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.     

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.     

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.     

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.     

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.     

清除加热炉灰垢提高炉效

由于原油的深加工，作为加热炉主要燃料的渣油质量越来越差，加热炉炉管结灰、结垢现象十分严重。分析灰垢组分，针对金陵石化公司烷基苯厂加热炉结垢状况，选用合适的清灰剂，改变清灰方式，在不停炉的情况下清除加热炉辐射段炉管灰垢，不仅确保了加热炉的安全运行，提高炉效，也创造了经济效益。     

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.     

火焰加热炉与加热缺陷

本文简要介绍了法国工业炉的状况及加热缺陷研究的最新成果。通过模型实验和模拟计算掌握了炉内的流场，这样就可通过一些简单、易行，但有效的措施改善钢坯的出炉热状态。     

利用层流炉研究玉米秸秆粉末的快速热解特性

为了研究闪速加热条件下生物质的热解挥发特性，设计了等离子体加热高温层流炉作为实验设备。由于该设备内部的流动特性对于实验结果影响巨大，为此特别设计了一套1：1比例的透明有机玻璃冷态模拟装置，用于观察层流炉的流动状态，为热态实验参数设计提供实践指导。根据冷态研究观察结果，进行了层流炉热态实验。采用灰分示踪法测定了玉米秸秆粉末在800，850，900，950K的热解失重曲线。通过数据处理得到了玉米秸秆粉末在快速加热条件下的热解动力学方程和参数。     

Control characteristics and heating performance analysis of automatic thermostatic valves for radiant slab heating system in residential apartments

Computer simulations and experiments are carried out to research the control characteristics and heating performances for a radiant slab heating system with automatic thermostatic valves in residential apartments. An electrical equivalent R–C circuit is applied to analyze the unsteady heat transfer in the house. In addition, the radiant heat transfer between slabs, ceilings and walls in the room is evaluated by enclosure analysis method. Results of heating performance and control characteristics were determined from control methods such as automatic thermostatic valves, room air temperature-sensing method, water-temperature-sensing method, proportional control method, and On–Off control method.     

Mineral scale formation and mitigation on metals and a polymeric heat exchanger surface

An experimental set-up was built to study heat transfer fouling of different pipe materials used in heat exchangers. Fouling mitigation investigations using wood pulp fibres in suspension in the fouling liquid were also performed. The new set-up allows progressive visual observation of fouling with time together with a recorded history under the same solution conditions. On completion, the tube under investigation could be removed to obtain quantitative data on the progressive build up of the deposit as well as the composition of the deposit.The experimental technique involved a pipe test specimen being centrally located in a cylindrical tank concentric with a vertical agitator to give constant and uniform flow conditions near the tube surface. The investigation of calcium sulphate deposition on four different metal surfaces (copper, aluminium, brass and stainless steel SS 316 respectively) and a polycarbonate surface reveals that the fouling increases with time but at a decreasing rate. The deposition on a metal surface can be seen to increase with increasing thermal conductivity and decreasing total surface energy over the range of experiments. Low surface energy material such as polycarbonate causes less attraction to the floating crystals and receives less deposition in comparison to the SS surface.Bleached Kraft softwood fibres at various concentrations were added to the solution to examine their effects on fouling. The results indicate that fouling is reduced as fibre concentration increases. It was also found that the fouling on stainless steel, brass and copper surfaces were all retarded in presence of fibre in the solution.     

高效长寿蓄热体的研究与开发应用

蓄热体作为蓄热室余热回收设备的核心材料,承担着冷热介质热量传递的任务,是蓄热式燃烧技术能否高效运作的关键。本文对蓄热体尺寸、形状、热工特性和材质进行了研究,并在分析韶钢蓄热式加热炉生产实践的基础上,寻找蓄热体寿命低的原因,实验高效长寿蓄热体材料,介绍了应用的经验与效果。     

悬垂水滴与悬浮气泡表面气体水合物形成特性对比

基于悬垂水滴和悬浮气泡表面形成气体水合物的可视化耐高压实验装置,分析探讨了反应压力、温度、水质等因素对水滴和气泡表面气体水合物成核和生长规律的影响.对已有的关于研究单个静止悬垂水滴和悬浮气泡表面气体水合物生长特性的实验现象及结果进行了对比分析,得出结论:温度和压力是影响表面水合物结晶与生长的重要因素;温度的降低或压力的升高均使水合反应速度加快.研究为发展喷雾法和鼓泡法这两种强化制备水合物的方式提供了有效的实验支撑.     

