喷动流化床造粒实验研究

喷动流化床用于粉体造粒，是一种新型的造粒方法。与其它几种造粒方法相比．具有设备投资省、能耗低、设备结构简单等优点。作者经过实验发现，气流雾化器安装于底部或侧部，或是二者结合。可实现对多种粉体的造粒和包衣。气流雾化喷嘴是喷动流化造粒装置的主要部件。为此对气流雾化喷嘴作了一些实验研究。     

液—固喷动流化床的膨胀特性和液体混合

在Φ１０４ｍｍ×１５００ｍｍ的液－固喷动流化床内，对２种不同孔径的喷嘴分别进行喷动流化，利用轴向扩散柱塞流到了液体轴向扩散系数，讨论了流体速度，床层空隙率，颗粒物性和喷嘴孔径等因素对液体轴向扩散系数的影响，并得到了轴向扩散系数的关联式。     

喷动流化床的最小喷动流化速度和床层压降

在一喷动流化床（直径 ５０ ｍｍ）实验台上采用 ０．６３～１．６０ ｍｍ的神府原煤颗粒,在连续进料的情况下进行了最小喷动流化速度以及固定流化气、改变喷动气和固定喷动气、改变流化气的床层压降变化的实验研究．结果表明,最小喷动流化速度可以参考鼓泡流化床的临界流化速度的计算方法;床层压降变化证实,喷动流化床具有良好的调节能力．     

喷动流化床最小喷动流化速度的多因素影响与关联

在一Ф125 mm、锥角60°的喷动流化床内测定了混合和分离体系的混合二组分及其单一组分的最小喷动流化速度u_msf.实验表明,最小喷动速度随静床高增加而增大,随流化气速和浮升组分分率增大而减小;混合体系中最小喷动速度随浮升组分分率接近线性递减,而分离体系却呈曲线降低.对比分析了文献umsf数据,除喷口直径外,多孔分布板形式和床径明显影响u_msf的大小,采用cos(aθ)、sin(bθ)、tan(cβ)和f(D_c/D_cref)来分别修正分布板夹角θ、均匀布气结构、开孔方向角β和床径D_c的影响.根据本文和文献不同结构与体系的590组数据,又用6个量纲1参数和上述4个修正函数进行了多重影响因素的综合回归,得出新的预测u_msf的普适关联式,该式偏差±29.5%,平均偏差11.5%,相关系数0.97.     

喷动流化床流动形态变化的试验研究国家

在一个可视化的半圆柱喷动流化床试验台上研究了喷动流化床的流形变化规律。研究表明：随着喷动气量和流化气量的改变,床内会呈现不同的流动形态：固定床、带射流的流化床、喷动床、充气喷动床和喷动流化床。同时研究了量小喷动速度和最小喷动流化速度随喷动管内径、颗粒粒径、静止床高的变化规律,归纳了预测量小喷动速度和最小喷动流化速度的试验关联式,绘制了喷动流化床的流形划分相图。     

新型流化床造粒器的研究

本文对新型流化床造粒器进行了研究。通过对尿素、氯化钙等物料进行了冷态和热态涂敷造粒实验,确定了适合于涂敷造粒的流化床和分布板的形式,并成功地进行了造粒中试实验。对尿素、氯化钙等物料,单喷嘴产量达到９０ｋｇ／ｈ。     

喷动流化床流动特性研究

选用密度与尿素相近而粒度不同的三种模拟物料，在内径为１８２ｍｍ的有机玻璃喷动流化床中，对喷动流化床的流体力学行为进行了研究。测定了不同物料最大操作区所对应的静床高及喷动流化气速与床层压降、床层空隙率分布的关系。为喷动流化床尿素造粒热态试验提供了可资借鉴的设计及操作依据     

喷动流化床流动特性数值模拟

为了捕捉喷动流化床中微观层次上的颗粒运动信息,建立了基于CFD的二维非稳态喷动流化床欧拉-欧拉两相流模型。分析了不同流化气速对喷动流化床气固流动特性的影响,即不同工况下的炉内压力降、颗粒浓度、床内空隙率分布、气体速度分布和固体颗粒速度分布。数值模拟研究结果表明:随流化气速的增大,压降和炉内平均空隙率逐渐增大,密相床层高度逐渐增加,沿着轴向方向的气体流量增大,喷动气的射流深度逐渐增加,同时射流半径也逐渐增加。     

