Submitted Successfully!
To reward your contribution, here is a gift for you: A free trial for our video production service.
Thank you for your contribution! You can also upload a video entry or images related to this topic.
Version Summary Created by Modification Content Size Created at Operation
1
Heng Zheng
 + 1785 word(s) 1785 2022-01-05 04:00:59 |
2 corrected the format
Dean Liu
 -26 word(s) 1759 2022-02-11 02:06:15 |

Video Upload Options

We provide professional Video Production Services to translate complex research into visually appealing presentations. Would you like to try it?
No, upload directly Yes

Confirm

Are you sure to Delete?
Yes No
Cite
If you have any further questions, please contact Encyclopedia Editorial Office.
Zheng, H. Metallurgical Coke Structures. Encyclopedia. Available online: https://encyclopedia.pub/entry/19349 (accessed on 15 November 2024).
Zheng H. Metallurgical Coke Structures. Encyclopedia. Available at: https://encyclopedia.pub/entry/19349. Accessed November 15, 2024.
Zheng, Heng. "Metallurgical Coke Structures" Encyclopedia, https://encyclopedia.pub/entry/19349 (accessed November 15, 2024).
Zheng, H. (2022, February 11). Metallurgical Coke Structures. In Encyclopedia. https://encyclopedia.pub/entry/19349
Zheng, Heng. "Metallurgical Coke Structures." Encyclopedia. Web. 11 February, 2022.
Metallurgical Coke Structures
Edit
This entry is adapted from the peer-reviewed paper 10.3390/ma15010174

The structure of coke affects its reactivity and strength, which directly influences its performance in the blast furnace.

coke quality coke structures characterization molecular model

1. Introduction

The blast furnace (BF) is a high-efficiency shaft furnace. The high heat utilization rate and production efficiency make the BF route the dominant ironmaking process globally [1]. About 70% of the hot metal used in producing crude steel comes from the BF route [2][3][4]. Coke is an indispensable burden in the blast furnace, and its performance shows a substantial impact on the ironmaking process [5]. The coke plays the role of the skeleton, which ensures the gas and liquid penetration through the blast furnace. The Coke reactivity index (CRI) and the coke strength after reaction (CSR) are the most widely used indexes to indicate the coke degradation potential in a blast furnace. A coke with good quality shows a lower CRI and a higher CSR.
To cut CO2 emissions during BF ironmaking process, many methods have been developed for substituting part of the coke, such as the application of ferro coke [6][7] and biomass coke [8][9], injection of pulverized coal or biomass, or natural gas, etc. [10][11][12][13][14]. Oxygen-enriched blast technology is another well-used method to decrease the coke ratio by increasing the production rate of hot metal through enhancing the combustion intensity of coke and pulverized coal [15][16]. However, these methods result in higher requirements of coke quality, especially the coke strength. The coke quality should be adequate to ensure a continuous production of hot metal in the BF [17].
Coke shows different deterioration degrees in different parts of the blast furnace. During the movement from the top to the lower part of the furnace, most lump cokes break into smaller particles consumed in the hearth. In this process, the structures of the coke change significantly [18]. It is well known that the reactivity [19][20] and the strength of coke [21][22][23][24] are closely related to its structures. Therefore, it is essential to characterize the coke structures comprehensively. It should be noted that the properties of the parent coal and coking condition also influence the coke properties. Currently, there is no specific test for coals to guarantee high-quality coke products. Instead, multitudes of empirical laboratory tests have been developed to investigate aspects of the physical, chemical, and thermoplastic behavior of individual coals and blends [25]. Some researchers summarized some models for predicting the metallurgical coke quality based on maceral composition and properties of coals. However, the models were not satisfactory when applied to coals or blends of different geological histories [26]. Generally, in terms of coal properties, coke quality is primarily influenced by coal rank, coal type (reactive and inert macerals), and its inherent ability to soften, become plastic, and re-solidify into a coherent mass when heated [25]. As a general comment on model replication, they cannot be used beyond the conditions under which they were derived [27]. It is more acceptable to conclude the relations between coke structure and the properties.
Many studies discussed the relationship between coke structures and properties, but there is a lack of systematic discussion on characterization methods of coke structures. 

