Chemical Safety Database - Application for Explosion Limits of Biogases

Maria Molnarne and Volkmar Schröder. II. Chemical Safety Engineering, Federal Institute for Materials Research and Testing (BAM), D-12200, Berlin, Germany

The chemical safety database CHEMSAFE® contains safety characteristics for more than 3000 flammable substances and approximately 1000 mixtures of gases, liquids and dusts. The data is evaluated by experts of two Federal Institutes in Germany, BAM and PTB. The main advantage of CHEMSAFE® is that the data based on own tests of these institutes. The temperature and pressure influence on safety properties are also taken into account. Flammability limits are measured up to 400 °C and 10 MPa. In this paper an application of the database is shown for calculation of flammability limits of biogases. Biogas consists mainly of methane and carbon dioxide, with low levels of hydrogen sulfide and other gases. For the explosion protection in biogas plants, it is necessary to know the flammability limits of the process gases in the air. The composition of biogases from agricultural plants is varying very strongly, so that for each mixture composition the flammability limits should be determined experimentally. This is associated usually with considerable time and effort. A method is presented here which shows that the flammability limits of a biogas with known composition can be assessed with the help of two explosion diagrams, namely the diagrams of the systems methane-carbon dioxide-air (see Figure) and methane-water-air, measured by DIN EN 1839-T (former DIN 51649) at 20 °C and atmospheric pressure. In addition to the methane and carbon dioxide content of the biogas a portion of water vapor is included in the calculation method and the influence of oxygen content in the system is considered. Figure: Explosion region of methane-carbon dioxide-air mixtures (test: DIN 51649).