In-situ monitoring of axial particle mixing in a rotating drum using bulk density measurements

A device is described for measuring changes in the local composition of particulate materials in a rotary mixer by continuously monitoring changes in the bulk density. The bulk density is measured using a small cup mounted to the mixer wall that fills with powder during rotation through the bed of particles in the lower part of the mixer. The mass of material in the cup is measured using a load cell during rotation of the cup above the free surface of the particles, and the cup empties before re-entering the particle bed. For mixing of materials with a difference in either particle density, or packing density, the localised bulk density measurement gives a good measure of mixing progress. The measurement device is demonstrated in a 1 m diameter horizontal rotating drum in which two materials are mixed along the axis of the drum. Measurements of the rate of dispersion along the axis are consistent with other work in inclined rotary kilns and can be fitted with a simple diffusion model for the axial mixing of the two species.     

Material transport in a continuous rotary drum. Effect of discharge plate geometry

Experimental results on the influence of the discharge plate geometry on the dimensionless residence time distribution (RTD) for material transport in a continuous rotary drum are described. The RTD obtained by a stimulus-response technique for the different discharge plates can be described well by the axial dispersed flow model. Based on the characteristic Peclet number of the flow regime, material flow tended more towards the plug flow condition at an intermediate size discharge opening. Calculation of the axial dispersion coefficient in each case revealed that the open-ended drum behaved more like an ideal mixer. The implication of these results on the design of continuous rotary devices is discussed.     

Calculation of phase diagrams of heterophase two- and three-component liquid mixtures ‘α-pinene-water’ and ‘α-pinene-water-ethanol’

Phase behaviors of two- and three-component mixtures ‘α-pinene-water’ and ‘α-pinene-ethanol-water’ were studied over a wide range of their composition, temperature, and pressure. Conditions were found that provide heteroazeotropic states of binary mixture ‘α-pinene-water’ and ternary mixture ‘α-pinene-ethanol-water’ depending on the ratio of ‘water/(α-pinene+ethanol)’ fractions at the ‘α-pinene+ethanol’ ratio of 1:1. Critical curves were calculated to demonstrate an anomalous dependence of these curves on the mixture composition, with the temperature minimum points typical of the mixtures that form heteroazeotropes.     

A Novel Machine Vision Based Image Analysis Method for the Analysis of Mixing Elements in Rotary Drums

Mixing performance in continuous rotary drums has been studied. The video analysis method was developed to evaluate different configurations of straight lifters in the rotary drum. The method converts a captured video into a single image, called stack image. The color marker tracking was estimated based on the color saturation of the stack image. Coefficients of variation and mixing indices were calculated from the color saturation profiles for different straight blade lifter configurations. The video analysis method was confronted to the impulse response of acid concentrations in water solutions. The developed analysis method has been superior with viscous fluids compared to traditional tracer impulse method in mixing evaluations. Water and 1% CMC-water solution were used in this mixing study for covering broadly different viscous materials. The drum lengthwise results for one lifter configuration were obtained from a single experiment due to the block representation of the image analysis method. It enables mixing analysis of axial segments and interaction analysis of mixer configurations. Thus, the axial mixing can be studied in more detail with rotary drums. The increase of lifters, residence time, and tip speed improved axial mixing in the studied experimental setup.     

Measurement of the size, shape and orientation of convex bodies

Different types of solid bodies (particles) with specific shape and size are needed for industrial processes. For spherical particles, ‘sizer’ measurements are usually reported as sphere diameters. For non-spherical particles, particle shape and especially orientation must be taken into account. Particles of a specific shape will present different views when looked at from different directions.We have employed a Camsizer^® instrument to measure the distribution of projected area under different physical conditions for solid cylindrical particles:

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Under ‘ideal’ conditions, corresponding to a uniform distribution of particle orientation, measurements agreed with predictions. The celebrated theorem of Cauchy applies only to this case.

