fe2O3 on combustion and explosion characteristics of ABS resin

The global increase in the use of, and reliance on, plastics has prompted the demand for acrylonitrile-butadiene-styrene (ABS) resin in various fields. With this increased requirement, numerous failures have occurred in the ABS process. Those incidents, resulting from electrostatic discharge, powder accumulation, heat accumulation, construction sparks, and plant fires, have caused dust fire and explosions.In this study, the ABS resin was gleaned from the site and tested for its explosion parameters, including minimum ignition temperature of dust cloud (MITC), minimum ignition energy (MIE), and minimum explosion concentration (MEC). To improve loss prevention in the manufacturing process, ferric oxide (Fe2O3) as an inert additive was added in the ABS powder. According to the MIE test, Fe2O3 has an apparent inhibiting effect on dust explosion for the ABS dust. With the proportion of Fe2O3 increased from 25 to 50 mass% in ABS, the MIE increased from 67 to 540 mJ. The explosion tests via 20-L apparatus indicated that Fe2O3 mixed with ABS could not increase the MEC significantly. However, the explosion pressure dropped by increasing in the ratio of Fe2O3 in ABS. This inerting strategy of ABS was deemed to substantially lessen the probability and severity of fire and explosion.

Ignition temperature and mechanism of carbonaceous dust clouds: The roles of volatile matter, CH4 addition, O2 mole fraction and diluent gas

Minimum ignition temperature of dust clouds (MITC) was studied experimentally and theoretically in different atmospheres. Three carbonaceous dusts were tested in both air and O2/CO2 atmospheres with CH4 mole fraction from 0% to 2%. Results showed that the ignition risk of the three dusts significantly increases (decrease of MITC by ~100 ℃) with increasing XO2 from 21% to 50%, but significantly decreases replacing N2 in air with CO2. The inhibition effect of CO2 on MITCs could be diminished by increasing XO2 or adding CH4. The addition of small amount of CH4 has different effects on the MITCs of different dust samples, following the opposite order of volatile matter content: anthracite>bituminous coal>starch. Two modified steady-state ignition models, considering the density of mixture gas and dust cloud, XO2 and its diffusivity, were developed to interpret the experimental observations. The analysis revealed that the global heterogeneous ignition model suits well for the hybrid mixtures of anthracite or bituminous coal dusts. In contrast, the proposed global homogeneous ignition model was found to be only valid for the pure starch dust, and the extra CH4 addition could strongly affect the ignition process of starch, particularly in O2/CO2 atmospheres with higher XO2.

Minimum ignition temperature of carbonaceous dust clouds in air with CH4/H2/CO below the gas lower explosion limit

Godbert-Greenwald furnace was used to investigate the minimum ignition temperature of dust clouds (MITC) in air with the presence of flammable gas which is lower than its lower explosion limit (LEL). Three flammable gases (CH4, H2 and CO) and three carbonaceous dusts (anthracite coal, bituminous coal and sweet potato starch) were tested. Results showed that all flammable gases have distinct effects on the MITC of the dust samples and volatile matter content of dust plays an important role during the ignition process. Specifically, the MITC of anthracite coal dust decreased from 610 °C to 560 °C, 580 °C and 570 °C with 3% CH4, 3% CO and 2.5% H2, respectively. Moreover, a heterogeneous ignition mechanism model was proposed to verify the equally global ignition characteristic between hybrid anthracite coal-CxHy mixture and bituminous coal. All three gases had an ignorable effect on the MITC of starch dust considering the experimental error. The presence of CO and H2 slightly promoted the ignition of bituminous coal dust, but the addition of CH4 showed a distinct concentration effect on the MITC of bituminous coal: the MITC decreased with 1% CH4 while increased with 2% and 3% CH4. This negative-effect of flammable gases at such low concentrations on ignition temperature of bituminous coal dusts was found for the first time. Furthermore, the presence of the 2nd flammable gas had a smaller effect on the MITC of dust samples with a higher volatile content, resulted from the competition of heterogeneous and homogeneous ignition mechanisms.

Analysis of susceptibility to ignition of dust layer and dust cloud of selected hardened unsaturated polyester resins

In the article there were described combustible properties of selected dust types formed of plastic materials. Those properties decide on fire and explosion hazard for dust in layer and in cloud, according to PN-EN 50281-2-1:2002. The article also consists of safety requirements concerning using appliances in explosion hazard areas, according to PN-EN 50281-1-2:2002. In the article there are presented results of investigations on minimal ignition temperature of layer (MITL) and minimal ignition temperature of dust cloud (MITDC) as a function of dust layer thickness of chosen industry dust with different addition of modification and values of maximum acceptable surface temperature (MAST) of machines operating in the presence of dust cloud and chosen dust layer with thickness of 5 and 12.5 mm.

