Rafael Oliveira Defendi

Optimization study of soybean intermittent drying in fixed-bed drying technology

ABSTRACT Intermittent drying of materials is an alternative operation that aims at reducing energy consumption, improve the preservation of dried products or decrease effective drying time. Intermittent drying supplies the system with time-varying input air properties that are opposite to traditional operations, where air properties are constant at the dryer inlet. The major objective of this study is to establish the most satisfactory patterns of air temperature and velocity modulation at the dryer entrance to reduce energy consumption. This optimization study was based on a heterogeneous model for the drying of grains in fixed bed validated with experimental data. Intermittent and conventional operation experiments were conducted using equal energy consumption, and the influence of air temperature and velocity modulation on the drying rates related to the percentage of evaporated water were assessed. Results indicated that higher drying rates can be achieved under intermittent operation, and the validated model based on these results could reasonably predict temperature and moisture content profiles. Simulations pointed out that the best modulation patterns of air properties is a function of a variety of system conditions such as initial temperature and moisture content of both soybean and drying air. However, a tendency to reduce energy consumption was observed when the system operation is initially at high temperature and constantly at low velocity.

The air temperature modulation impact on the drying of soybeans in a fixed bed

ABSTRACT This work aimed to explore an alternative to reduce costs in the soybean drying process using a periodic drying operation, which can enhance mass and energy transfer, leading to lower energy consumption in comparison with the conventional operation carried out with entrance drying air in steady-state conditions. A fixed bed dryer for laboratory scale was used to dry soybean grains and experiments were carried out, applying the periodic and conventional operations with the same drying time and energy consumption. Results indicated with 5% of significance that the experiments conducted with entrance air temperature modulation achieved higher levels of the percentage of evaporated water improving the dryer performance. These results were in agreement with predicted data obtained with heterogeneous models and they indicated that the periodic drying operation can demand less energy to achieve a specific safe level of soybean moisture content for storage.

Assessment of the initial moisture content on soybean drying kinetics and transport properties

ABSTRACT Several researchers have developed studies to obtain a mathematical model able to describe grain drying kinetics. However, most of these studies neglect the effect of grain initial moisture content on drying curves. In this study, we assessed the dependence of drying curves and mass transfer coefficients on this initial moisture, air temperature, and its velocity by measuring grain mass losses within time on a tray dryer. Mathematical models were adjusted and results indicated that initial grain moisture content has significant influence on drying curves and mass transfer coefficients.

Integrated Analysis of an Evaporation and Distillation Bioethanol Industrial System Using Direct and Indirect Heating

Abstract In this work we simulate and integrate the systems of evaporation, fermentation and distillation with direct heating. In addition, we propose a new scenario using indirect heating in order to decrease the quantity of stillage, and consequently, minimize environmental and economic impacts associated. In this sense, a reboiler using the steam produced in the evaporators is included in the distillation column to analyse the effect of such revamping. Sensitivity analyses were performed to detect some key operational variables with effect on the process. Results show that the replacement of direct steam injection by use of reboilers decreases significantly the quantity of stillage, consequently, minimizing the problems generated by it. Moreover, once there are no changes in flegma and ethanol mass flows, and the bleeding heat flow is suitable to exchange heat with reboilers, it means the replacement may be done without modify the industrial productivity.