低温氯化炉内颗粒停留时间分布研究

利用攀钢含钛高炉渣低温氯化炉冷态模型,采用电导率法对脉冲示踪粒子进行试验研究,分别考察了内部挡板、物料流量、表观气速等操作参数对低温氯化炉中颗粒停留时间分布(RTD)的影响。结果表明,挡板纵向切割流化床相对空间,消除短路,有利于颗粒与流化气的充分混合,双挡板条件下,碳化渣颗粒在流化床内RTD更为集中(方差σ2t由0.67明显降低至0.5);加料速率由1.9 g/s减小至1.1 g/s,物料平均停留时间延长一倍,碳化渣反应时间增加。表观气速增大至0.15 m/s时,虽然在一定程度上弱化了碳化渣停留时间分布的集中性,但返混强化了颗粒与气体的接触和反应,保证了流化状态,有利于提高碳化渣氯化效率。     

钙法钒渣熟料流态化浸出工艺研究

利用散式直管流化床进行了钙法钒渣熟料流态化浸出工艺研究,测定了熟料颗粒的粒度分布并分成7个粒级开展试验,首先计算出不同粒级下的临界速率及带出速率,考察了钒渣粒度对表观流化速率、停留时间分布以及钒浸出率的影响。结果表明,不同粒级的临界流化速率和停留时间差异较大,且存在显著的短路或者沟流现象,需分级处理,其中-39μm颗粒的浸出效果最好,尾渣残钒为0.54%,钒浸出率可达94%。     

球团烟气脱硫除尘改造关键技术研发与应用

竖炉球团烟气以其成分复杂、温度低、SO₂质量浓度高、流量波动大等特点，对循环流化床脱硫工艺的流场分布提出了更高的要求。本文通过分析循环流化床的脱硫机理以及影响脱硫效率的因素，采用Fluent数值模拟方法，重点研究文氏管布置、塔内扰流环、除尘器导流板对循环流化床流场的影响；并结合某钢厂球团烟气改造实例，进行对比分析，验证仿真分析的可靠性。仿真结果表明：在脱硫塔烟气入口对称布置文氏管后，气流的速度偏差减小到5.70%;在塔内增加扰流环后，速度突变增加到9.80 m/s;在布袋除尘器入口增设导流板后，各分室的速度偏差减小到7.53%,上述改进均满足设计要求。项目投产后，球团烟气中SO₂、颗粒物质量浓度分别小于20、5 mg/Nm³,优于钢铁行业超低排放标准，并能长期稳定运行。     

连续运转的加压喷动流化床内颗粒停留特性

在一喷动流化床（直径５０ｍｍ）试验台上，采用０．６３￣１．６０ｍｍ的原煤颗粒，进行了加料速率、流化气、喷动气以及压力等不同因素对颗粒在床内停留时间影响的实验研究，发现改变喷动床中气体流量，物料停留时间基本不变；改变流化气或喷动气，尤其后者，对仪时间影响明显；而一旦增加压力，会使停留时间延长。实验数据可为此类床型作为干燥器、气化裂解炉等的研究和应用提供有益参考。     

稀土永磁磁粉气流粉碎过程的模拟计算

通过使用Solid Works建立几何模型,用ICEM CFD软件划分网格,利用FLUENT软件进行模拟计算分析。本文中的计算采用2ddp求解器,计算方法为SIMPLEC算法Segregated隐式方法,湍流模型选取标准k-ε两方程模型,压力速度耦合采用SIMPLEC算法。在二维模型的计算中,研究了高速气流粉碎研磨室内部的气流速度场情况,并探讨了不同质量分数气体对气流速度场分布的影响。实验结果表明,研磨室内部气流的最大速度出现在3个喷管中心线几何交汇点上方,磁粉将在此处碰撞最激烈,形成一个粉末破碎区域;随着研磨气体的压力增大,喷嘴处的气流速度和气流交汇处的气流速度均增大,相反地,单独改变底部喷嘴压力时,随着底部喷嘴压力的减小,底部喷嘴口处的气流速度呈减小的趋势,而在气流汇聚处,气流速度变化不大;随着气体的质量分数减小,气流速度越大,在同等气流速度需求量情况下,将需要小的气流初始压力。     

