Minimum Ignition Temperature Research Articles

Research on Explosion Characteristics of Sulfur Dust and Risk Control of the Explosion

As dust explosion is a major risk factor threating the safety of sulfur production, evaluating and controlling the hazards of sulfur dust produced in the wet process are very important. Several characteristic parameters including minimum ignition temperature, minimum ignition energy, lower explosive limit, maximum explosion pressure, explosion index, limit oxygen concentration of sulfur dust were determined and investigated by the experimental device such as hot plate, Godbert-Greenwald furnace, Hartmann tube, 20L spherical container of explosive testing. The experimental results indicated the influence rules of particle size, water content and concentration on the explosion characteristics of sulfur dust. The results showed that sulfur dust could be lighted easily and had high explosibility. The explosion risk and strength of sulfur dust decreased with the increase of the particle size. The minimum ignition energy and the minimum ignition temperature increased as the water content increased. The maximum explosion pressure and the explosion index rose at first and went down latter as the dust concentration increases. Prevention and control measures of sulfur dust explosion, from two aspects of building control and process control, were proposed for production, storage and transportation process of sulfur produced in the wet process.

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.

Industry specific dust explosion likelihood assessment model with case studies

Dust explosion is a potential threat to the process facilities handling dusts. Dust explosion occurrences are frequently reported in these industries. Industrial professionals and researchers have been trying to develop effective measures to assess and mitigate and/or prevent dust explosion. To develop effective prevention and mitigation strategies, it is important to understand the interaction of dust explosion controlling parameters and also to assess likelihood of occurrence in given conditions. Authors have proposed a conceptual framework to model dust explosion likelihood. In this paper, a detailed implementation of the conceptual model is presented. Three different dust classes (i.e. food feed; plastic, resin and rubber; and metal alloys) are considered for model development. The proposed model considers six key parameters of dust explosion: dust particles diameter, minimum ignition energy, minimum explosible concentration, minimum ignition temperature, limiting oxygen concentration and explosion pressure. These parameters are conditional to the type of dust and chemical composition. A conditional probabilistic approach is used to determine the total probability of dust explosion in a given process facility. Use of this model will help to assess the likelihood of dust explosion in given operating conditions. Moreover, it will help to develop prevention strategies focusing on the parameters that are responsible for dust explosion. Three case studies are presented here to demonstrate the application of the model in real life.

Explosion characteristics of micron- and nano-size magnesium powders

Explosion characteristics of micron- and nano-size magnesium powders were determined using CSIR-CBRI 20-L Sphere, Hartmann apparatus and Godbert-Greenwald furnace to study influence of particle size reduction to nano-range on these. The explosion parameters investigated are: maximum explosion pressure (Pmax), maximum rate of pressure-rise (dP/dt)max, dust explosibility index (KSt), minimum explosible concentration (MEC), minimum ignition energy (MIE), minimum ignition temperature (MIT), limiting oxygen concentration (LOC) and effect of reduced oxygen level on explosion severity. Magnesium particle sizes are: 125, 74, 38, 22, 10 and 1 μm; and 400, 200, 150, 100, 50 and 30 nm. Experimental results indicate significant increase in explosion severity (Pmax: 7–14 bar, KSt: 98–510 bar·m/s) as particle size decreases from 125 to 1 μm, it is maximum for 400 nm (Pmax: 14.6 bar, KSt: 528 bar·m/s) and decreases with further decrease of particle size to nano-range 200–30 nm (Pmax: 12.4–9.4 bar, KSt: 460–262 bar·m/s) as it is affected by agglomeration of nano-particles. MEC decreases from 160 to 30 g/m3 on decreasing particle size from 125 to 1 μm, its value is 30 g/m3 for 400 and 200 nm and 20 g/m3 for further decrease in nano-range (150–30 nm). MIE reduces from 120 to 2 mJ on decreasing the particle size from 125 to 1 μm, its value is 1 mJ for 400, 200, 150 nm size and <1 mJ for 50 and 30 nm. Minimum ignition temperature is 600 °C for 125 μm magnesium, it varies between 570 and 450 °C for sizes 38–1 μm and 400–350 °C for size range 400–30 nm. Magnesium powders in nano-range (30–200 nm) explode less violently than micron-range powder. However, likelihood of explosion increases significantly for nano-range magnesium. LOC is 5% for magnesium size range 125–38 μm, 4% for 22–1 μm, 3% for 400 nm, 4% for 200, 150 and 100 nm, and 5% for 50 and 30 nm. Reduction in oxygen levels to 9% results in decrease in Pmax and KSt by a factor of 2–3 and 4–5, respectively, for micron as well as nano-sizes. The experimental data presented will be useful for industries producing or handling similar size range micron- and nano-magnesium in order to evaluate explosibility of their magnesium powders and propose/design adequate safety measures.

