回转窑传热模型与数值模拟

对回转窑内传热过程进行了分析 ,在已有研究基础上归纳了各项换热系数的关联式 ,尤其结合热渗透模型完善了回转壁面与料床之间传热机制的研究 ,并提出通用的计算关联式。进而提出了内热式炉型的一维轴向传热模型 ,并根据已发表的试验数据验证了该模型和各换热系数的适用性。计算表明在窑内低温段 ,物料的受热主要来自其覆盖的回转壁面对其加热 ;而在高温段 ,气体的辐射热量成为加热料床的主要热源。此外 ,由物料进口端沿轴向窑壁散热增大 ,在窑内高温段窑壁的散热甚至高于物料吸热量 ,因此在回转反应器的设计中应充分考虑窑壁散热造成的热效率降低并采取相应措施。     

Oxygen enrichment in rotary lime kilns

The operation of a pilot-scale rotary lime kiln, fired with natural gas, was studied to determine the effects of enriching the combustion air with oxygen. The variables of interest were the temperature, calcination and heat flow patterns within the kiln as functions of the fuel rate, oxgyen concentration and limestone feed rate. All tests were conducted with essentially a stoichiometric fuel/oxygen ratio and employed two different limestones. Data are presented to show the increase in kiln throughput that can be achieved using oxygen enrichment. The results are interpreted using detailed measurements of axial solids, gas and wall temperatures and axial calcination profiles. These permit the evaluation of the driving forces for the various heat exchange processes, and of local heat flow to the solids bed.     

Numerical simulation of the transient temperature distribution inside moving particles

This work is devoted to the two‐dimensional (2D) numerical simulation of heat and fluid flow by granular mixing in a horizontally rotating kiln. The heat and fluid flow in the gas phase are solved directly using a fixed Eulerian grid. At the same time, the particle dynamics and their collisions are solved on a Lagrangian grid. The no‐slip boundary condition on the particle surface is implemented using the fictitious boundary method. The heat transfer inside the particles is calculated utilising two models: the first is the direct solution of the energy conservation equation in Lagrangian and Eulerian space and the second is the so‐called linear model, which assumes a homogeneous distribution of the temperature inside each particle. Numerical simulations showed that if the thermal diffusivity of the gas phase significantly exceeds the same parameter of the particles, the linear model over‐predicts the heating rate of the particles. The analysis of the time‐averaged flow field inside the kiln showed that in the gas phase a double vortex structure is formed which increases the convective heat transfer in the upper part of the particulate bed. The influence of the particle size, the angular velocity of the drum and the fluid on the heating rates of particles is studied and discussed.     

回转窑内滚动状态下颗粒横向运动的影响因素的实验研究

回转窑内物料颗粒的横向运动使物料的传热和传质得到加强,其研究对于回转窑的优化设计和运行是十分重要的。本文在数学模型的基础上采用数码摄像的方法对多种物料颗粒在旋转筒体内的横向运动进行了实验研究,考察了筒体直径、旋转速度、料床内物料的动态休止角等参数对于泻落层厚度、颗粒运动速度、流量以及物料在料床表面停留时间的影响,并通过实验验证了数学模型。     

城市垃圾在回转窑内传输过程的模型和优化

基于物料在回转窑内传输过程是由其在表面层内滚落运动和固定层内回转运动组成的这一特征 ,从散体运动的机理出发继承和发展了回转窑单颗粒轨道模型 ,并首次采用统计平均分析和受力矢量分析研究了窑内颗粒的运动轨迹 ,从而得出了平均停留时间 (MRT)和体积流率 (MVF)的简化模型 ,结合试验采取修正系数ε_t 和ε_f 完善了模型对非均质物料 (如城市垃圾 )、内构件等工况的适用性 ,同时对本文模型和几种已有的计算模型进行了比较研究 ,最后提出了回转窑热解反应器的设计和运行的优化模型 .     

Rotary Cement Kiln Simulator (RoCKS): Integrated modeling of pre-heater, calciner, kiln and clinker cooler

This paper presents an integrated reaction engineering based mathematical model for clinker formation in cement industry. Separate models for pre-heater, calciner, rotary kiln and cooler were initially developed and coupled together to build an integrated simulator. Appropriate models for simulating gas-solid contact and heat transfer in pre-heaters were developed. Calciner was modeled by considering simultaneous combustion of coal particles and calcination of raw meal. Complex heat transfer and reactions (solid-solid, gas-solid and homogeneous reactions in gas phase) in rotary kiln were modeled using three sub-models coupled to each other. Solid-solid reactions in the bed region of the kiln were modeled using pseudo-homogeneous approximation. Melting of solids in the bed and formation of coating within the kiln were accounted. Clinker cooler was simulated by developing a two-dimensional model to capture cross-flow heat transfer between air and hot clinkers. The individual models were coupled with each other via mass and energy communication through common boundaries. The coupled model equations were solved iteratively. The model predictions agree well with the observations and experience from cement industry. The model was used to gain better understanding of influence of operating conditions on energy consumption in cement plant. Several ways for reducing energy consumption were computationally investigated. The integrated model, the developed software RoCKS (for Rotary Cement Kiln Simulator) and results presented here will be useful for enhancing our understanding and for enhancing the performance of clinker manufacturing.     

