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Karen M. Steel - One of the best experts on this subject based on the ideXlab platform.
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influence of thermoplastic properties on coking pressure generation part iv further evidence of the role of bubble Coalescence in the mechanism for pressure generation
Fuel, 2014Co-Authors: Miguel Castro Diaz, Karen M. Steel, John J. Duffy, Colin E. Snape, Merrick R MahoneyAbstract:The fundamental mechanism(s) for high oven-wall pressure are still not completely understood. The hypothesis put forward in this series of papers is that bubble-growth combined with a lack of bubble-Coalescence in the plastic-layer is the primary reason for high oven-wall pressure, and that a lack of bubble-Coalescence occurs when the minimum viscosity and elasticity are above a certain threshold. Because it is known that Coal oxidation decreases its fluidity, an examination of the changes to both viscoelastic properties of the plastic-layer and oven-wall pressure during the coking of oxidised Coals was considered to be a promising way to test the hypothesis, as most of the other properties of the Coal, such as volatile matter, remain unaltered. Viscoelastic properties were measured using high-temperature oscillatory shear rheometry. For the fresh Coals studied, the viscoelastic properties were such that bubble-growth and bubble-Coalescence occurred and the oven-wall pressure was low. After subjecting the Coal to enhanced oxidation, the minimum viscosity and elasticity increased to a level whereby bubble-growth occurred but bubble-Coalescence did not. A large increase in OWP was found to coincide with this change. It is envisaged that bubble-Coalescence enables channels to form in the plastic-layer and that the continuous release of volatiles keeps the channels open. Therefore, bubble-Coalescence is considered to strongly influence gas permeability. When gas permeability through the semi-coke is severely restricted, volatiles would be forced to move to the centre of the charge, condense, and then revolatilise as the temperature rises, leading to high late OWP peaks. If oxidation was allowed to progress further, it is anticipated that viscosity and elasticity would increase to a level whereby bubble-growth would be restricted and OWP would not be high, but the coke would be highly non-fused and very weak. These results may elucidate why variable OWP results are found for different Coals before and after oxidation; it depends on the initial and final viscoelastic properties. For another Coal, OWP remained low at <6 kPa. Although the viscoelastic properties might have suggested that the Coal undergo very little bubble-Coalescence, this Coal was found to expand to only a limited extent (as evidenced by the expansion profile and axial force measurements). The limited expansion suggested that gas was able to escape. It is proposed that for this Coal volatiles are escaping via the solid-like inertinite and semifusinite components within the Coal, which is a mechanism that has been previously proposed. This work reinforces the proposed coking pressure mechanism and indicates that coking pressure could be controlled by manipulating the viscosity and elasticity to provide a significant region of bubble-Coalescence or by adding inert solids. It follows that the phase angle - complex viscosity mapping plots, in conjunction with the ΔL and/or axial force profiles, could be used to identify whether a Coal or Coal Blend is likely to generate a high pressure. Considerable refinement of the tests is thought to be necessary to enable more accurate and reliable predictions.
