Venting of deflagrations: hydrocarbon–air and hydrogen–air systems

A set of 34 experiments on vented hydrocarbon–air and hydrogen–air deflagrations in unobstructed enclosures of volume up to 4000 m³ was processed with use of the advanced lumped parameter approach. Reasonable compliance between calculated pressure–time curves and experimental pressure traces is demonstrated for different explosion conditions, including high, moderate, low and extremely low reduced overpressures in enclosures of different shape (L_max:L_min up to 6:1) with different type and position of the ignition source relative to the vent, for near-stoichiometric air mixtures of acetone, methane, natural gas and propane, as well as for lean and stoichiometric hydrogen–air mixtures. New data were obtained on flame stretch for vented deflagrations.The fundamental Le Chatelier–Brown principle analog for vented deflagrations has been considered in detail and its universality has been confirmed. The importance of this principle for explosion safety engineering has been emphasized and proved by examples.A correlation for prediction of the deflagration–outflow interaction number, χ/μ, on enclosure scale, Bradley number and vent release pressure is suggested for unobstructed enclosures and a wide range of explosion conditions. Fractal theory has been employed to verify the universality of the dependence revealed of the deflagration–outflow interaction number on enclosure scale.In spite of differences between the thermodynamic and kinetic parameters of hydrocarbon–air and hydrogen–air systems, they both obey the same general regularities for vented deflagrations, including the Le Chatelier–Brown principle analog and the correlation for deflagration–outflow interaction number.     

Numerical analysis of hydrogen deflagration mitigation by venting through a duct

This paper presents a model and simulation results for the mitigation of a hydrogen–air deflagration by venting through a duct. A large eddy simulation (LES) model, applied previously to study both closed-vessel, and open atmosphere hydrogen–air deflagrations, was developed further to model a hydrogen–air explosion vented through a duct. Sub-grid scale (SGS) flame wrinkling factors were introduced to model major phenomena which contribute to the increase of flame surface area in vented deflagrations. Simulations were conducted to validate the model against 20% hydrogen–air mixture deflagrations (vent diameters 25 and 45 cm) and 10% hydrogen–air mixture deflagration (vent diameter 25 cm). There was reasonable correlation between the simulations and the experimental data. The comparative importance of different physical phenomena contributing to the flame wrinkling is discussed.     

Unified correlations for vent sizing of enclosures at atmospheric and elevated pressures

Innovative vent sizing technology is presented for explosion safety design of equipment at atmospheric and elevated initial pressures. Unified correlations for vent sizing are suggested. They are modifications of previously reported correlations verified thoroughly for experimental data on vented gaseous deflagrations under different conditions but only at initial atmospheric pressure. Suggested correlations are based on experimental data on vented deflagrations of quiescent and turbulent propane–air mixtures at initial pressures up to 0.7 MPa. Typical values of turbulence factor and deflagration–outflow interaction number are obtained for experimental vented deflagrations at initial pressures higher than atmospheric.

“Blind” examination of new vent sizing technology on another set of experiments with methane–air and propane–air mixtures has shown that predictions by suggested vent sizing technology are better than by the NFPA 68 guide for “Venting of Deflagrations”.

In the development of recently reported results for initial atmospheric pressure it has been concluded that the innovative vent sizing technology is more reliable compared to the NFPA 68 guide at elevated initial pressures as well. Moreover it is crucial that the calculation procedure remains the same for arbitrary deflagration conditions.     

