Coking Properties Of Coal Research Articles

Effect of Microlithotype Maceral Distribution on Coke Quality

The coking behavior of coal is an important facet in utilization of coal in metallurgy and in other industries. The carbonization behavior of coal mainly depends on coal rank, petrographic composition, ultimate composition and rheology of coal. Coal petrography has become very useful technique for establishment between formulation of coal blend composition and coke quality prediction. It is generally established that blend containing optimal reactives produces the coke of maximum strength. The coking properties of coal not depend only on the macerals composition, but also on the way in which the macerals are distributed among one another, forming preferential associations called microlithotypes. The measurements of relative proportion of microlithotypes are called microlithotype analysis. In present work, distribution of macerals (microlithotype) in coal samples were studied and correlated with the coke quality. Beneficiation by wet method were carried out (only indigenous coal) by washing media of specific gravity 1.30 to 1.40 to achieve <10% ash level. Coal microlithotypes plays an important role on coke quality. Bi-maceral and tri-macerals microlithotype distribution (vitrinertite and duroclarite and clarodurite) in coal samples act as a vital role for coke quality. Inter-growth of internite within vitrinite macerals has also significant role on coke quality. Therefore, the combined analysis of maceral and microlithotype distribution is important for coke quality. Distribution of bi-maceral and tri- maceral in coal improved coke quality (M40 and M10 indices). The microlithotype distribution measurement by petrography analysis gave considerable correlations with M40, M10, Coke Reactivity Index (CRI) and Coke Strength after Reaction (CSR) parameters. It gave details the adaptability of Indian coke quality in favor of macerals assemblages in coal.

Perchloroethylene (PCE) adsorption on coal macerals as derived from micro-FTIR spectroscopic analysis and mapping of the C=C bonds from PCE

ABSTRACT Organic liquids are used to prepare the density medium to produce clean coal composites for coal quality and coking test evaluations during the coal exploration stage. Perchloroethylene (PCE) is commonly used as a density medium for this procedure; however, it has been shown before that PCE affects Gieseler Fluidity and Ruhr Dilatation indices of coal, as well as the quality of the resulting coke. It was also found that PCE has a negative effect on the coking properties of coals with a high inertinite content. This paper investigates the adsorption of PCE on various coal maceral surfaces using micro-Fourier Transform Infrared Spectroscopy (micro-FTIR) analysis to observe the changes in the absorbance of the double carbon bond C = C (C = C absorbance peak is used as a marker to indicate the presence of PCE) before and after PCE was applied onto their surfaces. The micro-FTIR mapping of absorbance intensity of the C = C bond on coal macerals showed an increasing trend in the presence of these bonds on the surface of all macerals with the time after exposure to the PCE. The SEM- energy-dispersive X-ray spectroscopy was used to analyze the composition of minerals associated with fusinite and semifusinite, as they were filling the pores in these macerals.

Impact of weathering on coal properties and evolution of coke quality described by optical and mechanical parameters

Changes of coals properties due to weathering and its impact on the properties of derived cokes were investigated. Four coking coals collected from Polish coal mines were stored for one year in order to simulate weathering conditions. Samples of fresh and weathered coals were analysed in terms of different coking properties, e.g. fluidity, contraction, thickness and gas permeability of the plastic layer. All coals were also pyrolysed and the optical and mechanical properties of the produced cokes were determined. Results showed that the fluidity clearly decreased with elongation of the storage time. Other coking properties of coals also changed with the storage time in different ways depending on their rank and initial fluidity. Oxidation of all coal samples resulted in a shift of the observed texture of derived cokes towards smaller (worse ordered) textures. However, it was found that the coke from 6–month stored Budryk coal, referring to the coke originated from the respective fresh coal, is characterized with slightly better quality, in terms of reflectance and coke post-reactive strength, CSR. No significant changes in quality of other coke samples were observed.

Rank assignment of coal in terms of its clinkering and coking properties

Comparison of the clinkering and coking properties of coal from different basins indicates that the rank boundaries adopted in State Standard GOST 25543–2013 in terms of the plastic-layer thickness do not correspond to the boundaries in terms of the coking properties. The coal samples are arranged in order in terms of the coking capacity K cc and the coke-forming capacity K cfc, and a classification of coal ranks on the basis of the coking properties is proposed.

