Fluidization characteristics of sawdust in a cold flow fluidized bed

India has abundance of biomass such as rice husk, bagasse, wheat straw, sawdust etc. which is used as a main or auxiliary fuel in the fluidized bed combustor, gasifier and pyrolizer. Design of such fluidized bed equipments require the knowledge of minimum fluidization velocity (U_mf), complete fluidization velocity (U_cf) and transport disengagement height (TDH). The present work reports the fluidization characteristic, U_mf, U_cf and TDH of the individual size groups of sawdust and mixture thereof. The results indicate that the U_mf and U_cf have a tendency to increase with increase in particle diameter, however the TDH shows the reverse trend. The sawdust particle size of 925 and 1200 ​μm showed significant difference between their U_mf and U_cf, an essential parameter for controlled fluidization. Based on the experimental work new correlations for the prediction of U_mf, U_cf and TDH for sawdust sample are proposed. The proposed correlations of U_mf, U_cf and TDH are in good agreement with experimental values and the deviations found within the range of nearly ±10% for all the samples.     

二组分混合物的最小流化特性 Ⅱ.混合物平均物性与最小流化速度

理论上引入二组分完全混合时的平均物性概念,并给出确定混合物最小流化速度的合理步骤。根据混合物最小流化速度随组成的指数性变化规律,推荐出对工程设计很有价值的经验关联式。     

非磁性纳米SiO_2颗粒在磁场流化床中的流态化

研究了非磁性纳米SiO2颗粒在添加磁性大颗粒磁场流化床中的流化性能。磁性大颗粒的添加量在20%～60%(wt)之间,磁感应强度的大小分别为0.0477、0.0596、0.0715 T。实验中通过测定床层膨胀曲线、床层压降曲线,详细地考察了磁性大颗粒的添加量、磁感应强度及气速的大小对纳米SiO2颗粒流化性能的影响。结果表明:把磁场能引入普通流化床中之后,加入的磁性粗颗粒能够有效地破碎纳米SiO2床层中的活塞、沟流和大聚团,降低最小流化速度,且在最小流化速度时无气泡,使床层膨胀比增加,提高床层的整体流化质量;在流化颗粒相中,磁场能的加入还可以保持床层的稳定性,维持流态化所需的气体体积。     

木屑在鼓泡流化床和循环流化床中气化特性的对比研究

对木屑在内径分别为0.3m×0.3m的鼓泡流化床气化炉（BFBG）和内径0.4m的循环流化床气化炉(CFBG)中的气化特征进行了对比，重点考察了当量比对生物质气化特性的影响。实验结果表明,在相同当量比下，由于CFBG操作气速明显高于BFBG，床内强烈的气固传热传质，使得CFBG可以获得较高的热解速率,同时可以使 CFBG在较高温度下运行。较高的运行温度不仅有利于二次裂解气化反应，使可燃气体质量明显好于BFBG，同时也减少了燃气中焦油的量。在较低气化当量比下(ER≤0.28)，CFBG比BFBG可以获得更高的气体产率、碳转化率和气体效率;在较高当量比下,(ER＞0.28)，CFBG和BFBG的气体产率、碳转化率和气体效率则相差不大。     

Perte de pression et vitesse minimum de fluidisation dans un lit de particules 2D

In order to determine the pressure drop equation and the minimum fluidization velocity of a 2D bed of monodispersed particles, an experimental setup has been devoloped. The first results show clearly that the well-known equations for 3D bed are not reliable for this configuration. In particular, the minimum fluidization velocity is underestimated. A new pressure drop law is proposed which allows the determination of the minimum fluidization velocity, and is in good agreement with the experimental measurements.     

Design of a fluidized bed reactor for microencapsulated urease

A fluidized bed reactor was designed, constructed, and tested for handling microencapsulated urease. The working volume of the reactor was 10 mL, with a minimum fluidization velocity of 7.7×10⁻⁵ m/s. An even suspension of the microcapsules was obtained at fluid velocities between 1.5×10⁻⁴ and 6.0×10⁻⁴ m/s without breakage of the shear-sensitive microcapsules. The mixing behavior in the reactor was evaluated using pulse input tracer experiments and the hydrolysis rates of urea in continuous flow experiments were evaluated under various operating conditions.     

