Effects of coal interactions during cokemaking on coke properties under simulated blast furnace conditions

Fuel Processing Technology 199 (2020) 106274

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Research article

Effects of coal interactions during cokemaking on coke properties under simulated blast furnace conditions

T

Xing Xing School of Materials Science and Engineering, UNSW Sydney, Kensington, NSW 2052, Australia

A R T I C LE I N FO

A B S T R A C T

Keywords: Coal interactions Coke properties Blast furnace conditions

The cokes produced from single coals and blends of these coals were investigated under the simulated blast furnace (BF) conditions. Comparison of the weighted average values of single coal cokes and the measured values of cokes from blends revealed the coal interactions during carbonisation and the effects of these interactions on coke properties under the simulated BF conditions. Blending coals together resulted in a significant fluidity reduction from the expected values. The large amount of volatile matter released from the low rank coal provided better conditions of crystallites growth for other coal components in the blends, thereby resulting in the pervasively higher measured graphitization degree. Raman spectroscopy analysis indicated that the higher measured graphitization degree was mainly contributed by the lenticular and ribbon microtextures. Although the caking properties of the blends were remarkably reduced from the expected values, the measured microstrength did not have a significant difference from the calculated values. However, the measured macrostrength were higher than the calculated values. The differences in the softening and resolidification temperatures of coals restricted the dilatation but promoted the contraction of the blends, which resulted in a reduced porosity development from the expected value, thereby improving the strength of the produced cokes.

1. Introduction Metallurgical coke plays an important role in the modern BF ironmaking process to provide fuel, reducing agent and structural support media. The metallurgical coke is produced by the pyrolysis of coal in the absence of air at the temperature around 1000–1100 °C. During the carbonisation process, the coal starts softening in the temperature range between 300 and 475 °C to form plastic layers companied with both physical and chemical transformations in the microstructure [1]. The behaviours of plastic layer, which has a great impact on coke quality, are significantly affected by the petrographic and rheological properties of parent coals [2,3]. At the temperature from 300 to 600 °C, remarkable amount of tar and aromatic hydrocarbon compounds are released from the plastic mass, then the plastic layer resolidifies to form semi-coke [4]. The semi-coke transforms into coke with further increase of the temperature to 1100 °C. The thermoplastic stage is regarded as the most important stage during coal pyrolysis to determine the properties of formed coke [5–8]. Due to the limited premium coking coal resources in the world, coal blending plays the dominant role in the steelmaking industries. The optimised design of coal blend compositions requires a comprehensive understanding of the coal interactions during the thermoplastic stage. The thermoplastic behaviour of coal blends was determined using

maximum dilatation, Gieseler maximum fluidity, temperature-variable dynamic viscoelasticity, proton magnetic resonance thermal analysis (PMRTA), Ruhr and Audibert-Arnu dilatometric analyses [9–13]; the behaviours of coal blends were compared with the weighted average values of each component behaviour following additivity law to identify the potential interactions between coals [14]. Sakurovs [15,16] investigated the thermoplastic behaviours of binary coal blends using PMRTA and suggested different types coal interactions, either physical or physical and chemical, which could influence the blends fluidity in either positive or negative way; the specific effect depended on the differences in fluidity and rank between coals in the blends and the maximum fluidity of the coal with lower rank in the blends [15]. The study of blend fluidity using Gieseler plasticity analysis further confirmed the observation in the PMRTA study; both positive and negative differences were obtained between the calculated and measured values [17]. In these studies, the calculated fluidities of the most samples were higher than the measured values. The measured fluidity was only higher than the calculated value when the coals with similar properties were blended; the increase of the property difference among coal components aggravated the fluidity reduction from the expectation [17,18]. The mechanical strength is one of the most important properties in determining coke suitability for the BF ironmaking. The correlation

E-mail address: [email protected]. https://doi.org/10.1016/j.fuproc.2019.106274 Received 10 September 2019; Received in revised form 5 November 2019; Accepted 5 November 2019 0378-3820/ © 2019 Elsevier B.V. All rights reserved.

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between the thermoplastic behaviour and coke strength has been established previously [6,19]. Given that the interactions between coals during cokemaking can have varying influences on the blend fluidity, it is not surprising that the coke strength is also significantly affected by the coal interactions. Alvarez et al. [20] studied the effect of coal interactions on the coke cold strength and found that the measured cold strength of cokes from binary to quaternary blends were better than the calculated strength following additivity law, the addition of a coal of either good or bad quality to the complex industrial blends also resulted in the cokes with stronger cold strength than the expected values. However, the precise mechanism for such effect was still unclear. To fulfil the requirement of the BF ironmaking, it is essential for coke to remain the mechanical strength, lump size and minimise the fine generation upon the BF operating conditions. During the coke passage through the BF, it is exposed to the chemical reactions with gases (CO, CO2, H2, and H2O) in the region between BF thermal reserve zone and cohesive zone; the operating temperature of BF increases from 1400 to 2000 °C (close to the typical raceway flame temperature) in the region below the BF cohesive zone. The coke properties change significantly due to the gasification, annealing and the reactions with mineral matters. Coke extracted from BF showed a remarkable graphitization of coke carbon crystallite with an ideal hexagonal prism shape [21]. Li et al. suggested that such coke graphitization in the high temperature region of the BF started from the lump surface and led to a significant fine generation [22]. The high temperature test of coke properties indicated that the resistance to fracture of cokes degraded at 2000 °C as the significant change in the microstructure accompanied with graphitization [23,24]; the anisotropic microtextures of coke was more susceptible to graphitization and expressed greater degradation than the isotropic microtextures [25,26]. The pore structure of cokes also changed significantly due to the solution loss reaction and mineral carbon reactions upon the high temperature in the furnace [27–29]. The deterioration of the coke microstrength together with the change in pore structure contributed to the degradation of coke macrostrength in the BF [27,30,31]. The previous study simulated the BF operating conditions by gasification of cokes in the CO-CO2-N2 atmosphere from 900 to 1400 °C, and gasification with subsequent annealing in the N2 atmosphere up to 2000 °C. The characterisation of the post-treated cokes demonstrated that the cokes produced from the coals with higher rank had greater change in the carbon structure upon the high temperature in the BF; consequently, the microstrength and macrostrength experienced more significant degradation than those produced from the lower rank coals. It should be noted that one coke in that study was produced from a trinary coal blend; the crystallite size growth of this coke upon high temperature was clearly above the trendline of the cokes made from single coals, which implied the potential interactions between coal components during carbonisation and the effect of these interactions on coke behaviours upon simulated BF condition [32]. However, very few studies were conducted to systematically investigate the effect of coal interaction in the blends on the coke performance under the BF conditions. In this study, three coals in the previous study with low, medium and high ranks were selected to produce the binary and trinary blend cokes. The properties of cokes produced from single coals and blends were studied under the simulated BF conditions; the gasification and annealing atmospheres in this study were changed to CO-CO2-N2-H2H2O and CO-N2-H2 atmospheres, respectively, to achieve the more realistic conditions in the BF. The measured coke properties were compared with the calculated values following additivity law. The aim of this study is to investigate the coal interactions during carbonisation and the effects of these interactions on coke properties under the simulated BF conditions.

