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.     

Convective heat transfer in a rotary kiln

An experimental study of convective heat transfer from hot air to the solid charge and walls in a non-fired rotary kiln is reported. Ottawa sand was heated by passing it counter-current to a flow of preheated air in a 2.5 m × 0.19 m I.D. rotary kiln. Axial temperature profiles of gas, wall and solids were measured. Local and average convective heat transfer coefficients from gas to solids and from gas to wall were determined assuming plug flow of gas and solids. Solid feed rates to 1750 kg/m² h and air rates to 3300 kg/m² h were investigated at rotational speeds to 6 r/min, holdup ratios to 17% and gas temperatures from 350–590 K. The gas/solids convective coefficient was found to depend on the gas through-put and to a lesser extent on solids holdup and rotational speed. Over the range tested, the angle of kiln inclination, solids throughput and particle size showed no significant effect on heat transfer. Gas/wall coefficients were about a factor of ten below gas/solid coefficients. Heat transfer results are compared to the limited data available in the literature, and to commonly used equations. Correlations of the experimental data on gas/solids, and gas/wall coefficients are presented; data from the literature on the wall/solids heat transfer coefficient are summarized.     

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。     

Modelling the Rotary Lime Kiln

A three‐dimensional steady‐state model to predict the flow and heat transfer in a rotary lime kiln is presented. All important phenomena are considered for the pre‐heat and calcination zones including turbulent gas flow, buoyancy, all modes of heat transfer, evolution and combustion of species and granular bed motion with calcination reaction. The model is based on a global solution of three sub‐models for the hot flow, the bed and the rotating wall/refractories. Information exchange between the models results in a fully coupled 3‐D solution of a rotating lime kiln. The overall model is validated using UBC's pilot kiln trials (5.5 m laboratory kiln). Results for this case are presented and potential implications are discussed.     

Experimental Apparatus for Studying Heat Transfer in Externally Heated Rotary Kilns

Rotary kilns are widely used in several branches of the chemical industry. In order to control the temperature of the solid and the gas flowing through the kiln, it is important to understand the heat exchange phenomena that occur. The design and construction of a novel experimental device to study heat exchange in rotary kilns is described. The device, which comprises a rotary kiln equipped with an external electrical heating system, enables the study of the influence of various parameters such as the solid flow rate, the kiln inclination angle, the rotational speed, or the presence of lifters on heat exchange and in particular on the heat exchange coefficient between the solid and the wall. Preliminary experimental results concerning the influence of the solid flow rate and the rotational speed on the solid‐to‐wall heat exchange coefficient are presented.     

回转窑内传热及燃烧过程的数值模拟

运用流体模拟软件Fluent和Matlab分别对碳素煅烧回转窑内气体空间和物料料层内的传热过程进行了研究,预测了窑内烟气、窑内壁和料层的温度分布。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;二、三次冷空气的引入均会使窑内烟气温度明显下降,但对料层温度影响不显著。将窑外壁的计算结果与其实际测试结果进行了比较,两者吻合较好,说明该模拟方法的适用性,从而为碳素回转窑的优化设计和经济运行提供了指导和依据。     

Modelling low-temperature carbonisation of solid fuels in a heated rotary kiln for clean fuel production

A numerical simulation of the physico-chemical processes occurring inside a heated rotary kiln reactor, where coal, lignite or biomass are treated in vacuum for the production of clean solid fuel, has been performed with FLUENT6 Computational Fluid Dynamics (CFD) code. The model accounts for the rotation of the kiln walls and mixing blades, multiphase flow modelling of the solid (fuel) and gaseous (mixture of gases) phases, heat transfer between phases and the heated kiln walls and mass transfer due to chemical reaction between species of different (heterogeneous) phases. The objective is to contribute towards a reliable numerical methodology as a design tool with reference to the fuel feed properties (e.g. solids size, volatile, carbon and moisture content, feed rate) and process requirements (e.g. desired residence time). Kiln wall erosion is also assessed.     

A SIMPLE DYNAMIC MODEL FOR SOLID TRANSPORT IN ROTARY DRYERS

ABSTRACT

The solid particle movement in a rotary drum plays an important role in drying processes. The solid distribution in the drum affects the amount of contact surface between the solid and the gas. The retention time of solids influences the time particles can stay in contact with the gas in order to transfer heat and mass. Any heat and mass transfer model for a solid particle dryer must be able to predict solid flowrate and solid hold-up. There have been several reports in the literature regarding the modelling aspects of solid transport in dryers. If the model is developed for model-based control, it must be simple and yet represent dynamics of the system accurately. This paper addresses solid motion modelling and the effects of different variables involved in solid transport phenomena. Sugar drying process is the case study in this work. A steady state semi-empirical model was modified to predict solid hold-up and flowrate in rotary dryers. This model was incorporated into a heat and mass transfer model ;o predict solid moisture and temperature for inferential and model-based control purposes. Results of several experiments that have been used to investigate dynamics of the system in terms of solid motion and to validate the model are also presented. The approach advocated in this paper is directly applicable to the transport of other solids in rotary drum equipment and can thus be regarded as a generalized model.     

