Abstract
Two bituminous coals of different rank and coking characteristics were oxidized at low temperature for two months. Bituminous additives obtained in-situ in the coking plant were used to improve the thermoplastic properties of the oxidized coals. The Gieseler fluidity test was applied to evaluate their coking properties. A thermogravimetric analysis (TGA) of the fresh, oxidized coals and their blends with the bituminous additives was carried in order to evaluate the interaction between the blend components. In addition, carbonization tests of the fresh and oxidized coals and the blends with the additives were carried out in a movable wall oven of 17kg capacity and the quality of the cokes tested by means of standardized methods generally used by the steel industry. The additives increased coal fluidity but the original fluidity values could not be recovered. From TGA it was concluded that the blend components behave independently of one another during co-carbonization. The oxidation of coal leads to an increase in the dangerousness of the low volatile coal which was related to the porous texture of the cokes. In addition, it was found that the decrease in the quality of the coke produced from low rank oxidized coal can be partially recovered by using bituminous additives.
Highlights
The natural oxidation of coal is a complex process involving several chemical processes, which are accompanied by physical changes [1,2]
This is directly reflected in a reduction in carbonization rate, coke yield, and coke quality [4,5,6,7,8], effects which reduce the productivity of the coke plant and undermine the economic feasibility of coke production
While the quality of the coke prepared with lowest volatile coal (LV) is not affected either by oxidation or the additives, with HV oxidation there is a decrease in the quality of the coke which is only partially recovered by the use of a bituminous additive
Summary
The natural oxidation of coal (weathering) is a complex process involving several chemical processes, which are accompanied by physical changes [1,2]. The effect of additives on the coking process includes modifications to the thermoplastic properties of the coal, the generation of coking pressure [9,10] and a deterioration of the quality of the resultant cokes [11,12,13]. In this work two bituminous coals of different rank were investigated in order to study the effect of mild oxidation on their coking properties and the effectiveness of adding carbonaceous additives as a means of restoring these properties without impairing the quality of the resulting cokes. The thermoplastic properties of the fresh coals, oxidized coals and blends were assessed by means of the Gieseler test in a R.B. Automazione Gieseler plastometer PL 2000 following the ASTM D2639-08 standard procedure [19]. FE-SEM images were obtained on a Quanta FEG650 microscope (FEI Company) at 25 kV
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