Préparation des mélanges charbon-eau: Effet de la nature du charbon et amélioration de la qualité des suspensions par action sur les propriétés des particules

Abstract

Since 1983, CERCHAR has been studying coal-water mixtures (CWM) with the objective of valorizing some waste and fine products from washing plants. It appeared through this study that the nature of coal is a decisive parameter in the formulation and preparation of coal-water suspensions. Indeed, in identical operatory conditions, the high-rank coals (bituminous and anthracite) give more concentrated suspensions than those realized from low-rank coals (lignite and high volatile bituminous). This difference in behaviour can be explained by properties related to rank such as ratio of oxygen/carbon (O/C), capacity of water absorption, state of surface and shape of particles. Diluted milling was the preparation mode used (50 to 55 wt.% of solids), followed by filtration and mixing with additives. With this procedure, the desired rheological properties were not obtained when using low-rank coals. Another procedure was devised in which the coal is wet milled in the presence of additives and at high coal concentration (about 70 wt.% of solids). The interest of this procedure is to simplify drastically the process flow sheet, but the control of the wet milling at a high concentration is much more difficult. CERCHAR succeeded in developing a two-stage, high-slurry concentration, wet-milling process allowing the preparation of better quality, high-concentration suspensions than those obtained from the classical procedure. This innovative process was patented. The quality improvement can be explained by the effect of this procedure on particle size distribution, state of surface and shape of particles.