Improvement of atomization characteristics of coal-water slurries

Abstract

Coal-water slurries are promising fuels for thermal power engineering despite some problems associated with their combustion in steam and hot water boilers. One of these problems is formation of sufficiently large (more than 1 mm) fuel droplets during coaxial spraying through the nozzles. The aim of this work is to substantiate efficiency of ethyl or isoamyl alcohol addition as a third component of coal-water fuels, which significantly improve atomization technology, by the results of experimental determination of distribution of coal-water slurry droplets by velocity and size in the process of coaxial spraying. Based on the results of experimental studies of atomization process of coal-water slurries prepared on the basis of lignite with addition of ethyl and isoamyl alcohol, instantaneous fields of fuel droplet velocities and sizes in a wide range (from 20 μm to 1 mm) in several cross-sections of the jet at several values of air and fuel pressure were determined using a non-contact method of jet visualization. It was experimentally established that substitution of water (no more than 3% by weight) in the composition of coal-water slurry by fairly typical alcohols leads to decrease in droplet velocities during atomization of alcohol-coal-water slurries in comparison with conventional coal-water fuel by 5–8% at air pressure of 0.28 MPa and fuel pressure of 0.3 MPa. Concentration of sufficiently small fuel droplets (up to 200 μm) increases by 13.4% and by 6.6% during atomization of alcohol-coal-water slurries with addition of ethyl and isoamyl alcohol, respectively, in comparison with conventional coal-water fuel. Influence of small additives of ethyl and isoamyl alcohol in the composition of coal-water fuel, established in experiments for the first time, on flow characteristics of the droplets after spraying proves the possibility of effective application of such three-component suspensions in thermal power engineering. The results obtained are of significant practical value, since they illustrate the possibility of ignition delay time reduction of droplets of promising three-component coal-water slurries with addition of such alcohols.