When predicting coke quality or coking behaviour, the more accurate models typically include vitrinite content in addition to rank. This work explores how the two most abundant vitrinite macerals (collotelinite and collodetrinite) behave during carbonisation. The insights gained highlight important differences, paving the way for more sophisticated coke quality prediction models and enhanced blending/processing strategies. Australian bituminous coals from Bowen Basin with random vitrinite reflectance (%Ro) ranging 0.81–1.18% were cut and polished into coal blocks having a 15 mm × 15 mm face running perpendicular to the bedding plane. Following petrographic analysis, these blocks were carbonised at 3 °C/min to 525 °C, set in resin, and repolished to examine coking behaviour of identified macerals. Vitrinite concentrates (VCs) were prepared alongside “whole coal” samples to measure viscosity using rheometry. Collotelinite underwent considerably more expansion than collodetrinite with the extent of collotelinite expansion greater for the lower reflectance bituminous coals; characterised by large pores and thin pore walls, while higher reflectance coals gave rise to smaller pores and thicker pore walls. Separated VCs were rich in collotelinite and generated significant fluidity, i.e. low viscosity. For whole coals, viscosities were higher due to the presence of inertinite, however, this work suggests that higher viscosities are also due to increased collodetrinite. The maceral picking process for one coal led to a situation where the VC and the whole coal had similar levels of vitrinite, however, the VC was richer in collotelinite and exhibited a significantly lower viscosity. This result suggests that fluidity development and expansion behaviour for these two vitrinite macerals is different, and aligns with visual observations. It is proposed that volatile release behaviour is different for collotelinite and collodetrinite due to the differences in microstructure. More specifically, volatiles are better retained in collotelinite which contributes to its greater fluidity development and expansion behaviour. The process of geochemical gelification that gives rise to collotelinite may enable it to have no, or very few, defects and therefore limited pathways for volatiles to leave. Instead, volatiles are trapped and contribute to both the liquid development and bubble expansion. With no inclusions and defects to destabilise bubble interfaces, significant expansion occurs. In contrast, whilst collodetrinite arises via a similar process, it is less than 10 μm in size and co-occurs with other macerals and minerals, held together physically owing to its detrital origin and/or its mechanical degradation within the palaeomires. Accordingly, there are defects and grain boundaries between components through which volatiles may diffuse out, preventing fluid development and expansion. Overall, the outcome of this study shows that the vitrinite size and relative ease of volatile release for different maceral types may play a crucial role in a coal's fluidity development, and consequently its coking behaviour. 

The reactivity of metallurgical coke is a key contributory factor to its integrity in the ironmaking blast furnace. Herein, the factors that influence the CO2 gasification reactivity of individual coke inert maceral derived components (IMDC) and reactive maceral derived components (RMDC) were examined, including: Parent inertinite types, degree of microtextural anisotropy, accessibility of the IMDC; and ash chemistry.

Individual IMDC and RMDC components were formed by coking inertinite group concentrates (IC) and vitrinite group concentrates (VC), respectively. Cokes were also formed from head coals and by using different proportions of IC and VC in the coking blend. Coke lump and intrinsic gasification kinetics were compared for each case, where “intrinsic” refers to the gasification behaviour of powdered samples. The most influential factors on which the reaction rate was dependent were distinctly different between lump and powdered samples. The degree of isotropy of the carbon structure was the most important parameter controlling coke lump gasification kinetics with CO2 at 1100°C, followed by the basicity index of head coal. Conversely, intrinsic reactivity was closely correlated with microporosity.

Importantly, the isotropy of the carbon structure was not found to be a critical parameter controlling the intrinsic gasification kinetics up to the 40% carbon conversion point. These results suggest that in the lump form where gas diffusion limits the reaction rate, carbon structure and catalytic effect of coke minerals play the dominant role in coke gasification. Such behaviour leads to a selective reaction of gas with IMDC in coke lumps due to the isotropy of carbon and greater association with minerals.

