Influence of Atomizing Parameters on Droplet Properties in a Pulse Combustion Spray Dryer

A pulse combustor employed in a spray-drying system offers a new approach for liquid atomization that yields high-quality powders at low cost. Using a pulse combustion atomizer, there is no need for any form of nozzle dispersion and its atomization mechanism differs from those of conventional atomizers, such as rotary atomizers and pressure and pneumatic nozzles. In this work, based on the analysis of atomization mechanism, experiments of unsteady pulsating atomization were carried out in an experimental system of a Helmholtz-type pulse combustor. An optical analyzer was used for measuring the mean diameter of atomized droplet and droplet distribution. The effects of liquid feed rate, air flow oscillatory frequency, and liquid viscosity on atomized droplet size and size distribution were investigated and analyzed. The results indicate that the uniform droplet size distribution can be obtained under the conditions of a low feed rate, high-frequency pulsating flow, and moderate viscosity. The range of the droplets' Sauter mean diameter (SMD) is between 50 and 80 µm. The pulsating air flow from the pulse combustor can be used to atomize liquid or slurry without a nozzle and the atomizing quality can meet the requirements of spray drying.     

Influence of Nozzle Parameters on Spray Pattern and Droplet Characteristics for a Two-Fluid Nozzle

In this study, a two-fluid nozzle, as, e.g., used in fluidized-bed or spray drying applications, is comprehensively characterized regarding the spray pattern and droplet size. To analyze the spray cone, the spray cone angle and the radial mass distribution of the nozzle were measured at varied liquid flow rate, spray air pressure, liquid insert bore diameter, and air cap position. Additionally, droplet size distributions were recorded at different spray settings. In general, the overall spray cone and single droplets are significantly influenced by the spray parameters, especially the spray air pressure, as well as the nozzle geometry.     

Droplet Size Distribution Obtained by Atomization with Two‐Fluid Nozzles in a Spray Dryer

The possibility of predicting the droplet size distribution from the particle size distribution was investigated. For that purpose, suspensions of different types of materials were dried in a laboratory‐scale spray drier. Drying of suspensions was performed with different sizes of two‐fluid nozzles. Droplet size distribution was evaluated from the data obtained for spray drying of bismuth molybdate suspension. The method was validated experimentally with other tested materials. Investigated systems involve processes of drying, crystallization, and coating. The proposed methodology can be applied when nonagglomerated particles, spherical particles, or spherical agglomerates were obtained by spray drying.     

实验室用压力式喷雾干燥器的研究

实验室用压力式喷雾干燥器是目前建筑陶瓷行业所急需的.笔者主要介绍了研究本课题的意义及创新之处,并阐述了本课题的研究内容及关键技术.     

Challenges of Simulating Droplet Coalescence within a Spray

Abstract

This article reports various challenges that have been encountered in the process of developing validated Lagrangian and Eulerian models for simulating particle agglomeration within a spray dryer. These have included the challenges of accurately measuring droplet coalescence rates within a spray, and modeling properly the gas–droplet and droplet-droplet turbulence interactions. We have demonstrated the relative versatility and ease of implementation of the Lagrangian model compared with the Eulerian model, and the accuracy of both models for predicting turbulent dispersion of droplets and the turbulent flow-field within a simple jet system. The Lagrangian and Eulerian droplet coalescence predictions are consistent with each other, which implies that the numerical aspects of each simulation are handled properly, suggesting that either approach can be used with confidence for future spray modeling. However, it is clear that considerable research must be done in the area of particle turbulence modeling and accurate measurement of particle agglomeration rates before any Computational Fluid Dynamics tool can be employed to accurately predict particle agglomeration within a spray dryer.     

R&D Needs and Opportunities in Pulse Combustion and Pulse Combustion Drying

This short communication attempts to summarize briefly the authors’ opinions on R&D needs and opportunities for basic as well as applied research in pulse combustion and pulse combustion drying. It is not all-inclusive. Only minimal citations are made to relevant literature as readers interested in pro-actively pursuing this area can locate it reasonably easily. The objective in presenting this verview is to encourage new researchers in this fascinating and challenging field.     

Challenges of Simulating Droplet Coalescence within a Spray

This article reports various challenges that have been encountered in the process of developing validated Lagrangian and Eulerian models for simulating particle agglomeration within a spray dryer. These have included the challenges of accurately measuring droplet coalescence rates within a spray, and modeling properly the gas-droplet and droplet-droplet turbulence interactions. We have demonstrated the relative versatility and ease of implementation of the Lagrangian model compared with the Eulerian model, and the accuracy of both models for predicting turbulent dispersion of droplets and the turbulent flow-field within a simple jet system. The Lagrangian and Eulerian droplet coalescence predictions are consistent with each other, which implies that the numerical aspects of each simulation are handled properly, suggesting that either approach can be used with confidence for future spray modeling. However, it is clear that considerable research must be done in the area of particle turbulence modeling and accurate measurement of particle agglomeration rates before any Computational Fluid Dynamics tool can be employed to accurately predict particle agglomeration within a spray dryer.     

