Bonding of solid additives in cokes from coals: a microscopy study

Cortonwood Silkstone (NCB class 401) and Betteshanger (NCB class 301 a/204) coals were co-carbonized with solid additives such as anthracite, coke breeze, green and calcined petroleum cokes. The resultant carbonization products (cokes) were examined by optical microscopy and SEM was used to investigate polished surfaces etched by chromic acid and fracture surfaces. For both coals only the anthracite and green petroleum coke become bonded to the coal cokes. This probably results from softening and interaction of interfaces of the anthracite and green coke with the fluid coal via a mechanism of hydrogenating solvolysis during the carbonization process. The coke breeze and calcined petroleum cokes were interlocked into the matrix of coal coke.     

Carbonization of coals into anisotropic cokes: 6. Formed cokes of high density and optical anisotropy from non-fusible and slightly fusible coals

A procedure for the preparation of solid formed coke of enough adhesion and anisotropic development for use in the blast furnace has been studied, using non-fusible and slightly fusible coals with petroleum cocarbonizing additives. The coke precursor was prepared through the copreheat-treatment of coal and a suitable additive in adequate quantity under stipulated conditions. The desired coke was produced by carbonization after forming with a press. The conditions for the copreheat-treatment have been carefully examined in terms of the temperature, time and heating devices. The behaviour of coals during copreheat-treatment and carbonization were discussed in terms of coal ranks, comparing this behaviour to the liquefaction reactivity and thermal stability of their liquefied product.     

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.     

Ultimate analysis of coals and cokes using instrumental techniques

This Paper describes instrumental techniques for the rapid determination of carbon, hydrogen, nitrogen, oxygen and sulphur. Two Perkin-Elmer Model 240 elemental micro-analysers were used, one for the direct determination of oxygen and the other for the simultaneous analysis for carbon, hydrogen and nitrogen. The Leco Automatic Sulphur Titrator was used for the sulphur assay. Accuracy and repeatability similar to that obtained by the classical methods described in the relevant British Standards were found, and data are presented to illustrate the comparison. Special aspects of developed procedures are emphasized which are essential for the attainment of good precision and accuracy.     

Sulphur capture during gasification of oil sand cokes

The capture of sulphur via the H₂S-CaO reaction during gasification of delayed coke has been investigated in a 6.4 cm dia. semi-batch stirred bed reactor. Calcines from one of three limestones or a dolomite were mixed with coke which was then gasified in a steam-nitrogen mixture at atmospheric pressure and 930°C. The H₂S content of the gas, and the sulphur content of the sorbent were determined as functions of time. The effects of sorbent surface area, percentage calcination, and the Ca/S ratio on the extent of sulphur capture and the conversion of sorbents were determined. The sulphidation reaction was analyzed using continuous and grain models. After an initial stage of chemical control the reaction appears to be controlled by diffusion through the product layer of the grain.     

单种煤性质对其焦炭性质的影响

通过测定11种单种煤和所炼坩埚焦的性质，得出单种煤挥发分与平均最大反射率在合适的范围内，所炼坩埚焦的反应性最小，结构强度最大。     

Applications of laser Raman microprobe spectroscopy to the characterization of coals and cokes

Optical microscopy is widely used in the characterization of coals and cokes. This Paper shows that the laser Raman microprobe (MOLE) which combines an optical microscope and a Raman spectrometer can provide useful additional information. Three main areas were investigated: identification of minerals in coal and coke; structural characterization of coals and cokes; and the interaction of inorganic additives and coal. Where possible, the results were compared with conventional optical microscopy measurements whereby it was shown that the optical texture and Raman spectra of cokes are not closely related. The Raman spectra of high temperature cokes were used to estimate the size of microcrystalline regions.     

Ultrasonic study of the effects on metallurgical cokes of heat treatment and gasification

To monitor changes in the fissure density in the interior of coke, pieces of an industrial metallurgical coke,were examined before and after heat treatment and gasification in carbon dioxide at 1173 K, using an ultrasonic non-destructive method (PUNDIT). Seven coke pieces were heat treated to 1173 K in nitrogen and six showed increases in pulse velocity of 30–40%. Ten coke pieces were gasified at 1173 K in carbon dioxide and all showed decreases in pulse velocity of about 10%. The effects of extended heat treatment and gasification are reported.     

Carbonization of coals to produce anisotropic cokes. 1. Modifying activities of some additives in the co-carbonization of low-rank coals

Using low-rank coals, the modifying activities of some petroleum, coal tar and aromatic hydrocarbon additives have been examined to find procedures for their utilization in the preparation of blast furnace coke. Petroleum pitch, especially after hydrogenation, exhibited excellent modifying activity even with non-fusible coals. In contrast, the activity of coal tar was very limited with such coals. The napththenic component, revealed by n.m.r. of the additives, appears to be important in the co-carbonization by inducing fusibility and anisotropic development in such coals. Co-carbonization to recover the dehydrogenated additives was attempted. However, there was no development of the anisotropy in the resultant coke by dissolution of the coal particles although the coal particles were firmly fixed in the matrix. Acid-refluxing treatment of non-fusible coals was found to enhance their modification susceptibility, indicating that some of the acid-soluble mineral matter is important in the thermal depolymerization or fusion process of the coal.     

