Coal blends

For by-product coke ovens, it is general practice to blend two or more types of coals that have complimentary technical as well as economic characteristics. Because most by-product coke plants are located near the large industrial users of the coke and by-products, coals usually have to be transported from the coal mines to the coke plants. Thus coal blends are designed on integration of coke quaUty needs, by-product quaUty needs, coal costs, transportation costs, impacts of productivity, and impacts on the coke ovens themselves. The physical behavior of coal blends during coking can damage coke ovens. 

The United States possesses a wealth of good quaUty coking coals in the Appalachian states as well as in locations in some southern and western states (4) (see Coal). Coal blends normally consist of higher rank (more metamorphosed) coals in minor proportion relative to certain lower rank coals. 

SRC yields are greater than 100 percent due to the presence of solvent in the SRC. The average SRC prepared from West Kentucky 9/14 coal blends does not meet new source standards for SO2 emissions after the first step of the two-step process although all of the inorganic sulfur and an average 12 percent of the organic sulfur are removed. 

Softening, fusion and semicoke texture for different coals and coal blends... 

Coal Blend No. A 500-lb. Oven Stability B As-Received Basis A-B C Corrected for Oxidation A-C... 

Isenberg, N., Jackman, H. W., Investigation of Beckley Seam Coal Blended with Wheelwright Coal for Use in the Production of Metallurgical Coke, Inland Steel Co., East Chicago, 1945. 

The plastic behavior of coal is of practical importance for semiquantitative evaluation of metallurgical coal and coal blends used in the production of coke for the steel industry. When bituminous coals are heated in the absence of air over the range 300 to 550°C (570 to 1020°F), volatile materials are released and the solid coal particles soften, to become a plasticlike mass that swells and eventually resolidifies. 

Figure 4. Liquid synthetic fuel combustion test nitrogen oxides vs. excess oxygen. H-Coal (blend) low N0X at 40 MW.

In Japan, NKK was the first company to use petroleum coke as the source for metallurgical coke making in 1967. Since then, petroleum coke has been utilized to increase carbon content and decrease ash content of coal blends used by Japanese iron and steel companies. This report includes the following subjects ... 

Figure 3. Relation between MF of coal blends and strength of coke made by small test oven.

Figure 5. Effect of fluidity and coal rank of coal blend on coke strength.

Blending Limit of Petroleum Coke, The blending limit of petroleum coke is considered to be about 5% as already mentioned above. This can be explained from the current average value of MF of about 200 to 500 DDPM for coal blends in the Japanese coking industry. Figure 13 shows limit quantities of added petroleum coke for various values of fluidity for the base coals. In the determination of these limit quantities, the quantity of added petroleum coke with which the fluidity of the coal blend decreased to below 200 DDPM under the effect of this blending was deemed as the limit. 

Biomass and coal have fundamentally different fuel properties that can lead to benefits or deterrents to co-firing. For instance, biomass is a more volatile fuel than coal and has higher oxygen content. Coal, on the other hand, has more fixed carbon than biomass. Wood fuels tend to contain very little ash (on the order of 1% ash or less) and consequently increasing the ratio of wood in biomass/coal blends can reduce the amount of ash that needs to be disposed. A negative aspect of biomass is that it can contain more chlorine than coal. This is particularly true for some grasses, straws, and other agricultural residues. 

For all combustion processes, the total PAH emitted, as a function of the feed and the bed nature, are shown in Table 2. This Table 2 shows that the total PAH emissions depend on the feed. The PAH total quantity detected in the combustion runs carried out with limestone-coal blend feed are one order of magnitude higher than the detected ones for the corresponding runs carried out just with coal feed. 

It could be thought that the small efficiency differences were relevant on the PAH emissions. However, by comparing the data obtained from LCL runs No 3, 4 and 5, at which the same efficiency value is reached but the emitted PAH amount was different, and those obtained from LCL runs No 2 and No 4, with very close efficiencies but at which the emitted PAH amount were the most extreme values detected, it can be deduced that this influence is negligible and the small differences among the high efficiencies reached in all the runs carried out do not seem to be the only determinant effect on PAH emissions. These results allow inferring the importance of the pyrosynthesis step on the PAH emissions, when a limestone-coal blend is added to the reactor. 

Fig. 1PAH ( 4g/Kg) Distribution between Solid an Gas Phases as a Function of the Feeding and Bed Nature SC, sand/coal LCL Limestone/Limestone-coal blend and LC Limestone/coal...

It could be also concluded that the porous character of the limestone facilitates the radical interactions, pyrosynthesis reactions, by hindering the oxidation process. That is corroborated by the Coronene emissions detected when limestone-coal blend is fed into the fluidised bed to control SO emissions. Coronene formation, the most stable PAH studied... 

Fuel analysis results presented in Table 1 provide a comparison between the biofuels and coal. On an as-fired basis, the four bio els had significantly lower calorific values (8- 3 MJ/kg) compared to coal (21 MJ/kg), partly attributable to the higher moisture content of the biofuels. Also, biofuels had lower ash and fixed carbon contents but relatively higher volatile matter contents than both coal and bark/coal blend. 

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