Industrial Spray Research Articles

Numerical Calculations of Spray Roasting Reactors of the Steel Industry with Special Emphasis on Fe2O3‐Particle Formation

AbstractThis work presents numerical calculations for the lay‐out of spray roasting reactors for the steel industry. In these reactors, a pickling liquor based on water and HCl containing FeCl2 is regenerated in a combustor leading to the formation of Fe2O3 particles. For the lay‐out of these reactors, detailed knowledge of the flow and temperature field, the associated gas phase reactions, and especially, of the formation of the Fe2O3 particles is required. An extended particle formation model is presented which is based on earlier work. Finally, results for an industrial spray roasting reactor are given showing the potential of the numerical tools developed for the improvement of the technical lay‐out of such thermal reactors.

Production of spherical and uniform‐sized particles using a laboratory ink‐jet spray dryer

AbstractThere is a need in the area of particle technology and powder manufacturing to produce particles with uniform characteristics for attaining stringent product quality. In this paper, a new concept of spray drying is proposed to assess the possibility of adapting the same concept to industrial spray drying operations for producing spherical and uniform‐sized particles. This concept is based on ink‐jet technology, where single streams of identical droplets can be achieved using ink‐jet devices. The ink‐jet device, similar to nozzles found in office ink‐jet printers, was introduced to spray drying operations as an innovative atomizer because of its attractive ability to produce monodisperse droplets with a precise control over droplet characteristics. In this paper, a new concept of single stream drying and some calculations on feasibility of a newly built Ink‐Jet Spray Dryer (IJSD) are discussed. The single stream drying technique could provide a promising tool for producing uniform particles and also for testing and designing new products. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

Simulation of an Industrial Spray Dryer and Prediction of Off-Design Performance

A computational fluid dynamic model along with a new drying kinetics model was employed to simulate the spray-drying performance of an industrial-scale co-current spray dryer for a relatively heat-sensitive product. Predictions are compared with experimental measurements made on a full-scale spray dryer. Satisfactory agreement was achieved. Predictions of zones where deposits are likely to occur are close to those in operational experiments. Off-design performance predictions were also made to show the effects of various operating parameters on the dryer performance, which can be used to improve the dryer efficiency and minimize wall deposits.

A study on the aerodynamic instability of attenuating liquid sheets

We describe the characteristics of a radially spreading unstable liquid sheet in quiescent air via optical measurement techniques and linear instability theory. A high speed CCD camera system and a complimentary laser refraction method were employed to measure the intact sheet diameter, unstable wave lengths, wave speed, wave frequency spectrum and spatial wave growth rates. Linear instability models for thinning, viscous and inviscid liquid sheets, which are available from the literature, allow for a comparison of experimental data and predicted sheet behaviour. The last section evaluates the differences and similarities between the current liquid sheet experiment and industrial spray applications such as fuel atomisation via pressure-swirl nozzles.

Dermal, inhalation, and internal exposure to 1,6-HDI and its oligomers in car body repair shop workers and industrial spray painters

Objectives: To study inhalation and dermal exposure to hexamethylene diisocyanate (HDI) and its oligomers as well as personal protection equipment (PPE) use during task performance in conjunction with urinary hexamethylene...

Imaging Diagnostics Study on Obliquely Impacting Plasma-Sprayed Particles Near to the Substrate

Real time close-up images of in-flight particles plasma sprayed onto a substrate and in freestream condition (without substrate present) are captured. Besides the images, particle behavior in terms of temperature, velocity, and heading are measured by the Spray Watch particle imaging diagnostics system. The monitoring and measurement of particle behavior have been performed for substrates inclined at various angles to investigate the effect of the substrate on particle behavior. The close-up images show that particles propelled from the torch travel with high momentum and are not affected by the substrate and inclination angle. Quantitative analyses of the particle average velocity and heading data with and without the different inclined substrates also lead to similar conclusions. The particle velocity is resolved into tangential and normal velocity components parallel and perdendicular to the substrate, respectively. The tangential velocity component controls the degree of splat elongation into elliptical shape from the circular shape seen in perpendicular impact. This is of practical importance in industrial spraying of engineering components of complex curvatures. A higher tangential velocity component also implies that more powders are lost through rebounding and overspraying and thus reducing the deposition efficiency. The normal velocity component decreases when substrate inclination increases, which tends to weaken the coating adherence.