A SIMPLE DYNAMIC MODEL FOR SOLID TRANSPORT IN ROTARY DRYERS

The solid particle movement in a rotary drum plays an important role in drying processes. The solid distribution in the drum affects the amount of contact surface between the solid and the gas. The retention time of solids influences the time particles can stay in contact with the gas in order to transfer heat and mass. Any heat and mass transfer model for a solid particle dryer must be able to predict solid flowrate and solid hold-up. There have been several reports in the literature regarding the modelling aspects of solid transport in dryers. If the model is developed for model-based control, it must be simple and yet represent dynamics of the system accurately. This paper addresses solid motion modelling and the effects of different variables involved in solid transport phenomena. Sugar drying process is the case study in this work. A steady state semi-empirical model was modified to predict solid hold-up and flowrate in rotary dryers. This model was incorporated into a heat and mass transfer model ;o predict solid moisture and temperature for inferential and model-based control purposes. Results of several experiments that have been used to investigate dynamics of the system in terms of solid motion and to validate the model are also presented. The approach advocated in this paper is directly applicable to the transport of other solids in rotary drum equipment and can thus be regarded as a generalized model.     

流化床反应器气固传热面积模型

研究了流化床反应器内发生气固反应时间的传热机理,认为气固间的传热面积包括两部分,即气泡内所含颗粒的表面积与一气泡和泡晕间的有效传热面积 ,据此首次导出了气固传热面积模型A＝u0-umf/22.26db0.5-umf[4.5unf ρgCpg/db 5.85(λgρgCpg)0.5g^0.25/db^1.25]LmS/a将该模型 应用于半间歇的裂化催化剂烧炭再生过程,与实验数据的比较表明,模型预测是可靠的。     

周期性变化边界条件下窑墙非稳态导热的数值模拟

本文采用简谐波处理周期性变化边界条件的方法，探讨了一维非稳态导热问题的数值计算问题，并给出了两间间歇窑窑墙传热过程的计算示例；计算结果表明，对周期性的传热过程，采用这种数值分析方法是适宜的。此外，本文还针对非稳态导热蓄热能力计算方法存在的不足之处，提出了一种新的计算周期性非稳态导热过程中窑墙蓄热能力的方法。     

Process simulation of activated carbon production using a rotary kiln

The rotary kiln used for the activation of charcoal is simulated using mass and energy balances to obtain the temperature distributions of environmental gas and solid in the kiln. The computed results are used to find the optimal operation condition. In finding the optimal gas temperature for the reductive gas environment necessary to the charcoal activation, the outcome gives the amount of fuel required and the effects of other operational variables, such as feed and steam rates. While the fuel and feed rates give large variation of gas and solid temperatures, the activation steam and moisture and volatile contents in feed do not affect the temperatures significantly. It was found that the temperature distribution has a similar pattern to that of coal pyrolysis because of the similarity of heat transfer mechanism.     

Development of process model of a rotary kiln for volatile organic compound recovery from coconut shell

The volatile organic compounds (VOCs) contained in coconut shell are wasted in the carbonization process of coconut shell due to the difficulty of recovery. The VOCs recovery is useful and necessary, because the VOCs are a sustainable energy source, and the recovery is an economically feasible project. A simulation model of the VOC recovery process from coconut shell using a rotary kiln is developed to investigate the process characteristics and the role of model parameters. The model includes the energy and material balances for the processing solid and the gas in the kiln. The validity of the proposed model is partially examined with the experimental results. From the simulation, the dominant heat transfer mechanism is determined for the understanding of the process operation. In addition, the optimal operating conditions of the rotary kiln are found for the use in the design and control of the kiln.     

气化炉拱顶耐火隔热衬里层传热关键影响因素分析

以某化肥装置天然气气化炉的典型工业运行实测数据为基准,采用稳态传热理论对气化炉拱顶外壁温度进行理论传热计算校验,通过对拱顶耐火隔热衬里层传热关键因素的灵敏度分析,表明莫来石隔热砖层对拱顶外壁温度的影响最大,从理论上证明了控制拱顶耐火隔热衬里层传热的关键物性参数是隔热砖的导热系数。因此,在拱顶耐火隔热衬里层设计计算中选取...     

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.     

水泥回转窑筒体表面余热吸收式制冷技术研究

水泥生产是一个高耗能的行业,回转窑筒体表面的余热损失可达输入能量的10%。通过在回转窑表面布置集热罩,可得到平均温度为100℃的热水。这些热水用于溴化锂吸收式制冷机组,可以得到制冷量1516 kW,相较于普通空调和电动压缩机制冷技术,采用溴化锂吸收式制冷技术回收回转窑表面余热进行制冷每年夏天可以节省20万元左右电费。     

利用窑尾废热干燥入窑料以节能提效

钛白粉的煅烧回转窑多为湿法进料,游离水干燥段占回转窑总长度的1/3,导致生产效率及热能利用率偏低。新工艺将饼状物料送入闪蒸干燥机,经来自回转窑尾部的热废气干燥,粉碎后送入回转窑煅烧,可使尾气排放的温度从300～350 ℃降至100 ℃左右,从而提高热利用率,减少尾气降温的成本,回转窑的生产能力也可提高30％。     

Mass transfer in rolling rotary kilns: a novel approach

A novel approach to modeling mass transfer in rotary kilns or rotating cylinders is explored. The movement of gas in the interparticle voids in the bed of the kiln is considered, where particles move concentrically with the geometry of the kiln and gas is entrained by these particles. The approach considers a differential section along the length of a rotary kiln where the gas concentration in the freeboard is assumed to be uniform in that section. A reactor modelling approach has been used to derive effectiveness factors for the bed as a function of bed fill, reaction kinetics and rotation speed. In many cases, the entrained gas becomes depleted within the bed, leading to a simplified model for the bed effectiveness factor. Experimental data confirms the validity of this model for slower rates. At faster rates, mass transfer can be much higher than the model predicts, indicating that other mechanisms, such as dispersion or diffusion are also important in these conditions.