Effect of Isopropyl Alcohol Concentration on the Size and Number of Droplets after Coal-Water Fuel Spraying

Abstract

Coal-water slurries are promising fuels for thermal power engineering. One of the main problems with their combustion is formation of fairly large (with characteristic sizes of more than 1 mm) droplets during spraying with nozzles. It results in their late ignition in the furnaces of steam and hot water boilers. The aim of this work is to establish by experimental results distribution of coal-water fuel droplets by size with the addition of isopropyl alcohol after coaxial spraying and justify the effectiveness of using this alcohol as the third component that affects the number and diameter of fuel droplets after spraying. It was found that the number of small droplets (no more than 100 micrometers) in the jet increases by 19% in comparison with typical coal-water fuel after spraying coal-water fuel prepared on the basis of lignite due to the introduction of IPA (no more than 3% by weight). Concentration of small droplets (no more than 100 µm) increases by 16% after spraying coal-water slurry prepared on the basis of long-flame coal and addition of no more than 3% by weight of isopropyl alcohol in comparison with typical coal-water fuel. Increase in the proportion of isopropyl alcohol in the slurry composition to no more than 5% by weight is the reason for increase of sufficiently large (more than 400 micrometers) droplets of such fuel after spraying by 14%. The number of fuel droplets of small sizes decreases similarly to large fragments after spraying coal-water slurry prepared on the basis of lean coal with small weight (no more than 3%) additives of isopropyl alcohol. Increase in the viscosity of fuels in several times is conditioned by increase in the concentration of the third component. This significantly degrades jet characteristics after spraying. The expansion angle of the jet increases by 20%. Medium-sized droplets (200–600 micrometers) and fairly large fragments (more than 600 micrometers) prevail in the jet. Concentration of droplets up to 200 micrometers in the diameter decreases. The results obtained are of sufficient practical significance, because they illustrate the possibility of increasing the number of small fuel droplets after spraying. The efficiency of insertion a small amount (no more than 3% by weight) of isopropyl alcohol additive into the composition of coal-water fuel was experimentally proven, and the application feasibility results in the analysis of optimal ignition conditions for droplets of alcohol-coal-water slurries in conditions corresponding to the combustion chambers of steam and hot water boilers.