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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.
The explosion regions of 1-propanol, 2-propanol, acetone and 1-butanol in air were measured in the presence of CO2, He, N2 and Ar in accordance with EN1839 method T at high temperatures and at atmospheric pressure. The experimental results show that 1-propanol, 2-propanol and acetone have very similar lower explosion limits (LELs). 1-Butanol shows a slightly wider explosion area near the LEL line. In addition, the explosion regions of all combustible/inert gas/air mixtures were calculated with the method of constant adiabatic flame temperature profiles (CAFTP), using the flame temperature profile along the explosion region boundary curve of each combustible/N2/air mixture as a reference to determine the explosion regions of combustible/inert gas/air mixtures with inert gases other than N2 at different initial temperatures. To calculate the explosion regions for systems containing He, the calculation method was modified to include the very different physical transport properties of He. Moreover, the procedure for calculating the apexes in the ternary explosion diagrams was modified. The calculation results show good agreement with the experimental results.
In this study, experimental determination and modelling investigations for the explosion regions of 1,3-dioxolane/inert gas/N2O and 1,3-dioxolane/inert gas/air mixtures were carried out and compared. The experimental measurements were carried out at 338 K and atmospheric pressure according to EN1839 method T using the inert gases N2, CO2, He and Ar. The results showed that the ratio of the lower explosion limit in N2O (LELN2O) to the lower explosion limit in air (LELair) is 0.52 and the ratio of the maximum oxygen content in air (MOCair) to the limiting oxidizer fraction in nitrous oxide (LOFN2O) is 0.36 ± 0.02 independent of the inert gas. When comparing the inert gas amount at the apex based on the pure oxidizing component, which is O2 in case of air, N2O-containing mixtures need less inert gas to reach the limiting oxidizer quantity whereas the efficiency of inert gases is in the same order. The coefficients of nitrogen equivalency however were found to differ to some extent. The explosion regions of 1,3-dioxolane/inert gas/oxidizer mixtures were modelled using the calculated adiabatic flame temperature profile (CAFTP) method as well as corrected adiabatic flame temperatures. The results indicate good agreement with experimental data for CO2, N2 and Ar- containing mixtures. The noticeable deviations that occur when He is the inert gas are due to the lacking transport data of that mixture.
In Gasphasen aus Ethylenoxid (EO) und Propylenoxid (PO), die bei technischen Alkoxylierungsreaktionen vorkommen, können auch ohne den Zutritt von Luft Zerfallsreaktionen stattfinden, die explosionsartig mit einer vielfachen Temperatur- und Drucksteigerung verlaufen. Zur Abschätzung der Auswirkungen solcher Explosionen wurden die Explosionsdrücke und die zeitlichen Druckanstiege von reinem EO und EO/PO-Gemischen bei Temperaturen von 100°C bis 200°C und Drücken von 1 - 10 bar in einem 3-dm³-Behälter und punktuell in einem 100-dm³-Behälter experimentell bestimmt.
The EU F-Gas Regulation grants exceptions from the GWP-related placing on the market prohibition for stationary refrigeration equipment for applications below -50 °C. Nonetheless, non-flammable refrigerants, which can be used for that temperature range, become increasingly expensive and rare inside the EU due to the phase down of HFCs under the regulation. Flammable alternatives based on methane, ethane and ethylene are available, but are not viable for all applications due to their flammability. Carbon dioxide cannot be used for applications below -50 °C due to CO 2 ’s triple point at -56 °C. Nitrous oxide with a triple point at -92 °C seems to be an alternative. However, possible exothermal decomposition of N 2 O calls for additional measures in order to be able to operate such systems safely. Two low-temperature systems have been developed, built and successfully operated at evaporation temperatures down to - 80 °C with mixtures of N 2 O and CO 2 and different lubricants at ILK and Karlsruhe University of Applied Sciences. The units achieved similar energy efficiency as the standard HFC-equipment used for freeze drying. Possible decomposition of N 2 O could successfully be supressed by various measures.
Für die sicherheitstechnische Beurteilung von Sterilisationsprozessen wurden die Explosionsgrenzen von Gasgemischen aus Ethylenoxid, Inertgas und Luft experimentell bestimmt. Die Messungen sind mit Stickstoff, Kohlenstoffdioxid und Wasserdampf bei 20 und 100 °C sowie bei 0,4 und 1,0 bar durchgeführt worden. Mit Hilfe der Daten wurde ein halbempirisches Modell entwickelt, mit dem die Explosionsfähigkeit von Prozessgasgemischen berechnet werden kann.