Table 1 Characterisation of coal samples. Coal (identifier)

Coal B

Coal F

Coal H

MMR Ash, % (ad) Volatile matter, % (ad) Inertinite, % Ash composition, % SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O Modified Basicity Index (MBI)

1.04 8.1 26.9 41.2

1.39 10.9 19.7 24.2

1.66 9.3 17.8 21.2

51.9 25.7 11.2 3.2 1.2 0.4 1.6 2.51

69.1 23.2 2.19 0.93 0.55 1.24 0.48 0.79

51.3 35.0 3.72 2.87 0.84 1.03 1.16 1.26

2. Materials and methods 2.1. Sample materials Three coal samples with low, medium and high ranks were selected from the previous study (Coals B, F and H) to produce coal blends. The vitrinite mean maximum reflectance (MMR) of the coals were 1.04, 1.39 and 1.66, respectively; the properties of the coal samples are shown in Table 1. The coal blends (CB1 and CB2) were designed as follows:

Blend CB1 − 30% × Coal B + 70% × Coal F

Blend CB2 − 24% × Coal B + 56% × Coal F + 20% × Coal H The thermoplastic behaviours of coals and blends were determined using Gieseler plasticity test. The parameters derived from Gieseler plasticity test are shown in Table 2. The MFcalculated was the calculated maximum fluidity assuming the additivity law: n

Pb =

∑ xi Pi

(1)

i=1

where Pb is the calculated coke properties, Pi and xi are the property and the mass fraction of coal i respectively, and n is the number of component coals. Coal constituents in the blends CB1 and CB2 showed significant differences in the thermoplastic behaviours. Blending Coal B and Coal F together resulted in a significant reduction of the measured maximum fluidity from the expectation; addition of Coal H, which had the lowest fluidity, further reduced the maximum fluidity of the resulted blend. The softening, maximum fluidity and resolidification temperatures of coals increased with the increasing rank; the reduced maximum fluidity of the blends could be attributed to the difference temperature ranges of the coal thermoplastic stage [33]. During the heating process of the blend CB1, the Coal B reached the maximum fluidity at 450 °C, at which temperature Coal F did not reach the maximum fluidity; therefore, at 450 °C, Coal F acted as a relatively inert material to restrict the fluidity of the blend. With further increase of the temperature, Coal B Table 2 Gieseler plasticity parameters of coals and blends. Coal/blend (identifier)

Coal B

Coal F

Coal H

Blend CB1

Blend CB2

Ts (°C) Tf (°C) Tr (°C) MFmeasured (ddpm) MFcalcualted (ddpm)

415 450 480 750 –

415 465 505 400 –

460 480 510 20 –

430 465 490 105 505

440 470 495 20 408

Ts: softening temperature; Tf: maximum fluidity temperature; Tr: resolidification temperature; MFmeasured: measured maximum fluidity; MFcalculated: calculated maximum fluidity. 2

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balance N2. After gasification, the gas atmosphere was switched to 100% N2 to stop the reaction, the reactor was removed out of the furnace and cooled down to the room temperature. The samples were gasified to 1400 °C, then kept at the final condition (10% H2, 40% CO and 50% N2) for additional 2 h. The gasified samples were further annealed for 2 h at 1800 and 2000 °C in a graphite furnace with water cooling furnace chamber. Different from the inert atmosphere used in the previous study, annealing in this work was conducted in the CO-N2-H2 atmosphere (45% CO, 45% N2 and 10% H2). The gasified samples were contained in the graphite crucible of the furnace, 1 L/min of CO-N2-H2 gas mixture was continuously blown through a graphite tube attached to the bottom of the crucible. After annealing, the gas atmosphere was switched to 100% N2, the coke samples were cooled down with furnace to the room temperature. The feed cokes and the cokes subjected to simulated BF gasification and annealing conditions were labelled sequentially as: Coke 1 (Feed cokes); Coke 2 (Cokes gasification to 1100 °C); Coke 3 (Cokes gasification to 1400 °C); Coke 4 (Cokes gasification to 1400 °C + annealing at 1800 °C); Coke 5 (Cokes gasification to 1400 °C + annealing at 2000 °C).

started resolidification at 480 °C, at which temperature Coal F was still in the liquid phase; therefore, the Coal B started acting as an obstruction of the fluidity at this temperature. Coal H had the lowest maximum fluidity, it started softening at 460 °C, which was close to the maximum fluidity temperatures of Coals B and F, it reached the maximum fluidity at the temperature which Coal B already started resolidification. Therefore, Coal H effectively acted as an inert material during the entire carbonisation process; the fluidity of blend CB2 decreased to 20 ddpm, which was as same as the fluidity of Coal H, even only 20% of this coal was added into the blend. The production of cokes from single coals and coal blends were conducted in a 400 kg pilot-scale movable wall coke oven. The coals/ blends were packed into the oven chamber with charge bulk density of 825 kg/m3 and charge moisture of ~5%, then carbonised with a total coking time of 20 h. the charge centre temperature at the end of coking was around 1030 °C. The cokes were pushed out of the oven at the end of coking and water quenched, the formed coke samples were subsequently stabilised by three drops through 4 m height onto cement. All the coke samples in this study were sized to a range of +19–21 mm for the bench-scale testing. A summary of the coke characterisation is presented in Table 3. The optical microscopy assessments of coke microtextural types were carried out based on the classification described by Gray et al. [34]. The inert maceral-derived components (IMDC) microtexture of the cokes in this study was mainly the organic inert microtextural type; the reactive maceral-derived components (RMDC) microtextures were grouped into incipient, circular, lenticular and ribbon anisotropic types. The representative RMDC microtextures of cokes are shown in Fig. 1. The measurements of coke properties were carried out on organic inert (IMDC) and different types of RMDC microtextures separately to understand their different behaviours under the simulated BF conditions.

