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Powder deposition and accumulation on walls of spray drying chamber has been known to impact spray drying processes, resulting in lower yield, frequent shutdowns, and downtimes. Critical factors that impact the extent and rate of wall deposition have been studied extensively in the chemical and food industry. In this paper, we present an atypical process yield issue wherein acceptable yield is obtained during the first batch of spray drying but undergoes significant yield loss in consecutive batches. Through understanding the interplay of the process, material properties, and equipment, we identify key mechanisms that are playing a role in causing the process yield issue. These mechanisms include surface roughness of the inner wall of the spray dryer, variation in gas flow due to the introduction of process analytical technology, start-up and shutdown operating parameters that expose the wall deposited powder from the prior batch to temperatures close to the onset of glass transition temperature and cause depression of its glass transition temperature. These factors result in more wall accumulation and impact the yield in subsequent batches. By correcting for most of these factors, the yield reduction issue was mitigated, and processing efficiency was improved. [ABSTRACT FROM AUTHOR]

The effects of lactic acid concentration (LA) and spray drying conditions on stickiness of acidified skim milk powder (SMP), which impacts process efficiency and powder properties, were examined using a fully replicated 24‐1 fractional factorial design. The wall deposition was significantly affected by LA, and yield was positively influenced by the drying temperature difference. Drying temperature difference significantly affected particle size, moisture content and water activity of acidified SMP. Particle size was also significantly influenced by nozzle airflow rate. Moisture content and water activity were significantly affected by LA, while glass transition temperature was only influenced by the outlet temperature. [ABSTRACT FROM AUTHOR]

Abstract Cascade impactors are useful tools in the measurement of particle size mass distribution of workplace aerosols. The application of cascade impactors, however, is sometimes challenging. Personal aerosol samples were collected by Sioutas cascade impactors and respirable cyclones in parallel in a silicon (Si) metal smelter to investigate the different particulate matter (PM) fractions. In a second campaign, nine new air samples were collected with the Sioutas personal cascade impactors using stationary sampling. It was found that wall deposition was substantial in the upper stages of the Sioutas cascade impactors, which meant that quite often more PM was deposited on the inner walls of the impactor than on the filter substrates. At the same time, wall deposition did most probably not affect the collection of the finest particles (< 0.25 µm). Besides wall deposition of the particles, the effect of high PM concentration on the impactor performance, particle bouncing and blow off, high particle mass loading and impact fragmentation of the particle agglomerates were considered for explaining the malfunctioning of the Sioutas impactors in the Si metal smelter. Furthermore, concentrations of the finest PM fraction (< 0.25 µm) and respirable fraction both collected by personal sampling are reported and discussed in the paper.

A new type of spray dryer was developed for drying milk and the like efficiently. To this end, freely rotatable propellers powered with air-flow were placed in the drying chamber to increase thermal efficiency and the product yield in the newly developed spray dryer. Milk samples were dried in both the developed system and a standard spray dryer to compare thermal efficiencies and product yields of each. It was observed that the propellers placed in the drying chamber of the developed spray dryer had caused a change in the flow direction of the drying air, decreased the temperature of the drying walls, and increased the thermal efficiency and product yield in drying. Consequently, in the developed dryer, the adhesion of the powder particles to the drying wall and to each other is significantly reduced, resulting in a more efficient drying. [ABSTRACT FROM AUTHOR]

Enzyme-less chemistry appears to control the growth rate of the green alga Chara corallina. The chemistry occurs in the wall where a calcium pectate cycle determines both the rate of wall enlargement and the rate of pectate deposition into the wall. The process is the first to indicate that a wall polymer can control how a plant cell enlarges after exocytosis releases the polymer to the wall. This raises the question of whether other species use a similar mechanism. Chara is one of the closest relatives of the progenitors of terrestrial plants and during the course of evolution, new wall features evolved while pectate remained one of the most conserved components. In addition, charophytes contain auxin which affects Chara in ways resembling its action in terrestrial plants. Therefore, this review considers whether more recently acquired wall features require different mechanisms to explain cell expansion. [ABSTRACT FROM AUTHOR]