Numerical study of flow maldistribution and depressurization strategies in a small-scale axial adsorber

Flow maldistribution and local high velocity in an axial adsorber is numerically studied to investigate the potential occurrence of sorbent pulverization and uneven utility. A considerable maldistribution induced by the entrance effect and local high velocity caused by rapid gas discharge during depressurization is observed. Three types of gas distributors and different depressurization strategies are then proposed and studied to determine their capabilities to create uniform velocity profiles. Results show that locating the predistributor in the dead zone is critical to flow distribution. The maldistribution factor (Mf) can decrease to a minimum of 0.055 when a perforated inlet plenum is used with a conventional distributor. In addition, the internal ring can effectively reduce wall effects. Moreover, both gas expansion and desorption have a significant influence on the evolution of local velocity during depressurization. In this step, local high velocity can possibly exceed incipient fluidization velocity and cause attrition and pulverization of the sorbent. To a certain extent, employing methods to control the depressurization rate is necessary. Applying linear depressurization ( \(p = 101,325 - p_{AD} /t_{DP} \times t + p_{AD}\) ) or downward convex conic depressurization ( \(p = p_{AD} - \sqrt {\left( {p_{AD} - 101,325} \right)^{2} /t_{DP} \times t}\) ) can reduce local high velocity, and thus, improve flow conditions.     

Photocatalytic degradation intrinsic kinetics of gaseous cyclohexane in a fluidized bed photocatalytic reactor

The special photocatalytic degradation intrinsic kinetics of gaseous cyclohexane were investigated in a designed fluidized bed photocatalytic reactor (FBPR). A series of photocatalytic kinetic reaction equations were developed to explore the relationship of degradation efficiency and operating variables based on photocatalytic mechanism and particle fluidization hydrodynamic characteristics. The corresponding results indicated that the initial concentration has influenced the photocatalytic degradation reaction conversion, and having a concentration inflexion point which theoretically divided the photocatalysis into a first-order apparent kinetic rate equation at low concentrations and a zero-order kinetic rate equation at high concentrations. Furthermore, these results were validated theoretically by the intrinsic kinetic models of photocatalytic degradation conversion developed according to variation of cyclohexane concentration and gas velocity. Based on the experimental results, the optimal operating gas velocity range was determined. The multi-factors synergy effect resulting from gas velocity on photocatalytic degradation efficiency was explored and proved by mass transfer, illumination transmission and adsorption models. Finally, the degradation pathways of the cyclohexane and deactivation mechanism of the photocatalyst were studied according to the intermediates degraded on TiO₂ surface, and a feasible method presented for catalyst regeneration.     

Slip flow in fixed and fluidized bed plasma reactors

The characteristics of low-pressure gas low through fixed and fluidized bed plasma reactors for the study of plasma-solid reactions are presented. In the plasma fluidized bed reactor (PFBR), solid particles are fuidized at subatmospheric conditions in a resonantly sustained high frequency 2.45 GHz) plasma. The reactor operates in a previously uninvestigated regime of fuidization and microwave breakdown. A modified version of Darey's law is developed to describe and compare fixed and fluidized bed behavior, as well as to rationalize experimental measurements of pressure drop and gas flow in the absence of information about the bed temperature profile. The study has shown for a bed operating in or near the slip flow region that minimum fluidization can be predicted for slip flow fluidization in the absence of a plasma. However, the results of this work indicate that the mass fluxes and pressure drops at minimum fluidization in the presence of a plasma are significantly different from nonplasma fuidized bed. The pressure drop at minimum fluidization, in the presence of a high-frequency electrical discharge, is as much as 25% above that required to levitate the bed contents, and appears to corroborate otherfndings that link increased stability of the bed with the presence of electromagnetic fields.Notation A cross-sectional area of tube, m₂ - B ₀ bed permeability - D _p diameter of glass bead, m - D hydraulic diameter, m, defined as the ratio of the cross-sectional area to the wetted perimeter - E electric field strength, J/(C m) - F slip flow correction factor - F _d volume driving force, N/m'm³ - g gravitational acceleration, N/kg - G mass flow rate, kg/s - G _min mass flow rate at minimum fluidization, kg/s - k Boltzmann's constant - K ₀ slip correction - L bed height, m - M molecular weight of gas, kg/kg-mole - M _p mass of particles in bed, kg - n _p,e number of density of positive ions or electrons, m^–3 - P _1,2,3 bed pressure below frit, above frit, and above bed, Pa - q electronic charge, C - Q volumetric flow rate of gas, m³/s - R gas constant - Re_p,mf Reynolds number at minimum fluidization - T temperature, K - u superficial gas velocity, m/s - U _mf superficial velocity at minimum fluidization, m/s XKnudsen number - x length variable, m or dimensionless Greek gl _o coefficient in expression for mean free path - c _n mean free path - gas viscosity, kg/(m s) - ₀ prefactor in expression for viscosity - 3.14159 ... - _g mass density, kg/m³ - hard sphere diameter, m     

