Ignition of coal‐water fuel droplets with addition of isopropyl alcohol

Abstract

Coal-water fuels have been actively studied in the last decade due to the fact that when they are burned in the furnaces of steam and hot-water boilers, much less anthropogenic oxides of sulfur, nitrogen, and carbon are formed in comparison with coal. The main problem that hinders the widespread introduction of such fuels in the energy sector is long (up to 30 seconds) ignition delay times. Significant (10%-50%) reduction in the ignition delay time is possible when a small (up to 10%) amount of available and inexpensive liquid combustible organic compounds are added to the suspension. The purpose of the work is to substantiate (from the results of experimental studies) the possibility of significant reduction of the ignition delay times of coal-water fuels by introducing a third component into the suspension—isopropyl alcohol in relatively small (from 3% to 8%) concentrations. According to the results of experimental studies on the ignition process of multicomponent coal-water fuel droplets, based on long-flame coal, with addition of isopropyl alcohol in oxidizer (still air) heated to high temperatures (from 873 to 1273 K), with recording the processes of heating, ignition, and combustion by a high-speed video camera (speed of shooting up to 105 frames per second), the mechanism, characteristics, and conditions of ignition of the researched compositions of quite promising fuels were established. Experiments have shown that the delay time of stable ignition of the studied suspensions based on long-flame coal decreases by 12% to 47% with the increase (from 3% to 8%) of the mass concentration of isopropyl alcohol in the composition of coal-water fuel at the initial characteristic size of droplets from 1.5 to 3.5 mm. Each studied composition was compared with conventional coal-water fuel burned under similar conditions. The influence of mass concentration of isopropyl alcohol in the composition of the coal-water fuel on the characteristics of the initiation of ignition and combustion processes, established in the experiments, proves the possibility of effective an application of such three-component suspensions in thermal power engineering. The possibility of formation of a significantly larger quantity (about 80%) of small droplets (250-400 μm) in the flow during atomization of coal-water fuel with addition of isopropyl alcohol in comparison with the usual coal-water suspension was experimentally proved. The results are of significant practical importance because they illustrate the possibility of achieving optimum conditions for ignition and combustion of promising multi-component coal-water slurries with the addition of alcohol in the furnaces of boiler plants of large- and small-scale power engineering.