Particle sizes, coal

There is a general understanding that the size of ash particles produced during coal combustion decreases with decreasing coal particle size and with decreasing mineral content of the parent coal particles. There are, however, no fundamental models that allow the researchers to predict the change in the size of ash particles when coal is finely ground or beneficiated or how ash size is affected by combustion conditions. 

Effect of Coal Particle Size on Analytical Precision of Trace Elements... 

Table V gives the combined means of the differences between duplicate trace element determinations for each coal particle size analyzed. Both the means of the absolute differences (in ppm) and the means of...

Table V. Mean Error for All Elements at Various Coal Particle Sizes...

Progressive reduction in coal particle size from —60 to —400 mesh improved the precision for all elements except bromine. The combined mean relative error for all elements was reduced below 5% for coal ground to —200 mesh. 

The spectra were run on potassium bromide discs of the specimens at about 0.35% w/w concentration using a Perkin-Elmer Model 21 spectrometer. Microscopic examination of the discs showed that in spite of long grinding, the coal particle size was relatively large (<1(V, except for CGL 105, which contained many particles in the range 10- 50m). Consequently, a fair amount of scatter was observed in the spectra. 

Time at temperature Total time above 315°C ZnCl2/MF coal feed ratio H2 partial pressure Coal particle size... 

Factors that affect the rate of low-temperature ashing other than radiofrequency power and oxygen flow rate are the coal particle size and depth of sample bed. Typical conditions for ashing are a particle size of less than 80 mesh, a sample layer density of 30 mg/cm2, oxygen flow rate of 100 cm3/min, chamber pressure of about 2 torr, and a 50-W net radio-frequency power. The total time required is 36 to 72 hours, and specified conditions must be met during the procedure to obtain reproducible results. 

COAL PARTICLE SIZE DISTRIBUTION Particle Size (Microns) Weight Percent... 

Pressure Temperature Coal particle size Coal residence time... 

Sample Preparation. Herrin No.6 (Illinois No.6) and Indiana No.5 (Illinois No.5) coals obtained from the Illinois Geological Survey Sample Bank were used in this study. The whole coals were split into four fractions each of which was placed in a sealed, 5-gallon drum. The fourth fraction was ground to minus 200 mesh and then introduced into a nitrogen gas powered (100 psi) Sturtevant fluid energy mill. In this device the coal particle size is reduced to the micron level by impaction between coal particles themselves and with the impaction chamber walls. Proximate and elemental data for these micronized coals are reported in Table I. 

The dynamic and steady-state characteristics of a shallow fluidized bed combustor have been simulated by using a dynamic model in which the lateral solids and gas dispersion are taken into account. The model is based on the two phase theory of fluidization and takes into consideration the effects of the coal particle size distribution, resistance due to diffusion, and reaction. The results of the simulation indicate that concentration gradients exist in the bed on the other hand, the temperature in the bed is quite uniform at any instant in all the cases studied. The results of the simulation also indicate that there exist a critical bubble size and carbon feed rate above which "concentration runaway" occurs, and the bed can never reach the steady state. 

A chrome -alumel thermocouple was set in close proximity to the sample inside a reactor. The reactor was made of a quartz tube which was surrounded by a tubular furnace. In a typical coal pyrolysis run, the coal sample (20-30 mg) was placed in a platinum boat which was suspended from the quartz beam of the TGA balance. The coal particle size used was 100-200 mesh. Samples were heated to desired temperatures at linear heating rates or heated iso-thermally under various gaseous environments. 

Figure 7. Effects of pressure and coal particle size on yields of total volatiles, tar plus hydrocarbon liquids, all hydrocarbon gases, and methane, from bituminous coal pyrolysis. Heating rate = 1000°C/sec. Temperature = 1000°C. Isothermal holding time = 2-10 sec. Particle diameters, ixm C) 74 (X) 297-833 (O) 833-991 (14).

The total recovery of organic sulfur was independent of the coal particle size used. 

A new approach for the chemical removal of pyritic sulfur from coal is described. The process is based on the discovery that aqueous ferric salts selectively oxidize the pyritic sulfur in coal to chemical forms which can be removed by vaporiza-tion, steam, or solvent extraction. Data for removal of the pyritic sulfur from four major coals (Lower Kittanning, Illu nois No. 5, Herrin No. 6 and Pittsburgh) are presented together with a discussion of the process chemistry. The effect of variables, such as coal particle size, acid and iron concern tration, reaction time, and temperature are discussed. The results show that near complete removal of pyritic sulfur can be obtained under mild conditions, resulting in a reduction of the total sulfur content of the coals from 40 to 80%, depending on the original pyritic sulfur content. 

We studied the effect of acid concentration, coal particle size, ferrous and sulfate ion concentrations, and reaction time on pyrite removal. These parameters were studied under conditions see Experimental) that give 40-70% pyritic sulfur removal, rather than 85-90%, so that the effects of parameter variations are clear and not so small as to be masked by experimental error. In addition, studies were performed to demonstrate... 

As discussed in the previous section, the main step of the gasification process is the heterogeneous reaction of char. The reaction rate of char gasification is much lower than that of oil gasification. Therefore, a longer residence time is necessary for reasonable coal conversion. In the GE gasification process, the residence time is typically 4-10 s. Residence time is determined by reactor size, coal particle size, char reactivity, and operating conditions (T and P). 

Son, S.Y. Kihm, K.D. Effect of coal particle size on coal-water slurry (CWS) atomization. Atomization Sprays 1998, 8, 503-519. 

Figure 6. The effects of three chemical additives on product coal particle size distribution while milling at constant conditions, (O) No Additives (A) 2 Ibs/ton Calcium Hydroxide (D)...

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