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For two other situations, measured and predicted results differed. However, from the experimental data it was possible to infer the particle orientations and hence theoretically predict the projected area distribution. Excellent agreement between theory and practice was then restored.

     

Experimental cloud points for polybutadiene + light solvent and polyethylene + light solvent systems at high pressure

The hydrogenation of unsaturated heavy compounds is conventionally carried out in the presence of two fluid phases, because the immiscibility in the binary subsystem ‘hydrogen + heavy substrate’ cannot be overcome by adding a standard solvent. Using a supercritical or quasicritical solvent allows the hydrogen and the unsaturated heavy substrate to dissolve into a single phase. To select the operating conditions of a supercritical reactor, it is necessary to determine the phase boundaries of the subsystems ‘solvent + hydrogen’ and ‘solvent + heavy compound’. In this work, we measured cloud points for binary systems made of polybutadiene (PB) or polyethylene (PE) and a light solvent, i.e., propane or dimethyl ether (DME) or diethyl ether (DEE). The temperature range studied was from 50 to 160 °C for ‘PB + DME’ and ‘PB + Propane’ and from 100 to 190 °C for ‘PB + DEE’ and ‘PE + DEE’. We found that in PB-containing binary systems, at the ranges of conditions of the experiments, the minimum pressure required to guarantee homogeneity, at any temperature, is below 200 bar for DEE, below 300 bar for DME and in the order of 500 bar when using propane as solvent. Our data for ‘PE + DEE’ indicate the need for a minimum pressure of about 240 bar to keep the system within a single phase. The results from this work and from the literature suggest that the use of binary solvent mixtures may be convenient to carry out the supercritical hydrogenation of PB.     

De-dusting Filter Bags Reduce Indian Petcoke Mill Emissions

BWF Envirotec has installed more than 400 filter bags in a pulse jet clean filter system at an Indian industrial mill producing petroleum coke, a fuel commonly used in rotary kilns for cement production. The pulse jet filter separates the fine grain ‘petcoke’ product from the exhaust gases escaping out of the mill. The installation by the German-based company has reduced the mill’s measured emissions over the last nine months to under 10 mg/Nm³.     

Mechanism of lithium transport through an MCMB heat-treated at 800-1200 °C

Mechanism of lithium transport through a mesocarbon-microbeads (MCMB) heat-treated at 800-1200 °C was elucidated in 1 M LiPF₆-ethylene carbonate-diethyl carbonate (50:50 vol.%) solution by the quantitative analysis of potentiostatic current transient considering the difference in the relative amount of lithium deintercalation sites having different activation energies for lithium deintercalation. From the coincidence between the current transients experimentally measured and theoretically calculated based upon the modified McNabb-Foster equation along with ‘cell-impedance-controlled’ constraint as the governing equation with the boundary condition, respectively, it is suggested that lithium transport through the MCMB electrode is limited by the ‘cell-impedance’, and at the same time the difference in the kinetics of lithium transport between through the four different lithium deintercalation sites is due to the difference in activation energy for lithium deintercalation between from the four different lithium deintercalation sites present within the MCMB. Moreover, it is realised that since the degree of microcrystallinity of the MCMB is increased with rising heat-treatment temperature, the relative charge amount of lithium deintercalated from the lattice-site is increased, but that amount from the extra-sites is decreased. Thus, the inflexion point, i.e. ‘quasi-current plateau’ in the current transient is less clearly observed with rising heat-treatment temperature.     

Confocal imaging of porosity in hardened concrete

We present the results of an exploratory 3D study of fine pore structures in hardened cement paste. A laser scanning confocal microscope was used in reflected (epi) fluorescent imaging mode, allowing for the very high optical resolution of features well below 1 μm in size. Images of pore structures were captured using a ‘reverse imaging contrast’ technique where spaces in the material were impregnated with a fluorescent, dyed epoxy-resin, and scanned in the x-y plane by a laser probe. A vertical ‘stack’ of these optical sections was acquired by imaging sequentially through the z-axis. Using this technique it was possible to observe, partially hydrated cement grains, porous natural quartz aggregate interfaces, micro-cracking in the hydrated cement paste and aggregate particles, as well as fine capillary pores and very small air voids. Operating at the limit of its capability the microscope was able to perform high resolution imaging of the internal areas of partially reacted cement grains, and pore structures approximately 0.17 μm across were measured. 3D models were produced to help visualise the true morphology and distribution of porous features.     