마그네슘 분진의 열분해 및 발화온도 특성

본 연구에서는 Mg분진의 분진입경과 승온속도에 따른 열분해 및 발화온도 특성을 실험적으로 조사하였다. 이를 위해 시료는 평균 입경이 서로 다른 38, 142, <TEX>$567{\mu}m$</TEX>의 Mg분진을 사용하였다. 실험에서는 열중량분석장치(TGA)와 IEC 61241-2-1규격에 따라 제작한 자연발화온도(MIT) 실험장치를 사용하여 실시하였다. 실험 결과 퇴적 Mg에 있어서 공기중 승온속도가 증가하면 중량개시온도는 증가하였으며, 동일한 승온속도 조건에서 입경의 증가는 발화온도의 증가로 나타났다. 또한 부유 Mg분진의 최저발화온도(MIT)는 평균 입경이 증가할수록 증가하는 경향을 보였다. The study was conducted experimentally on characteristic of thermal decomposition and minimum ignition temperature of magnesium dusts. For this purpose, three different Mg dusts of mean diameter (38, 142, <TEX>$567{\mu}m$</TEX>) were used. Experimental investigations were conducted by using TGA(Thermo gravimetric analysis) and MIT(Minimum Ignition Temperature) apparatus made in accordance with IEC 61241-2-1 standard. As the results, temperature of weight gain in Mg dust layers increased with increasing of heating rates in air and, under the same heating rate condition, minimum ignition temperature increased with particle size. Also the MIT of suspended Mg dust clouds tended to increase with increasing of mean diameter.

Study of ignition in a high compression ratio SI (spark ignition) methanol engine using LES (large eddy simulation) with detailed chemical kinetics

Methanol has been recently used as an alternative to conventional fuels for internal combustion engines in order to satisfy some environmental and economical concerns. In this paper, the ignition in a high compression ratio SI (spark ignition) methanol engine was studied by using LES (large eddy simulation) with detailed chemical kinetics. A 21-species, 84-reaction methanol mechanism was adopted to simulate the auto-ignition process of the methanol/air mixture. The MIT (minimum ignition temperature) and MIE (minimum ignition energy) are two important properties for designing safety standards and understanding the ignition process of combustible mixtures. The effects of the flame kernel size, flame kernel temperature and equivalence ratio were also examined on MIT, MIE and IDP (ignition delay period). The methanol mechanism was validated by experimental test. The simulated results showed that the flame kernel size, temperature and energy dramatically affected the values of the MIT, MIE and IDP for a methanol/air mixture, the value of the ignition delay period was not only related to the flame kernel energy, but also to the flame kernel temperature.

Explosibility of polyamide and polyester fibers

The current research is aimed at investigating the explosion behavior of hazardous materials in relation to aspects of particulate size. The materials of study are flocculent (fibrous) polyamide 6.6 (nylon) and polyester (polyethylene terephthalate). These materials may be termed nontraditional dusts due to their cylindrical shape which necessitates consideration of both particle diameter and length. The experimental work undertaken is divided into two main parts. The first deals with the determination of deflagration parameters for polyamide 6.6 (dtex 3.3) for different lengths: 0.3 mm, 0.5 mm, 0.75 mm, 0.9 mm and 1 mm; the second involves a study of the deflagration behavior of polyester and polyamide 6.6 samples, each having a length of 0.5 mm and two different values of dtex, namely 1.7 and 3.3. (Dtex or decitex is a unit of measure for the linear density of fibers. It is equivalent to the mass in grams per 10,000 m of a single filament, and can be converted to a particle diameter.) The explosibility parameters investigated for both flocculent materials include maximum explosion pressure (Pmax), size-normalized maximum rate of pressure rise (KSt), minimum explosible concentration (MEC), minimum ignition energy (MIE) and minimum ignition temperature (MIT). ASTM protocols were followed using standard dust explosibility test equipment (Siwek 20-L explosion chamber, MIKE 3 apparatus and BAM oven). Both qualitative and quantitative analyses were undertaken as indicated by the following examples. Qualitative observation of the post-explosion residue for polyamide 6.6 indicated a complex interwoven structure, whereas the polyester residue showed a shiny, melt-type appearance. Quantitatively, the highest values of Pmax and KSt were obtained at the shortest length and finest dtex for a given material. For a given length, polyester displayed a greater difference in Pmax and KSt at different values of dtex than polyamide 6.6. Long ignition delay times were observed in the BAM oven (MIT measurements) for polyester, and video framing of explosions in the MIKE 3 apparatus (MIE measurements) enabled observation of secondary ignitions caused by flame propagation after the initial ignition occurring at the spark electrodes.

