Spontaneous Ignition Temperature Research Articles

Instantaneous Ignition of Activated Carbon

The spontaneous ignition temperature as defined using the American Society for Testing and Materials (ASTM) methods may not accurately determine the temperature at which carbon will combust when a step change in bed temperature occurs; therefore, an instantaneous ignition temperature is defined. Seven different activated carbons have been heated at various heating rates in three different bed configurations, and the data show that the instantaneous ignition temperature can be significantly lower than the spontaneous ignition temperature. In some cases, the carbon ignited at temperatures 100 °C lower than the spontaneous ignition temperature. The results show that ignition temperatures are dependent not only on the carbon source and bed dimensions but also on the rate of heating used in the experiment. The results emphasize the importance of evaluating carbon combustion with experiments that closely resemble the operational conditions of the fixed-bed.

Activation Energy of Teak and Oak Wood Spontaneous Ignition

This article deals with evaluation of the spontaneous-ignition activation energy of the Teak wood (Tectona grandis L.f.) and the Oak wood (Quercus robur L.). Spontaneous-ignition activation energy was calculated from dependence of ignition time to inverse value of thermodynamic temperature. This dependence was measured in the hot-air (Setchkin) furnace according to ISO 871:2006 standard by modification of the test procedure. The modifications of test procedure lay in measurement of the time to ignition of sample loaded by various temperatures (at spontaneous ignition temperature and at temperatures above this value). The mass of investigated samples was (3 ± 0.05) g and its moisture contents was 0 wt %. The dimensions of sample was (20 x 20) mm, the third dimension was adjust to achieve required mass of sample. The activation energy of spontaneous-ignition for Teak wood was 78.23 kJ.mol-1 and for Oak wood was 59.24 kJ.mol-1. The spontaneous-ignition temperature for Teak wood was 460 °C and for Oak wood was 450 °C. Thus despite slight difference between spontaneous-ignition temperatures of investigated materials the difference between activation energy of spontaneous-ignition is significant.

Experimental Investigation into the Spontaneous Ignition Behavior of Upgraded Coal Products

The propensity for spontaneous ignition of nine coal samples and their upgraded products were experimentally investigated. The basket method was used to study the effects of the variation of mineral matter and volatile content on the spontaneous ignition of coal. The removal of mineral matter by chemical leaching caused the spontaneous ignition temperature (SIT) to decrease, which indicated a higher propensity for ignition. As the mineral matter increased, SIT increased approximately linearly. The results indicated that the SIT of coal char first decreased with a decreasing volatile content and then rapidly increased as the volatile content continued to decline, because of the deepening of the devolatilization. This paper proposes a prediction model based on the oxygen and carbon ratio (O/C) parameter in raw coal, which can be used to predict its SIT.

Fire Risk Assessment of Spruce Pellets

In the presented paper is assessed fire risk of pellets made from spruce wood (Picea abiesL.) without bark, processed by hot pressing without the use of additional chemicals. Fire risk was assessed on the basis of heat release rate (HRR), the specific carbon monoxide production rate (SCPR) and the time dependence of the induction period of spontaneous ignition on temperature. HRR and SPCR were determined on the cone calorimeter test performed according to ISO 5660-1:2002 standard. Samples were loaded by 20 kW/m2heat flux during the test. The maximum HRR was 229 kW/m2and average HRR was 55 kW/m2. Maximum SCPR was 0.37 g/(m2s) and the average SCPR was 0.16 g/(m2s). The dependence of the induction period of spontaneous ignition on temperature was determined by a modified test performed according to ISO 871:2006 standard. Modification of the test procedure was based on measurement of the induction time period of the spontaneous ignition on temperature, and temperatures higher of 20, 40, 60, 80 and 100 °C than spontaneous ignition temperature. The obtained data proved an exponential dependence of the induction period of spontaneous ignition on temperature.

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 Polymeric Materials Burning

The article deals with determination of spontaneous ignition temperature and flash ignition temperature of polymeric materials and monitoring of mass loss rate during their degradation. An experiment was conducted in accordance with standard STN ISO 871: 2010 Plastics. Determination of ignition temperature using a hot-air furnace.