Es wurde ein Verfahren zur Berechnung von Explosionsgrenzen ethylenoxidhaltiger Gasphasen in Sterilisatoren entwickelt. Mit Hilfe der Software GasEq® und des neu entwickelten Makros SterEx für MS-Excel® lassen sich die Explosionsgrenzen für Gemische aus Ethylenoxid, Luft und Inertgasen bei Temperaturen zwischen 20°C und 100°C sowie 0,4 bar und 1,0 bar berechnen. Somit ist es schnell möglich, sichere Betriebsbedingungen für Sterilisationsprozesse mit Ethylenoxid festzulegen. Das halbempirische Modell basiert auf der Annahme konstanter Flammentemperaturprofile an den Explosionsgrenzen in Abhängigkeit der EO-Konzentration für verschiedene Gemische. Durch systematische Zündversuche wurden Explosionsgrenzen für Gemische aus Ethylenoxid, Stickstoff, Kohlenstoffdioxid, Wasserdampf und Luft zur Bestimmung von Modellparametern und zur Validierung des Verfahrens bestimmt. Um die Prozessbedingungen in Sterilisatoren möglichst genau zu simulieren, wurden die Versuche in einem geschlossenen Autoklav in Anlehnung an DIN EN 1839-B durchgeführt. Berechnungen der Explosionsgrenzen von Prozessgasgemischen mit SterEx ergeben eine gute Übereinstimmung mit experimentell ermittelten Werten.
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A calculation method for flammability limits of gas phases with ethylene oxide in sterilisers was developed. Using the Software GasEq® and the newly developed Makro SterEx for MS-Excel®, flammability limits of mixtures with ethylene oxide, air and inert gases at temperatures between 20°C and 100°C and pressures between 0.4 bar and 1.0 bar can be calculated. This method can be used to easily determine safe operating conditions. The used semi-empirical model is based upon the assumption of constant flame temperature profiles at the flammability limits subject to the EO-concentration for different mixtures. To collect model parameters and to validate the model, several experiments with mixtures of ethylene oxide, nitrogen, carbon dioxide, water vapour and air were carried out to determine flammability limits. To simulate the structural conditions of sterilisers, the experiments were conducted in accordance to DIN EN 1839-B in a closed autoclave with temperatures and pressures relevant for sterilisation processes. The calculation of flammability limits of process gas mixtures with SterEx provides good agreement with flammability limits that were determined in experiments.
For evaluation of explosion scenarios in closed systems involving the mildly flammable refrigerants R1234yf, R1234ze and R32 dependent on the ignition energy, ignitions were carried out in a closed autoclave. A newly developed ignition system was used, which allows generating electric arcs with defined energies in a range between 3 J and 1000 J. The lower explosion limit of R32 decreases with increasing ignition energy. R32-explosions can be more severe than explosions involving highly flammable substances.
However, in case of R1234yf and R1234ze, the ignition energy had to be increased to more than 100 J and more than 500 J to detect explosions in the closed system at all, although flame Propagation phenomena can already be observed if these substances are ignited with much weaker ignition sources in open glass tubes. The explosions were very mild with these substances.
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”.
Die Einführung von Wasserstoff als sicherer Energieträger braucht eine robuste Wissensbasis, darauf aufgebaute Werkzeuge zur Auslegung und Sicherheitsbewertung von Wasserstofftechnologien und ein international harmonisiertes Regelwerk. Viele der innovativen Technologien implizieren Wasserstoff bei hohen Drücken und/oder kryogenen Temperaturen, mit denen in verteilten Anwendungen erstmalig private Nutzer in Kontakt kommen. Um überkonservative, teure Sicherheitslösungen zu vermeiden, gleichzeitig aber die Einsetzbarkeit und Sicherheit von Wasserstoffanwendungen zu demonstrieren und die Akzeptanz für die Technologie aufrecht zu halten, muss auch die Sicherheitsforschung mit den Trends der technologischen Entwicklung Schritt halten, oder sie besser noch antizipieren. So beschreibt dieser Überblicksartikel nicht nur den gegenwärtigen Stand der Kenntnisse und Technik bezüglich Wasserstoffsicherheit, sondern auch ihre Weiterentwicklung.