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influence of Coal thermoplastic properties on coking pressure generation part 2 a study of binary Coal Blends and specific additives
Fuel, 2010Co-Authors: John J. Duffy, Merrick R Mahoney, Karen M. SteelAbstract:A number of Coal Blends and pitch/Coal Blends were evaluated using rheometry, thermogravimetric analysis and microscopy to confirm and further elucidate the coking pressure mechanism previously proposed by Duffy et al. (2007) [1]. We confirm that Blending a low rank, high fluidity, low coking pressure Coal, with a high rank, low fluidity, high coking pressure Coal can significantly reduce the coking pressure associated with the latter. Interestingly, Blending does not necessarily result in a fluidity that is midway between that of the two Coals; sometimes the fluidity of the Blend is less than that of the low fluidity Coal, especially when the Coals are significantly different in rank. This occurs because the increase in complex viscosity (η*) through resolidification of the low rank, high fluidity Coal counteracts the reduction in η* resulting from softening of the high rank, low fluidity Coal. It has also been confirmed that the η* of the resultant Blend can be estimated from the η* of each component Coal using a logarithmic additivity rule commonly employed for polymer Blends. Polarised light microscopy has indicated that the degree of mixing between Coals of different rank is minimal, with fusion restricted to the particle surface. It is therefore inappropriate to think of such a Coal Blend in the same way as a single Coal, since each component Coal behaves relatively independently. This limited fusion is important for understanding the coking pressure mechanism for Blends. It is proposed here that the lower rank Coal, which softens at lower temperature, is able to expand into the interparticle voids between the high rank Coal that is yet to soften, and these voids can create channels for volatiles to traverse. Then, and importantly, when the high rank Coal begins to expand, the pore structure developed in the resolidified structures of the low rank Coal can facilitate removal of volatiles, while the resolidified material may also act as a suitable sorbent for volatile matter. This is considered to be the primary mechanism by which Coal Blending is able to alleviate coking pressure, and applies to addition of inert material also. Addition of a Coal tar pitch was found to increase fluidity but also to extend the thermoplastic range to lower temperatures. This caused an increase in the swelling range, which was accompanied by a long plateau in η*, a feature which has previously been observed for certain high fluidity, high pressure Coals. Elasticity and η* at the onset of expansion were also higher for both the pitch impregnated Coals and the high pressure Blends, which supports previous findings for singly charged high pressure Coals, and confirms the potential use of such criteria for identifying potentially dangerous Coals/Blends. © 2009 Elsevier Ltd. All rights reserved.
Kunio Yoshikawa - One of the best experts on this subject based on the ideXlab platform.
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a comparative study on co combustion performance of municipal solid waste and indonesian Coal with high ash indian Coal a thermogravimetric analysis
Fuel Processing Technology, 2010Co-Authors: Marisamy Muthuraman, Tomoaki Namioka, Kunio YoshikawaAbstract:Abstract In recent years there has been an increasing utilization of Coal Blends in the Indian power industry, with Indonesian Coal, due to high ash content and shortages in domestic Coal production. On the other hand, rapid economic growth is aggravating the municipal solid waste (MSW) related environmental problems. In this study, an attempt has been made to compare the co-combustion characteristics of hydrothermally treated MSW and Indonesian Coal with high ash Indian Coal, so as to replace the Indonesian Coal with MSW. The effect of Blending Indonesian Coal and hydrothermally treated MSW with Indian Coal on ignition behavior was studied. MSW Blends of 10%, 20%, 30% and 50% (in wt.%), and an Indonesian Blend of 10% with Indian Coal were tested in a thermogravimetric analyzer (TGA) in the temperature from ambient to 700 °C with a temperature increase of 10 °C/min. From the results, at 10% of Blend, ignition and carbon burnout were similar for Indonesian and MSW Blend, analogous to Coal combustion and even better than the Indonesian Coal Blend, which indicated the feasibility for replacing Indonesian Coal with hydrothermally treated MSW. Further, the results show a scope to increase the MSW Blend in Indian Coal up to 20%, as the constituents behave as a single fuel.
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characteristics of co combustion and kinetic study on hydrothermally treated municipal solid waste with different rank Coals a thermogravimetric analysis
Applied Energy, 2010Co-Authors: Marisamy Muthuraman, Tomoaki Namioka, Kunio YoshikawaAbstract:This study presents an investigation on the influence of hydrothermally treated municipal solid waste (MSW) on the co-combustion characteristics with different rank Coals, i.e. Indian, Indonesian and Australian Coals. MSW Blends of 10%, 20%, 30% and 50% (wt.%) with different rank Coals were tested in a thermogravimetric analyser (TGA) in the temperature range from ambient to 700 °C under the heating rate of 10 °C/min. Combustion characteristics such as volatile release, ignition and burnout were studied for the Blend fuel. Different ignition behavior was observed depending on the Blends composition and the Coal rank. The result of this work indicates that the Blending of MSW improves devolatization properties of Coal. But it was found that the co-combustion characteristics of MSW and Coal Blend cannot be predicted only from the pyrolytic and or devolatization phenomena as the other factors such as the Coal quality also plays a vital role in deciding the Blends co-combustion characteristics. The TGA combustion profiles showed that the combustion characteristics of Blends followed those of parent fuels in both an additive and non-additive manners. These experimental results help to understand and predict the behavior of Coal and MSW Blends in practical applications.
Carmen Barriocanal - One of the best experts on this subject based on the ideXlab platform.
