Structure of cokes from coking coal vitrites

The coking process of vitrites and thermobitumens separated from vitrites was examined; structural X-ray and microscopic examinations of the cokes obtained were carried out. A correlation between reflectance distribution of vitrites and microscopic structure of their cokes was found.An increase in the structural ordering of the cokes from vitrites, passing from cokes of gas coal to cokes of orthocoking coals, is observed. It is accompanied by an increase of the optical anisotropy of the resultant cokes; this anisotropy first appears in coke from gas-coaking coal.The cokes from the thermobitumens are lower ordered than the cokes from parent vitrites but all these cokes are partially or entirely optically anisotropic.Total removal of the thermobitumens from coals deprives the cokes from the residues after the extraction of any optical anisotropy.     

Properties and structure of group components separated from vitrites of coking coals by selective thermosolvolysis

The process of progressive and continuous thermosolvolysis of coking coal vitrites was carried out. The properties and structure of the extracts and the extraction residue as well as the influence of the degree of extraction on the properties of the resultant group components were examined. An increase in aromatic character of the extracts with increasing degree of extraction is observed, and the same increase of aromatic character can be seen for the extracts obtained in the same extraction time with an increase of the degree of coalification of the parent vitrites. The changes in the coal structure after extraction of thermobitumens depend on the degree of coalification of the parent vitrites, they are largest for the gascoal vitrite.     

Properties and structure of vitrites from coking coals of the High Silesian Coal Basin

Investigations of the properties and structure of vitrites separated from gas coal type 33 (International class 632), gas-coking coal type 34 (Int. class 634) and orthocoking coals type 35.1 and 35.2 (Int. class 535 and 433) from the High Silesian Coal Basin are presented. Basic differences in properties and structure appear between the vitrite of gas coal and the other vitrites. Vitrites from orthocoking coals are characterized by the highest degree of aromatic unit condensation, the packing of aromatic lamellas and by the highest height of crystallites.The process of continuous thermosolvolysis of these vitrites with chloroform was carried out. Properties and structure of the extracts and extraction residues are also presented. The increase of the aromatic character of the extracts with increase of the rank of the parent vitrites is observed.     

Co-carbonization of hard coals and coal extracts 1. The co-carbonization of low rank coals with extracts

Studies on the influence of an additive derived from coal on the coking properties of lower-rank coals and on the structure of cokes obtained from blends have been undertaken in our laboratory since 1978. The two coal extracts from flame coal (Int. Class. 900) and gas-coking coal (Int. Class. 632) were used as additives. The results indicate that the blends prepared from low-rank coals — flame coal (Int. Class. 900), gas-flame coal (Int. Class. 721) and the extracts possess better coking properties in comparison to the parent coals. The optical texture and the degree of structure ordering of the cokes obtained from blends is related to the amount of extract in the blend. With increasing extract content in the blend, increases were observed in the amount of optically anisotropic areas in cokes from low-rank coal/extract blends and the crystallite height (L_c) of cokes from the blends. The isotropic optical texture of cokes from low-rank coals can be modified by coal extracts to an anisotropic optical texture. The non-fusible coal is the most difficult to modify. An explanation of the observed phenomena is given.     

Co-carbonization of hard coals and coal extracts 2. The co-carbonization of medium- and high-rank coals with extracts

Studies on the influence of anthracene coal extracts on the carbonization process of medium- and high-rank coals were undertaken. Extracts from flame coal (Int. Class. 900) and gas-coking coal (Int. Class. 632) were used as additives. The blends prepared from the examined coals and the extracts exhibited better coking properties than the parent coals. The addition of extract to the coals gave an increase in the microstrength of the resultant cokes. The effects of co-carbonization of coking coals with extracts were increases in the size of the optical texture as well as in the degree of structural ordering of cokes. In the co-carbonization of semicoking coal with addition of coal extracts, a reduction in the size of the anisotropic units and a decrease in the crystallite height of cokes were observed. No modification of the basic anisotropy of coke from anthracite by coal extract was observed. With increasing extract content in anthracite/extract blends there was an increase in the degree of structural ordering of co-carbonization products. Extract addition was unable to modify the behaviour of fusinite. Based on the results of investigation of the influence of coal extracts on the carbonization of different-rank coals, a division of coals according to the modification of the optical texture of coke is given.     