等离子体-喷动流化床性能研究

等离子体-喷动流化床结合了先进的等离子体技术与喷动流化床装置,由流过中心喷口的等离子射流(喷动床)以及通过分配器的辅助流化气流(流化床)组成,目前对等离子体-喷动流化床的操作特性及基本现象研究较少。本研究中,搭建了一套等离子体-喷动流化床装置并进行了性能测试,直流等离子体炬功率12 kW,流化物料采用石英砂颗粒。研究中使用上部内径为198 mm柱状、下部为60°锥体的锥柱形反应器,以等离子体射流作为喷动气流,氮气作为流化气流构成了等离子体-喷动流化床。对比研究了物料在常温下与等离子体条件下在装置内的流动情况;在等离子体状态下研究了喷动流化床内物料的磨损情况;测试了等离子状态下喷动流化床装置内的温度分布。研究结果表明:在等离子体条件下实现物料喷动流化所需的气体流量大大减少,高温区集中于物料喷动流化区,体系的能量利用效率高,该装置适宜进行生物质等离子体热解或气化。     

A new approach to jet phenomena gas entrainment and recirculation in a bidimensional spouted fluidized bed

Although gas jets injected into fluid beds fluctuate, previous models assumed that they were steady. A new model separates the bed in a zone in which the jet is never present and a zone in which the jet fluctuates (a point in this zone will alternately be in the jet and in the emulsion phase). Its predictions matched the rate of gas entrainment into the jet and the rate of gas recirculation between emulsion and jet which were observed in a large 2 dimensional bed equipped with a “V” grid and a central jet.     

Aerodynamics of a novel rotating jet spouted bed

A novel rotating jet spouted bed (RJSB) is developed and tested. It consists of a rotating air distributor with two radially located spouting air nozzles. The effects of bed height, distributor rotational speed, nozzle diameter and particle properties on the flow characteristics were examined. Various flow regimes were mapped as functions of distributor rotational speed and superficial air velocity for different materials and column dimensions. Empirical correlations were developed for the minimum spouting velocity, peak pressure drop and steady spouting pressure drop.     

Wear on tubes by jet impingement in a fluidized bed

This study investigated wear on heat-transfer tubes resulting from impingement of particles entrained by a jet in a fluidized bed. The particular application is the fluidized-bed boiler for the Liquid Metal Fast Breeder Reactor in which a steam-tube failure might cause a high-velocity jet, accelerate particles, and erode adjacent tubes.Croloy and 304 SS tubes immersed in a fluidized bed were subjected to impingement wear from a sonic-jet issuing through a 1.17 mm diam. hole. Wear on target tubes was severe (when spaced near the leak source (1.6 cm)). With spacings of 20 cm, wear was scarcely measurable, being less than 0.002 cm/min.Impingement wear was measured in beds of rounded nickel, angular magnesia and angular iron. Results clearly show that increasing the hardness or angularity of particles increases impingement wear rate.An analysis of impingement wear was performed to project results of room-temperature tests to actual conditions. At 800 K and 1400 kPa, wear is projected to occur at 3 – 5 times the rate measured in tests.     

Batch drying kinetics of corn in a novel rotating jet spouted bed

The batch drying kinetics of corn as a test material were investigated experimentally in a novel rotating jet spouted bed (RJSB) using both continuous and intermittent (on/off) spouting and heating schemes. The parameters investigated include inlet air temperature, bed height, superficial air velocity, nozzle diameter, distributor rotational speed and intermittency of spouting and heat input. The results indicate that the drying kinetics are comparable with conventional spouted and fluidized beds for slow drying materials and that intermittent drying can save up to 40% of the thermal energy as well as air consumption with better quality product.     

