Reduction of Fuel Utilization Through Oxygen-Enriched Combustion in a Reheat Furnace Pusher-Type

Steelmaking is an energy-intensive process. Thus, energy efficiency is highly important. Several stages of steelmaking involve combustion processes. One of the most energy-consuming processes in steelmaking is the slab reheating process in a reheat furnace (RF). The energy released by fuel combustion is used to heat steel slabs to their proper hot-rolling temperature. The steel slabs move through the reheat furnace passing the three stages of heating called: Preheating Zone (PZ), Heating Zone (HZ), and Soaking Zone (SZ) to finally leave the discharge door at a rolling temperature of 2375 °F. One way to improve a reheat furnace’s fuel consumption is by implementing oxygen-enriched combustion. This study investigates the implementation of oxygen-enriched combustion in a pusher-type reheat furnace. The increment of oxygen in the combustion process allows for increasing the furnace gas temperature. Consequently, the oxygen enrichment approach allows for the reduction of fuel injection. The principal goal of this investigation is to model the combustion-based on oxygen-enrichment and develop parametric studies of fuel injection rates. The different simulations aim to match the slab heat flux profile of the industrial reheat furnace pusher-type. Computational fluid dynamics are used to generate the slab heat flux distribution. To reach more uniform slab heating, oxygen and fuel ports were alternated. Also, injection angles were modified to optimize slab heating and avoid the impact of hot spots. Thermocouple readings of the industrial reheat furnace are compared to simulation results. The results determined that 40–45% fuel reduction can be achieved.

Numerical Analysis of Thermal Stress Development of Steel Slabs in a Pusher-Type Reheat Furnace

During the steelmaking and hot rolling processes, various defects and cracks appear throughout the steel product. These cracks may initiate and grow throughout the hot rolling process and result in a lower quality of the product than is acceptable. The most energy-intensive part of the hot rolling process is the reheating furnace, where slabs are heated up to a target rolling temperature largely through radiant heat transfer. In the reheat furnace, large stresses may develop due to the thermal gradients within the steel product. A thermal-stress analysis is proposed based on finite element method (FEM) to study the impacts of charging temperature, slab velocity, and heating rate on stress development as the steel slab travels through an industrial pusher-type reheat furnace. Furnace zone information is taken from a previously validated computational fluid dynamics (CFD) model and applied as thermal boundaries and constraints within the thermal-stress FEM models. Temperature and stress results were taken at the core, top, bottom, top quarter, and the bottom quarter of the steel slab at different residence times. Moreover, temperature lines and contour plots taken along the length of the slab allow visualization of the gradual development of temperature and identification of the locations corresponding to temperature variations as the slabs move in the furnace. The slab temperature predicted by the FEM model was found valid when compared with industrial data. Stress predictions found similar trends with previously published works as well as evidence of thermal shock in the sub-surface near the beginning of the residence time.

Modelica model of industrial gas furnaces

Modelica models for the prediction of the temperature of the load inside a walking basket type reheat furnace of the aluminium industry have been developed. The loads move through the furnace with discrete movements. Several library components have been developed using the Modelica Standard Fluid Library. In order to validate them a full 1D furnace simulation model has been built. It allows calculating the heat transfer through walls, the temperature and the composition of combustion gases, the temperature of the aluminium products, as well as the fumes flow and the pressure drops. The library provides the necessary resources for modelling this type of furnaces flexibly and quickly. The objective of the work is to validate Modelica as analyse tool for evaluating the different possibilities of heat recovery in this kind on furnaces.

Reheat Furnace Thermodynamic, Kinetic and Combustion Considerations for TMCP Processing

The reheat furnace process step has a profound effect on the TMCP performance, final hot rolled steel quality and mechanical property consistency during the production of hot rolled steels. The uniformity of heating applied across the entire width and length of the slab or billet is critical in the achievement of customer properties regardless of the chemistry. The resultant ferrite grain size in the final hot rolled product is significantly governed by the initial prior austenite grain size. Numerous reheat furnace process metallurgy and combustion parameters in actual operation affect mill productivity, microstructure, austenite grain size, scrap rate and diverts. This reheating step in the steelmaking process often receives low priority in the evaluation of product quality and mechanical property performance, especially the toughness through the plate thickness. Heat transfer conditions of radiation, convection and conduction affect furnace heating efficiency. In laboratory studies, the furnace heating step is typically quite uniform resulting in a homogeneous and fine prior austenite grain size. During production, it is much more difficult to control the uniformity of heating and heat transfer consistency along the entire length and through the thickness of the work piece. The furnace conditions are correlated to product quality via furnace process variables such as the air to gas ratio, furnace burner condition, furnace pressure, energy efficiency, adiabatic flame temperature (AFT) and furnace refractory condition. Operational practice recommendations are presented to minimize inhomogeneous heating which results in inferior product quality, hot rolling model anomalies and toughness variations in the through-thickness-direction.