2.3. Microstructure of cokes X-ray diffraction (XRD) was used to determine the coke crystallinity, which was characterised by the crystallite size. XRD spectra of powdered samples were obtained using a Philips X'Pert Multipurpose X-ray Diffraction System (MPD). Copper Kα radiation (45 kV, 40 mA) was used as the X-ray source. Samples were scanned in the range of 2θ from 10 to 50° with a step size of 0.02° and 0.6 s scanning time at each step. Coke crystallite size, Lc, was calculated using the Scherrer equation [35]. G fraction, which characterised the proportion of graphitic structure, of cokes was determined using Raman spectroscopy. The Raman spectrum of coke samples was obtained using a Renishaw inVia Raman microscope with a 514-nm excitation wavelength. The beam size was 1.5 to 2 μm, which allowed different microtextural types to be analysed separately. The Raman measurements were carried out on IMDC and different RMDC microtextures to understand the behaviours of different microtextures under the BF conditions. Raman spectra were scanned from 600 to 2000 cm−1 with 25 mW laser power for an exposure time of 15 s. The Raman spectra consisted two board bands G* and D*, they were deconvoluted into G, D, D′, R1 and R2 peaks using Lorentzian band fitting following the procedure described previously [23]. The G fraction was calculated as the ratio of the areas under the G peak to the total area [36].

2.2. Treatments of cokes under the simulated BF conditions 200 g of sized coke samples were reacted from 900 to 1400 °C following the simulated BF gas composition-temperature profile in a vertical furnace. Different from the previous study, the gasification atmosphere in this study was changed to CO-CO2-N2-H2-H2O to achieve more realistic conditions within the furnace thermal reserve zone and cohesive zone. The effect of different gasification atmospheres on coke properties was discussed with comparison of the findings in the previous paper [32]. The proposed gas composition and temperature profile was designed following the actual BF vertical probe measurement (Fig. 2). The samples were contained in a silicon carbide reactor and heated from room temperature to 900 °C in 100% N2 atmosphere; a CO-CO2-N2-H2-H2O gas mixture (5 L/min) was then introduced into the reactor to start the gasification. As shown in Fig. 2, gasification started at 900 °C, and stopped once the temperature reached either 1100 °C or 1400 °C; the composition of the gas mixture varied over time within the following ranges: 31–40% CO, 0–15% CO2 8–10% H2, 6% H2O with

2.4. Microstrength of cokes Microstrength of cokes was measured using a UMIS2000 ultra micro-indentation system, which was designed to carry out the mechanical measurement of sample using an ultra-low load with penetration depths around 1 μm. The hardness, H, of cokes was determined separately on the IMDC and different RMDC microtextural types using a Berkovich diamond indenter with maximum applied load of 100 mN. The instantaneous penetration depth of the indenter with increasing load was recorded to form a loading-unloading curve. The hardness of different coke microtextures was calculated based on this loading-unloading curve according to the method developed by Oliver and Pharr [37].

Table 3 Characterisation of the produced coke samples. Coke (identifier)

Coke B

Ash, % (ad) 11.9 Volatile matter, % (ad) 0.3 CSR, % 31.9 CRI, % 46.7 Ash composition, wt% (ab) SiO2 51.4 Al2O3 23.1 Fe2O3 14.3 CaO 3.68 MgO 0.82 Na2O 0.39 K2 O 1.42

Coke F

Coke H

Coke CB1

Coke CB2

13.5 0.1 69.7 22.2

12.0 0.4 69.5 20.1

12.3 0.8 67.1 26.5

11.8 0.5 66.0 25.7

68.3 23.7 3.13 1.04 0.55 0.55 0.82

50.1 33.6 5.09 3.05 0.83 1.16 1.20

57.9 27.6 5.25 2.59 0.66 0.38 0.97

55.9 29.2 5.48 2.39 0.64 0.51 0.90

2.5. Macrostrength of cokes Tensile strength of each coke was determined by measuring 50 cylindrical specimens using diametrical-compression test on an Instron 1185 screw universal testing machine. The cylindrical specimens were 3

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Fig. 1. Representative RMDC microtextures of cokes produced from coals and blends.

the gray scale for each pixel using ImageJ. After conversion, the walls and pores of cokes were presented by white and black areas, respectively. The porosity of cokes was calculated as the area fraction of the black area [39].

3. Results and discussion 3.1. Effect of coal interactions on coke microstructure under the simulated BF conditions The typical XRD patterns of feed coke and cokes subjected to simulated BF conditions are presented in Fig. 3. The peaks located at 26.6 and 20.8° in the feed coke were assigned to quartz in coke mineral; they were substantially removed after annealing at 1800 °C through the carbothermal reduction. The peak located at 25.5–26° was the carbon 002 peak which was used to calculate coke crystallite size after peak fitting. The shape of this peak could be used as a qualitative indicator of

Fig. 2. Gas composition-temperature profiles under the simulated BF conditions.

prepared by core drilling coke lumps and sizing the specimens to 8 mm in diameter and 8 mm in height. Therefore, the specimen of the tensile testing was extracted from the core of coke lump and represented the local mechanical property. A compressive load was applied across the diameter of the cylindrical specimen; the fracture of coke occurring along the diameter as a result of the development of tensile stress at right angles. The tensile strength, T, was calculated from the applied load at breakage and the dimensions of the specimen [38]. 2.6. Porosity of cokes Porosity of cokes was measured using the image analysis software developed by NIH. The cokes were mounted in epoxy resin and polished to provide samples for image analysis. The images were captured using a Nikon Model EPIPHOT 600 microscope equipped with a Nikon digital camera. Since the large pores were of most interest in relation to coke strength degradation, 5× magnification objective lens was used. The captured images were converted to binary (black and white) based on

Fig. 3. XRD pattern of feed Coke CB1 and Coke CB1 subjected to simulated BF conditions. 4

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Table 4 Crystallite height, Lc, of feed cokes and cokes subjected to simulated BF conditions, Å. Coke (identifier)

