Abstract
Replacement of part of the coal in the coking blend with lignin would be an attractive solution to reduce greenhouse gas emissions from blast furnace (BF) iron making and for obtaining additional value for lignin utilization. In this research, both non-pyrolyzed and pyrolyzed lignin was used in a powdered form in a coking blend for replacing 5-, 10- and 15 m-% of coal in the raw material bulk. Graphite powder was used as a comparative replacement material for lignin with corresponding replacement ratios. Thermogravimetric analysis was performed for all the raw materials to obtaining valuable data about the raw material behavior in the coking process. In addition, chemical analysis was performed for dried lignin, pyrolyzed lignin and coal that were used in the experiments. Produced bio cokes were tested in a compression strength experiment, in reactivity tests in a simulating blast furnace shaft gas profile and temperature. Also, an image analysis of the porosity and pore shapes was performed with a custom made MatLab-based image analysis software. The tests revealed that the pyrolysis of lignin before the coking process has an increasing impact on the bio coke strength, while the reactivity of the bio-cokes did not significantly change. However, after certain level of lignin addition the effect of lignin pyrolysis before the coking lost its significance. According to results of this research, the structure of bio cokes changes significantly when replacement of coal with lignin in the raw material bulk is at a level of 10 m-% or more, causing less uniform structure thus leading to a less strong structure for bio cokes.
Highlights
Blast furnace (BF) iron making faces important changes
The results suggest that the increase of graphite decreases the reactivity of the produced coke in the simulated blast furnace (BF) gas atmosphere, despite the weakened pore shape factor
The effect of pre-pyrolysis of lignin was investigated for getting answers to following questions: Does the pre-pyrolysis of lignin improve the properties of produced coke and what are the mechanisms or factors behind the different effect? Graphite powder-containing cokes were produced to determine whether the effect pyrolyzed lignin addition to the coking blend is more inert like, or is the effect a consequence from properties of lignin
Summary
Blast furnace (BF) iron making faces important changes. Tightening environmental legislation, increasing prices of GHG emission allowances and competition between the steel manufacturers encourage the steel manufacturers to research and implement new, less GHG –generating processes and raw materials. The BF- basic oxygen furnace (BOF) route is the leading pathway to produce crude steel in a sense of produced tons of steel annually. The share of the steel that is produced via the BF-BOF route is approximately 70%, of which approximately 85% of the raw materials is BF–produced pig iron [1]. In a BF-based iron production, metallurgical coke is a primary fuel of the process. Besides working as a fuel the metallurgical coke works as a reducing agent for the iron ore and as a bed material for the raw material burden by creating a layer with a permeable matrix for ascending gases and for descending melts (steel and slag) [2]. The consumption of metallurgical coke with the existing BF process technology can be as low as 250 kg/tHM (tons of hot metal), while it has been over 500 kg/tHM
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