Combined effects of initial pressure and turbulence on explosions of hydrogen-enriched methane/air mixtures

Hydrogen-enrichment has been proposed as a useful method to overcome drawbacks (local flame extinction, combustion instabilities, lower power output, etc.) associated to turbulent premixed combustion of natural gas in both stationary and mobile systems. For the safe use of hydrogen-enriched hydrocarbon fuels, explosion data are needed.In this work, a comparative experimental study of the explosion behavior of stoichiometric hydrogen-enriched methane/air (with 10% of hydrogen molar content in the fuel) and pure methane/air mixtures is presented. Tests were carried out in a 5 l closed cylindrical vessel at different initial pressures (1, 3 and 6 bar), and starting from both quiescent and turbulent conditions.Results allow quantifying the combined effects of hydrogen substitution to methane, pressure and turbulence on maximum pressure, maximum rate of pressure rise, burning velocity and Markstein lengths.     

Explosion of solvent vapor in a ring partition of the floating roof

The relative importance of the vapor cloud explosion (VCE) hazard has grown in recent years. Many of large disasters were attributed to the VCE. This article introduced an explosion accident of solvent vapor in a ring partition of floating roof in detail. Source of explosive materials and ignition reason were analyzed, and the blast equivalency in ring partition was estimated in the specific conditions. The case would provide a reference for preventing the similar accident.     

Experimental and simulation studies on the influence of carbon monoxide on explosion characteristics of methane

In underground coal mining, methane explosions often can cause tremendous disasters. In the meantime, carbon monoxide (CO), generated during the process of coal oxidation, may appear in the air. Therefore, the explosion characteristics of the mixture of CH₄ and CO must be investigated to prevent gas explosion accidents in coal mines. We conducted experiments by using a 20-L nearly spherical gas explosion testing device. The software FLACS was used to simulate the explosion of the mixture of CH₄ and CO at various mixing concentrations, and the simulation results corresponded to experimental results. With the increase of CO concentration, both upper and lower explosive limits of CH₄ decreased. On the whole, the explosion characteristic parameters of CH₄ and the mixture are similar. When CH₄ concentration was below the stoichiometric concentration, the addition of CO could promote the intensity of gas explosion; oppositely, excessive CO would inhibit the gas explosion reaction. The inhibitory effects become more significant as the concentration of CH₄ increases.     

Flameless venting of dust explosion: Testing and modeling

Flameless venting is a sort of dual mitigation technique allowing, in principle, to vent a process vessel inside a building where people are working without transmitting a flame outside the protected vessel. Existing devices are an assembly of a vent panel and a metal filter so that the exploding cloud and the flame front is forced to go through the filter. Within the frame of ATEX Directive, those systems need to be certified. To do so a standard (NF EN 16009) has been issued describing which criteria need to be verified/measured. Among them, the “efficiency” factor as defined earlier for standard vents. This implies that flameless venting systems are basically considered as vents. But is it really so? This question is discussed on the basis of experimental results and some implications on the practical use and certification process are drawn. The practical experience of INERIS in testing such systems is presented in this paper. Schematically, with a flameless vent the pressure is discharged but not the flame so that combustion is proceeding to a much longer extent inside the vessel than with a classical vent so that the physics of the explosion is different. In particular it is shown that besides the problem of the unloading of the confined explosion, there is a highly complicated fluid mechanics problem of a fluid-particle flow passing through a porous media (the flameless device grids arrangement in the filter), which passing surface is progressively reduced. To characterize Flameless venting the problem can be addressed sequentially, considering separately the vent panel and the flameless mesh. A model is proposed to estimate the overall venting efficiency of the flameless vent. However, it does not address the flame quenching issue, which is a different problem of heat exchange between the devices and the evacuated burnt products.     

Insight into vented explosion mechanism and premixed flame dynamics in linked vessels: Influence of membrane thickness and blocking rate

To effectively prevent and mitigate explosion hazards and casualties, relief venting of flammable gas explosions has been applied in production processes in a broad variety of industries. This work conducted fully vented experiments to investigate the influence of venting membrane thickness, and partially vented experiments to investigate the influence of baffle blocking rate on the explosion characteristics of 9.5 vol% methane-air mixtures in linked vessels with a 0.5 m long vented duct. Results indicate that the membrane thickness and blocking rate for the two types of vented explosions significantly affected the explosion overpressure. The smaller the membrane thickness and blocking rate, the lower the explosion overpressure. Secondary explosions were observed in the vented duct through experiments and a weaker explosion flame appeared at a small blocking rate of 20%. With the further increase in the blocking rate, the flame became extremely weak, and no secondary explosions occurred. The overpressure evolution process at different positions in the explosion duct and secondary explosion phenomenon in the vented duct were investigated. This work could probably serve as an important reference for the selection of technical parameters of explosion venting in the practical industrial processes.     

