Anthracite char

Eor the free swelling index which is also known as the cmcible swelling number (ASTM D720), a coal sample is rapidly heated to 820°C in a covered cmcible. Then the profile of the resulting char is compared to a series of standard numbered profiles (18). Eor the Roga index weighed amounts of coal and standard anthracite are mixed and carbonized, and the product coke is tested in a Roga dmm for its resistance to abrasion (89). 

Contrary to H2S, the amount of S02 evolution remains constant with coal maturation. The peak temperature of S02 rises from about 350 C for the peat sample to about 650 C for the anthracite sample. This temperature increase with coal maturation could be due to a loss of inflammable volatile matter which accelerates the char oxidation, and a relative enrichment of the char in condensed aromatic nuclei more resistant to pyrolytic breakdown, as seen by PTP and Py-GC, but also to a reduction of the size of micropores during coalification which hampers oxygen penetration into the solid matrix. 

In this paper the combustion reactivities of four flash pyrolysis chars are compared with the results for chars produced from low and high-rank coals under conditions simulating pulverized-coal combustion, for anthracite and semianthracite, and petroleum coke. Reactivity is expressed as the rate of combustion of carbon per unit external surface area of the particle, with due correction being made for the effect of mass transfer of oxygen to the particle. 

Published data for wood char shows reaction rates six to ten times as rapid as reaction rates for coke or anthracite coal. 

FIGURE 7.26 Complex index of refraction of coal/char panicles [237] (a) Anthracite (6) bituminous (BLV). 

The burning rate of chars at a pressure of 1 atm for petroleum coke and the different coal rank has been compared by Sergeant and Smith [27]. The collected experimental data show that the char burning rates expressed in (kg m- s ) is slightly lower for the same particle temperature, for petroleum coke against anthracite however the behavior of both coke residue (petroleum coke) and char (anthracite) is similar. The burning profile technique is a method for predicting the relative combustion characteristics of fuels. 

Steam activation is the most widely used method for producing activated carbons in the world. In terms of adsorption capacity, it easily reaches specific surface areas of 1000 m g" at 50% of activation conversion degree (regardless of carbonization yield), when an acceptable raw material with an initial ash content helow 10% is used. Basically, steam activated carbons are microporous materials, with a mlcropore size that increases with the activation degree, but with no mesopore development. As an example. Fig. 11 shows the nitrogen adsorption isotherms of activated carbon produced by the steam activation of an anthracite [33]. Each adsorption isotherm corresponds to an activated carbon with activation degrees of 20, 35, 50, 70 and 80% bum-off (samples AC-720, AC-735, AC-750, AC-770 and AC-780 respectively), the sample AC-700 being the non-activated char. These isotherms not only provide specific numerical parameters correlated with adsorption capacity, but also provide certain qualitative infonnation derived from their shape. 

In this paper, we have described how minerals in coal can be quantitatively determined by the combination of SEM-AIA and Mi5ssbauer spectroscopy. These techniques can be applied to all coals, from lignite to anthracite, with little or no modification. Although such applications are not discussed in any detail here, these techniques can also be applied to cokes, chars, solvent-refined coals, and other products of coal conversion. 

There is also a German standard (TGL 15388 [65]) for reactivity determination in a fixed bed, which is derived from the coke reactivity index for lump coke (CRI, ISO 18894 [66]). A mass of 5 g of 1-3 mm char is exposed to 2.51/h CO2 flow (>95 vol%) in a reaction tube of 40-mm diameter at a temperature of 900 °C. The product gas is analyzed after 15 and 30 minutes. The reactivity value km in cm /(g s) is calculated from the gas concentrations. Typical char reactivity values for km are 10-15 for wood, 5-10 for peat, 4-8 for lignite, 1-4 for sub-bituminous coal, 0.1-1 for bituminous coals, and <0.1 for anthracite. The number has been mainly used to compare the gasifiability of fuels in fixed-bed and fluid-bed systems. 

---