Effect of Charcoal and Kraft-Lignin Addition on Coke Compression Strength and Reactivity

Abstract

Abstract:The aim of this research was to investigate the effects of charcoal and Kraft-lignin additions on the structure, cold compression strength, and reactivity of bio-cokes produced at the laboratory scale. Bio-cokes were prepared by adding charcoal and Kraft-lignin (2.5, 5.0, 7.5, and 10.0 wt %) to medium-volatile coal and coking the mixture with controlled heating rate (3.5 • C/min) up to 1200 • C. In addition, four particle sizes of charcoal were added with a 5 wt % addition rate to investigate the effect of particle size on the compression strength and reactivity. Thermogravimetric analysis was used to evaluate the pyrolysis behavior of coal and biomasses. Optical microscopy was used to investigate the interaction of coal and biomass components. It was found that by controlling the amount of charcoal and Kraft-lignin in the coal blend, the compression strength of the bio-cokes remains at an acceptable level compared to the reference coke without biomass addition. The cold compression strength of the charcoal bio-cokes was higher compared to Kraft-lignin bio-cokes. The reactivity of the bio-cokes with charcoal addition was markedly higher compared to reference coke and Kraft-lignin bio-cokes, mainly due to the differences in the physical properties of the parental biomass. By increasing the bulk density of the coal/biomass charge, the cold compression strength of the bio-cokes can be improved substantially.

Lignin from Bioethanol Production as a Part of a Raw Material Blend of a Metallurgical Coke

“…However, the biggest size fractions were cut out because of the limited size of the mini coke oven. The choice of 125-250 µm size fraction for lignin based on the report from Suopajärvi et al, in which the replacement of coking coal with the charcoal with the corresponding size fraction produced the strongest coke in comparison to other charcoal containing cokes in which the particle size of charcoal was different [7]. The amount of raw materials in the charges of different types of cokes are presented in Table 2.…”

“…Ng et al studied the effect of charcoal addition to the coking blend [6]. Suopajärvi et al studied the effect of charcoal and kraft-lignin addition to the produced coke strength and reactivity properties [7]. One of the least studied fractions of biomass as a part of the coking blend is lignin.…”

“…As an injectable reductant for BF iron making, multiple properties of pyrolyzed lignin were as good as or better than the properties of pulverized coal (PC) according to Farrokh et al [10]. Suopajärvi et al, have stated that the replacement of the coal in the raw material blend of the coking process with lignin by 2.5% of the total bulk mass leads to 26.3% decrease in the coke cold strength in comparison to reference coke [7]. They have also reported that kraft-lignin loses major share of its mass before the softening stage of the coal thus leading to empty spaces in the coke structure.…”

“…The same behavior was not observed with the use of charcoal in the coking blend but instead the strength of coke remained even with 7.5-10 m-% replacement of coal with charcoal. The charcoal was pyrolyzed in 600 • C, and, according to thermogravimetric analysis, the charcoal acted mainly as inert material in the coking blend throughout the coal plastic phase in the coking process [7]. The earlier study [7] did not consider the effect of pre-pyrolysis of lignin before using it as a raw material in a coking blend.…”

“…The charcoal was pyrolyzed in 600 • C, and, according to thermogravimetric analysis, the charcoal acted mainly as inert material in the coking blend throughout the coal plastic phase in the coking process [7]. The earlier study [7] did not consider the effect of pre-pyrolysis of lignin before using it as a raw material in a coking blend. It is not clear if it is better that lignin or any other biomaterial has an active role during the coke formation or should the behavior of biomaterial be inert.…”