Spontaneous ignition temperature for the compacted mixture of Ni–Al system: Experiment, theory, and comparisons

Spontaneous ignition of compacted mixture has been examined not only experimentally but also theoretically, relevant to materials synthesis for Ni–Al system. Spontaneous ignition temperature, determined from the inflection-point of the temporal variation of surface temperature, is found to decrease at first, reach the minimum, and then increase gradually, with increasing size ratio, being defined as the ratio of compact and particle diameters and reported to be useful in correlating experimental results. The lowest temperature observed is as low as that, more than 200K below the melting point 934K of Al, at the size ratio of c.a. 700. While its decrease is attributed to the increase in the particle surface per unit spatial volume of compacted mixture, as reported in the literature, its increase found in the course of the present study can fairly be correlated to an enhancement of heat loss from each particle in the compacted mixture, by conducting a theoretical consideration. As for the dependence of spontaneous ignition temperature on the mixture ratio, a shifting occurs from a decreasing trend with increasing mixture ratio at small size ratios, less than about 700, to an insensitive trend to the mixture ratio, had not been reported in the literature. In addition, a fair degree of agreement, shown in experimental comparisons with theoretical results, indicates that the present formulation has captured the essential features of the spontaneous ignition of compacted mixture, especially for size ratios with large values. Since this kind of particle size effects, relevant to the spontaneous ignition of the compacted mixtures, has not been captured in the previous studies, its elucidation can be considered not only notable but also useful, in manipulating combustion process in materials synthesis, especially, in choosing a specific condition for the lowest spontaneous ignition temperature by varying the size ratio.

Spontaneous Ignition Temperature and Burning Velocity Just after the Ignition in the SHS Process for Ti-Al System with Rectangular Shape

Relevant to materials synthesis by combustion, not only spontaneous ignition of compacted mixture but also flame propagation just after the ignition has been examined for Ti-Al system with rectangular shape. Not only experimental but also theoretical study has been conducted, after confirming that the size ratio, defined as the ratio of compact thickness and particle diameter, can be useful parameters in correlating experimental results. It is found that with increasing size ratio, the spontaneous ignition comes to occur below the melting point of Al (934 K), due to an increase in the particle surface per unit spatial volume of compacted mixture. Effects of mixture ratio and/or degree of dilution on the spontaneous ignition temperature have also been examined. In addition, effects of various system parameters on the burning velocity just after the ignition have been examined. Experimental comparisons with theoretical results have also been conducted and a fair degree of agreement is demonstrated, indicating that the formulations referred to have captured the essential features of the spontaneous ignition of compacted mixture and the SHS flame propagation that passes through it. Since this kind of particle size effect, especially, relevant to the spontaneous ignition and the flame propagation after the ignition, has not been captured in the previous studies, its elucidation can be considered not only notable but also useful, especially, in manipulating combustion process in materials synthesis.

Determination of Fire and Burning Properties of Spruce Wood

This paper deals with the determination of selected fi re properties of spruce wood. It describes the general characteristics of spruce wood, microscopic and macroscopic features. Broad application of this material requires the assessment of its properties regarding the fi re aspects, being a cause of fi re in forests or due to frequent occurrence of wildland fi res in the Slovak territory, and being a fl ammable material used in building industry, furniture industry, etc. This paper analyses the following fi re properties: fl ash-ignition temperature, spontaneousignition temperature, mass burning rate, ignitability of material exposed to a small open fl ame.