2. Relations between Coke Structures and Properties

The most important properties of coke are the reactivity and the strength. To measure the reaction characteristics of coke under high temperature conditions, the reactivity index (CRI), and coke strength after reaction (CSR) are proposed. CRI refers to the ability of the coke to react with carbon dioxide at 1100 °C. CSR refers to the strength of the coke after the reaction with carbon dioxide. CRI and CSR are two critical indicators of the thermal performance of coke. It is believed that a good quality metallurgical coke should have low CRI and high CSR. If the CRI is too high, the starting temperature of the reaction between the coke and CO2 will decrease. In other words, the reaction may start at the upper part of the blast furnace, resulting in the generated CO escaping from the top of the blast furnace. The cold/hot compressive strength of the coke is measured by two flat plates in room/high temperature conditions. One of the plates moves to compress the coke sample till the coke is destroyed. When the coke is used in a giant blast furnace, the compressive strength should be sufficient to support the iron-containing burdens. The following subsections introduce the relations between coke structures and the coke properties.

2.1. Coke Structure and Reactivity

The main factors influencing the reactivity of coke include the pore structures, the mineral types and contents, and the inherent properties of the carbon matrix. Guo et al. [28] analyzed the porosities, pore wall thicknesses, and pore size distributions of 10 types of cokes to find the relations between these parameters and CRI. The reactivity of the coke was mainly affected by the content of pores with a size between 60 and 120 μm. These pores were important channels for the diffusion of the reaction gas into the coke. The coke with a larger pore wall thickness showed a lower CRI. Fott et al. [29] found a similar phenomenon in that the effective diffusion rate of CO2 in the ultra-micropores and macropores of the coke was relatively small. In these pores, the reaction only occurred in a small local area.
There are two primary sources of minerals that affect coke’s reactivity: the inherent minerals in the coke matrix and the extrinsic minerals that are enriched in the blast furnace. A large number of studies have pointed out that the minerals in the coke matrix showed different promotion effects on the reactivity of the coke [30][31][32][33][34]. Generally, the cations of the minerals played a critical role in the promotion effects. The catalytic effect in descending order were K+ > Na+ > Ca2+ > Mg2+ > Fe2+ > Al3+ > Si4+. To study the impact of the specific types of the minerals, a so-called coke analogue was developed for simulating the industrial coke. Reid et al. [30] used the coke analogue to simulate the metallurgical coke with a particular type of mineral. It was found that K+ showed the most potent catalytic effect. Due to the strong catalytic effect, alkali elements are regarded as detrimental for the blast furnace [35][36]. The influence of alkali elements in the blast furnace on coke reactivity has been a hot topic [37]. The impact of Zn has also been extensively studied [38][39]. The extrinsic minerals enriched in the blast furnace are not within the scope. In general, the appearance of these alkali and Zn elements could strongly accelerate the degradation of the coke.
Coke is a brittle material with a developed pore system composed of pore walls, pores, and cracks. The basic unit of the coke pore wall is the microcrystallite structure [40]. Ignoring the influence of the pore structures and the mineral effect, the inherent property of the coke matrix is the decisive factor that determines the reactivity of the coke. The two crucial intrinsic properties of the coke matrix are microcrystallite and optical characteristics. The method of determining the microcrystallite parameters, such as the average stacking height (Lc) of crystalline, the average size (La) of crystalline layer, and the average spacing (d002) of crystalline, are introduced in 2.2. Zhang et al. [41] evaluated 30 different metallurgical cokes and found that d002, Lc, and La were in the ranges of 3.46–3.51 Å, 28.95–42.18 Å, and 41.40–53.05 Å, respectively. The interlayer spacing of cokes showed a neglectable difference. It was found that when the mineral effect was not strong, the CRI decreased with the increasing Lc and La. During the CO2 gasification reaction, the isotropic texture in the coke reacted more quickly than the anisotropic texture [42][43][44][45]. The higher value of the ∑ISO of the coke is, the higher CRI of the coke will be. OTI is another index but describes the same optical phenomenon of the coke matrix. Generally, the coke with a higher value of OTI shows lower CRI.