Wall deposition is one of the most conventional problems in the spray drying process. The operation of a spray dryer is affected by the wall deposition fluxes inside the equipment. In this study, computational fluid dynamic (CFD) simulation was used to investigate the effect of spray dryer geometry on wall deposition. A CFD model was developed for different geometries of spray dryer with a conical (case A) or a parabolic (cases B and C) bottom. The results implied that the parabolic geometry resulted in a lower deposition rate on the spray dryer walls. A comparison of results using the P-values (F-test) of the air velocity, in the conical and parabolic geometries, showed that there was a significant difference in air stability between them. The flow field in conical geometry case A was significantly more unstable, and parabolic geometry case C produced the most uniform airflow patterns. Moreover, the higher wall shear stress in case C, with lower values of the vorticity, would result in less wall deposition. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Using POD, a new dynamical system with a small number of modes is built. [•] Two other systems known from the literature are also studied. [•] They are evaluated by comparison with DNS data for the statistics of fluid velocity. [•] Inertial particles are tracked in the velocity field generated by these systems. [•] Elastic collision of the particles with the walls and particle deposition are treated. [Copyright &y& Elsevier]

The wall deposition phenomenon in a pilot-scale spray dryer was investigated based on mathematical modeling and experimental trials. For this purpose, the governing equations were obtained and solved numerically by applying a mathematical modeling technique and an open-source computational fluid dynamics (CFD) software. The wall deposition, velocity distribution of the existing phases, and droplet trajectory in the drying chamber were determined. The effect of the operating parameters including the feed flow rate, inlet concentration of dissolved solid, and initial droplet diameter on the air flow pattern, droplet trajectory, and wall deposition was investigated. Through the experiments, the wall deposition of powder product in different positions of the drying chamber was measured. In modeling part of this study, we attempted to determine the effect of particle diameter on the percentage of wall deposition and the position where it occurred. The model results obtained for wall deposition were compared with collected experimental data and good agreement was observed. [ABSTRACT FROM AUTHOR]

This article presents both theoretical and experimental determination of the hydrodynamics of drying air in an industrial countercurrent spray dryer. Air velocity measurements were performed in selected areas of the tower to determine the flow pattern in the dryer and to collect data to validate the computational fluid dynamics (CFD) modeling and verify the results. For no-swirl operation mode, 3D CFD calculations showed high instability of the air flow in the dryer. A bent, pillow-shaped flow above the drying air inlet, which promotes deposition of particles in this area of the wall, was detected. CFD calculations also proved that when drying air was introduced to the tower tangentially; from 20° to 30° in relation to the initial air flow configuration in the spray-drying tower, the air flow was stabilized and air velocity near the wall increased, which might reduce wall deposition of particles. Comparison of experimental and theoretical results showed that the CFD model of countercurrent spray-drying process developed in this study can be used for a reliable estimation of tower performance. [ABSTRACT FROM AUTHOR]

It is now well-established that flows occurring when a jet enters a large vessel are highly transient. Such is the case in spray dryers, where the inlet gas flow can generate transient flow patterns that affect the droplet trajectories and wall deposition behaviour in the dryer significantly. This paper applies the relatively recent scale-adaptive simulation (SAS) approach to the simulation of flow in a pilot-scale dryer. It is shown that this approach produces a much more realistic flowfield than use of URANS equations that have not been adapted to resolve problems associated with their inability to predict turbulence length-scale distributions correctly. A study of the effect of the inlet swirl angle is used to illustrate some features of the transient results. This work makes it clear that transient, 3D simulations of spray dryers can now be made that capture the large-scale turbulence behaviour and that the questionable practice of using unconverged steady-state simulations to provide information is no longer justified. [ABSTRACT FROM AUTHOR]

