Investigation into the Hot Briquetting of Fine‐Grained Residual Materials from Iron and Steel Production

Abstract

Hot briquetting tests with mixtures of direct reduced iron (DRI) pellets and residues of the Midrex direct reduction process are conducted on a hydraulic piston press with a closed die. The trials seek to test the feasibility of recycling these residues by introducing them directly into hot briquetted iron (HBI). The inclusion of residues is possible if a high pressure of 350 MPa and a high briquetting temperature of 800 °C are applied. It is ascertained that up to 20 wt% of the HBI can consist of residues and still meet the quality requirements for the safe transportation to the steel plant if the mixture contains sufficient HBI screened fines and HBI classifier dust. Under such conditions, the HBI briquettes have a compressive strength of >300 MPa, an abrasion resistance of >80%, and, most importantly, an apparent density of >5 g cm−3. It is further shown that the hot briquetting of Midrex residues is also possible without DRI pellets so that they can be reused as educt in the Midrex direct reduction process.

Use of Bentonite and Organic Binders in the Briquetting of Particulate Residues from the Midrex Process for Improving the Thermal Stability and Reducibility of the Briquettes

“…In the Midrex shaft, the moving bed of pellets is penetrated in a counter‐current mode by the reducing gas at temperatures of up to 1173 K. At the bottom exit of the Midrex process, the porous DRI is compacted to hot briquetted iron (HBI) to decrease its oxidation tendency when exposed to air and to prepare it for transportation to and further processing in steel plants electric arc furnace (EAF). [ 1 ] A sketch of the Midrex process with a roller press for hot briquetting and without an attached EAF and a detailed description is provided in Lohmeier et al [ 2 ]…”

“…We refer to all the iron‐containing material that does not leave the Midrex process as screened HBI as “residues.” Table 1 summarizes the chemical composition of the residues depending on where in the Midrex process they accrue. [ 2–5 ]…”

“…The residue is composed of about 40 wt% dried sludge, 30 wt% oxide screened fines, 15 wt% HBI screened fines, 5 wt% remet fines, 5 wt% HBI classifier fines, and 5 wt% process classifier fines. [ 2–4,6 ] Returning these ferrous residues to the Midrex process means improving plant efficiency. As the residual briquettes already contain metallic iron, less reduction gas is required and less oxygen has to be removed, which means that more DRI can be produced for the same input quantity.…”