Food treatment with high pressure carbon dioxide: Saccharomyces cerevisiae inactivation kinetics expressed as a function of CO2 solubility

Experimental survival curves of Saccharomyces cerevisiae cells exposed to high pressure carbon dioxide (HPCD) treatments under several constant temperatures (35, 40 and 50 °C), pressures (7.5, 10.0 and 13.0 MPa) and suspended in distilled water with different sodium phosphate monobasic buffer concentrations (0.02, 0.10, 0.20 and 0.40 M) were obtained. The Peleg model was applied to the isobaric and isothermal conditions described by the power law equation log[S(t)] = −btⁿ, where S(t) is the momentary survival ratio and ‘b’ and ‘n’ are the rate and the shape parameters, respectively. The values of the coefficients ‘b’ and ‘n’ were calculated for each experiment at fixed pressure and temperature. For each suspending medium the power law model was proposed to describe the combined effects of pressure and temperature. Taking into account the CO₂ solubility as a function of the sodium phosphate monobasic concentration, ‘b’ and ‘n’ were correlated to the CO₂ solubility values and temperature. An equation was proposed for ‘b’ as a function of CO₂ solubility and temperature while ‘n’ was a weak function of temperature. The resulting equation was much simpler that the one obtained correlating the microbial inactivation to pressure and temperature and, more important, it was independent of the suspending medium. The results indicate that the coupling of carbon dioxide solubility, also predicted with commercial software, and the use of inactivation models referred to solubility and temperature may provide a powerful instrument for the interpretation of microbial inactivation experiments and for the design of HPCD processes and equipments.     

Modeling and simulation of drying characteristics on flexible filamentous particles in rotary dryers

Experiments were conducted to demonstrate the effects of the drum wall temperature on the heat and mass transfer in rotary dryers. The drying characteristics of flexible filamentous particles in rotary dryers were further explored. In addition, the inlet and outlet temperatures and moisture contents of granular particles were measured. As a result, the good agreement between the simulations and experiments verified the rationale and feasibility of the numerical method. Therefore, the approach was adopted to evaluate the temperature and moisture content of wet granular particles in a rotary dryer in different conditions, for instance, drum wall temperature and rotational speed. The results revealed that the higher drum wall temperature led to hotter particles with lower outlet moisture content. Conversely, the higher rotational speed resulted in cooler particles with higher outlet moisture content due to the decrease of residence time in the rotary dryer.     

Solids mixing and residence time distribution in a horizontal rotary drum reactor

For the design of a rotary drum reactor, knowledge of the mechanism of both heat transfer and the dispersion of the solids is important. In this contribution the movement of solids in a horizontal rotary drum is investigated. Residence time distribution measurements were performed in an industrial scale reactor. Also, in model sections of this reactor, the behaviour of solids was studied visually. In the model sections the rotational speed of the drum, the number and height of the strips on the reactor wall and the angle between strip and wall, as well as the degree of filling, were varied.Model sections 0.60 and 1.40 m in diameter were used: the length of the industrial scale drum was 9.0 m, its diameter 0.60 m.Potato starch, particle size range from 15 to 100 μm, was used as the solid material.It was shown that in a drum provided with strips for rotational speeds above 5 r.p.m. and a degree of filling less than 15%, the transverse mixing was virtually completed within 2 revolutions of the drum. At these speeds and degrees of filling the extent of axial mixing is still very low as was shown by the residence time distribution measurements, the length of a mixing unit being 0.1 m or less.     