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influence of biomass on metallurgical coke quality
Fuel, 2014Co-Authors: M G Montiano, Carmen Barriocanal, E Diazfaes, R AlvarezAbstract:Abstract Two industrial Coal Blends used in coke making were subjected to tests in order to assess the influence of waste sawdust (SC2 from chestnut and SP1 from pine) on the quality of the coke produced. The biomass was added in quantities of up to 5 wt.%. It was observed that biomass produced a substantial decrease in the plastic properties of the industrial Coal Blend, with reductions in Gieseler maximum fluidity of around 50% for 3 wt.% additions of the two different sawdusts. Carbonizations with sawdust additions ranging from 0.75 to 5 wt.% were carried out in a movable wall oven of 17 kg capacity. The bulk density of the charge was observed to decrease with increasing amounts of sawdust with negative consequences on the quality of the cokes produced. Mechanical strength was determined by means of the JIS test. Coke reactivity and post-reaction strength (CRI/CSR indices) were also assessed. The amount of sawdust added was low to prevent any deterioration in coke quality. The advantage of using biomass in coking Blends should be seen as a possible way to reduce costs and CO 2 emissions and to incorporate alternative raw materials in coke production.
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relevance of the composition of municipal plastic wastes for metallurgical coke production
Fuel, 2011Co-Authors: Sonia Melendi, M A Diez, R Alvarez, Carmen BarriocanalAbstract:This study is concerned with the effects of the composition of mixed plastic wastes on the thermoplastic properties of Coal, the generation of coking pressure and the quality of the resulting cokes in a movable wall oven at semipilot scale. The mixed plastic wastes were selected to cover a wide spectrum in the relative proportions of high- and low-density polyethylenes (HDPE and LDPE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET). From the results it was deduced that the reduction in Gieseler fluidity in the Coal Blend is linked to the total amount of polyolefins in the waste. It was also found that these thermoplastics increase the pressure exerted against the wall in the course of the coking process and that coke quality is maintained or even improved. However, when the level of aromatic polymers such PS and PET are increased at the expense of polyolefins, the coking pressure decreases. Thus, the amount of aromatic polymers such as PS and PET in the waste is critical, not only for controlling Gieseler fluidity and coking pressure, but also for avoiding deterioration in coke quality (reactivity towards CO CRI and mechanical strength of the partially-gasified coke CSR). An amount of polyolefins in the waste lower than 65 wt.% for a secure coking pressure is established.
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weathering study of an industrial Coal Blend used in cokemaking
Isij International, 1998Co-Authors: R Alvarez, Carmen Barriocanal, M A Diez, M D Casal, J L G Cimadevilla, J J Pis, C S CangaAbstract:Weathering studies were carried out on a coking Coal Blend prepared and ground at industrial scale and stored in the open yard. This typical and complex Blend, composed of 13 different Coals was used by the Spanish Steel Company. Several methods were applied for detecting weathering in the Blend. Gieseler maximum fluidity was the most sensitive indicator of the loss of thermoplastic properties. Carbonization tests were carried out in a movable-wall oven and a semi-industrial oven of 6 t capacity. In addition to the measurements of internal gas pressure and coking pressure, laboratory tests were performed to measure expansion/contraction behaviour of the Coal Blend. A clear decrease in internal gas pressure with weathering was observed in the semi-industrial oven. As regards coke quality, no significant changes were produced in a storage period of ten months, however after this date impairment was observed.