2.2. Coke Structure and Strength

The direct forces that cause the degradation of the coke in the blast furnace are the friction and collision between the bulk burden materials, such as iron ore sinter, iron ore pellet, and cokes. The coke strength can be comprehensively indicated by cold compressive strength, CSR, and hot compressive strength. The pore structures play an essential role in determining the strength of the coke. Mihashi et al. [46] found that the matrixes of different cokes showed similar strength. Young et al. [22] used the 3-dimensional discrete element method to simulate the compressive cracks of coke. It was found that porosity is the main factor affecting the strength of the coke. A uniform pore distribution and less porosity contributed to the coke’s higher cold compressive strength. Saito et al. [23] used the rigid bodies–spring model to analyze the relations between the pores and the cold compressive strength. He found that slight roundness and large distorted pores might cause stress concentration and significantly reduce the strength of coke. Gornostayev et al. [24] found a similar result by directly observing the coke using a scanning electron microscope. The elliptical, elongated, and flattened pores, compared with circular pores, showed a lower ability to resist load pressure. The high cold compressive strength of coke could not guarantee its high CSR. The CSR presents a good negative correlation with the CRI [21][47][48]. The factors that affect the CRI of the coke inevitably affect the CSR of coke. The aim of measuring hot compressive strength is to simulate the load borne by the coke in an actual blast furnace. Haapakangas et al. [49][50] used the Gleeble thermomechanical simulator to evaluate the coke hot compressive strength at 1000 °C, 1600 °C, and 1750 °C. It was found that the coke was brittle at 1000 °C but partially plastic at 1600 °C and 1750 °C. The high-temperature treatment above the temperature of the coking furnace may cause further graphitization. The non-graphitizing carbons became harder, and the graphitizing carbons became softer at temperatures between 1000 °C and 2000 °C. The low coke compressive strength at high temperature was considered to be due to the high graphitization degree of the coke. Fang et al. [51] investigated the relations between temperature, carbon loss of the coke, and hot compressive strength. It was found that the hot compressive strength was significantly decreased with the increasing carbon loss of the coke and the temperature. However, the effects of individual factors affecting coke hot strength were not illustrated. Guo et al. [52] studied the influence of the pore structure features on the hot compressive strength of coke. It showed that in the temperature between 1000 °C and 1300 °C, the temperature presented a limited influence on the strength. The coke with a higher hot compressive strength showed a smaller pore size with a more uniform distribution. The following chapter introduced the relevant characterization methods of the coke structures.

