Liquid Feed Injection in a High‐Density Riser

Initial investigations on liquid feed injection in a high density circulating fluidized bed of fluid catalysed cracking (FCC) particles were performed by means of fast responding thermocouples and capacitance probes. The results imply very limited radial mixing between dry solids, wet solids, and liquids for injection parallel to the hot up‐streaming gas‐solid flow.     

Titania-Supported Gold Catalysts: Comparison between the Photochemical Phenol Oxidation and Gaseous CO Oxidation Performances

A series of Au/TiO₂ samples with gold loadings ranging from 0.11% to 1.26% have been prepared by deposition–precipitation, characterised by means of XRD, S_BET, XRF, TEM, XPS and DR UV–Vis techniques and tested in the gaseous CO oxidation and photocatalytic degradation of phenol in aqueous media. The catalytic performances of the solids on both reactions depend on the gold content. Besides this, the gold particle size plays a determinant role in the catalytic activity for the CO reaction, but apparently its influence on the photocatalytic activity appears to be negligible and only very small gold particles seem to participate on the photocatalytic process. On the other hand, the electronic properties of the solids, measured by its band gap energy, are a key factor in the photochemical activity but do not have a clear influence in the CO oxidation reaction.     

Solids exit discontinuity in slurry bubble columns

The exit discontinuity in slurry bubble columns, i.e., the difference in the apparent solids concentration at the very top of the column (C_t) and the concentration in the effluent (C_e), was studied in a 0.3 m ID bubble column, using air as the gas phase, water, a light hydrocarbon oil (Varsol) and trichloroethylene as liquids and glass beads of different sizes and density as solids. The results showed that the drop in solids concentration occurs in a very small layer at the gas/liquid interface. By changing the column exit configuration and removing the gas/liquid interface the exit discontinuity disappeared. The extent of the exit discontinuity depended on the liquid properties and appeared to be related to the foaming tendency of the liquid. In addition, in those systems where the exit discontinuity was significant, it depended on the solids properties and the gas and liquid superficial velocities.     

Kinetic study of concentrated clay suspension gelling by dynamic viscoelasticity measurements: effect of solids and deflocculant content

Abstract

The effect of solids volume fraction &phis; and state of deflocculation on the gelling kinetics of clay suspensions has been studied, using a new model based on the following premisses: the recovery of structure after shearing takes place by two consecutive steps of very different velocity; the structure arising is homogeneous; and the rate at which interparticle bonds are formed depends on the number of bonds that can potentially arise but have not yet formed. The evolution of G′ and G″ with time was determined continuously for each suspension by very small amplitude dynamic oscillation tests. An empirical equation has been derived, based on the model described, which satisfactorily describes the kinetic process. It has been established that the gelling process rate rises as solids content decreases and/or deflocculant content increases. The starting and equilibrium storage moduli rise as solids content increases and deflocculant content decreases.     

Three-dimensional vibrational mixing

When working with disperse solid matter systems, one uses the effect of vibration in numerous processes. Solid matter mixing with vibration has only occurred in very simple units up to now. By means of the 3D-vibrational mixer from the company Kuston, Kleve, the influence of vibration on bulk materials and new mixing techniques are demonstrated. The 3D-vibrational mixer is suitable for liquids and solids, does not require mixing tools that need to be cleaned, and does not carry out rotary motions which would hinder incoming lines. It is used for mixing small amounts, where the mixing tank can be used simultaneously as the transportation container, so that a transfer is unnecessary. With the aid of 4 linear motors, the vibrational amplitudes and the frequencies can be varied within wide boundaries in all three spatial directions. By analyzing the vibrational system by means of Lissajous figures, it can be demonstrated that the optimal mixing effect occurs in the case of small frequency differences between the three axes. For freeflowing bulk materials, the best possible mixing state, the uniform coincidence mixing, is achieved after 2 min.     

Thickener dynamic analysis,accounting for compression effects

The dynamic behaviour of the thickening zone of a continuous thickener has been analysed, and numerical solutions of the resulting differential equations obtained for a range of conditions. For high throughput, low underflow concentration operation, mechanical (compressive) support of the solids can be very small, providing that sludge funnelling is taken into account. Neglecting mechanical support in such cases gives results which are fairly accurate, but limited by the presence at the top of the sediment of a shallow layer in which mechanical support is significant. For low throughput, high underflow concentration operation hydrodynamic support of the solids can be small, and its neglect gives again fairly accurate results. In general, both hydrodynamic and mechanical support of solids have to be taken into account.     