(1,3;1,4)-β-D-Glucans consist of unbranched and unsubstituted chains of (1,3)- and (1,4)-β-glucosyl residues, in which the ratio of (1,4)-β-D-glucosyl residues to (1,3)-β-D-glucosyl residues appears to influence not only the physicochemical properties of the polysaccharide and therefore its functional properties in cell walls, but also its adoption by different plant species during evolution. The (1,3;1,4)-β-D-glucans are widely distributed as non-cellulosic matrix phase polysaccharides in cell walls of the Poaceae, which evolved relatively recently and consist of the grasses and commercially important cereal species, but they are less commonly found in lower vascular plants, such as the horsetails, in algae and in fungi. The (1,3;1,4)-β-D-glucans have often been considered to be components mainly of primary cell walls, but recent observations indicate that they can also be located in secondary walls of certain tissues. Enzymes involved in the depolymerisation of (1,3;1,4)-β-D-glucans have been well characterized. In contrast, initial difficulties in purifying the enzymes responsible for (1,3;1,4)-β-D-glucan biosynthesis slowed progress in the identification of the genes that encode (1,3;1,4)-β-D-glucan synthases, but emerging comparative genomics and associated techniques have allowed at least some of the genes that contribute to (1,3;1,4)-β-D-glucan synthesis in the Poaceae to be identified. Whether similar genes and enzymes also mediate (1,3;1,4)-β-D-glucan biosynthesis in lower plants and fungi is not yet known. Here, we compare the different fine structures of (1,3;1,4)-β-D-glucans across the plant kingdom, present current information on the genes that have been implicated recently in their biosynthesis, and consider aspects of the cell biology of (1,3;1,4)-β-D-glucan biosynthesis in the Poaceae. [ABSTRACT FROM PUBLISHER]

Calcium pectate chemistry was reported to control the growth rate of cells of Chara corallina, and required turgor pressure ( P) to do so. Accordingly, this chemistry should account for other aspects of growth, particularly the ability of plants to compensate for brief exposure to low P, that is, to ‘store’ growth. Live Chara cells or isolated walls were attached to a pressure probe, and P was varied. Low P caused growth to be inhibited in live cells, but when P returned to normal (0.5 MPa), a flush of growth completely compensated for that lost at low P for as long as 23–53 min. This growth storage was absent in isolated walls, mature cells and live cells exposed to cold, indicating that the cytoplasm delivered a metabolically derived growth factor needing P for its action. Because the cytoplasm delivered pectate needing P for its action, pectate was supplied to isolated walls at low P as though the cytoplasm had done so. Growth was stored while otherwise none occurred. It was concluded that a P-dependent cycle of calcium pectate chemistry not only controlled growth rate and new wall deposition, but also accounted for stored growth. [ABSTRACT FROM AUTHOR]

Wall deposition occurs in spray dryers when dried or partially dried particles contact and adhere to the walls during operation, thus reducing the yield of product collected. Wall deposits also present a product contamination risk and a fire or explosion risk when spray drying products that oxidize exothermically, such as milk powder. Re-entrainment is the resuspension of spray dryer wall deposits into the main gas stream for collection as product. Literature suggests that the process for re-entrainment of particles from spray dryer wall deposits is strongly dependent on particle size and gas velocity. [ABSTRACT FROM AUTHOR]

Abstract: The relative amounts of wall deposition between skim milk and maltodextrin have been compared in a pilot-scale spray dryer of 1.5 m height, equipped with a two-fluid atomizer. The atomizer air pressure was 200 kPa, the inlet air temperature was 230 °C, the liquid feed flowrate was 1.6 L h−1, and there was no swirl at the air inlet. Both maltodextrin and skim milk, both with a solids content of 9% by mass, were each sprayed in three repeat experiments. The same rates of cohesion and adhesion were observed for skim milk, while the maltodextrin (DE 18) showed lower overall deposition rates, and particularly a lower rate of adhesion than for the subsequent cohesion of particles to each other after the initial spraying period. The differences in the cohesiveness and adhesiveness of maltodextrin have also been noted by previous workers, and the lower deposition rates with maltodextrin than with skim milk are consistent with the higher glass transition temperature for dry maltodextrin. [Copyright &y& Elsevier]

This article reviews developments in the simulations of spray dryer behavior, including the challenges in modeling the complex flow patterns inside the equipment, which are often highly transient and three-dimensional in nature. There appears to be considerable scope for using CFD simulations for investigating methods to reduce the rates of wall deposition and of thermal degradation for particles by modifying the air flow patterns in the chamber through small changes in the air inlet geometry. Challenges include building particle drying kinetics and reaction processes, as well as agglomeration behavior, into these simulations. The numerical simulations should be valuable supplements to pilot-scale testing, enabling more extensive and accurate optimization to be carried out than hitherto possible. New understanding of reaction processes and materials science, in combination with recent knowledge of the application of CFD to these problems, may enable new engineered powder products to be developed from the one-step spray-drying process. [ABSTRACT FROM AUTHOR]

