Determination of explosion limits – Criterion for ignition under non-atmospheric conditions

• Published in: Journal of loss prevention in the process industries Vol. 36; pp. 562 - 568
• Main Authors: Tschirschwitz, Rico, Schröder, Volkmar, Brandes, Elisabeth, Krause, Ulrich
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.07.2015; Elsevier Science Ltd
• Subjects: Atmosphere; Explosion limits; Explosions; Ignition criterion; Non-atmospheric conditions; Pressure; Propagation; Standardization; Temperature; Non-atmospheric conditions; Ignition criterion; Explosion limits; Standardization
• ISSN: 0950-4230; 1873-3352
• DOI: 10.1016/j.jlp.2015.01.012

Many industrial processes are run at non-atmospheric conditions (elevated temperatures and pressures, other oxidizers than air). To judge whether and if yes to what extent explosive gas(vapor)/air mixtures will occur or may be generated during malfunction it is necessary to know the safety characteristic data at the respective conditions. Safety characteristic data like explosion limits, are depending on pressure, temperature and the oxidizer. Most of the determination methods are standardized for ambient conditions. In order to obtain determination methods for non-atmospheric conditions, particularly for higher initial pressures, reliable ignition criteria were investigated. Ignition tests at the explosion limits were carried out for mixtures of methane, propane, n-butane, n-hexane, hydrogen, ammonia and acetone in air at initial pressures up to 20 bar. The tests have been evaluated according to different ignition criteria: visual flame propagation, temperature and pressure rising. It could be shown that flame propagation and occasionally self-sustained combustion for several seconds occurred together with remarkable temperature rise, although the pressure rise was below 3%. The results showed that the combination of a pressure rise criterion of 2% and a temperature rise criterion of 100 K seems to be a suitable ignition criterion for the determination of explosion limits and limiting oxidizer concentration at higher initial pressures and elevated temperatures. The tests were carried out within the framework of a R&D project founded by the German Ministry of Economics and Technology. •Results are presented for an ignition criterion (LEL, UEL) at high initial pressure.•We conducted ignition tests (fuel/air-mixtures) in a windowed autoclave up to 20 bar.•We recorded explosion pressure, temperature and the flame propagation at LFL an UFL.•Four different criteria for ignition (visual, pressure threshold) have been compared.•Most reliable criterion for ignition: 2% pressure rise and 100 K temperature rise.