Vitrinite heated coals

Figure 9. Plot of the ratio of the decreases in M2j due to heating and to exposure to pyridine against carbon content for vitrinite-rich (> 60 H-iS7t% vitrinite) bituminous coals.

In ordar to determine the effect of coal rank (at established by reflectance measurement of vitrinite in coal) on the reactions of coal as related to carbonization, gasification, combustion, and other processes, a wide range of bituminous coals were studied. The results show that reflectance measurements can be used effectively (1) to determine accurately yields of coal carbonization products such as coke, tar, gas, light oil, and liquor from pilot and commercial coke oven (2) to obtain the heating value and specific gravity properties of gases from these processes (3) to determine the free swelling index and B.t.u. content of coals ... 

Figure 15 compares the heating value of gas, as expressed in B.t.u. per pound of coal, to the R of the samples analyzed. In general, as the R of vitrinite in coal increases, the heating values decrease (r = —0.72). As indicated by the low coefficient of correlation in Figure 5 (r = —0.72), a close relationship between R and gas heating value does not exist. Therefore, any reference to these data can only be in very general terms. 

Seam correlations, measurements of rank and geologic history, interpretation of petroleum (qv) formation with coal deposits, prediction of coke properties, and detection of coal oxidation can be deterrnined from petrographic analysis. Constituents of seams can be observed over considerable distances, permitting the correlation of seam profiles in coal basins. Measurements of vitrinite reflectance within a seam permit mapping of variations in thermal and tectonic histories. Figure 2 indicates the relationship of vitrinite reflectance to maximum temperatures and effective heating time in the seam (11,15). 

The molten part of a vitrinite is similar to the gross maceral, and a part of the maceral is converted to a form that can be melted after heating to 300—400°C. The molten material is unstable and forms a soHd product (coke) above 350°C at rates that increase with temperature. The decomposition of the Hquid phase is rapid for lower rank noncoking coals, and less rapid for prime coking coals. The material that melts resembles coal rather than tar and, depending on rank, only a slight or moderate amount is volatile. 

Low volatile bituminous coal rank and heating values, 6 726t vitrinite reflectance limits and ASTM coal rank classes, 6 708t Low volatile bituminous coal grade (U.S.), 6 713t... 

Pressure of the overburden does not cause chemical reactions which lead to a higher rank. Experiments have shown that static pressure even retards coalification processes. By contrast, pressure affects the physical properties, notably the porosity and moisture content in low rank coals. Further, the optical anisotropy of vitrinites (which is a tension anisotropy) is caused by pressure. Shearing movements have influenced the chemical coalification only occasionally and locally in the foredeeps that we have studied (for instance in the immediate vicinity of overthrusts). In such cases the tectonic movements probably were so quick that the friction heat and the shearing could operate. Shearing in no way can account for the gradual increase in coal rank with depth. 

The fact that Duxite was formed through a natural pyrolysis and yielded an intermediate form of spectrum was an encouragement to examine the spectra of resinites carbonized in the laboratory. It was possible that the lower rank resinites would alter on heating to give spectra similar to those of resinites in bituminous coals. Also, the experiments allowed a comparison between the spectra of carbonized resinites and vitrinites in bituminous coals, the latter having been studied by Brown (4) some years ago. 

Several of the resinite samples were carbonized in nitrogen at various temperatures up to 800°C. using a heating rate of 1.75°C. for one hour. The alterations in the infrared absorption curves of Duxite and resinite from bituminous coals have already been reported (18) and shown to be similar to one another and comparable to the changes produced in the spectrum of carbonized low rank vitrinite. 

Recent work in this Division has shown that various substances other than vitrinites, such as pitches from coal tars and petroleum tars, polyvinyl chloride, and polynuclear hydrocarbons, develop similar mosaic structures on heating. In fact this effect occurs with most high carbon materials which pass through a plastic stage during carbonization. 

Under the conditions of rapid heating used, the quantity of volatile matter might well have proved quite different from that obtained with slow rates of heating. Nevertheless, Figure 8 shows that the yield of acetylene under the present conditions is directly proportional to the standard volatile matter of the coal, irrespective of whether the coal consists mainly of vitrinite or spori-nite. This suggests that the acetylene is derived mainly from the coal volatiles rather than from complete volatilization of the coal. The small extent of reaction with Neospectra carbon black, and the soot itself when returned for further reaction, show that there is little volatilization of these materials even though they have a very small particle size. 

Because of the complexity of the coalification processes, different measures are used to define different levels of rank (Table I) high moisture, low heating value, and nonagglomerating character of the coal define the rank (group) within the lignite and subbituminous classes and volatile matter (or fixed carbon) define the various groups of rank in the bituminous and anthracite classes. In addition to these properties, the reflectance of vitrinite, carbon content of the coal (dry, mineral matter free), and some other properties change proportionately as rank increases (Table I). 

The rank and proportions of liptinite, vitrinite, and inertinite do dictate the behavior of a coal during heating whether in a coke oven or a combustion flame. But other properties of the coal also have a signiflcant influence, such as the following ... 

The FSI or crucible swelling number (CSN), which is a measure of the ino-ease in volume of the coal when it is heated in the absence of air. This test is also used to characterize coals for combustion. The FSI is at least in part a rank-dependent parameter but also depends on the maceral composition of the coal, the vitrinite maceral group being the main contributor to the swelling properties. 

At constant rank, as the inertinite content of a coal increases, the self-heating propensity of the coal decreases. The general trend also indicates an increase in self-heating propensity with either increasing vitrinite or Uptinite content. 

Reflectivity studies using vitrinite, an organic component, were initially carried out on coal to determine its rank, or thermal maturity. These studies were then applied to hydrocarbon generation, as hydrocarbons such as oil and gas are generated over time by the action of heat on fossil organic material. The reflectivity of vitrinite in the hydrocarbon source rocks reveals maturity and the likelihood of the presence of oil and gas in the sediments. 

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