采用辐射管加热的辊底式热处理炉数值仿真及其分析

以某公司拟建的采用辐射管加热的辊底式热处理炉为研究对象,在详细分析其传热机理的基础上,建立了炉内钢坯加热过程的二维传热数学模型.采用交替隐式格式的TDMA数值计算方法,开发出了采用辐射管加热的辊底式热处理炉钢坯加热过程二维传热模型计算机数值仿真系统,并进行了大量的数值仿真计算.所得结论为该公司即将开展的辊底式热处理炉模型优化控制奠定了坚实的理论基础.     

Investigation of the slab heating characteristics in a reheating furnace with the formation and growth of scale on the slab surface

In this work, the development of a mathematical heat transfer model for a walking-beam type reheating furnace is described and preliminary model predictions are presented. The model can predict the heat flux distribution within the furnace and the temperature distribution in the slab throughout the reheating furnace process by considering the heat exchange between the slab and its surroundings, including the radiant heat transfer among the slabs, the skids, the hot combustion gases and the furnace wall as well as the gas convection heat transfer in the furnace. In addition, present model is designed to be able to predict the formation and growth of the scale layer on the slab in order to investigate its effect on the slab heating. A comparison is made between the predictions of the present model and the data from an in situ measurement in the furnace, and a reasonable agreement is found. The results of the present simulation show that the effect of the scale layer on the slab heating is considerable.     

Radiative slab heating analysis for various fuel gas compositions in an axial-fired reheating furnace

A transient radiative slab heating analysis was performed to investigate the effect of various fuel mixtures on the performance of an axial-fired reheating furnace. The various fuel mixtures tested were assumed to be attained by mixing COG (coke oven gas) and BFG (blast furnace gas), which are the two main byproduct gases found in the integrated steel mill industry. The numerical prediction of radiative heat transfer was calculated using an FVM radiation solving method, which is a well-known and efficient method for curvilinear coordinates. The WSGGM (weighted sum of gray gas model) was also adopted to calculate the radiative heat transfer in composition dependent media. The entire furnace was divided into fourteen sub-zones to calculate the radiative thermal characteristics of the furnace without flow field calculations. Each sub-zone was assumed to have homogeneous media and wall temperatures. All of the medium and wall temperatures were computed by calculating the overall heat balance using some relevant assumptions. The overall heat balance was satisfied when the net heat input equaled the three sources of heat loss in each sub-zone, wall loss, skid loss, and slab heating loss.     

蓄热式连续加热炉内流动与换热特性的数值模拟

以某公司大方坯蓄热式连续加热炉为研究对象,对该炉建立了三维物理数学模型,分别采用可实现双方程湍流模型,PDF非预混燃烧模型、离散坐标法辐射模型(DO模型),应用Fluent数值仿真软件进行了模拟研究,得到了蓄热式连续加热炉内的流场和温度场的分布规律,并对炉内对流换热系数的分布进行了详细的分析研究.结果表明:钢坯表面局部对流换热系数在各加热段内分布不均匀,这主要是由于烧嘴进口射流所引起的局部流速的差异性,从整体上来看,预热段和加热1段的对流换热系数要高于其它各段.     

Fracture prediction of electromagnetic silicon steel in reheating furnace

This article proposes the use of strain energy density (SED) for the prediction of fracturing in silicon steel slabs undergoing reheating in a furnace. Reheating is commonly used to soften steel before hot rolling into ultra-thin silicon steel sheets referred to as electromagnetic steel. High heating rates are required to reduce the time spent in the reheating furnace to increase the efficiency of producing ultra-thin electromagnetic steel sheets and decrease fuel consumption. However, an excessive increase in heating rates may induce fracturing due to the comparatively brittle nature of the silicon used in electromagnetic steel slabs to enhance the electromagnetic properties. In this study, the authors used finite element numerical calculation to elucidate the fracture mechanism of electromagnetic steel slabs undergoing heating. The authors then used SED as a criterion by which to optimize the heating rates without inducing fracturing in electromagnetic steel. The proposed model could be used as a guide to shorten the time required for heating various types of steel in reheating furnaces.     

Efficiency analysis of radiative slab heating in a walking-beam-type reheating furnace

The thermal efficiency of a reheating furnace was predicted by considering radiative heat transfer to the slabs and the furnace wall. The entire furnace was divided into fourteen sub-zones, and each sub-zone was assumed to be homogeneous in temperature distribution with one medium temperature and wall temperature, which were computed on the basis of the overall heat balance for all of the sub-zones. The thermal energy inflow, thermal energy outflow, heat generation by fuel combustion, heat loss by the skid system, and heat loss by radiation through the boundary of each sub-zone were considered to give the two temperatures of each sub-zone. The radiative heat transfer was solved by the FVM radiation method, and a blocked-off procedure was applied to the treatment of the slabs. The temperature field of a slab was calculated by solving the transient heat conduction equation with the boundary condition of impinging radiation heat flux from the hot combustion gas and furnace wall. Additionally, the slab heating characteristics and thermal behavior of the furnace were analyzed for various fuel feed conditions.     

