Spouted bed and microwave-assisted spouted bed drying of parboiled wheat

The effect of spouted bed and microwave-assisted spouted bed drying on drying rates of parboiled wheat was investigated. In addition, the effective moisture diffusivities of parboiled wheat were calculated. The drying experiments were performed using 200 g of parboiled wheat, at three different air temperatures (50, 70, 90 °C) and at two different microwave powers (3.5 W/g (db), 7.5 W/g (db)). Microwave-assisted spouted bed drying at microwave power of 3.5 W/g and 7.5 W/g reduced drying time by at least 60% and 85%, respectively compared to spouted bed drying. The effective diffusivity values were in the range of 1.44 × 10^?10–3.32 × 10^?10 in spouted bed drying while they were between 5.06 × 10^?10 and 11.3 × 10^?10 in microwave-assisted spouted bed drying at different experimental conditions.     

振动三相流化床水力阻力特性研究

利用空气、水和聚乙烯颗粒为工作介质,对外加振动力的Ⅱ型湍球塔流态化操作的水力阻力特性进行了研究,主要研究了气体速度、喷淋密度、静床高度、振动强度与床层压降的关系。与无振动情况相比较,引入振动可以扩大气速的操作范围,增加操作的稳定性。     

双层混床改造为三层混床的技术应用

在双层混床的基础上,在不增加设备、改变设备外部设施的情况下,通过应用多功能单向节流滤水帽等多项新技术,将双层混床改造为三层混床。改造后的三层混床解决了混床树脂体内再生时中排附近阴、阳树脂交叉污染的问题,具有出水质量好,周期制水量大等特点。     

循环流化床锅炉床温及床压的控制

0　前　言循环流化床锅炉 (后称 CFB锅炉 )与常规煤粉炉相比 ,汽水一侧的控制基本相同 ,但床温及床压的控制不同。CFB锅炉的炉膛类似于一个低温的化学反应器 ,一般将密相区物料温度控制在 850～ 90 0℃ ,这是最佳脱硫、脱硝温度 ,床温过低使锅炉燃烧效率下降 ,床温过高则会造成 NOx 及 SOx 排放增多 ,污染环境 ,甚至造成床料结焦 ,影响设备安全运行。1　床温影响因素1 .1　设计因素炉膛传热计算方法不准确 ,没有考虑宽筛分床料的特性 ,导致计算偏差大 ,炉内受热面配置不合理。1 .2　运行因素锅炉的实际运行条件往往同设计不一致 ,尤其是…     

丙烯聚合卧式搅拌床反应器中持料量的检测

利用单点声发射检测技术,根据颗粒撞击壁面产生声信号的机理,建立了卧式搅拌床反应器内持料量的预测模型,该模型可以定量描述单点声能量随床层持料量的变化规律.在搅拌转速、吹气量等条件保持不变时,以空气-聚丙烯颗粒体系为例,在冷模装置中考察了床层持料量在11.5～23 kg条件下单点声发射信号的变化情况.实验发现,单点声信号能...     

循环流化床锅炉床温动态简化模型

在分析了循环流化床锅炉床温动态特性的基础上,将循环流化床锅炉沿着炉膛高度方向分为密相区和稀相区2个部分,各个部分集中参数化,分别对2个部分进行氧浓度、床料质量、残碳质量以及总能量进行衡算,提出了以给煤、一次风、二次风以及排渣为操作变量的床温动态简化模型.最后采用MATLAB 6.5软件对所建方程进行求解仿真,结果证实了该模型的正确性.     

Prediction of bed pressure drop and top packed bed formation in gas-liquid-solid semi-fluidized bed with irregular homogeneous binary mixtures

We studied the hydrodynamics of a gas-liquid-solid semi-fluidized bed relating to packed bed formation and bed pressure drop with irregular homogeneous binary mixtures in a 0.05 m internal diameter Perspex column, with water and air (secondary) as fluidizing medium at constant static bed height of 0.08 m. A homogeneous binary mixture has been taken for easy formation of a semi-fluidized bed. Air is supplied centrally below the bottom grid in radial direction with a special design air sparger after the bed is first fluidized by the liquid. Experimental parameters studied included superficial gas and liquid velocities, average particle size and density and the bed expansion ratio. Empirical and semi-empirical models were developed. The calculated values from predicted models were compared with the experimental values and fairly good agreement was obtained.     

Effect of bed characteristics on local liquid spreading in a trickle bed

Trickle bed reactors are important to several chemical process applications. While the available computational fluid dynamics models can predict overall liquid volume fraction, the prediction of spatial liquid distribution continues to be a challenging task. In the present work, Eulerian multifluid simulations were performed to investigate the effects of particle size, gas and liquid flow rates, and bed structure on local liquid spreading, and the predictions were validated using measured liquid spreading. It was found that the capillary pressure force caused liquid to spread in the lateral direction and that the interphase interaction forces pushed it in the downward direction and the relative magnitudes of these forces governed the local liquid distribution. While the use of existing capillary pressure force model led to satisfactory prediction of the observed trends of dynamic and steady state local liquid spreading, the modified capillary pressure force led to quantitatively correct predictions of local liquid spreading. © 2016 American Institute of Chemical Engineers AIChE J, 63: 347–357, 2017     