Recovery (spring-back) of polyethylene from an imposed bend

Measurements have been made of the recovery of polyethylene samples from bending deformations of varying severity. The amount of spring-back from a severe bend is quite different for different densities (degrees of crystallinity), especially at short times after release, being much greater for lower-density polyethylenes. Short-term spring-back measurements thus afford a simple and rapid means of determining the approximate density. Immediate recovery is small, 5 to 15 percent, and is in rough accord with expectations for elastic-plastic solids. A major protracted recovery process follows. It is accelerated by raising the temperature, in reasonable agreement with the WLF relation for segmental mobility. It is therefore attributed to retarded molecular motions in the amorphous fraction. Final recovery is greater for lower-density materials, but it is incomplete even after very long times or for mild degrees of bending. Thus, some irreversible processes appear to take place, even when bending strains as low as 3 percent are imposed.     

流动方向对循环流化床中颗粒混合行为的影响

对循环流化床提升管及下行床两种不同气固流动方式对颗粒混合行为的影响进行了较为深入的对比分析，发现在影响循环流化床颗粒混合的众多因素（如操作条件、床层直径、颗粒性质及床层内构件等）中，气固流动方向是影响颗粒轴向混合的最主要因素．当气固流动为顺重力场时（下行床），颗粒的轴向混合很小，流型接近平推流；当气固流动为逆重力场的提升管时，轴向颗粒混合将成倍增大，颗粒流动远离平推流流动．分析表明，下行床中颗粒混合仅为单一的弥散颗粒扩散，而提升管中则存在着两种颗粒混合机制：弥散颗粒扩散及颗粒团扩散．弥散颗粒的扩散基本以平推流的形式通过循环流化床，提升管中大量的颗粒轴向返混归因于颗粒团的严重返混并由此形成了提升管中颗粒停留时间的双峰分布．     

Dolomite decomposition in a high temperature fluidised bed reactor

The decomposition of dolomite was investigated in a bench-scale fluidised bed reactor (30 cm diameter) at temperatures between 600°C and 1000°C in batch and continuous operations. The composition of the solids was determined by X-ray analysis, the gas composition by infrared (i.r.) spectroscopic analysis. The reaction kinetics were investigated in a small fluidised bed (2.6 cm diameter) as well as in the bench-scale equipment and compared with kinetic data evaluated from differential thermal gravimetric (DTG) curves. The measurements were carried out by adding small amounts of dolomite into the isothermal fluidised bed. The resulting CO₂ concentration within the gas could then be very low, thus MgCO₃ and CaCO₃ decompose as parallel reactions (singlestage reaction). At somewhat higher CO₂ gas concentrations prevailing in technical operational conditions the decomposition mechanism changes into a two-stage reaction where MgCO₃ decomposes first. The bed temperature, pressure drop, superficial gas velocity, solid conversion, and specific interfacial area of solids were determined as functions of time and/or reactor wall temperature with a constant temperature increase rate for batch runs. The distributions of the residence time of solids indicate that in the continuously operated fluidised bed well-mixed conditions prevail. The concentrations of dolomite, CaCO₃, MgO, CaO, and solid conversion as well as the specific surface area of particles were determined as functions of the mean residence time in the continuous reactor. By means of the CO₂ concentration in the gas phase and the mean residence time the conversions of the consecutive reactions can be controlled.     

Fundamental studies on the hydrodynamics and mixing of gas and solid in a downer reactor

The effect of flow direction on hydrodynamics and mixing in the upflow and downflowcirculating fluidized beds is discussed in details.Similar profiles of gas and solids velocities andsolids concentration are found in both risers and downers.When the flow is in the direction ofgravity(downer),the radial profiles of gas and particle velocity are more uniform than that inthe riser,the solids mixing is very small and the flow pattern approaches plug flow,while theflow is against gravity(riser),the solids backmixing significantly increase and the flow pattern isfar from plug flow.Among many of factors the flow direction has the largest influence onhydrodynamics and axial mixing of gas and solids.     

