Abstract
The refractory preheating process in oxygen furnaces is a dynamic input of energy in a chemically complex system requiring special attention to chemical emissions relative to permissible release limits. This particular industrial and regulatory interest is the emission of volatile organic compounds (VOC), given their detrimental impacts on human health. In the present work, a mathematical model was developed to predict the emission rates of volatile organics during the preheating of a 260-ton basic oxygen furnace. A numerical heat transfer model was developed using finite difference techniques to obtain the thermal profile and then integrated with chemical thermodynamics using FactSage 7.0 (CRCT, Polytechnique Montreal Quebec Canada, H3C 3A7). The parameters that affected VOC emissions were preheating process times, burner gas composition, heating rate, and burner geometry. Two different preheating procedures were compared, and emission rates were predicted with extended use of a top burner providing the greatest degree of emissions control. The mathematical model was validated against plant data with respect to average emission rates of CO, CO2, SOX, and NOX.
Highlights
The Klockner Oxygen Blown Maxhutte (KOBM) process is a modern steelmaking technique that involves the oxidative refining of hot metal to liquid steel
With the heat transfer model used to obtain the temperature distribution through the refractory wall and steel shell of the KOBM vessel throughout the various preheating procedures, the emission rate for volatile organic compounds (VOC) and sulfur compounds can be inferred from that temperature distribution via chemical thermodynamics
The mathematical model underpredicts the emission rates of CO2 and NOX. This can be attributed to the fact that a homogeneous composition of VOCs was assumed inside the brick
Summary
The Klockner Oxygen Blown Maxhutte (KOBM) process is a modern steelmaking technique that involves the oxidative refining of hot metal to liquid steel. The first procedure reflects current field practices with the second procedure designed to assess the effects of a slower preheating rate on minimizing thermal shock as well as the capability of a assess the effects of a slower preheating rate on minimizing thermal shock as well as the capability top-burner to combust released VOCs and sulfur compounds prior to emission from the furnace. Fuel and oxygen injections are separated, and mix together ‘locally’ with inert gasses before they react, which produces lower maximum flame temperatures with lower NOX emissions and uniform temperature distributions [18] This particular combustion system improves ladle/basic oxygen furnace (BOF) preheating performance by reducing the average fuel consumption by 50–60% [19,20]. Indirect preheating for ladle/BOF by utilizing a radiative heat source can be achieved by using porous burner technology, where combustion takes place in a porous high temperature ceramic instead of an open flame.
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