Sorptional dehydration and thermochemical sintering of converter sludge

Abstract

Global steel output in 2016 exceeded 1.6 billion t, of which more than 1.2 billion t was produced in converters. The smelting of 1 t of steel produces up to 25 kg of fine dust, depending on various factors. This dust contains up to 65% iron, in oxide form. Recycling of the waste formed in steel production costs half or a third as much as the preparation of ore concentrates. For the recycling of converter sludge, methods of conditioning wet wastes by isothermal sorptional dehydration and subsequent thermochemical sintering have been developed. The adsorbent used in the present work is the solid residue from lignite pyrolysis: fine-grain lignite semicoke produced by a pilot plant at the Berezovskii-1 mine. The lignite-semicoke samples produced have a highly developed pore structure and correspondingly are characterized by excellent sorptional and energy properties. The granulometric composition of lignite semicoke is practically the same as that of the sludge. At the same time, the density of the lignite-semicoke particles is 2.5 times less than that of the sludge particles, even when the pores of the semicoke are completely filled with adsorbed moisture. On mixing the lignite semicoke and converter sludge, the semicoke absorbs moisture. The resulting mixture is highly friable, whereas the moisture adsorbed in the pores passes to the bound state and becomes an active participant in redox processes. As a result of the experiments, new material containing up to 39% Femet and 49% C is obtained. On that basis, an effective technology may be developed for the utilization of converter sludge to produce ferrocoke that may be employed as a fuel and reducing agent in blast furnaces and smelters. The proposed technology does not require complex mechanical and thermal dehydration and briquetting with binder.