Burning Velocity for the Compacted Mixture of Ti-Al System Just after the Spontaneous Ignition

Burning velocity just after the spontaneous ignition has been examined not only experimentally but also theoretically, relevant to the Self-propagating High-temperature Synthesis (SHS) process, for Ti-Al system. By varying mixture ratio, degree of dilution, and compact and particle sizes, not only the spontaneous ignition temperature, determined from the inflection-point of the temporal variations of the surface temperature, but also the burning velocity, defined as the normal component to the flame surface, has been measured. It is found that the burning velocity just after the spontaneous ignition first increases and then decreases with increasing mixture ratio, due to an increase and a decrease, respectively, in the heat of combustion, that it decreases with increasing degree of dilution, due to a decrease in the heat of combustion, and that it increases with increasing size ratio, defined as a ratio of compact and particle sizes, due to an increase in the reaction surface per unit spatial volume in the compacted mixture. Experimental comparisons with theoretical results have also been conducted and a fair degree of agreement is demonstrated, indicating that the formulation used has captured the essential features of the SHS flame propagation that passes through the compacted mixture. Since this kind of particle size effect, especially, relevant to the flame propagation after the spontaneous ignition, has not been captured in the previous studies, its elucidation can be considered not only notable but also useful, especially, in manipulating combustion process in materials synthesis.

Spontaneous ignition temperature for the compacted mixture of Ti–Al system: Theory and experimental comparisons

Spontaneous ignition of compacted mixture has been examined not only experimentally but also theoretically, relevant to materials synthesis by combustion for Ti–Al system. By varying compact and particle sizes, mixture ratio, and degree of dilution, spontaneous ignition temperature has been measured, which is determined from the inflection-point of the temporal variations of the surface temperature. It is found that the spontaneous ignition temperature decreases with increasing aspect ratio, defined as the ratio of the sample height and compact diameter, due to an establishment of the stationary temperature distribution in the radial direction in the compacted mixture, as the sample height becomes tall. It is also found that the spontaneous ignition temperature decreases with increasing size ratio, defined as the ratio of compact and particle diameters, due to an increase in the particle surface per unit spatial volume of the compacted mixture, caused by a decrease in the particle diameter and/or an increase in the compact diameter. By further examining its dependence on mixture ratio and/or degree of dilution, it is confirmed that the limit of flammability also exerts influences on the spontaneous ignition temperature. In addition, a fair degree of agreement, shown in experimental comparisons with theoretical results, indicates that the present formulation has captured the essential features of the spontaneous ignition of compacted mixture. Since this kind of particle size effect, especially, relevant to the spontaneous ignition of compacted mixtures, has not been captured in the previous studies, its elucidation can be considered not only notable but also useful, especially, in manipulating combustion process in materials synthesis.

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 investigate in a systematically way the spontaneous ignition behaviour of a packed bed heated with a preheated air stream. Experiments on a lab scale packed bed reactor are carried out for various fuel types. Because MSW is an highly inhomogeneous fuel, wood and char are used as model fuels. To include the inhomogeneous character of MWS, also experiments are carried out with RDF. Parameters such as primary air flow velocity and temperature, addition of inert material, moisture content of the fuel (wood chips) and particle size (char) have been changed to see their effect on the spontaneous ignition temperature and on the minimum air temperature needed for ignition. The spontaneous ignition temperature is defined as the bed temperature at which a transition takes place from a negligible or slow fuel reaction rate to a rapid oxidation of either the volatiles or the solid fuel without an external source such as a spark or a flame. The minimum or critical air temperature is defined as the lowest air temperature at which ignition can be obtained. It is found that the type of fuel has influence on the ignition temperatures. Besides both the critical air temperature needed for the spontaneous ignition and the spontaneous ignition temperature increase with an increase in the primary air velocity (between 0.1 and 0.5 m/s) and increasing the added inert fraction (between 0 and 40 wt%), irrespective of the fuel type. The effect of air flow velocity and temperature and also the effect of inert on both the critical air temperature and the spontaneous ignition temperature can be explained qualitatively by using Semenov’s analysis of thermal explosions. Semenov’s theory is quantitatively applied to predict the spontaneous ignition and the critical air temperatures for wood.

