Coal structural evolution

Advances in the understanding of coal structure and its evolution during devolatilization have led to the development of several coal network models... 

Solum, M.S., Pugmire, R.J., Grant, D.M., Fletcher, T.H., and Solomon, P.R., Solid State C NMR Studies of Coal Char Structure Evolution. Western States Section/The Combustion Institute, Pullman, WA (3/89). 

Another possible correlation between coal structure and pyrolysis behavior is indicated by the temperature dependence of the evolution of pyrolytic water being strikingly different for the two coals. Figure 5 shows pyrolytic water evolution data for experiments in which the sample was heated at 1000°C/sec to the peak temperature indicated on the abscissa and then immediately allowed to cool at around 200°C/sec. The smooth curves are based on a single reaction, first-order decomposition model (7,8) and on the stated temperature-time history. Parameters used for the lignite have been published (8) while for the bituminous coal the Arrhenius frequency factor and activation energy were taken as 1013 sec"1 and 35 kcal/mol, respectively, with the yield of pyrolytic water ultimately attainable estimated from experimental measurements as 4.6 wt % of the coal (as-received). 

Dereppe, J. M., Boudou, J. P., Moreaux, C., and Durand, B. (1983). Structural evolution of a sedimentologically homogeneous coal series as a function of carbon content by solid-state C NMR. Fuel 62, 575-580. 

The coal lithotype of coal layer No. 15-1 and No. 15-3 are both semibright and semidull coal (Table 2), and coal structures of each delamination of coal seam No. 15 are all from types of primary texture to cataclastic texture, which are advantageous to preservation of H S generated from the buried and evolution stage of coal seam No. 15 and provide prerequisite for HjS abnormity in certain areas of coal seam No. 15. 

Ibarra, JV. Munoz, E. Moliner, R. (1996). FTIR study of the evolution of coal structure during the coalification process. Org Geochem, Vol.24, pp. 725-735. 

Spectroscopic methods have been applied to the elucidation of the structures in coal from very early in the development of the methods (Speight, 1978). In the initial stages of the evolution of the spectroscopic methods, the data derived by their application to coal were more of a diagnostic nature as, for example, determination of functional entities or carbon-hydrogen bonds by means of infrared spectroscopy or determination of aromatic and aliphatic hydrogen by proton magnetic resonance spectroscopy. However, virtually all of the methods have at one time or another been applied to coal as a means of deriving more detailed information about coal structure with special emphasis on the... 

At temperatures in excess of 200°C (390°F), carbon isomerization appears to commence as evidenced by the evolution of small amounts of alkyl benzenes. The exact mechanism of these low-temperature reactions is unknown and remains open to speculation, but it has been noted that these reactions are significant enough insofar as the original coal structure is sufficiently changed to influence any subsequent thermal behavior of the coal. 

Examination of the data on C02 and pyrolytic water evolution may provide some insight into the thermal decomposition behavior of specific organic and inorganic structures in the parent coals. Some C02 may arise from the decomposition of inorganic matter within the coal. It also has been suggested (16) that decomposition of carboxyl groups in the... 

Tn a recent study the thermal decomposition of 13 coals was examined in over 600 vacuum devolatilization experiments (1). The results for all 13 coals were successfully simulated in a model that assumes that large molecular fragments (monomers) are released from the coal polymer, with only minor alteration, to form tar, while simultaneous cracking of the chemical structure forms the light molecules of the gas (2, 3). The evolution of each species is characterized by rate constants that do not vary with coal rank. The differences between coals are due to differences in the mix of sources in the coal for the evolved species. The sources were tentatively related to the functional group concentrations in the coal. 

A better understanding of the chemical structure of coal will help in the improvement of the known procedures for coal liquefaction and the evolution of new technology for the transformation of coal into more petroleumlike products. 

Probably the rotary horizontal kiln is the most versatile, since it allows a feed of lumps or fines of limestone or marble, or wet or dry calcium carbonate sludges (Fig. 7.1). The main component of this calcination system is a 2.5- to 3.5-m diameter by 45- to 130-m long firebrick-lined inclined steel tube. Heat is applied to the lower end of this via oil, gas, or coal burners [7]. The feed to be calcined is fed in at the top end. Slow rotation of the tube on its axis gradually moves the feed down the tube, as it tumbles countercurrent to the hot combustion gases. In this way, wet feed is dried in the first few meters of travel. Further down the tube, carbon dioxide loss begins as the temperature of the feed rises. By the time the solid charge reaches the lower, fired end of the kiln it reaches temperatures of 900-1,000°C and carbon dioxide evolution is virtually complete. Normally the temperature of the lower end of the kiln is not allowed to go much above this as it reduces the life of the kiln lining. It also adversely affects the crystal structure of the lime product since it produces a dead-burned or overburned lime. Overburned lime is difficult to slake to convert it to calcium hydroxide and raises... 

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