Horizontal Rotary Drum Research Articles

DEM Simulation of a Rotary Drum with Inclined Flights Using the Response Surface Methodology

Conventional flighted rotary drums usually have flights parallel to the rotating axis, which cannot facilitate the axial motion of the materials in the drum. Here, a new type of horizontal rotary drum with inclined flights and beads was designed. Inclined flights are used to facilitate the axial movement of beads and material, while beads are used as fillers to increase the gas-liquid contact area and to crush the solid materials. We simulated the drum and studied the axial motion of fillers using the discrete element method (DEM). To improve the mass and heat transfer performance, we optimized the distribution of beads in the active phase. The effects of the rotational speed, joint angle, and inlet flow rate in the drum were investigated systematically. The individual effects were evaluated in terms of the mass of particles in the active phase (MAP) and passive phase (MPP), the percentage of the active phase occupied by the particles (OAR), and the axial speed (AS). The response surface methodology (RSM) was used to investigate the significant effects of the interaction between the parameters. The maximum MAP value can be obtained by the following parameters: a rotational speed of 37 rpm, joint angle of 139°, and inlet flow rate of 7.83 kg/s. The interaction between rotational speed and inlet flow rate is the most significant for MAP. The joint angle and inlet flow rate have a significant interactive effect on AS. Besides, the rotational speed, joint angle and inlet flow rate show an interactive effect on OAR and AS. Based on the optimization results, the effect of the inclined angle on the axial motion of beads was also evaluated. The axial motion of the beads occurs mainly in the active phase. Compared to the drum without inclined flights, the drum with inclined flights has an enhanced axial speed increased by 26%. This study will be helpful for the design and optimization of drums with inclined flights.

Preparation and Evaluation of Bacterial Nanocellulose/Hyaluronic Acid Composite Artificial Cornea for Application of Corneal Transplantation.

The treatment for corneal damage requires donor corneal transplantation, but there is a serious scarcity of donor corneas worldwide. In this study, we aimed to design a new artificial cornea with good cytocompatibility, excellent optical properties and suture resistance, and great moisturizing properties. A new bacterial nanocellulose (BNC) membrane with anisotropic mechanical properties and high light transmission was produced in a horizontal rotary drum reactor. However, as a potential material for artificial keratoplasty, the transparency and mechanical properties of the new BNC membrane were not satisfactory. Thus, hyaluronic acid (HA) was introduced in the BNC to synthesize the BNC/HA composite membrane by using 1,4-butanediol diglycidyl ether (BDDE) as the chemical cross-linking agent. The micro-morphology, light transmittance, mechanical properties, water content, moisture retention ability, and cytocompatibility of the composite membranes were further evaluated. HA was fixed in the BNC network by the ether bond, and the composite membrane was found to have excellent light transmittance (up to 95.96%). The composite membrane showed excellent mechanical properties, for instance, its tensile strength exceeded the human normal intraocular pressure (IOP) (1.33-2.80 kPa), the maximum burst pressure was about 130 kPa, 46-97 times that of the normal IOP, and its suture force was close to that of the human amniotic membrane (0.1 N). Based on the three-dimensional network scaffold of BNC and the high water absorption characteristics of HA, the artificial cornea had high water content and high moisture retention ability. The rabbit corneal stromal cells cultured in vitro showed that the artificial cornea substitute had excellent cytocompatibility. BDDE is the most frequently used cross-linker in most HA products in the current cosmetic medicine industry owing to its long-term safety records for over 15 years. Therefore, the BNC/HA composite hydrogel cross-linked with BDDE has great potential in artificial keratoplasty or ocular surface repair.