The Effect of Rotary Disk Atomizer RPM on Particle Size Distribution in a Semi-Industrial Spray Dryer

Spray drying is the most commonly used method in industry to produce powders on a large scale. One of the major problems in spray drying is control of the product particle size distribution since it is very important for most industries; e.g., catalyst, chemicals, foods, pharmaceuticals, ceramics, etc. The objective of this work is to study the effect of the atomizer rotational speed on the product size distribution. In order to obtain the typical particle size distribution of the required product, a specially designed atomizer disk is used in the study. The particle size distributions under atomizer rotating speeds in the 9,000–10,000 rpm range were measured and discussed.     

Experimental Study and CFD Modeling of Wall Deposition in a Spray Dryer

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.     

喷雾干燥四种燃煤热风炉的比较

阐述了喷雾干燥4种燃煤热风炉的结构、工作原理、使用性能，并分析了其投资成本和运行成本。     

CFD Evaluation of Droplet Drying Models in a Spray Dryer Fitted with a Rotary Atomizer

Computational fluid dynamics (CFD) modeling of spray dryers requires a simple but sufficiently realistic drying model. This work evaluates two such models that are currently in discussion; reaction engineering approach (REA) and characteristic drying curve (CDC). Two versions of the CDC, linear and convex, drop in drying rate were included. Simulation results were compared to the overall outlet conditions obtained from our pilot-scale experiments. The REA and CDC with a linear drop in drying rate predicted the outlet conditions reasonably well. This is contrary to the kinetics determined previously. Analysis shows that the models exhibit different responses to changes in the initial feed moisture content. Utilizing different models did not result in significantly different particle trajectories. This is due to the low relaxation time of the particles. Despite the slight differences in the drying curves, both models predicted similar particle rigidity depositing the wall. For the first time in a CFD simulation, the REA model was extended to calculate the particle surface moisture, which showed promising results for wet particles. Room for improvement was identified when applying this concept for relatively dry particles.     

The Influence of the Spray Drying Process on Product Properties

Abstract

Uniform and repeatable product characteristics are critical in the performance and acceptance of consumer products, and the spray drying process can have a major influence on achieving these characteristics. This article shares experiences in the Spray Drying of powdered detergent granules in Procter & Gamble. It looks at the influence of both process operation and process equipment design on product characteristics. Procter & Gamble (P&G) is a major global producer of consumer products in the areas of fabric and home care; personal and beauty care; health care; and snacks and beverages. Whilst different drying operations, and product quality measuring tools are mentioned by Genskow (Genskow, L.R.¹ Considerations in Drying Consumer Products, Proceedings of 6th International Drying Symposium, Versailles, September, 1988; Keynote lecture, 39–46.) as being involved in all of the categories of Company production, I will concentrate on the counter-current Spray Drying process and controls, used in the manufacture of most of the detergent granules business of P&G. This area is the oldest and largest of the Company's core business activities. Innovative technology development is critical in continuing to satisfy the consumer need for performance and value. Use of modeling in the spray drying process is helping the Company to move faster in delivering these advanced technologies. And, through better understanding of the process, it is possible to minimize capital expenditure, and improve trouble-shooting ability across the global production facilities.     

The Influence of the Spray Drying Process on Product Properties

Uniform and repeatable product characteristics are critical in the performance and acceptance of consumer products, and the spray drying process can have a major influence on achieving these characteristics. This article shares experiences in the Spray Drying of powdered detergent granules in Procter & Gamble. It looks at the influence of both process operation and process equipment design on product characteristics. Procter & Gamble (P&G) is a major global producer of consumer products in the areas of fabric and home care; personal and beauty care; health care; and snacks and beverages. Whilst different drying operations, and product quality measuring tools are mentioned by Genskow (Genskow, L.R.¹ Considerations in Drying Consumer Products, Proceedings of 6th International Drying Symposium, Versailles, September, 1988; Keynote lecture, 39-46.) as being involved in all of the categories of Company production, I will concentrate on the counter-current Spray Drying process and controls, used in the manufacture of most of the detergent granules business of P&G. This area is the oldest and largest of the Company's core business activities. Innovative technology development is critical in continuing to satisfy the consumer need for performance and value. Use of modeling in the spray drying process is helping the Company to move faster in delivering these advanced technologies. And, through better understanding of the process, it is possible to minimize capital expenditure, and improve trouble-shooting ability across the global production facilities.     