Modelling the mitigation of a hydrogen deflagration in a nuclear waste silo ullage with water fog

During the decommissioning of certain legacy nuclear waste storage plants it is possible that significant releases of hydrogen gas could occur. Such an event could result in the formation of a flammable mixture within the silo ullage and, hence, the potential risk of ignition and deflagration occurring, threatening the structural integrity of the silo. Very fine water mist fogs have been suggested as a possible method of mitigating the overpressure rise, should a hydrogen–air deflagration occur. In the work presented here, the FLACS CFD code has been used to predict the potential explosion overpressure reduction that might be achieved using water fog mitigation for a range of scenarios where a hydrogen–air mixture, of a pre-specified concentration (containing 800 L of hydrogen), uniformly fills a volume located in a model silo ullage space, and is ignited giving rise to a vented deflagration. The simulation results suggest that water fog could significantly reduce the peak explosion overpressure, in a silo ullage, for lower concentration hydrogen–air mixtures up to 20%, but would require very high fog densities to be achieved to mitigate 30% hydrogen–air mixtures.     

Experimental investigation of the complex deflagration phenomena of hybrid mixtures of activated carbon dust/hydrogen/air

This paper aims to develop quantitative insights based on measured deflagration parameters of hybrid mixtures of activated carbon (AC) dust and hydrogen (H₂) gas in air. The generated experimental evidence is used to reject the claim of the null hypothesis (H₀) that severity of deflagrations of H₂/air mixtures always bound the severity of deflagrations of heterogenous combustible mixtures of AC dust/H₂/air containing the same H₂ concentrations as in the H₂/air binaries. The core insights of this investigation show that the maximum deflagration pressure rise (ΔP_MAX) and maximum rate of pressure rise ((dP/dt)_MAX) of this hybrid mixture are greater than those corresponding to deflagrations of H₂/air mixtures for all the dust and H₂ concentrations being examined. The deflagration severity indices (K_St and ES) of the hybrid mixture containing 29 mol% H₂ are found to be greater than those of the H₂/air mixture containing 29 mol% H₂. Also, the minimum explosible concentration (MEC) of the hybrid mixture is lower than that of the AC dust in air only. The insights gained should lead to better realization of the severity of a postulated safety-significant accident scenario associated with on-board cryoadsorption H₂ storage systems for fuel-cell (FC) powered light-duty vehicles. The identified insights could also be relevant to other industrial processes where combustible dusts are generated in the vicinity of solvent vapors. Moreover, these insights should be useful for supporting quantitative risk assessment (QRA) of on-board H₂ storage systems, designing improved safety measures for cryoadsorption H₂ storage tanks, and guiding H₂ safety standards and transportation regulations.     

Effects of hydrogen addition on the confined and vented explosion behavior of methane in air

Multi-component gas mixture explosion accidents occur and recur frequently, while the safety issues of multi-component gas mixture explosion for hydrogen–methane mixtures have rarely been addressed.Numerical simulation study on the confined and vented explosion characteristics of methane-hydrogen mixture in stoichiometric air was conducted both in the 5 L vessel and the 64 m³ chamber, involving different mixture compositions and initial pressures. Based on the results and analysis, it is shown that the addition of hydrogen has a negative effect on the explosion pressure of methane-hydrogen mixture at adiabatic condition. While in the vented explosion, the addition of the hydrogen has a significant positive effect on the explosion hazard degree. Additionally, the addition of hydrogen can induce a faster reactivity and enhance the sensitivity of the mixture by reducing the explosion time and increasing the rate of pressure rise both in confined and vented explosion. Both the maximum pressure and the maximum rate of pressure rise increase with initial pressure as a linear function, and also rise with the increase of hydrogen content in fuel. The increase in the maximum rate of pressure rise is slight when hydrogen ratio is lower than 0.5, however, it become significant when hydrogen ratio is higher than 0.5. The maximum rate of pressure rise for stoichiometric hydrogen-air is about 10 times the one of stoichiometric methane-air.Furthermore, the vent plays an important role to relief pressure, causing the decrease in explosion pressure and rate of pressure rise, while it can greatly enhance the flame speed, which will extend the hazard range and induce secondary fire damages. Additionally it appears that the addition of hydrogen has a significant increasing effect on the flame speed. The propagation of flame speed in confined explosion can be divided into two stages, increase stage and decrease stage, higher hydrogen content, higher slope. But in the vented explosion, the flame speed keeps increasing with the distance from the ignition point.     