Explosibility of micron- and nano-size titanium powders

Explosibility of micron- and nano-titanium was determined and compared according to explosion severity and likelihood using standard dust explosion equipment. ASTM methods were followed using a Siwek 20-L explosion chamber, MIKE 3 apparatus and BAM oven. The explosibility parameters investigated for both size ranges of titanium include explosion severity (maximum explosion pressure (Pmax) and size-normalized maximum rate of pressure rise (KSt)) and explosion likelihood (minimum explosible concentration (MEC), minimum ignition energy (MIE) and minimum ignition temperature (MIT)). Titanium particle sizes were −100 mesh (<150 μm), −325 mesh (<45 μm), ≤20 μm, 150 nm, 60–80 nm, and 40–60 nm. The results show a significant increase in explosion severity as the particle size decreases from −100 mesh with an apparent plateau being reached at −325 mesh and ≤20 μm. Micron-size explosion severity could not be compared with that for nano-titanium due to pre-ignition of the nano-powder in the 20-L chamber. The likelihood of an explosion increases significantly as the particle size decreases into the nano range. Nano-titanium is very sensitive and can self-ignite under the appropriate conditions. The explosive properties of the nano-titanium can be suppressed by adding nano-titanium dioxide to the dust mixture. Safety precautions and procedures for the nano-titanium are also discussed.

Minimum Ignition Temperature of Wood Dust Layers

Abstract Fire characteristic (properties) are used to determine the fire risk and explosion hazard of materials. They are defined as numerical values which describe behavior in the process of burning. They can be determinate by standardized test methods. In this paper is described the most important fire technical characteristic of dust layer (minimum ignition temperature) and the results of standard laboratory method determination for wood dusts, aswell.

Effect of inerts on ignition sensitivity of dusts

This work studies the influence of added inert dust on the ignition sensitivity of the combustible/inert dust mixture. Different types of combustible dust of various sizes, such as coal, powdered sugar, lycopodium, anthraquinone, rice and coffee husks, beech wood flour or ground coffee were mixed with alumina and kieselguhr before being tested. Parameters measured were 1) minimum ignition temperature (MIT) in 5 mm layer, 2) minimum ignition temperature in cloud (Godbert-Greenwald oven) and 3) minimum ignition energy (MIE) (in a Kuhner-Mike 3 apparatus). It appears from this study that the MIT in 5 mm layer is strongly influenced by an inert fraction >= 60 % (weight). There is also a significant increase in MIT in cloud form when the fraction of inert dust exceeds 60 % (weight). This threshold is a function of the bulk density of the inert substance selected for these tests. However, in cases where the density of the inert dust is different from that of the combustible dust, there appears to be a separation of the two constituents of the mixture after its pneumatic dispersion during the test. As a consequence, the influence of inert dust is less pronounced in the case of MIT for dust clouds than for the MIT of a dust layer. A similar phenomenon is observed for the MIE of dust clouds.

The Minimum Ignition Energy of Coal Dust in an Oxygen Enriched Atmosphere

In oxy/fuel combustion of coal, the pulverised coal is burned with oxygen at concentrations greater than the currently allowed value of 21 %. This may well provide advantages in carbon sequestration against other technologies such as pre- and post-combustion capture. However the risk of dust explosions increases significantly with increasing oxygen concentration and temperature. In this study the influence of enriched oxygen concentrations is researched on the dust explosion characteristics of Indonesian (Sebuku) coal dust and of Pittsburgh coal n°8. First the ignition sensitivity characteristics (minimum ignition energy and minimum ignition temperatures) and explosion severity characteristics (maximum explosion pressure, Pmax, and maximum rate of pressure rise, Kst ) are determined in air. Thereafter the minimum ignition energy is determined of both coals in an oxygen enriched CO2 atmosphere. The minimum ignition energy in air of the Sebuku coal was equal to 55 mJ, while the minimum ignition energy of the Pittsburgh coal was higher than 1000 mJ. The ignition sensitivity in a 30 vol% O2 in CO2 mixture was in good agreement to the ignition sensitivity in air. In a 50 vol% O2 in CO2 mixture the ignition energy decreased significantly to a value of 1.4 mJ for the Sebuku coal and 4.7 mJ for the Pittsburgh coal n°8.

