Coal Particle Size Distribution Research Articles

Atomization of coal-water slurry using twin-fluid jet atomizer

This paper presents both experimental and modelling results of airblast atomization of coal-water mixtures or slurries (CWMs) using a twin-fluid jet atomizer. Specifically, the mass median diameter (MMD) of atomized droplets is related to the slurry properties and atomization conditions through its power dependencies on the Weber number ( We), the Ohnesorge number ( Z) and liquid or fuel-to-air mass ratio ( W F W A ), namely, MMD D F = (A · We −x + B · Z 2x) (1 + W F W A ) y , where D F = the diameter of the fuel passage and A, B, x and y are constants determined by the least square method. The coal particle size and size distribution has substantial effects on both the droplet sizes and the exponents x and y. In addition, the presence of hydrophobic coal particles shifts the fundamental mechanisms of airblast atomization to the predominance of the fuel viscosity included in Z over the liquid surface tension included in We. Other factors such as particle packing efficiency also make significant contributions.

Viscometry and rheology of coal water slurry

This paper presents the results of a detailed experimental study on rheological behaviour of coal water slurry (CWS). In contrast to earlier rheological studies at shear rates of rather narrow ranges, this study covered a much wider range of shear rates: 0–800 s −1 in a rotational viscometer and 400–10000 s −1 in a capillary viscometer. While the gap width of a rotational viscometer had no effect on the apparent viscosity of CWS, it was found that selection of proper tube dimensions in a capillary viscometer was important, Thus, the viscosities of CWS measured in both viscometers at the overlapping shear rates of 400–800 s −1 were in good agreement. Consequently, it was possible to study the effect of shear rate higher than 800 s −1 on slurry rheology. In addition, the effects of coal content, coal particle size and size distribution, and temperature on the slurry rheology were investigated. The slurry, a dispersion of coal particles in a pseudoplastic fluid, became more viscous and less pseudoplastic as the coal content was increased. The pseudoplasticity of a highly concentrated utility grind CWS approached that of a concentrated suspension of 40–50 μm solids in a Newtonian fluid. Also, the slurry pseudoplasticity was enhanced at a slightly elevated temperature, but significantly reduced as the shear rate exceeded a threshold dependent on coal content and particle size and size distribution.

Settling stability of coal slurries prepared by wet grinding in the szego mill

AbstractStatic sedimentation experiments on coal‐#2 oil and coal‐water slurries, wet ground in a Szego mill, were conducted. These slurries contain more flaky particles as compared to those conventionally ground.Concentration and size distribution of the coal, diameter and height of the settling columns and settling time were the independent variables. Coal concentration and particle size distribution along the columns, and settling rates were measured.Despite their particle shape differences, these slurries were similar to others in terms of settling stability due to particle flocculation.

ボールミルによる石炭の油中粉砕に関する研究

The preparation of coal-oil slurry for the coal liquefaction plant has been studied using a ball mill (batch). The particle size distribution and the slurry viscosity, which vary with the grinding time, were measured for these three coals of Horonai, Taiheiyo and Wandoan.Anthracene oil and creosote oil were used as the vehicle oil to be mixed with coals.The following results were obtained.1) The particle size distribution of the ground coal in the coal derived oil can be expressed by Rosin-Ra mmler's equation and the coefficient “n” in that equation does not vary with the grinding time.2) The particle size varies with the grinding time to the power of 0.7∼0.84.3) Slurry viscosity increases linearly with the decrease in the average particle size of coal. And the greatest increase in the slurry viscosity was observed in the case of Horonai coal. It appears that the swelling of coal causes the increase in the slurry viscosity.

Kinetics of short contact time coal liquefaction. Part I: Effect of operating variables

AbstractThe liquefaction kinetics of Powhatan No.5 mine coal (Pittsburgh Seam) in the presence of SRC‐II recycle solvent at short contact times (<10 min) and temperature and pressure ranges of 573–723 K and 10.3–13.8 MPa is examined in a well‐mixed reactor. In the initial stages of liquefaction, while overall coal conversion (tetrahydrofuran solubles) increases with temperature, oil (pentane solubles) is lost with an increase in temperature. An increase in solvent‐to‐coal ratio results in an increase of conversion. The initial coal particle size distribution, total pressure, and nature of gas phase (nitrogen or hydrogen) have no significant effect on the production of any of the product of liquefaction for contact times up to 10 min. A lumped kinetic model is presented to describe the product distribution.

The sedimentation stability and viscosity of coal oil dispersions

Measurements of the sedimentation stability and viscosity of a number of suspensions of coal particles in heavy fuel oil known as Coal Oil Dispersions (COD) are described. It is shown that an estimate of the stability of a coal oil dispersion prepared by grinding coal in fuel oil can be made from simple viscosity measurements. The method is based on the use of the coal volume fraction and a parameter V which is characteristic of a given coal oil dispersion. V is determined from the variation of dispersion viscosity with coal volume fraction using the Krieger—Dougherty equation. The stability of an unknown dispersion is predicted by determining V and its coal content and using previously calibrated stability charts. The parameter V is a function of coal—coal interaction and particle size distribution. It is suggested that the method might be applicable to the quality control of other concentrated suspensions.

Carbon fines production and elutriation from the bed of a fluidized coal combustor

Rates of elutriated carbon from a fluidized bed coal combustor 160 mm ID are measured under different operating conditions. The content and size distribution of coal particles in the bed are also determined. The excess air factor, bed height, and temperature, fluidizing gas velocity, bed inert material, and coal feed sizes are changed during the experiments. Rates of carbon loss are analyzed, accounting for the two contributions: that of elutriated unburnt parts of feed coal particles and that of elutriated carbon fines produced by attrition of coal while it is burning in the bed. The latter contribution can be expressed as a function of carbon loading, excess of fluidizing velocity above the minimum for fluidization, and average particle size of coal in the bed.

公害防止用球形活性炭の石炭を原料とした製造法

There are growing markets for activated carbon for such purposes as water treatment and air pollution control. Although these new markets are not developing as fast as expected, the ultimate potential is considered to be huge. Therefore, intensive research is being conducted in the field of production of activated carbon to develop a new manufacturing process or to seek new kinds of raw materials. Under these circumstances we have developed the new manufacturing technique for the production of spherical activated carbon from coal, which may be promising as effective adsorbents for pollution control.The manufacturing process of the activated carbon from coal consists of five steps. They are pulverizing of coal, pelletizing of fine coal, precarbonization, carbonization and steam activation. The choice of raw coal species is very important to produce good spherical activated carbon. Coking-coal with a carbon content of 80-85% has proven to be a good raw material. After pulverizing, the coal is pelletized into spherical particles with a disk-type pelletizer. In this process, particle size distribution of the fine coal, water content, kind and amount of binder added all influence the pelletizing effect. To obtain strong and dense spherical carbon, carbonization is carried out at a temperature of 500-600°C at heating rate of 0.5-5°C/min. It appeared that an indirectly heated rotary kiln is the most suitable carbonization apparatus. The carbonized pellets are activated with steam. Spherical activated carbon exhibiting a high adsorption property and strength can be prepared with an indirectly heated rotary kiln or directly fired rotary kiln in the presence of limited quantities of oxygen.