Experimental study on vented deflagration of hydrocarbon fuel-air mixtures in a 20-L semi-confined cylindrical vessel with a slight static activation pressure

The overpressure peaks and flame propagation characteristics of hydrocarbon fuel-air mixtures vented deflagration in a 20-L cylindrical vessel with a slight static activation overpressure (P_ST = 2.5 kPa) and five vent opening ratio were studied by a series of experiments. The experiments focused on the effect of vent opening ratio on the overpressure peaks and flame propagation characteristics of hydrocarbon fuel-air mixture vented deflagration. The internal overpressure-time profiles and high-speed photographs of flame propagation processes were obtained. The results showed that three overpressure peaks were distinguished in the internal overpressure-time profiles, caused by the burst vent cover (p_burst), the acceleration of burnt gas (p_fv), and the fierce external deflagration of vented unburned fuel (p_ext), respectively. The changing of the vent opening ratio had almost no effect on the value of p_burst and (dp_burst/dt). With increasing vent opening ratio, the values of p_fv, p_ext, (dp_fv/dt) and (dp_ext/dt) showed a decreasing trend while the values of p_burst and (dp_burst/dt) were nearly constant. The flame presented a hemispherical shape before the vent cover ruptured then developed as a mushroom shape after accelerated to external field. There were three flame speed peaks during flame propagation process, resulted from venting flow acceleration, external deflagration, and axial heat flux formed by internal combustion. With the increase of vent opening ratio, all of the maximum flame speed, external average flame speed, maximum flame distance and external flame duration showed a downward trend, excepting for the internal average flame speed almost remained constant.     

The nature and large eddy simulation of coherent deflagrations in a vented enclosure-atmosphere system

The nature of coherent deflagration phenomena in a vented enclosure-atmosphere system is analysed. The study is based on experimental observations of SOLVEX programme in the empty 547-m³ vented enclosure and consequent analysis of the same test by large eddy simulations (LES). A comparison between simulated and experimental pressure transients and dynamics of flame front propagation inside and outside the enclosure gave an insight into the nature of the complex simultaneous interactions between flow, turbulence and combustion inside the enclosure and in the atmosphere. It is revealed through LES processing of experimental data that the substantial intensification of premixed combustion occurs only outside the empty SOLVEX enclosure and this leads to steep coherent pressure rise in both internal and external deflagrations. The external explosion does not affect burning rate inside the enclosure. There is only one ad hoc parameter in the LES model, which is used to account for unresolved subgrid scale increase of flame surface density outside the enclosure. The model allows reaching an excellent match between theory and experiment for coherent deflagrations in the empty SOLVEX facility. The mechanism of combustion intensification in the atmosphere is discussed and the quantitative estimation of the model ad hoc parameter is given.     

Effect of ignition position on vented hydrogen–air deflagration in a 1 m3 vessel

This study investigates the effect of the ignition position on vented hydrogen-air deflagration in a 1 m³ vessel and evaluates the performance of the commercial computational fluid dynamics (CFD) code FLACS in simulating the vented explosion of hydrogen-air mixtures. First, the differences in the measured pressure-time histories for various ignition locations are presented, and the mechanisms responsible for the generation of different pressure peaks are explained, along with the flame behavior. Secondly, the CFD software FLACS is assessed against the experimental data. The characteristic phenomena of vented explosion are observed for hydrogen-air mixtures ignited at different ignition positions, such as Helmholtz oscillation for front ignition, the interaction between external explosion and combustion inside the vessel for central ignition, and the wall effect for back-wall ignition. Flame-acoustic interaction are observed in all cases, particularly in those of front ignition and very lean hydrogen-air mixtures. The predicted flame behavior agree well with the experimental data in general while the simulated maximum overpressures are larger than the experimental values by a factor of 1.5–2, which is conservative then would lead to a safe design of explosion panels for instance. Not only the flame development during the deflagration was well-simulated for the different ignition locations, but also the correspondence between the pressure transients and flame behavior was also accurately calculated. The comparison of the predicted results with the experimental data shows the performance of FLACS to model vented mixtures of hydrogen with air ignited in a lab scale vessel. However, the experimental scale is often smaller than that used in practical scenarios, such as hydrogen refueling installations. Thus, future large-scale experiments are necessary to assess the performance of FLACS in practical use.     