Sugarcane bagasse was pyrolyzed to various temperatures and blended with three coking coals comprising two medium volatile bituminous (MVC 1 and MVC 2) and one high volatile bituminous (HVC 1) to assess carrying capacities and mechanisms behind fluidity loss during co-carbonization.MVC 2 showed no fluidity loss when blended with 10 wt% char pyrolyzed to 600 °C and 800 °C. However, with higher char additions (20 and 25 wt%), fluidity loss progressively worsened due to reduced amount of coal-derived liquid filling voids, causing volatiles to exhaust the system more easily. Complete fluidity loss occurred at 30 wt% char addition. Conversely, for MVC 1, despite having similar properties to MVC 2 in terms of rank and volatile matter, a 10 wt% 800 °C char addition caused fluidity loss. MVC 2 swells to a greater extent than MVC 1 and it is hypothesized that char addition disrupts the bubble growth phase, promotes bubble coalescence, and exacerbates volatile release. Further, it is hypothesized that higher swelling coals, such as MVC 2, can better incorporate char, negating its effects on bubble growth and thereby retaining liquid.For HVC 1, the addition of 5 wt% 800 °C char caused substantial fluidity loss which is attributed to the limited swelling behaviour of the coal alone, with bubble coalescence dominating over bubble growth early in the softening phase. The premature loss of volatiles caused by the addition of the char inhibits fluidity development and renders the blend unable to carry biochar. These results suggest that a coking blend’s carrying capacity for char may depend on its swelling behaviour, with greater swelling being advantageous.

Derived through the thermochemical conversion of biomass, biochar is a carbon-rich substance recognized for its significance in environmental applications and sustainable agriculture. As interest in its utilization continues to rise, it becomes crucial to comprehend how the source material and pyrolysis parameters influence the properties of biochar and, consequently, to research the suitability of various analytical methods for characterizing it. Despite the current utilization of numerous physical and chemical methods, the untapped potential of reflected light microscopy warrants further exploration.

While a few recent studies suggest a correlation between certain microscopic characteristics and selected physical and chemical properties of biochar, the data are limited and difficult to compare. This is primarily due to variations in the types of original biomass used and lack of information about pyrolysis conditions. Moreover, because only a limited number of photographs taken under a reflected light microscope are publicly available to-date, it is difficult to evaluate morphological differences between various biochars and other organic materials such as inertinites from coal, charcoal, etc.

To address limited availability of publicly available data, this “Atlas of Microscopic Images of Biochar” presents a collection of more than 300 images contributed by researchers from Poland, the United States, Canada, Australia, Brazil, and Denmark. These photomicrographs capture optical characteristics of a diverse array of biochar, demonstrating its unique morphological and structural features. This visual documentation can serve as a valuable resource for researchers, industry professionals, educators, and enthusiasts interested in investigating the complexities of biochar forms.