The rise of a buoyant sphere in a gas-fluidized bed

The rise velocity, V, of a single sphere, released in the bottom of a bed of sand fluidized by air, was measured: the sphere had a diameter of 9.0 or 13.2 mm; its density ranged from 900 to . These experiments with a single sphere used: (i) a bubbling bed, diameter 141 mm, with 1.05<U/U_mf<2.00, (ii) a slugging bed, diameter 24 mm, with 1.70<U/U_mf<3.20. Here U is the fluidizing velocity; U=U_mf at incipient fluidization. It was found that, for each sphere in a given bed, V=V_mf+C(U-U_mf): the constant C was up to 10 times larger for bubbling beds than slugging beds.The rise velocity at incipient fluidization, V_mf, is governed, for both types of bed, by the apparent viscosity of the incipiently fluidized bed. Therefore, Stokes's law was used to predict V_mf, but using an important modification: since each buoyant sphere appears to carry on its top a defluidized ‘hood’ of particles, Stokes's law was applied to the composite ‘particle’ consisting of the sphere plus its hood. Analysis of the measured V_mf then gave the volume of the hood, in agreement with direct measurements of it above a fixed cylinder in a two-dimensional bed. In addition, the analysis gave the apparent viscosity of the incipiently fluidized bed to be 0.66 Pa s, in excellent agreement with the estimate of Grace (Can. J. Chem. Eng. 48 (1970) 30) for similar sand.     

Effect of aging on the mechanical properties of cold-crystallized poly(trimethylene terephthalate)

The changes in the mechanical and thermal properties of cold-crystallized poly(trimethylene terephthalate) during aging at 60 and 80 °C were investigated. A significant increase in the tensile modulus and stress at yield and a decrease in strain at yield were observed for both aging temperatures. Differential scanning calorimetry (DSC) scans of the aged sample showed an endothermic annealing peak 10-20 °C above the previous aging temperature, the maximum temperature and enthalpic content of these peaks increased with aging time. Dynamic mechanical measurements indicated a relaxation process starting at about 20 °C above the aging temperature and correlate with the annealing peak detected by DSC. Density measurements and wide-angle X-ray scattering investigation revealed that neither the crystallinity increased significantly nor did the crystal structure changed. These results were explained by the existence of a third phase besides the crystalline and the ‘classical amorphous’ which involves oriented and constrained ‘non-crystalline’ polymer chain sequences close to the crystalline lamellae.     

Analysis of granule breakage in a rotary mixing drum: Experimental study and distinct element analysis

Rotary drums are commonly used in particulate solid industries for mixing, coating and reactions. The process is often accompanied by undesirable breakage of granules. For this reason, a scaled-down version is sometimes used as an attrition testing device. In this work, the attrition of granules inside a rotary drum at 18, 35 and 52 rpm drum rotation speeds for 4000 cycles is studied. The granules used in this study have been produced by extrusion and spheronisation with a size range of 500 to 1000 μm. The rotary drum has an internal diameter of 0.39 m, axial length of 0.3 m and a single baffle. The extent of breakage is quantified by sieving out fine debris which is two sieve sizes smaller than the feed particles. To relate the extent of breakage in the drum to granule characteristics, single granule impact tests have been performed on one type of granule at several velocities. The effects of particle size and impact velocity are analysed and a power-law relationship is fitted between impact velocity and single granule breakage. This information is then used to simulate granule breakage in a rotary drum by Distinct Element Method (DEM). The drum is simulated for 5 rotations at the rotational speeds stated above and the breakage rate is extrapolated to 4000 cycles where it is compared to experimental results obtained. The trends for particle breakage in both experiments (determined by sieving) and extrapolated DEM simulations are in agreement however the orders of magnitudes are different. The comparison shows that the extent of breakage obtained from extrapolated simulations is overestimated at drum speed of 35 and 52 rpm and underestimated at 18 rpm. There is close agreement between experiments and extrapolated DEM simulations for particle breakage at 18 rpm only after 4000. Furthermore, the effect of air drag on the attrition of granules by impact at a drum rotation speed of 52 rpm is investigated, where it is found to significantly reduce the breakage results.     