Application of the TNO multi-energy and Baker-Strehlow-Tang methods to predict hydrogen explosion effects from small-scale experiments

Analytical models or abacus are of importance to predict explosion effects in open and congested areas for industrial safety reasons. The goal of this work is to compare overpressure and flame speed values of small-scale deflagration experiments to predicted values from the TNO multi-energy (TNO ME) method and the Baker-Strehlow-Tang (BST) method. Experiments were performed in cylindrical congested volumes of hydrogen – air mixtures varying from 1.77 L to 7.07 L. The reactivity was controlled by the equivalence ratio of hydrogen-air mixtures, ranging from 0.5 to 2.5. The congestion was realized with varying numbers of grid layers and configurations. The influence of the obstacle density and the importance of the mixture reactivity to choose the strength index in order to predict the effects of an explosion has been highlighted for the TNO ME method. Predictive flame speed values from the BST method are in accordance with almost half of the experimental results and the method is conservative in most tested configurations. The use of the TNO ME method has been validated on a small-scale experiment to predict maximal overpressures generated by the deflagration of medium and large-scale H₂/air clouds.     

Suppression of metal dust deflagrations

Dust explosions continue to pose a serious threat to the process industries handling combustible powders. According to a review carried out by the Chemical Safety Board (CSB) in 2006, 281 dust explosions were reported between 1980 and 2005 in the USA, killing 119 workers and injuring 718. Metal dusts were involved in 20% of these incidents. Metal dust deflagrations have also been regularly reported in Europe, China and Japan.The term “metal dusts” encompasses a large family of materials with diverse ignitability and explosibility properties. Compared to organic fuels, metal dusts such as aluminum or magnesium exhibit higher flame temperature (T_f), maximum explosion pressure (P_max), deflagration index (K_St), and flame speed (S_f), making mitigation more challenging. However, technological advances have increased the efficiency of active explosion protection systems drastically, so the mitigation of metal dust deflagrations has now become possible.This paper provides an overview of metal dust deflagration suppression tests. Recent experiments performed in a 4.4 m³ vessel have shown that aluminum dust deflagrations can be effectively suppressed at a large scale. It further demonstrates that metal dust deflagrations can be managed safely if the hazard is well understood.     

Experimental study on vented gas explosion in a cylindrical vessel with a vent duct

A study of vented explosions in a length over diameter (L/D) of 2 in cylindrical vessel connecting with a vent duct (L/D = 7) is reported. The influence of vent burst pressure and ignition locations on the maximum overpressure and flame speeds at constant vent coefficient, K of 16.4 were investigated to elucidate how these parameters affect the severity of a vented explosion. Propane and methane/air mixtures were studied with equivalence ratio, Φ ranges from 0.8 to 1.6. It is demonstrated that end ignition exhibited higher maximum overpressures and flame speeds in comparison to central ignition, contrary to what is reported in literature. There was a large acceleration of the flame toward the duct due to the development of cellular flames and end ignition demonstrated to have higher flame speeds prior to entry into the vent due to the larger flame distance. The higher vent flow velocities and subsequent flame speeds were responsible for the higher overpressures obtained. Rich mixtures for propane/air mixtures at Φ = 1.35 had the greatest flame acceleration and the highest overpressures. In addition, the results showed that Bartknecht's gas explosion venting correlation is grossly overestimated the overpressure for K = 16.4 and thus, misleading the impact of the vent burst pressure.     

