Investigating char agglomeration in blast furnace coal injection

Dane C Sexton,Julian M Steer,Richard Marsh,Mark Greenslade

doi:10.1016/j.fuproc.2018.05.013

Dane C Sexton, Julian M Steer + Show 2 more

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https://doi.org/10.1016/j.fuproc.2018.05.013

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Abstract

Blast furnace iron manufacturers aim to reduce expensive coke usage through the injection of coal. This paper investigates contrasting agglomeration behaviour with a view towards optimising blast furnace operations and limiting furnace permeability issues.A drop tube furnace (DTF) was used to investigate the performance of two coal particle size specifications that were representative of injection coal sizes: pulverised (100% < 300 μm, 50% < 75 μm), and granulated (100% < 1 mm, 50% < 250 μm). A range of coals was subjected to DTF testing with issues arising from the injection of caking coals. Results show these coals exhibit signs of agglomeration, a potentially problematic effect concerning blast furnace permeability. Considering gasification reactivity upon leaving the blast furnace raceway, it was found that the agglomerated coal chars do not suffer from poor reactivity and are more reactive than the non-agglomerated chars. Pre-treatment through oxidation was found to be an effective means of eliminating agglomeration in the DTF as a result of the reduction in caking properties.

Highlights

Coke is a crucial ingredient in blast furnace operation, used as a principal source of both fuel and reducing agent in smelting iron ore [1]
A drop tube furnace was used in order to simulate the initial heating of injection coals in the blast furnace with key parameters being temperature, heating rate, and residence time
The coal chars collected at this residence time are not fully devolatilised and only partially burnt; as a result, the term char is used to describe the partially burnt residue collected from the drop tube furnace (DTF)

Summary

Introduction

Coke is a crucial ingredient in blast furnace operation, used as a principal source of both fuel and reducing agent in smelting iron ore [1]. Aside from cost savings by reducing coke demands, coal injection provides a range of processing, economic, and environmental benefits with improved furnace operability, higher productivity, and reduced plant emissions [6,7]. Coal injection has been known to generate various furnace challenges such as reduced flame temperatures and impacts on slagging, one of the most problematic issues and the primary concern for this work is furnace instability as a result of lowered permeability [8,9,10]. Following injection into the furnace, coal char particles that remain unburned after leaving the raceway region are prone to accumulating, often causing blockages and lowering permeability [8,11,12,13]. Schott [14] explains that a key factor causing permeability issues is inefficient char gasification

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