Numerical Study On Slab Reheating Process Optimization In A Walking Beam Reheating Furnace

Under the carbon neutral and carbon peak,the iron and steel industry as one of the largest energy-consuming industries,is an important breakthrough to achieving the goal of reducing emissions and consumption.Industrial reheating furnaces（IRFs）are essential reheating equipment in the process of steel production.The reheating process contains complex physical and chemical processes and is influenced by many factors,among which the slab reheating rate,temperature distribution and energy efficient improvement techniques have been the hot spots of research.However,most of the reported are based on the laboratory-scale,and few studies have been reported for the large-scale IRFs due to the complex geometries and operating conditions.Therefore,in this work,a mathematical model of an IRF under an actual operating condition is constructed to simulate the reheating process of slabs and the optimization of energy-saving in IRFs.Firstly,based on the geometry and operating parameters of the actual reheating furnace,a three-dimensional computational fluid dynamics（CFD）model is built and developed to predict the reheating process of the slab and the temperature distribution gradient inside the furnace.The 28-step reaction mechanism is used to predict the combustion flame by comparing different reaction mechanisms of oxy-fuel combustion.The results show that oxy-fuel combustion obtains higher flame temperature but reduces fuel usage,the average temperature inside the furnace increases and radiation is enhanced,the slab discharge temperature increases by 8%and the reheating furnace efficiency increases by 6.25%.Secondly,the effect of fuel supply and oxygen excess coefficient on the slab reheating process under oxy-fuel combustion is investigated.The results show that under the same residence time,the fuel supply has an obvious effect on the slab discharge temperature,the slab discharge temperature is positively correlated with the fuel supply.Although the oxygen excess coefficient can change the position of the combustion flame front,it has no significant effect on the overall flame morphology.It is also found that production efficiency can be improved by increasing the slab movement speed in the preheating zone during the actual production process.Finally,the effect of the natural gas（NG）/H₂ fuel mixture on the combustion flame as well as the thermal behavior in the reheating furnace is investigated.The results show that the flame temperature of the fuel increases with the increase of H₂,the maximum flame temperature increases by 3.4%,the combustion efficiency increases by 5.27%,and the flame high-temperature zone gradually divided into three obvious partitions with the increase of H₂.The high-temperature gas inside the furnace increases,the NO_x as well as CO₂ of the exit flue gas reduces significantly,and H₂O is the main component,which is more friendly to the environment.Compared with air combustion,the radiation intensity of oxy-fuel combustion is enhanced by about 60.87%,but hydrogen has almost no effect on the radiation.