喷雾干燥机节能探讨

本文简要介绍了陶瓷面砖原料制备设备喷雾干燥机的工作原理和使用特点,重点探讨了喷雾干燥机的节能方法。它将对陶瓷厂的节能具有一定的参考价值。     

Kinetic Modeling of Reactive Absorption of Carbon Dioxide in a Spray Dryer

A semi‐empirical kinetic correlation was obtained through a shrinking core model assumption for reactive absorption of CO₂ with NaOH solution by applying response surface method analogy in a laboratory‐scale spray‐dryer absorber. The effect of approach temperature, absorbent concentration, nozzle diameter, and L/G ratio on the kinetic coefficient was studied and the optimum operating conditions to reach the maximum absorption were determined.     

Atomization and Drying Characteristics of Sewage Sludge inside a Helmholtz Pulse Combustor

Sewage sludge of pasty consistency was atomized and dried directly using a high-temperature, highly turbulent gas flow in the tailpipe generated by a Helmholtz gas-fired pulse combustor (PC). Parametric studies were carried out to investigate the effect of drying pipe length and sludge feed tube size on the PC sludge drying process. Experimental results showed that the pulsating gas stream can disperse the sludge into small particles with a narrow size distribution between 0.01 and 4 mm and the granular sludge was dried rapidly due to the increased particle surface area and the high temperature of the drying medium. PC drying of sewage sludge was compared to convective- and microwave-drying processes. The application potential of the PC sludge-drying process is discussed based on the experimental results.     

Three-Dimensional Numerical Investigation of a Mono-Disperse Droplet Spray Dryer: Validation Aspects and Multi-Physics Exploration

Many studies have been carried out on using computational fluid dynamics (CFD) to explore spray-drying phenomena. However, due to the complexity of the drying process in a conventional spray dryer, including the wide droplet size distribution, complicated particle trajectory, and difficulty in taking online measurements, validation of the computational codes or the models remains a challenging task. In this study, experimental conditions employed in a more defined spray-drying condition, published recently on the spray drying of mono-disperse skim milk droplets in a vertical cylindrical chamber, are simulated using ANSYS FLUENT. We have examined the effects of droplet-dispersion patterns on the drying results and found ways to incorporate more practical shrinkage models into the code to make simulations more realistic. Through a comparison with the relevant experimental results on 10～50 wt% skim milk published recently by the same group, we have identified a few areas that urgently need more detailed research. Using the revised sets of codes established here, we simulated skim milk droplets (with a uniform size between 180 μm to 220 μm) spray dried by 90°C to 180°C hot-air streams. The quantitative drying history data predicted by our new model would help ensure better understanding of the system.     

纸张脉动燃烧尾气冲击流干燥过程的实验研究

脉动燃烧因其传热效率高、结构紧凑、环境污染小等优点而广泛应用于生产生活中,冲击干燥同样也能形成强烈的热质交换,本文将上述两种干燥技术结合应用。为了探讨脉动燃烧尾气冲击流干燥的性能,研制了小型Helmh01tz脉动燃烧器,并对脉动燃烧尾气冲击流干燥技术应用于纸张的干燥过程进行了实验研究。分析了气流辐射半径和燃料流量两个参数对干燥过程的影响,可以看出随着气流辐射半径的增加,干燥速度降低。此外还对不同干燥条件下的纸张干燥时间进行了估计,为实际生产提供参考。     

A Novel Way to Measure the Concentration of a Spray in a Spray Dryer

A new experimental technique to capture milk concentrate droplets from inside a 150-kg powder/h pilot spray dryer is presented. The technique uses liquid nitrogen to capture the droplets in the dryer and to preserve their moisture content. The droplets are kept frozen until the moisture content can be measured. This technique can be applied to sample the sprays from any semi-commercial-scale spray dryer or similar apparatus.     

Thermal Processing of Particulate Solids in a Gas-Fired Pulse Combustion System

Abstract

An experimental study on thermal processing of particulate solids has been carried out on a valved pulse combustion unit. The test-bench consists of a 60 kW natural gas-fired valved (flappers) pulse combustor having a 4.63 × 10^?3 m³ combustion chamber, horizontal tailpipe with variable geometry, and a cylindrical drum. The particulate solid used is clean sand (311 µm and 2646 kg/m³), which flows within the tailpipe and the cylindrical drum located at its end. The sand flowrate was varied from 10 to 50 kg/h and it was heated from 20 to 600°C. Local pressure measurements showed clearly that the propagation of sonic waves remain stable when they are in direct contact with the sand particles. The heating time of sand particles in the pulsed system was found shorter than the one observed when operating with a conventional burner under the same conditions; this resulted in a 25.5% reduction of natural gas consumption.