湍动流化床过渡段固含率分布特征的实验及数值模拟

在湍动流化床中,过渡段对于包括甲醇制烯烃在内的气固催化快反应有着重要的作用。采用PV6D反射型光纤探针对内径95 mm的湍动流化床内过渡段的固含率分布和脉动参数进行了测量,分别考察了表观气速和静床高的影响,并采用修正的基于颗粒动力学的三段曳力双流体模型进行模拟。实验表明,湍动流化床过渡段中固含率的轴向分布呈现S型和指数型两种类型,固含率轴向与径向分布都在过渡段内出现最大梯度,表明过渡段中固体浓度分布比稀相段和密相段更不均匀。表观气速和静床高的变化将导致S型和指数型分布的相互转变,并且对过渡段底部与壁面附近的固体高浓度区影响最为显著。局部固含率脉动概率密度分布表明,在静床高较小时,随着气速的增大,床层下部气含率最大值位置将从中心区移动至环隙区,呈现气含率的双峰型分布。本文提出的修正三段曳力模型考虑了颗粒团聚的影响,对过渡段中分布板影响区之外的固含率分布均能较好地模拟。     

Impact of Aggregate Size and Structure on Biosolids Settleability

Settling is an important solid–liquid separation process in wastewater treatment. While solids concentration is an important factor influencing settling velocity of particles, other solids characteristics including particle size, shape, and structure also play an important role in settling rate. The “compactness” of bacterial aggregates in particular is recognized to exert a great influence on solid phase dynamic behavior since it has a substantial effect on fluid flow through the aggregate, which, in turn, affects the particles buoyancy. With the recognition that biosolids structure can be described by fractal methods, we now have a convenient means of parameterizing aggregate “compactness.” In this article, we examine the fractal nature of bacterial aggregates (which are the main component of the solids in wastewater treatment processes) using small angle light-scattering methods and assess the impact of aggregate compactness (as described by fractal dimension) on settling velocity of both single aggregates and large aggregate clusters. The results indicate that settling velocity is strongly dependent on both size and aggregate structure, with the larger and less compact flocs settling more quickly as a result of the significant extent of flow through the bacterial assemblages.     

Effects of Particle Size and Molecular Weight of Polyethylenimine on Properties of Nanoparticulate Silicon Dispersions

The effect of particle size on the zeta potential and rheology of nanoparticulate SiO₂ dispersions stabilized with the polymer polyethylenimine (PEI) was investigated experimentally. The particle size and molecular weight of the polymer had only a small influence on the amount of PEI needed and the achieved zeta potential of the suspensions. The polymer concentration range within which a stable dispersion could be produced was very narrow for the smallest particle size. Higher-molecular-weight PEI was more suitable to stabilize small particle dispersions. Under optimum conditions, Newtonian flow behavior was achieved for dispersions of 20 nm particles with a solids content as high as 25 vol%.     

Preparation of bitumen from oil sand by ultracentrifugation

Ultracentrifugation was investigated as a means to obtain solvent-free bitumen from oil sand. The bitumen from three oil sands of varying grades was separated by placing the sands in specially designed tubes and centrifuging for 2 h at 198 000 at 20 °C. For all grades of oil sand, approximately 70% of the bitumen was recovered. The recovered bitumen was compared to the residual remaining on the sand, and to that extracted by the conventional Soxhlet technique. The ultracentrifuged bitumen contained some emulsified water and a small amount of fine solids. The solvent-extracted material was water-free, but contained a small amount of residual solvent and fine solids. The ultracentrifuge caused some fractionation of the bitumen, resulting in a product slightly enriched in asphaltene components compared to the solvent-extracted material. The residual bitumen remaining on the sand was correspondingly slightly depleted in asphaltenes. However, as evidenced by gas Chromatographic simulated distillation data, ultracentrifugation did retain the light (180–220 °C) components of the bitumen which were lost during the solvent removal step following solvent extraction. Other analyses such as density, viscosity and elemental composition verified that ultracentrifugation resulted in some fractionation of bitumen components.     