Coke B

Coke F

Coke H

Coke CB1

Coke CB2

Coke Coke Coke Coke Coke

16.9 21.5 36.9 79.6 115.0

19.9 23.5 40.8 107.1 155.2

27.7 31.0 42.5 124.2 163.4

25.8 26.7 38.8 107.1 155.3

25.9 27.0 41.4 115.0 163.4

1 2 3 4 5

the coke graphitization degree. In this study, the shape of 002 carbon peak became sharper with the increasing temperatures, which indicated the development of graphitization degree upon BF conditions. The crystallite height, Lc, of feed cokes and cokes subject to simulated BF gasification and annealing are shown in Table 4. Compared to the previous gasification conducted in the CO-CO2-N2 (15% CO2) atmosphere [32], the addition of H2O in this study promoted the crystallite size growth of cokes during gasification, which indicated that greater ordering of aromatic nucleus in coke carbon was formed during the H2O containing gasification. This was consistent with previous studies on the coke gasification with different atmospheres [40,41]. It was suggested that the disordered amorphous carbons in coke had higher reactivity than the ordered aromatic carbons, and was preferentially consumed during gasification [42,43]. Due to the higher reaction rate of coke with H2O, addition of H2O promoted the consumption of amorphous carbon; thereby increasing the ordering of coke [41]. The crystallite height of Coke H after gasification in H2O containing atmosphere to 1400 °C was 4.1% higher than it gasified to the same temperature in the atmosphere without H2O; such difference for Coke B was 26.3% after gasification to 1400 °C, The greater effect of H2O on Coke B could be attributed to the higher reactivity of Coke B (CRI = 46.7%), which led to greater consumption of disordered carbon in the microstructure. The change of annealing atmosphere from the inert atmosphere to CO-N2-H2 also caused greater crystallite growth with a more significant effect on coke produced from low rank coal. The crystallite size of Coke H annealed in CO-N2-H2 atmosphere was same as the one annealed in the inert atmosphere; the crystallite size of Coke F in this study was 5.0% higher than that annealed in N2 atmosphere; for Coke B, 11.1% increase in the crystallite size was achieved by changing the inert annealing atmosphere to CO-N2-H2 atmosphere. The crystallite height of feed Coke CB1 was greater than that of feed Cokes B and F, although Coke CB1 was produced from the blend of Coals B and F; the crystallite size of feed Coke CB2 also exceeded the expectation from the blend composition. These implied the potential effect of coal interactions on the coke crystallinity. Compared with the feed Coke CB1, the addition of Coal H did not cause significant increase in the crystallite height of the feed Coke CB2, although Coal H could form coke with higher crystallinity. It should be noted that the addition rate of Coal H was only 20%, the coking temperature for the carbonisation was 1030 °C. The relatively low addition rates and the temperature feed cokes experienced did not cause any visible difference in the crystallite size between the feed cokes. The remarkably different performance between cokes were observed upon the high temperature in the BF. Coke CB2 had the higher crystallite size after gasification with subsequent annealing at 1800 and 2000 °C as a result of the addition of high rank coal, which expressed greater capacity to form large carbon crystallite upon high temperatures. The typical Raman spectra of feed coke and cokes subjected to simulated BF conditions are shown in Fig. 4. The two board bands G* and D* centred at around 1600 and 1360 cm−1 became sharper with the increasing temperatures during gasification and annealing; G* band split into G and D′ peaks after annealing at 1800 °C, and the D′ peaks became more evident after temperature raising to 2000 °C. The change of Raman spectra of coke upon simulated BF conditions indicated that the microstructure of coke transformed towards graphite structure with

Fig. 4. Raman spectra of feed Coke CB1 and Coke CB1 subjected to simulated BF conditions. Table 5 G fraction of feed cokes and cokes subjected to simulated BF conditions, %. Coke (identifier)

Organic inert

Incipient

Circular

Lenticular

Ribbon

Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke

13.6 13.5 17.0 21.0 31.6 14.6 14.3 17.6 21.5 31.9 12.9 14.0 17.0 21.6 31.8 13.3 14.5 17.5 22.2 32.7 13.1 14.4 17.7 21.9 32.6

12.4 12.8 17.4 28.0 35.3 – – – – – – – – – – 11.2 11.7 15.6 26.1 36.1 10.9 12.7 16.5 29.5 36.5

12.7 12.4 15.6 28.9 35.5 – – – – – – – – – – 12.8 13.1 16.3 28.8 36.0 12.0 12.8 16.3 29.8 36.6

– – – – – 12.0 13.0 16.7 28.2 35.1 12.0 12.7 18.3 30.0 34.8 12.8 13.5 16.9 28.9 38.9 12.4 13.4 17.1 33.2 40.9

– – – – – 13.4 14.2 17.9 34.6 38.8 12.4 12.6 15.4 32.6 37.3 13.5 13.6 17.2 35.4 40.8 13.3 13.8 17.4 37.4 44.2

B-1 B-2 B-3 B-4 B-5 F-1 F-2 F-3 F-4 F-5 H-1 H-2 H-3 H-4 H-5 CB1-1 CB1-2 CB1-3 CB1-4 CB1-5 CB2-1 CB2-2 CB2-3 CB2-4 CB2-5

the increased treatment temperatures [23]. The G fraction of feed cokes and cokes subjected simulated BF conditions are shown in Table 5. The optical microscopy assessment of cokes showed that the organic inert (IMDC) prevalently presented in all coke samples; however, the RMDC microtextural types in cokes strongly depended on the rank of parent coals/blends. The fused component of Coke B only consisted of incipient and circular anisotropic types due to the low rank of the parent coal. On the other hand, the RMDC microtextures of Cokes F and H were only dominated by lenticular and ribbon anisotropic carbon forms as a result of the higher rank of Coals F and H. Full complement of RMDC microtextural types were observed in the cokes produced from blends (Cokes CB1 and CB2) due to the wide coal rank range in the blends. The G fractions of organic inert microtextural type (IMDC) in the feed cokes were generally higher than that of the RMDC microtextural groups. The G fractions of both the IMDC and RMDC microtextural types increased with increasing treatment temperatures; the effect of temperature was more significant for the RMDC microtextures. Among the different types of RMDC microtextures, the G fraction increased 5

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treatments at high temperatures. After gasification with subsequent annealing at 1800 °C, the differences between measured and calculated values increased to 7.8 Å for Coke CB1 and 10.5 Å for Coke CB2; the elevation of annealing temperature to 2000 °C further enlarged these differences to 11.5 Å and 15.5 Å, respectively. The discrepancy between the experimental and calculated data in coke graphitization can be explained by the specific interactions between coal components in the blend [44]. During carbonisation, the volatile matter contained in the coals with lower softening temperature could be moved and stored in other coals of higher softening temperature in the blend. The captured volatile acted as a coal plasticiser that improved the blend thermoplastic properties and resulted in the property changes of the plastic layer, the semi-coke and the produced coke in the terms of mesophase formation, optical texture and carbon ordering [15,45]. A study about the effect of coal interactions on coke graphitization degree suggested that one kind of coal component reached the maximum fluidity at a lower temperature than the other coal in the blend; the large amount of volatile matter released from the former coal provided a better condition of crystallites growth for the latter one [44]. In current study, Coal B had the largest amount of volatile matter (34.1%), it reached the maximum fluidity at temperature lower than other coal components. Therefore, the large amount of volatile matter it released during carbonisation had potential to promote the crystallite growth of other coal constituents in the blends. The relationships between the experimental and calculated G fraction of cokes are shown in Fig. 6. For the incipient microtexture in the feed cokes, the calculated G fraction was 10.5% higher than the measured value for Coke CB1, such difference was 13.8% for Coke CB2. These indicated that the graphitization development of incipient microtextures were not benefited from the coal interactions during carbonisation. Gasification and annealing to high temperatures reduced the differences between the calculated and measured values for incipient microtexture. Similar tendency was also found for the circular microtexture, the differences between the calculated and measured G fraction remained around 3% after gasification with subsequent annealing at high temperatures. The coal interactions in the blends only promoted the graphitization of the RMDC microtextural groups with larger isochromatic units. The measured G fraction of lenticular microtexture in feed Coke CB2, for example, was 3.6% higher than the calculated value; this difference increased to 16.6% after annealing at 2000 °C, a consistent tendency was also observed on the ribbon microtexture. In current study, the incipient and circular microtextures of Coke CB2 were mainly generated from Coal B; the lenticular and ribbon microtextures were generated from both Coals F and H. As discussed above, the large volatile matter released from Coal B provided better graphitization condition for Coal F and H, which resulted in the greater graphitization development of the lenticular and ribbon microtextures. The G fraction of lenticular microtextures in the Coke CB2, for example, was 3.4% and 3.5% higher than the same microtexture within Cokes F and H; these differences were enlarged to 14.0% and 14.8% after annealing at 2000 °C. Similar observation was returned for the ribbon microtexture in the cokes. After high temperature annealing, the G fraction of ribbon microtexture in Coke CB2 was 12.1% and 15.6% higher than the same microtexture within the cokes produced from the single coal components in Blend CB2 (Cokes F and H). Therefore, the higher measured crystallinity shown in Fig. 5, was mainly contributed by the greater graphitization development of the lenticular and ribbon microtextures.

