惰性粒子流化床中的悬浮液干燥

用惰性粒子流化床干燥器对混凝土外加剂等5种物料进行了干燥实验研究，提出了计算体积传热系数的关联式．实验结果表明，由于惰性粒子的存在，强化了传热传质，体积传热系数可达3000W·m~(-3)·K~(-1)，但是，床层压力降较高．干燥强度（以蒸出水计）可达50～60kg·m~(-3)·h~(-1)，热效率30％～43％，若提高热风进口温度，后两项指标还可提高.     

DRYING OF GRANULAR MATERIALS IN AN INCLINED VIBRATED FLUIDIZED BED BY COMBINED RADIATIVE AND ONVECTIVE HEATING

In an inclined-vibrated fluidized bed (IVF-bed), solid particles are fluidized easily at a relatively low air velocity. Good mixing of the fluidized particles in the direction of the air flow and the renewal of the bed surface take place as a result of the vibration effect. Accordingly when the bed surface is heated by thermal radiation from the top surface, radiant heat is absorbed more effectively on the surface than on a stagnant bed surface. This characteristic of an IVF-bed indicates the applicability to a solar dryer and other similar dryers.

The present study reports the result of model experiments carried out to confirm the effectiveness of radiative heating on drying of wet granular materials. Further, for quantitative evaluation of the radiation effect, a theoretical model is offered and its validity is examined.     

DRYING OF TOBACCO PARTICLES IN A MOBILISED BED

ABSTRACT

The drying performance of a novel device capable of mobilising a bed of fibrous materials is evaluated. The drying kinetic of the vegetable product used for this work, cut lamina tobacco particles, was determined from fixed bed experiments. A falling-rate period was observed for the entire drying curve. The results showed that the drying rate is controlled by internal mass transfer mechanism for gas superficial velocities above 0.8 m/ s. The proposed model is based on an effective liquid diffusion coefficient that varies with solids temperature according to an Arrhenius-type relationship. Batch drying experiments were carried out in the mobilised bed apparatus under various conditions of inlet air temperature, humidity and flowrate. Assuming perfect mixing and no internal resistance to heat transfer for the solids, the performance of the mobile bed can be predicted using the proposed internal liquid diffusion model     

AMARANTH GRAIN DRYING IN A FLUIDIZED BED

ABSTRACT

An empirical equation as a function of drying time and temperature was developed to calculate the moisture ratio required Tor balch fluidized bed dryers design for amaranth grain drying

The relative deviations of the moisture ratio values calculated with the proposed equation with regard to the experimental ones ranged between 0.014 and 0.095 for a drying air temperature between 60 and 100 ° C, and a grain initial moisture content between 23.5 and 16.6 % wb.     

DRYING OF STICKY GRANULAR MATERIALS DWING THE CONSTANT RATE PERIOD IN A VIBRATED FLUIDIZED BED

Experimental results on the drying characteristics in a vibrated fluidized bed IVFB) for sticky and agglomerating materials under various conditions of the operating parameters are presented.The dynamics of the 'FB of wetted materials and the effects of parameters, such as vibration amplitude and frequency, initial moisture content, initial bed height, particle size, and air velocity and temperature on the drying rate during the constant rate period were studied experimentally.     

STUDIES OF STEAM DRYING IN A FLUIDIZED BED

In general, drying processes are described by the quantity of air humidity of the exiting gases. This approach is not possible however by the drying medium of water in steam drying, since the air humidity naturally possesses a constant value of 100%. This paper presents a model which represents the drying processes on the basis of the observation of temperature profiles of the material and energetic balancing of all components involved as well as the wall of the apparatus. The modeling differentiates three intervals: the condensation phase, the 1st drying period and the 2nd drying period. In addition, a validation of the model on the basis of experiments in an experimental plant DN100 belonging to the university is dealt with. The satisfying concurrence of the theoretical and practical results shows that, with the help of the theoretical model, discontinuous steam drying processes can be theoretically described with sufficient accuracy.     

