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.     

Carbonization properties of hydrogenated aromatic hydrocarbons—III: Modifying activities of hydrogenated pryene and its oxidized derivatives in the co-carbonization of coals and coal liquids

The modifying activities of hydrogenated pyrene (HP) and its oxidized derivatives were examined in co-carbonization with solvent refined coal, solvent treated coal, a fusible and a non-fusible coal. The present additives all showed a significant activity, with HP oxidized at 150°C exhibiting the highest activity. The activity of the additive is discussed from its structural indices and coke yield in relation to its dissolving and hydrogen donating abilities. The modifying susceptivility of the carbonizing substance is rated in the order described above, being correlated with its single carbonization properties, such as fusibility and potential for anisotropic development. A consecutive treatment of partial hydrogenation and oxidation is emphasized as a useful technique for producing active additive and an excellent coking substance from the pitch material.     

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.     

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 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.     

Flash pyrolysis of coals. Devolatilization of bituminous coals in a small fluidized-bed reactor

The devolatilization behaviour of ten bituminous coals was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal particles being injected at a rate of 1–3 g h^?1 directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbon gases, and total volatile-matter and an agglomeration index are reported for all coals. Maximum tar yields were obtained at about 600 °C and were always substantially higher than those from the Gray-King assay. Total volatile-matter yields were also substantially higher than the proximate analysis values. The maximum tar yields appear to be directly proportional to the coal atomic $\text{H}\text{C}$ ratio. The elemental analysis of the tar is strongly dependent on pyrolysis temperature. The tar atomic $\text{H}\text{C}$ ratio is proportional to that of the parent coal. The effect on the devolatilization behaviour of two coals produced by changes in the pyrolyser atmosphere and the nature of the fluidized-bed material were also investigated. Substituting an atmosphere of hydrogen, helium, carbon dioxide or steam for nitrogen, has no effect on tar yield and, with one exception, little effect on the hydrocarbon gas yields. In the presence of hydrogen the yield of methane was increased at temperatures above 600 °C. Tar yields were significantly reduced on substituting petroleum coke for sand as the fluid-bed material. A fluidized bed of active char virtually eliminated the tar yield.     

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.     

Solvolytic liquefaction of coals with a series of solvents

Solvolytic liquefaction of coals of different rank was studied with a variety of solvents at 370–390 °C under nitrogen in order to elucidate the role of solvent in coal liquefaction of this kind and to find a suitable solvent for the highest yields of liquefaction. The yield was found to depend strongly upon the nature of the coal as well as the solvent under these conditions. Pyrene and a SRC-BS pitch were excellent solvents for Miike coal, which was fusible with high fluidity at these temperatures. However, the former was less efficient for Itmann and Taiheiyō coals which were fusible at a higher temperature and non-fusible, respectively. The mechanism of solvolytic liquefaction is discussed, including nature of coal and solvent at reaction temperatures, in order to understand the properties required for high yields with non-fusible coals in solvolytic liquefaction. It is found that for liquefaction with a high yield if the coal is non-fusible, solvolytic reaction should take place between solvent and coal, so giving a liquid phase of low viscosity at the reaction temperature. The solvolytic reaction may be one of hydrogen transfer when SRC-BS is used as the solvent.     

Coking behaviour of coals recovered from slurry pipelines using a selective agglomeration technique

The coking behaviour of coking coals after transport in experimental slurry pipelines and recovery from the slurry by oil agglomeration has been studied using a 100 kg test coke oven. It was shown that excellent quality coke could be made, in some cases stronger than would be produced from the same coals after conventional preparation. The improved coke strength was due to the fine grinding of the coals which was a characteristic of the agglomeration technique. The presence of diesel oil or kerosene had a retarding effect on heat transfer and in some conditions decreased coke oven productivity. Normal productivity was observed when tar was used as the agglomeration agent.A two-step process with recovery and re-use of oil is suggested and the potential improvement in yields of blast furnace coke per tonne of raw coal are presented.     

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.     

Flash pyrolysis of coals: influence of cations on the devolatilization behaviour of brown coals

The influence of cations on the pyrolysis behaviour of brown coals under flash heating conditions was investigated by means of a small fluidized-bed pyrolyser. A stream of coal particles in nitrogen was injected at rates of 1–3 g coal/h directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbons and total volatile matter from four Gelliondale brown coals and a Montana lignite were determined as a function of pyrolysis temperature. With all coals the maximum tar yield was obtained at 600 °C. Removal of cations present in the coals markedly increased the yields of tar and total volatile matter, with little effect on the yields of hydrocarbon gases. The converse was also observed in that the addition of Ca²⁺ to a cation-free coal decreased the yields of tar and total volatile matter. The extent of the reduction in tar yield at 600 °C in the presence of cations was found to be similar for all coals. After acid washing, tar yields appear to correlate with the atomic $\text{H}\text{C}$ ratios of the coals in a manner similar to that observed previously with bituminous coals.     