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Characterization of Petroleum Coke as an Additive in Metallurgical Cokemaking. Modification of Thermoplastic Properties of Coal
Energy & Fuels, 1996Co-Authors: J.a. Menéndez, Carmen Barriocanal, J J Pis, Ramon Alvarez, E. Fuente, Maria A. DiezAbstract:It is often assumed that green petroleum coke behaves as an inert material in cocarbonization with coking Coal Blends and has no active behavior on the important thermoplastic properties of the Coal Blend. This paper investigates that assumption. The objective of this study is to clarify effects arising when different petroleum cokes are added to a single Coal or an industrial Blend. The effects studied include changes during the pyrolysis stages of the cocarbonization, using a bituminous Coal. This was done to study if petroleum coke is totally inert at the plastic stage of a given Coal or there is an influence at the plastic stage. A further aim is to show how conventional and nonconventional techniques for petroleum coke characterization relate to its activity with the plastic stage of Coal. A range of six petroleum cokes was used. The petroleum cokes were studied in terms of (a) optical texture, (b) FTIR spectroscopy, (c) hydrogen donor ability, (d) thermogravimetric analysis of the pyrolysis stage, (e) free-swelling index, and (f) thermoplastic properties of Blends made up of a bituminous Coal and petroleum coke. Evidence for a significant activity of some petroleum cokes was assessed using the above techniques, which can be considered as nonconventional in petroleum coke characterization. A good correlation among the parameters obtained from the above techniques/methods was found, indicating that the presence of unreacted and partially carbonized material, the hydrogen donor ability, the relative proportion of methyl and methylene groups, the amount of volatile matter released at a temperature range between 400 and 500 °C, the temperature of maximum volatile matter evolution and, finally, the agglomeration degree of petroleum cokes can be considered as important factors in the plastic properties of cocarbonization systems with coking Coals.
Merrick R Mahoney - One of the best experts on this subject based on the ideXlab platform.
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Estimating coke fracture toughness using acoustic emissions and changes in coefficient of friction during scratch testing
Fuel, 2018Co-Authors: Hannah Lomas, Richard Roest, Tizshauna Thorley, Adam Wells, Zhengyi Jiang, Richard Sakurovs, Russell Stuart, Lauren North, Merrick R MahoneyAbstract:Abstract Acoustic emission profiles generated during scratch testing of a range of metallurgical coke samples were recorded and linked to the concurrent energy release, dispersal or absorption on coke fracture or damage. Three different signatures were identified, which were based on the simultaneous measurement of acoustic and total energy release profiles, and these signatures could be correlated with both the microstructure and microtexture of the coke being traversed at the time. The acoustic emission signature for fracture or damage to the coke reactive maceral derived constituents (RMDC) was correlated to the rank of the parent Coal or Coal Blend, with the signature number generally increasing with increasing rank. Conversely, the signature numbers did not vary with parent Coal rank for fracture or damage to the inertinite maceral derived constituents (IMDC), with the majority of IMDC fractures associated with a release of mechanical energy. The incidence of the signature associated with a release of mechanical energy (type 1) became increasingly dominant from RMDC to RMDC-IMDC interfaces to IMDC. Conversely, signature types associated with a dispersal (type 2) or absorption (type 3) of mechanical energy become increasingly dominant from IMDC to RMDC-IMDC interfaces to RMDC. The findings suggest acoustic emissions recorded during scratch testing and their subsequent characterisation can be used to indicate the fracture toughness of a given coke. This study contributes towards a broader program of research to improve understanding of the factors which influence the strength of coke and its microtextural constituents and interfaces, and how this relates to the properties of the parent Coals.
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influence of thermoplastic properties on coking pressure generation part iv further evidence of the role of bubble Coalescence in the mechanism for pressure generation
Fuel, 2014Co-Authors: Miguel Castro Diaz, Karen M. Steel, John J. Duffy, Colin E. Snape, Merrick R MahoneyAbstract:The fundamental mechanism(s) for high oven-wall pressure are still not completely understood. The hypothesis put forward in this series of papers is that bubble-growth combined with a lack of bubble-Coalescence in the plastic-layer is the primary reason for high oven-wall pressure, and that a lack of bubble-Coalescence occurs when the minimum viscosity and elasticity are above a certain threshold. Because it is known that Coal oxidation decreases its fluidity, an examination of the changes to both viscoelastic properties of the plastic-layer and oven-wall pressure during the coking of oxidised Coals was considered to be a promising way to test the hypothesis, as most of the other properties of the Coal, such as volatile matter, remain unaltered. Viscoelastic properties were measured using high-temperature oscillatory shear rheometry. For the