Determination of Ignition Temperature of Organic Dust Layers

Fire characteristics of wood dusts serve for qualitative comparison of combustibility and explosibility, for suggesting precautionary measures, for predicting consequences of fires and explosions. Setting of given characteristics by calculation is not possible yet. Therefore the most reliable results are set by experiment. The article deals with the testing of the minimum ignition temperature depending on the different types of dust layer and different heights of surface.

Modelling spontaneous ignition of wood, char and RDF in a lab-scale packed bed

Many municipal waste combustors use preheated primary air in the first zone to dry the waste. In most cases the preheat temperature does not exceed 140°C. In previous experiments it is found that at temperatures around 200°C, in some circumstances, self- or spontaneous ignition can be achieved. Using preheated air can be a powerful tool to control the ignition and combustion processes in a waste combustion plant. To use this tool effectively, the influence of the preheated air on the fuel bed needs to be well understood. The present work is done to develop a model that predicts the spontaneous ignition temperature of the fuel bed and the critical temperature of the primary air at which the fuel bed ignites. The influence of primary air flow rate and addition of inert are modeled for a packed bed of wood. From the model a dimensionless parameter is derived in which all investigated parameters (fuel type, air flow rate and inert fraction) are combined. This parameter appears to be sufficient to describe both the spontaneous ignition and the critical air temperature. The results from the model are validated with experiments presented in previous work [1]. The model slightly over-predicts the temperatures by 6–7°C, and the trends are predicted well. Besides calculations for the temperatures, the ignition time and location are calculated as well. The ignition time is under-predicted due to the assumption of a uniform temperature distribution inside the particles. The location of ignition is predicted well. For char, a minimum spontaneous ignition temperature is derived from DSC measurements. The temperature at which the interaction of char and oxygen switches from endo- to exothermic seems to coincide with the spontaneous ignition temperature.

Study of the spontaneous ignition of stoichiometric tetrafluoroethylene–air mixtures at elevated pressures

The Ignition Temperature (IT) of stoichiometric tetrafluoroethylene–air mixtures on hot walls was determined in a 3-dm³-reactor. Tests at elevated pressure conditions were performed, namely at 5, 15 and 25 bar(a), showing a decrease of the IT with the initial pressure. Furthermore, the measured ignition temperatures of stoichiometric tetrafluoroethylene–air mixtures were lower than the ignition temperatures required for the decomposition pure tetrafluoroethylene (Minimum Ignition Temperature of Decomposition, MITD) reported in previous works.Equations from the Semenov thermal explosion theory on spontaneous ignition were used to identify approximate combustion kinetics of tetrafluoroethylene from the experimental results. The determined kinetics was used for the prediction of the IT of stoichiometric tetrafluoroethylene-air by simplified calculation methods. A very good agreement with the experimental results was observed.

Ignition behavior of magnesium powder layers on a plate heated at constant temperature

The minimum temperature at which dust layers or deposits ignite is considered to be very important in industries where smoldering fires could occur. Experiments were conducted on the self-ignition behavior of magnesium powder layers. The estimated effective thermal conductivity k for modeling is 0.17Wm−1K−1. The minimum ignition temperature (MIT) of magnesium powder layers for four different particle sizes: 6, 47, 104 and 173μm, are also determined in these experiments. A model was developed describing temperature distribution and its change over time while considering the melting and boiling of magnesium powder. Parameter analysis shown that increasing particle size from 6 to 173μm increased MIT from 710 to 760K, and increased thickness of the dust layer led to a decreased MIT. The calculation termination time more than 5000s didn’t significantly impact MIT. Comparing predicted and experimental data showed satisfactory agreement for MIT of magnesium powder layers at various particle sizes. According to the ignition process of magnesium powder layer, a meaningful definition for the most sensitive ignition position (MSIP) was proposed and should be taken into consideration when preventing smoldering fires induced by hot plates.

