Emissivity and oxidation evolution in reheating furnace environments

加热炉是塔塔钢铁欧洲热米尔斯厂的重要组成部分。再加热炉由气体燃烧器加热，目的是将钢板坯加热到其轧制温度，并在整个厚度上具有已知的温度分布。 加热炉主要依靠热辐射传递到板坯。由于钢容易氧化，板坯在其表面上生长氧化层。这对从炉子到板坯的热传递有两个主要影响：它改变了表面的发射率，从而改变了板坯从炉子吸收的功率。它在板的表面上引入了隔热层，这减缓了热扩散到板中。 简单的钢的氧化层厚度可以近似计算，但是发射率随时间和温度的演变以及其对氧化物厚度或氧化物表面拓扑结构的依赖性是未知的。 已知氧化皮的发射率受许多参数的影响，包括气氛的组成、钢的等级、温度、钢的表面状况和时间。其中一些参数在我们的控制范围内，例如加热炉中的气氛成分、温度循环或钢成分。 在这个项目中，我们想了解温度循环和最终炉内气氛如何影响氧化皮的表面状况，从而影响发射率。第一个工业目标是能够在炉模型中引入准确的发射率值作为时间和温度的函数，第二个目标是将该预测外推到不同的钢成分。如果时间允许，另一个目标是了解如何控制发射率以最大化发射率并提高炉效率。该项目的目标包括：开发和验证一种实验装置，可以测量氧化物鳞片的发射率作为温度和时间的函数。测量在代表再加热炉气氛的环境中加热的HSLA和低碳等级的发射率随温度和时间演变的函数。将发射率变化与氧化物层的变化联系起来，例如形态、结构或成分变化。制定工业模型中使用的发射率、时间、温度和钢成分之间的关系。如果时间允许，建议优化的熔炉参数，或板坯表面修改，以实现板坯的最大发射率。

Reheating furnaces are an essential part of Tata Steel Europe's hot mills. Reheating furnaces are heated by gas burners and aim to heat the steel slabs to their rolling temperature with a known temperature profile through the thickness. Reheating furnaces rely predominantly on heat being radiatively transferred to the slabs. Since steel is prone to oxidation, the slabs grow an oxide layer on their surface. This has two major effects for the heat transfer from the furnace to the slab: It changes the emissivity of the surface, and therefore the power the slab absorbs from the furnace. It introduces an insulating layer on the surface of the slab, which slows thermal diffusion into the slab. The oxide layer thickness can be approximately calculated for simple steels, however the evolution of emissivity with time and temperature as well as its dependency on the oxide thickness or topology of the oxide surface is unknown. The emissivity of oxide scales is known to be affected by a number of parameters, including the composition of the atmosphere, steel grade, temperature, steel surface condition and time. Some of these parameters are within our control, for example the composition of the atmosphere in the reheating furnace, the temperature cycle or the steel composition. In this project, we would like to understand how temperature cycle and eventually furnace atmosphere affects the surface condition of the oxide scale, and therefore the emissivity. The first industrial aim is to be able to introduce accurate emissivity values in the furnace model as a function of time and temperature, the second aim is to extrapolate this prediction to different steel compositions. An additional aim, if time permits, is to understand how to control the emissivity to maximise it and improve furnace efficiency. The objectives of the project include: Develop and validate an experimental setup that can measure the emissivity of oxide scales as a function of temperature and time. Measure emissivity as a function of temperature and evolution in time for HSLA and low carbon grades heated in an environment representative of a reheating furnace atmosphere. Relate emissivity changes to changes in the oxide layer, e.g. morphological, structural, or compositional changes. Formulate the relation emissivity, time, temperature, and steel composition to be used in the industrial model. Suggest, if time permits, the optimised furnace parameters, or slab surface modifications to achieve maximum emissivity on the slabs.