Carbonization and liquid-crystal (mesophase) development. 8. The co-carbonization of coals with acenaphthylene and decacyclene

Several coals of different rank have been carbonized singly and also co-carbonized with acenaphthylene and decacyclene. The resultant cokes were mounted in resin and polished surfaces were examined for optical texture using a polarized-light optical microscope fitted with a half-wave retarder plate. The optical texture can be assessed qualitatively (visually) or quantitatively by a point-counting technique in terms of size and shape of constituent isochromatic anisotropic units. Some cokes from coals were Isotropic. Acenaphthylene was only able to exert a smaller influence than decacyclene on the optical texture of the resultant cokes from co-carbonizations. Decacyclene was able to modify the optical texture for both the low-rank non-fusible and the caking coals. The effects of changing the proportions of coal to additive were examined. Results are interpreted in terms of ‘depolymerization’ of the coal by the action of the additive (as solvent) and also by the action of the additive in modifying the processes of formation of semi-coke via nematic liquid crystals.     

Carbonization and liquid-crystal (mesophase) development. 12. Mechanisms of the co-carbonization of coals with organic additives

In industrial situations, coals interact with solvents or additives to produce liquid fuels, solvent-refined coal, coal extract and metallurgical coke. In these processes there occurs a wide variation in effects or modifications of the coal by these additives. This paper describes the modifications which can occur, using a wide range of rank of coal, when these coals interact and are co-carbonized with a wide range of additives of different chemical properties. The optical texture of the resultant cokes is given special attention. The objective of the paper is to summarize the current state of knowledge of the mechanisms of these interactions. Possible mechanisms of interactions are summarized, kinetic and chemical structural aspects of reactions are outlined, the importance is mentioned of the formation of liquid phases enabling anisotropic optical textures in modified cokes to be created, and the industrial relevance of its possible development is discussed.     

Influence of polyethylene terephthalate on the carbonisation of bituminous coals and on the modification of their electric and dielectric properties

The purpose of this research was to study the influence of 2 wt% of polyethylene terephthalate (PET) on carbonization of two bituminous medium-volatile coals being different in maximum fluidity (MF). During the research into consideration were taken the structure of the coal plastic layer, the value and the distribution of the intralayer pressure, the changes in volume of the heated coal charge and in the development of the porous structure of the coke, so the changes in electric and dielectric properties of the solid residues obtained from the co-carbonisation of the coals with PET and a coal-tar pitch.The investigations were carried out in a laboratory unit using X-raying and tracing the coal charge with markers of copper foil. Changes in the porous structure of the carbonized coals were estimated on the basis of micrographs taken with a scanning electronic microscope (SEM). It was established that under the influence of PET the thickness of the plastic layer of coals decreases; its zone structure modifies, value and the distribution of the intralayer pressure in the heated charge of bituminous coals changes. PET can change the mechanism of formation of coke obtained from coals with a lower MF index, which leads to appearance of a less dense coke. PET facilitates the formation of a denser coke when blended with a coal with higher MF.The change of electric and dielectric properties of co-carbonisation products of coals with PET and coal tar pitch is analysed. The analysis shows that PET reacts with coals with distinct MF indices in a different way and has an influence on them opposite to that of pitch. Namely: when blended with a coal of low MF, PET facilitates the formation of cross-links between the macromolecules, and with high MF—the processes of macromolecular chains' growth due to the increase in their length.     

Carbonization of coals to produce anisotropic cokes: 3. Evaluation of low-rank bituminous and subbituminous coals by single and co-carbonizations with pitch

Single carbonizations and co-carbonizations of 17 low-rank bituminous and subbituminous coals have been studied to evaluate their suitability as sources of blast furnace coke in terms of pore-wall profile and anisotropic development within the cokes. Co-carbonizations suggest the possible use of low-rank coals which from single carbonizations would not have been considered suitable. To evaluate semi-quantitatively the coke quality, two structural characteristics of the cokes produced by single and co-carbonizations are graded on a scale of 1 to 5. Overall assessments for each coal are plotted against the atomic H/C and 0/C ratios of the original coals. Although there are a few exceptions, coals with similar assessments are located in the same region of the plot, indicating that, to a first approximation, the H/C and 0/C ratios are suitable indicators of the single and co-carbonization properties of a coal. The presence of cations in the coal appears to be an additional factor influencing the carbonization properties and may explain the exceptional behaviour of some coals. Removal of these cations by pretreatment of the coals improves the carbonization properties.     

