Abstract: Disclosed is a method for steel making which includes charging a direct reduction reactor (DRR) with iron ore from a charging system. The iron ore is reduced to hot direct reduced iron (DRI) in the DRR and discharged to rotary kiln(s). The rotary kiln(s) does not process the DRI, but transports the hot DRI to one or more electric arc furnaces (EAF). Top gas (i.e., spent reducing gas) is drawn off of a top section of the DRR. A portion of the top gas is used to pressurize the rotary kiln to prevent air from entering the rotary kiln. Another portion of the top gas flows to a pressure swing adsorber or a vacuum pressure swing adsorber (PSA/VPSA) for CO2 and H2O removal. A cool reducing gas exits the PSA/VPSA. A plasma torch burns natural gas and oxygen to form a hot reducing gas. The hot reducing gas is mixed with the cool reducing gas to form a final reducing gas. The final reducing gas is delivered to the DRR. Also disclosed is a mini-mill to perform the method of steel making.

Abstract: A method of controlling a reheat furnace to deliver pieces at an aim discharge temperature comprises the steps of determining the ratio between calculated reheat furnace discharge temperatures and measured temperatures of pieces in a rolling mill receiving the output of the reheat furnace, filtering this ratio based upon time in the rolling mill to provide the current filtered relationship between calculated discharge temperatures and said measured temperatures to provide filtered ratios, comparing desired temperatures in the rolling mill with said measured temperatures of pieces in the rolling mill to establish error values, filtering the error values based upon time in the mill to provide filtered error values, and processing the filtered error values and the filtered ratios to establish a short-term bias to the aim extract temperature.

Abstract: A rotary hearth furnace includes a base having a plurality of first plenums, an upper chamber having a plurality of second plenums and a hearth rotatable between the base and the upper chamber and having a plurality of third plenums. The hearth is moveable between the base and the upper chamber so that two or more of the third plenums are positionable to receive gas exhausted by one of the first plenums and to discharge the received gas into one of the second plenums.

Abstract: A rotary hearth furnace has a mixing rabble arrangement that includes a first rabble disposed upstream a flow of material on the hearth and a second rabble disposed downstream a flow of material on the hearth. The first and second rabbles are disposed at an acute angle with respect to a center of rotation of the hearth in a manner so that a plane defined by a plow of the first rabble intersects a plane defined by a plow of the second rabble adjacent the leading edge or training edge of the plow of the second rabble. The rabbles cooperate to produce a counter-rolling action in the material as the material is advanced into contact with the rabbles by movement of the hearth relative to the rabbles.