Modeling of Strip Heating Process in Vertical Continuous Annealing Furnace

 The mechanism for heat transfer of radiation is usually adopted to heat strip in vertical continuous annealing furnace. The rate of heat transfer among strip and other objects can be hugely affected by the parameters of strip speed, geometry factors and radiating characteristic of surfaces of strip, radiating tubes and walls of furnace. A model including all parameters is proposed for calculating the heat transfer coefficient, predicting the strip temperature and boundary temperature of strip through analyzing these parameters. The boundary temperature is a important datum and different from average arithmetic value of temperature of strip and temperature in furnace. Also, the model can be used to analyze the relation for temperature of strip and heat transfer coefficient, total heat transfer quantity and heating time. The model is built by using the radiating heat transfer rate, the Newton′s law of cooling, and lumped system analysis. The results of calculation are compared to the data from production line. The comparisons indicate that the model can well predict the heating process. The model is already applied for process control in production line. Also, this research will provide a new method for analyzing the radiation heat transfer.     

CSP辊底加热炉供煤气量随坯厚、坯温变化规律的模拟研究

研究了CSP辊底加热炉内的传热过程及其规律.采用数值模拟的方法,在进行合理简化后,建立总能量平衡基础上的炉内热过程数学模型,其中辐射传递方程的求解采用离散坐标法.自主开发了该炉型的通用热过程模拟软件,采集包钢CSP薄板坯连铸连轧厂的生产数据进行验证计算,计算所得钢坯温度与实际温度的相对误差小于1%,表明该模型假设合理,建模正确;该软件能够应用于该类型加热炉的设计、管理和研究等领域,为确定CSP生产线高拉速(提高入炉坯温)、多钢种的生产工艺参数创造了条件.     

Numerical determination of heat transfer coefficient for boiling phenomenon at runout table of hot strip mill

Abstract

The heat transfer coefficient during film boiling at the runout table of the hot strip mill is usually determined by experimental methods. Described in the present paper is a finite difference based model for analysis of the thermal behaviour of the strip during cooling at the runout table of the hot strip mill at Tata Steel, India. The model, developed for the prediction of strip temperature, is used to determine the heat transfer coefficient at the water/strip interface while water cooling occurs. A simple form of polynomial as a function of the strip surface temperature is proposed to describe the heat transfer coefficient at the water/strip interface. Good correlation has been found between model predicted temperatures considering the polynomial type heat transfer coefficient and the actual coiling temperature.     

Analysis of Strip Temperature in Hot Rolling Process by Finite Element Method

 The program was developed by finite element method to calculate the temperature distribution in hot strip rolling. The heat transfer coefficient of air cooling, water cooling and thermal resistance between work roll and strip were analyzed. A new heat generate rate model was proposed according to the influence of source current density, work frequency, air gap and distance to edge on induction heating by finite element method (FEM). The heat generate rate was considered into the thermal analysis to predict the temperature distribution in the induction heating. The influence of induction heating on the strip temperature was investigated with different strip thicknesses. The temperature difference became more and more obvious with the increase of thickness. The strip could be heated quickly by the induction heating both in surface and center because of the thermal conductivity and skin effect. The heat loss of radiation has important influence on the surface temperature. The surface temperature could be heated quickly with high frequency when the strip is thicker.     

大型光亮退火马弗炉加热段温度场模拟

建立了大型光亮退火马弗炉加热段温度场的三维仿真模型.该模型考虑了马弗炉实际结构、带钢退火速度和升温曲线特点,采用等效热流密度表征马弗管内保护气体和带钢的换热;选择组分传输燃烧模型、离散坐标辐射模型和标准k-ε双方程湍流模型描述马弗炉内燃烧、换热和气体流动;应用SIMPLE计算方法进行求解.典型规格304不锈钢带光亮退火过程实测特征点温度值和模拟结果基本吻合.分析得到了马弗炉内温度场、流场和速度场分布规律.结果表明:马弗管温度比较均匀,喷嘴正对区域温度偏高;燃气气流沿马弗管壁螺旋流动实现均匀加热.喷吹量较小时,喷吹量(入口速度)越大,马弗炉内温度越高;喷吹量继续增大,马弗炉内温度反而开始降低.      