References

  1. Zhou, C.; Tang, G.; Wang, J.; Fu, D.; Okosun, T.; Silaen, A.; Wu, B. Comprehensive numerical modeling of the blast furnace ironmaking process. JOM 2016, 68, 1353–1362.
  2. Liu, W.; Zuo, H.; Wang, J.; Xue, Q.; Ren, B.; Yang, F. The production and application of hydrogen in steel industry. Int. J. Hydrog. Energy 2021, 46, 10548–10569.
  3. Chen, Y.; Zuo, H. Review of hydrogen-rich ironmaking technology in blast furnace. Ironmak. Steelmak. 2021, 48, 749–768.
  4. Patisson, F.; Mirgaux, O. Hydrogen ironmaking: How it works. Metals 2020, 10, 922.
  5. Lyalyuk, V.P.; Sheremet, V.A.; Kekuh, A.V.; Otorvin, P.I.; Tarakanov, A.K.; Kassim, D.A. Investigation of coke reactivity effect on parameters of blast furnace operation. Metall. Min. Ind. 2010, 2, 317–323.
  6. Wang, H.; Chu, M.; Bao, J.; Liu, Z.; Tang, J.; Long, H. Experimental study on impact of iron coke hot briquette as an alternative fuel on isothermal reduction of pellets under simulated blast furnace conditions. Fuel 2020, 268, 117339.
  7. Yin, C.; Qiu, S.; Zhang, S.; Sher, F.; Zhang, H.; Xu, J.; Wen, L. Strength degradation mechanism of iron coke prepared by mixed coal and Fe2O3. J. Anal. Appl. Pyrolysis 2020, 150, 104897.
  8. Castro-Diaz, M.; Vega, M.F.; Diaz-Faes, E.; Barriocanal, C.; Musa, U.; Snape, C. Evaluation of demineralized lignin and lignin-phenolic resin blends to produce biocoke suitable for blast furnace operation. Fuel 2019, 258, 116125.
  9. Koveria, A.; Kieush, L.; Svietkina, O.; Perkov, Y. Metallurgical coke production with biomass additives. Part 1. A review of existing practices. Canadian Metall. Q. 2021, 59, 1–13.
  10. De Assis, C.F.C.; Tenório, J.A.S.; Assis, P.S.; Nath, N.K. Experimental simulation and analysis of agricultural waste injection as an alternative fuel for blast furnace. Energy Fuels 2014, 28, 7268–7273.
  11. Toloue Farrokh, N.; Suopajärvi, H.; Mattila, O.; Sulasalmi, P.; Fabritius, T. Characteristics of wood-based biochars for pulverized coal injection. Fuel 2020, 265, 117017.
  12. Majeski, A.; Runstedtler, A.; D’alessio, J.; Macfadyen, N. Injection of pulverized coal and natural gas into blast furnaces for iron-making: Lance positioning and design. ISIJ Int. 2015, 55, 1377–1383.
  13. Jampani, M.; Gibson, J.; Pistorius, P.C. Increased use of natural gas in blast furnace ironmaking: Mass and energy balance calculations. Met. Mater. Trans. B 2019, 50, 1290–1299.
  14. Liu, Y.; Shen, Y. Modelling and optimisation of biomass injection in ironmaking blast furnaces. Prog. Energy Combust. Sci. 2021, 87, 100952.
  15. Zhou, Z.; Wang, R.; Yi, Q.; Wang, G.; Ma, C. Combustion enhancement of pulverized coal with targeted oxygen-enrichment in an ironmaking blast furnace. Processes 2021, 9, 440.
  16. Kou, M.; Zhou, H.; Hong, Z.; Yao, S.; Wu, S.; Xu, H.; Xu, J. Numerical analysis of effects of different blast parameters on the gas and burden distribution characteristics inside blast furnace. ISIJ Int. 2020, 60, 856–864.
  17. Gangopadhyay, M.; Bayen, G.K.; Kumar, M.; Mukherjee, A.; Ranjan, R.; Kumar, S. Preheating upto tarrification point and compaction: A promising way for coke quality enhancement. Int. J. Coal Geol. 2021, 1–9.
  18. Pusz, S.; Krzesinska, M.; Smedowski, L.; Majewska, J.; Pilawa, B.; Kwiecinska, B. Changes in a coke structure due to reaction with carbon dioxide. Int. J. Coal Geol. 2010, 81, 287–292.