Structure in cokes from coals of different rank

A range of bituminous coals has been carbonized to 1273 K. Polished surfaces of the solid products, carbons or cokes, are examined for optical texture by optical microscopy. Fracture surfaces of the carbons are examined by scanning electron microscopy (SEM). The carbon from the lowest rank coal (NCB Code No. 702) is isotropic and fracture surfaces are featureless. Carbons from coals of ranks 602, 502 are optically isotropic but fracture surfaces are granular (size 0.1–0.2 μm), indicating small growth units of mesophase. In the carbon/coke from a 401 coal, the anisotropic optical texture and grain size are both ≈0.5–10 μm diameter. Coke from a coking coal (301a, 301b) has a layered structure extending in units of at least 20 μm diameter with sub-structures ~ 1.5 μm within the layers, indicating perhaps that the bedding anisotropy of these coals is not totally lost in the fluid phase of carbonization. The carbons from the higher rank coals have the bedding anisotropy of the parent coal. The combined techniques of optical microscopy and SEM (both before and after etching of the fracture surfaces of coke in chromic acid solution) reveal useful detail of structure in carbons/cokes and of the mechanism of carbonization of coking coals.     

Carbonization and liquid-crystal (mesophase) development. 16. Carbonizations of soluble and insoluble fractions of coal-extract solution

A coal-extract solution prepared by extraction of a coking coal (CRC 301a) with anthracene oil by the National Coal Board is separated into fractions using solvents of increasing solvent power. These fractions are carbonized to 823 K and the optical textures of resultant cokes are assessed. The objective of the study is to examine the role of the molecular components of the coal-extract solution including the residual anthracene oil in mechanisms of formation of the optical texture of the anisotropic coke. Generally, the low-molecular-weight fractions of the coal-extract solution produce cokes with larger sized optical textures than the coke from the parent coal-extract solution. The higher-molecular-weight fractions produce cokes with smaller sized optical textures. Isotropic coke is produced from material which is not soluble in benzene and tetrahydrofuran. Within this parent-coal-extract solution it would appear that the dominant partner effect is influential over the size of the optical texture of coke from the coal-extraction solution, that is the minor component of smaller molecules controls the necessary growth of liquid crystals. Also, the presence of anthracene oil augments the size of optical texture of resultant cokes by providing the necessary physical fluidity of the system and possibly some chemical stability.     

Effect of parent coal rank on the yield and properties of carbonization extracts

The paper describes the study of carbonization of solvent extracts derived from coals of different rank. The solvent was hydrogenated anthacene oil. The characteristics of the parent coals and of their extracts are presented here as well as the mass balance from carbonization of each extract at a final heat-treatment temperature of 803 K, the physicochemical and structural analysis of the cokes obtained, and the chemical analysis of the liquid and gaseous products. The experiments showed that the properties of the carbonization products significantly depend on the physicochemical properties of the parent extracts. Parent coal rank had a slight effect on carbonization yields from extracts, but markedly influences the structure and texture of the solid carbonization products.     

Carbonization and liquid-crystal (mesophase) development. 10. The co-carbonization of coals with solvent-refined coals and coal extracts

Coals (NCB rank 102 to 902) were co-carbonized with solvent-refined coals and coal extracts, mixing ratio of 7:3, to 873 K, heating at 10 K min^?1 with a soak period of 1 h. Resultant cokes were examined in polished section using reflected polarized-light microscopy and optical textures were recorded photographically. These optical textures were compared to assess the ability of the additive pitch to modify both the size and extent of optical texture of resultant cokes. The objective of the study is to provide a fundamental understanding of the use of pitch materials in co-carbonizations of lower-rank coals to make metallurgical coke. A Gulf SRC was able to modify the optical texture of cokes from all coals except the anthracite. Soluble fractions of this Gulf SRC were less effective than the parent SRC. A coal extract (NCB D112) modified coke optical texture, the extent being enhanced as the rank of coal being extracted was increased. Hydrogenation of the coal extract increased the penetration of the pitch into the coal particles but simultaneously reduced the size of the optical texture relative to the non-hydrogenated pitch. This indicates a positive interaction of pitch with coal in the co-carbonization process. The optical texture of the cokes from the hydrogenated coal extract in single carbonizations was larger than that from the non-hydrogenated material. Mechanisms explaining these effects are briefly described.     