Correspondence between the composition and plastic properties of British coals and the structural properties and reactivity of the corresponding cokes

The chemical composition and the physico-chemical properties of a suite of British coals, mainly of types 501/2 as defined by the NCB classification, but including some coals of higher and lower rank (NCB classification 204,401/2 and 601/2), were comprehensively investigated. Each coal was subsequently carbonized under controlled conditions of size distribution, bulk density and temperature on the 250 kg scale and the tensile strength, coke structure and coke reactivity were determined. This data highlighted the significance of the atomic ratio of the oxygen and carbon of the coals and the lack of relations between coal properties and coke structure and strength. As regards coke reactivity only complex relations with coal properties could be found, with coal rank, the oxygen/carbon ratio and the chlorine content being of greatest importance.     

不同沉积环境下煤的热解与气化特性

采用煤热解.气化连续方法,在TG-DTA/DSC热分析仪器上对煤化程度接近但沉积环境不同的5种煤的热解与气化特性进行研究,运用Coats-Redfem积分法求解煤热解动力学参数.研究结果表明:5种煤的热解机制是相似的,反应级数n=3;还原程度较弱的SH与SF煤,热解表观活化能在43-54 kJ/mol,而还原程度较强的...     

Studies related to the structure and reactivity of coals : 18. The chemical structures of products from reactions of a suite of higher rank Australian coals

The structure of the oils, asphaltenes and residues obtained by the thermal reactions of a suite of Australian higher rank coals under hydrogen or nitrogen have been studied by chemical and spectroscopic methods. The host-guest model that has been used to describe the structure of Australian brown coals cannot be applied directly to the higher rank coals. Evidence is provided that suggests that a modified version of the model may be of use in describing the structure of some subbituminous coals. The methodology has proved to be useful in the understanding of structural features of coals which are often not rank dependent, e.g. Callide coal (ABL2), a subbituminous coal, has been shown to have characteristics of both very high and also low rank coals.     

Structural study of cokes using optical microscopy and X-ray diffraction

Cokes exhibiting a range of optical texture from isotropie to anisotropic domains > 60 μm diameter were examined by X-ray diffraction. The variation of an optical texture index (OTI) with crystallite height and interlayer spacing was studied. The OTI varies little with the X-ray parameters for cokes whose optical texture is larger than medium-grained (1.5–5.0 μm) mosaic anisotropy. For cokes of smaller optical texture there is a sharp decrease in crystallite height and an increase in interlayer spacing. These results are discussed in terms of fluid mesophase removing defects in cokes of optical texture of size of coarsegrained mosaics and larger. The cokes of smaller optical texture are formed from less fluid mesophase which does not coalesce. Defects therefore remain in this anisotropic carbon of the coke so reducing crystallographic order.     

Mineral matter effects on air-oxidation of cokes from a coking coal

Indigenous mineral matter in coal affects the chemical reactivity of resulting cokes through both catalytic graphitization and catalytic gasification. The significance of both catalytic effects on air-oxidation was examined using cokes from a medium-volatile bituminous coking coal with 9 wt% mineral matter. Catalytic graphitization by mineral matter enhanced the reactivity of the resulting coke in spite of the formation of highly crystalline carbons. This effect, however, was less than that of catalytic gasification by mineral matter. The coke from the acid-treated predemineralized coal exhibited no catalytic effects but was the most reactive. The implications of these results are discussed in detail.     

Dry gas cleaning process by adsorption of H2S into activated cokes in gasification of carbon resources

Gasification of carbon resources including biomass and coal is one of promising energy production technologies. The R&D on effective and convenient gas cleaning processes for removal of contaminants as well as high efficient reliable gasifiers is essential for industrial application in broad fields. In this study, a dry process of synthesis gas cleaning by adsorption of H₂S into activated cokes was proposed as a candidate of desulfurization technologies in gasification. The H₂S adsorption performance of activated coke produced from coal, which are used industrially for de-SO_x and de-NO_x, was evaluated by the thermogravimetric analyses and the adsorption examination in a fixed bed under the atmospheric and high pressures. Activated coke was not only the most active at about 423 K for the H₂S adsorption rate but also regenerative over 573 K by H₂S desorption with a sufficient rate under an inert gas flow of nitrogen. The H₂S adsorption performance of the activated coke was not inhibited by the co-existence of CO₂ or COS but enhanced rather by the co-existence. The adsorbent was promisingly active for both H₂S and COS adsorption as well. These behaviors suggest that the activated coke are available for simultaneous desulfurization of H₂S and COS. The H₂S breakthrough examination in the fixed bed revealed that it was possible to remove H₂S to lower level than 1 ppm for a long time depending on the residence time of gas flow in the bed. When the adsorption operation was carried out under high pressures up to 0.6 MPa, the regeneration of activated coke by H₂S desorption took place under the pressure reduced to the atmosphere. As the results, it was implied that the present activated coke could be applicable to the desulfurization process in coal gasification.     

