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

Hannu Suopajärvi,Aki Koskela,Essi Dahl,Timo Fabritius,Stanislav Gornostayev,Antti Kemppainen

doi:10.3390/en10111850

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.

Highlights

The sustainability of iron and steel production is heavily dependent on the used fuels
A medium volatile coking coal, charcoal produced from pine chips and Kraft-lignin, recovered from the pulping process were used as raw materials in this study
Kraft-lignin loses a major share of its mass before the coal starts to soften, creating empty spaces that coal has to fill

Summary

Introduction

The sustainability of iron and steel production is heavily dependent on the used fuels. Coal is considered to be a non-renewable fuel and the emitted CO2 emissions are accumulated in the atmosphere. The use of biomass in metallurgical unit processes has been identified as one of the future technologies to decrease the use of non-renewable fuels, thereby decreasing the CO2 emission accumulation in the atmosphere [1]. The carbon cycle of biomass, such as wood, is short; the CO2 released in the burning of the wood is captured back to the wood as it grows again. This means that the CO2 level in the atmosphere is not growing. Biomass could be used in several applications in iron and steelmaking, including injection to the blast furnace (BF) and use in the coking plant to produce bio-coke [2]

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