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Hosseinzadeh S.,Catholic University of Leuven | Norman F.,Adinex NV | Verplaetsen F.,Adinex NV | Berghmans J.,Adinex NV | Van Den Bulck E.,Catholic University of Leuven
Chemical Engineering Transactions | Year: 2015

Safety is of major importance to facilities and companies working with combustible materials like dust. To reduce the risk associated with dust, we need to assess the risk of explosion. This assessment can be based on the determination of the explosion characteristics of the dust. A fuel such as coal was allowed to combust in oxy-fuel atmospheres (mixtures of oxygen and carbon dioxide). The explosion risk was found to increase especially in oxygen enriched atmospheres with an O2-concentration greater than 21 %. To determine the explosion characteristics of the bituminous South African coal, experiments were performed with different mixture concentrations of coal, CO2 and O2. Measuring the minimum ignition energy (MIE) which is an important ignition sensitivity parameter showed that the MIE decreased significantly when the oxygen concentration in the mixture was increased. The violence of the explosion, which is a parameter for the explosion severity, is expressed by the maximum rate of pressure rise (dP/dt)max or Kst-value. This Kst was measured with a standard test apparatus with a content of 20 L using pyrotechnical igniters. This paper also explores the maximum burning velocity which was derived from the pressure histories. In order to achieve the burning velocities, experimental data were analyzed based upon the theoretical model of Dahoe and Van den Bulck. These models were induced by using a two-zone model for the adiabatic combustion in closed vessels. The results revealed that there is a strong relationship between the severity characteristic, the burning velocity and the oxygen concentration. However it was also observed that these coal characteristics were strongly dependent on the dust concentration. Furthermore the burning velocity reached its maximum value when the rate of pressure rise reached its maximum. Copyright © 2015, AIDIC Servizi S.r.l.


Norman F.,NV Adinex | Berghmans J.,Catholic University of Leuven | Verplaetsen F.,NV Adinex
Procedia Engineering | Year: 2012

The ability to mix pulverised coal with oxygen at concentrations greater than the currently applied 21% may well provide advantages for burner design in oxy/coal fired systems. 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) high volatile bituminous coal dust and on Pittsburgh Coal n°8. Both 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 investigated. © 2012 The Authors. Published by Elsevier Ltd.


Hosseinzadeh S.,Universitieit Leuven | Norman F.,Adinex NV | Verplaetsen F.,Adinex NV | Berghmans J.,Adinex NV | Van den Bulck E.,Universitieit Leuven
Journal of Loss Prevention in the Process Industries | Year: 2015

Most industrial powder processes handle mixtures of various flammable powders. Consequently, hazard evaluation leads to a reduction of the disaster damage that arises from dust explosions. Determining the minimum ignition energy (MIE) of flammable mixtures is critical for identifying possibility of accidental hazard in industry. The aim of this work is to measure the critical ignition energy of different kinds of pure dusts with various particle sizes as well as mixtures thereof. The results show that even the addition of a modest amount of a highly flammable powder to a less combustible powder has a significant impact on the MIE. The MIE varies considerably when the fraction of the highly flammable powder exceeds 20%. For dust mixtures consisting of combustible dusts, the relationship between the ignition energy of the mixture and the minimum ignition energy of the components follows the so-called harmonic model based upon the volume fraction of the pure dusts in the mixture. This correlation provides results which show satisfactory agreement with the experimental values. © 2015 Published by Elsevier Ltd.


Wu D.,Catholic University of Leuven | Huang X.,Imperial College London | Norman F.,Adinex NV | Verplaetsen F.,Adinex NV | And 2 more authors.
Fuel | Year: 2015