步进式加热炉内热工过程的数值模拟

建立步进式加热炉内流动、燃烧和传热的数学模型.炉内流场的模拟采用κ-ε双方程模型,辐射换热计算采用P-1辐射模型,气相燃烧采用Species Transport模型,流场计算采用Simpler算法.采用上述模型与算法得到了炉内详细合理的温度、速度和浓度分布,并对其中影响板坯加热的温度场进行了试验验证.     

THREE-DIMENSIONAL ANALYSIS OF THE WALKING-BEAM-TYPE SLAB REHEATING FURNACE IN HOT STRIP MILLS

Three-dimensional analysis is performed for the turbulent reactive flow and radiative heat transfer in the walking-beam-type slab reheating furnace by FLUENT. A simplified burner is validated against the results of the actual burner with the detailed grid resolution to avoid an excessive number of grids. The predicted temperature distribution in the furnace and global energy flow fractions are in reasonable agreement with available data. Distribution of the heat flux to the slabs, velocity vectors, and all major scalar variables in the furnace also are predicted. This study shows that three-dimensional analysis may be a useful tool to understand quantitatively the complicated combustion and heat transfer characteristics in the furnace.     

体心立方球床高温气冷堆流动及传热数值模拟

在规则球床模块式高温气冷堆中,氦气在规则燃料球之间流动,并对燃料球进行冷却。将燃料球分为发热区和石墨包壳,考虑了燃料球内部热传导。以三个规则燃料球为一组,对氦气在燃料球中的流动与传热进行数值模拟,获得氦气在燃料球孔隙间的流场,以及燃料球与氦气的温度分布;并将燃料球出口边界的流动和传热参数传递给下一组燃料球入口边界,以实现大规模规则燃料球模块化高温气冷堆的数值模拟,预测燃料球与氦气的升温速率和压降率。     

A heat transfer model for the analysis of transient heating of the slab in a direct-fired walking beam type reheating furnace

A mathematical heat transfer model for the prediction of heat flux on the slab surface and temperature distribution in the slab has been developed by considering the thermal radiation in the furnace chamber and transient heat conduction governing equations in the slab, respectively. The furnace is modeled as radiating medium with spatially varying temperature and constant absorption coefficient. The steel slabs are moved on the next fixed beam by the walking beam after being heated up through the non-firing, charging, preheating, heating, and soaking zones in the furnace. Radiative heat flux calculated from the radiative heat exchange within the furnace modeled using the FVM by considering the effect of furnace wall, slab, and combustion gases is introduced as the boundary condition of the transient conduction equation of the slab. Heat transfer characteristics and temperature behavior of the slab is investigated by changing such parameters as absorption coefficient and emissivity of the slab. Comparison with the experimental work show that the present heat transfer model works well for the prediction of thermal behavior of the slab in the reheating furnace.     

混合煤气成分变化对加热炉内温度场影响的数值模拟研究

以燃用高炉、焦炉混合煤气的实验加热炉为研究对象,建立炉内二维稳态传热、流动及燃烧的数学模型,研究混合煤气成分变化对加热炉内温度场的影响,计算结果显示高炉煤气含量在一定范围内增加时,炉内温度水平和钢坯加热区温度均匀性逐渐降低.这些与华凌涟钢集团轧钢加热炉的实际情况基本一致.     

板坯加热炉内加热特性的数值分析

以某公司热轧厂常规与双蓄热烧嘴组合供热的板坯加热炉为研究对象,建立该加热炉炉内流动、传热、燃烧和板坯运动吸热过程的三维物理数学模型,运用CFD仿真技术对其进行详细的数值计算,得到炉内稳态的速度场和温度场分布规律、板坯的升温曲线以及板坯温度分布均匀性,计算结果与"黑匣子"实验测量数据吻合良好。本文给出的板坯加热特性计算方法为研究加热炉新工艺、优化板坯加热温度制度提供了科学依据。     

Online simulation model of the slab-reheating process in a pusher-type furnace

This paper presents an online simulation model of the slab-reheating process in a pusher-type furnace in Acroni d.o.o. in Slovenia. The simulation model is connected to the information system of a hot-processing plant that provides online measuring and charging data of the furnace. The simulation model considers the exact geometry of the furnace enclosure, including the geometry of the slabs inside the furnace. A view-factor matrix of the furnace enclosure was determined using the Monte Carlo method. The heat exchange between the furnace gas, the furnace wall and the slab’s surface is calculated using a three-temperature model. The heat conduction in the slabs is calculated using the 3D finite-difference method. The model was validated using measurements from trailing thermocouples positioned in the test slabs during the reheating process in the furnace.A graphical user interface (GUI) was developed to ensure a user-friendly presentation of the simulation-model results.     