  19. Xu, R.; Dai, B.; Wang, W.; Schenk, J.; Bhattacharyya, A.; Xue, Z. Gasification reactivity and structure evolution of metallurgical coke under H2O/CO2 atmosphere. Energy Fuels 2018, 32, 1188–1195.
  20. Guo, R.; Wang, Q. Relationship between coke properties and solution loss behavior and its influence on post-reaction strength of coke. Metall. Res. Technol. 2012, 109, 443–452.
  21. Lech, K.; Jursova, S.; Kobel, P.; Pustejovska, P.; Bilik, J.; Figiel, A.; Romański, L. The relation between CRI, CSR indexes, chemical composition and physical parameters of commercial metallurgical cokes. Ironmak. Steelmak. 2019, 46, 124–132.
  22. Sun-Young, K.; Sasaki, Y. Simulation of effect of pore structure on coke strength using 3-dimensional discrete element method. ISIJ Int. 2010, 50, 813–821.
  23. Saito, Y.; Matsuo, S.; Kanai, T.; Toishi, A.; Uchida, A.; Yamazaki, Y.; Matsushita, Y.; Aoki, H.; Nomura, S.; Hayashizaki, H.; et al. Effect of random pore shape, arrangement and non-adhesion grain boundaries on coke strength. ISIJ Int. 2014, 54, 2519–2526.
  24. Gornostayev, S.; Heino, J.; Fabritius, T. Effect of micro-pores on cracks formation in metallurgical coke. Can. Metall. Q. 2017, 56, 252–258.
  25. Lu, L.; Devasahayam, S.; Sahajwalla, V. Evaluation of coal for metallurgical applications. Coal Handb. Towards Clean. Prod. 2013, 2013, 352–386.
  26. Diez, M.A.; Alvarez, R.; Barriocanal, C. Coal for metallurgical coke production: Predictions of coke quality and future. Int. J. Coal Geol. 2002, 50, 389–412.
  27. North, L.; Blackmore, K.; Nesbitt, K.; Mahoney, M.R. Methods of coke quality prediction: A review. Fuel 2018, 219, 426–445.
  28. Guo, R.; Duan, C.; Sun, Z.; Wang, J.; Sun, X.; Liang, Y. Effect of pore structure and matrix reactivity on coke reactivity and post-reaction strength. Metall. Res. Technol. 2017, 114, 504.
  29. Fott, P.; Straka, P. Effect of pore diffusion on reactivity of lump coke. Fuel 1987, 66, 1281–1288.
  30. Reid, M.H.; Mahoney, M.R.; Monaghan, B.J. A Coke Analogue for the Study of the Effects of Minerals on Coke Reactivity. ISIJ Int. 2014, 54, 628–633.
  31. Grigore, M.; Sakurovs, R.; French, D.; Sahajwalla, V. Coke gasification: The influence and behavior of inherent catalytic mineral matter. Energy Fuels 2009, 23, 2075–2085.
  32. Gornostayev, S.S.; Heikkinen, E.-P.; Heino, J.J.; Huttunen, S.M.M.; Fabritius, T.M.J. Behavior of alkali-bearing minerals in coking and blast furnace processes. Steel Res. Int. 2016, 87, 1144–1153.
  33. Dastidar, M.G.; Bhattacharyya, A.; Sarkar, B.K.; Dey, R.; Mitra, M.K.; Schenk, J. The effect of alkali on the reaction kinetics and strength of blast furnace coke. Fuel 2020, 268, 117388.
  34. Wang, G.; Ren, S.; Zhang, J.; Ning, X.; Liang, W.; Zhang, N.; Wang, C. Influence mechanism of alkali metals on CO2 gasification properties of metallurgical coke. Chem. Eng. J. 2020, 387, 124093.
  35. Bhattacharyya, A. Effect of alkaline elements on cokes structure under blast furnace process conditions. In Proceedings of the 25th Anniversary International Conference on Metallurgy and Materials. Metal, Brno, Czech Republic, 25–27 May 2016.
  36. Bhattacharyya, A. Effect of alkaline elements on the reactivity, strength and structural properties of blast furnace cokes. Metalurgija 2015, 54, 503–506.
  37. Li, K.; Zhang, J.; Barati, M.; Khanna, R.; Liu, Z.; Zhong, J.; Ning, X.; Ren, S.; Yang, T.; Sahajwalla, V. Influence of alkaline (Na, K) vapors on carbon and mineral behavior in blast furnace cokes. Fuel 2015, 145, 202–213.