For the oxy-coal combustion, the accumulation of coal dust in the system has a fire risk of self-ignition. Therefore, understanding the ignition dynamics of coal dust deposits in oxygen-enriched environment is essential for the prevention of fire and dust explosion. In this work, both hot-oven and hot-plate tests were conducted to study the self-ignition behaviour of coal dusts in O2/CO2 ambient with O2 mole fraction from 21% to 50%. Three coal dusts: Indonesian Sebuku coal, Pittsburgh No. 8 coal and South African coal were tested with different sizes. Experimental results revealed that the self-ignition risk increased significantly with the increasing O2 mole fraction: reducing both the critical ignition temperature (10°C in hot-oven test and 40°C in hot-plate test) and the ignition delay time. Comparatively, the inhibiting effect of CO2 was found to be small for self-ignition. In addition, a modified Frank-Kamenetzkii analysis was proposed to explain all measured critical ignition temperatures, and the genetic algorithm was used to determine kinetic parameters of the one-step global reaction. The analysis showed that as the coal maturity/rank increased, both the self-ignition risk and the sensitivity to oxidation decreased, along with the decreasing apparent activation energy and pre-exponential factor. Such trend did not change with the ambient oxygen condition for all three coal dusts. These results improve our understanding of the self-ignition behaviour and the fire risk of coal dust in the oxy-fuel combustion system. © 2015 Published by Elsevier Ltd.


Hosseinzadeh S.,Catholic University of Leuven | Norman F.,Adinex NV | Verplaetsen F.,Adinex NV | Berghmans J.,Catholic University of Leuven | Van den Bulck E.,Catholic University of Leuven
Journal of Loss Prevention in the Process Industries | Year: 2016

In this study, the explosion characteristics of coal powder in O2CO2 atmospheres are studied. All experiments are performed in a 20 L spherical vessel. The maximum explosion pressure and the maximum rate of pressure rise are derived from the pressure time evolutions. A three-zone theoretical model has been applied to calculate the flame speed. To overcome the drawbacks of the non-spherical flames generated by pyrotechnical igniters, a continuous ignition spark is used as an alternative ignition source. The experimental results show that maximum explosion pressures are similar when different ignition sources are used. The maximum rate of pressure rise and the flame velocity are very sensitive to the ignition source. © 2016 .


Wu D.,Catholic University of Leuven | Vanierschot M.,Catholic University of Leuven | Verplaetsen F.,Adinex NV | Berghmans J.,Catholic University of Leuven | Van den Bulck E.,Catholic University of Leuven
Applied Thermal Engineering | Year: 2016

Understanding the fundamental basis of coal dust layers ignition behavior is of interest for the mitigation of industrial fires and explosions. This paper develops a 2D numerical method to investigate the self-ignition of coal dust layers with an emphasis on the roles of the oxygen mole fraction and diluent gas. A global one-step 2nd-order reaction kinetic model considering both coal density and oxygen density is used to estimate the reaction rate of self-heating process until ignition. In addition, the overall heat transfer coefficient is evaluated based on a steady state method and the kinetic parameters are estimated by fitting experimental and numerical temperature evolution figures. This model has been found to be valid to predict the transient temperature and concentration profiles until ignition. The numerical results of the minimum ignition temperature of dust layers (MITL) are in close agreement with experimental observations. The ignition delay time and the most sensitive ignition position (MSIP) of dust layer are found to vary with varying ambient gas conditions, hot plate temperatures and ambient temperatures using the verified model. The model provides a satisfactory explanation for the dependence of ignition characteristics of coal dust layer in oxygen-enriched oxy-fuel atmospheres. © 2016 Elsevier Ltd


Wu D.,Catholic University of Leuven | Norman F.,Adinex NV | Verplaetsen F.,Adinex NV | Van den Bulck E.,Catholic University of Leuven
Journal of Hazardous Materials | Year: 2016