并列流化床煤气化系统冷态模型

本文建立了双室流化床煤气化系统的冷态模型，对该系统正常运行的关键技术──两流化床间固体颗粒的循环特性进行了实验研究，对影响两流化床间固体颗粒循环量的各种因素（流化速度、静止床层高度、颗粒尺寸、辅助气流量等）进行了分析和讨论，实验和分析表明；本文所发展的煤气化系统在技术上是可行的，本文的工作为后期的热态实验打下了良好基础。     

连铸中间包湍流控制器水模实验研究

通过水模实验，研究了湍流控制器对连铸中间包流体流动的影响。合理结构的湍流控制器能够改善中间包流体流动特性，最小停留时间增加，活塞流体积提高，死区体积下降。实验观察发现，中间包采用湍流控制器后，在两块上渣堰之间的液面流动平稳，可以减少卷渣现象。     

高密度颗粒相HfO_2的流态化特性研究

研究了高密度物料HfO2在流态化方面的特点。在物料类型的研究中,使用床层塌落法对粒度为74~100μm的HfO2颗粒进行研究,结果表明:粒度为74~100μm的Hf O2属于B类物料,适用于鼓泡床或者湍流床。使用公式计算和实际实验进行对比,结果表明:低密度物料的临界流化速度经验公式同样适用于高密度物料HfO2的临界流态化速度计算;74~100μm的HfO2颗粒物料在流化过程未形成散式流态化状态,直接从沟流状态进入聚式流化状态;在粒度为74~100μm的HfO2颗粒的冷态流态化实验中,气流速度小于5 m3·h-1时,床层局部出现气孔,气流速度为5~8 m3·h-1时,床层处于沟流和完全流态化的过渡态;气流速度大于8 m3·h-1后基本完成了流态化;气流速度大于12 m3·h-1时,底部死角区域开始流动;气流速度从12降到6 m3·h-1的过程中,床层保持了一个较为稳定的床高和压力波动,可以获得更多的稳态流态化操作范围。     

新型侧搅拌流化床气-固流化质量的模拟

在流态化炼铁的过程中,由于气-固分布不均匀,导致节涌、沟流、气体利用率低、粘结失流等现象,甚至出现死床的状况.本实验建立新型侧搅拌流化床反应器的物理模型,研究了搅拌方式、空气体积流率、搅拌器转速、搅拌器倾斜角度四个因素对流化床内颗粒与气泡运动行为及压强变化规律的影响.结果表明:侧搅拌流化床的气-固流化质量优于垂直搅拌流化床,气泡尺寸显著减小;空气体积流率的增加会使流化床内颗粒运动情况加剧,气泡尺寸增大,压强变化加剧;搅拌桨转速增加可有效地剪切、破碎床内气泡;倾斜角度为45°的侧搅拌流化床内的气-固流化质量最优.     

循环流化床导热油炉设计参数的分析与计算

对循环流化床导热油炉的一些关键设计参数,包括流化床温和燃烧室出口烟温、煤碳粒子的平均停留时间和燃尽时间、流化速度和颗粒带出速度、物料循环倍率和灰渣量、导热油炉的计算最高液膜温度等进行了分析研究与计算方法的讨论,最后对循环流化床导热油炉进行了设计开发,并给出了几种常用规格型号的循环流化床导热油炉主要技术参数。     

Flow Behavior in Z-Path Fluidized-Moving Bed with Inclined Perforated Plate

Ｔｈｅｓｔａｃｋｅｄ/ ｐａｃｋｅｄｂｅｄｉｓｇｅｎｅｒａｌｌｙｕｓｅｄｆｏｒｌａｒｇｅｐａｒｔｉｃｌｅｓ .Ｉｎｓｕｃｈａｂｅｄ ,ｇａｓ ｓｏｌｉｄｒｅａｃｔｉｏｎｉｓｒｅｌａｔｉｖｅｌｙｓｌｏｗ ,ａｎｄｐａｒｔｉｃｌｅｓｓｈｏｕｌｄｂｅｏｆｇｏｏｄｍｅ ｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓ .Ｓｏ ,ｉｔｓａｐｐｌｉｃａｔｉｏｎｉｓｌｉｍｉｔｅｄ .Ｔｈｅｒａｉｎｉｎｇｂｅｄｉｓｏｐｅｒａｔｅｄｗｉｔｈｌｅｓｓｅｎｔｒａｉｎｍｅｎｔｏｆｐａｒｔｉｃｌｅｓ .Ｔｈｅｒｅａｒｅｆｅｗａｐｐｌｉｃａｔｉｏｎｓｉ…     

钛精矿颗粒在内构件流化床内停留时间特性的研究

在气固并流向上的有内构件流化床装置上,采用攀枝花钛精矿,研究了表观气速、加料速率、颗粒粒径以及挡板间距等不同因素对攀枝花钛精矿颗粒在床内停留时间特性及压降的影响.试验结果表明:流化床中增设水平内部构件可消除节涌,破碎气泡,强化气固接触,抑制颗粒返混,可形成均匀稳定的流化状态,非常有利于气、固接触反应.     

