High-Strength Formed Coke from Torrefied Biomass and Its Blend with Noncaking Coal

Abstract

In continuation of our previous study on production of high-strength metallurgical coke from torrefied softwood (cedar), we studied coke production from a mixture of torrefied cedar (TC) and noncaking coal by pulverization to sizes <100 μm, mixing, binderless hot briquetting, and carbonization. These sequential processes produced coke with a tensile strength of 5–17 MPa, which was equivalent to or greater than that of conventional coke (5–6 MPa), from TC-coal mixtures over the entire ranges of TC mass fraction in briquette of 0–100%, torrefaction temperature of 250–300 °C, and choice of coal (sub-bituminous or medium-volatile bituminous coal). The mixing of TC and coal hindered densification of coke due to hindrance of shrinkage of more-shrinkable TC-derived particles during the carbonization under many of the conditions. Nevertheless, positive synergy occurred in the coke strength at TC mass fractions of over 50%, where coal-derived particles were dispersed in the matrix of TC-derived particles, bonded to them during the carbonization, and behaved as a reinforcement of the matrix. The bonding between TC-derived and coal-derived primary particles was revealed by scanning electron microscopy. Copulverization of mixed TC and coal to sizes <40 μm before the briquetting gave cokes having strengths as high as 23–28 MPa. The fine pulverization increased the frequencies of mutual bonding of TC-derived particles and coal-derived particles and bonding between TC-derived and coal-derived particles per coke volume. The strength of coke from the TC-coal mixture generally followed volume-based additivity of strengths of cokes from TC and coal. This was realized by mixing primary particles of TC and coal within ≈10 μm scale or even smaller.

Control of Reactivity of Formed Coke from Torrefied Biomass by Its Washing with Torrefaction-derived Acidic Water

“…In continuation of the above-mentioned studies by Wibawa et al, 6,12) the present authors have been investigating formed coke production from woody biomass by torrefaction, pulverization, washing with torrefaction-derived acidic water, hot briquetting, and carbonization, as shown in Fig. 1, focusing on the removal of AAEM species by the acid-water washing and examining its effects on the strength and reactivity of the resulting coke.…”

“…Wei et al 11) torrefied woody biomass in the presence of acid-catalysts, which greatly enhanced the formation of anhydrosugars. They also converted the torrefied biomass to high-strength coke by applying the sequence proposed by Wibawa et al 6) Wibawa et al 12) also prepared coke from mixtures of non-caking coal and torrefied cedar and demonstrated co-pulverization of the coal and torrefied cedar before briquetting led to coke with a TS as high as 28-32 MPa regardless of the mixing ratio.…”

“…Such coke is even favored due to a decrease in the temperature of the thermal reserve zone and then an increase in the thermal efficiency of the blast furnace operation. 22,23) The cokes prepared by Wibawa et al 6,12) had a TS much greater than commercially available cokes and this leads to an expectation of 'high CRI but high CSR', which has not been proven yet.…”

Three-Dimensional Evaluation of Internal Structure of Coke Made by Blending Non-coking Coal Using X-ray Computed Tomography

“…Proposed solutions to this issue are formed coke [7][8][9] and briquette blending carbonization process 10) , which are believed to facilitate particle adhesion by pre-compressing and molding the coal, thereby improving inter-particle bonding. Researchers have explored the use of briquette blended with biomass [11][12][13] , iron ore 14) and non-and slightly coking coals 15) , low volatile non-coking coal 13) , coke breeze 16) and alumina beads 17) .…”

Production of High-Strength Coke by Pressurization Carbonization of Modified-Biomass Blended Coal

“…Torrefaction, hydrothermal treatment, hot briquetting, and combinations of these methods have been proposed as methods for physical treatment of biomass, and it has been shown that the coke produced by these methods has high strength and high gasification reactivity. [9][10][11][12] Although the above methods can also be applied to 100% biomass usage and low-quality coal to give extremely high-strength coke, the coke obtained by these methods is too highly reactive. [13][14][15][16] In terms of chemical treatment methods, there have been studies into binding biomass and low-quality coal by solvent modification, [17][18][19][20][21] and it is possible to manufacture highstrength coke by blending of modified-materials.…”