Impact of Oven Bulk Density and Coking Rate on Stamp-Charged Metallurgical Coke Structural Properties

Abstract

Coke samples obtained by carbonizing a commercial coal blend in a pilot-scale moveable wall slot-oven were studied to evaluate the influence of oven bulk density and coking rate on coke structural quality. Coke samples were investigated using the coke strength after reaction (CSR) test, gas adsorption techniques, optical microscopy, and X-ray diffraction analyses. The results show that an increase in oven bulk density and coking rate led to an increase in CSR, a phenomenon attributed to enhanced coal particle adhesion and improved plasticity during the plastic stage. Surface area, total porosity, pore area, and cell wall measurements indicate that the compact nature of coal charge under high oven bulk density and accelerated events under a rapid coking rate result in limited pore structural development, leading to a less porous coke. An increase in coke oven bulk density resulted in the growth of carbon forms and also improved the degree of crystallization. However, the proportion of less-reactive carbon forms and extent of crystallization decreased with an increase in coking rate, a limitation ascribed to a lack of sufficient time to fully develop when a faster coking rate is employed. Furthermore, as indicated by a decrease in the range of CSR and structural properties, coke quality homogeneity along the oven width improved with higher oven bulk density and coking rate. A positive relationship was found between CSR and crystallite height, as well as between CSR and carbon forms development. Contrary to literature reports, a weak relationship was found between CSR and surface area; however, the importance of all pore sizes was shown by a positive relationship between CSR and total porosity.

Use of Alternative Raw Materials in Coke-Making: New Insights in the Use of Lignites for Blast Furnace Coke Production

“…The increased bulk density of the coal charge due to briquetting can enhance particle adhesion, which improves sintering conditions. In various studies [57,58], together with a decrease in total porosity caused by the increase of the charge density, an increase in the coke wall thickness was also noted, which positively affects the mechanical properties of the porous coke structure. The improved quality parameters for cokes from briquetted charges could also be a result of slightly lower total porosity, which in general influences the reactivity and strength of coke [47,59].…”

“…Higher micropore volumes and surface areas create easier access for carbon CO 2 to the coke matrix. Moreover, the coke matrix of cokes obtained from blends with BC, are characterized by a lower degree of optical anisotropy, which can also affect coke reactivity [6,46,48,53,54,[57][58][59]. When the coke microtexture is built of large objects (domains), more carbon atoms are inside them, making access to CO 2 molecules more difficult.…”

Compaction tests on coking coals. Part 1: Laboratory-scale compaction with a 4-ton hydraulic press

“…This phenomenon is attributed to enhanced coal particle adhesion and improved plasticity during the plastic phase. This, in turn, results in the growth of carbon forms and improves the degree of carbon crystallization; thus also the coke strength (Nyathi et al, 2013). Coke strength development is dependent on (i) the extent of coal particle adhesion, and (ii) the presence of unfilled gaps between particles (porosity) (Nishioka and Yoshida, 1983).…”

“…A less porous coke product, which is beneficial for mechanical strength (Nishioka and Yoshida, 1983). The decrease in total porosity is indicative of limited swelling, restraining pore enlargement and this, presumably, is attributable to the compact nature of the coal bed under high oven bulk density (Nyathi et al, 2013) Closer proximity of coal particles during softening, which results in the development of a stronger bond between the coke cells (Kumar et al, 2008) The induction of homogeneity throughout the coal cake (Kuyumcu, Rosenkranz, and Abel, 2010) An increase in the proportion of less-reactive carbon forms, and an improved degree of crystallization (Nyathi et al, 2013) Decreased porosity causing an increase in the water saturation index, i.e. filling of the total pore volume (Rejdak and Wasielewski, 2015) Improvement in the coke strength owing to increased coal particle contact and increased coke density (Rejdak and Wasielewski, 2015).…”

“…The bulk density and mechanical strength of compressed coal cake are controlled by varying the compressing energy, compacting time (when stamping with cyclic impacts of the stampers), coal type, coal surface moisture, coal granulometric properties (particle size distribution, particle shape, and particle density), and coal surface properties, as well as by using bulk density modifiers, such as oil (Nyathi et al, 2013;Kuyumcu and Sander, 2014;Burat. Kuyumcu, and Sander, 2015;Rejdak and Wasielewski, 2015).…”