Propane-air mixture deflagration hazard with different ignition positions and restraints in large-scale venting chamber

In order to better assess the hazards of explosion accidents, propane-air mixture deflagrations were conducted in a large-scale straight rectangular chamber (with a cross-section of 1.5 m × 1.5 m, length of 10 m, and total volume of 22.5 m³). The effect of initial volume, ignition position, and initial restraints on the explosion characteristics of the propane-air mixtures was investigated. The explosion overpressure, flame propagation, and flame speed were obtained and the computational fluid dynamics (CFD) software was used to simulate the flame-propagation process and field flow for auxiliary analysis. The hazards of large-scale propagation explosion under weak and strong constraints were evaluated and the different phases of flame propagation under weak and strong constraints were discriminated. Results indicate that the hazards caused by propane deflagration under weak constraint are mainly caused by flame spread. And the maximum overpressure under strong constraint appeared at the front part of the chamber under the large-scale condition, which is consistent with the previous small-scale test. Moreover, the simulations of flame structures under weak and strong constraint are in good agreement with experimental results, which furthers the understanding of large-scale propane deflagration under different initial conditions in large-scale spaces and provides basic data for three-dimensional CFD model improvement.     

Scaling of dust explosion violence from laboratory scale to full industrial scale – A challenging case history from the past

The standardized K_St parameter still seems to be widely used as a universal criterion for ranking explosion violence to be expected from various dusts in given industrial situations. However, this may not be a generally valid approach. In the case of dust explosion venting, the maximum pressure P_max generated in a given vented industrial enclosure is not only influenced by inherent dust parameters (dust chemistry including moisture, and sizes and shapes of individual dust particles). Process-related parameters (degree of dust dispersion, cloud turbulence, and dust concentration) also play key roles. This view seems to be confirmed by some results from a series of large scale vented dust explosion experiments in a 500 m³ silo conducted in Norway by CMI, (now GexCon AS) during 1980–1982. Therefore, these results have been brought forward again in the present paper. The original purpose of the 500 m³ silo experiments was to obtain correlations between P_max in the vented silo and the vent area in the silo top surface, for two different dusts, viz. a wheat grain dust collected in a Norwegian grain import silo facility, and a soya meal used for production of fish farming food. Both dusts were tested in the standard 20-L-sphere in two independent laboratories, and also in the Hartmann bomb in two independent laboratories. P_max and (dP/dt)_max were significantly lower for the soya meal than for the wheat grain dust in all laboratory tests. Because the available amount of wheat grain dust was much larger than the quite limited amount of available soya meal, a complete series of 16 vented silo experiments was first performed with the wheat grain dust, starting with the largest vent area and ending with the smallest one. Then, to avoid unnecessary laborious changes of vent areas, the first experiment with soya dust was performed with the smallest area. The dust cloud in the silo was produced in exactly the same way as with the wheat grain dust. However, contrary to expectations based on the laboratory-scale tests, the soya meal exploded more violently in the large silo than the wheat grain dust, and the silo was blown apart in the very first experiment with this material. The probable reason is that the two dusts responded differently to the dust cloud formation process in the silo on the one hand and in the laboratory-scale apparatuses on the other. This re-confirms that a differentiated philosophy for design of dust explosion vents is indeed needed. Appropriate attention must be paid to the influence of the actual dust cloud generation process on the required vent area. The location and type of the ignition source also play important roles. It may seem that tailored design has to become the future solution for tackling this complex reality, not least for large storage silos. It is the view of the present author that the ongoing development of CFD-based computer codes offers the most promising line of attack. This also applies to design of systems for dust explosion isolation and suppression.     

