Liquid Spray Rate Research Articles

Influence of cycle time distribution on coating uniformity of particles in a spray fluidized bed by using CFD-DEM simulations

Cycle Time Distribution (CTD) plays a critical role for determining uniformity of particle coating in spray fluidized beds. However, the CTD is influenced by both geometrical structure and operating conditions of fluidized bed. In this study, a spray fluidized bed of coating process is simulated by a comprehensive Computational Fluid Dynamics-Discrete Element Model (CFD-DEM). To achieve different behaviors of CTD, some modifications are designed on a pseudo-2D internally circulating fluidized bed, which traditionally composes of a high-velocity upward bed and low-velocity downward bed. These modifications include making the air distributor slope and/or laying a baffle in the downward bed. First, the CTD and evolution of particle size distribution under different bed structures are compared. The CTD directly influences the coating uniformity. By making the particles flowing along a parallel direction in the downward bed through the geometrical modifications, the CTD becomes narrower and the coating uniformity is significantly improved. Second, under the optimized bed structure, the influence of operating conditions on the coating uniformity is studied. Properly increasing the fluidization gas velocity and the fluidization gas temperature and reducing the liquid spray rate can improve the coating uniformity.

Experimental Observation of a Regression Dependence for Hydrodynamic Performance of the Regular Packing

The investigational studies of regression dependence of the new efficient regular packing bed’s flow friction on gas velocity and liquid spray rate has been carried out. The tests were made by the procedure of a complete two-factor experiment. On account of experiment design matrix, there are four tests to be made to determine the regression dependence. It is found that the packing bed’s flow friction builds up along with increase of superficial gas velocity and liquid spray rate. The regression dependence that puts packing bed’s flow friction in touch with superficial gas velocity and liquid spray rate is procured. The specific dependence is valid for air velocity 1.21-3.12 m/sec and liquid spray rate 0.0080-0.0304 m3/(m2 sec). The conclusion on significance of regression dependencies has been made in terms of Student’s t-test. The sufficiency of regression equation has been inspected via the Fisher’s criterion. The resulting regression equation can be utilized in the design and engineering process of absorbers with the shock-spray packing.

Modeling fluidized bed impregnation of active pharmaceutical ingredients onto porous excipients

Impregnation of active pharmaceutical ingredients (APIs) onto porous excipients offers several advantages to solid dosage pharmaceutical preparation over conventional formulation methods. Previous work has successfully introduced fluidized bed (FB) impregnation of APIs onto porous carriers as a robust manufacturing process with numerous benefits (easy to implement, excellent blend uniformity and dissolution kinetics, stabilization of amorphous APIs). This study aims to develop a simple, multi-scale modeling approach to FB impregnation. The model consists of three main parts: (1) an energy/mass balance on the FB and an evaporative flux calculation, (2) an impregnation model for a single particle and (3) a drying model for a single particle. The model allows the calculation of some important process parameters (e.g. product temperature, maximum liquid spray rate) for given drying conditions. These are important process parameters needed to achieve successful impregnation. The model accounts for convection, diffusion and crystallization within the particle. The main characteristic is the 2D modeling of the liquid and API distributions within the particle during impregnation and drying. Several cases are presented to illustrate the effect of some material properties (fast crystallization, slow diffusion, low porosity) on the final API profile. Simulation results regarding API profiles of impregnation are in a very good agreement with experimental measurements carried out in our previous work.

Model Development and Validation of Fluid Bed Wet Granulation with Dry Binder Addition Using a Population Balance Model Methodology

An experimental study in industry was previously carried out on a batch fluid bed granulation system by varying the inlet fluidizing air temperature, binder liquid spray atomization pressure, the binder liquid spray rate and the disintegrant composition in the formulation. A population balance model framework integrated with heat transfer and moisture balance due to liquid addition and evaporation was developed to simulate the fluid bed granulation system. The model predictions were compared with the industry data, namely, the particle size distributions (PSDs) and geometric mean diameters (GMDs) at various time-points in the granulation process. The model also predicted the trends for binder particle dissolution in the wetting liquid and the temperatures of the bed particles in the fluid bed granulator. Lastly, various process parameters were varied and extended beyond the region studied in the aforementioned experimental study to identify optimal regimes for granulation.