fresh Coals studied, the viscoelastic properties were such that bubble-growth and bubble-Coalescence occurred and the oven-wall pressure was low. After subjecting the Coal to enhanced oxidation, the minimum viscosity and elasticity increased to a level whereby bubble-growth occurred but bubble-Coalescence did not. A large increase in OWP was found to coincide with this change. It is envisaged that bubble-Coalescence enables channels to form in the plastic-layer and that the continuous release of volatiles keeps the channels open. Therefore, bubble-Coalescence is considered to strongly influence gas permeability. When gas permeability through the semi-coke is severely restricted, volatiles would be forced to move to the centre of the charge, condense, and then revolatilise as the temperature rises, leading to high late OWP peaks. If oxidation was allowed to progress further, it is anticipated that viscosity and elasticity would increase to a level whereby bubble-growth would be restricted and OWP would not be high, but the coke would be highly non-fused and very weak. These results may elucidate why variable OWP results are found for different Coals before and after oxidation; it depends on the initial and final viscoelastic properties. For another Coal, OWP remained low at <6 kPa. Although the viscoelastic properties might have suggested that the Coal undergo very little bubble-Coalescence, this Coal was found to expand to only a limited extent (as evidenced by the expansion profile and axial force measurements). The limited expansion suggested that gas was able to escape. It is proposed that for this Coal volatiles are escaping via the solid-like inertinite and semifusinite components within the Coal, which is a mechanism that has been previously proposed. This work reinforces the proposed coking pressure mechanism and indicates that coking pressure could be controlled by manipulating the viscosity and elasticity to provide a significant region of bubble-Coalescence or by adding inert solids. It follows that the phase angle - complex viscosity mapping plots, in conjunction with the ΔL and/or axial force profiles, could be used to identify whether a Coal or Coal Blend is likely to generate a high pressure. Considerable refinement of the tests is thought to be necessary to enable more accurate and reliable predictions.
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influence of Coal thermoplastic properties on coking pressure generation part 2 a study of binary Coal Blends and specific additives
Fuel, 2010Co-Authors: John J. Duffy, Merrick R Mahoney, Karen M. SteelAbstract:A number of Coal Blends and pitch/Coal Blends were evaluated using rheometry, thermogravimetric analysis and microscopy to confirm and further elucidate the coking pressure mechanism previously proposed by Duffy et al. (2007) [1]. We confirm that Blending a low rank, high fluidity, low coking pressure Coal, with a high rank, low fluidity, high coking pressure Coal can significantly reduce the coking pressure associated with the latter. Interestingly, Blending does not necessarily result in a fluidity that is midway between that of the two Coals; sometimes the fluidity of the Blend is less than that of the low fluidity Coal, especially when the Coals are significantly different in rank. This occurs because the increase in complex viscosity (η*) through resolidification of the low rank, high fluidity Coal counteracts the reduction in η* resulting from softening of the high rank, low fluidity Coal. It has also been confirmed that the η* of the resultant Blend can be estimated from the η* of each component Coal using a logarithmic additivity rule commonly employed for polymer Blends. Polarised light microscopy has indicated that the degree of mixing between Coals of different rank is minimal, with fusion restricted to the particle surface. It is therefore inappropriate to think of such a Coal Blend in the same way as a single Coal, since each component Coal behaves relatively independently. This limited fusion is important for understanding the coking pressure mechanism for Blends. It is proposed here that the lower rank Coal, which softens at lower temperature, is able to expand into the interparticle voids between the high rank Coal that is yet to soften, and these voids can create channels for volatiles to traverse. Then, and importantly, when the high rank Coal begins to expand, the pore structure developed in the resolidified structures of the low rank Coal can facilitate removal of volatiles, while the resolidified material may also act as a suitable sorbent for volatile matter. This is considered to be the primary mechanism by which Coal Blending is able to alleviate coking pressure, and applies to addition of inert material also. Addition of a Coal tar pitch was found to increase fluidity but also to extend the thermoplastic range to lower temperatures. This caused an increase in the swelling range, which was accompanied by a long plateau in η*, a feature which has previously been observed for certain high fluidity, high pressure Coals. Elasticity and η* at the onset of expansion were also higher for both the pitch impregnated Coals and the high pressure Blends, which supports previous findings for singly charged high pressure Coals, and confirms the potential use of such criteria for identifying potentially dangerous Coals/Blends. © 2009 Elsevier Ltd. All rights reserved.
R Alvarez - One of the best experts on this subject based on the ideXlab platform.