  38. Wang, W.; Wang, J.; Xu, R.; Yu, Y.; Jin, Y.; Xue, Z. Influence mechanism of zinc on the solution loss reaction of coke used in blast furnace. Fuel Process. Technol. 2017, 159, 118–127.
  39. Wang, J.; Qie, L.; Hu, Y.; Liu, H.; Zheng, G. Influence of Zinc on nonisothermal gasification kinetics of coke in a blast furnace. ACS Omega 2021, 6, 28838–28847.
  40. Hu, D.S. Crystall ite structure characteristics of coke. Iron Steel 2006, 41, 10–12.
  41. Zhang, H.; Bai, J.; Li, W.; Cheng, F. Comprehensive evaluation of inherent mineral composition and carbon structure parameters on CO2 reactivity of metallurgical coke. Fuel 2019, 235, 647–657.
  42. Piechaczek, M.; Mianowski, A.; Sobolewski, A. Reprint of “The original concept of description of the coke optical texture”. Int. J. Coal Geol. 2015, 139, 184–190.
  43. Flores, B.D.; Borrego, A.G.; Diez, M.A.; da Silva, G.L.; Zymla, V.; Vilela, A.C.; Osório, E. How coke optical texture became a relevant tool for understanding coal blending and coke quality. Fuel Process. Technol. 2017, 164, 13–23.
  44. Li, K.; Khanna, R.; Zhang, J.; Liu, Z.; Sahajwalla, V.; Yang, T.; Kong, D. The evolution of structural order, microstructure and mineral matter of metallurgical coke in a blast furnace: A review. Fuel 2014, 133, 194–215.
  45. Zhang, W.; Shi, T.; Zhang, Q.; Cao, Y.; Qian, H.; Wu, X.; Li, J.; Zhang, Q.; Yang, G.; Yang, J. Coke texture, reactivity and tumbler strength after reaction under simulated blast furnace conditions. Fuel 2019, 251, 218–223.
  46. Mihashi, M.; Soejima, M.; Asakuma, Y.; Yamamoto, T.; Aoki, H.; Miura, T.; Katou, K.; Itagaki, S. Evaluation of matrix of coke strength by nano-indentation method. Tetsu-to-Hagane 2002, 88, 188–194.
  47. Wang, Q.; Guo, R.; Zhao, X.; Sun, J.; Zhang, S.; Liu, W. A new testing and evaluating method of cokes with greatly varied CRI and CSR. Fuel 2016, 182, 879–885.
  48. Lundgren, M.; Sundqvist Ökvist, L.; Björkman, B. Coke reactivity under blast furnace conditions and in the CSR/CRI test. Steel Res. Int. 2009, 80, 396–401.
  49. Haapakangas, J.; Uusitalo, J.; Mattila, O.; Kokkonen, T.; Porter, D.; Fabritius, T. A method for evaluating coke hot strength. Steel Res. Int. 2013, 84, 65–71.
  50. Haapakangas, J.A.; Uusitalo, J.A.; Mattila, O.J.; Gornostayev, S.S.; Porter, D.A.; Fabritius, T.M.J. The hot strength of industrial cokes—Evaluation of coke properties that affect its high-temperature strength. Steel Res. Int. 2014, 85, 1608–1619.
  51. Fang, J.; Li, C.; Wang, X.; Ren, R. Raw material strength in a blast furnace at operating temperature. Steel Res. Int. 2008, 79, 5–10.
  52. Guo, W.T.; Xue, Q.G.; Ling, C.; Zuo, H.B.; Wang, J.S.; Han, Y.H. Influence of pore structure features on the high temperature tensile strength of coke. Chin. J. Eng. 2016, 38, 930–936.
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license; additional terms may apply. By using this site, you agree to the Terms and Conditions and Privacy Policy.
Upload a video for this entry
Information
Subjects: Metallurgy & Metallurgical Engineering
Contributor MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Heng Zheng
View Times: 2.1K
Revisions: 2 times (View History)
Update Date: 11 Feb 2022
Table of Contents
    1000/1000
    Hot Most Recent
    ScholarVision Creations
    Feedback