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Explosion regions of propane, isopropanol, acetone, and methyl acetate/inert gas/air mixtures
(2016)
The explosion regions for propane, isopropanol, acetone, and methyl acetate with air in the presence of nitrogen, argon, helium, and carbon dioxide were determined experimentally according to EN 14756/EN1839, method T. Except for propane, all the measurements were executed at 323 K and 1 bar. Propane experiments were carried out at 293 K and 1 bar. The results show that for the same type of inert gas, propane, isopropanol, and acetone have great closeness concerning the concentration of the inert gas at the apex of the explosion envelope in a ternary diagram with air as oxidizer. This leads to consistency in the limiting oxygen concentration (LOC) and minimum required amount of inert gas (MAI) values. Concerning methyl acetate, the apex was always reached at higher percentages of inert gases compared with the other fuels. This can be attributed to the presence of two oxygen atoms inside the chemical structure. Calculation of the explosion regions was carried out based on calculated adiabatic flame temperature (CAFT) method. The flame temperatures for the experimentally determined fuel/air/N2 mixtures were calculated. Then, these temperatures were used to predict the explosion limits of similar mixtures with other inert gases than nitrogen. The modeling results show reasonable agreement with the experimental results.
In this presentation the results of the Project HySpark are shown. Mechanical impacts are among the important possible ignition sources to be considered in explosion protection. Hydrogen is particularly prone to be ignited by mechanical impacts compared to natural gas. The effectivity of mechanical impacts as ignition source is dependent from different parameters. In this work the effectivity of impacts as an ignition source for hydrogen containing atmospheres was studied experimentally depending on the inhomogeneous material pairing of the impact. Moreover it was studied, how the effectivity of mechanical impacts as ignition source changes when hydrogen is added to natural gas.
In this presentation the capabilities and different research activities at BAM in the field of hydrogen safety are outlined. A deep dive focussing the transport of hydrogen in pipelines adressing issues on material compatibility, gas quality and test methods is presented. Another deep dive is presented focussing on safety aspects of liquid hydrogen adressing issues of rapid phase transition (RPT) and Boiling liquid expanding vapour explosion (BLEVE). Finally a brief overview on other safety related research activities is given.
Mechanical friction, impact or abrasion is one of the ignition sources that must be avoided in hazardous zones with explosive atmospheres. The effectiveness of mechanical impacts as ignition source is dependent from several parameters including the minimum ignition energy of the explosive atmosphere, the properties of the material pairing, the kinetic impact energy or the impact velocity. By now there is no standard procedure to determine the effectiveness of mechanical impacts as ignition source. In this work the effectiveness of mechanical impacts with defined and reproducible kinetic impact energy as ignition source for hydrogen containing atmospheres was studied systematically in dependence from the inhomogeneous material pairing considering materials with practical relevance like stainless steel, low alloy steel, concrete, and non-iron-metals. It was found that ignition can be avoided, if non-iron metals are used in combination with different metallic materials, but in combination with concrete even the impact of non-iron-metals can be an effective ignition source if the kinetic impact energy is not further limited. Moreover, the consequence of hydrogen admixture to natural gas on the effectiveness of mechanical impacts as ignition source was studied. In many cases ignition of atmospheres containing natural gas by mechanical impacts is rather unlikely. No influence could be observed for admixtures up to 25% hydrogen and even more. The results are mainly relevant in the context of repurposing the natural gas grid or adding hydrogen to
the natural gas grid.
Safety characteristics for explosion protection of natural gas/hydrogen mixtures relevant in connection with the Power2Gas technology were studied in this work. Lower explosion limits (LEL) and upper explosion limits (UEL), limiting oxygen concentrations (LOC), maximum experimental safety gaps (MESG), maximum explosion pressures (pmax) and maximum rates of pressure rise (dp/dt)max were determined experimentally in dependence of the hydrogen fraction. Adding hydrogen did mainly effect the UEL, LOC, MESG and (dp/dt)max. The mixtures become more "critical" concerning the explosion hazards with increasing hydrogen fraction. However, the dependency of the safety characteristics from the hydrogen fraction is mainly not linear. Adding up to 10% hydrogen to natural gas had nearly no effect on the safety characteristics. More significant effects on the safety characteristics were observed at hydrogen fractions of more than 25%. For example the explosion group changes from IIA to IIB. Considering the huge explosion region and very high (dp/dt)max of hydrogen compared to natural gas, even adding 50% hydrogen to natural gas has a rather small effect on these characteristics. Furthermore pmax of hydrogen/natural-gas mixtures can be calculated with good accuracy assuming ideal adiabatic conditions. EL and LOC of natural gas/hydrogen mixtures in ternary systems with inert gas and air were calculated in dependence of the type of inert gas with the so called “model of constant adiabatic flame temperature profiles”.
The introduction of hydrogen as a safe energy carrier needs a robust knowledge base, tools for the design and safety assessment of hydrogen technologies built on it, and an internationally harmonized set of standards and regulations. Many of the innovative technologies imply hydrogen at high pressures and/or cryogenic temperatures, with which private users come into contact for the first time in distributed applications. In order to avoid over-conservative, expensive safety solutions, while at the same time demonstrating the usability and safety of hydrogen applications and maintaining acceptance for the technology, safety research must also keep pace with, or better yet anticipate, trends in technological development. Thus, this overview article describes not only the current state of knowledge and technology regarding hydrogen safety, but also its further development.
Chemically unstable gases - flammability of ethylene oxide mixtures in sterilization processes
(2008)
For the assessment of explosion hazards by industrial
sterilization processes with ethylene oxide (EO), the flammability
regions of 3-component systems EO/nitrogen/air, EO/carbon
dioxide/air and EO/water vapor/air were determined. The tests were
performed at temperatures of 20 °C and 100 °C and at pressures of
40 kPa and 100 kPa in accordance with the standard test method EN
1839-B.
The observed flammability regions are similar in shape and
typical for mixtures with ethylene oxide. According to the molecular
heat capacities the regions get larger with nitrogen and smaller with
carbon dioxide. They become larger with increasing pressure and
increasing temperature.
Using experimental data a semi-empirical model was created
that allows the calculation of flammability limits of process gases in
sterilization processes. Such process gases can consist of EO,
nitrogen, carbon dioxide, water vapor and air.
The model is based on the assumption that the adiabatic flame
temperatures along the boundary curves of a flammability region
have a certain temperature profile that is nearly independent of the
type of the inert gas. The adiabatic flame temperatures were
calculated by using the Gaseq Code.
Using a temperature profile calculated from only one
experimental system EO/inert gas/air it is possible to predict the
flammability limits of systems with other inert gases or of process
gases containing several inert gases.