Manufacture of a novel anisotropic bacterial nanocellulose hydrogel membrane by using a rotary drum bioreactor

Since anisotropic hydrogel membranes have great potential in tissue engineering and bioseparation, the aim of this study was to produce an anisotropic BNC hydrogel membrane for the first time with enhanced BNC productivity by using a newly designed 30-L horizontal rotary drum bioreactor. As compared with the traditional tray static cultivation, the BNC hydrogel from the rotary drum bioreactor showed anisotropic morphology, sparser network, lower dry matter content of 0.16 w/w%, thicker fiber diameter, and lower degree of polymerization that was still 1.8 times higher than cotton, and featured with much higher ultraviolet-visible light transmittance, as well as demonstrated anisotropic tensile properties, lower Young’s modulus of 0.23 MPa and compressive modulus of 0.99 kPa. The productivity of dry and wet BNC was enhanced by 1.65 times and 3.73 times, respectively. The proposed technology may not only obtain anisotropic BNC hydrogel membranes with high transparency, but also promote the BNC productivity.

Enhanced enzymatic hydrolysis of mild alkali pre-treated rice straw at high-solid loadings using in-house cellulases in a bench scale system

In the present study, scale-up systems for cellulase production and enzymatic hydrolysis of pre-treated rice straw at high-solid loadings were designed, fabricated and tested in the laboratory. Cellulase production was carried out using tray fermentation at 45°C by Aspergillus terreus in a temperature-controlled humidity chamber. Enzymatic hydrolysis studies were performed in a horizontal rotary drum reactor at 50°C with 25% (w/v) solid loading and 9 FPUg(-1) substrate enzyme load using in-house as well commercial cellulases. Highly concentrated fermentable sugars up to 20% were obtained at 40h with an increased saccharification efficiency of 76% compared to laboratory findings (69.2%). These findings demonstrate that we developed a simple and less energy intensive bench scale system for efficient high-solid saccharification. External supplementation of commercial β-glucosidase and hemicellulase ensured better hydrolysis and further increased the saccharification efficiency by 14.5 and 20%, respectively. An attempt was also made to recover cellulolytic enzymes using ultrafiltration module and nearly 79-84% of the cellulases and more than 90% of the sugars were recovered from the saccharification mixture.

Modeling study of oil shale pyrolysis in rotary drum reactor by solid heat carrier

The mathematic model of oil shale thermal decomposition (pyrolysis) was constructed on the base of analysis of available experimental data. The model was applied to the engineering procedure that simulates the Galoter process, namely, pyrolysis of oil shale in a horizontal rotary drum reactor in contact with fine-grained solid heat carrier (hot ash). The model includes the kinetics of organic matter (kerogen) decomposition, the processes of heat and mass transfer inside of single oil shale particle, polydispersity of the particles, their fragmentation, and the secondary chemical reactions such as the carbonization of the emitted shale oil on the ash particles as well as shale oil decomposition the free volume of the reactor. Calculations show that the secondary reactions lead to reduce the shale oil yield from 0.27 to 0.13kg/kg of dry shale, what is close to operating data of the various industrial units based on the Galoter technology.

Particles motion in a cascading rotary drum dryer

AbstractA mathematical model was built and used to show the motion of particles in a cascade rotary drum dryer. In a cascade rotary drum the flights pick up the particles at a number of points in the lower half of the drum while, in the upper half, the particles fall freely. A model is derived where the drag force exerted on the particles throughout the falling period is emphasised. The motion of the particles in a rotary drum is described by three actions: Cascade; Kiln and Bouncing. In this study a horizontal rotary drum was used where both the kiln and bouncing actions have minimal effect, therefore, the focus is on the cascade motion of the particles. A characteristic of the model is the “falling number” which is found to be dependent on the curtain properties. The model has demonstrated its ability to predict the effect of many important parameters such as drying medium velocity, drum rotation speed, particle size and feeding flow rate. It has been shown that increasing the drying medium velocity by 2.5 times results in an 85% decrease in the residence time. Also, the number of falling is shown to be limited and a function of the drum rotation speed, in this case 0.59 falling per second. An important feature of this model is the ability to predict the mean resident time, contact time interval and the resting time interval. The maximum error between the predicted and the measured data was <10%.