Ti-Al系燃焼合成における自己着火温度に及ぼす主要パラメタの影響(熱工学,内燃機関,動力など)

Relevant to materials synthesis by combustion, spontaneous ignition of compacted mixture has been examined with Ti-Al system taken as a research object. Not only experimental but also theoretical study has been conducted, after confirming that the size ratio, defined as the ratio of compact diameter and particle diameter, and the aspect ratio, defined as the ratio of compact height and diameter, can be useful parameters in correlating experimental results. It is found that with increasing aspect ratio and/or size ratio, the spontaneous ignition temperature decreases within the present experimental conditions, below the melting point 934K of Al. The decrease with increasing aspect ratio is attributed to an establishment of the stationary temperature distribution in the compacted mixture, being balanced between heat release and loss. The decrease with increasing size ratio is attributed to an increase in the particle surface per unit spatial volume of compacted mixture. Effects of mixture ratio have also been examined, showing that the spontaneous ignition temperature decreases with increasing mixture ratio. Effects of the degree of dilution on the spontaneous ignition temperature are also examined. Experimental comparisons with theoretical results have also been conducted and a fair degree of agreement is demonstrated, indicating that the present formulation has captured the essential features of the spontaneous ignition of compacted mixture.

Thermal characteristics of Hydroxypropyl Methyl Cellulose

This study was designed to investigate the thermal characteristics of Hydroxypropyl Methyl Cellulose (HPMC). Because HPMC is used in various industries extensively, it is very important to clarify the thermal characteristics in terms of its potential hazards and the spontaneous. In this study, we performed thermal analysis with the TG–DTA and Spontaneous Ignition Tester (SIT). Based on the data of the SIT, we know that the critical spontaneous ignition temperature and the apparent activation energy of HPMC were about 185 °C and 104.54 kJ/mol respectively. However, when the amount of sample is larger to a certain degree, ignition can occur below this temperature. At a thickness of 1 m sample of infinity flat was calculated to have a critical temperature value of approximately 180 °C by Frank-Kamenetskii's method. Upon analyzing thermal behavior using the TG–DTA, we found that the pyrolysis transpired at 200 °C, below the rate of temperature of 1 K/min, which is slightly lower than that of common cellulose. Regarding gas analysis, carbon monoxide (CO) was emitted at the start of the reaction.

Spontaneous ignition of ultra-fine magnesium powder without an original oxide coat at room temperature in O 2/N 2 mixture streams

To examine the pyrophoric characteristics of Mg powder, we generated ultra-fine Mg particles (average particle diameter: about 0.3 μm) without an original oxide coat in an Ar stream. The ignition of the powder was measured by using the impinging O 2/N 2 mixture streams over a wide range of the experimental parameters: pressure, oxygen concentration and velocity of the streams. The Mg powder was found to ignite even at room temperature. The spontaneous ignition temperatures in the range of 278 ∼ 324 K were insensitive to all the experimental parameters. The ignition delay time had a tendency to decrease with increasing experimental parameters. The ignition process of the Mg powder was found to be controlled by the surface reaction rate without an oxide coat. We proposed a new ignition hypothesis considering a critical oxide thickness on the Mg powder particles at the transition temperature from protective to non-protective nature: that is, the ignition of the Mg powder occurs when the powder temperature rises above the transition temperature before surface reactions form a protective oxide coat with the critical thickness on the individual particle surfaces. According to this hypothesis, an ignition model of Mg powder cluster was developed, and the relation between the spontaneous critical ignition temperature and the ultra-fine powder size, depending on the critical thickness of the protective oxide coat, was clarified. The critical oxide thickness was estimated.

Statistical quantification of the influence of material properties on the oxidation and ignition of activated carbons

The influence of material properties on the reactivities of activated carbon materials have been studied on a laboratory scale. Carbon samples having diversified origin and properties were characterized using a thermogravimetry (TG) coupled with a differential scanning calorimetry (DSC). Reactivity parameters like the Point of Initial Oxidation (PIO) representing the beginning of the oxidation reactions and the Spontaneous Ignition Temperature (SIT) where the bed combustion takes place in a self sustaining manner were experimentally determined. The intrinsic properties of the activated carbons influencing oxidation and ignition were examined qualitatively followed by quantitative statistical correlations. Results from both qualitative and statistical correlations showed that increase in the oxygen content in the form of surface oxygenated groups increased the reactivity of activated carbons. It was by far the single most influential property discriminated from the analysis. The porosity characteristics like the specific surface area and pore volume did show some vague trends but could not be validated like that of the oxygen content. The effects of these individual properties on the oxidation and ignition reactivity are discussed.