The co-carbonization of oxidized coals with pitches and decacyclene

Coals of rank (NCB) 701, 401 and 204 were oxidized in air at 371 K for up to 15 days. The changes in optical texture of cokes from these coals were monitored by optical microscopy and point counting. The oxidized coals were cocarbonized to 1273 K with up to 30% of A240 petroleum pitch, a hydrogenated coal extract and decacyclene, and the resultant cokes were reassessed. The increase in isotropy in cokes caused by the oxidation treatment was never completely removed by use of the additives, but significant improvements existed for the less extensively oxidized coals. The possibility exists of using co-carbonization of oxidized coals with additives in coke making. Additives with good hydrogen donor ability, as with the coal extract, appear to be the most suitable.     

Pyrolysis of western canadian coals in a spouted bed

Coal pyrolysis has been studied to determine conditions for maximum liquid yields from some Western Canadian coals. Gas, tar and char yields were determined for four coals in a 12.8 cm dia. reactor. A characteristic temperature for maximum tar yield existed for each coal at a fixed feed rate and particle size. A steady increase in tar yield was found as the average coal particle size was reduced from 2.28 to 0.65 mm. Composition of gas, and ultimate analyses of tar and char are presented as a function of operating temperature. A simple first-order devolatilization model adequately describes the effects of coal feed rate, reaction time, and temperature on the yield of volatiles, but is insufficient to describe particle size effects.     

Influence of additives of various origins on thermoplastic properties of coal

Two coking coals of different rank were chosen in order to assess the influence of various additives on their thermoplastic properties. Six additives of different origin and characteristics were selected: two non-coking coals, together with a commercial coal tar pitch, a residue from the bottom of the benzol distillation tower and two residues from the tyre recycling industry. The effect of the additives on coal thermoplastic properties was assessed by means of the Gieseler test. The additives were pyrolyzed to a final temperature of 550 °C and the tar characterized by means of Fourier transform infrared spectroscopy (FTIR) and gas chromatography (GC). The influence of the additives on coal thermoplasticity is related to the volatile matter content of the additive, its evolution profile with temperature and the composition of the tar obtained during the pyrolysis of the additives.     

Plastic wastes, lube oils and carbochemical products as secondary feedstocks for blast-furnace coke production

Two plastic wastes (polyolefin-enriched and multicomponent), two lube oils (paraffinic and synthetic) and one coal-tar were assessed as individual and combined additives to coal blends for the production of blast furnace coke. The effects of adding 2 wt.% of these additives or their mixtures (50:50 w/w) on the coking capacity of coal, coking pressure and coke quality parameters were investigated. It was found that the two plastic wastes reduce fluidity, whereas the addition of oils and tar helps to partially restore the fluidity of the coal-plastic blend. From the co-carbonization of the coking blend with the different wastes in a movable wall oven of over 15 kg capacity, it was deduced that polyolefins have a detrimental effect on coking pressure. The addition of oils and tar to the coal-plastic blend has different modifying effects. Whereas paraffinic oil eliminated the high coking pressure caused by the polyolefins, polyol-ester oil had a weak reducing effect unlike coal-tar which had a strong enhancing effect. The compatibility of the oils/tar with plastics and coal and the beneficial influence of these combinations on coking pressure is discussed in relation to the miscibility of the plastic and the oily and bituminous additives, and the amount and composition of the volatile matter evolved from each additive during pyrolysis as evaluated by thermal analysis. Furthermore, it was found that coke reactivity towards CO₂ (CRI) and coke strength after reaction with CO₂ (CSR) are heavily dependent on the composition of the plastic waste, with polystyrene (PS) and polyethylene terephthalate (PET) having a clear negative effect. The porosity of the cokes obtained from blends containing plastic wastes is always higher, but the pores are smaller in size.     

Carbonization and liquid-crystal (mesophase) development. Part 4. Carbonization of coal-tar pitches and coals of increasing rank

Coal-tar pitches, from coals of different rank and with various quinoline-insoluble contents, were carbonized under pressure (67 to 200 MN m⁻²) to maximum temperatures of 923 K. The resultant cokes were examined by optical and scanning electron microscopy in terms of size and shape of anisotropic structures within the coke. Natural quinoline-insolubles and carbon blacks both destroyed growth of the mesophase and development of anisotropy. Graphite particles (<10 μm) promoted growth and coalescence of the mesophase. Fourteen coals, of carbon content 77 to 91 wt%, VM 41 to 26%, were similarly carbonized under pressure. In the lower-rank coals no microscopically resolvable anisotropic mesophase was produced, but at a carbon content of 85% anisotropic units 1–2 μm in diameter were detected, increasing in size at a carbon content of 90% to 5 μm diameter. Results are discussed in terms of the origins of anisotropic mosaics observed in cokes, their variation in size with coal rank, and their significance in the carbonization of coal.