Characterization of liquid entrainment in a counter flowing gas using Phase Doppler Interferometry

An 8inch ID spray column was used to characterize the entrainment of water droplets into counter flowing air. The ability of Phase Doppler Interferometry (PDI) to measure the size and velocity distributions of entrained droplets resulting from a single full cone Bete® nozzle was proven, and the total volume of liquid entrained was gravimetrically quantified. The experimental setup consisted of a variable speed pump and air blower which allowed for droplet measurements over a range of gas and liquid rates. This work illustrates the effect of nozzle supply pressure and air rate on the entrainment rates and PDI measured droplet size distributions. The magnitude of the droplet size distribution, as well as the rate of entrainment, increased with the liquid spray rate, but the unimodal distribution peak diameter remained consistent. The same conclusion was true at an increased gas rate, in addition to an overall decrease in entrained droplet Sauter mean diameter and an increase in the total liquid entrained. The use of a theoretical entrainment model with PDI measured droplet diameters was explored. Applying the measured PDI diameters was found to significantly decrease the estimated entrainment from the theoretical entrainment based on a droplet buoyancy concept. This effect was further explored by comparing the sizing of a de-entrainment mesh pad for both cases.

Water Dispersion and Distinction of Its Low-Head Efflux Down Through the Small Hole

Background. Low-head dispersion of water by impact with a hard surface is suitable for organization of water freezing on vertical surfaces and on horizontal attachments with icicles. When placing a set or sets of devices for water discharge, we have to consider radiuses of drops dispersion, and when irrigation of vertical surfaces, we have to consider the width of the moistened area and the height of drops flow-up above the striking face that depends on drops’ motion trajectory.Objective. The task of our work is the detailed study of the primary (after discharge from a hole (a nozzle)) and also of the secondary liquid atomization on drops. It is of the utmost importance to explore the heights of drops dispersion and also width and height of wetting of a vertical surface depending on distance to the center of percussion.Methods. At irrigation of horizontal attachments, the nearby holes for water discharge are disposed at close range or in the distance, which is smaller than the peak radius of drops dispersion, taking into account reduction in irrigation density when radius increases. At irrigation of vertical attachments, the distance from the center of percussion is selected, depending on objectives to the liquid spray rate and to the initial irrigation point under the striking face, which constitutes from 60 to 150 mm for conditions of research in the higher point.Results. As a result of pilot studies of characteristics of primary (after discharge from the small-diameter hole) and secondary (after impact with the horizontal surface) drops dispersion, we found that the maximum height of drops upsurge is increased with the altitude of their recession and is horizontal-bias away from the center of percussion. The width of the wetted vertical surface area is determined geometrically on the basis of maximum dispersion ranges in a percussion plane.Conclusions. For the holes with the diameter of 1-2 mm in the reviewed pressure ranges (up to 350 mm w.c.), the correlation of discharge from pressure is straight-line, in contradistinction to level 0.5 for the correlation known for large-diameter holes. Dependencies to determine the range of primary drops dispersion after the discharge from a hole are obtained. Experimental data on the width of the wetted vertical surface area and on the maximum height of drops upsurge over the percussion plane are obtained.

NEW STRUCTURED PACKING CUB FOR PURIFICATION OF EXHAUST GASE

New structured packing for heat and mass transfer processes named CUB is presented in our article. The packing can be applied in packed towers for exhaust gas cleaning instead random packing, for example, rings type that are the most used in such processes. The advantages of the new packing over random packing are lower pressure drop, capability of purification and as a consequence long-term service of the packing. The researches of intensity of liquid-phase mass-transfer in packed bed depending on liquid spray rate and gas velocity were carried out. Obtained data show that packing CUB is more effective than the most popular type of structured packing under all other conditions being equal. As experimental data shown heat transfer coefficient was up by 17% and mass transfer coefficient was up by 51%. We found out optimal geometry of cross section of the new packing, namely, number of elements and parameters of one element. The new construction of structured packing is applicable for both type of column cross-section round and square.

Aqueous Benzene Oxidation in Low-Temperature Plasma of Pulsed Corona Discharge

AbstractWastewaters polluted with non-biodegradable volatile organic compounds (VOCs), such as aromatic substances, present a growing problem meeting no adequately affordable technological response. Low-temperature plasma generated in the gas-phase pulsed corona discharge (PCD) presents competitive advanced oxidation technology in abatement of various classes of pollutants, although the process parameters, the pulse repetition frequency and the liquid spray rate, require optimization. The experimental research into aqueous benzene oxidation with PCD was undertaken to establish the impact of the parameters to the energy efficiency. The oxidation reaction was found under the experimental conditions to mostly proceed in the gas phase showing little influence of the pulse repetition frequency and the gas-liquid contact surface. Oxidation of benzene and, presumably, other volatile pollutants in the volume of PCD reactor compartment presents an effective strategy of aqueous VOCs abatement.