Voidage characteristics and prediction of bed expansion in liquid-solid inverse fluidized bed

Studies on voidage fluctuations, axial voidage profile and bed expansion are carried out by measuring the local void fraction using particles of wide ranging characteristics in liquid-solid inverse fluidized bed. The quality of fluidization is elucidated by the local voidage fluctuations. The RMS voidage fluctuation depicts a maximum with respect to average bed void fraction and increases with increase in Archimedes number. The fluidization quality has been quantified using average normalized RMS voidage fluctuation in terms of Transition number. The axial void fraction is almost uniform throughout the bed except for particles with size distribution. All the literature and present experimental data on bed expansion are unified in terms of Richardson and Zaki equation using experimental terminal velocities. A new correlation is proposed for predicting the wall effect corrected experimental terminal velocities, as a substitute for standard drag equation. The bed expansion data are also predicted using the drift flux model.     

The crossflow piston bed

The moving piston bed is a device for producing washed crystals from a slurry feed. Necessary for predicting the quality of a conceptual bed geometry is an evaluation method which accurately reveals the flow patterns in the dynamic system. The electrical analog method serves as a versatile guide to an evolutionary development of improved designs.All beds with a submerged drainage port have, for a given geometry, a unique relationship between loss of displacement fluid and rate of bed advance. The hydraulic diagram is unchanged, by the magnitude of applied forces. For rating productive capacity the use of gravity forces as a reference standard is recommended.A crossflow design is developed that predicts a productive rate over three times that achievable by downflow washing.     

A circulating fluidised bed

Induced particle circulation was studied in a 0.3 m diam. air fluidised bed of sand with central draught tubes of 0.2 m and 0.15 m diam. and 0.6 m and 1.2 m in length. A “two-dimensional” bed, 0.3 m in width, of similar cross-section, was also used to study catalyst particle circulation. Superficial gas velocities of up to 0.4 m/s of air were supplied to the base of the draught tube to induce particle circulation rates in the annular downcomer of up to 400 kg/m² s. The circulation rate was shown to be affected by the gap height between the distributor and the draught tube, but was not affected by the draught tube length of height of bed above it. A model was developed to predict the circulation rate, assuming that the driving force for circulation was the density difference between draught tube and annulus and that energy was dissipated by particle shear at the walls. The theory is in reasonable agreement with the experimental results. A tentative model for predicting the shear stress at the wall of a flowing fluidised bed is presented.     

Shear-assisted fluidized bed powder-coating

This study addresses a novel concept of dense-fluidized bed coating of objects where the effectiveness of coating is promoted by the intentional and controlled establishment of shear flow around the object. The fluidized powder is sheared by the controlled oscillatory motion of the object with respect to the fluidized bed. The proof-of-concept is given with experiments carried out using a commercial powder specifically manufactured for dry coating applications in fluidized bed. Systematic analysis of the effect of different levels of shear rate on particle mobility/adhesion and effectiveness of coverage was performed. A simple model has been developed to provide a mechanistic framework for the interpretation of the results.     

Fluidised bed gas distributors

The literature on gas distributors for gas fluidised beds is reviewed from the point of view of stable operation of the bed. An equation is suggested relating the minimum value of the ratio of the distributor pressure drop for stable operation and the bed pressure drop to the aspect ratio of the bed. This equation could be used for design purposes.     

Fluidized bed catalytic combustion

The principles and applications of fluidized bed catalytic combustion are described. The experience and current activities of the Boreskov Institute of Catalysis in the development of fluidized bed catalytic combustion of various fuels and organic wastes are briefly reviewed. Prospects for new applications of this technique are discussed.     

流化床与颗粒剂

流化床造粒融合了设备、辅料和颗粒设计等多项技术。本文分析了造粒机理 ,并从造粒芯、辅料及颗粒设计等方面介绍了流化床造粒技术的最新进展     

Reactive bed materials for improved biomass gasification in a circulating fluidised bed reactor

Reactive bed materials for the optimisation of the biomass gasification in a fast internally circulating fluidised bed (FICB) reactor system were tested under sulphur-free (S-free) and H₂S enriched conditions in a micro-scale fluidised bed reactor. In the experiments, the bed materials (natural olivine, (Fe_xMg_1-x)₂SiO₄, perovskite-type oxides, Ba_0.3Sr_0.7Fe_0.9Mn_0.1O_3-δ and La_0.65Sr_0.35Cr_0.5Mn_0.5O_3-δ, Gd_0.1Ce_0.9O₂ and a natural calcite, CaCO₃) were examined under realistic redox-cycling conditions to study their oxygen capacity and release, their catalytic activity towards toluene reforming as well as their mechanical and chemical stability.It was found that the synthesised materials outperform the natural materials as reactive bed materials for the FICFB process under S-free atmosphere. Gd_0.1Ce_0.9O₂ has better catalytic properties, perovskites show a higher oxygen storage capacity. However, in the presence of H₂S, the perovskite loose their oxygen capacity, while calcite can form a sulphide/sulphate cycle which allows for significant oxygen capacity. Additionally, the catalytic activity goes up. Therefore, under real conditions, the two natural materials, calcite and to a lower extent olivine, have clear advantages with respect to price, catalytic activity and oxygen capacity.