This paper focuses on the introduction of sugarcane bagasse, an agricultural byproduct, as a renewable carbon-based additive to metallurgical coal to produce biocoke for the steel industry. Through subjecting pelletized sugarcane bagasse samples to various pyrolysis conditions, chars with varying properties were generated. With increasing final pyrolysis temperature (200, 400, 600, and 800 °C), a rise in carbon content and decline in oxygen, nitrogen and hydrogen levels in the chars were observed. The presence of an inert purge gas during pyrolysis prompted abundant micropore formation between 400 and 600 °C, yielding high specific surface area (SSA > 300 m2/g) chars at 600 °C and 800 °C. Conversely, chars produced in a fixed (unpurged) nitrogen environment exhibited minimal porosity and consequently low SSAs (<5m2/g). These various chars were then blended (at 10 % addition) with a medium-volatile bituminous coal to evaluate their impact on the viscoelastic properties of the coal. Chars pyrolyzed to lower final temperatures had the greatest detrimental effect on blend fluidity due to (1) their continued devolatilization which introduced void spaces in the blend creating pathways for the exhaust of coal volatiles, and (2) their elevated oxygen content, which scavenged essential mobile hydrogen needed to facilitate viscoelastic behaviour. Furthermore, chars with similar oxygen content but substantially different (by over two orders of magnitude) SSAs generated comparable coal-char blend viscosity profiles, indicating that the presence or absence of micropores in an additive does not significantly influence the viscoelastic behaviour of the coal. The reduction in blend fluidity for the addition of chars pyrolyzed to 800 °C was comparable to the modelled addition of inertinite macerals, implying that these high-temperature chars predominantly serve as inert solid additives. Comparison to a blend with 10 % mesoporous activated charcoal as the additive confirmed that it is mesopores that destroy fluidity, while micropores do not play a significant role. Mesopores were identified to adsorb/trap the relatively large tar-like compounds that are responsible for coal plasticity. Collectively, this research identifies three key factors contributing to fluidity reduction in coal-additive blends: void creation, oxygen content, and mesoporosity. These findings offer insights into optimizing biocoke production processes.

Coal petrography as a tool for predicting coke quality has been employed for many decades. This paper first provides a brief review of some of the founding research in this area and secondly proposes and demonstrates a technique for direct optical comparison of a semicoke to its exact piece of precursory coal to observe the pyrolysis behaviour of individual macerals. The technique involves imaging a polished block sample of coal (with the polished face of interest having orientation perpendicular to the bedding layers), pyrolysing the sample in a furnace up to 525°C under conditions attempting to mimic those in a coke oven, embedding the resulting semicoke in resin and lightly re-polishing and re-imaging the surface of interest. Comparison of the optical images of the sample pre- and post-pyrolysis enables a 2-dimensional visual assessment of the coking behaviour of the inherent macerals. This method was applied to two Permian coals: a Mozambican coal with random reflectance of 1.21% and an Australian coal with random reflectance of 1.28%. The main observations were (i) anisotropic swelling, with swelling much greater in the direction perpendicular to the bedding layers compared to that parallel, (ii) noticeably different pore structure arising from the vitrinite macerals collotelinite and collodetrinite, and (iii) visual evidence of semifusinite reactivity. It is intended that application of this technique will enhance the fundamental understanding of maceral specific coking behaviour and thus assist coke-makers with their blend formulations.

Considering global market trends and concerns about climate change and sustainability, increased biomass use for energy is expected to continue. As more diverse materials are being utilized to manufacture solid biomass fuels, it is critical to implement quality assessment methods to analyze these fuels thoroughly. One such method is reflected light microscopy (RLM), which has the potential to complement and enhance current standard testing, leading to improving fuel quality assessment and, ultimately, preventing avoidable air pollution.An interlaboratory study (ILS) was conducted to test the reproducibility of biomass fuels component identification using a reflected light microscopy technique. The exercise was conducted on thirty photomicrographs showing biomass and various undesired components (like plastics or mineral matter), which were purposely added (by the ILS organizers) to contaminate wood pellets and charcoal-based grilling fuels.Forty-six participants had various levels of difficulty identifying the marked components, and as a result, the percentage of correct answers ranged from 52.2 to 94.4%. Among the most difficult components to distinguish were petroleum products and inorganic matter. Various reasons led to the misidentification, including insufficient morphological descriptions of the components provided to participants, ambiguities of the nomenclature, limitations of the analytical and exercise method, and insufficient experience of the participants.Overall, the results indicate that RLM has the potential to enhance the quality assessment of biomass fuels. However, they also demonstrate that the petrographic classification used in this exercise requires further refinement before it can be standardized. While a new simplified classification of solid biomass fuels components was created as an outcome of this study, future research is necessary to refine the nomenclature, develop a microscopic morphological description of the components, and verify the accuracy of component identification with a follow-up ILS.Previous article in issue