The purpose was to evaluate how these CaO-containing materials could affect the AOD process and the steel quality. In this study, fly ash and waste lime from Swedish pulp and paper mills were made into briquettes and for the first time utilized as slag formers to replace primary lime in a pilot-scale Argon Oxygen Decarburization (AOD) stainless steelmaking process. Due to high CaO contents, these secondary lime materials can be potentially utilized in the steelmaking process to partially replace primary lime. This study confirms that a multidisciplinary analytical approach is essential for selecting the best raw mix for achieving the highest lime reactivity in TSR kilns.įly ash and waste lime are solid wastes generated in pulp and paper mills. Secondly, locally concentered dolomitic marly limestones, and sporadic back shales negatively affects the quicklime reactivity, as well. In fact, the highest calcination velocity determined by thermal analysis is consistent with the highest slaking reactivity of the lower stratum of the quarry, enriched in poikilotopic calcite.
The presence of burial cementation, especially poikilotopic calcite, seems to promote higher burnability, either in terms of starting calcination temperature, or in terms of higher carbonate dissociation rate. The predominant micritic microbial textures, coupled with the organic carbon, are key-factors influencing the low burnability and the high sintering tendency. The slaking reactivity, according to EN 459-2 is high for lime burnt at 1050 ☌, but rapidly decreases for lime burnt at 1150 ☌. Burning and technical tests widely attest that the Neoarchean limestone is sensitive to high temperature, showing an unusual and drastically pronounced sintering or overburning tendency. Diagenetic modifications include hypidiotopic dolomite, micrite to microsparite recrystallization, stylolites, poikilotopic calcite, chert and saddle dolomite replacements. This limestone consists of laminated clotted peloidal micrite and fenestrate microbial boundstone with herringbone calcite and organic carbon (kerogen) within stylolites. This study evaluates the influence of chemical, mineralogical and petrographic features of the Neoarchean limestone from the Ouplaas Mine (Griqualand West, South Africa) on its burnability and quicklime reactivity, considering the main use as raw material for high-grade lime production in twin shaft regenerative (TSR) kilns. These integrated operations allowed to obtain satisfactory results for the client, in terms of reactivity, available lime index, and residual CO2 of the quicklime product. The aim of the paper is to show improvements on the quality control of the quicklime deriving from different synergic operations, summarized, as follow: 1) the judicious selection of the raw material feeding the kiln, based on burning and technological tests of the limestone from different benches of the mine plant 2) the careful setting of the Twin Shaft Regenerative Kiln (TSR) parameters, including regulations of heat distribution, burning temperature, flame behavior & combustion air, retention time, and fast discharging of the material.
Considering that the average product deriving from the mixture of these different lime types was qualitatively low, especially in terms of reactivity, and available lime content, therefore a deep and comprehensive technical assistance has been planned for supporting the client on reaching the target quality. Especially, it was possible to distinguish almost four groups of lime with different colors, reactivities, and residual CO2 contents. Significant criticalities observed during the initial stage of the production regarded the evident heterogeneity in the color of the lime, which was related to the variation in the reactivity, as determined according to the slaking method test (EN 459-2). New insights and improvements in controlling the calcination process, and the quicklime reactivity have been achieved during the start-up of two new 560 tpd Twin Shaft Regenerative (TSR) kilns, recently installed by Cimprogetti Spa.
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