Assessment of Two Surface Monte Carlo (TSMC) method to find stationary points of (H2O)15 and (H2O)20 clusters

The Two Surface Monte Carlo (TSMC) technique reduces computational cost by using a computationally cheap biasing potential, which guides the molecular system to explore the potential energy surface of interest. It was shown earlier that the Effective Fragment Potential (EFP) can be a good choice for this biasing potential (Bandyopadhyay, J Chem Phys 122:091102, 2005) when the potential energy surface of interest is quantum mechanical. This may help in expanding the applicability of TSMC, since finding a good biasing potential is a major challenge. In the present work, the viability of TSMC method in finding stationary points of large molecular system is investigated using EFP as the biasing potential and RHF theory as the potential of interest. TSMC is applied to find the stationary points of water clusters of size 15 and 20. A semi-automated method starting from random geometries, without using any chemical intuition, found several stationary points. The simulated annealing method was used to refine the structures obtained from TSMC. Among the several low-energy structures obtained for 15 water cluster, one minimum, about 1 kcal/mol higher than the global minimum, was found. However, for 20 water cluster, no structure very close to the global minimum was obtained. Several strategies, learned from the experience of the present work, are discussed for improving the TSMC method, including the acceptance between the two energy surfaces. Contribution to the Mark S. Gordon 65th Birthday Festschrift Issue.     

Computation of distribution of minimum resolution for log-normal distribution of chromatographic peak heights

General equations are derived for the distribution of minimum resolution between two chromatographic peaks, when peak heights in a multi-component chromatogram follow a continuous statistical distribution. The derivation draws on published theory by relating the area under the distribution of minimum resolution to the area under the distribution of the ratio of peak heights, which in turn is derived from the peak-height distribution. Two procedures are proposed for the equations' numerical solution. The procedures are applied to the log-normal distribution, which recently was reported to describe the distribution of component concentrations in three complex natural mixtures. For published statistical parameters of these mixtures, the distribution of minimum resolution is similar to that for the commonly assumed exponential distribution of peak heights used in statistical-overlap theory. However, these two distributions of minimum resolution can differ markedly, depending on the scale parameter of the log-normal distribution. Theory for the computation of the distribution of minimum resolution is extended to other cases of interest. With the log-normal distribution of peak heights as an example, the distribution of minimum resolution is computed when small peaks are lost due to noise or detection limits, and when the height of at least one peak is less than an upper limit. The distribution of minimum resolution shifts slightly to lower resolution values in the first case and to markedly larger resolution values in the second one. The theory and numerical procedure are confirmed by Monte Carlo simulation.     

Macrokinetics of the cationic copolymerization of isobutylene with isoprene

A theoretical model has been developed for the macrokinetics of cationic isobutylene–isoprene copolymerization in a stirred reactor and in a tubular turbulent reactor. The model provides means to calculate the reaction mass temperature, velocity, and turbulence kinetic energy fields. The adequacy of the model has been demonstrated using the Fisher criterion. Computational experiments have been carried out to estimate the effects of the catalyst concentration and the rotational speed of the stirrer (in the case of the synthesis conducted in a stirred reactor) and the effects of reaction mixture velocity and apparatus diameter (in the case of the synthesis conducted in a tubular turbulent reactor) on molecular weight characteristics of the resulting copolymer (butyl rubber).     

Mechanism of lamellar spacing adjustment in directionally frozen agar gels

A theory is presented for predicting the size of ice crystals which result from steady-state, unidirectional growth within aqueous agar gels. Cellular arrays of adjacent ice crystals were separated by an amorphous water-agar membrane at a composition near the vitrification point. Using this vitrification composition and both a steady-state condition and a minimum free energy criterion, the size of ice crystals was predicted for a given solidification velocity and diffusion condition. It was found, however, that this simple model could not predict the trend towards larger crystal sizes that was observed when the initial agar concentration in the gels increased from 3% to 10% by weight agar.     

An Experimental Study on Fluidization of Binary Mixture in Particulate Flows

In this article, we studied experimentally the fluidization of binary mixture in particulate flows. A laboratory fluidized bed is built with water being used as carrying fluid. Three types of solid particles, nylon, glass, and aluminum of the same size and different densities, were used in the experiments. We investigated the wall effect to the fluidization of a single particle, the fluidization of binary mixture of nylon and aluminum with a density ratio of 0.42, and the fluidization of binary mixture of glass and aluminum with a density ratio of 0.91. Our results show that the presence of narrow walls reduces the minimum fluidization velocity for a single particle up to 40%. We also found that in the case of binary mixture of glass and aluminum particles, uniform mixing can be easily achieved with no segregation observed; on the other hand, in the case of binary mixture of nylon and aluminum particles, significant segregation and separation are observed. Based on experimental results, correlation relationships between fluidization velocity and bed height are also reported.     