with increasing RMDC isochromatic units size in the order of incipient, circular, lenticular and ribbon. Compared to the incipient and circular microtextures, the high temperature annealing at 1800 and 2000 °C caused more significant G fraction increase for the lenticular and ribbon microtextures. The G fraction of ribbon in Coke H after annealing at 1800 °C was 1.63 times higher than that in the feed Coke H; the G fraction increase of ribbon in Coke F was 1.59 times upon annealing at the same temperature. After annealing at 1800 °C, on the other hand, the G fraction increase of incipient in Coke B was 1.26 times. The comparison of coke G fractions annealed at 2000 °C returned a same tendency but slightly smaller differences between different anisotropic carbon forms. Compare to the cokes produced from the single coals (Cokes B, F and H), blending coals together slightly promoted the G fraction of lenticular and ribbon microtextures in the produced cokes (Cokes CB1 and CB2). Such differences were enlarged by the high temperatures upon simulated BF gasification and annealing. After annealing at 2000 °C, the G fraction of lenticular microtextures in Coke CB1 was 10.1% higher than the same microtexture in Cokes F and H; this difference between Coke CB2 and Cokes F and H was 14.4%. The comparison of ribbon microtexture between cokes produced from single coals and coal blends returned a same tendency. Compared to the Coke CB1, the addition of high rank coal in the coal blend did not caused significant difference in the G fraction of the resulting feed coke (Coke CB1-1 vs Coke CB2-1), but remarkably promoted the ability of lenticular and ribbon microtextures to form higher ordering carbon upon high temperatures (Cokes CB1-4/CB1-5 vs Cokes CB2-4/CB2-5). It implied the potential interactions between coals during carbonisation and the effect coal interactions on the coke behaviours upon the subsequent BF treatments. The different behaviours of individual anisotropic forms in Coke CB2 also contributed to the greater crystallite size growth upon high temperatures. Fig. 5 shows the relationship between the measured crystallite sizes and the values calculated following additivity law. Due to the different volatile matter contents of the coal components, the actual proportions of coke matrix formed from each coal components were calculated by assuming the volatile matter in all the coals was completely released during the carbonisation process. The bold and italic numbers in the figure are the calculated crystallite sizes, the dash line represents that the calculated values equal to the measured ones. The trend line of the data points was clearly below the dash line, which indicated the greater measured crystallite sizes. The differences between calculated and measured crystallite size of the feed cokes were 6.8 Å and 5.1 Å for Cokes CB1 and CB2, respectively. Such differences increased during the

3.2. Effect of coal interactions on coke microstrength under the simulated BF conditions The hardness of feed cokes and cokes subjected to simulated BF conditions are shown in Table 6. The hardness of organic inert of feed cokes was in the range of 6.2–6.4 GPa, except Coke H which had a lower hardness of 5.9 GPa. The hardness of the anisotropic

Fig. 5. Relationship between the experimental and calculated crystallite sizes of cokes. 6

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Fig. 6. Relationship between the experimental and calculated G fractions of cokes.

example, was 14.6% higher than the incipient microtexture and 28.9% higher than the circular microtexture. Such differentials were more remarkable for the lenticular and ribbon carbon forms as 36.2% and 42.1%, respectively. No significant difference was identified when comparing the hardness of same anisotropic carbon form in Cokes CB1 and CB2. Gasification to 1100 °C did not caused any significant degradation of the anisotropic carbon forms, more remarkable degradation (more than 25%) was observed as the gasification temperature increased to 1400 °C. Annealing at 1800 °C aggravated hardness degradation of the RMDC microtextures with greater effect on the lenticular and ribbon microtextures. After annealing at 2000 °C, degradation of lenticular and ribbon carbon forms was further increased with a slightly more significant effect on the cokes originated from higher rank coals. Compared to the hardness of cokes gasified and annealed in different atmospheres [32], gasification in H2O containing atmosphere and annealing in CO-N2-H2 atmosphere did not caused any considerable difference in coke hardness, which indicated that the hardness degradation of coke mainly depended on the temperatures that coke be exposed to. Compare to the anisotropic microtexture, gasification and annealing at elevated temperatures caused less microstrength degradation in the coke isotropic microtextures. Gasification did not cause any significant degradation in the organic inert until the temperature raised to 1400 °C; the degradation in hardness occurred at this temperature was 20.0% for Coke H and 3.6% for Coke B. However, the degradation in coke anisotropic microtextures reached 32.8% after gasification to the same temperature. Subsequent annealing at 1800 °C resulted in more serious degradation in organic inert of cokes in the range 31.8–34.4% with more significant degradation on Coke H. Increasing of annealing temperature to 2000 °C promoted these figures to 36.1–39.9%, the order of

Table 6 Hardness, H, of feed cokes and cokes subjected to simulated BF conditions, GPa. Coke (identifier)

Organic inert

Incipient

Circular

Lenticular

Ribbon

Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke Coke

6.29 6.24 6.07 4.29 4.02 6.37 6.28 5.71 4.22 3.94 5.89 5.80 4.71 3.87 3.54 6.37 6.36 5.91 4.22 3.91 6.16 6.13 5.79 4.11 3.72

5.53 5.41 3.42 2.16 1.41 – – – – – – – – – – 5.44 5.31 3.53 2.13 1.41 5.52 5.52 3.46 2.15 1.40

4.62 4.53 3.09 1.58 1.19 – – – – – – – – – – 4.53 4.44 3.02 1.57 1.16 4.78 4.58 3.10 1.45 1.18