A New Approach for Predicting Flame Spread along Combustible Solid based on Cellular Automaton

In this study, a new approach for predicting flame spread along a combustible solid is developed. This presented approach consists of a two-dimensional flame spread model coupled with a one-dimensional pyrolysis model in the thickness direction. The flame spread model is based on a cellular automaton combined with piloted ignition temperature, spontaneous ignition temperature, and pyrolysis temperature of a combustible solid. In addition, this approach is used to predict two typical kinds of flame spread, i.e., upward flame spread and ceiling flame spread. The existing experimental data including the upward flame spread over plywood and the ceiling flame spread beneath medium density fiberboard (MDF) are used for comparison to validate this approach. The results obtained from numerical simulations using this approach are consistent with these two kinds of experimental tests.

Effective utilization of Mongolian coal by upgrading in a solvent

Liquid-phase upgrading of Mongolian low-rank coals, which are rich in oxygen, having low heating value, was investigated using 200 ml autoclave at 380–440 °C in the presence of t-decalin and coal tar as solvent under 2 MPa of initial nitrogen atmosphere. The upgrading of Baganuur-2A and Shivee ovoo coal at 440 °C in t-decalin gave 9.7–10.2 wt.% of gas, 3.7–4.5 wt.% of oil, 4.4–8.4 wt.% of water and 77–82 wt.% of upgraded solid product. The heating value of the upgraded solid product from Baganuur-2A coal increased to 32.9 MJ/kg as compared to the heating value of raw coal, which was 26.3 MJ/kg, and for the Shivee ovoo coal, it was reached from 21.2 to 28.8 MJ/kg. The upgrading process has influenced significantly the enhancement of the aromaticity and the spontaneous ignition temperature of the raw coal. The distribution of aromatic stacking layers ( N) is slightly higher for the upgraded solid products treated at 440 °C than raw coal. The Baganuur-2A, Shivee ovoo coals and these upgraded solid products were mixed with Goonyella bituminous coal and tested on gieseler plastmeter to characterise thermoplastic behaviour.

Characterizing the ignition process of activated carbon

Properties of activated carbons at elevated temperature, specifically the spontaneous ignition temperature ( SIT) and the point of initial oxidation ( PIO), are of great significance in a number of unit operations. Although the SIT and PIO should be evaluated for each individual use, a standard method is required to compare products, insure quality, and optimize processes. Different methods for determining the SIT and PIO are compared using base (BPL, Coconut Shell, and MaxSorb) and impregnated carbons (ASC, ASZM, and ASZM-T). The SIT was determined by the ASTM and thermal analysis (TG and DSC) methods. The PIO was determined by effluent CO 2 concentration analysis, thermal analysis (TG and DSC) and temperature profiling. These comparisons show that not all of these methods have general utility, some are not easily correlated, and that there is evidence of the validity of two reaction regimes of interest. The simplest method that provides the most consistent conservative estimate of reaction commencement is measuring the PIO with the temperature profiling technique.

THE USE OF BIOMASS RESIDUES IN THE BRAZILIAN SOLUBLE COFFEE INDUSTRY

The objective of this paper is to discuss the use of coffee grounds in the Brazilian soluble coffee industry. This residue is used as a fuel in the boilers of the same industry; so, data about their utilization are presented and analysed, discussing the actual technology and the advantages of improving the drying of the biomass with the exhaust combustion gases. After that, an experimental study is reported on the characteristics of this material, which are important for the combustion process, including the transport, storage and drying, the mean diameter of the particles, talus angle, apparent and real density, sphericity, surface area, terminal velocity, spontaneous ignition temperature and heat of combustion.