Enhancement of Coking Properties of Coal by Differential Screening

Coke plays a major role in blast-furnace operation. Quality of coke mainly depends upon the coal used in blend. As the reserve of good coking coal is diminishing, at this point of time, it is important to give emphasis on coal-preparation techniques. Keeping this in mind, this article presents a coal-preparation technique named “differential screening” based on a selective crushing principle. Different types of indigenous and imported coals are characterized and screened in different size fractions. These size fractions are again characterized and carbonization tests are designed based on their properties under stamp-charging condition. This research suggests that the use of a specific fraction of coal in the blend in order to achieve the higher coke strength after reaction (CSR).

Oxidation of coal in industrial conditions. 3. Mechanical strength of coke

The change in mechanical strength of coke is investigated as a function of the storage time of the coal from which it is produced. Considerable variability is noted in the limiting coal-storage time due to deterioration in strength of the coke produced. Accordingly, care must be taken in specifying different storage times for different coal stocks. When oxidized coal is employed, wear of the coke is aggravated, because its strength is reduced. Analysis of graphical and mathematical relationships indicates that, in both summer and winter, coal of moderate metamorphic development may be stored for the longest times in terms of loss of coke strength. The change in the coking properties of coal is assumed to depend on the ease of penetration of the plastic mass through the surface layer of rigid thermostable structure formed on oxidation. Improvement in the coking properties of bituminous coal on natural oxidation is attributed to the increase in expansion pressure.

00/01822 Methods for evaluation of coking properties of coals

00/01822 Methods for evaluation of coking properties of coals

95/01147 Evaluation of coking properties of coals by quantification of pyrolysis products

95/01147 Evaluation of coking properties of coals by quantification of pyrolysis products

The effect of oxidation on the thermoplastic and coking properties of coal at elevated pressures

The effects of oxidation on coal thermoplastic and coke properties have been investigated using a variety of techniques. The methods used include thermogravimetric analysis, high pressure dilatometry, constant shear rate plastometry and optical anisotropy. The apparent effects of oxidation are strongly influenced by the temperature and time of oxidation as well as the experimental conditions under which the coal carbonization behaviour is studied. Oxidation decreases swelling, the maximum rate of volatile evolution and optical anisotropy except under very mild conditions where usually little or no effect was observed. Oxidation can cause the shape of the dilatation versus pressure curves to change dramatically. This may result in the dilatation of an oxidized coal being higher at elevated pressure than at atmospheric pressure in contrast to the results for the fresh coal. However, under the same experimental conditions, the dilatation of the oxidized coal is either identical within experimental error or less than that of the original fresh coal. Comparison of coals with varying extents of oxidation has shown that an increase in the carbonization pressure tends to decrease the apparent effect of oxidation on the coal swelling and coke optical anisotropy index. There are good correlations between the changes in the swelling, maximum rate of devolatilization and coke optical anisotropy parameters, resulting from oxidation indicating the relationship between these concurrent processes during carbonization. The perturbation of the structure of a coal by oxidation in conjunction with the investigation of the dependence of caking, swelling, devolatilization and coke structure factors on experimental conditions provides a clear insight into the development of coal thermoplasticity and coke structure during carbonization and gasification.

Proposal for coal classification

Several critiques to the ‘International Classification of Hard Coals by Type’ (ECE, Geneva, 1956) have been made in the past and a revision of its usefulness is currently being carried out by several investigators. The principal drawback of this classification is that it is not applicable to coals of variable maceral composition, especially those displaying a high content of inertinite. Furthermore, the parameters hitherto used in the International Classification and in some other national systems to define degree of coalification (rank), i. e. volatile matter and calorific value, are dependent on variable maceral composition. On the other hand, the parameters used in the International Classification to determine the agglutinating and coking properties of coals are competing parameters, instead of following a hierarchy. The proposed classification scheme is based on two primary parameters determined with microscopic techniques: (1) mean maximum reflectance of vitrinite, which is a good single measure of rank; and (2) petrographic composition (vitrinite and exinite) as an indication of the type of coal. A third parameter is chosen to qualify the different classes of coal: volatile matter for anthracitic coals; dilatation for semianthracitic and bituminous coals; and calorific value for subbituminous coals and lignites. The scheme is expressed by mean of a code number of four digits, which refers to the rank (first digit), type (second and third digits) and qualification (fourth digit) of coal.