Mathematical model of metallurgical thermal processes and application

There are lots of physical changes and chemical reactions in the processes of iron and steel making, these processes are quite complex in the aspect of heat transfer.The processes of iron and steel making can be approximately divided into three kinds.The first kinds are the processes of fusion metallurgy which involve enormous chemical reactions,such as blast furnace,converter,electric furnace and coke oven.The second kinds are the processes of heating and cooling which are mainly the physical changes,such as walking-beam reheating furnace,annular heating furnace and car-type furnace.The third kinds are the processes of heat treatment which mainly adjust metallurgical structure of metal,such as roller hearth heat treatment furnace, strip continuous heat treatment vertical/horizontal furnace and HPH bell-type annealing furnace.Every process can only be finished in particular thermal equipment.And all the physical and chemical processes mentioned above must obey first principles of engineering thermodynamics,heat & mass transfer,hydromechanics, combustion,metallurgy physical chemistry etc,and which can be summarized as principle of heat transfer,mass transfer,momentum transfer and chemistry reaction.In this paper,based on first principle of heat and mass transfer in iron and steel making processes,a series of mathematical models of thermal equipments and processes are presented.Such as the model of hot-blast stoves,coke oven,CDQ-boiler system,sintering, reheating furnace,soaking furnace,annular heating furnace,roller hearth heat treatment furnace,strip continuous heat treatment vertical/horizontal furnace,HPH bell-type annealing furnace,control cooling of medium plate,burner,heat exchanger and regenerative burner etc.The on-line application of the model is based on experimental certification of the mathematical model.And finally the computer optimization system of metallurgical thermal process is obtained.     

Modeling of Strip Temperature in Rapid Cooling Section of Vertical Continuous Annealing Furnace

 The strip temperature is affected by many factors in rapid cooling section (RCS) of the vertical continuous annealing furnace (VCAF). They can be divided into four types: the physical properties of cooling gas, the geometry characteristics of configuration of cooling equipment, the heat transfer between the strip and the cooling gas, and the conductivity of the strip. It aims to model the strip temperature in the cooling section based on the fundamental heat transfer theory and the four aspects factors. The model for transient Nusselt number is obtained by considering Reynolds number, Prandtl number and geometry characteristics of RCS. Then cooling model of the strip transient temperature is built by Nusselt number, heat transfer coefficient and heat conductivity of the strip. The results are compared with the data from production line. The comparisons indicate that the model can well predict cooling temperature of the strip. It is hoped that the proposed model can be used for design and control of the vertical continuous annealing furnace.     

立式炉内转向辊传热过程数学模型

应用粗糙表面间接触换热数学模型,建立了带钢连续热处理立式炉内转向辊辊室传热过程数学模型,综合考虑了接触换热、对流换热、辐射换热等换热方式.对转向辊辊室传热的仿真分析表明:转向辊辊面温度变化层的厚度不超过10mm,同时在带钢连续热处理立式炉中,可以忽略转向辊传热对带钢温度的影响.     

Study on strip running deviation at exit of heat section in continuous annealing furnace for cold rolling

In order to solve strip reciprocating and quick- moving running deviation at the exit of heat section for vertical continuous annealing furnace, the thermal crown of furnace roller was analyzed quantitatively and regression method was used to determine the impact of roller crown on strip running deviation. And then the alarm program for strip running deviation was established, which can give early warning of strip running deviation and adjust the model parameter and the heating and cooling temperature rate simultaneously. With the application of this system on a continuous annealing machine for cold rolling in Shougang Jingtang Company, the strip running deviation which caused by thermal crown of furnace roller can be solved.     

Sustainability–steel and the environment

Abstract

A two-dimensional heat and fluid flow model was used to simulate the plasma arc furnace, where the flow is governed by the steady state incompressible Navier–Stokes equations. The flow has been taken as turbulent and the standard k-epsilon model was used to simulate the turbulence in the flow. The coupled non-linear differential equations were solved with suitable boundary conditions and temperature dependent plasma properties at atmospheric pressure by employing an efficient finite volume method. The calculations and heat transfer to various parts of the furnace were calculated for argon, nitrogen and hydrogen plasmas. The voltage–current characteristic for the different types of plasma and the effect of other process parameters on heat transfer are discussed.     

薄板坯连铸连轧辊底加热炉内传热过程的数学模型

研究了包头钢铁(集团)公司薄板坯连铸连轧厂辊底加热炉内的传热过程,在辐射平衡态的条件下建立了炉内辐射与板坯、炉衬固体壁相耦合求解的炉内热过程数学模型,其中辐射传递方程的求解采用离散坐标法.采用控制体积法对数学模型进行离散,自主开发了辊底加热炉型的通用热过程模拟软件,经计算得到炉气、板坯温度沿炉长的分布,炉子出口处板坯温度与生产实测值的最大误差小于10%.该软件对理论研究和生产实践具有一定的指导意义.     

不锈钢带钢卧式连续热处理炉内传热过程数学模型

建立了带钢在卧式连续热处理炉内传热过程的数学模型,并通过TDMA方法求解得到了相同炉温制度下不同带钢厚度、宽度和速度对带钢温度分布的影响。计算出了特定工况下的极限带宽、带速和带厚,同时对不同炉温制度下带钢在全炉的温度分布进行了预测和分析。所得结论对带钢卧式连续热处理炉计算机优化控制具有重要的指导意义。     

Modelling recalescence after stock reduction during hot strip rolling

Abstract

The relationships between stock recalescence time/distance and process variables, such as exit thickness, reduction, rolling speed, work roll diameter and slab–roll heat transfer coefficient during hot strip rolling, have been established. The behaviour of the temperature gradient was analysed and used to estimate the slab and transfer bar mean temperatures from measured surface temperature in three hot strip mills located in northeast México. It was found that the recalescence critical variables, in order of importance in minimising temperature measurement variation, are slab–roll heat transfer coefficient, reduction, exit thickness and roll speed.     