Design principles for spray-roasted iron oxides for the manufacturing of ferrites

A range of high purity iron oxides are prepared by varying basic operation parameters of an industrial spray roasting process. These iron oxides are investigated in relation to their morphology and subsequently evaluated as raw materials for MnZn–ferrite preparation. It appears that the most important morphological parameters for determining the reactivity (defined as firing shrinkage at equal compaction density) of the high purity iron oxide, and consequently the final density and magnetic properties of the ferrite specimens, are the primary particle size and the number of primary particles per aggregate. As found, the specific surface area of the iron oxide is of no predictive value for the behavior of the iron oxide in a MnZn–ferrite manufacturing process. A small primary particle size is important for a high reactivity; however, when particles are packed together in large aggregates, they are not available for the prefiring reactions. As a result, reactive sintering takes place leading to high porosity and bad microstructure. As found by the characterization methods employed in this article, the optimum iron oxides for MnZn–ferrite preparation should have a primary particle size between 0.45 and 0.55 μm with an aggregate size below 1.60 μm.

Inhalation Exposure to Isocyanates of Car Body Repair Shop Workers and Industrial Spray Painters

As part of a large-scale epidemiological study, occupational isocyanate exposure was assessed in spray-painting environments. The aim was to assess which compounds contribute to isocyanate exposure in car body repair shops and industrial painting companies, and to identify tasks with high risk of isocyanate exposure. Mainly personal task-based samples (n = 566) were collected from 24 car body repair shops and five industrial painting companies using impingers with DBA in toluene. Samples were analysed by LC-MS for isocyanate monomers, oligomers and products of thermal degradation. From the 23 analysed compounds, 20 were detected. Exploratory factor analysis resulted in a HDI, TDI and MDI factor with the thermal degradation products divided over the TDI and MDI factors. The HDI factor mainly consisted of HDI oligomers and was dominant in frequency and exposure levels in both industries. Spray painting of PU lacquers resulted in the highest exposures for the HDI factor (<LOD-2643 microg/m(3) NCO), with no significant difference between the industries. Exposure variability during PU spray painting was large with a variability over time of (ww)S(2) = 9.1 compared with between-worker variability of (bw)S(2) = 1.6. Lower level exposure to the HDI factor was found during other painting-related tasks and even tasks without direct exposure to paint. Exposure to the TDI factor was found more regularly in car body repair shops than in industrial painting companies. Exposure levels were low (<LOD-5 microg/m(3) NCO) compared with the HDI factor and no clear contrast in levels between the tasks was observed. Exposure to the MDI factor was found incidentally during spraying and welding in car body repair shops (<LOD-0.5 microg/m(3) NCO). The results indicate that paint is the most important source and major contributor of isocyanate exposure in both industries with highest exposures during PU spraying. However, since respiratory protection is less extensively used during other tasks, lower level exposure during these other tasks may significantly contribute to the internal dose.

Experimental Setup to Examine Fe2O3 Particle Formation in Spray Roasting Reactors

Investigations of particle formation processes are an important field of research due to the multitude of applications in industrial facilities. The present article is focused on the investigation of Fe2O3-particle formation. The particles form during the thermal decomposition of an iron chloride solution in so-called spray roasting reactors. For detailed analysis of the iron oxide formation a laboratory reactor was developed which simulates the boundary conditions of industrial spray roasting reactors. Temperature, gas composition, and droplet size are comparable to industrial application. To examine the influence of droplet size on the particle formation process, a droplet generator was installed which provides monodisperse size distributions. Furthermore, industrial constraints and first results are discussed.