– – – – – 4.11 4.00 2.80 1.07 0.57 4.02 3.73 2.76 0.94 0.51 4.07 4.02 2.72 1.04 0.60 3.89 3.85 2.79 0.96 0.47

– – – – – 3.81 3.67 2.59 0.74 0.39 3.47 3.10 2.42 0.71 0.30 3.69 3.68 2.56 0.69 0.37 3.59 3.57 2.16 0.63 0.31

B-1 B-2 B-3 B-4 B-5 F-1 F-2 F-3 F-4 F-5 H-1 H-2 H-3 H-4 H-5 CB1-1 CB1-2 CB1-3 CB1-4 CB1-5 CB2-1 CB2-2 CB2-3 CB2-4 CB2-5

microtextures was generally lower than the co-existing isotropic carbon forms; the hardness of different anisotropic microtextural types decreased in the order of incipient, circular, lenticular and ribbon microstructure. The hardness of organic inert in feed Coke CB1, for 7

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Fig. 7. Relationship between the experimental and calculated hardness of cokes.

the relative degradation still followed the order of the parent coal rank. After annealing at same temperature, on the other hand, the degradation of coke anisotropic microtextures was in the range of 74.2–91.5%. Fig. 7 shows the relationships between the measured and calculated hardness of individual microtextures in the cokes. No distinct differences were noticed between the calculated and experimental values in the feed cokes and the cokes after simulated BF treatments. In the feed cokes, the differences between the calculated and measured hardness of incipient microtexture were 1.6% for Coke CB1 and 0.1% for Coke CB2, such differences remained after gasification and annealing under the simulated BF conditions. After annealing at 2000 °C, the measured hardness of incipient of Coke CB1 and CB2 were 1.4 GPa, which were as same as the calculated values. Similarly, no significant differences were found between the calculated and measured hardness of the microtextures with larger isochromatic units. These indicated that the coal interactions in the blends had no significant effect on the coke microstrength.

Table 7 Tensile strength, T, of feed cokes and cokes subjected simulated to BF conditions, MPa. Coke (identifier)

Coke B

Coke F

Coke H

Coke CB1

Coke CB2

Coke Coke Coke Coke Coke

5.49 5.14 4.92 4.42 4.22

5.51 5.30 5.07 3.43 3.15

4.47 4.11 4.03 2.71 2.38

5.61 5.33 5.08 4.03 3.72

5.44 5.18 4.99 3.74 3.43

1 2 3 4 5

Fig. 8 shows the micrographs of Coke CB2 gasified to 1400 °C in the H2O containing atmosphere. The degradation of coke mainly took place at the periphery of the coke lump. The topochemical gasification significantly consumed the organic inert (point a) located at the lump surface and left relics in the original location; the reaction of anisotropic microtextures collapsed the pore walls and generated connections between the adjacent pores (point b). Different from the lump surface, the lump core was generally intact after gasification. Only limited degradation was observed on few organic inert particles; however, the neighbouring anisotropic microtextures were well preserved (point c). As the specimens of coke tensile testing were cored from the lump centre of the reacted cokes, no extra degradation was determined on coke tensile strength with the H2O containing gasification. The results from the previous studies indicated that coke macrostrength degradation upon BF conditions was contributed by both microstrength degradation and pore structure development [24,27,28,30]. The micrographs of Coke CB2 annealed at 2000 °C are shown in Fig. 9. Compared to gasification (Fig. 8), annealing at high temperature promoted the coke pore structure development across through the entire coke lump. It could be mainly attributed to the carbon-mineral reaction

3.3. Effect of coal interactions on coke macrostrength under the simulated BF conditions The tensile strength of feed cokes and cokes subjected to simulated BF conditions are shown in Table 7. Compared to the cokes gasified in the CO-CO2-N2 atmosphere [32], the addition of H2O vapour did not cause extra degradation of coke tensile strength, although the reactivities of cokes were significantly increased by H2O injection. It was suggested that the CO2 could partially diffuse towards the interior zone to some extent through different pores during gasification; however, the coke gasification with H2O prevailingly took place at the external part of coke lumps due to the higher reaction rate of H2O, and resulted in serious destruction on coke surface [40]. 8

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Fig. 8. Morphology of Coke CB2 after gasification to 1400 °C.

values, this difference increased to 7.6% after gasification with subsequent annealing at 2000 °C. Such difference in feed Coke CB2 was 2.9% and increased to 6.0% after high temperature annealing. Similar tendency was returned from the comparison between the calculated and measured CSR (Table 3). The measured CSR of Coke CB1 was 67.1%, which was 13.7% higher than the calculated value; such differential was 7.9% for Coke CB2. These indicated that the coal interactions in the blends could promote the macrostrength of the produced cokes. The consistent correlation was also found by Sakamoto et al. [46], who studied the effect of the interaction of coal covered wider range of properties on the coke cold strength. Blending of coals with different ranks and caking properties together resulted in the higher experimental strength than the calculated ones. When the coals with different caking properties were blended together, the differences in the softening and resolidification temperatures restricted the dilatation but promoted the contraction of the blend [47]. The different behaviours of the dilatation and contraction from weight average values resulted in the reduced porosity from expectation, thereby increasing the strength of the produced cokes [46,48]. Previous study indicated that the coke macrostrength was determined by both the microstrength and pore structure [32]. No significant differences were identified between the calculated and measure microstrength in this study; therefore, the greater measured macrostrength should be attributed the different measured porosity from the calculated ones. Fig. 11 presents the relationship between experimental and calculated coke porosity. The coal interactions during carbonisation caused a reduced porosity compared to the expected values; such differences between measured and calculated values remained after subjection of cokes to the simulated BF gasification and annealing, which resulted in the greater measured coke

at high temperature [27,28]. The mineral reactions associated with the organic inert particles generated cracks within the inert particles (point a); such cracks could act as the origins of fracture upon mechanical load and led to the coke degradation. The reactions between minerals and coke RMDC microtextures consumed the coke matrices and created new pores with ragged shape edge, the reacted minerals resolidified during cooling and presented as either a coating on the pore internal surface (point b) or a filler of the pore (point c). The minerals reactions at some points (points a and b) also generated new channels between the adjacent pores and changed the local pore structure, thereby reducing the coke mechanical strength. The binary blend coke (Coke CB1) had slightly higher tensile strength than the cokes produced from the single coal constituents in this blend (Cokes B and F). Compared with Coke CB1, only marginal decrease (3.2%) was noticed in the feed Coke CB2, which was paralleled with the high rank coal addition. 5.1 and 4.7% degradations were observed on the cokes gasified to 1100 °C, further gasification to 1400 °C promoted the degradation to 9.5 and 8.3%, respectively. The subsequent annealing at high temperatures aggravated the coke strength degradation. The tensile strength of binary blend coke (Coke CB1) degraded by 28.3% after annealing at 1800 °C; the addition of high rank coal resulted in greater degradation (31.2%) on the formed coke (Coke CB2). Increasing the temperature to 2000 °C further increased the coke degradation with greater effect on the coke produced with high rank coal addition. The relationships between the calculated and measured coke macrostrength are shown in Fig. 10. Although the measured fluidity of the blends was reduced from the expected values, the measured macrostrength was slightly higher than the calculated value. The measured tensile strength of feed Coke CB1 was 2.0% higher than the calculated 9

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Fig. 9. Morphology of Coke CB2 after gasification and annealing at 2000 °C.