Separation of small nonferrous particles using a two successive steps eddy-current separator with permanent magnets

The paper presents a method for separating the small metallic nonferrous particles from two component metallic nonferrous mixtures using a new type of dynamic eddy-current separator with permanent magnets. The so-called two successive steps eddy-current separator (TSECS) consists of a horizontal rotary drum covered with permanent magnets, alternately N–S and S–N oriented. The separation process takes place in two stages , first the strongly conducting particles are separated on the upper part of the drum, and then the remaining undecided and poorly conducting particles are separated at the lower part of the magnetic drum. The experimental results and comments regarding the values obtained for separation efficiency, grade and recovery for wastes consisting in Cu–Pb and Cu–Al mixtures are given. The obtained results are in good agreement with the theoretical analysis.

Solid state bioconversion of oil palm empty fruit bunches for cellulase enzyme production using a rotary drum bioreactor

Bioconversion of oil palm lignocellulosic biomass in the form of empty fruit bunches (EFB) as the major substrate into cellulase enzyme was studied in the laboratory. A fungal strain, Trichoderma harzianum T2008 was used to evaluate the solid state bioconversion of EFB for cellulase production. The study was conducted in two systems: an Erlenmeyer flask (EF, 500 mL) and a horizontal rotary drum bioreactor (RDB, 50 L), designed and fabricated locally. The highest cellulase activity on the fourth day of fermentation in the EF was 8.2 filter paper activity (FPA)/gram dry solids (gds) of EFB, while its activity from the RDB was 10.1 FPA/gds on the second day of fermentation. Glucosamine, reducing sugar and pH were also determined to evaluate the substrate uptake and growth conditions during the entire fermentation period.

Separation of small nonferrous particles using an angular rotary drum eddy-current separator with permanent magnets

The paper presents a method for separating the small metallic nonferrous particles from two component nonferrous mixtures using a new type of dynamic eddy-current separator with permanent magnets. The so called Angular Drum Eddy-Current Separator (ADECS) consists of a horizontal rotary drum covered with permanent magnets, alternately N–S and S–N oriented. The rotor is placed oblique, under the superior part of a horizontal conveyor belt, coplanar with its surface. The axis of the drum and the direction of displacement of the belt make a certain angle, depending on the physical properties of the particles subjected to the separation process. The separator functions on the basis of the jump effect of the strongly conducting particles which assume different trajectories in the active zone of the field, namely, upper part of the drum. The experimental results and comments regarding the values obtained for grade and recovery for wastes consisting in Cu–Pb and Cu–Al mixtures are given.

Flow of slightly settling slurries in a horizontal rotary drum

AbstractAn experimental study was conducted to examine the flow of slightly settling slurries in a horizontal rotary drum. The effects of the slurry flow rate, feed solids concentration, particle settling velocity and drum rotational speed on the hold‐up solids concentration were investigated.At low drum speeds, the hold‐up solids concentration was much higher than that of the feed. However, at higher drum speeds, the hold‐up solids concentration approached that in the feed. At a given drum speed, the hold‐up solids concentration was found to vary linearly with the feed solids concentration. A semi‐empirical correlation was developed to predict the hold‐up solids concentration using the drum Froude number, the single particle drag coefficient and a dimensionless slurry feed rate.

Slurry hold-up in a horizontal rotary drum with open-end discharge

The transport of sand—water slurries through a rotating, horizontal open-end drum was investigated. The effects of the slurry feed solids concentration, particle size, slurry feed rate, drum rotational speed and fluid surface tension on the drum hold-up were examined. The experimental results showed that the drum slurry hold-up and the hold-up solids concentration are strong functions of the slurry feed solids concentration, particle size, and drum speed. The effect of the water feed rate on the solids motion in the drum was found to be insignificant for the coarse ( d 50 = 2.0 mm) particles and that the solids hold-up in the drum can be predicted using the Kramers and Crookewit's model for flow of dry solids through rotary drums. The concentration of the solids within the drum was found to be higher than that of the slurry feed. The fluid surface tension had no effect on the drum slurry hold-up for the range of variables considered.

