The tunnel furnace raises the slab’s temperature to the rolling point and offers storage capacity. Acting as a “buffer” during the casting, heating, and rolling sequence. The tunnel furnace setup comprises a steel enclosure lined with refractory materials, featuring burners positioned along the sidewalls. The furnace is structured using a modular design, with removable roof sections. Allowing convenient top access for maintenance within the furnace. To traverse the furnace, cast slabs are upheld and moved via individually powered in-furnace rolls.
Analytical models play a crucial role in the design of tunnel furnaces. Custom-tailoring them to meet the specific operational and process needs of each client. This objective is achieved through the use of four analytical models:
(1) Transient Heat Transfer Models
(2) Dynamic Simulation Models
(3) Heat Balance Models
(4) Flow Distribution Models
Transient Heat Transfer Models
Utilizing one-dimensional finite-difference models for transient heat transfer. Calculations are performed to determine both the temperature along the length of the slab at the point of discharge. And the uniformity of temperature across the thickness of the slab. Notably, tunnel furnaces exhibit significant disparities in heating times between the leading. And trailing edges of the slabs being heated, unlike traditional reheat furnaces. This variation arises from a slower casting speed, typically around 5 meters per minute, and a faster takeaway speed at the rolling mill. Typically around 15 meters per minute. These conditions result in the slab’s head undergoing an additional 10 to 20 minutes of heating compared to the slab’s tail.
Dynamic Simulation Models
In terms of operational readiness, the furnace must possess the capability to manage unexpected disruptions and delays in the rolling mill process. The gauge of a furnace’s capacity to accommodate such occurrences is referred to as the Caster Abort Buffer or CAB. This metric quantifies the duration during which operators can continue casting at the current rate. Before the furnace reaches its maximum capacity for additional steel slabs. CAB significantly influences furnace design and is contingent upon factors. Such as caster speed, mill takeaway speed, slab length, and transfer point.
Heat Balance Models
A heat balance model for a furnace system considers the interplay between process heating iterations and furnace dynamics to accurately size the combustion system components, including burners, recuperators, and exhaust stacks. This model accounts for losses such as heat dissipated to the steel and the overall system, including refractory materials and water-cooled in-furnace rolls.
Furthermore, it presents another challenge: determining the flow patterns of combustion waste gases responsible for distributing heat throughout the furnace. In a conventional reheat furnace, gas flows counter to the steel’s movement, flowing from the discharge end to the charge end and exiting through the uptake or downtime. However, in a tunnel furnace spanning over 200 meters with multiple flues, gas flows are no longer unidirectional.
Flow Distribution Models
These models are created to scrutinize the flow behaviors within the tunnel furnace configuration. Computational Fluid Dynamics (CFD) techniques are applied in the gas flow model to precisely ascertain the flow paths throughout the furnace’s length. This flow model allows for the strategic selection of flue positions to enhance the distribution of furnace pressure, consequently reducing air infiltration and the potential for hot gas stingout.
A Glass Melters is specifically engineered to transform raw materials into glass. Depending on their intended applications, a variety of designs for glass melters exist. These furnaces are powered by different energy sources, primarily relying on either fossil fuels or fully electric power. Some may even utilize a combination of both energy sources. Typically, a glass melter is constructed using refractory materials.
Tunnel furnaces serve a critical role in the steel industry providing temperature control and storage capacity during the production process. Their design is a complex task, involving analytical models like transient heat transfer models, dynamic simulation models, heat balance models, and flow distribution models to optimize their performance. These models ensure efficient heating, operational readiness, and heat balance in the furnace system. Additionally, tunnel furnaces offer unique challenges due to their elongated structure.
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