Fig. 10. Relationship between the experimental and calculated of tensile strength.

Fig. 11. Relationship between the experimental and calculated of porosity.

1800 and 2000 °C in the N2-H2-CO atmosphere (corresponding to the conditions within and at the back of raceway region). The post treated cokes were characterised using specific materials characterisation techniques to determine the change of coke properties in both microand macro-scales. The measured properties were compared with weight average values assuming additivity law to understand the effect of coal interactions during carbonisation on the coke properties under the simulated BF conditions. The major finds are:

macrostrength. 4. Conclusions The cokes produced from single coals and blends of these coals were studied under the simulated BF conditions. The specific methodologies included gasification of cokes in the BF gas atmosphere (CO-CO2-N2-H2H2O) from 900 to 1400 °C (corresponding to the conditions from the thermal reserve zone to the cohesive zone) and annealing of cokes at

1. Gasification under the simulated BF conditions caused degradation 10

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2.

3.

4.

5.

of coke microstrength; compared to gasification, the subsequent annealing at high temperatures led to a more significant microstrength degradation. Such degradation on coke anisotropic microtexture was more serious than that occurred on coke isotropic microtexture. Gasification mainly took place on the coke lump periphery and resulted in a local degradation of coke pore structure; the extend of degradation was significantly reduced towards the lump core. Therefore, the tensile strength measured on the lump core was not greatly reduced by gasification. However, high temperature annealing caused degradation across the entire and coke lump thereby resulting in the greater degradation in coke tensile strength. Blending coals together resulted in a significant fluidity reduction from the expected values. The coal with lower rank in this study reached the maximum fluidity at the temperature lower than the other coal constituents in the blends and resolidified at which temperature the other coal constituents were still in the liquid stage. The different temperature ranges of the coal thermoplastic stages restricted the blends to develop the high fluidity. The large amount of volatile matter released from the low rank coal provided a better graphitization condition for the other coals in the blends, thereby resulting in the pervasively higher measured crystallinity. The Raman analysis conducted on individual microtextures indicated that this greater measured graphitization degree was mainly contributed by the lenticular and ribbon microtextures. Although the caking properties of the blends were remarkably reduced from the expected values, the measured microstrength did not have a significant difference from the weighted average values; the measured macrostrength, on the other hand, was greater than the calculated values. The different thermoplastic temperature ranges of coal components restricted the dilatation but promoted the contraction of the blends, thereby limiting the porosity development. Blending of coals for coke production could optimize the macrostrength of the produced cokes through such reduced porosity development.

[8] M. Dıez, R. Alvarez, C. Barriocanal, Coal for metallurgical coke production: predictions of coke quality and future requirements for cokemaking, Int. J. Coal Geol. 50 (2002) 389–412. [9] S. Nomura, T. Arima, K. Kato, Coal blending theory for dry coal charging process, Fuel 83 (2004) 1771–1776. [10] Y. Mochizuki, R. Naganuma, K. Uebo, N. Tsubouchi, Some factors influencing the fluidity of coal blends: particle size, blend ratio and inherent oxygen species, Fuel Process. Technol. 159 (2017) 67–75. [11] T. Yoshida, T. Takanohashi, M. Iino, H. Kumagai, K. Kato, Interactions among different fractions in the thermoplastic state of Goonyella coking coal, Energy Fuel 18 (2004) 349–356. [12] R. Sakurovs, Interactions between coking coals and plastics during co-pyrolysis, Fuel 82 (2003) 1911–1916. [13] J.W.S. James, J.A. MacPhee, J.T. Price, J.F. Gransden, Specific dilatation of coking coals: a means of reconciling the Ruhr and Audibert-Arnu methods, Fuel 72 (1993) 1161–1165. [14] R. Sakurovs, A method for identifying interactions between coals in blends, Fuel 76 (1997) 623–624. [15] R. Sakurovs, Interactions between coking coals in blends, Fuel 82 (2003) 439–450. [16] R. Sakurovs, Direct evidence that the thermoplastic properties of blends are modified by interactions between the component coals, Fuel 76 (1997) 615–621. [17] E. Díaz-Faes, C. Barriocanal, M. Díez, R. Alvarez, Characterization of different origin coking coals and their blends by Gieseler plasticity and TGA, J. Anal. Appl. Pyrolysis 80 (2007) 203–208. [18] E. Díaz-Faes, C. Barriocanal, M. Diez, R. Alvarez, Applying TGA parameters in coke quality prediction models, J. Anal. Appl. Pyrolysis 79 (2007) 154–160. [19] S. Ragan, H. Marsh, Carbonization and liquid-crystal (mesophase) development. 22. Micro-strength and optical textures of cokes from coal-pitch co-carbonizations, Fuel 60 (1981) 522–528. [20] R. Alvarez, M.A. Diez, C. Barriocanal, E. Diaz-Faes, J.L.G. Cimadevilla, An approach to blast furnace coke quality prediction, Fuel 86 (2007) 2159–2166. [21] S.S. Gornostayev, J.J. Härkki, Graphite crystals in blast furnace coke, Carbon 45 (2007) 1145–1151. [22] K. Li, J. Zhang, M. Sun, C. Jiang, Z. Wang, J. Zhong, Z. Liu, Existence state and structures of extracted coke and accompanied samples from tuyere zone of a largescale blast furnace, Fuel 225 (2018) 299–310. [23] X. Xing, G. Zhang, H. Rogers, P. Zulli, O. Ostrovski, Effects of annealing on microstructure and microstrength of metallurgical coke, Metall. Mater. Trans. B Process Metall. Mater. Process. Sci. 45 (2014) 106–112. [24] X. Xing, H. Rogers, G. Zhang, K. Hockings, P. Zulli, O. Ostrovski, Coke degradation under simulated blast furnace conditions, ISIJ Int. 56 (2016) 786–793. [25] B. van der Velden, J. Trouw, C. Atkinson, L.C.G.M. Bol, High temperature properties of coke, critical for the lower part of the blast furnace, Ironmaking Conference Proceedings, 2002 (p. CD). [26] X. Xing, H. Rogers, G. Zhang, K. Hockings, P. Zulli, A. Deev, J. Mathieson, O. Ostrovski, Effect of charcoal addition on the properties of a coke subjected to simulated blast furnace conditions, Fuel Process. Technol. 157 (2017) 42–51. [27] X. Xing, H. Rogers, G. Zhang, K. Hockings, P. Zulli, O. Ostrovski, Changes in pore structure of metallurgical cokes under blast furnace conditions, Energy Fuel 30 (2015) 161–170. [28] X. Xing, Pore structure and integrity of a bio-coke under simulated blast furnace conditions, Energy Fuel 33 (2019) 2133–2141. [29] X. Xing, G. Zhang, M. Dell'Amico, G. Ciezki, Q. Meng, O. Ostrovski, Effect of annealing on properties of carbonaceous materials. Part II: porosity and pore geometry, Metall. Mater. Trans. B Process Metall. Mater. Process. Sci. 44 (2013) 862–869. [30] X. Xing, G. Zhang, M. Dell'Amico, G. Ciezki, Q. Meng, O. Ostrovski, Effect of annealing on properties of carbonaceous materials. Part III: macro and microstrengths, Metall. Mater. Trans. B Process Metall. Mater. Process. Sci. 44 (2013) 870–877. [31] S.Y. Kim, Y. Sasaki, Simulation of effect of pore structure on coke strength using 3dimensional discrete element method, ISIJ Int. 50 (2010) 813–821. [32] X. Xing, H. Rogers, P. Zulli, K. Hockings, O. Ostrovski, Effect of coal properties on the strength of coke under simulated blast furnace conditions, Fuel 237 (2019) 775–785. [33] N. Guelton, The prediction of the Gieseler characteristics of coal blends, Fuel 209 (2017) 661–673. [34] R.J. Gray, K.F. Devanney, Coke carbon forms: microscopic classification and industrial applications, Int. J. Coal Geol. 6 (1986) 277–297. [35] T.F. Yen, J.G. Erdman, S.S. Pollack, Investigation of the structure of petroleum asphaltenes by X-ray diffraction, Anal. Chem. 33 (1961) 1587–1594. [36] S. Dong, N. Paterson, S.G. Kazarian, D.R. Dugwell, R. Kandiyoti, Characterization of tuyere-level core-drill coke samples from blast furnace operation, Energy Fuel 21 (2007) 3446–3454. [37] W.C. Oliver, G.M. Pharr, An improved technique for determining hardness and elastic-modulus using load and displacement sensing indentation experiments, J. Mater. Res. 7 (1992) 1564–1583. [38] J. Patrick, A. Stacey, The strength of industrial cokes: part 1. Variability of tensile strength in relation to fissure formation, Fuel 51 (1972) 81–87. [39] Y. Kubota, S. Nomura, T. Arima, K. Kato, Quantitative evaluation of relationship between coke strength and pore structure, ISIJ Int. 51 (2011) 1800–1808. [40] W. Wang, B. Dai, R. Xu, J. Schenk, J. Wang, Z. Xue, The effect of H2O on the reactivity and microstructure of metallurgical coke, Steel Res. Int. 88 (2017) 1700063. [41] R. Xu, B. Dai, W. Wang, J. Schenk, A. Bhattacharyya, Z. Xue, Gasification reactivity and structure evolution of metallurgical coke under H2O/CO2 atmosphere, Energy Fuel 32 (2018) 1188–1195.