Decomposition of powders in horizontal rotary drum reactors

In a continuously operated laboratory rotary drum reactor 600 mm long and 250 mm in diameter, the mixing of cold and hot particles of soda was investigated and the mixing time was evaluated. The formal kinetics of the decomposition of sodium hydrogen carbonate to sodium carbonate (soda) was evaluated in a batch-operated drum. The distribution of residence times of the particles was measured by means of a radiotracer (Na 24) technique. The longitudinal temperature profiles and the conversion of the reaction were also measured. To describe the longitudinal temperature profile in the particle bulk without reaction, the variations of the cross-sectional area of the particle bulk and temperature of the wall must be taken into account. The heat transfer coefficients evaluated in [7] yield satisfactory results under these conditions. It is possible to calculate the longitudinal conversion and temperature profiles in the rotary drum by applying the energy and material balances for every small section of the reactor and by using reaction rates and transport coefficients estimated by separate measurements.

Longitudinal mixing in horizontal rotary drum reactors

The longitudinal mixing of sodium carbonate (soda) (mean particle size 137 μm) has been investigated in a laboratory horizontal rotary drum reactor 250 mm in diameter and 600 mm long. The distributions of residence times have been estimated by means of a pulse of a small amount of sodium bicarbonate. The concentration of the tracer at the reactor discharge has been evaluated by thermal decomposition of the samples and by measuring their weight loss. The hold-ups, the mean residence times and the variances of the distribution of residence times were evaluated as a function of the rotational speed of the reactor and the feed rate of the particles. By applying a dispersion model, the Peclet numbers were evaluated from the standardized variances and plotted as a function of the feed rate and rotational speed. The mean residence time of the particles was calculated by means of an extended model of Vahl and Kingma. They correspond with the experiments.

Transverse mixing and heat transfer in horizontal rotary drum reactors

The transverse mixing of quartz sand (mean particle sizes 157, 323, 794 and 1038 μm) and sodium carbonate (soda) (mean particle size 137 μm) has been investigated in a laboratory rotary drum reactor of 300 mm length and 310 mm diam. Solid movement in the drum was observed by means of colored tracers and successive exposures as well as by means of hot tracers and recording the local temperature in the bulk of particles. Three different types of the particles and bulk behaviour could be observed for stickly particles. The time constant of the mixing was estimated as a function of the rotational speed of the drum. The “cooling-down” curves of the bulk of particles were measured in a laboratory oven of 250 mm diam. and 600 mm length. The temperature variation as a function of the time can be described by the Newtonian cooling law, from which the heat transfer coefficient at the wall α w was estimated. The absolute value of α w's and their dependence on the contact time and particle diameter cannot be calculated by the heat penetration model, which disregards the film resistance at the bulk/wall contact. By taking into account this resistance a good quality of fitting can be achieved.

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.

Heat transfer in a horizontal rotary drum reactor

The heating of carbohydrates (particle size 15 – 100 μm) has been studied in an industrial scale horizontal drum reactor. The drum was 9.0 m long and had a diameter of 0.6 m. Strips were mounted on the inside wall and the drum was heated externally by steam. Solid movement in the drum was observed in a transparent experimental segment of the drum. From these experiments it became clear that the heat transfer between wall and solids may be described by the penetration model. In separate experiments the product of the effective thermal conductivity of the bulk material and its heat capacity has been determined. The theoretical heat transfer coefficients agree quite well with the experimental values verified by heat transfer measurements in the large-scale drum. The heat transfer coefficients between wall and gas phase and between bulk solid and gas phase have also been measured. The magnitude of the heat transfer coefficient between wall and gas phase indicates a natural convection mechanism.