Abstract: Spray dryers are of considerable importance in many industrial drying operations, yet their modelling has been relatively neglected. Here we present a summary of many years work performed at Sydney University investigating the fundamental flow behaviour in dryers and their modelling using a commercial CFD code. The key point to emerge is the need to perform three-dimensional, transient calculations and to include hindered drying and wall interaction models if important issues of flow stability and wall deposition are to be studied. This issue of the need to have proper resolution of the flow at an affordable cost is addressed. [Copyright &y& Elsevier]

The pattern of wall deposits in a pilot-scale spray dryer has been studied, using skim milk, by changing the flow rate to the nozzle and measuring the resultant deposition fluxes at different positions inside the dryer. The solids concentration was maintained at 30%. The deposition was measured at three locations of the conical section and in the cylindrical section of the spray dryer. Particle deposition can be either due to the inertia of the particles or turbulent diffusion, and it is not immediately obvious which of these mechanisms is dominant. Inertial deposition appeared to be present mainly at the bottom location of the conical section and was the largest amount in quantitative terms, being at least an order of magnitude larger compared with diffusion deposition, which seemed to be dominant on the side (cylindrical) walls of the spray dryer. In addition to the above observations, the deposition patterns in the conical section have been quantified. The relative deposition flux, in m -2 , which is the ratio of the deposition flux, in g m -2 h -1 , to the solids flow rate into the dryer, in g h -1 , was between 0.04 and 0.09 m -2 at a solids concentration of 8.8% and between 0.15 and 0.4 m -2 at a solids concentration of 30%. The fused appearance of the microstructure in the wall deposits of skim milk powder, as seen in the Micro-CT study, suggests that re-entrainment of the wall deposits is unlikely. [ABSTRACT FROM AUTHOR]

Wall deposition of particles in spray dryers is a key processing problem, and information about the glass transition temperature of the amorphous material that arises from spray drying can be used to guide the selection of operating conditions that may minimise wall deposition. The glass transition temperatures for skim milk powder with various moisture contents were determined using Differential Scanning Calorimetry (DSC), and a repeatable glass transition temperature diagram was established from these results. The glass transition temperature decreased as the moisture content increased, as expected (low moisture content 1.65 g/100 g of dry powder, glass transition temperature 87.7°C; high moisture content 4.52 g/100 g of dry powder, glass transition temperature 46.7°C). The glass transition temperature was found to be virtually the same as the sticky-point temperature measured using a thermo-mechanical test. The difference is essentially due to the difference between doing a mechanical test for viscosity (sticky-point) and a phase transition measurement (DSC). [ABSTRACT FROM AUTHOR]

A method to measure the emission rate of an airborne pollutant source using a tracer gas was tested in the case of an aerosol source. The influence of particle deposition on the walls of a test room of 72 m³ was studied. The deposition rate of an aerosol of MgCl2 was determined by means of two methods: one based on measuring the aerosol concentration decay inside the ventilated room, the other based on calculation of the material mass balance. The concentration decay was monitored by optical counting and the aerosol mass concentration determined by means of sampling on a filter and analysis of the mass deposited by atomic absorption spectrometry. Four series of measurements were carried out. The curve giving the deposition rate according to the particle aerodynamic diameter (dae) was established and shows deposition rates higher than those predicted using the model of Corner. The decay method gives the best results. The study carried out has shown that the phenomenon of deposition has little effect on the measurement of the aerosol source emission rate using a tracer gas for particles of aerodynamic diameter <5 μm (underestimation <25%). For particles of a greater diameter, wall deposition is an extremely limiting factor for the method, the influence of which can, however, be limited by using a test booth of small volume and keeping the sampling duration as short as possible. [ABSTRACT FROM AUTHOR]