Energy Consumption of Industrial Spray Dryers

: In 2000, the U.K. government's Energy Efficiency Best Practice Programme commissioned a survey to determine the energy consumption of spray dryers within the chemicals, foods, and ceramics industries. The results of this survey, which included dryers having evaporation rates ranging from 0.1 to 12 t/h, revealed values of the specific energy consumption E s varying from around 3 to 20 GJ/t water evaporated. The average for all dryers included in the survey was 4.87 GJ/t. The fuel-to-electricity consumption ratio averaged around 27. The data obtained in the survey were interpreted with the aid of a newly developed model that enabled the performance of a particular dryer to be compared with that of its ideal adiabatic counterpart. Using the model, it was estimated that around 29% of the energy supplied to the dryers included in the survey was being wasted.

Computation of continuous cooling transformation diagrams for the heterogeneous nucleation in Sn-5 mass pct Pb droplets

A method was developed to compute continuous-cooling-transformation (CCT) diagrams for the heterogeneous nucleation of alloy droplets from a few experimental data. The developed model addresses both oxidation-catalyzed surface nucleation and internal nucleation caused by another catalyst. Droplet surface oxidation is regarded as a first-order reaction in order to account for the effects of the gradual increase in surface oxidation on the kinetics of surface nucleation. CCT curves were computed for Sn-5 mass pct Pb droplets cooling in atmospheres with various oxidation potentials using data determined with monosize droplets produced by capillary jet breakup. The developed model may be used to predict droplet nucleation kinetics in industrial thermal spraying processes.

Current Market-Driven Spray Drying Development Activities

Spray drying is a highly a complex operation with the movement of countless droplets/particles in turbulent drying medium flows under changing temperature and humidity conditions. Market (or custom) driven technology development has therefore always played a significant role in industrial spray drying activities owing to the difficulties in designing and operating spray dryers on the basis of theoretical analysis. Indeed, it was the breakthrough as a result of industrial motivated developments in the 1960s of being able to handle solvent based and abrasive liquid formulations plus the incorporation of supportive drying technologies to dry “difficult” products that laid the foundation for a rapid increase in the number of different spray drying applications covering a wide range of industries. In past decades, it was technology advancement alone that was sufficient as the driving force. Today this is not the case. Market-driven development programmes need also to focus on accompanying aspects of safety and environmental impact, and for new ideas to be applied in industry, there must be a strong economic element to enhance a profitable value-added powder production. Although spray drying is considered a mature drying technology by today's industrial standards, the technology still needs to develop to cope with new product and dried product quality demands. Furthermore, there remains the ever-present situation of spray dryer end-users faced with continuous increasing market competition for their products and the need to comply with changing national and international environmental and operational safety directives. This situation and the further evolution of a global economy will continue to stimulate market driven development programmes. Current activities in the field are the subject of this article.

Estimating Personal Exposures Based on Mass Balance Material Usage Rates: Validation of a Ventilation Model in a Spray Paint Booth

The goal of this research was to evaluate an estimating model (box model) with direct measurements of contaminants in an industrial spray painting operation. The research involved a dilution ventilation efficiency experiment that was devised to estimate the effective ventilation rate, sampling for organic compounds (xylene, ethyl benzene, methyl ethyl ketone, and methyl isobutyl ketone) in a paint booth, and simultaneously measuring the mass usage of these compounds during painting operations in order to compare measured with predicted concentrations. The results of the dilution ventilation experiment indicated that channeling of air was occurring due to a high ventilation rate in the painting area. The results of the mass balance usage and air sampling comparisons indicated that predicted concentrations were within the 95% upper/lower confidence interval about the geometric mean in 14 out of 16 area samples taken within the paint booth (87.5%). Correlation analysis between predicted concentrations and area, personal, and exhaust stack concentrations were strongest with exhaust (r = 0.923). Correlations with personal concentrations were not as strong (r = 0.828), and the area concentrations were even less strong (0.757). In conclusion, the box model does appear to be a useful additional tool for estimating worker exposures. However, the characteristics of any particular ventilation system must be understood before modeling is conducted.

