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- Explosionsgrenzen (3)
- Sicherheitstechnik (3)
- Sterilisation (3)
- Ethylenoxid (2)
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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.
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.
In order to prevent incidents in the
industrial production of Teflon® from
Tetrafluoroethylene (TFE), the safety related
aspects of the self-heating process of TFE must
be taken into account. Simulations of this self
heating process were performed with COMSOL
Reaction Engineering Lab® and COMSOL®
COMSOL Multiphysics®. A complex reaction
net was employed, resulting in a model allows
for a good agreement with experimentally
achieved results.