Hazards of Explosibility Dust from Wood Pellets

The main purpose of this publication is to determine minimal ignition temperature of dust cloud. The flammable and explosive dust is formed during the production, transport, storage and usage of the wood pallets. The examined samples in experimental part of the work were made from different kind of pallets. Contribution deals with analysis of fire and explosion hazards of dust particles generated during transportation and handling of wood pellets. Minimum ignition temperature of dust cloud were performed according to STN EN 50281-2-1. In terms of forensic approach, by using of selected methods, the conditions in which initiation and explosion of dust can be occurred were simulated the exposibility for wood pellets dust was tested under different condition using various pressures and various weight to samples. Defining the conditions in which the risk of formation of dangerous situation exists, helps to predict the fire and explosion in the premises where the pellets are used.

Experimental Analysis of Minimum Ignition Temperature of Dust Cloud Obtained from Thermally Modified Spruce Wood

This article deals with study of minimum ignition temperature (MIT) of thermally modified spruce dust. Dust of several species of spruce was mixed, sieved, dried and subjected to Thermo-S temperature programme. Samples of dust (200 250 μm) were tested in Goldbert-Greenwald furnace apparatus for determination of the MIT of dust clouds. The influence of air pressure and sample weight to the MIT was studied. The results show that the MIT of thermally modified spruce dust gradually decreases as the sample weight and air pressure rise. The lowest value of MIT (470 °C) was measured, when the air pressure was 50 kPa and the sample weight 0,5 g. To reach even lower values of MIT (˂468 °C), the air pressure should gradually rise to approx. 42 46 kPa and the weight of dust sample should be approx. 0,46 0,53 g.

Experimental Research on Minimum Ignition Temperature of 7-ACA Dust Cloud

7-aminocephalosporanic acid (7-ACA) is the key intermediate powder to product cephalosporin. The ignition temperature test device (NU-TC1000) for dust cloud was used to test the minimum ignition temperature of 7-ACA dust cloud. When the dispersion mass of 7-ACA dust is 0.8g, the minimum ignition temperature of dust cloud is 496°C. The minimum ignition temperature increases first and then reduces with the increase of dispersion mass. When 7-ACA and acetone are mixed in the ratio of 1g 7-ACA plus 0.75ml acetone and the dispersion mass of mixture sample is 0.6g, the minimum ignition temperature of dust cloud is 400°C. Experimental results show that the minimum ignition temperature of dust cloud decreases markedly by adding acetone into 7-ACA dust. How to set powder has a quite influence on the results.

Ignition temperature of magnesium powder clouds: A theoretical model

Minimum ignition temperature of dust clouds (MIT-DC) is an important consideration when adopting explosion prevention measures. This paper presents a model for determining minimum ignition temperature for a magnesium powder cloud under conditions simulating a Godbert–Greenwald (GG) furnace. The model is based on heterogeneous oxidation of metal particles and Newton's law of motion, while correlating particle size, dust concentration, and dust dispersion pressure with MIT-DC. The model predicted values in close agreement with experimental data and is especially useful in predicting temperature and velocity change as particles pass through the furnace tube.

Research on Characteristic Parameters of Coal-dust Explosion

The parameters of explosive characteristics of the coal-dust are assessed systematically with the test device of minimum ignition temperature of dust clouds and 20L sphere explosion test units. The minimum ignition temperature of dust is a main safety index when handling combustible dusts in industrial production, and while hazard evaluation, the maximum explosion pressure and the explosion index are key parameters. Five kinds of coal-dust with different particle diameters were tested in order to determine the temperature sensitivity and the ferocity under the given conditions, which can be used as the criteria to classify dust explosion hazards. The experiment results indicate that the minimum ignition temperature of coal-dust cloud reduces with the decrease of particle diameter under temperature of (293±5) K and powder spraying pressure of 0.08MPa, and when the particle size reduces to (25-48) μm, the minimum ignition temperature is between (793-803)K; Besides that, the results can also show that minimum explosive concentration of coal-dust cloud is between 20 gam-3 and 30 gam-3under temperature of (293±5) K, powder spraying pressure of 2MPa and ignition energy of 10kJ, the maximum explosion pressure is 0.45MPa and the maximum explosion index is 11.14 MPaamas-1, which classifies coal-dust explosion hazards to Level I. The conclusions drawn from the experimental results are of great significance to the safe application of these combustible substances.