A mechanistic population balance model for granulation processes: Effect of process and formulation parameters

This work is concerned with the theoretical development of a semi-mechanistic aggregation kernel in a population balance model (PBM) which takes into account the effect of droplet spreading on a particle surface that aids in the coalescence of particles. Empirical aggregation kernels are more commonly used in simulations however they do not reflect the true physics of the system. The proposed kernel is computationally less expensive, yet it takes into account the various key operating parameters that affect the process. The kernel has been validated qualitatively and the lumped and distributed properties show good agreement with the expected behavior of the process. The various empirical parameters present in the granulation model have been identified and expressed as a function of the measurable operating quantities, thus providing a better knowledge regarding the effect of the process parameters on the final product with the help of a more fundamental, first principle based model. A detailed sensitivity analysis (involving viscosity, impeller speed, contact angle and liquid spray rate) has also been conducted in order to study the influence of the process parameters on the final granule properties. This knowledge provides a theoretical basis for the high-shear wet granulation process design space development. The model has also been able to successfully capture the steady and induction behavior of the process under the expected operating conditions.

Multi-component population balance modeling of continuous granulation processes: A parametric study and comparison with experimental trends

Abstract In the recent few years, continuous processing has been considered as a promising process alternative to batch processing in pharmaceutical manufacturing. Via a novel population balance model framework, a multi-dimensional multi-component model for a continuous granulation process was developed, describing time evolutions of distributions with respect to granule size, liquid distribution and granule composition. A parametric study was performed to analyze the effects of various process and design parameters, including granulator size and configuration, liquid spray rate and particle velocity, on evolutions and distributions of key granule properties. Simulation results capture experimentally observed sensitivities and trends thus demonstrating the use of a model-based framework for granulation process design, control and optimization to enable QbD in drug product development.

Identification of thermal zones and population balance modelling of fluidized bed spray granulation

Air temperature measurements in a fluidized bed of glass beads top sprayed with water showed that conditions for particles growth were fulfilled only in the cold wetting zone under the nozzle which size and shape depended on operating conditions (liquid spray rate, nozzle air pressure, air temperature, and particles load). Evolution of the particle size distribution during agglomeration was modelled using population balance and representing the fluidized bed as two perfectly mixed reactors exchanging particles with particle growth only in the one corresponding to the wetting zone. The model was applied to the agglomeration of non-soluble glass beads and soluble maltodextrin particles spraying respectively an acacia gum solution (binder) and water. Among the three adjustable parameters, identified from experimental particle size distributions evolution during glass beads agglomeration, only one describing the kinetics of the size distribution evolution depended on process variables. The model allowed satisfying simulation of the evolution of the particle size distribution during maltodextrin agglomeration.

Fluidized drum granulation: studies of agglomerate formation

Agglomerate formation in fluidized drum granulation was studied experimentally using a 0.3 m diameter laboratory fluidized drum granular. Glass ballotini of various sizes were coated molten paraffin wax. The effect of particle size (1.5 to 8 mm), liquid spray rate (17 to 43 g/min) and drum speed (20 to 40 rpm) on the fraction of agglomerates formed was measured. The formation of agglomerates was controlled by collisions between wetted granules in the falling particle curtain in or near the spray zone. There is a sharp transition between high fractions of agglomerates (non-inertial regime) and almost no agglomerates (coating regime) as particle size increases. This transition point increases strongly with increasing liquid spray rate but is only a slight function of drum speed. These results agree, qualitatively and quantitatively, with the granulation regime analysis proposed by Ennis. Tardos and Pfeffer, Powder Technol., 65 (1991) 257 which is based on the balance between inertial energy and viscous dissipation during a collision between two wetted granules. Analysis of the data shows the characteristics collision velocity is low, of the order of 0.02 m s −1, and this is consistent with agglomerates forming in the falling particle curtain near the spray zone. A better understanding of particle-particle and particle-binder interactions in the spray zone is needed to extend the theoretical analysis and develop design and scale-up rules.

The influence of liquid spray rate and atomizing pressure on the size of spray droplets and spheroids

The effects of liquid spray rate and atomizing pressure on the size of spray droplets and spheroids were investigated in this study. The range of droplet sizes tended to narrow and relatively smaller droplets were formed at higher atomizing pressures. When liquid spray rate was increased, the droplets were larger and had a wider size range. Although alterations in liquid spray rate could affect spray droplet size, greater changes in droplet size were achieved by varying atomizing pressure. In these investigations, changes in spray droplet size and atomizing pressure did not appear to greatly affect mean spheroid size. However, the presence of an atomizing pressure was necessary for the even distribution of the moistening liquid to reduce localized overwetting during spheronization by rotary processing. The amount of oversized particles may thus be decreased and a more uniformly sized yield may be achieved with the use of relatively higher atomizing pressures. With a fixed volume of moistening liquid sufficient for spheronization, larger spheroids were produced with increasing liquid spray rates. The increased wetting per unit time resulted in the formation of larger nuclei and enhanced the growth rate of spheroids.