旋转盘式混合器混合过程数值模拟

基于旋转盘式混合器的研制实践,采用Polyflow软件在分析其速度和剪切速率分布的基础上,研究了物料粒子的动态混合过程;并从物料停留时间和最大剪切应力分布角度分析了旋转盘式混合器的分布和分散混合性能。结果表明,旋转盘式混合器可提供强大的剪切、置换和压缩作用,随着动盘旋转体转速增加,分散混合性能增强,不利于轴向分布混合。     

Potassium intercalation of carbon onions ‘opened’ by carbon dioxide treatment

The potassium intercalation of onion-like carbon (OLC) samples consisting of aggregates of carbon onions is studied with photoemission spectroscopy. OLC samples were initially prepared by annealing nanodiamonds (3-20 nm in diameter) at 1800 K in vacuum. The resulting OLC consists of closed fullerene-like shells. The ‘closed’ OLC was subsequently treated with carbon dioxide at 1020 K in order to open the carbon shells by partial oxidation to create ‘opened’ OLC. Core level and valence band photoelectron spectroscopy have been employed in characterizing the changes in electronic structure of the samples. Upon intercalation of the closed OLC with K the C1s core level and valence band features shift to higher binding energies and the density of states at the Fermi level increases, while this effect is significantly smaller for intercalated opened OLC. These results indicate that opening the shells of carbon onions allows potassium to penetrate inside the particles and thus opens up a possible route to fill carbon onions with desired substances and their application as nanocapsules.     

Binder addition methods and binder distribution in high shear and fluidised bed granulation

Fluidised beds and high shear mixers are both important in industrial granulation. The binder addition method (pouring, melt-in, spraying) affects the growth and properties of granules and is therefore of vital importance to the fundamental understanding of this detailed process. Non-uniformity of binder distribution is well known in high shear melt granulation, however, there is limited literature surrounding binder distribution in fluidised bed granulation. It was therefore the aim of the paper to compare the binder distribution using alternative addition methods in both high shear mixer and fluidised bed.In this work two binder addition methods, ‘wet’ and ‘dry’, in a fluidised bed and high hear mixer were used to successfully produce granules with a typical pharmaceutical size, 150-300 μm. The granules were analysed for final binder distribution in different size classes using Patent V blue dye and ultra-violet spectrometry.All binder addition methods supported previous work showing non-uniformity of binder distribution throughout the size classes. High shear mixer results show great similarity in binder content whichever binder addition method was chosen. This is likely to be due to the same mechanisms occurring due to the impeller forces in the process, mean while the fluidised bed results show little similarity. The binder distribution by mass is also investigated and shows that although most studies show a relative higher binder content in the larger size classes that actually the majority of binder can instead be found around the mean size of the batch.     

Catalyst ‘light-off’ experiments on a diesel oxidation catalyst connected to a diesel engine—Methodology and techniques

A methodology was developed, which helped to investigate the ‘light-off’ characteristics of a real diesel oxidation catalyst (DOC) while it was connected to a diesel engine. As a demonstration of the technique, trials were performed on a Ford 2.0 L engine, with a Pt on γ-alumina DOC (o.d. = 106 mm; length = 114 mm). By operating the engine at a constant speed (e.g. 2000 rpm), it was shown that when the engine torque was varied (e.g. from 5 to 47 N m), the gas inlet temperature to the DOC could also be varied (e.g. from 146 to 285 °C), while the gas composition and the mass flow of gas remained relatively constant—this enabled more scientific studies of catalyst ‘light-off’ to be performed on a real exhaust system. Experiments were also performed with higher background levels of a reactant (e.g. CO concentrations = 3000, 4000 and 5000 ppm), and hysteresis between ‘light-off’ and ‘light-down’ was observed. It was also shown how valuable additional information may be obtained from experiments using a thin-slice DOC (o.d. = 106 mm; length = 5 mm), and the CO inhibition effect was demonstrated on a real engine exhaust.