Impact of the Addition of Pyrolysed Forestry Waste to the Coking Process on the Resulting Green Biocoke

Jon Solar,Alexander Lopez-Urionabarrenechea,Carmen Barriocanal,Blanca María Caballero,Esther Acha

doi:10.3390/met11040613

Jon Solar, Alexander Lopez-Urionabarrenechea + Show 3 more

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https://doi.org/10.3390/met11040613

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Abstract

The suitability of the charcoal obtained from woody biomass pyrolysis in a continuous screw reactor at 573, 773, 973, 1173 K temperature profile as fuel and reducing agent in metallurgical applications has been evaluated, in order to reduce the CO2 emissions in these processes. On the one hand, a comparative study between charcoal and commercial reducers has been carried out. On the other hand, different proportions of this charcoal have been added to an industrial coking coal blend and carbonized together in a semi-pilot movable wall oven, to study the influence in the plastic and mechanical properties of the produced biocoke. The charcoal obtained fulfills the requirements to be used as fuel and reducer in non-ferrous processes where no mechanical strength is required, like rotary kilns, in substitution of fossil reducers. Its higher heating value (>32 MJ kg−1) is in the range or over those of fossil coals, with the advantage of not containing polluting elements (S, N) and having less ash. The addition of up to 0.9 wt.% almost does not affect the quality of the biocoke; but the addition of ≥2 wt.% degrades the biocoke mechanical and plastic properties below the demanded requirements. Moreover, biocoke reactivity seems independent of the amount of charcoal added.

Highlights

The raw material used in the cokemaking process usually consists of a blend of different properties coals whose characteristics and price fit the best with the technical and economic needs of the blast furnace (BF) industry
The suitability of the charcoal produced by pyrolysis of pinus radiata waste chips in a continuous auger reactor at high temperatures (573, 773, 973, 1173 K) with a vapor’s thermal treatment step (1073 K) as reducing agent in steel making operations has been evaluated, in order to reduce CO2 emissions
The charcoal obtained can be used, on the one hand, as a good quality renewable solid fuel with neutral CO2 emissions to replace fossil reducers; its higher heating value is in the range or over those of conventional fossil coals and has the advantage of not containing polluting elements (S, N) and having less ash content

Summary

Introduction

The raw material used in the cokemaking process usually consists of a blend of different properties coals whose characteristics and price fit the best with the technical and economic needs of the blast furnace (BF) industry. The partial substitution of these coals by additives such as biomass is an option that has been studied as a way to reduce the need for this fossil fuel and CO2 emissions [1,2,3,4]. A priori, the addition of carbonized biomass to the coking coal blend to produce biocoke (i.e., coke partially produced with a renewable source of carbon), seems a viable option to reduce the CO2 emissions [5,6]. High reactivity can cause shrinkage of coke particles in the interior of the BF due to the loss of mechanical strength produced by chemical and abrasion phenomena, impoverishing the process performance due to the loss of permeability of the coke bed by occlusion. The development of metallurgical techniques such as tuyere injection lessens the importance of the reductant and fuel functions of coke [14,15]; it is increasingly regarded to limit the reactivity of coke in order to minimize its use

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