提高炼油厂加热炉热效率的方法

加热炉的能耗问题是炼油厂中非常关键的问题。文章全面系统地介绍了提高加热炉热效率的方法：降低过剩空气系数；预热燃烧用空气和燃料气；利用对流室增加吸收热量；设计高效燃烧器；设置有效的吹灰器；减小加热炉漏风量；以及使用高温辐射涂层等。并且提出了提高加热炉热效率的新方法，即采用计算流体动力学(CFD)方法对加热炉内所发生的各过程进行数值模拟，在此基础上进行数值实验，最终确定最有效的提高加热炉热效率的方法。     

A numerical analysis of slab heating characteristics in a walking beam type reheating furnace

Numerical analysis of slab heating characteristics in a reheating furnace has been accomplished using FLUENT, a commercial software. The phenomena in the furnace are periodically transient because the slabs are transported toward a rolling mill with every time interval controlled. Unsteady calculation has been performed to obtain a periodically transient solution. A User-Defined Function (UDF) program has been developed to process the movement of slabs because FLUENT cannot handle the movement using its default functions. When the mean temperature of a slab emitted to the rolling mill does not change, calculation is considered to have converged and is stopped. This convergence criterion is appropriate for achieving an analytical solution. With the boundary and initial conditions given, over 55 new slabs are inserted to get a converged solution. Skid posts and beams are included in the calculation because they disturb radiation heat transfer from hot combustion gas to the slabs. This article examines what the slabs experience in the furnace before they are emitted to the rolling mill and whether a slab emitted to the rolling mill satisfies the required slab conditions, such as target temperature and skid severity.     

连续式轧钢加热炉在线控制数学模型与应用

以理论计算和实测数据为依据,开发了连续式加热炉最佳炉温设定和在线控制数学模型,并应用于安钢中型厂5点供热推钢式加热炉。结果表明：在轧机产量波动时,不但加热炉供热合理,而且钢温波动小、加热质量好、节能效果显著。     

超临界碳氢燃料流动换热的仿真研究

建立了适用于温度、压力大范围变化的超临界碳氢燃料换热特性研究的一维模型,试验验证了模型的可靠性,基于该模型分析了质量流率、换热状态转换和压力等因素对超临界碳氢燃料的换热特性的影响。结果表明:4.0 MPa的低压力工况下,在超临界碳氢燃料的拟临界温度附近存在传热强化现象,而7.0 MPa的高压力工况下,该传热强化现象消失;不论质量流率的大小,4.0 MPa工况下的传热系数始终高于7.0 MPa工况下的传热系数,压力的高低在超临界碳氢燃料的汽相换热区对传热性能的影响更为显著;40kg/(m2.s)的低质量流率条件下,由液相换热区向汽相换热区的换热状态转换将导致转换区附近的传热恶化,而增大质量流率则可避免该问题的发生。     

板坯加热炉内常规燃烧与富氧燃烧数值计算对比分析

以某公司热轧厂板坯加热炉为研究对象,建立该加热炉内流动、传热、燃烧和板坯运动吸热过程的三维物理数学模型,运用CFD仿真技术对其进行详细的数值计算,重点对比分析了常规燃烧和富氧燃烧特性,得到了各自的炉内速度场和温度场分布规律、板坯的升温曲线以及板坯温度分布均匀性,计算结果与“黑匣子”实验测量数据吻合良好.总结出的富氧燃烧...     

Performance analysis of a SOFC button cell using a CFD model

In this study, a 2-D numerical model is investigated to predict and evaluate the performance of an anode-supported SOFC button cell. The flow field is calculated using 2D Navier–Stokes equations. Heat and mass transfer equations are solved to calculate species and temperature distribution in the cell body and in fuel and air channels. The electrical and electrochemical processes are simulated coupled with the heat and mass transfer model. A discretized network circuit is adopted to the cell geometry for considering the ohmic losses and joule heating of the current that passes through the cell body. The model predicts the cell output voltage, the local EMF and the state variables pressure, temperature and species concentrations. The local electrical parameters are calculated based on the local pressure, temperature and concentration of the species. The numerical results are compared with the experimental data and good agreement is observed. The simulation is carried out for different input fuel flow rates and humidification. The results show how the input fuel mass flow rate and humidification level affects the button cell SOFC performance. In addition, influences of the anode thickness on cell performance through the ohmic over potential are investigated.     

Transient radiative heating characteristics of slabs in a walking beam type reheating furnace

Transient radiative heating characteristics of slabs in a walking beam type reheating furnace is predicted by the finite-volume method (FVM) for radiation. The FVM can calculate the radiative intensity absorbed and emitted by hot gas as well as emitted by the wall with curvilinear geometry. The non-gray weighted sum of gray gas model (WSGGM) which is more realistic than the gray gas model is used for better accurate prediction of gas radiation. The block-off procedure is applied to the treatment of the slabs inside which intensity has no meaning. Entire domain is divided into eight sub-zones to specify temperature distribution, and each sub-zone has different temperatures and the same species composition. Temperature field of a slab is acquired by solving the transient 3D heat conduction equation. Incident radiation flux into a slab is used for the boundary condition of the heat conduction equation governing the slab temperature. The movement of the slabs is taken into account and calculation is performed during the residence time of a slab in the furnace. The slab heating characteristics is also investigated for the various slab residence times. Main interest of this study is the transient variation of the average temperature and temperature non-uniformity of the slabs.