Ignitability characteristics of aluminium and magnesium dusts that are generated during the shredding of post-consumer wastes

The authors investigated the ignitability of aluminium and magnesium dusts that are generated during the shredding of post-consumer waste. The relations between particle size and the minimum explosive concentration, the minimum ignition energy, the ignition temperature of the dust clouds, etc. the relation between of oxygen concentration and dust explosion, the effect of inert substances on dust explosion, etc. were studied experimentally. The minimum explosive concentration increased exponentially with particle size. The minimum explosive concentrations of the sample dusts were about 170 g/m 3 (aluminium: 0–8 μm) and 90 g/m 3 (magnesium: 0–20 μm). The minimum ignition energy tended to increase with particle size. It was about 6 mJ for the aluminium samples and 4 mJ for the magnesium samples. The ignition temperature of dust clouds was about 750 °C for aluminium and about 520 °C for magnesium. The lowest concentrations of oxygen to produce a dust explosion were about 10% for aluminium and about 8% for magnesium. A large mixing ratio (more than about 50%) of calcium oxide or calcium carbonate was necessary to decrease the explosibility of magnesium dust. The experimental data obtained in the present investigation will be useful for evaluating the explosibility of aluminium and magnesium dusts generated in metal recycling operations and thus for enhancing the safety of recycling plants.

Laser ignition of dust clouds

In a previous paper [1], the possibility of igniting a combustible dust-air mixtures by a light beam in contact with a substrate made of an inert matter and heated by a light beam was investigated. The objective of the present work is to produce more data on the subject. The available results suggest a strong similarity between combustible dust-air mixtures and explosible gas-air mixtures within the scope of the investigated ignition phenomena. In particular a relationship between the standard ignition temperature of dust clouds and the temperature of the target at the minimum incident power at ignition (continuous irradiation) has been highlighted which seems to be similar to the one obtained for gases. If confirmed, this would imply that the knowledge of these standard parameters would help in predicting the danger of igniting any kind of explosible mixtures including hybrid mixtures (combustible gas-combustible dust-air) or oxygen depleted/enriched mixtures.

Minimum ignition temperature of polyethylene dust: a theoretical model

Dust explosion hazard exists in plants and facilities handling combustible dusts. The minimum ignition temperature of dust clouds is an important parameter requiring special attention to designing the explosion preventive measures. This paper presents a model developed for determining the minimum ignition temperature for an organic dust cloud, polyethylene, simulating the conditions in the Godbert-Greenwald furnace. The model correlates the particle size, as well as the dust concentration with the minimum ignition temperature. It is based on the two-stage oxidation mechanism involving devolatilization/decomposition of the solid particle and homogeneous oxidation of volatile combustible products. In the case of polyethylene, the main combustible gas responsible for ignition and flame propagation has been confirmed to be butylene. The results of the computations were compared with the experimental values and those predicted by Mitsui and Tanaka. The predicted values by the model developed are in close agreement with the experimental data which confirm the proposed ignition mechanism. The model can be used for the prediction of minimum ignition temperature of organic dusts having an autoignition mechanism similar to polyethylene dust. © 1997 John Wiley & Sons, Ltd.

Models for minimum ignition temperature of organic dust clouds

AbstractThe minimum ignition temperature of dust clouds is one of the important factors required for the design of preventive measures against dust explosion. The mathematical models available to predict this parameter have been analyzed for thier application to organic dust clouds. A solution of the most general model proposed by Mitsui and Tanaka is presented, together with its comparision with experimental data. It has been found to be quite successful in predicting the minimum ignition temperature for metal dusts but not for organic dusts. Recommendations for the development of a new model to predict the minimum ignition temperature of an organic dust, such as polyethylene, have been given.

Study of Ignition Temperature of a Polyethylene Dust Cloud

Dust explosion hazard exists in plants and facilities wherever combustible dusts are handled. The minimum ignition temperature of dust clouds is an important factor requiring special attention for the design of any explosion preventive measures. The present paper is confined to a study of the minimum ignition temperature of the cloud of polyethylene, an organic dust. This parameter was determined using the Godbert-Greenwald furnace apparatus for different particle sizes and dust concentrations. Some preliminary experiments were carried out for determination of minimum explosive concentrations of polyethylene dust to specify experimental conditions for determination of minimum ignition temperature. The experimental results, particularly variation of minimum ignition temperature with particle size and dust concentration, have been explained on the basis of a two-stage ignition involving devolatilization of solid particles into gaseous intermediates and homogeneous combustion of these gaseous components. A model was also developed for determining the minimum ignition temperature of polyethylene dust simulating conditions in the test furnace and this will be presented in a separate paper.