回转窑中固体颗粒平均停留时间的计算

在倾斜的出口有挡料环的回转窑中,采用脉冲示踪法研究了回转窑中固体颗粒的流动模型,运用正交试验法安排实验,实验证明固体颗粒在回转窑中的运动接近于平推流;通过对固体颗粒在回转窑中运动机理的分析,导出了平均停留时间的计算公式,实验值与理论计算值吻合得较好.     

大缩口回转窑运转功率的计算

采用理论推导和实验验证计算了窑头大缩口回转窑运转所需功率、物料的停留时间和填充系数,确定了回转窑电机功率.与原回转窑相比,新回转窑在转速提高、投料量增加的情况下,电机选用功率大幅降低,节能降耗效果显著.     

固体废弃物在回转窑内停留时间的试验研究

在回转窑冷态试验台上，采用着色示踪粒子的试验方法研究了固体废弃物的物料特性（主要是堆积特性）、回转窑的结构特性（壁面粗糙度、长度及内构件）和操作特性（倾角和转速）等因素对固体废弃物在回转窑内停留时间的影响。物料的物理性质对停留时间的影响主要是通过对堆积角的作用而体现出来的。试验物料在回转窑内停留时间的分布与正态分布比较接近。回转窑转速的提高和倾角的增大都将使用得物料停留时间减少，同时，σT^2也减少。沿回转窑长度方向的物料的平均速度是逐渐增加的。出口挡板对MRT的影响是非常显著的。纵肋和环肋的各种组合形式都增加了物料的MRT，但组合式内构件对MRT的影响远小于出口挡板对MRT的影响。壁面粗糙度对停留时间的影响主要是通过其对料床床态的改变而产生的。     

NSP窑设计参数的优化及对传动功耗影响篚计算和分析探讨

根据早期日产2000t,Ф4．0m×60m窑的生产和部分研究成果,结合当前最新生产数据研究建立了以物料停留时间、物料负荷率、窑内物料量和物料运动功耗四个公式为主的NSP窑设计参数优化和传动功率计算模型。介绍了Ф4．0m×60m,斜度4．0％的回转窑的运行参数与功率计算实例,在此基础上提出了NSP窑设计中应采用大斜度、大直径、小长径比的增产节能新设计理念。     

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。     

预分解窑挖潜增效的措施与实践

目前,我国预分解窑产量由常见公式计算所得普遍偏低,因此,预分解窑的设计产量都定得较低.即使采取了扩大筒、管,炉容,增加分解炉发热能力的措施,但因前后配套装置能力仍普遍偏小,回转窑发热能力不能得到充分发挥.由于物料性质不同,在窑内各带的休止角和运行速度并不相同,计算得出在各带的停留时间与实际存在较大差异,影响了燃烧带停留时间的控制和产能的提高.比较先进的窑型,除在保证窑内和燃烧带物料停留时间的前提下合理提高窑速之外,窑内物料的填充率也在逐步提高.     

炭素煅烧回转窑加料方式的研究

炭素煅烧回转窑在生产运行过程中，窑尾返料的问题较为严重，影响生产率的提高。本文从下料管安装位置的角度分析了回转窑窑尾返料的原因，提出了炭素煅烧回转窑加料装置的改进方案，以期使窑尾返料问题得到改善。     

回转窑窑尾漏料的处理措施

回转窑在运行中,经常因物料或者操作原因出现窑尾跑料的情况,非常容易造成窑尾密封片损坏,而且造成现场的扬尘。在窑尾平台下部安装一个集料仓,仓下部加装2台FU270链式输送机,转运窑尾漏料入生料磨排渣斗式提升机,再次入磨,从而较好地解决了窑尾漏料问题。     

列管式回转窑物料停留时间的分析

为了能较精确地预测列管式回转窑的物料停留时间,通过理论分析内部构件对物料填充率及停留时间的影响,并通过Φ500mm×8 100mm回转窑上对三种物料进行物料停留时间试验,提出在列管式回转窑填充率15%~25%时,动态安息角对物料停留时间的影响,并提出原煤、油砂物料的近似计算值,基本符合原煤、油砂实际生产设备的运行数据。该结果可为列管式回转窑的物料的停留时间提供参考。     

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 .     

Prediction of axial velocity profiles and solids hold-up in a rotary kiln

Axial bed depth profiles were experimentally measured in a rotary kiln containing ilmenite particles under steady state and transient conditions. The variables include feed rate of solids, inclination and rotational speed of the kiln. and dam height. The variation of the axial velocity with kiln axis was estimated. The semi-experimental model proposed by Perron and Bui (1990) was modified to include the effect of the variables of the present study. The mean residence time of solids was estimated from the fractional hold-up and expressed in terms of the process variables. The transients induced by a step change in any of the operating conditions were measured as variation of discharge rate of solids with time.     