Study on the influence of material thermal characteristics on dust explosion parameters of three long-chain monobasic alcohols

Sensitivity and severity parameters are critical for risk assessment and safety management of dust explosions. In this paper, to reveal the effects of material thermal characteristics on dust explosions parameters during monobasic alcohols dust explosions, three long chain monobasic alcohols, being solid at room temperature and similar in physical–chemical properties, were chosen to carry out experiments in different functional test apparatus according to the internationally accepted ASTM standards. As a result, it was found that the material thermal characteristics strongly affected these basic explosive parameters. On the one hand, for the sensitivity parameters, Minimum Ignition Temperature, Minimum Ignition Energy and Electrical Resistivity were the highest in the Eicosanol dust cloud, while Minimum Explosible Concentration in this cloud was the lowest. On the other hand, for severity parameters, Maximum Explosion Pressure in Eicosanol dust cloud always maintained the highest values as varying the dust concentrations. In contrast, Deflagration Index showed a complex trend.

Experimental determination of dust cloud deflagration parameters of selected hydrogen storage materials: Complex metal hydrides, chemical hydrides, and adsorbents

This paper discusses the results of an experimental program carried out to determine dust cloud deflagration parameters of selected solid-state hydrogen storage materials, including complex metal hydrides (sodium alanate and lithium borohydride/magnesium hydride mixture), chemical hydrides (alane and ammonia borane) and activated carbon (Maxsorb, AX-21). The measured parameters include maximum deflagration pressure rise, maximum rate of pressure rise, minimum ignition temperature, minimum ignition energy and minimum explosible concentration. The calculated explosion indexes include volume-normalized maximum rate of pressure rise (KSt), explosion severity (ES) and ignition sensitivity (IS). The deflagration parameters of Pittsburgh seam coal dust and Lycopodium spores (reference materials) are also measured. The results show that activated carbon is the safest hydrogen storage media among the examined materials. Ammonia borane is unsafe to use because of the high explosibility of its dust. The core insights of this contribution are useful for quantifying the risks associated with use of these materials for on-board systems in light-duty fuel cell-powered vehicles and for supporting the development of hydrogen safety codes and standards. These insights are also critical for designing adequate safety features such as explosion relief venting and isolation devices and for supplementing missing data in materials safety data sheets.

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.

Dust explosion risk moderation for flocculent dusts

The research presented in this paper is focused on dust explosions of coarse and fine flocculent (or fibrous) samples of wood and polyethylene. Hybrid mixtures of fibrous polyethylene and admixed ethylene were also studied. Experimentation was conducted by following standardized test procedures and using standardized apparatus for determination of maximum explosion pressure, size-normalized maximum rate of pressure rise, minimum explosible concentration, minimum ignition energy, and minimum ignition temperature. A general trend was observed of enhanced explosion likelihood and consequence severity with a decrease in material diameter, as well as enhanced consequence severity with admixture of a flammable gas to the combustion atmosphere. The same phenomena are well-established for dusts composed of spherical particles; this highlights the importance of inherently safer design and the principle of moderation in avoiding the generation of fine sizes of flocculent dusts and hybrid mixtures of such materials with flammable gases.In addition to presenting experimental findings, the paper describes phenomenological modelling efforts for the flocculent polyethylene using four geometric equivalence models: radial equivalence, volumetric equivalence, surface area equivalence, and specific surface area equivalence. The surface area equivalence model was found to yield the best estimates of maximum rate of pressure rise for the flocculent polyethylene samples investigated experimentally.

When solids meet solids: A glimpse into dust mixture explosions

Mixing an inert solid or a less flammable compound with a combustible dust can be regarded as a direct application of the inherent safety principle of moderation. An experimental investigation was carried out to determine the evolution of the ignition sensitivity and the explosion severity of such various mixtures as a function of their compositions. It demonstrates that the introduction of small amounts of highly combustible powders (such as sulphur or nicotinic acid) to a less flammable dust (such as microcrystalline cellulose or carbon black) can strongly influence the ignition sensitivity as well as the explosion severity.It has notably been shown that the ignition sensitivity of solid/solid mixtures significantly rises up when only 10–5%wt. of highly flammable dust is introduced. Simple models can often be applied to estimate the minimum ignition energy, minimum ignition temperature and minimum explosive concentration of such mixtures. Concerning the dust explosivity, three cases have been studied: mixtures of combustibles dusts without reaction, dusts with reactions between the powders, combustible dusts with inert solid. If the evolution of the maximum explosion pressure can be estimated by using thermodynamic calculations, the maximum rate of pressure rise is more difficult to predict with simple models, and both combustion kinetics and hydrodynamics of the dust clouds should be taken into account. These results were also extended to flammable dust/solid inertant mixture. They clearly show that the concentration of solid inertant at which the ignition is not observed anymore could reach 95%wt. As a consequence, the common recommendation of solid inertant introduction up to 50–80%wt. to prevent dust explosion/ignition should be reconsidered.