STOCHASTIC BEHAVIOR OF FLUIDIZED PARTICLES IN A LIQUID-SOLID FLUIDIZED BED

In a liquid-solid fluidized bed, the apparently irregular or stochastic behavior of particles gives rise to various flow regimes depending on parameters such as the particle size, liquid flow rate, static bed height and axial position in the bed. It is highly plausible that this irregular behavior manifests itself as pressure fluctuations; thus, the effects of these parameters on the particle behavior or the particle flow regime were investigated through measurement and spectral analysis of the pressure fluctuations. The results indicate that the amplitude of pressure fluctuations exhibits a maximum and that the decay constant in the autocorrelation function attains its minimum at the intermediate liquid flow rate where the particle flow regime undergoes transition from the cluster circulation to the individual quasi random motion. The model composed of the periodic and stochastic components of pressure fluctuations, is in good accord with the experimental results in terms of both the autocorrelation and power spectral density functions.     

A STOCHASTIC APPROACH TO THE DRYING OF SOLIDS IN A MULTI-STAGE FLUIDIZED BED

The residence times of solids flowing through a fluidized bed dryer exhibit dispersion about the mean. In this paper, expressions for the probability density functions of solids moisture content in the various stages of a multi-stage dryer are derived. A simple recurrence relationship for the moments of the distribution is also presented. The analysis is applied to the drying of cereal grains, and it is shown that the degree of drying increases with the number of stages in the dryer. Probability density functions of the moisture content are presented.     

快速流化床内颗粒速度的关联

颗粒速度是快速流化床内重要的流体力学参数,直接测定是困难的,一般都是通过测定其他参数,来计算颗粒的速度。本研究在内径6.6cm 和9.7cm,高3m 的快速流化床内测定颗粒的轴向滞留量分布及压头损失,分析床层内颗粒速度及其影响因素,对三种不同颗粒进行测定,将实验数据进行关联,得出颗粒速度的关联式:适用范围:气体流速:1.4～6.0m/s颗粒循环速度:30～130kg/m~2·s颗粒终端速度:0.133～0.880m/s将实验值与计算的结果比较,基本一致。故可认为该式在实验范围内,可用于推算快速流化床内的颗粒速度。     

大颗粒作用下微细粉流态化干燥研究

为了克服湿微细粉易于结团形成“细粉群”、不易流化和干燥的缺点，在微细粉中加入惰性大颗粒物料，由于大颗粒的“搅动”作用，使细粉分散，可提高流化质量，从而提高微细粉的流化干燥热效率．在实验基础上进行了物料衡算和热量衡算，并进行连续干燥热效率的计算．该方法为微细粉的流化干燥提供一条新的途径．     

流化床中侧向射流穿透深度的研究

流化床中侧向射流穿透深度的研究李海滨，王洋，张海生（中国科学院山西煤炭化学研究所，太原０３０００１）关键词：流化床，侧向射流，穿透深度１前言气固流化床反应器中，分布板起着气体分布和支持床层物料的作用，分布板区是气体与所处理固体接触最强的区域，在氧化反...     

DISPERSION AND FLUCTUATION OF FLUIDIZED PARTICLES IN A LIQUID-SOLID FLUIDIZED BED

Axial dispersion coefficient and fluctuating frequency of fluidized particles have been determined in a liquid-solid fluidized bed by resorting to the relaxation method from the histograms of pressure fluctuation in the bed. Dependence of the axial dispersion coefficient and fluctuating frequency of fluidized particles on the liquid flow rate and particle size, and further on the bed porosity has been discussed. The axial dispersion coefficient and fluctuating frequency of particles have attained their maxima with increasing liquid flow rate and bed porosity, and those values increase with an increase in particle size under fully fluidized concitions. It also has been found that the axial dispersion coefficient shows its maximum at the liquid flow rate where the fluctuating frequency of particles reaches its maximum point.     

加压流化床煤气化炉衬里材料的选择与烘制

加压流化床煤气化技术是近年来随着洁净煤技术的兴起而发展起来的新一代大型、先进煤气化技术。就加压流化床煤气化炉耐火衬里的特殊要求进行了耐火材料的选型,并根据所选耐火材料特性制定了烘炉工作曲线,并比较了烘炉所需实际燃料气量和估算值,结果表明计算值与实际值吻合较好,并为大型流化床反应器的烘炉工艺制定和实施提供一种理论参考和估算方法。     

气固流化床中侧向射流穿透深度的研究

本文以小米和两种硅胶为物料，在314×25mm的二维射流流化床中，用摄像法研究侧向射流穿透深度，并得到了关联式，误差小于25％．当射流倾角变化范围不大、并忽略射流位置的影响时，可以得到简化公式，误差小于40％使用基于对流体模型的计算机程序进行模拟，分析了射流产生的机理，研究了射流气速、直径、倾角和位置对射流穿透深度的影响．模拟值和实验值较吻合．     

DRYING OF CARROTS IN A FLUIDIZED BED. I. EFFECTS OF DRYING CONDITIONS AND MODELLING

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70°C and 160°C, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75°C. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D_e) was determined by a correlation based on the air velocity (v), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X_o). Loss of carotenes is minimized when dehydration is carried out at about 130°C with a drying time below 12 min.     