Mean residence time and hold-up of solids in rotary kilns

The influence of operational variables on the mean residence time (MRT) and hold-up of the solids in rotary kilns has been investigated by many researchers. However, their reports on the influence of the feed rate on MRT, for example, are not consistent with one another. In this study, experiments are conducted on a 400 mm ID pilot kiln with a cylindrical discharge dam. Sand is used as the testing solids. MRT and the hold-up are measured under various feed rates and rotation speeds. Experimental results indicate that MRT increases slightly with the feed rate, and that the gradient is smaller at high rotation speeds. The hold-up shows a near-linear increase with the mass of feed per kiln rotation. The experimental data are then used to test equations provided by different researchers for the prediction of MRT. Comparisons show that, results of the empirical equation from Sullivan, J.D., Maier, C.G., Ralson, O.C. [1927. Passage of solid particles through rotary cylindrical kilns. U.S. Bureau of Mines Technical Paper No. 384.] agree well with measurements for the cases of low kiln loadings, while the numerical model of Saeman, W.C. [1951. Passage of solids through rotary kilns: factors affecting time of passage. Chemical Engineering Progress 47, 508-514.] gives good predictions over the entire range of parameters considered.     

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.     

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.     

城市垃圾在回转窑内传输过程的冷态实验

研究了城市垃圾 (MSW)在回转窑反应器内的传输特性 .实验表明 :MSW在回转窑内停留时间总体上服从正态分布曲线 ,但与石英砂相比 ,MSW停留时间的分布更偏离出统计规律 ;非均质的MSW比石英砂具有较高的动休止角 ,从而使其在窑内的平均停留时间 (MRT)较长而体积流率 (MVF)较低 ;回转窑转速的提高和倾角的增大都使得MRT减少 ,MVF增大 ;出口挡板对颗粒的MRT具有十分显著的影响 ,而不同纵肋和环肋组合的内构件对MRT的影响主要取决于窑出口处环肋的高度 ;壁面粗糙度通过改变料床床态对MRT和MVF施以影响 .     

Pyrolysis of oil sand from the Whiterocks deposit in a rotary kiln

A rotary kiln reactor was evaluated for thermal recovery of oil from Utah oil sands. A series of continuous-flow pyrolysis experiments was conducted. Process variables investigated included temperature (748–848 K), solids retention time (10–27 min) and sweep gas flow rate (1.27–2.83 m_s³ h⁻¹). The results indicated that the pyrolysis temperature and the solids retention time were the two most important variables affecting the liquid and gas yields. The liquid yield (C₅⁺]) decreased and the gas yield (C₁–C₄) increased with increasing temperature. The liquid yield increased with decreasing solids retention time, while the gas yield decreased. No significant effect of the sweep gas flow rate on the product distribution and yields was observed. The quality of the bitumen-derived liquids was significantly better than that of the bitumen. A preliminary process kinetics model which conforms to the observed trends was proposed.     

Experimental study of residence time,particle movement and bed depth profile in rotary kilns

Experiments were performed in a pilot scale rotary kiln with coal and coke particles to study their mean residence time, residence time distribution, bed depth profile and time spent at the bed surface. The influence of filling ratio on residence time was studied with a uniform bed depth in the kiln. Residence time distribution and bed depth profile measurements were performed in a kiln without end constriction, at different rotational speeds and different solid inputs. The residence time fraction corresponding to the passage of the particles at the bed surface was measured with a photographic study of the movement of a coloured particle. Various equations were tested to represent the experimental results. The equations of Kramers and Croockewit (1952) and Ronco (1965) were adequate to calculate mean residence times, while only the former could represent correctly the bed depth profile. An equation is proposed which turns out to be quite accurate in predicting the fraction of the residence time spent in the upper layer of the bed.     

COMPUTER SIMULATION OF HEAT TRANSFER DURING DRYING AND PREHEATING OF WET IRON ORE IN A ROTARY KILN

In the present study, an improved numerical heat transfer model has been developed for a rotary kiln used for drying and preheating of wet iron ore. The present model includes radiation exchange among hot gas, refractory wall and the solid surface, transient conduction in the refractory wall, and mass and energy balances of the hot gas and the solids. The contribution of gas convection has also been taken into account in terms of a fraction of the radiative heat transfer to the inner refractory wall and the solid surface. The computer results show that the present model can predict the length of the kiln as well as axial solid and gas temperature distributions with reasonably good accuracy. A detailed parametric study reveals that a good design of a rotary kiln requires medium gas flow rate, small angle of inclination and low rotational speed of the kiln.     

外热式回转窑焙烧5A分子筛原粉系统调试研究

利用外热式回转窑高温焙烧5A分子筛原粉,可以有效脱除其中的吸附水及结晶水,生产出合格的活化粉产品。研究了焙烧温度、停留时间及物料在窑内填充系数等相关工艺参数对产品指标的影响,从而确定回转窑焙烧5A分子筛的最优工况参数。结果表明,在焙烧温度为620 ℃,物料在烧成区停留时间为45 min,窑内填充系数为0.07～0.08的条件下,回转窑稳定运行时产量为295 kg/h,活化粉静态水吸附量为24.4%～24.45%,烧失率为1.04%～1.15%,回转窑产量及产品指标均达到设计要求。