A Study of the Limitations to Spray Dryer Outlet Performance

The concept of the product moisture locus was tested in this work using a pilot-scale modified Niro spray dryer (diameter 0.8 m, height 2 m), where the residence time of the particles inside this spray dryer is lower compared with larger industrial spray dryers. The moisture contents of skim milk powder produced from spray drying skim milk (solids content 8.8% w/v) at different operating conditions, namely different swirl vane angles (0°, 25°, 30°), inlet air temperatures (170°C, 200°C, 230°C) and process fluid flowrates (1.4 kg h−1, 1.6 kg h−1, 1.8 kg h−1), were compared with the predicted equilibrium moisture contents. In addition, the residence time of the particles was also increased in the spray dryer by decreasing the inlet air mass flowrate from 0.016 to 0.013 kg s−1. The outlet moisture contents of the skim milk powder for all the 23 runs carried out in this work were within 0.4% of the equilibrium values. Thus, the skim milk powder particles were in close equilibrium with the gas inside the drying chamber. These equilibrium limitations are confirmed by other literature data (Boonyai, P. Comparative Evaluation of Soymilk Drying in a Spray Dryer and Spouted Bed of Inert Particles. M.Sc. Thesis. Asian Institute of Technology: Bangkok, Thailand, 2000; 90 pp; Harvie, D.J.E.; Langrish, T.A.G.; Fletcher, D.F. A computational fluid dynamics study of a tall-form spray dryer. Trans IChemE 2002, in press). The use of this finding to predict spray dryer performance is demonstrated by mass and energy balance calculations.

Plasma Sprayed LSGM Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells

A strontium-and-magnesium-doped lanthanum gallate (LSGM) electrolyte was processed into a thick film ranging from 100 - 550 μm using a plasma spray technique, followed by post heat-treatment at elevated temperatures (500 - 800°C). The processed LSGM electrolyte was characterized in terms of its (1) physical properties including phase purity, crystallinity, density, and (2) electrochemical properties, including open circuit voltage, ionic conductivity, and ac impedance. The electrochemical properties of the plasma sprayed LSGM were also compared with press-and-sintered LSGM pellets. The as-sprayed electrolyte exhibited a single LSGM phase in a mixture of amorphous and crystalline states. The amorphous phase can completely transform into a crystalline phase at temperatures up to 800°C as revealed by the XRD and impedance studies. The successful processing of LSGM using an industrial plasma spray technique offers a potential opportunity for fabrication of solid oxide fuel cells (SOFCs) for intermediate temperature applications (500 - 800°C).

Spray‐Dried Particle Morphologies

AbstractParticulate powders and particle morphologies produced by spray drying are discussed, along with factors that affect powder quality, e.g. process conditions, and particle properties. Structural categories of spray‐dried particles are demonstrated and related to various drying mechanisms. The methods of studying particle morphology are also outlined with particular reference to the single droplet drying method, reportedly analogous to industrial spray drying and possibly other particulate formation processes. The advantages and disadvantages of the method are discussed and the importance of particle morphology to powder technology emphasised.

