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The paper discusses a new method to approximate the sometimes missing apex point of the explosion limit curves of flammable substances with diluents in air. The base of the new method is to vary the frame points of the co-monotonic splines using de Casteljau algorithm. We show several examples for flammable/inert/oxidising gas containing systems selected by the program TRIANGLE where the method was applied. Due to the definition of the frame of splines it can be stated that the new method never restricts the explosion range around the apex and shifts the explosion limit curve into the direction of higher inert gas concentrations. This means that the new method can correct the highly cut down nose of the co-monotonic splines and gives a safer explosion range of these systems.
Biogas is an important source of renewable energy. It consists mainly of methane and carbon dioxide, with low levels of hydrogen sulphide and other gases. That means, that the toxicological aspects and the flammability of biogas has to be taken into account. A serious accident has happened just recently in a biogas production plant in Germany, accompanied with injuries and four totalities. The methane content of the different types of biogases varies from about 82 % till 40 % and the rest is mostly carbon dioxide with trace gases depending on the anaerobe digestion process. These plants must also be controlled to avoid pollution and the risk of explosion. The 1999/92/EC Directive (ATEX 137) addressed to employer. The employer of such plants needs to implement safety requirements, such as prevention of explosive atmospheres, avoiding ignition sources, etc. In addition he has to prepare an explosion protection document and carry out a hazard assessment. The basic information for these documents based on the safety characteristics of the produced gases. These data can be taken e. g. from the database CHEMSAFE® using explosion diagrams of methane/carbon dioxide/air mixtures. In the literature the biogas explosion limits often presented in a confusing way. In this presentation a simple method will be shown to get correct values by correlation of the explosion limits with the methane content of the biogas. While biogas production will be forecast with an acceleration of growth in the future, it is essential to clear this important safety problem.
The knowledge of the explosion limits of biogases in air is necessary to define explosion protection measures. Biogases from agricultural plants vary however in their composition, so that for each gas composition the explosion limits would have to be measured. Frequently the explosion limits of biogas are therefore referred in the safety-relevant literature only to the methane fraction of the gas mixture, without indicating this additionally. This leads to the fact that the explosion ranges for the total mixture consists of methane, carbon dioxide and further residual gases are falsely specified.
For this reason a simple method is presented in the following, which show, how the explosion limits of a biogas can be determined from its methane content using an explosion diagram of methane/carbon dioxide/air system. The explosion diagram was measured according to the German Standard DIN 51649-1.
The presented calculation method supplies however correct results only if the nitrogen fraction in the biogas does not exceed approx. 5 % by volume.
The paper discusses a new method to approximate the sometimes missing apex point of the explosion limit curves of flammable substances with diluents in air. The base of the new method is to vary the frame points of the co-monotonic Splines using the de Casteljau algorithm. We show several examples for flammable/inert/oxidizing gas containing systems - selected by the program TRIANGLE - where the method was applied. Due to the definition of the frame Splines it can be stated that the new method never restricts the explosion range around the apex and shifts the explosion limit curve into the direction of higher inert gas concentrations. This means that the new method can correct the highly "cut down nose" of the co-monotonic Splines and gives a more safer explosion range of these systems.
An important method to prevent fires and explosions is to avoid explosive fuel-air mixtures. For this purpose the exact knowledge of the explosion range is required as a function of the combustible, oxidizer and inert gas concentrations. Frequently triangular diagrams are used in order to display the explosion range of such three component gas mixtures. Beside the explosion limits and the explosion range other characteristics can be deduced from explosion diagrams. More than 200 of such explosion diagrams are available in the database CHEMSAFE®, included among others. The in-house version of the database is able to provide all characteristics of a chosen system by means of a TRIANGLE-software. Furthermore a recently published German data book contains 158 explosion diagrams. Many diagrams were measured according to the German DIN 51649 standard. Other systems are available for elevated initial pressures and temperatures. This paper describes how to use the TRIANGLE software for flammability diagrams and the meaning and use of derived characteristics (MOC, MXC, MAI) for explosion prevention. Furthermore a calculation method for the flammability of gas mixtures is shown using the MXC values.