Numerical Study of Gas‐Solid Flow in the Raceway of a Blast Furnace

This paper presents a numerical study of gas‐solid flow in a blast furnace raceway using a 2D slot cold model. Numerical experiments are conducted by combining the discrete element method for the solid phase with computational fluid dynamics for the gas phase. The motion of particles caused by lateral gas blasting under conditions similar to that in the blast furnace process is examined at a particle scale. Combustion and associated solids movement around the raceway are simulated by extraction of particles from the bottom of the bed. The effect of bed height or solid pressure is considered by imposing a downward force on the top layers of particles in the bed. It is shown that depending on the gas velocity, the bed can transit from a fixed bed to a fluidized bed or vice versa. Two zones can be identified in such a bed: a stagnant zone in which the particles remain at their initial positions, and a moving zone in which particles can move in various flow patterns. In particular, if the gas velocity is in a certain range, the moving zone is formed just in front of the gas inlet, giving the so‐called raceway in which the particles can circulate. The effects of gas velocity, solid pressure and solid extraction are quantified. The fundamentals governing the gas‐solid flow and the formation mechanisms of a raceway are discussed in terms of particle‐particle and particle‐fluid interaction forces.     

Iron ore reduction in a continuously operated multistage lab-scale fluidized bed reactor—Mathematical modeling and experimental results

Industrial-scale fluidized bed processes for iron ore reduction (e.g., FIOR and FINMET) are operated by continuous feeding of ore, while laboratory tests are mostly performed under batchwise operation. The reduction behavior under continuous operation is influenced by both the residence time of the iron ore particles and the reduction kinetics, which is obtained by batch tests. In a mathematical model for such a process, the effect of both phenomena has to be considered. The residence time distribution of iron ore particles in a laboratory fluidized bed reactor was obtained by measuring the response of a step input and described by mathematical models similar to a continuously stirred tank reactor. In the same reactor, reduction tests with continuous feeding of iron ore were performed. Based on batch tests in a fluidized bed reactor, a mathematical model was developed to describe the kinetics of iron ore reduction under fluidized bed conditions. This kinetic model was combined with the fluidized bed reactor model to describe continuous iron ore reduction. In this detailed model, the change of gas composition while rising in the fluidized bed was considered. The degree of reduction and the gas conversion for reactors in series were calculated. The results obtained by the mathematical model were compared with experimental data from the laboratory-scale reactor.     

The kinetics of nickel oxide reduction by hydrogen; Measurements in a fluidized bed and in a gravimetric apparatus

The suitability of a batch fluidized bed laboratory reactor for measuring the rates of gas-solid reactions was investigated. Experiments were carried out on the reduction of Falconbridge nickel oxide by hydrogen in a batch fluidized bed reactor within the tem-perature range 550 K to 650 K using particles in the range of 60 to 100 mesh. The reactor was operated at approximately atmospheric pressure and gas flow rates were in the range of two to four times the minimum fluidization velocity at temperature. The results showed internal consistency and rough agreement with the results of previous workers. The re-sults were interpreted and correlated by means of a structural model for gas-solid reac-tions. As a check on the fluidized bed measurements, experiments were also carried out using the conventional gravimetric technique to measure the rate of reduction of compac-ted pellets of nickel oxide by hydrogen. When due allowance was made for the change of surface area of the oxide during compaction, the results were in close agreement with the fluidized bed results. Rate measurements using hydrogen-nitrogen mixtures revealed that the reaction is not first order with respect to hydrogen, as usually assumed, but is ap-proximately of order two-thirds at one atmosphere hydrogen partial pressure. Formerly Graduate Student at Berkeley     

Thermal decomposition of limestone in a fluidized bed

Particles of limestone of 16 to 28 and 60 to 100 mesh sizes were decomposed in a fluidized bed. A mathematical model for the thermal decomposition was proposed comprising the thermal decomposition at the interface within particles and the related heat and mass transfer steps. It was assumed in this model that the particles are completely mixed within the fluidized bed and that gas is in upward plug flow. Fractional decomposition of limestone particles and the bed temperature during thermal decomposition calculated from this model coincide very well with the experimental results. It was further revealed that the overall reaction rate of 60 to 100 mesh size particles is virtually determined by the rate of heat transfer from the reactor wall to the fluidized bed, and that both rates of interfacial reaction and heat transfer from the wall to the bed contribute to the overall decomposition rate of 16 to 28 mesh size particles. Former Graduate Student at Kyoto University, is now with the Railway Technical Research Center, JNR, Tokyo, Japan.     