Experimental Measurement and Numerical Simulation of the Effect of Swirl on Flow Stability in Spray Dryers

A 0.29 m, 0.5 m tall, hydraulic model of an industrial spray dryer, constructed from perspex, has been used to study the precession of the central jet of air inside this equipment, where this central jet may be connected to the occurrence of wall deposits inside this equipment,. Experiments showed that the flow was strongly time-dependent, with two characteristic frequencies that depended on the angle of the inlet swirl vanes over a range of angles from 0° to 40°. The main frequency of precession of the central jet occurred over a time scale of a few seconds, and image analysis allowed the characteristic frequencies of the precession to be quantitatively assessed. Numerical simulations of the flow, conducted with CFX5, a CFD package, predicted Strouhal numbers for the jet precession that were within experimental errors of those observed for no swirl and 40° swirl, and only slightly outside the error bounds for 25° swirl. This agreement suggests that the k – ɛ turbulence model is suitable for estimating the frequencies of precession in spray dryers. This is of industrial significance, since the precession may be linked to the occurrence of wall deposits.

Characteristics of Spray from Pressure-Swirl Nozzle with Different Liquid Properties and Nozzle Geometries

The purpose of this study was to investigate the significant characteristics in atomization process of industrial etching spray fur the design or Precise pressure-swirl nozzles. The experiment was carried out with different viscosities and densities of the liquid. The macro characteristics of liquid spray, such as the spray angle and breakup process were captured by PMAS and the micro characteristics of liquid spray. such as droplet size and velocity measurements were obtained by PDA. The droplet axial and radial velocity and SMD were measured along axial and radial direction. The RMS of two velocities was measured along radial direction. It was found that the fluid with higher kinematic viscosity resulted in the larger SMD and the lower mean droplet velocity. And we could divide breakup processes into three regions that is atomization, non-dilution and dilution one in spray of pressure-swirl nozzle. The radial as well as axial velocity of droplet played an important role in the atomization process of higher kinematic viscosity fluid.

Temperature profile in countercurrent/cocurrent spray towers

The classical theory of the cooling tower does not include a suitable mathematical solution for a direct and quick calculation of gas/liquid temperature profiles. This forces in most of practical cases, for example in case of industrial spray absorbers, to simplify the problem and to assume a complete cooling of exit gases down to the adiabatic saturation temperature of the incoming gases. In the present paper, a new method is described to develop an acceptable mathematical solution for cooling towers, taking into account the main influencing parameters, especially the liquid to gas ratio (L/G) and the actual liquid and gas interface. Calculations with the new solution show, that the exit gas temperature is strongly influenced by the liquid inlet temperature. In case of closed loop and counter current systems, this liquid inlet temperature is more or less close to the adiabatic saturation temperature of the incoming gases. In these cases, the exit gas temperature is only slightly higher than the currently assumed adiabatic saturation temperature of the inlet gases. This is completely different to the open loop systems, where the liquid inlet temperature is not influenced by the incoming gases at all. In these cases, the gas outlet temperature is mostly far from the adiabatic saturation temperature of the inlet gases, so that the current assumption can initiate great errors.

On droplet formation from capillary waves on a vibrating surface

The formation of sprays from a liquid film on a vibrating surface is used by ultrasonic atomizers for applications ranging from humidification to metal–powder manufacturing. The received opinion in the literature is that droplets are formed periodically from the apexes of an orderly pattern of standing capillary waves, with a wavelength that can be related to vibration frequency by stability analysis. It is described how this assumption may be incorrect in that, after droplet formation commences, the orderliness of the standing–wave pattern is lost due to one or more secondary instability phenomena. These phenomena, which lead to disorderliness, are investigated by using high–speed imaging techniques and a low–frequency vibrating film to model the high–frequency case, because of the difficulty of penetrating clouds of small droplets in the latter case. Different modes of droplet formation are identified and the flow patterns responsible for these modes are discussed. Physical mechanisms are proposed from which it is deduced that only a proportion of standing–wave crests can eject droplets, for a given wall–vibration period, and the identity of these ejecting waves should vary from period to period. The model thus developed demonstrates an apparently random ejection of droplets from one wave cell, even though the model itself is deterministic. The disorder of the capillary waves and the occurrence of several droplet–formation routes are sufficient to explain the range of droplet sizes that is produced by ultrasonic atomization.