Coal-water Slurry Fuels Research Articles

A Model of the Enhancement of Combustion of Coal-Water Slurry Fuels Using High-Intensity Acoustic Fields

Combustion of coal-water slurry fuels is simulated in the presence of high-intensity acoustic fields which increases heat and mass transfer from the droplets and particles, and thereby enhances the combustion. The steady-slip velocity and acoustically induced slip velocity are calculated along particle trajectories, giving the augmented Nusselt and Sherwood numbers in the presence of high-intensity acoustic fields compared with no-sound conditions. The paper also presents the water evaporation and char burn-out history for particles with diameters between 90–110 μm exposed to sound pressure levels of 160–170 dB and compares the results to similar cases under no acoustic field. A decrease in the char burn-out length of about 12.1 percent at 160 dB, 18 percent at 165 dB, and 24 percent at 170 dB sound pressure level is obtained compared to the case with no sound for 100-μm particles introduced at centerline.

Experimental Study of Micronized Coal/Water Slurry Rheology at High Shear Rates

The rheological behavior of four micronized coal water slurry (CWS) samples was studied experimentally for a wide range of shear rates between 3 and 30,000 s−1. The systematic rheological characterization of the slurry fuel shows that the rheological behavior of these CWS is very complex and depends on coal particle size, temperature, coal loading, conditioning additives, and the capillary tube diameter as well as the shear rate. This study indicates that better appreciation of the unique and complex rheological behavior of non-Newtonian CWS fuels is vital to developing high-quality slurries suitable for use in coal-fired diesel engines, and suggests that a more comprehensive data base for CWS rheology under actual diesel engine operating conditions is needed prior to using such CWS fuels in diesel engines.

Coal-fueled diesel engines: Analytical evaluations of ignition options

An engine cycle simulation was developed to investigate the ignition and combustion characteristics of coal-water slurry fuels in a reciprocating, internal combustion engine. The simulation includes models for fuel and air mixing, wall heat transfer, solid coal particle combustion, coal devolatilization, and liquid evaporation and combustion. These models together with a thermodynamic analysis of the cylinder gas yield instantaneous cylinder conditions and overall indicated engine performance. The engine parameters and operating conditions were selected to be representative of a locomotive engine operating at 1000 RPM. Engine and fuel parameters investigated include engine inlet conditions (temperature and pressure), coal particle sizes and size distributions, fuel additives, and coal properties. Increases in the initial (at BDC) gas temperature or pressure, or the addition of small amounts of diesel oil improved the ignition characteristics. Slurries with smaller particle sizes exhibited better ignition qualities and resulted in higher peak indicated thermal efficiencies than slurries with larger particle sizes. Results obtained using monosize sauter mean diameter particles agreed well with results obtained for the corresponding distribution. Finally, ignition was achieved at lower initial gas temperatures for higher reactivity coals.

CHEMICAL COMMINUTION OF COAL

Chemical comminution is an effective means for size reduction and beneficiation of coal. Sodium hydroxide and isopropyl alcohol (IPA) show synergism in chemical comminution of Illinois No. 6 bituminous coal. This system is effective at low alkali concentrations with low consumption of NaOH. Much of the NaOH consumed is for neutralization of acidity of the coal. The IPA serves only as a reaction medium and could be recovered nearly quantitatively for recycling. The system lends itself to application in preparation of coal-water mixtures and coal-alcohol slurry fuels.