This review examines existing knowledge on the genesis and flame acceleration of explosions from methane–air mixtures. Explosion phases including deflagration and detonation and the transition from deflagration to detonation have been discussed. The influence of various obstacles and geometries on explosions in an underground mine and duct have been examined. The discussion, presented here, leads the readers to understand the considerations which must be accounted for in order to obviate and/or mitigate any accidental explosion originating from methane–air systems.

A review on understanding explosions from methane-air mixture

Titanium containing γ-MnO 2 octahedral molecular sieves having hollow sphere structures are successfully prepared for the first time using a one-step synthesis method. Titanium cations are used as structure-directing agents in the synthesis process. The assembly of the hollow spheres is carried out at the beginning of the process. Various techniques including XRD, N 2 adsorption, SEM, EDX, RAMAN, TEM, XPS, and TGA are employed for the materials characterization. Ti is incorporated into the MnO 2 framework in isolated sites, and TiO 2 phases (anatase and rutile) are not observed. When introduced in medium-sized lithium-air batteries, the materials give very high specific capacity (up to 2.3 A h g ―1 ). These materials are also catalytically tested in the oxidation of toluene with molecular oxygen at atmospheric pressure, showing significant oxidative catalytic activities in this difficult chemical reaction.

Titanium Containing γ-MnO2 (TM) Hollow Spheres: One-Step Synthesis and Catalytic Activities in Li/Air Batteries and Oxidative Chemical Reactions

INTRODUCTION Flash point measurements of various types are used as one measure of the flammability of liquid materials. The flash point is also related to the lower flammability limit, which is the minimum content of the combustible in a combustible–air mixture that will propagate flame [1]. Many manufacturing processes involve flammable chemicals; therefore, flash points and flammability limits are essential to maximize safety in process design and operational procedures. Flammability is an important factor in the development of safe practices for handling and storage of liquid mixtures. Regulatory authorities use flash point determinations made from small-scale test apparatus to classify flammable and combustible liquids. These determinations are based mainly on the use of the closed cup flash point temperature as the key property for classifying liquids according to their degree of flammability. Based on these classifications, regulators then specify or provide guidance on the appropriate methods for transporting, handling, packaging, storing, dispensing, and protecting these materials [2]. Also, federal regulations require that the mixture flash point be provided as part of materials safety data information. Industry works with mixtures under different conditions of temperature, pressure, and oxygen concentrations according to the process involved. The flash point can be used to determine the level of risk in different stages of a process because it is the temperature at which sufficient vapor is generated to bring the concentration of flammable vapor above the lower flammability limit. One question that must be answered to ensure a safe level of operation in a certain process is “What is the minimum oxygen concentration requirement for flame propagation?” Or, in terms more directly applicable to process operations, “What is the minimum amount of inerts required to prevent flame propagation?” The quantity of air that is required to decrease the combustible vapor concentration to a safe level in a particular process carried out at a specific temperature should be based on flammability measurements at that temperature. Knowledge of flammable limits at elevated temperatures and pressures is needed for safe and economical operation of some chemical processes. This information may be needed in order to start up a reactor without passing through a flammable range, to operate the reactor safely and economically, or to store or ship the product safely [3]. Flash points are available for most pure liquids, but the information for mixtures is very limited and is usually at ambient pressures. For mixtures of flammable liquids, or more importantly, liquid mixtures containing both flammable and nonflammable constituents, the precise level of risk is more difficult to predict. Mixtures of flammable and nonflammable constituents are especially significant because the vapor phase composition differs from the liquid composition, and it can change from nonflammable to flammable as the mixtures evaporates or its temperatures changes. Flammability limits obtained experimentally under conditions similar to those found in practice are most reliable for designing installations that are safe and assessing potential gas-explosion hazards. Predictive theoretical methods are needed to estimate the flash point of mixtures when experimental data are unavailable. Flash point determinations for mixtures generally are based on the Le Chatelier equation together with a vapor–liquid equilibrium model calculation of the vapor composition when liquids are involved. Most existing predictive methods are appli© 2004 American Institute of Chemical Engineers

A review of estimation methods for flash points and flammability limits

Direct partial oxidation of methane to synthesis gas on AFeO3 (A = La, Nd, Eu) oxides by a novel sequential redox cyclic reaction in the absence of gaseous oxygen was investigated over a fixed-bed reactor These oxides were prepared by the sol−gel method and characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques XRD analysis showed that all AFeO3 (A = La, Nd, Eu) oxides, calcined at 1173 K, are single-phase perovskites The CH4-TPSR/MS and continuous reaction experiments indicated that the AFeO3 (A = La, Nd, Eu) oxides provide mostly oxygen species, as the sole oxidant originated from lattice oxygen instead of gaseous oxygen, which can oxidize CH4 to synthesis gas with high selectivity in the absence of gaseous oxygen In terms of material economics and the amount of oxygen species for synthesis gas formation, the LaFeO3 sample exhibits the best performance among these tested AFeO3 oxides for synthesis gas production The pulse experiments at different temperatures

Unsteady-state direct partial oxidation of methane to synthesis gas in a fixed-bed reactor using AFeO3 (A = La, Nd, Eu) perovskite-type oxides as oxygen storage

The expense, danger, planning and precision required to create explosions suggests that the computational visual modelling of explosions is worthwhile. However, the short time scale at which explosions occur, and their sheer complexity, poses a difficult modelling challenge. After describing the basic phenomenology of explosion events, we present an efficient computational model of isotropic blast wave transport and an algorithm for fracturing objects in their wake. Our model is based on the notion of a blast curve that gives the force-loading profile of an explosive material on an object as a function of distance from the explosion’s centre. We also describe a technique for fracturing materials loaded by a blast. Our approach is based on the notion of rapid fracture: that microfractures in a material together with loading forces seed a fracturing process that quickly spreads across the material and causes it to fragment.

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A visual model for blast waves and fracture

Experimental study of the pressure and temperature dependence on the upper flammability limit of methane/air mixtures

Experimental study of the flammability limits of toluene-air mixtures at elevated pressure and temperature.

This paper deals with blast waves generated by a bursting spherical vessel filled with a pressurized gas. A large number of numerical simulations are performed. From the results of the simulations, a simple model comparable to the TNT-equivalent model is derived. The new blast wave model consists of a single relationship between the scaled peak overpressure and the scaled distance. Moreover, a closed-form expression for the explosion efficiency as function of the initial velocity only is provided.

B Vanderstraeten

Papers

Experimental study of the pressure and temperature dependence on the upper flammability limit of methane/air mixtures

Experimental study of the flammability limits of toluene-air mixtures at elevated pressure and temperature.

A simple blast wave model for bursting spheres based on numerical simulation

A simple blast wave model for bursting spheres based on numerical simulation

Flammability limits of methane/air mixtures at elevated pressure and temperature