自增强高性能聚合物的成型工艺同力学性能间相关性研究——1.超高分子量聚乙烯的应力诱导结晶理论和其自增强作用

本文发展了一种高分子量聚合物熔融体的应力诱导结晶结构形态模型,它是由微晶聚集体(以下简称微区)-高分子链组网和缠结网的网络结构组成。基于上述模型,把二种网中的单个链组作为独立的统计单元和形变单元,计算了二种网中单个链组的末端距分布函数,进一步计算了二种网和总网的形变自由能。在此基础上,讨论了诱导结晶结晶机理和自增强聚合物网络自由能的依赖性,并着重地研究了超拉伸高聚物的起始熔点拉伸比间的关系。用超高分子量聚乙烯膜和超取向高密度聚乙烯纤维的起始熔点和拉伸比的实验数据进行处理,得到理论予期的近似直线关系,初步验证了聚合物网应力诱导结晶理论。     

加压流化床流化性质的实验与模拟研究

在二维射流流化床装置中,考察了压力对颗粒和气泡运动的影响规律.通过使用摄像技术详细的记录了压力下气泡的行为,并对其进行了分析,由此解决了较高压力下测量流态化性质较为困难的问题.数值研究通过CFD双欧拉模型模拟了带有V形分布器和中心射流的二维流化床内压力对气泡大小、床的膨胀率和射流深度的影响.实验和理论结果表明,在加压状态下,射流气速和分布板气速对气泡的产生、大小及形状有不同的影响.在较高的操作压力下,射流气速增加,气泡变长;分布器气速增大,气泡则变大;射流高度随着分布器气速的增加而降低.模拟结果与实验数据吻合较好,由此该模型为研究较高操作压力下射流流化床流化性质提供了有利的工具.     

MACRO-KINETICS BEHAVIOR OF GOLD RECOVERY BY ACTIVATED CARBON FIBERS（ACFs)IN A FLUIDIZED BED

The recovery of Au by activated carbon fibers (ACFs) was carried out in a 40mm diameter,1200mm height fluidizedbed The rates of reaction of the functional fibers with Au3+ in the pureaurum solution and in the aurum-containing wastewater were measured respectively at the differentsolution fiow rates, and compared with the results under the static solution conditions. Experimentalresults indicated that the reaction rates in fluidization are notably higher than those in the static stateand increase with the increase of solution flow rate. It demonstrates that the thickness of theconcentration boundary layer is decreased and a uniform temperature field is established in the beddue to increasing of the turbulent extent with the relative fiber/solution velocity.     

How energy funnels from the phycoerythrin antenna complex to photosystem I and photosystem II in cryptophyte Rhodomonas CS24 cells

We report an investigation of energy migration dynamics in intact cells of the photosynthetic cryptophyte Rhodomonas CS24 using analyses of steady-state and time-resolved fluorescence anisotropy measurements. By fitting a specific model to the fluorescence data, we obtain three time scales (17, 58, and 113 ps) by which the energy is transferred from phycoerythrin 545 (PE545) to the membrane-associated chlorophylls (Chls). We propose that these time scales reflect both an angular distribution of PE545 around the photosystems and the relative orientations of the donor dihydrobiliverdin (DBV) bilin and the acceptor Chl. Contrary to investigations of the isolated antenna complex, it is demonstrated that energy transfer from PE545 does not occur from a single-emitting bilin, but rather both the peripheral dihydrobiliverdin (DBV) chromophores in PE545 appear to be viable donors of excitation energy to the membrane-bound proteins. The model shows an almost equal distribution of excitation energy from PE545 to both photosystem I (PSI) and photosystem II (PSII), whose trap times correspond well to those obtained from experiments on isolated photosystems.     

Influence of reagent collision energy on the rotational distribution of BaO in the reaction of SO2 with Ba

The rotational distribution of the product BaO of the crossed molecular beam reaction of Ba with SO₂ was studied with interest in its dependence on collision energy. The distribution was probed by laser-induced fluorescence at collision energies ranging from 1.2 to 7.2 kcal/mol. The rotational excitation was found to increase very slowly with collision energy. The observed distribution was compared with calculations based on the phase space theory and the transition state theory. As a result, the phase space theory reproduced the observed distribution only at low collision energy, while the transition state theory reproduced it satisfactorily over a wide range of collision energy. This feature was interpreted in terms of the angular momentum restriction involved in the reaction. The present result was consistent with the angular distribution and recoil velocity spectrum study.