doctoralThesis
Estudo da dinâmica de secagem em um secador rotatório com alimentação intermitente
Fecha
2016-04-15Registro en:
MOURA, Bríggida Dantas de. Estudo da dinâmica de secagem em um secador rotatório com alimentação intermitente. 2016. 100f. Tese (Doutorado em Engenharia Química) - Centro de Tecnologia, Universidade Federal do Rio Grande do Norte, Natal, 2016.
Autor
Moura, Bríggida Dantas de
Resumen
The industrial fruit pulp processing is responsible for the generation of a significant amount of
by-product in waste form, consisting essentially of seed, husk and rest of the fruit. These subproducts
are still underutilized and their direct discard may result in considerable
environmental damage. Therefore, it is of great scientific and technological interest to develop
strategies able to add economic value to these waste. Drying is one of the processes most used
for preservation of food products and represents an alternative for use in fruit waste. Drying
processes can produce materials with potential application, mainly in form of ingredient for
animal food. In this work, a drying study of passion fruit waste was performed using a rotary
dryer containing inert loading and operating in concurrent flow with intermittent feed of
material. Different experimental conditions were studied for intermittent material feed and air
temperature, in order to evaluate the response behavior at the dryer outlet, verifying the
following variables: moisture content of material; air absolute humidity; air temperature; mass
(produced cumulatively during drying). Also, a mathematical model of the process was
developed and implemented in order to describe the dynamic response characteristics in the
studied conditions. This mathematical model was written based on microscopic balance of
mass and energy for solid and gas phases, resulting in partial differential equations (PDE),
where the process variables (temperature and moisture for solid and gas) are dependent on the
time and space. Some physicochemical and compositional properties of passion fruit waste
were evaluated, allowing to infer important parameters for the mathematical model. Drying in
thin layer showed that the drying kinetics presents a characteristic of constant rate dependent
linearly with the drying temperature. A similar behavior was observed in fitting the
mathematical model of rotary dryer with the experimental data. It was noted that the drying
constant for the mass transfer term also presented a strong correlation with the operating
temperature. In general, the values calculated by the mathematical model were adequate in
respect to all response variables and for all conditions studied. Analyzing the influence of
operating conditions with respect to the model parameters, it was observed that the axial
dispersion and the velocity of the solid were influenced moderately by the feed intermittence,
while the constant of drying and the convective coefficient of heat transfer were strongly
influenced by the temperature. From the mathematical model adjusted with the experimental
conditions, exploratory simulations were performed in both continuous and intermittent
regime and assuming different conditions of flow for the material. The main purpose with
such simulations was to investigate the dimensional design feature (L/Dc) of the dryer, able to
ensure better production and to comply with a product moisture specification. These results
demonstrated that the mathematical model is able to perform a dimensional evaluation in
equipment design as well as it can be applied for process optimization and advanced process
control.