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This project was financially supported by ACARP (ACARP Project C26043). Author acknowledges the industry partners for the provision of samples and advices in this investigation. References [1] I.M. Butterfield, K.M. Thomas, Some aspects of changes in the macromolecular structure of coals in relation to thermoplastic properties, Fuel 74 (1995) 1780–1785. [2] S. Lee, J. Yu, M. Mahoney, A. Tahmasebi, R. Stanger, T. Wall, J. Lucas, In-situ study of plastic layers during coking of six Australian coking coals using a lab-scale coke oven, Fuel Process. Technol. 188 (2019) 51–59. [3] S. Lee, J. Yu, M. Mahoney, P. Tremain, B. Moghtaderi, A. Tahmasebi, R. Stanger, T. Wall, J. Lucas, Study of chemical structure transition in the plastic layers sampled from a pilot-scale coke oven using a thermogravimetric analyzer coupled with Fourier transform infrared spectrometer, Fuel 242 (2019) 277–286. [4] H.S. Valia, Coke Production for Blast Furnace Ironmaking, American Iron and Steel Institute, 2014. [5] T. Takanohashi, T. Shishido, I. Saito, Effects of HyperCoal addition on coke strength and thermoplasticity of coal blends, Energy Fuel 22 (2008) 1779–1783. [6] C. Chang, T. Whang, D. Huang, D. Wang, S. Tsai, M. Hung, Thermoplasticity and strength improvement of coking coal by addition of coal extracts, Fuel 117 (2014) 364–371. [7] Y. Mochizuki, R. Naganuma, N. Tsubouchi, Influence of inherently present oxygenfunctional groups on coal fluidity and coke strength, Energy Fuel 32 (2018) 1657–1664.

11

Fuel Processing Technology 199 (2020) 106274

X. Xing

properties, Fuel 60 (1981) 1115–1120. [46] S. Sakamoto, K. Igawa, Effect of coal interaction on coke strength, Tetsu-to-Hagané 87 (2001) 238–244. [47] M. Mahoney, S. Nomura, K. Fukuda, K. Kato, A. Le Bas, D.R. Jenkins, S. McGuire, The mechanism of coking pressure generation II: effect of high volatile matter coking coal, semi-anthracite and coke breeze on coking pressure and contraction, Fuel 89 (2010) 1557–1565. [48] K. Steel, R. Dawson, W. Xie, R. Stanger, T. Wall, M. Mahoney, Physical and chemical interactions occurring during cokemaking and their influence on coke strength, ACARP Project C24055 Final Report, 2016, pp. 9–12.

[42] L. Lu, V. Sahajwalla, C. Kong, D. Harris, Quantitative X-ray diffraction analysis and its application to various coals, Carbon 39 (2001) 1821–1833. [43] L. Lu, V. Sahajwalla, C. Kong, A. Mclean, Chemical structure of chars prepared under conditions prevailing in the blast furnace PCI operation, ISIJ Int. 42 (2002) 816–825. [44] Ł. Smędowski, M. Krzesinska, W. Kwasny, M. Kozanecki, Development of ordered structures in the high-temperature (HT) cokes from binary and ternary coal blends studied by means of X-ray diffraction and Raman spectroscopy, Energy Fuel 25 (2011) 3142–3149. [45] A. Grint, H. Marsh, Carbonization of coal blends: mesophase formation and coke

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