罐式炉烘炉系统研究

烘炉质量是影响炉衬使用寿命的重要因素之一,很多罐式炉以不定型材料为工作衬,本身不带有加热系统。针对罐式炉烘炉系统,介绍了烘炉时需要的不同种类的燃料临时供应方案和高低温烘炉系统的组成以及配套的测量和控制系统,分析了影响烘炉质量的主要因素,对此类炉型的烘烤有较强的指导意义。     

换热表面水垢形成机理与规律的实验研究

为了探索换热表面水垢的形成规律,为抗垢器的应用研究打基础,开展了人工配制高硬度水循环在换热面的结垢实验.实验中观察到澄清的溶液循环一段时间后开始变混浊,几乎同时加热铜管内表面也开始形成水垢.经过多次实验,加上采用钙离子络合滴定监测溶液的钙离子浓度变化,最终确定了溶液变混浊的真正原因,同时也确定了实验系统铜管内表面形成的水垢为微粒垢.实验中借助高分辨率数码相机对溶液从澄清到混浊整个过程进行拍照观察,发现其中蕴含的一些规律.澄清了一直关于实验系统铜管内水垢是何种类型的模糊看法.通过实验,使得对结垢的认识更进一步,这为接下来的抗垢实验打下坚实的基础.     

CO2 capture from reheating furnace based on the sensible heat of continuous casting slabs

Carbon capture and storage adopted by power plants has been extensively studied in recent years. However, little attention has been paid to carbon capture and storage for steel plants. After considering the differences between steel and power plants, a carbon capture system of reheating furnace flue gas is designed, based on the sensible heat of continuous casting slabs. As a result, a significant amount of waste heat resource from rolling mills can be effectively reused. By using Aspen Plus to optimize parameters of the capture system, such as regeneration pressure and reflux ratio, the regeneration energy consumption is obtained and the result is verified by comparing the data with that of other research. Under the constraint condition of 90% CO₂ capture rate, simulation results show that the purity of CO₂ obtained is 98.4%, and the annual CO₂ capture capacity is about 70 000 tons. Finally, main parameters of continuous casting slabs and the heat recovery boiler are calculated. The heat load of the steam supplied for the reboiler is 8.5 MW, indicating that this steam generation method matches the carbon capture system.     

Inverse boundary design of a radiant furnace with diffuse-spectral design surface

An optimization technique is applied to inverse design of radiative furnaces with diffuse-spectral surfaces. The variation of emissivity with respect to the wavelength is approximated by considering a set of spectral bands with constant emissivities and then the radiative transfer equation is solved by the net radiation method for each band. The conjugate gradient method is used for estimation of temperatures over reflector and heater surfaces. The sensitivity problem is approximated by differentiation of the radiative transfer equation with respect to the unknown variables. The performance of the present method is evaluated by comparing the results with the results obtained by considering a diffuse-gray design surface.     

Characteristics of phase formation in Angren deposit clays melted with a solar furnace

The effect different methods of thermoprocessing have on mullite formation in different clay materials is examined. It is shown that a concentrated radiant flux lowers the temperature of mullite crystallization by 100–150°C, while correlations between features of mullite formation and different admixtures go unchanged.     

Frost formation on a plate with different surface hydrophilicity

The objectives of this study are to develop frost maps for two different surfaces having two different hydrophilic characteristics and to find ambient conditions associated with the formation of frost structures. Test samples with two different surfaces having dynamic contact angle (DCA) of 23° and 88° were installed in a wind tunnel and exposed to a humid airflow. Frost structure is observed with a visualization system in the operating conditions of household refrigerator: airflow temperature in the range of +10-20 °C, humidity in the range of 2.64-9.36 g/kg^′, Reynolds number in the range of 7000-17,000 and cold plate temperature in the range of −11.6 to −28.4 °C. As results of this study, frost structures are classified and frost maps are proposed for two different surface hydrophilicities. Surface with low DCA (23°) shows lower frost thickness and higher frost density than that with high DCA (88°). It was found that frost structures on surfaces with different DCA are similar. However, low DCA surface at low humidity provides 20-30% denser frost formation due to the shift of areas with different structures.