回转窑煅烧烧结石灰的探索

在采用回转窑煅烧烧结石灰的过程中,在破碎、运输等环节经常出现堵料问题。对两种石灰石矿和石灰进行了深入的分析,采用适宜的石灰石来煅烧烧结石灰解决了堵料问题,对采用回转窑煅烧烧结石灰具有指导意义。     

石灰窑技术及发展方向

简述了活性石灰的新技术、影响石灰石煅烧质量的因素、窑控制技术及故障排除方法,以及石灰粉料的应用,指出了石灰行业面临的大好形势和发展特点。     

Rotary cement kiln coating estimator: Integrated modelling of kiln with shell temperature measurement

Coating thickness protection in the burning zone of a rotary cement kiln during operation is important from the viewpoint of the kiln productivity. In this paper, an integrated model is presented to estimate the coating thickness in the burning zone of a rotary cement kiln by using measured process variables and scanned shell temperature. The model can simulate the variations of the system, thus the impact of different process variables and environmental conditions on the coating thickness can be analysed. The presented steady‐state model derived from heat and mass balance equations uses a plug flame model for simulation of gas and/or fuel oil burning. Moreover, the heat transfer value from shell to the outside is improved by a quasi‐dynamic method. Therefore, at first, the model predicts the inside temperature profile along the kiln, then by considering two resistant nodes between temperatures of the inside and outside, the latter measured by shell scanner, it estimates the formed coating thickness in the burning zone. The estimation of the model was studied for three measured data sets taken from a modern commercial cement kiln. The results confirm that the average absolute error for estimating the coating thickness for the cases 1, 2, and 3 are 3.26, 2.82, and 2.21 cm, respectively.     

ON FLOW-INDUCED KINETIC DIFFUSION AND ROTARY KILN BED BURDEN HEAT TRANSPORT

The cross-section of a partially-filled cylindrical kiln rotating on its horizontal axis and processing granular solids produces a shear zone (active layer) at the free surface which grows with the kiln's rotational rate. The active layer, although relatively thin, compared with the rest of the bed burden, drives all physical/chemical reactions. This is because of the high rate of surface renewal which, in turn, promotes heat exchange between the exposed surface and the higher temperature freeboard gas. Unlike packed beds, particulate diffusion induced by the flow of granules, adds a significant component to the overall heat transfer in the bed. Problem formulation and modeling of heat conduction using flow fields derived from experiments suggest that at slow kiln speeds the diffusion effect may not be recognized due to long term duration of particle contacts and hence packed-bed heat conduction models may provide adequate characterization. However, at moderate and high kiln speeds particle collisions are short-termed and kinetic diffusion contributes to the effective thermal conductivity by as much as tenfold thereby resulting in well-mixed conditions and a homogeneous bed temperature. Industrial processing ramifications such as kiln speed control and product quality are discussed hereafter.     

回转窑煅烧活性石灰的工艺

结合生产和实验等有关资料,对回转窑煅烧活性石灰的生产工艺进行了深人研究,分析了煅烧温度、保温时间、助燃风量以及窑体转速等对石灰活性度的影响,并对回转窑煅烧优质活性石灰的生产工艺提出几点看法。     

梭式窑对流换热的模拟研究

在梭式窑空气动力模型上，采用不同规模的烽嘴，研究了烧嘴的流量与喷速对窑内对流换热的影响。提出了换热不均匀度的定义式，推导了入窑气体温度与换热不均匀度的关系，得到了梭式窑对流换热关系式。     

石油焦煅烧回转窑综合传热过程数值模拟

研究了石油焦煅烧回转窑内的物理和化学反应过程对回转窑内传热过程的影响,并在对回转窑内的物料输送过程、传质过程和传热过程具体分析的基础上,建立了石油焦煅烧回转窑的综合传热数学模型. 应用数值计算方法对传热数学模型进行计算求解,预测了窑内气体、物料和窑壁内外表面的轴向温度分布. 结果表明,窑内的高温区域主要集中在挥发分大量燃烧的区段上,三次风的注入会引起窑内气相温度的明显下降,但不会造成料床温度的明显变化;在物料与气体、窑内壁之间热交换过程中,物料与被覆盖的窑内壁表面之间的对流换热和气体与料床表面间的辐射换热为主要的传热机制. 计算预测的结果与测量数据在规律上和数值上都能较好地符合,从而为石油焦煅烧回转窑的优化设计和经济运行提供了指导和依据.     

套筒石灰窑余热尾气利用方法探索

废气余热在石灰窑的生产工艺过程中由于受到技术的限制,一直无法做到回收利用,是一项重要的热能损失,是造成石灰窑热耗高的重要因素之一,怎样做到将此热能回收再利用是决定煅烧行业能否低碳、高效的运行,本文重点对此部分热能的回收再利用方式进行了探索,并对套筒窑尾气余热烘干炭材进行了介绍。     

邢钢套筒窑冶金石灰煅烧试验浅析

邢钢现有1座石灰套筒窑,日产能力500t,其中冶金石灰约450t供炼钢使用,粉灰约50t供烧结使用。为了验证套筒窑冶金石灰CaO含量的控制指标,对冶金石灰进行了煅烧试验。试验发现:将冶金石灰CaO含量控制在88%~89%,无论是从节能降耗方面,还是从炼钢化渣效果方面都是可行的。     

A Model for Residence Time Distribution of Solids in a Rotary Kiln

A five‐parameter model for residence time distribution of low‐density particles in a bed of high‐density particles in a rotary kiln is derived based on combinations of flow regimes in several sub‐regions. The parameters of the model are the number of turnover stages, the cascade volume fraction, the Peclet number, the dead volume fraction in cascade region, and the cross‐flow ratio. The effect of feed rate of solids, rotational speed and inclination of the kiln on the model parameters is evaluated.     

国产小型回转窑煅烧活性石灰的经济价值

介绍用于以煤粉为燃料,煅烧活性石灰的国产小型回转窑之特点,及其与引进的多枪喷粉竖窑的比较