Electric spark and esd sensitivity of reactive solids (primary or secondary explosive,propellant, pyrotechnics) part one: Experimental results and reflection factors for sensitivity test optimization

An experimental study shows that spark energy transfer mechanisms are different for the explosive alone (HMX) and for the explosive containing 1% of graphite. This study is completed by literature data and underlines the need for parametric studies by systematically varying the electrodes gap as well as the spark duration to determine the true minimum value of the ignition energy. Grain size and shape are very important factors. The influence of the electrode shape is also discussed, as well as the environmental conditions. These data allow us to determine the conditions for testing the electric spark sensitivity of solids. The tests are then performed at a small scale. Moreover, for ionic solids or substances made of an electrically insulating matrix containing conductive inclusions, particular phenomena appear when they are submitted to electric fields for a certain time. These phenomena justify the development of specific tests to determine the capacitive discharge sensitivity.     

Impact of Aggregate Size and Structure on Biosolids Settleability

Settling is an important solid-liquid separation process in wastewater treatment. While solids concentration is an important factor influencing settling velocity of particles, other solids characteristics including particle size, shape, and structure also play an important role in settling rate. The “compactness” of bacterial aggregates in particular is recognized to exert a great influence on solid phase dynamic behavior since it has a substantial effect on fluid flow through the aggregate, which, in turn, affects the particles buoyancy. With the recognition that biosolids structure can be described by fractal methods, we now have a convenient means of parameterizing aggregate “compactness.” In this article, we examine the fractal nature of bacterial aggregates (which are the main component of the solids in wastewater treatment processes) using small angle light-scattering methods and assess the impact of aggregate compactness (as described by fractal dimension) on settling velocity of both single aggregates and large aggregate clusters. The results indicate that settling velocity is strongly dependent on both size and aggregate structure, with the larger and less compact flocs settling more quickly as a result of the significant extent of flow through the bacterial assemblages.     

Catalytic Removal of Toluene in Air over Co–Mn–Al Nano-oxides Synthesized by Hydrotalcite Route

Co–Mn–Al hydrotalcite type solids were synthesized as precursors of catalysts for the total oxidation of toluene in air. For the as-prepared solids, XRD measurements indicate the coexistence of hydrotalcite and MnCO₃ phases. When calcination is performed at 500 °C, different mixed oxides are found as a function of Co:Mn molar ratio and preparation method, and very high specific surface areas were obtained for the Co–Mn solids. The comparison of catalytic activities in the presence of calcined hydrotalcites with those in the presence of calcined hydroxides evidences the superiority of the first oxides due to their higher reducibility. Co–Mn–Al nano-oxides synthesized using hydrotalcite type solids as precursors, are very promising candidates for the substitution of noble metal based solids.     

Theory of Clarifier Operation. II. Hindered Settling of Flocculating Systems in Rectangular Clarifiers

Abstract

The operation of rectangular clarifiers is simulated by means of the continuity equations. The model permits the examination of hindered settling of solids which are undergoing flocculation and floc disruption. The steady-state solution requires very modest amounts of computer time and also lends itself to the analysis of quiescent settling in jar tests.     

Experimental study of the elutriation of particles from rotary kilns

The elutriation rate of fine solids from a rotary cylinder was studied as a function of air flowrate, rotational speed, percentage of solids fill, wall roughness and fine solids fraction. Local fines concentrations measured in the gas phase showed that solids travelled predominantly in saltation within 2 cm of the bed surface. The elutriation rate was influenced by cylinder exit dam geometry, wall roughness and segregation patterns in the bed. Gas velocity showed a very strong effect, with elutriation rate varying with velocity to a power of 4.6. An entrainment mechanism has been formulated based primarily on the collision of saltating particles on the solids bed.     

Cluster particle number and granular temperature for cork particles at the wall in the riser of a CFB

Operating conditions within a circulating fluidized bed (CFB) many times results in the grouping of circulating particles into clusters. Because of their different relative motion with respect to the balance of the flow, these clusters are believed to demonstrate different transport properties when compared to the balance of the particles. To investigate these differences, it is first necessary to have an objective means of identifying those particles that are within a cluster and those that are not. The concept of granular temperature is used to make this distinction. Using laser Doppler velocimetry (LDV) data for 800-μm cork particles, it has been found that groupings of six or more particles demonstrate a different distribution of granular temperatures than groupings with fewer particles. Based on this fact, it is concluded that groups of six particles as measured in the axial flow direction are the fewest number which can be still considered to be in a cluster for this bed material. Additionally, particles considered to be in the dispersed phase have granular temperatures which are low at low solids concentrations, again low at very high solids concentrations and pass through a maximum at intermediate values of solids flow and gas flow.