Zeyi Jiang

Numerical simulation of the direct reduction of pellets in a rotary hearth furnace for zinc-containing metallurgical dust treatment

A mathematical model was established to describe the direct reduction of pellets in a rotary hearth furnace (RHF). In the model, heat transfer, mass transfer, and gas-solid chemical reactions were taken into account. The behaviors of iron metallization and dezincification were analyzed by the numerical method, which was validated by experimental data of the direct reduction of pellets in a Si-Mo furnace. The simulation results show that if the production targets of iron metallization and dezincification are up to 80% and 90%, respectively, the furnace temperature for high-temperature sections must be set higher than 1300°C. Moreover, an undersupply of secondary air by 20% will lead to a decline in iron metallization rate of discharged pellets by 10% and a decrease in dezincing rate by 13%. In addition, if the residence time of pellets in the furnace is over 20 min, its further extension will hardly lead to an obvious increase in production indexes under the same furnace temperature curve.

Modeling of Thermochemical Behavior in an Industrial-Scale Rotary Hearth Furnace for Metallurgical Dust Recycling

Metallurgical dusts can be recycled through direct reduction in rotary hearth furnaces (RHFs) via addition into carbon-based composite pellets. While iron in the dust is recycled, several heavy and alkali metal elements harmful for blast furnace operation, including Zn, Pb, K, and Na, can also be separated and then recycled. However, there is a lack of understanding on thermochemical behavior related to direct reduction in an industrial-scale RHF, especially removal behavior of Zn, Pb, K, and Na, leading to technical issues in industrial practice. In this work, an integrated model of the direct reduction process in an industrial-scale RHF is described. The integrated model includes three mathematical submodels and one physical model, specifically, a three-dimensional (3-D) CFD model of gas flow and heat transfer in an RHF chamber, a one-dimensional (1-D) CFD model of direct reduction inside a pellet, an energy/mass equilibrium model, and a reduction physical experiment using a Si-Mo furnace. The model is validated by comparing the simulation results with measurements in terms of furnace temperature, furnace pressure, and pellet indexes. The model is then used for describing in-furnace phenomena and pellet behavior in terms of heat transfer, direct reduction, and removal of a range of heavy and alkali metal elements under industrial-scale RHF conditions. The results show that the furnace temperature in the preheating section should be kept at a higher level in an industrial-scale RHF compared with that in a pilot-scale RHF. The removal rates of heavy and alkali metal elements inside the composite pellet are all faster than iron metallization, specifically in the order of Pb, Zn, K, and Na.

The Introduction and Process Optimization Research of Oxygen Blast Furnace Ironmaking Technology

In order to reduce the energy consumption from iron and steel industry, decreasing coke rate by establishing oxygen blast furnace (OBF) ironmaking process is a favorable way. In recent years, many scholars and metallurgical workers from all over the world have made a lot of related work about this ironmaking process. The main content in this paper is as follows: The necessity, process characteristics and optimization research of OBF were introduced. The optimal OBF process were elected by the calculation of energy-mass balance mathematical model. In order to cope with the subsequent industrial test, theoretical calculation of the improved process is carried out. The process parameters under different oxygen enrichment rate 9, 19, 29%, and eventually reached 100% are calculated. Calculation results show that with the increase of oxygen enrichment rate, the recycling gas volume from both shaft tuyere and hearth tuyere were increased, the coke rate gradually is reduced and the coal rate increased gradually. After adopting the OBF ironmaking process the ironmaking costs and CO2 emissions can be greatly reduced.