Suppression of different functional group modified powders on 9.5% CH4-air explosion and molecular simulation mechanism

Thiol and urea functionalized montmorillonite powders were successfully prepared by silane coupling agent treatments in this work. The pyrolysis characteristics, surface functional groups, and distribution of particle size of untreated montmorillonite powders (Mt), the hydroxyl functionalized montmorillonite (O–Mt), the urea functionalized montmorillonite (N–Mt), and the thiol functionalized montmorillonite (S–Mt), which was derived from the previous research, were respectively characterized by utilizing the thermogravimetric differential scanning calorimetry, Fourier transform infrared spectroscopy, as well as the laser particle analyzer. The suppression effect of the S–Mt, O–Mt, Mt, and N–Mt on a 9.5% CH₄ explosion was tested in the duct system (5 L). The obtained results indicated that N–Mt and O–Mt exhibited a better explosion suppression effect than Mt and S–Mt at the same mass concentration. Additionally, the methane/air explosion suppression mechanism of these powders could be explained by molecular simulation results that indicated the negatively electrophilic potential regions exist on the surface of O–Mt and N–Mt. Moreover, NH₄∙、 NCO∙ and ∙OH radicals, which can interrupt explosive chain reactions, were easily generated by N–Mt and O–Mt.     

Investigation of an accidental explosion in a nitromethane rectification process

An explosion that occurred during a nitromethane rectification process is investigated. Experiments were performed in an effort to elucidate the cause of the explosion. All test samples analyzed, including reaction product, crude product, 99% pure product and raffinate, were collected from the accident site. Gas chromatography was used to analyze the components of the samples, thermal analysis determined the exothermic character of the samples and the sample evaporating experiment recorded the reaction phenomena occurring at low liquid level. Based on the experimental results, the excess heat released by the decomposition of overheated raffinate is pinpointed as the root cause of the explosion.     

Case study: T2 Laboratories explosion

A tragic explosion resulting from a runaway chemical reaction occurred at the T2 Laboratories, Inc. facility in December 2007. The U.S. Chemical Safety Board (CSB) completed an incident investigation of the T2 explosion, identifying the root cause as a failure to recognize the runaway reaction hazard associated with the chemical it was producing. Understanding the consequences of process upset conditions is critical to determine risk. This paper will focus on lessons learned from this incident including a comprehensive hazard assessment for reactive chemicals as well as proper collection and application of adiabatic calorimetry data to characterize the chemical reaction and determine appropriate mitigation strategies. Examples will be provided to establish safer operating conditions, implement safeguards and reduce the overall risk.     

Flammability estimation of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Ionic liquids (ILs) are known as room temperature molten salts, which are considered green replacement to traditional organic solvents. The fire hazards of traditional organic solvents mainly depend on the combustibility of their vapors, thus ILs are generally regarded as nonflammable owing to their low volatility. However, recent studies show that ILs may combust due to the potential hazards of thermal decomposition, indicating the issue of fire and explosion of ILs are eager to be evaluated during the applications. In this study, the fire and explosion hazards of IL 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₆mim][NTf₂]) are explored in different aspects. The traditional definition of the flammability for the common organic solvent is not thoroughly applicable to [C₆mim][NTf₂] due to the low volatility. Furthermore, the common definition of reactivity for traditional organic solvents also fails to apply, because the decomposition reaction is indeed an endothermic reaction. However, the auto-ignition of some decomposition products will result in fire and explosion hazards for [C₆mim][NTf₂]. Therefore the application of such data in safety purposes should be very careful.     

Application of Bayesian Regularization Artificial Neural Network in explosion risk analysis of fixed offshore platform

Computational Fluid Dynamics (CFD) is routinely used in Explosion Risk Analysis (ERA), as CFD-based ERA offers a good understanding of underlying physics accidental loads. Generally, simplifications were incorporated into CFD-based ERA to limit the number of simulations. Frozen Cloud Approach (FCA) is a frequently used simplification in the dispersion part of the CFD-based ERA procedure. However, its accuracy is questionable in the complex and congested environment such as offshore facility. Furthermore, in explosion part, some specific techniques, e.g. linear/double bin-interpolated techniques have been proposed while the corresponding accuracy is still unknown since the developers did not yet check their accuracy by considering the explosion computational data as the benchmark.This study presents a more accurate algorithm, namely Bayesian Regularization Artificial Neural Network (BRANN) and accordingly proposes the frameworks regarding BRANN-based models for the CFD-based ERA procedure. Firstly, the framework is proposed to develop the Transient-BRANN (TBRANN) model for transient dispersion study. In addition, the framework to determine the BRANN model for explosion study is developed. The proposed frameworks are explained by a case study of the fixed offshore platform. Consequently, this study confirms the more accuracy of the TBRANN model over FCA and the accuracy of BRANN model for CFD-based ERA.