Numerical Simulation of Heat Transfer and Scale Formation in a Reheat Furnace

Abstract

In steel rolling mills, reheat furnaces are used to reheat slabs to high temperatures in a highly oxidizing environment; this results in the formation of iron oxide scale on the slab surface. Scale formation poses an ongoing material and economic loss to industry and should be minimized where feasible. The kinetics of scale growth are complex and still not fully understood. Previous studies that modeled scale formation with mathematical methods are limited to simple case studies. Here, computational fluid dynamics (CFD) is used to simulate slab reheat furnace operations and to investigate complicated physical phenomenon. This paper proposes a new numerical method to model scale growth under varying conditions/characteristics including temperature, gas atmosphere composition, and steel grade. This method uses a mixed linear‐parabolic equation to model both the initial surface reaction (and scale formation) and the subsequent solid‐state ion diffusion through the developed scale. This model can be used to predict the amount of scale that will form on a slab under certain conditions. Model predictions were found to be consistent with experimental data.

Steady-State Heat Flux Prediction to Slabs in a Walking Beam Furnace

“…The contact between the blocks and the slab results in skid marks, local cold spots on the surface that cause temperature non-uniformity inside the slab. The combined effect of the skids and the rider blocks on the heating of the bottom surface of the slab has been found to be quite substantial [14,3]. In literature the skids are often disregarded [10,[15][16][17] or the skid losses are implemented as a constant percentage of the total heat input [2,4,18] .…”

Multi-Mode Model Predictive Control Approach for Steel Billets Reheating Furnaces

“…Billets' discharge from the furnace can be performed through tailored discharge devices, e.g., kick-out pushers (see Figure 1). After their exit, billets transit on a rotating roller track toward a descaling device which reduces the amount of scale on the billet's surface, e.g., using water at high pressure (see Figure 1) [40,41].…”

Performance evaluation of a walking beam type reheating furnace based on energy and exergy analysis

“…The reaction products, also called oxidized scale, are one of the important factors which have a direct influence on the surface quality of the steel, and the oxidation damage rate is a major index for evaluating reheating furnace. The scale yields a material loss, and the amount of material loss is related to furnace operating conditions such as steel temperature, excess combustion air, and steel residence time in the furnace [21]. The oxidized layer which forms on the slab surface is generally made up of wustite (FeO), magnetite (Fe 3 O 4 ) and hematite (Fe 2 O 3 ) from inside to outside.…”

“…The oxidized layer which forms on the slab surface is generally made up of wustite (FeO), magnetite (Fe 3 O 4 ) and hematite (Fe 2 O 3 ) from inside to outside. When the furnace temperature is higher than 873 K, the percent compositions of the three oxides, wustite, magnetite, and hematite are about 96%，4% and 1%, respectively [21]. Therefore，for simplicity, the scale layer is assumed to be wustite.…”