Nex-Hys: minimum ignition temperature of hybrid mixtures

Abstract

Although the minimum ignition temperature is an important safety characteristic and of practical relevance in industrial processes, actually only standard operation procedures are available for pure substances and single-phase values. Nevertheless, combinations of substances or mixtures are used in industrial processes and up to now it is not possible to provide a standardised minimum ignition temperature and in consequence to design a process safely with regard to the substances used.In order to get minimum ignition temperatures for frequently used hybrid mixtures, first, the minimum ignition temperatures and ignition frequencies were determined in the modified Godbert-Greenwald furnace for two single phase solids and a liquid substance. Second, minimum ignition temperatures and ignition frequencies were determined for several combinations as hybrid mixture of dust and liquid.In parallel to the determination of ignition temperatures a new camera and computer system to differentiate ignition from non-ignition is developed. First results are promising that such a system could be much less operator depended.By a high number of repetitions to classify regions of ignition the base is laid to decide about a new procedure for a hybrid standard and updating existing ones, too. This is one of the necessary aims to be reached in the Nex-Hys project.A noticeable decrease of minimum ignition temperatures below the MIT of the pure solids was observed for the one hybrid mixture tested, yet. Furthermore more widely dispersed area of ignition is shown. In accordance to previously findings, the results demonstrate a strong relationship between likelihood of explosion and amount of added solvent. In consequence the hybrid mixture is characterized by a lower minimum ignition temperature than the single dust.