Effect of low-volatile additives on the structure and strength of cokes

Blends of medium-volatile or high-volatile coals have been carbonized in a 7 kg oven with low-volatile coals (6–16% VM, dmmf). A comparison is made of the strength and structural properties of these cokes with those of the cokes made under corresponding conditions from the medium or high-volatile coals alone. With increasing levels of addition of the low-volatile coals the tensile strength of the blend cokes generally attains a maximum and then decreases. These strength changes are related to changes in porosity, pore-wall thickness and pore dimensions. Coals which display some degree of plasticity and which are weakly caking improve coke quality by altering the pore-structure due to the combined effects of decreasing the pore diameter and slightly increasing the wall thickness. Those additives which are non-caking act primarily as wall thickeners.     

Influence of pyrolysis conditions on the structure and gasification reactivity of biomass chars

The physical and chemical structure as well as gasification reactivities of chars generated from several biomass species (i.e. pinus radiata, eucalyptus maculata and sugar cane bagasse) were studied to gain insight into the role of heating rate and pressure on the gasification characteristics of biomass chars. Char samples were generated in a suite of reactors including a wire mesh reactor, a tubular reactor, and a drop tube furnace. Scanning electron microscopy analysis, X-ray diffractometry, digital cinematography and surface area analysis were employed to determine the impact of operating conditions on the char structure. The global gasification reactivities of char samples were also determined for a range of pressures between 1 and 20 bar using pressurised thermogravimetric analysis technique. Char reactivities were found to increase with increasing pyrolysis heating rates and decreasing pyrolysis pressure. It was found that under high heating rates the char particles underwent plastic deformation (i.e. melted) developing a structure different to that of the virgin biomass. Pressure was also found to influence the physical and chemical structures of char particles. The difference in the gasification reactivities of biomass chars at pressure was found to correlate well with the effect of pyrolysis pressure on the graphitisation process in the biomass char structure.     

Carbonization of coals to produce anisotropic cokes. 2. Up-grading of modification activities of petroleum process residues and their correlation with structural parameters

Modifying activities of petroleum pitches and up-graded pitches in the co-carbonization with a range of coals have been examined with the object of proposing an effective co-carbonization process for blast-furnace coke production. Up-grading of additives was attempted using thermal, acidic and oxidative reactions. Acidic reactions with aluminium chloride were most effective with lighter petroleum residues of initially poor modifying activity, this being attributed to dealkylation, ring-closure and ring condensation reactions. The relation between modifying activity and structural indices is discussed. The aromaticity (f_a) and the naphthenic ring number in the unit structure T_n,us can be used as appropriate parameters for the activity when the coking yield is taken into account.     

Carbonization of coals to produce anisotropic cokes: 5. Structural factors of coals influencing carbonization properties

The carbonization properties are studied of two particular coals (Zontag Vlei and Metla coals) which are markedly different despite their similar coalification rank, maceral composition, and oxygen and exinite contents. These coals possess different structural features which influence their carbonization. A demineralizing pretreatment improves the properties of Metla coal. However, this is still inferior to the Zontag Vlei coal. O-alkylation of the Metla coal improves fusibility in single carbonizations and susceptibilities, equalling those of the Zontag Vlei coal. Preheat-treatment differentiates between the coals: Metla coal loses its susceptibility at lower temperatures. The chemical analyses of oxygen functionalities of both the original and preheated coals show that their hydroxyl groups behave differently in carbonizations at lower temperatures, indicating that oxygen functionality may be another influential factor. Hydrogen shuttling within the coal may be a third factor as it may remove the oxygen functionality.     

Carbonization of coals into anisotropic cokes: 7. Copreheat-treatment under short contact-time conditions at high temperature

The copreheat-treatment of non-fusible and slightly fusible coals with A240 and hydrogenated A240 under high temperature-short contact-time conditions around 500 °C has been examined in an attempt to produce a formed coke with better anisotropic development. These conditions shortened the copreheat-treatment time and provided better anisotropic development in the resultant coke after carbonization. Effectiveness of short contact-time has been discussed in terms of the extent of depolymerization of coal molecules suitable for anisotropic development, this being related to coal liquefaction under similar conditions.