Cell shaping in the mesophyll of Nigella damascena was investigated with the aim of determining the origin of the arm-like protrusions, which are characteristic of, e.g., arm-palisade cells. It was found that hoops of cell wall were deposited during the early stages of cell expansion. The hoops were interconnected, thus embracing the cells with a wide-meshed net of local wall reinforcement. The pattern of wall deposition in the extra-cellular matrix correlated with a pattern of bands of microtubules in the cortical cytoplasm of the cells. During lateral expansion bulges were forced through the comparatively thin walls of spaces between the meshes, giving rise to the arm-like protrusions. After establishing the cell shape the bands of microtubules disintegrated and cell wall was uniformly deposited. The results are discussed in the context of the mode of cell shaping observed in the mesophyll of other systems and of a previous, classical hypothesis on the origin of arms in mesophyll cells. [ABSTRACT FROM AUTHOR]

At concentrations that did not affect growth, hydroxyurea and 2-deoxyadenosine inhibited DNA synthesis in Chlamydomonas. Evidence that initiation of mitosis is dependent upon completion of DNA replication was provided by the arrest of inhibited cells with undivided nuclei containing undispersed nucleoli. Initiation of cytokinesis is not dependent upon progress of nuclear division since, in arrested cells, cleavage microtubules became deployed in a phycoplast and a cleavage furrow developed fully, until obstructed by the undivided nucleus. Chloroplast constriction and division also continued independently of nuclear division. It is concluded that nuclear division, cytoplasmic cleavage and chloroplast division are in separate sequences of dependent events. This is supported by flexibility of their relative timing in successive divisions, since after the first commitment to divide nuclear division is followed by initiation of cleavage and then chloroplast division, whereas following subsequent commitments these events occur in reverse time order. This flexibility of order indicates changing rates of progress through separate sequences of events. Deposition of wall material was dependent upon the completion of cytokinesis, but this inhibition of wall deposition by incomplete cytokinesis did not extend to other daughters within the same mother cell. These observations are correlated with our earlier data concerning the rate-limiting control points for division and a model for the coordination of division events is presented. The relationships between different plant cell cycles is discussed in view of the findings presented. [ABSTRACT FROM AUTHOR]

This paper describes an approach to developing a predictive model for the spray drying of powder nutritional products, both infant and adult formulas, in order to optimize drying efficiency and avoiding the sticking of the powder on the dryer walls. The model is based on the glass transition temperature measurement by rheology method, and subsequent sticky point characterization of the products to set constrains for process variables which affect the drying efficiency and powder stickiness. Three different approaches are presented to characterize the products: 1) using theoretical data, 2) using experimental results based on laboratory tests, and 3) data from direct measurement of the dryer temperature and moisture sensors. Equations for variable manipulations to reach the target powder moisture content have also been developed. The developed models have been successfully applied in a real manufacturing environment, demonstrating how the sticky point model fits an industrial spray drying process and are a useful tool to improving efficiency and reduce quality issues related to powder properties. • Three different methods have been used to determine the glass transition temperature of powder products. • Four different powder formulas have been characterized. • Equations to predict powder moisture according to process conditions have been developed. • Sicky point models and prediction equations have been applied at industrial scale. [ABSTRACT FROM AUTHOR]

A new spray-drying system has been designed to overcome the limitations caused by existing designs. A key feature of the approach has been the systematic use of Computational Fluid Dynamics (CFD) to guide innovation in the design process. An example of an innovation is the development of a box-shaped transitional feature between the bottom of the main drying chamber and the entrance to the secondary chamber. In physical experiments, the box design performed better in all three representative operating conditions, including the current conditions, a higher feed solids concentration (30% solids rather than 8.8%), and a higher inlet drying temperature (230 °C rather than 170 °C). The current conditions showed a 3% increase in yield (solids recovery) while the 30% feed condition improved the yield by 7.5%, and the higher temperature test increased the yield by 13.5%. Statistical analysis showed that there were significant reductions in the wall flux at the high solids feed concentration. The observed deposition in the box was primarily from the predicted particle impacts by an inertial deposition process on the base of the box, which underwent little degradation due to lower temperatures. There is therefore evidence that the box design is a better design alternative under all operating conditions compared with other traditional designs. [ABSTRACT FROM AUTHOR]