Explosion of different ranks coal dust in oxy-fuel atmosphere

Fuel Processing Technology, Volume 148, July 2016, Pages 388-394

Wojciech Moroń, Wiesław Ferens, Krzysztof Marek Czajka

Abstract:Significant impact of the coal power generation onto the environment causes that new technological solutions aimed to reduce the impact of coal combustion onto the environment have currently been sought. Oxy-fuel is one of the technologies which reduces conventional pollutants such as NOx, SO2 and contribute to the elimination of CO2. The strategy for the implementation of this technology has currently been connected with two directions: (1) retrofitting of existing power plants to fit new combustion conditions or (2) design of new units. When air is replaced with CO2/O2, it leads to lots of doubts and concerns on boiler construction solutions. The article presents the results of research studies on four coals, on four coals, two bituminous coals and two lignite. The laboratory studies analysed the impact of CO2/O2 atmosphere onto explosion risks in fuel handling/preparation installations. These research studies were performed with the application of 20-litre sphere and TGA/DTG. It was found that the impact of the oxy-fuel atmosphere onto increased explosion risks is lower than it could be concluded from an increase in oxygen concentration in the system. The TGA/DTG studies showed, however, that devolatisation and fuel ignition in the oxy-fuel atmosphere occur at lower temperatures compared to the air atmosphere.

Chapter Seven -Dust Explosions

Explosion Hazards in the Process Industries (Second Edition), 2016, Pages 253-383

Rolf K. Eckhoff

Abstract:The chapter starts with the question: What is a dust explosion? Materials that can give dust explosions are then presented together with factors influencing the ignitability and explosibility of dust clouds. Flame propagation processes and explosive dust-concentration ranges of dust clouds in air are discussed. This includes close-to-laminar flame propagation and maximum pressure generated from constant-volume adiabatic combustion of dust clouds.

Turbulent flame propagation and detonation in dust clouds are also discussed. The important distinction between primary and secondary dust explosions is made. The discussion of potential ignition sources includes open flames, hot surfaces, heat from mechanical impacts, electric sparks and arcs and electrostatic discharges, jets of hot combustion products, shock waves and light radiation. Then a discussion of case histories of dust explosions from before 1800 till recent years follows. Means of preventing and mitigating dust explosions in the process industries are discussed in the final part of the chapter.

Estimation of the deflagration（爆燃）index KSt for dust explosions: A review

Journal of Loss Prevention in the Process Industries, Volume 44, November 2016, Pages 311-322

Anna Fumagalli, Marco Derudi, Renato Rota, Sabrina Copelli

Abstract:Combustible dust explosions are among the most serious criticalities affecting a broad number of industries around the world. According to a Chemical Safety and Hazard Investigation Board report, more than 50 accidents have occurred only in the U.S. between 2008 and 2012; this datum shows that such a problem requires a relevant attention from both researchers and authorities. The aim of this review is to provide an overview of the currently available techniques able to estimate the severity of a combustible dust explosion. Moreover, the main criticalities arising from these methodologies are discussed, also providing some suggestions for future works.

On the explosion and flammability behavior of mixtures of combustible dusts

Process Safety and Environmental Protection, Volume 94, March 2015, Pages 410-419

Roberto Sanchirico, Paola Russo, Valeria Di Sarli, Almerinda Di Benedetto

Abstract:In the work presented in this paper, the explosion and flammability behavior of combustible dust mixtures was studied. Lycopodium, Nicotinic acid and Ascorbic acid were used as sample dusts.

In the case of mixtures of two dusts, the minimum explosive concentration is reproduced well by a Le Chatelier's rule-like formula, whereas the minimum ignition energy is a linear combination of the ignition energies of the pure dusts.

An unexpected behavior has been found in relation to the explosion behavior and the reactivity. When mixing Lycopodium and Nicotinic acid or Ascorbic acid, the rate of pressure rise of the mixture is much higher than the rate of pressure rise obtained by linearly averaging the values of the pure dusts (according to their weight proportions), thus suggesting that strong synergistic effects arise; but it is comparable to that of the most reactive dust in the mixture.

The observed behavior seems to be linked to the presence of minerals in the Lycopodium particles which catalyze oxidation reactions of Nicotinic acid and Ascorbic acid, as suggested by TG analysis.

In the case of mixtures of three dusts, a similar behavior is observed when the concentration of Lycopodium is twice that of the other two dusts.

Numerical simulation of dilute and dense layered coal-dust explosions

Proceedings of the Combustion Institute, Volume 35, Issue 2, 2015, Pages 2083-2090

Ryan W. Houim, Elaine S. Oran

Abstract:Multidimensional time-dependent simulations were performed to study the interaction of a shock wave and resulting shear layer with layers of coal dust. The simulations used a high-order compressible numerical method for fluid dynamics and included a Eulerian kinetic-theory-based granular multiphase model applicable over a range from dense to dilute particle volume fractions. Two cases were considered: a loose dust layer with an initial volume fraction of 1%, and a dense dust layer with an initial volume fraction of 47%. For both cases, the final result is a coupled complex consisting of a shock leading a coal-dust flame. In the simulations presented here, a shock is initially produced from remnants of a natural gas detonation, which has decayed into a shock once it passes into a region containing no gaseous fuel. This shock weakens further due to mechanical and thermal losses from lifting and entraining the coal dust. The lifted dust subsequently ignites in the shock-heated air and produces a structure similar to a mixing-limited, nonpremixed flame. The flame consists of a burning coal dust wave that follows the shock. The distance between the shock and ignition point is determined by the induction length of carbon char, which is image170 cm and image15 cm for the 47% and 1% cases, respectively. The burning of coal particles is predominantly from heterogeneous reactions with carbon char, and volatilized methane combustion is a secondary effect. Air and particles are mixed by relative velocity between the gas and solid phases. Coal particles burn and produce pressure waves that accelerate the shock from Mach 2.2 to 2.6 for the dilute layer, and from Mach 1.7 to 1.8 in the dense layer.

Lower explosion limit of hybrid mixtures of burnable gas and dust

Journal of Loss Prevention in the Process Industries, Volume 36, July 2015, Pages 497-504

Emmanuel Kwasi Addai, Dieter Gabel, Ulrich Krause

Abstract:Hybrid mixtures – mixtures of burnable dusts and burnable gases – pose special problems to industries, as their combined Lower Explosion Limit (LEL) can lie below the LEL of the single substances. Different mathematical relations have been proposed by various authors in literature to predict the Lower Explosion Limit of hybrid mixtures (LELhybrid). The aim of this work is to prove the validity or limitations of these formulas for various combinations of dusts and gases. The experiments were executed in a standard 20 L vessel apparatus used for dust explosion testing. Permanent spark with an ignition energy of 10 J was used as ignition source. The results obtained so far show that, there are some combinations of dust and gas where the proposed mathematical formulas to predict the lower explosible limits of hybrid mixtures are not safe enough.