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influence of biomass on metallurgical coke quality
Fuel, 2014Co-Authors: M G Montiano, Carmen Barriocanal, E Diazfaes, R AlvarezAbstract:Abstract Two industrial Coal Blends used in coke making were subjected to tests in order to assess the influence of waste sawdust (SC2 from chestnut and SP1 from pine) on the quality of the coke produced. The biomass was added in quantities of up to 5 wt.%. It was observed that biomass produced a substantial decrease in the plastic properties of the industrial Coal Blend, with reductions in Gieseler maximum fluidity of around 50% for 3 wt.% additions of the two different sawdusts. Carbonizations with sawdust additions ranging from 0.75 to 5 wt.% were carried out in a movable wall oven of 17 kg capacity. The bulk density of the charge was observed to decrease with increasing amounts of sawdust with negative consequences on the quality of the cokes produced. Mechanical strength was determined by means of the JIS test. Coke reactivity and post-reaction strength (CRI/CSR indices) were also assessed. The amount of sawdust added was low to prevent any deterioration in coke quality. The advantage of using biomass in coking Blends should be seen as a possible way to reduce costs and CO 2 emissions and to incorporate alternative raw materials in coke production.
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relevance of the composition of municipal plastic wastes for metallurgical coke production
Fuel, 2011Co-Authors: Sonia Melendi, M A Diez, R Alvarez, Carmen BarriocanalAbstract:This study is concerned with the effects of the composition of mixed plastic wastes on the thermoplastic properties of Coal, the generation of coking pressure and the quality of the resulting cokes in a movable wall oven at semipilot scale. The mixed plastic wastes were selected to cover a wide spectrum in the relative proportions of high- and low-density polyethylenes (HDPE and LDPE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET). From the results it was deduced that the reduction in Gieseler fluidity in the Coal Blend is linked to the total amount of polyolefins in the waste. It was also found that these thermoplastics increase the pressure exerted against the wall in the course of the coking process and that coke quality is maintained or even improved. However, when the level of aromatic polymers such PS and PET are increased at the expense of polyolefins, the coking pressure decreases. Thus, the amount of aromatic polymers such as PS and PET in the waste is critical, not only for controlling Gieseler fluidity and coking pressure, but also for avoiding deterioration in coke quality (reactivity towards CO CRI and mechanical strength of the partially-gasified coke CSR). An amount of polyolefins in the waste lower than 65 wt.% for a secure coking pressure is established.
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weathering study of an industrial Coal Blend used in cokemaking
Isij International, 1998Co-Authors: R Alvarez, Carmen Barriocanal, M A Diez, M D Casal, J L G Cimadevilla, J J Pis, C S CangaAbstract:Weathering studies were carried out on a coking Coal Blend prepared and ground at industrial scale and stored in the open yard. This typical and complex Blend, composed of 13 different Coals was used by the Spanish Steel Company. Several methods were applied for detecting weathering in the Blend. Gieseler maximum fluidity was the most sensitive indicator of the loss of thermoplastic properties. Carbonization tests were carried out in a movable-wall oven and a semi-industrial oven of 6 t capacity. In addition to the measurements of internal gas pressure and coking pressure, laboratory tests were performed to measure expansion/contraction behaviour of the Coal Blend. A clear decrease in internal gas pressure with weathering was observed in the semi-industrial oven. As regards coke quality, no significant changes were produced in a storage period of ten months, however after this date impairment was observed.
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characterization of Coal tar pitches relationship with chemical composition of parent tars
1991 International Conference on Coal Science Proceedings#R##N#Proceedings of the International Conference on Coal Science 16–20 September 1991 Univer, 1991Co-Authors: A I Gonzalez, R Alvarez, M Granda, R Menendez, M A Diez, J BermejoAbstract:Publisher Summary This chapter describes the relationship of Coal tar pitches with chemical composition of parent tars. In a study described in the chapter, Coal tars obtained from the same Coal Blend at different temperatures and resultant pitches were characterized by extrography in conjunction with gas chromatography and Fourier transform infrared spectroscopy. Distribution of different classes of compounds of pitches was compared with those of parent Coal tars. Effects of Coal preheating on tars and pitches composition were also studied. Different carbonization temperatures produce tars of different quality from the same Coal Blend. Even operating under the same conditions and with the same Coal Blend, differences on oven dimensions can affect tar composition. Preheating of Coal reduces of the amount of polycyclic aromatic hydrocarbons (PAH), and increases the aromaticity and QI content.