BAM furnace apparatus tests were conducted to investigate the minimum ignition temperature of coal dusts (MITC) in O2/CO2 atmospheres with an O2 mole fraction from 20 to 50%. Three coal dusts: Indonesian Sebuku coal, Pittsburgh No.8 coal and South African coal were tested. Experimental results showed that the dust explosion risk increases significantly with increasing O2 mole fraction by reducing the minimum ignition temperature for the three tested coal dust clouds dramatically (even by 100°C). Compared with conventional combustion, the inhibiting effect of CO2 was found to be comparatively large in dust clouds, particularly for the coal dusts with high volatile content. The retardation effect of the moisture content on the ignition of dust clouds was also found to be pronounced. In addition, a modified steady-state mathematical model based on heterogeneous reaction was proposed to interpret the observed experimental phenomena and to estimate the ignition mechanism of coal dust clouds under minimum ignition temperature conditions. The analysis revealed that heterogeneous ignition dominates the ignition mechanism for sub-/bituminous coal dusts under minimum ignition temperature conditions, but the decrease of coal maturity facilitates homogeneous ignition. These results improve our understanding of the ignition behaviour and the explosion risk of coal dust clouds in oxy-fuel combustion atmospheres. © 2015 Elsevier B.V.


Norman F.,Adinex NV | Berghmans J.,Catholic University of Leuven | Verplaetsen F.,Adinex NV
Chemical Engineering Transactions | Year: 2013

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 n8. 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 n̊8. © 2013, AIDIC Servizi S.r.l.


Wu D.,Catholic University of Leuven | Norman F.,Adinex NV | Verplaetsen F.,Adinex NV | Berghmans J.,Catholic University of Leuven | Van Den Bulck E.,Catholic University of Leuven
Procedia Engineering | Year: 2014

An experimental investigation into the hot surface ignition of coal dust layers has been undertaken in oxy-fuel combustion atmospheres, with the oxygen mole fractions in the range of 21-50 vol. % (21%, 30%, 40% and 50%). Three coals were used to determine the minimum layer ignition temperature (MLIT) with a hot surface ignition apparatus according to the European EN50281-2-1 norm. In addition, thermal and kinetic parameters were also determined. Layer thicknesses of 5, 12.5, 15, 20 and 30mm were investigated. Firstly, 5 and 12.5mm thick coal dust layers were used to investigate the influence of the oxygen mole fraction on the MLIT, and the steady state dust layer temperature profile of a 30mm thick coal dust layer was used to estimate the thermal conductivity (k) at a low hot surface temperature. Secondly, the South African coal was used in this study to determine the kinetic parameters on the basis of the Frank-Kamenetskii theory. Results show that oxygen concentration has a significant influence on the MILT, (i.e., MLIT decreases with increasing oxygen concentration). It also shows that replacing N2 in the combustion air with CO2 a small increase of the MLIT will occur. The estimated k of the coal dust samples is respectively 0.1, 0.11 and 0.1 W·m-1 ·K-1 for South African coal, Sebuku coal and Pittsburgh coal. The region of the kinetic parameters of South African coal changes when there is a shift in the test from air to oxy-fuel combustion atmospheres, which means that the reaction mechanism of self-heating or ignition changed somewhat. © 2014 Published by Elsevier Ltd.


PubMed | Catholic University of Leuven and Adinex NV
Type: | Journal: Journal of hazardous materials | Year: 2016

BAM furnace apparatus tests were conducted to investigate the minimum ignition temperature of coal dusts (MITC) in O2/CO2 atmospheres with an O2 mole fraction from 20 to 50%. Three coal dusts: Indonesian Sebuku coal, Pittsburgh No.8 coal and South African coal were tested. Experimental results showed that the dust explosion risk increases significantly with increasing O2 mole fraction by reducing the minimum ignition temperature for the three tested coal dust clouds dramatically (even by 100C). Compared with conventional combustion, the inhibiting effect of CO2 was found to be comparatively large in dust clouds, particularly for the coal dusts with high volatile content. The retardation effect of the moisture content on the ignition of dust clouds was also found to be pronounced. In addition, a modified steady-state mathematical model based on heterogeneous reaction was proposed to interpret the observed experimental phenomena and to estimate the ignition mechanism of coal dust clouds under minimum ignition temperature conditions. The analysis revealed that heterogeneous ignition dominates the ignition mechanism for sub-/bituminous coal dusts under minimum ignition temperature conditions, but the decrease of coal maturity facilitates homogeneous ignition. These results improve our understanding of the ignition behaviour and the explosion risk of coal dust clouds in oxy-fuel combustion atmospheres.

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