The international steel market has recently seen an upturn in both price and demand for steel following last year’s downturn in Japan and S.E. Asia. Leading steel companies have cut costs and improved operating efficiency to maintain margins and CFD is being used extensively to achieve these goals. Fluent’s CFD codes are being used around the world to:

• Troubleshoot plant problems,
• Design and analyze processes, and
• Address environmental, safety, and regulatory issues.

Eliminating Thermal Stratification in Steel Ladles

During the post-tap holding period for liquid steel as it awaits further processing, the hot metal undergoes thermal stratification due to natural convection currents. Thermal stratification is detrimental to the quality of steel castings. It is also known to be linked to tap temperature, holding time, ladle preheating, and ladle life. To counter its effect, argon gas is bubbled into the bath of steel to help generate enough bath turbulence to produce thermal homogeneity. This argon stirring also enhances mixing rates for chemical additions. FLUENT has been used to optimize the argon nozzle position in ladles and the gas injection flow rates. Customization of the ladles in this manner is a very powerful application of CFD in the steel industry.

Velocity field during bottom purging of argon

Tundish Grade Change Simulation

A tundish is a liquid steel refractory lined tank used in continuous casting processes as an operational buffer. In many plants, it has a second important function, which is to cast different grades of steel sequentially through the same caster. The tundish allows for a change of ladles upstream and thus, a change of grade, but unfortunately, there is an unavoidable mixing of two different grades of steel in the vessel. This produces intermixed cast grades of steel that are hard to classify. Hence, keeping the intermixed volume of steel to a minimum is a plant target. FLUENT has been used to estimate the grade change-over time for a particular tundish. To do this, the flow distribution in the tundish is simulated. The flow field plays a critical role in the casting process in terms of productivity and economics. Therefore, CFD is used extensively to design and optimize tundish internals (weirs, dams, and baffles). It is then possible to study the effects of various parameters and practices and, thereby, optimize the steel process line for the minimum amount of intermixed steel grade.

Concentration contours in a continuous casting tundish during a grade change operation

Walking Beam Reheating Furnace Modeling

A walking beam furnace is used in steelworks to reheat billets of steel from room temperature to “red heat”, enabling the reheated billet to be subsequently rolled. Gas burners above and below the charge raise the temperature of the billets as they are slowly moved across the furnace over a period of hours. The goal of the furnace is to reheat the steel billets uniformly at minimum cost and maximum efficiency.

Danieli Centro Combustion S.p.A. in Italy and engineers from Fluent Italia carried out a simulation of a walking beam reheating furnace to provide information on:

• Overall furnace characteristics,
• Burner characteristics,
• Steel billet reheating profiles,
• The effect of supports on the billets, and
• Pollutant formation.

Contours of temperature in a steel reheating furnace with a full charge of billets

The goal of the CFD study using FLUENT was to improve the furnace performance, to provide savings of fuel and material costs, and to lead to a greater understanding of what is going on in the furnace. The analysis provided valuable information on burner flame shapes, flame lengths, and flame temperatures, as well as data on flame-flame and flame-wall interactions. Time dependent calculations were also carried out to describe the internal temperature profile of the steel billets, and in particular, to look at anomalies due to the insulated supports over which the beams are moved.

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