Development and use of an apparatus to measure the dynamic surface properties of coal-water slurry fuels for applications to atomization characteristics. Final report, September 1, 1992--December 31, 1993

Abstract

Experiments were conducted to measure the dynamic surface tension of coal-water slurry (CWS) mixtures containing various types of surfactants and with varied coal loadings. The dynamic properties will affect CWS fuel atomization, which constitutes highly dynamic processes. A maximum air bubble pressure technique measured the dynamic surface tension. The dynamic surface tension, which can be much higher than the corresponding static surface tension, was measured for the CWS made from the coal mined from the Upper Elkhorn seam in Virginia. The coal had 50 {mu}m volume mean diameter (VMD). Five surfactants were selected for the study: one nonionic Alkylphenol Ethoxylate (NP-100), and four anionic surfactants; Branched Dodecylbenzene Sulfonic Acid (DDBS-hard), Linear Dodecylbenzene Sulfonic Acid (DDBS-soft), a Sodium Salt of a Branched Alkylbenzene Sulfonic Acid (1223H), and a Sodium Salt of Sulfonated Fatty Acid (1840X). A du-Nouy ring tensiometer measured the static surface tension to determine the critical micelle concentration (CMC). Measured values of dynamic surface tension are presented for 40% and 50% CWS mixtures with surfactant concentrations ranging from 0.1% to 5.0% in weight. The experiment found that the critical micelle concentration (CMC) of CWS was considerably higher than an aqueous solution because of the absorption of surfactant by coalmore » particles. In addition, the dynamic surface tension continuously decreased beyond the CMC because suspended coal particles retarded the surfactant migration. The CWS dynamic surface tension showed wide variations of up to a factor of two depending on the type of surfactant whilst all the selected surfactants exhibited a same range of static surface tension values. The dynamic surface tension increased with increasing coal loadings in CWS. The primary reason for this is believed to be because of the increased absorption and physical blockings of coal particles.« less