Three-Dimensional Mathematical Model of Multiphase Combustion in Full Oxygen Blast Furnace

The complicated combustion of pulverized coal, free coke and cycle gas in the raceway of full oxygen blast furnace (FOBF) is different from the process in a traditional blast furnace. The differences of free nitrogen, cycle gas mixture, increased coal rate and decreased blast temperature contribute to the complexity of reductive conditions with temperature and composition. A three-dimensional CFD model considering the processes in the regions of raceway, blowpipe, deadman and dropping-zone is developed to describe the kinetic, thermal and chemical behaviors of the fuel combustion. The qualitative and quantitative analysis is conducted to evaluate the effects of operating conditions including temperature of cycle gas, injecting rate and particle diameter of pulverized coal. Simulation results show that large amount of pulverized coal injection (PCI) and also cycle gas injection is feasible with the high oxygen concentration for oxygen blast furnace. The coal injecting rate is a sensitive parameter for the combustion effect in raceway and corresponding measures must be considered for the enhancement of PCI. FOBF process could construct stronger reductive atmosphere than traditional blast furnace, which is beneficial to improve the productivity.Copyright

Numerical Simulation and Structure Optimization of Converter Gas Evaporative Cooler

In Lurgi-Thyssen dedusting system of steelmaking converter, the evaporative cooler represents a crucial operating unit, in which the hot dust-laden flue gas has to be cooled by saturation with water. The cooling process of the gas consists of gas-liquid two phase flow and interphase heat and mass transfer. In this paper, k-epsilon standard equations and Lagrange discrete phase model are employed to describe the gas turbulent flow and the heat/mass transfer with droplet evaporation individually. The computational fluid dynamics (CFD) simulation for practical engineering project shows that the large-flux cooling gas is commonly constructed in a non-uniform flow caused by the sharp turnings at the inlet and outlet channels. The unevenness of velocity distribution and the effective cooling height are defined in this paper to evaluate the cooling flow process. A series of newly designed structures with guide plate are investigated by CFD method to eliminate the problems with the non-uniformity. The results of numerical simulation show that optimal designed guide ring plate could improve the flow uniformity and the heat transfer. The investigations have been used to guide the engineering application.Copyright

Numerical Simulation of Burden Descending Behavior in Oxygen Blast Furnace

In consideration of the environmental degradation and global scarcity of coking coal resource, substituting coke with coal and improving the gas utilization are the developing trends of ironmaking technology. Oxygen blast furnace, an ironmaking technology with top gas recycling, is most likely to be used in large-scale industrial manufacture considering its advantages of high productivity, high pulverized coal injection rate, low coke rate, high top gas calorific value, etc. The purpose of this paper is to make a little contribution to this technology on burden descending behavior in the metallurgical process. The results would provide reference for the design and operation of oxygen blast furnace. In the complex metallurgical processes with countercurrent multi-phase reactions, solid material motion plays important roles in the process since it determines the path and the residence time of the solid reactants as well as the stress distribution. The continuum model is often employed in the kinetic process analysis for its simplicity and low computational load. In this study, a viscous flow model based on the Navier-Stokes equation was developed to investigate the behavior of solid flow in oxygen blast furnace. A three dimensional experimental apparatus was constructed to observe burden descending behavior. According to concerned experimental results, it show that the interaction between the burden and the wall is not significant in shaft zone of the furnace. The descending burden maintains initial pattern until it reaches the lower part where the size of the cross section starts to reduce and the strong friction appears obviously in the tracked materials. Consequently, slip boundary condition with the Fanning equation was used for computations to describe the friction between solid flow and the wall or the dead zone. In addition, the position and the gas flow rate of the upper tuyeres were investigated. It was demonstrated that if the upper tuyeres are higher than the top of the belly, the position will strongly influence the solid flow distribution. Thus, gas velocity must be limited in a proper range to keep the solid flow falling down smoothly. By analysis of various solid viscosities, it is shown that solid flow patterns are not sensitive to solid viscosity within certain range.Copyright

Mathematical Model and Optimum Control of Rotary Hearth Furnace for Pellet Direct Reduction

A mathematical model of direct reduction in carbon-based pellet and a subsectional model of energy/mass equilibrium for rotary hearth furnace are established. Heat transfer, mass transfer and chemical reactions for pellet reduction are simultaneously analyzed by numerical method. Based on the models, an optimum control system with functions of process simulation and optimum control is developed. The model-based optimum control can improve the automatic control level of the furnace by ensuring the quality of metalized pellets and minimizing the fuel consumption.