The Development and Problems of Studies on Coal and Coke

The author was engaged in research works on coal and coke, at the Technical Research Institute of Yawata Works, from the entrance into Nippon Steel Corporation after university graduation until the retirement (1938-1968).In this paper the author summarizes the development and problems of studies on coal and coke, describing author's main thoughts and anecdotal stories about the researches, especially in detail about the coking properties of coal.

Differential thermal analysis of extracts of Nova Scotia coals, and the effect of these extracts on the coking properties of coal

Phenanthrene has been used to separate coals into four separate fractions. The exothermic reactions and swelling of 100 mg samples of these fractions and fractions plus coal were studied by means of a vacuum differential thermal analyzer.The thermograms show that swelling and exothermic reactions occur in only a cyclohexane soluble fraction. Only good coking coals produce such a fraction. This fraction is believed to contain the coking properties of coal. The swelling occurred at approximately 200 degrees C.Samples of the cyclohexane soluble fraction were added in amounts up to 20 percent by weight to both coking and non-coking coals. These additions do not appear to enhance the coking properties of such coals.

Investigation of the coking properties of coal by vacuum differential thermal analysis

Vacuum differential thermal analysis has been used to study the coking properties of a number of bituminous coals. Samples of 200 mgs were run from room temperature to 600 degrees C at a heating rate of 10 degrees /min.The thermograms show two peaks that can be related to the plastic properties: (1) a strong exothermic peak beginning between 340-440 degrees C and reaching a maximum height between 440-520 degrees C; (2) a small, sharp exothermic peak superimposed on the limb of the larger peak and occurring between 430-500 degrees C. The beginning of No. 1 peak represents the softening temperature of the coal while its summit corresponds to the solidification temperature. No. 2 peak occurs in the temperature zone of maximum fluidity and maximum rate of swelling. The sharpness of this peak appears to be influenced by the fluidity of the coal.The changes that occur in the plastic properties of a coal through blending with other coals can be detected on the thermograms and in the small coke buttons formed in the thermocouple well. For example, by blending a high-volatile A coal with increasing amounts of a low-volatile coal, No. 2 peak occurs at progressively higher temperatures, diminishes in intensity and finally disappears. The coke buttons show changes in their cellular structure and degree of swelling.The thermograms and coke buttons can also be modified by the addition of diluents such as fusain, silica gel, quartz, clay, sulfur, charcoal, various inorganic salts and phenanthrene. The degree to which the thermal curves are affected depends on the type and amount of diluent, as well as the properties of the original coal.

Vacuum differential thermal analysis of coal

Samples of 25-30 mgs of various coals and their constituents were analyzed by vacuum differential thermal analysis using a heating rate of 20 degrees C per minute. Exothermic and endothermic peaks obtained by this technique provide graphic representations of the net thermal effects from the physical and chemical changes that take place during carbonization. Replicate analyses show that both peak temperature and the area under a peak can be reproduced readily.Thermograms of vitrains selected from a number of coals of widely different rank show an increase in peak temperature with increasing rank. Similar correlation is obtained between peak temperatures and fixed carbon values using vitrains from coals of the bituminous A group.A study of samples of known petrographic composition reveals that neither exinite nor opaque matter exerts any evident control on the peak temperature. Peak temperatures of average samples of coal from different intervals in a column sample show no correlation with the percentages of fixed carbon. The peak temperatures are relatively constant for average samples taken from a given column sample, but the fixed carbon values show considerable spread. It is concluded that the fixed carbon of a vitrain provides a better index of rank than the fixed carbon of an average sample.Further conclusions are that thermographic analysis is a useful method for the detection of cellulose in lignites and that the chemical fraction of the coal extractable with pyridine gives rise to the peaks. The suggestion is made that future investigators should consider the possibilities of relating the thermographic curves to the coking properties of coal.

Influence of Storage on Caking and Coking Properties of Coal

Influence of Storage on Caking and Coking Properties of Coal