An effective rate approach to modeling single‐stage spray drying

Abstract

An effective rate approach (ERA) is proposed to achieve a fast and reliable prediction of dryer outlet conditions for a given single-stage spray drying system operated under a range of scenarios. This approach is improved from existing methods based on simple mass and energy balances due to the incorporation of a reliable drying rate model, which is the reaction engineering approach for the material of interest. It allows quick solution procedure without the need to solve the partial differential equations that govern the heat and mass transfer in the spray drying process. By following a generic procedure, this technique has been exercised on the experimental results from running a monodisperse droplet spray dryer, that is, a well-established experimental platform for model validation. The proposed ERA has been shown to be rather promising. It could become a powerful approach for proactive control and optimization for existing spray drying facilities. V C 2015 American Institute of Chemical Engineers AIChE J, 61: [4140][4141][4142][4143][4144][4145][4146][4147][4148][4149][4150][4151] 2015 Keywords: spray drying, predictive modeling, effective rate approach, reaction engineering approach, proactive quality control IntroductionSpray drying is an effective process for large-scale powder production. Although this technique has been widely used in a variety of industries for many years, proactive control of powder product formation remains a challenge. [1][2][3][4][5] It is well known that the dryer inlet conditions that include the feed solution composition and operational settings all have significant influences on droplet formation through atomization, the airdroplet flow pattern, the air-droplet mass, and heat exchange in the drying chamber, and hence the dryer outlet conditions (i.e., the size, shape, moisture content, and morphology of the particles). 6,7 The quantitative relationships between dryer inlet and outlet conditions, however, remain unclear.Over the past decades, new dryer designs and optimized operations have been pursued by many research groups to deepen our scientific understanding of the spray drying process and to improve our control over powder formation dynamics. Counter-current spray drying towers are suitable for thermally stable products such as detergents and ceramics as the hot gas comes in contact with dry particles just before the particles exit the tower. Cocurrent spray dryers are the best choice for heat sensitive products like milk powders, where thermal degradation and aroma retention are of concern. Hot gas comes in contact with the droplets at the top where the droplets have maximum moisture content and are at the wet bulb temperature. 8,9 With this configuration, the driest particles are eventually coupled with the lowest temperatures Correspondence concerning this article should be addressed to J. Xiao at jie. xiao@suda.edu.cn or X. D. Chen at xdc@xmu.edu.cn; xdchen@suda.edu.cn. 4140AIChE Journal December 2015 Vol. 61, No. 12 (i.e., the outlet temperatures). A single-stream ...

Nonlinear Model-Based Inferential Control of Moisture Content of Spray Dried Coconut Milk

“…Correlations Used in REA Model and One-Dimensional Model Development Water vapor concentrations in drying air (ρ v,b ) and at droplet interface (ρ v,sat ) are calculated based on Equations (A1) and (A2), respectively [24].…”

“…Water vapor concentrations in drying air and at droplet interface ( are calculated based on Equations (A1) and (A2), respectively [ 24 ]. where is hot air temperature (K) and is droplet temperature (K), which is assumed equal to .…”

“…Patel and Chen [23] integrated the REA model in one-dimensional model and it was found out that this model is simpler in its mathematical formulation and superior in providing realistic results, compared to other lumped parameter drying kinetic models to represent the spray drying process of skim milk. George, et al [24] discovered that a one-dimensional model with integration of REA model provides a good fit to experimental data that can accurately predict the dynamic behavior of the co-current spray dryer.…”

“…The application of the dynamic model, especially a one-dimensional model, allows the application of an advanced control system in controlling moisture content of spray dried product such as cascade control [25], linear-quadratic-Gaussian (LQG) controller [26], and model predictive control [27]. However, the dynamic model is computationally intensive for real time applications due to time consuming issues in iteration of a complex model [24]. A simplified version of the nonlinear dynamic model is required to reduce simulation time in online control strategy such as linearization [28] and reduction [26] of a nonlinear model.…”

Primary breakup of shear‐thickening suspension jet by an annular air jet

“…This process can increase the surface area when the liquid jet breaks up into droplets; thus, the transfer velocity of mass and heat can be accelerated as well as the reaction rate. Therefore, atomization is of great importance in industrial processes and applied in fuel combustion, 1,2 spray cooling and drying, 3–5 production technology of microparticles or nanoparticles, 6–9 and medical technology 10–12 . The atomization process generally includes two parts: the primary atomization and the secondary atomization.…”