Oxidation of zinc sulfide in a fluidized bed

Kinetics of oxidation of ZnS particles in a batch-type fluidized bed were studied at temperatures between 800 and 910°C. A two-phase model was employed for the fluidized bed, and the partial pressure of oxygen and the gas-film mass transfer coefficient on the particle surface were separately evaluated in gas bubbles and in the emulsion phase. The calculated fractional reaction coincided well with the experimental results. The difference in O₂ partial pressure between gas bubbles and emulsion phase was found to be fairly large especially under the vigorous fluidizing condition. Furthermore, it was shown from the mathematical model that the reaction of ZnS particles in the gas bubbles is negligible because of the extremely low solid concentration and that the overall rate of reaction in the emulsion phase is virtually controlled by the rate of gas-film mass transfer at higher temperature. The resistance of interfacial reaction within the particle also becomes significant when the temperature is lowered. Y. Fukunaka and T. Monta are both former Graduate Students, Kyoto University, Kyoto, Japan.     

Use of a tapered fluidized bed as a continuous bioreactor

Reactor systems based on tapered fluidized beds are being developed for aqueous bioprocesses in which adhering microorganisms or immobilized active biological fractions are used. The use of a fluidized bed prevents biomass buildup, accommodates particulates in the feed stream, is compatible with gas sparging, and allows easy removal or addition of the active materials. The tapered reactor tends to stabilize the fluidized bed, thus allowing a much wider range of operating conditions. Preliminary experimental results and an empirical mathematical model of the tapered bed indicate that bed stability is associated with a decreasing velocity and void-fraction profile up the bed and the pressure drop across the bed decreases with increasing flow rates. The tapered fluidized bed bioreactor is being evaluated for use in the enzymatic production of hydrogen, microbiological denitrification, and microbiological degradation of coal conversion aqueous waste streams. The enzyme catalyzed conversion of lactose to glucose and galactose was used in the evaluation of the reactor concept.     

Analysis of reduction of iron ore and oxidation of reducing gas in moving bed

To investigate the influence of technical parameters on reduction of iron ore and oxidation of reducing gas in moving bed, the coupling kinetic model of iron oxide reduction and reducing gas oxidation in moving bed was established. The model was applied in pre- reduction shaft furnace of C- 3000, and main calculating results were in a good accordance with production data. At a certain ratio of gas flow to ore mass, improving gas velocity at standard state can increase output of metal iron, yet decrease ratio of metallization and gas utilization rate. At a certain gas velocity at standard state, improving ratio of gas flow to ore mass can increase ratio of metallization, yet decrease output of metal iron and gas utilization rate. Reduction potential of gas has a substantial effect on reduction efficiency. It is suggested to improve reduction potential of gas to a 95% level for a high ratio of metallization. At a certain gas velocity at standard state, increasing gas pressure can improve ratio of metallization and gas utilization rate. Inert gas content has a disadvantageous effect on reduction reaction in moving bed. It is advantageous for improving reduction efficiency in moving bed by adjusting increasing ratio of pellet or adding part of rich- hydrogen gas in reducing gas.     

Residence time distribution of solid particles in liquid fluidised bed separator

Abstract

Residence time distribution (RTD) of coal particles in a floatex density separator (FDS) was investigated using stimulus response technique. The mean residence time of the underflow particles was observed to increase with a decrease in the particle size as well as density. The resistance to settling is enhanced at higher bed pressure and the residence time of the particles increases. A linear correlation of the mean residence time with the terminal settling velocity of the particles was observed. The mixing behaviour in the FDS was neither plug flow type nor fully mixed type. The n-tank in series model described the mixing pattern in the FDS well with ‘n’ values in the range of 3–5. The relatively low values of ‘n’ indicated that the flow behaviour in the FDS was closer to the well mixed state.