Experimental study on solid circulation in a multiple jet fluidized bed

Particle image velocimetry was used to investigate the evolution of multiple inlet gas jets located at the distributor base of a two‐dimensional fluidized bed setup. Results were used to estimate the solid circulation rate of the fluidized bed as well as particle‐entrainment into the individual jets. The effects of fluidization velocity, orifice diameter, orifice pitch, particle diameter, and particle density were studied. It was determined from this study that the solid circulation rate linearly increased with an increase in the fluidization velocity until the multiple jet system transitioned from isolated to an interacting system. In the interacting system of jets, the solid circulation increased with fluidization velocity but at a much lower rate. For multiple jet systems, this phenomenon may indicate the presence of an optimum operating condition with high circulation rate and low air input in the bed. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3003–3015, 2012     

Modeling of wet jet in fluidized bed

A wet jet zone is established in many applications wherever feeding and dispersing a liquid, solution or slurry into fluidized bed by gases is needed. In the present study, a simple mathematical model has been developed to simulate the wet jet in fluidized bed. The different stages involved inside the jet zone have been estimated and analyzed.The evaporation stage of traveling droplets through the jet flare has been treated. The rates of evaporation of each size at all positions along the jet flare have been estimated according to the velocities and surrounding conditions. The final droplet sizes have been determined. Moreover, the total evaporation rate from traveling droplets, before collision either with entrained sand particles or flare boundaries, has been estimated. The traveling droplets, partially evaporated, may collide and settle on entrained sand particles. The model predicts the settlement rates of liquid droplets on entrained sand particles. The total part evaporated from settled liquid has been estimated as well.The study has been applied to the pneumatic feeding of liquid fuel into fluidized bed combustors operating at . The model has been utilized to predict the ratio of fuel vapor that releases inside the jet flare. The remaining part is assumed to evaporate inside the emulsion phase. Three different liquid fuels have been considered: a heavy oil, diesel fuel and gasoline. The main independent variables are those related to the injection conditions including the initial velocity of dispersing air, u₀, and air-to-liquid mass ratio, ALR.The model results demonstrate that only very small droplets completely evaporate inside the flare. The liquid settling over the entrained sand particles plays an essential role in the fuel evaporation inside the flare. The phenomenon is dominant at conditions that result in generation of droplets of larger sizes, i.e., heavier fuel, lower u₀, and greater ALR. The ratio of vapor fuel released in jet flare increases with lighter fuel, higher u₀ and lower ALR. At and ALR=1.0 nearly all-liquid fuel evaporates inside the flare.     

Study of gas-liquid jet boundaries in a gas-solid fluidized bed

The boundaries of gas-liquid jets formed during the air-assisted injection of liquids into gas-solid fluidized beds have been investigated using a small and a commercial scale fluidized bed and several injection nozzles. Two independent techniques (a triboelectric probe system and a thermal tracer method) have successfully allowed the characterization of the jet angle, of the jet penetration, and of the overall mapping of the jet cavity.The study demonstrated the effects of the nozzle geometrical configuration, of the air-to-liquid mass ratio fed through the nozzles, and of the scale of the fluidized bed on the jet boundaries.Finally, the experimental results obtained in this work confirmed the accuracy of an empirical correlation for jet penetration available in the literature.     

Heat transfer from a grid jet in a large fluidized bed

Heat transfer from a vertical grid jet within a 2 ft diameter and 4 ft deep fluidized bed of cracking catalyst was studied. The test nozzle diameter was varied from ¼ to 1 in. and the nozzle velocity from 50 to 250 ft /sec which is within the range of industrial practice. The axial temperature data have been related to a Froude, a Reynolds and a Nozzle number: In (δT/δT_o) = –58.1 Fr^?0.562 No^1.08 Re^?0.112 A simple jet quenching model yielded heat transfer coefficients between the fluid bed and grid jet which ranged from 300 to 1200 Btu/ft² hr.^o F.     

Numerical simulation of horizontal jet penetration in a three-dimensional fluidized bed

The introduction of reactant gas as a jet into a fluidized bed chemical reactor is often encountered in various industrial applications. Understanding the hydrodynamics of the gas and solid flow resulting from the gas jet can have considerable significance in improving the reactor design and process optimization. In this work, a three-dimensional numerical simulation of a single horizontal gas jet into a cylindrical gas-solid fluidized bed of laboratory scale is conducted. A scaled drag model is proposed and implemented into the simulation of a fluidized bed of FCC particles. The gas and particles flow in the fluidized bed is investigated by analyzing the transient simulation results. The jet penetration lengths of different jet velocities have been obtained and compared with published experimental data as well as with predictions of empirical correlations. The predictions by several empirical correlations are discussed. A good agreement between the numerical simulation and experimental results has been achieved.