Laminar burning velocities of hydrogen–air mixtures from closed vessel gas explosions

The laminar burning velocity of hydrogen–air mixtures was determined from pressure variations in a windowless explosion vessel. Initially, quiescent hydrogen–air mixtures of an equivalence ratio of 0.5–3.0 were ignited to deflagration in a 169 ml cylindrical vessel at initial conditions of 1 bar and 293 K. The behavior of the pressure was measured as a function of time and this information was subsequently exploited by fitting an integral balance model to it. The resulting laminar burning velocities are seen to fall within the band of experimental data reported by previous researchers and to be close to values computed with a detailed kinetics model. With mixtures of an equivalence ratio larger than 0.75, it was observed that more advanced methods that take flame stretch effects into account have no significant advantage over the methodology followed in the present work. At an equivalence ratio of less than 0.75, the laminar burning velocity obtained by the latter was found to be higher than that produced by the former, but at the same time close enough to the unstretched laminar burning velocity to be considered as an acceptable conservative estimate for purposes related to fire and explosion safety. It was furthermore observed that the experimental pressure–time curves of deflagrating hydrogen–air mixtures contained pressure oscillations of a magnitude in the order of 0.25 bar. This phenomenon is explained by considering the velocity of the burnt mixture induced by the expansion of combusting fluid layers adjacent to the wall.     

The effect of vent size and concentration in vented gasoline-air explosions

Experimental data from vented explosion tests using gasoline-air mixtures with concentrations from 0.88 to 2.41% vol. are presented. A 2L vessel was used for the tests with vent sizes of 25 cm², 50 cm² and 100 cm². The tests were focused on the effect of gasoline vapor concentration and vent size on the pressure development and the flame behavior inside and outside the vessel. It was found that the inner flame propagation speed was mainly dependent on the initial concentration, while the maximum flame spreading distance was mainly influenced by the vent size. The external flame speed and duration could be influenced by the combination of the two properties. The internal pressure increases gradually with the flame propagated inside the vessel and decreased sharply when the vent failed. High-pressure durations containing pressure peaks were recorded by transducers in front of the vent and oscillations could be observed besides the vent. At any measure point, the maximum external pressures for A = 25 cm² or 50 cm² were significantly larger than those for A = 100 cm².     

Experimental investigation of hydrogen–air deflagrations and detonations in semi-confined flat layers

This paper presents results of an experimental investigation on the deflagration and deflagration-to-detonation transition (DDT) in an obstructed (blockage ratio BR = 50%), semi-confined flat layer filled with uniform hydrogen–air mixtures. The effect of mixture reactivity depending on flat layer thickness and its width is studied to evaluate the critical conditions for sonic flame propagation and the possibility for detonation onset. The experiments were performed in a transparent, rectangular channel with a length of 2.5 m. The flat layer thickness was varied from 0.06 to 0.24 m and the experiments were performed for different channel widths of 0.3, 0.6 and 0.9 m. The experimental results show flame velocity vs. hydrogen concentration for different thicknesses and widths of the semi-confined flat layer. Three different flame propagation regimes were observed: slow subsonic flame (M << 1), sonic deflagration (M ～ 1) and detonation (M >> 1). It is shown that flame acceleration (FA) to sonic speed is independent of the width of the flat layer. The critical expansion ratio for effective flame acceleration to sonic speed was found to be linearly dependent on the reciprocal layer thickness.     

