This work presents a study on the agitation rate effects on the average diameter (% volume D(4,3)) in the batch crystallization of sugar cane in pilot-scale process. The mathematical model presented in this work includes the population balance equation (PBE), the mass and energy balances, and the kinetics equations of nucleation and growth rate. The kinetic parameters were calculated from optimization using experimental data obtained from a pilot-scale process. An uncertainty analysis was performed and used to specify robust agitation trajectories that minimize the variations of crystal size from batch to batch. Four cases studies are presented to obtain 920, 1000, 1200, and 1300 μm of D(4,3) subject to a constraint in the formed crystal mass (FCM) of 4700 g under uncertainty in the kinetic parameters. The resulting robust agitation trajectories were implemented in the pilot-scale process. Comparisons between experimental data and the model predictions are presented.
(2018) Effect of drying methods on the physicochemical and thermal properties of Mexican plum (Spondias purpurea L.), CyTA -Journal of Food, 16:1, 127-134, DOI: 10.1080/19476337.2017 To link to this article: https://doi.org/10. 1080/19476337.2017 Plum slices (diameter 2.5 cm and thickness 0.2 cm) were dried using vertical tray-drying (VTD) and freeze-drying. Models were used to determine the thermal conductivity (k) and specific heat (C p ). In addition, water activity (a w ), colour total change (ΔE), pectin yield (y pec ) and rehydration capacity were investigated. The moisture content of tray-and freeze-dried plum was relatively significant (p < 0.05). No significant difference was found in terms of a w . There was a maximum decrease in k and C p of 90% and 91.5% during drying process, respectively. In terms of quality, ΔE showed that tray-dried samples had slight darker (browning), whereas the freeze-dried samples had a lighter colouring compared to the fresh fruit. The quality and rehydration characteristics of freeze-dried plum were higher than that of a tray-dried product; however, VTD could be appropriate for industrial production because of its advantages in lower cost and energy consumption.Efecto de los métodos de secado sobre las propiedades fisicoquímicas y térmicas de la ciruela mexicana (Spondias purpurea L.) RESUMEN Las rebanadas de ciruela (diámetro 2,5 cm y espesor 0,2 cm) fueron secadas usando el secado vertical por charolas (VTD) y la liofilización (FD). Se utilizaron modelos para determinar la conductividad térmica (k) y el calor específico (C p ). Además, la actividad de agua (a w ), el cambio total de color (ΔE), el rendimiento de pectina (y pec ) y la capacidad de rehidratación fueron investigados. El contenido de humedad de la ciruela seca y liofilizada fue relativamente significativo (p < 0,05). No se encontraron diferencias significativas en términos de a w . Hubo un máximo decremento en k y C p del 90% y 95% durante el proceso de secado, respectivamente. En términos de calidad, ΔE mostró que las muestras secadas en charolas tuvieron un ligero oscurecimiento (pardeamiento), mientras las muestras liofilizadas tuvieron un color más luminoso en comparación con la muestra fresca. La calidad y las características de rehidratación fueron mayores que las de un producto secado por charolas; sin embargo, VTD podría ser apropiado para la producción industrial debido a sus ventajas de bajo costo y consumo energético. ARTICLE HISTORY
This paper presents a control strategy based on stage temperature measurements to control composition of the products in a Petlyuk-type distillation column. This column is formed by a prefractionator in which feed is introduced and a main column from which three product streams are extracted. Prefractionator and main-column modules are connected through the exchange of liquid and vapor streams resulting in a strong interaction that can result in operating problems, poor control performance, and instability due to their complex structure. Different steady-state methods for the selection of appropriate control structures were analyzed. The control structure comprises four controllers implemented as follows: three Proportional-Integral (PI) controllers to regulate the temperature of three stages along the main column and a cascade controller to regulate temperature at a stage in the main column manipulating temperature in a prefractionator stage. Controllers were designed using internal model control guidelines for traditional PI compensation. Feed composition disturbances were introduced in order to observe the response of the control system. The obtained results show that the control structure maintains the purity of the final products within acceptable ranges despite the existence of disturbance.
The purpose of this study was to investigate how the properties of Mexican kefir grains (MKG) are affected by the operating parameters used in the freeze-drying process. The factors investigated were the freezing time (3–9 h), freezing temperature (−20 to −80 °C), pressure (0.2–0.8 mbar), and lyophilization time (5–20 h). The maximum range of change and one-way analysis of variance showed that lyophilization time and freezing time significant affects (p < 0.05) the response variables, residual moisture content and water activity, and pressure had a significant effect on the color difference and survival rate of probiotic microorganisms. The best drying conditions were a freezing time of 3 h, a freezing temperature of −20 °C, a pressure of 0.6 mbar, and a lyophilization time of 15 h. Under these conditions, we obtained a product with residual moisture content below 6%, water activity below 0.2, and survival rates above 8.5 log cfu per gram of lactic acid bacteria and above 8.6 log for yeast.
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