Carbonization of coal blends: mesophase formation and coke properties

Laboratory investigations of strength of cokes from blends of coals incorporating pitch were supported by 7 kg trials. The stronger cokes showed a greater interaction between coal and pitch to produce an interface component of anisotropic mozaics which is relatively resistant to crack propagation. The process whereby coal is transformed into coke includes the formation of a fluid zone in which develop nematic liquid crystals and anisotropic carbon which is an essential component of metallurgical coke. Strength, thermal and oxidation resistance of coke can be discussed in terms of the size and shape of the anisotropic carbon which constitutes the optical texture of pore-wall material of coke. Coals of different rank form cokes with different optical textures. Blending procedures of non-caking, caking and coking coals involve the interactions of components of the blend to form mesophase and optical texture. Petroleum pitches used as additives are effective in modifying the carbonization process because of an ability to participate in hydrogen transfer reactions.     

Gasification studies of cokes from coals. The effects of carbonization pressure on optical texture and porosity

Ten coals were carbonized under various pressures (4 kPa, normal pressure and 10 MPa). Optical textures and physical structures of resultant cokes were monitored. The extent of optical anisotropy increased greatly with increasing carbonization pressure, such a trend being more pronounced with the lower-rank coals. Physical structure was also influenced by carbonization pressure. Gasification reactivities of the cokes with carbon dioxide and steam (1200 °C) were studied with respect to their optical anisotropy and physical structure. Gasification reactivities of optical textures were estimated using both the point-counting technique and regression analysis. The reactivities of cokes with the same optical texture produced from the same parent coal were similar. However, there were considerable differences when compared with cokes from different parent coals. Although the values estimated by regression analyses are consistent with those obtained by point-counting, except for the leaflet and inert textures, the physical locations of respective textures can be important in quantitative discussions of their reactivities.     

Carbonization and liquid-crystal (mesophase) development. 11. The co-carbonization of low-rank coals with modified petroleum pitches

Coals of rank ranging from medium quality coking to non-caking, non-fusible, have been co-carbonized with Ashland petroleum pitches A170, A240 and A200 as well as pitches modified by heat-treatment with aluminium chloride using A170, and by reductive hydrogenation of the A200. The mixing ratio was 7:3, the final HTT was 873 K, heating at 10 K min^?1 with a soak time of 1 h. The optical texture of the resultant cokes is assessed using polished surfaces and a polarized-light microscope using reflected light and a half-wave plate. The changes in optical texture are studied from the point of view of using coals of low rank in the making of metallurgical coke. The optical texture of resultant cokes is modified by co-carbonization and the mechanism involves a solution or solvolysis of the non-fusible coals followed by the formation of nematic liquid crystals and mesophase in the resultant plastic phase. The modified A170 pitch is more effective in modifying optical texture than the A170 because of an increase in molecular weight. The hydrogenated A200 is a very reactive additive probably because of an increased concentration of naphthenic hydrogen. The hydrogenated A200 can modify the optical texture of cokes from the organic inerts of coals and from oxidized, non-fusible coals.     

Optical anisotropy of carbonized coking- and caking-coal vitrains

The purpose of this work was to characterize in detail the optical anisotropy formed during carbonization of the range of coals used in the coking industry, the ultimate objective being to attain a better understanding of the coking process. Vitrains hand-picked from a series of coking and caking coals were carbonized to various temperatures between 380 and 1000 °C. The semicokes and cokes so produced were examined by polarized-light microscopy to determine the proportions of the different types of optical anisotropy developed during carbonization. The results demonstrated that coals normally grouped within one class of the coal classification system used by the National Coal Board can lead to cokes which are significantly different in terms of their optical anisotropy. The process of the anisotropic development during carbonization can be explained generally in terms of loss of volatile matter, variations in viscosity of the plastic mass, and distortion of ordered phases by the pressure of evolving gases. Differences in carbonization behaviour as judged by the coke anisotropy can be attributed to differences in the ‘molecular-structure’ of the parent coal. In this respect the oxygen in the coal is considered to be of primary significance.     