Hybrid H2/Al dust explosions in Siwek sphere

Explosion indices and explosion behaviour of Al dust/H₂/air mixtures were studied using standard 20 l sphere. The study was motivated by an explosion hazard occurring at some accidental scenarios considered now in ITER design (International Thermonuclear Experimental Reactor). During Loss-of-Vacuum or Loss-of-Coolant Accidents (LOCA/LOVA) it is possible to form inside the ITER vacuum vessel an explosible atmosphere containing fine Be or W dusts and hydrogen. To approach the Be/H₂ explosion problem, Be dust is substituted in this study by aluminium, because of high toxicity of Be dusts. The tested dust concentrations were 100, 200, 400, 800, and 1200 g/m3; hydrogen concentrations varied from 8 to 20 vol. % with 2% step. The mixtures were ignited by a weak electric spark. Pressure evolutions were recorded during the mixture explosions. In addition, the gaseous compositions of the combustion products were measured by a quadruple mass-spectrometer. The dust was involved in the explosion process at all hydrogen and dust concentrations even at the combination ‘8%/100 g/m3’. In all the other tests the explosion overpressures and the pressure rise rates were noticeably higher than those relevant to pure H₂/air mixtures and pure Al dust/air mixtures. At lower hybrid fuel concentrations the mixture exploded in two steps: first hydrogen explosion followed by a clearly separated Al dust explosion. With rising concentrations, the two-phase explosion regime transits to a single-phase regime where the two fuel components exploded together as a single fuel. In this regime both the hybrid explosion pressures and pressure rise rates are higher than either H₂ or Al ones. The two fuels compete for the oxygen; the higher the dust concentration, the more part of O2 it consumes (and the more H₂ remains in the combustion products). The test results are used to support DUST3D CFD code developed at KIT to model LOCA or LOVA scenarios in ITER.     

The effect of vent size and congestion in large-scale vented natural gas/air explosions

A typical building consists of a number of rooms; often with windows of different size and failure pressure and obstructions in the form of furniture and décor, separated by partition walls with interconnecting doorways. Consequently, the maximum pressure developed in a gas explosion would be dependent upon the individual characteristics of the building. In this research, a large-scale experimental programme has been undertaken at the DNV GL Spadeadam Test Site to determine the effects of vent size and congestion on vented gas explosions. Thirty-eight stoichiometric natural gas/air explosions were carried out in a 182 m³ explosion chamber of L/D = 2 and K_A = 1, 2, 4 and 9. Congestion was varied by placing a number of 180 mm diameter polyethylene pipes within the explosion chamber, providing a volume congestion between 0 and 5% and cross-sectional area blockages ranging between 0 and 40%. The series of tests produced peak explosion overpressures of between 70 mbar and 3.7 bar with corresponding maximum flame speeds in the range 35–395 m/s at a distance of 7 m from the ignition point. The experiments demonstrated that it is possible to generate overpressures greater than 200 mbar with volume blockages of as little as 0.57%, if there is not sufficient outflow through the inadvertent venting process. The size and failure pressure of potential vent openings, and the degree of congestion within a building, are key factors in whether or not a building will sustain structural damage following a gas explosion. Given that the average volume blockage in a room in a UK inhabited building is in the order of 17%, it is clear that without the use of large windows of low failure pressure, buildings will continue to be susceptible to significant structural damage during an accidental gas explosion.     

Explosion parameters of wood chip-derived syngas in air

The wood gasification process poses serious concerns about the risk of explosion. The design of prevention and mitigation measures requires the knowledge of safety parameters, such as the maximum explosion pressure, the maximum rate of pressure rise and the gas deflagration index, K_G, at standard ambient temperature (25 °C) and pressure (1 bar) conditions. However, the analysis at specific process conditions is strongly recommended, as the explosion behavior of gas mixtures may be completely different.In the work presented in this paper, the explosion behavior of mixtures with composition representative of wood chip-derived syngas (CO/H₂/CH₄/CO₂/N₂ mixtures with and without H₂O) was experimentally studied in a closed combustion chamber. Experiments were run at two temperatures, 300 °C and 10 °C, and at atmospheric pressure. Test conditions were requested by the safety engineering designer of an existing industrial-scale wood gasification plant. In order to identify the specific fuel–air ratios to be analyzed, thus reducing the number of experimental tests, a preliminary thermo-kinetic study was performed.Results have shown that the mixtures investigated can be classified as low-reactivity mixtures, the higher value of K_G found (∼36 bar m/s) being much lower than the K_G value of methane (55 bar m/s @ 25 °C).