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Coal agglomeration in blast furnace injection coals

Sexton, Dane 2019. Coal agglomeration in blast furnace injection coals. PhD Thesis, Cardiff University.
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In order to reduce expensive coke usage, blast furnace operators inject coal to replace a portion of the coke. However, the use of some injection coals can result in blast furnace instability and lowered permeability. This thesis is concerned with the injection of coal under entrained flow, high heating rate (104-106 °C/s) blast furnace conditions, namely the possibility of coal particle agglomeration via the use of caking coals. Methods of mitigating agglomeration via blending and pre-oxidation are tested, whilst the resultant performance implications of agglomerated coal chars are considered and analysed. A drop tube furnace (DTF) was used to experimentally test coal injection under conditions that are applicable to the blast furnace ‘hot blast’ region. Relatable DTF parameters include an operating temperature of 1100°C, and heating rate of 104 °C/s. Four industrial injection coals with varying volatile matter and caking properties were tested at both granulated and pulverised particle size specifications. It was found that coals defined as ‘caking coals’ showed consistent agglomeration during DTF injection, a potentially problematic effect regarding blast furnace injection. Agglomeration percentages (as defined by sieve classification) for the industrially problematic MV4 coal were 11% and 23% for the granulated and pulverised samples respectively. Blending of whole coals was effective in reducing the amount of agglomerated material in the char, as was sample pre-oxidation prior to injection. Regarding performance, agglomerated chars had greater combustion performance and gasification reactivity than the non-agglomerated samples. With agglomeration shown to be present under high heating rate conditions at temperatures akin to the blast furnace hot blast, it is concluded that agglomeration is a possibility during blast furnace injection. However, due to differing feed systems between the DTF and blast furnace, the precise form and extent of agglomeration in the blast furnace remains uncertain. Based on char combustion and gasification analysis, chars characterised by fine agglomerated material are not likely to be problematic for blast furnace operators relative to ‘standard’ injection coals.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Blast Furnace; Agglomeration; Caking; Drop Tube Furnace; Gasification Reactivity; Pre-Oxidation.
Funders: Engineering and Physical Sciences Research Council
Date of First Compliant Deposit: 21 February 2019
Last Modified: 11 Dec 2020 02:50

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