DRYING OF CARROTS IN A FLUIDIZED BED. I. EFFECTS OF DRYING CONDITIONS AND MODELLING

ABSTRACT

Drying curves were determined in a mechanically agitated fluidized bed dryer, at temperatures between 70°C and 160°C, air velocities between 1.1 m/s and 2.2 m/s and stirring rates between 30 rpm and 70 rpm for batch drying of 3 kg lots of carrot slices, measuring the moisture content and shrinking of the particles in time. This was complemented by a study of the rate and degree of swelling of dried carrot particles in water between 20 and 75°C. Drying kinetics were modeled by Fick's second law, for which an optimal agreement with the experimental data was obtained when the effective diffusivity (D _e ) was determined by a correlation based on the air velocity (v), the air temperature (T) and the dimensional moisture content of the carrot particles (X/X _o ). Loss of carotenes is minimized when dehydration is carried out at about 130°C with a drying time below 12 min.     

RAINING OF PARTICLES FROM AN EMULSION-GAS INTERFACE IN A FLUIDIZED BED

This paper deals with the raining of particles from an interface between a dense fluidized phase and a gas phase with the fluidized phase uppermost. Such interfaces occur at the upper surfaces of gas bubbles and slugs in fluidized beds. Particle rain in these cases would enhance contact between gas and particles within the bubbles and slugs.

The rise velocities of single square-nosed slugs injected in incipiently fluidized beds of different diameters were measured. Relatively small columns of internal diameters of 0.0125, 0.019 and 0.0254 m were employed in the experiments; In such beds, square-nosed slugs are formed which span the entire cross-section of the beds and rise entirely due to raining of particles from their top surfaces. Since the upper surface of such slugs is flat, their motion can be analyzed using the one-dimensional hydrodynamic theory. Glass ballotini and sand of different sizes were used as bed particles. Comparison of theory and experiment has enabled the determination of the dimensionless gradient diffusivity characterizing the motion of particles induced by a gradient in the void fraction. The results confirm the scaling proposed by Batchelor (1988). The use of the calculated gradient diffusivity in the criterion for stability of a gas fluidized bed predicts the systems under consideration to be always unstable.     

SIMULATION OF PLUM DRYING IN DEEP BED

Thin layer air drying of plum was studied. The drying conditions in this study are : dry bulb temperature ranging from 60 to 100 °C, air moisture content ranging from 0.008 to 0.089 kg water/kg dry air and air velocity ranging from 0.5 to 2 1x11s. An exponential model was used to describe the drying curve. The heat and moisture balances on the air were used to calculate the outlet air temperature and its moisture content. The heat balance on the product was used to calculate the product temperature. These equations were used to predict the drying of plum in deep bed. A good agreement between the experimental and calculated product moisture content, the product temperature and the outlet air temperature were obtained     

GRAPHICAL SOLUTION OF MULTISTAGE FLUIDIZED BED HEAT EXCHANGER

The design of multistage fluidized beds for heat exchange necessitates the solution of the mass and energy balance equations combined with the equilibrium relations for each stage. This paper presents a novel way of applying well known methodology to a different technology, one where it has not been widely applied.

In the present work a McCabe-Thiele type of graphical approach is presented for both counter-current and cross-current contacting multiple fluidized beds. The necessary equations for a multistage calciner are developed and the application of the proposed method is demonstrated. Generalized fluidized bed efficiency for counter-current and cross-current multiple fluidized bed is presented.     

GRAPHICAL SOLUTION OF MULTISTAGE FLUIDIZED BED HEAT EXCHANGER

The design of multistage fluidized beds for heat exchange necessitates the solution of the mass and energy balance equations combined with the equilibrium relations for each stage. This paper presents a novel way of applying well known methodology to a different technology, one where it has not been widely applied.

In the present work a McCabe-Thiele type of graphical approach is presented for both counter-current and cross-current contacting multiple fluidized beds. The necessary equations for a multistage calciner are developed and the application of the proposed method is demonstrated. Generalized fluidized bed efficiency for counter-current and cross-current multiple fluidized bed is presented.