辊底式连续热处理炉数模优化控制仿真系统

以某公司辊底式连续热处理炉为研究对象，在详细分析其传热机理的基础上，建立了钢坯在炉内加热过程数学模型，针对炉型紧凑，加热中厚板，有最小极限辊速限制等特点，开发了基于加热过程数学模型及连续、摆动运行加热控制策略的仿真系统。验证表明，该系统能有效地模拟钢板在炉内加热升温的全过程。可以对炉辊速度和炉区温度进行寻优计算，为在线控制提供辊速及炉温制度最佳数据。     

带钢镀锌退火炉热过程模拟

以三元模型法为基础,建立了带钢在立式炉内退火全过程的数学模型;模拟计算了带钢和退火炉的温度场;讨论了操作参数对带钢加热的影响以及冷却气体初始温度和喷射速度对带钢冷却过程的影响。其模拟的带钢加热曲线与工艺要求相吻合,为带钢温度的预测和合理的炉温决策创造了有利条件。     

Development of laboratory scale thin strip caster and investigation of direct casting of AISI 304 stainless steel

Abstract

An unequal diameter (1 : 3), two roll thin strip casting machine has been designed and fabricated for investigation of the direct casting of thin strip on a laboratory scale. The system consists of a preheatable shallow tundish with online heating facility, water cooled rotating rolls (chill and auxiliary) for solidification of the liquid metal, and a stripper assembly. The machine has a variable speed. Roll gap setting and roll pressure adjustment are two important features of the machine. It is also possible to vary the placement angle of the auxiliary roll with respect to the chill roll. A heat transfer model was developed, based on experimental casting results. Experiments were conducted using AISI 304 grade stainless steel. Up to 100 kg of steel was cast without interruption into strips of widths 100 and 200 mm and thickness varying between 1 and 2 mm. Some of the process parameters affecting the quality of the strip were identified.     

连续退火机组（CAPL）加热室板温动态模型

根据冷轧厂连续退火机组（ＣＡＰＬ）加热室的实际运行数据，应用系统辨识方法，建立了一个简单、有效、并适用于将来控制系统设计的线性模型。该模型的建立得到了理论和实践的检验。     

Application of the porous medium combustion technology in the chamber reheating furnaces at Baosteel

The design of the porous medium combustion ( PMC) system which has been applied to chamber reheating furnaces is presented in this study and its main application effects are described in detail. Porous medium materials are mainly ceramic ball sucked granular bed porous media and foam ceramic porous media. This study investigates the foam ceramic porous medium and a schematic diagram of the combustion inside this porous medium. The PMC takes a solid medium as its main heat exchange way,thus greatly improving the heat transfer efficiency. Judging from the application effects,the following conclusions have been made: the PMC technology can save more than 25% of energy with remarkable effects; the furnace temperature uniformity can be significantly enhanced; the porous media combustion technology can make the heating furnace design in a more compact way,reduce the time for heating up the furnace, improve the heating rate and reduce energy consumption.     

Numerical analysis of fluid flow and heat transfer in pool of twin roll strip caster

Abstract

Twin roll strip casting is regarded as a prospective technology offering many economic benefits. The control of fluid flow in the pool is, however, particularly difficult due to the high casting speed and small pool volume. In the present study, a three-dimensional mathematical model has been developed for the coupled analysis of fluid flow, heat transfer and solidification in the pool using the finite difference method. The characteristics of transport phenomena in the pool of a twin roll strip caster using a wedge type melt delivery system were analysed by numerical simulation. The results show that it is desirable for the wedge melt delivery system to provide the uniformity of flow and temperature in the pool to maintain the casting process and improve the strip quality.     

Heat transfer analysis of blast furnace cast steel cooling stave

Abstract

Cast steel blast furnace (BF) cooling staves are widely used in the Chinese steel industry. A heat transfer mathematical model of a BF cast steel cooling stave has been developed and verified by thermal state experiments. Calculation of a cooling stave working under steady state has been carried out based on the model. Effects of two factors, thickness of scale on the cooling water pipes and gas clearance between the pipes and main body, which are difficult for experimental measurement but determined mathematically, on the temperature field of the stave body are discussed. The results indicate that much importance should be attached to the two factors during manufacturing of cooling staves as they highly influence cooling capability of cooling stave and hence BF operation.