Carbonization and liquid-crystal (mesophase) development. 18. carbonization of coal-extract solutions (non-hydrogenated): influence of digestion conditions upon optical texture of cokes

Coal-extract solutions have been produced by the dissolution of a prime coking coal in anthracene oil followed by the removal of the undissolved solids. A range of coal-extract solutions prepared under different conditions was carbonized and the optical texture of the polished surfaces of the resultant cokes were assessed. The coal-extract solution prepared with the longest digestion time and at the highest temperature produced a coke with the largest anisotropic domains with some flow structure. Removal of the anthracene oil component of the coal-extract solution by extraction with selected solvents modified the carbonization behaviour such that although the coke yield increased substantially there was a significant decrease in the size of the anisotropic domains of the resultant cokes.     

低阶煤有机溶剂萃取的研究进展

鉴于煤有机溶剂萃取的迅速发展,以低温和高温热萃取作对比,对相应的萃取机理、影响因素及萃取物的应用等进行分析。结果表明:萃取温度在200℃以下的多为低温物理萃取,萃取率一般较低,所得萃取物多用于研究煤的分子结构;而温度在300~400℃的萃取多为高温溶剂萃取,所得萃取率较高,萃取过程中会伴随化学键的断裂及相应化学反应的发生,所得萃取物多用在研究配煤炼焦、劣质煤的气化液化、新型煤基材料等领域。     

煤的变质程度对焦炭性质影响的研究

对不同变质程度的5种烟煤进行了5 kg实验焦炉炭化实验.并就单种煤的结焦性与对应焦炭的微晶结构间的关系进行了探讨.结果表明,1/3焦煤焦炭、焦煤焦炭的冷态强度和热态强度较好;X射线衍射(XRD)分析结果表明,肥煤焦炭的炭结构因子(La/Lc)最小,石墨化程度最高.焦炭的真相对密度(TRD)随着La/Lc的增大而减小.     

Upgrading lignites via thermal reduction with coke-oven gas

Three Turkish lignites of varying rank were processed by using coke-oven gas under various processing conditions. Proximate and ultimate analyses and microscopic investigations with a polarized-reflected light microscope were carried out for all of these samples. Gaseous products were also determined after each process. Blends of processed lignites with coking coals were subjected to dilatation tests and cokes were produced in a laboratory scale coke oven using the same blends. The tensile strengths of the cokes produced were determined. The chemical and physical data showed that there are useful changes in lignite structures upon treatment with coke-oven gas under certain processing conditions. The dilatation and tensile-strength results showed that it would be possible to blend processed lignites with coking coals in significant proportions to produce metallurgical grade cokes.     

Aspects of gasification and structure in cokes from coals

Cokes were prepared from nine coals of different rank and characterized by surface area measurement, reactivity to carbon dioxide at 1473K and Raman-laser spectroscopy. Rates of gasification of cokes on a unit surlface area basis (K¹ = g m^?2 min^?1) decreased with increasing rank of parent coal based on maximum oil reflectances. However rates of gasification could not be related to coke structure as measured by Raman-laser spectroscopy.     

Catalytic graphitization of cokes by indigeneous mineral matter

Indigeneous mineral matter in coals acts catalytically towards graphitization during heat treatment of coals to 2273 K. Nineteen coals of a wide range of rank were demineralized by acid extraction. Original and demineralized coals were carbonized in the range 1073–2273 K, and the resulting cokes examined by optical microscopy, X-ray diffraction and phase-contrast high resolution electron microscopy. Optical microscopy indicated the extent of formation of anisotropic carbon in the resultant cokes. The (002) X-ray diffraction profiles indicated three types of catalytic effect, for which electron microscopy demonstrated different crystallite structures and interrelations. The importance of catalytic graphitization in metallurgical cokes in relation to their strength and reactivity is discussed.     

Carbonization and liquid—crystal (mesophase) development. 19. Co-carbonization of oxidized coals with model organic compounds

This study examines further the phenomena of the modification of coal carbonizations by organic additives. Anthracene, pyrene and chrysene modify the carbonization in a closed system of coking coals as observed from increases in the size of optical textures of resultant cokes. Weakly caking coals are unaffected. Chrysene is the most efficient modifier probably because of its lowest calculated free valence. The co-additives tetralin and hydrogenated anthracene oil further enhance the modification processes so obviating the necessity to use hydrogenated additives. Co-carbonizations of oxidized coking and caking coals with decacyclene are effective in removing the effects of mild oxidation. Increased rates of carbonization enhance the sizes of optical textures of resultant cokes.