Sandra Cristina dos Santos Rocha

DRYING OF PULPS OF TROPICAL FRUITS IN SPOUTED BED: EFFECT OF COMPOSITION ON DRYER PERFORMANCE

ABSTRACT Studies on drying of pulps of several tropical fruits in spouted beds had shown advantages in relation to the quality of the products. However, most of the processed pulps presented serious problems of accumulation in the bed and consequently, instability of the spouted bed dynamic. The objective of this work is to analyze the influence of the chemical composition on the spouted bed performance in drying pulps of tropical fruits. Mango pulp “in natura” was used as a standard pulp. Modified pulps were obtained increasing the concentrations of reducer sugars, lipids, fibers, starch and pectin. The effect of these compositions on the fluid-dynamic and efficiency of the powder production was investigated using a factorial design. The operational conditions were maintained fixed in all experiments. The efficiency of powder production, the stable spout pressure drop and the minimum spouting flow rate were the responses analyzed. The statistical analysis of the results showed that the concentration of fibers is not a significant variable for the process. The concentrations of reducer sugars and starch showed significant influence on the fluid dynamic and these concentrations together with the lipids and pectin concentrations showed significant influences on the efficiency of powder production.

COATING OF UREA WITH AN AQUEOUS POLYMERIC SUSPENSION IN A TWO-DIMENSIONAL SPOUTED BED

ABSTRACT In this work, a process of coating of urea with polymeric film was developed and analyzed experimentally in a two-dimensional spouted bed. An experimental design was utilized to investigate the effects of operational variables, e.g., air flow rate, air temperature, atomizing air pressure and coating suspension flow rate, on the efficiency of the process, particles growth, particles growth kinetics and physical properties. The results showed that the efficiency of the process and particle growth characteristics were strongly influenced by the operational variables. Coating of the polymeric suspension of Eudragit® improved up to four times the moisture holding capacity of coated urea in relation to uncoated urea. The bulk density, grain size and sphericity were found to be independent of operational conditions.

Time series analysis of pressure fluctuation in gas-solid fluidized beds

The purpose of the present work was to study the differentiation of states of typical fluidization (single bubble, multiple bubble and slugging) in a gas-solid fluidized bed, using spectral analysis of pressure fluctuation time series. The effects of the method of measuring (differential and absolute) pressure fluctuations and the axial position of the probes in the fluidization column on the identification of each of the regimes studied were evaluated. Fast Fourier Transform (FFT) was the mathematic tool used to analysing the data of pressure fluctuations, which expresses the behavior of a time series in the frequency domain. Results indicated that the plenum chamber was a place for reliable measurement and that care should be taken in measurement in the dense phase. The method allowed fluid dynamic regimes to be differentiated by their dominant frequency characteristics.

Drying of Tropical Fruit Pulps: Spouted Bed Process Optimization as a Function of Pulp Composition

Results of drying of tropical fruit pulps in spouted beds (SBs) are presented, focusing on the effects of fruit pulp composition on the SB fluid dynamics and process performance and the development of new products formulated from mixtures of pulps with varied composition. It was verified that high starch and lipid contents favored stable fluid dynamics and high powder production efficiency, while high reducing sugar concentrations resulted in bad dynamic regime and very low powder production. Powder production efficiency was statistically correlated with the pulp composition. Also, drying of mixtures of fruit pulps with addition of starch and lipids was investigated. Results of fluid dynamics, drying performance, and sensory tests of yogurts enriched with the powders revealed promising potential of the SB for obtaining high-quality fruit powders.

Adhesion of an Aqueous Polymeric Suspension to Inert Particles in a Spouted Bed

Abstract Among the several unit operations that seek the modification of superficial characteristics of solid particles, the spouted bed appears as efficient technology for coating of coarse particles (d p >1 mm). This work aimed at investigating the fluid-dynamics of the conventional spouted bed during a coating process, using several inert particles such as polystyrene, polypropylene, polyethylene of low density, ABS®, placebo tablet and glass beads, and analyze the influence of the physical properties of the particles and of the polymeric coating suspension on the fluid dynamics. The suspension was characterized by the surface tension, density, rheology, and contact angle between the suspension and the solid surface. It was verified that the particles having a high contact angle with the suspension (polystyrene, polypropylene, and low-density polyethylene) were not coated, and drying of the suspension was obtained in these cases. For the other particles (ABS, tablet, and glass beads), coating efficiencies in the range of 76–90% were obtained. The shape, angle of repose, and density of particles affected the fluid-dynamic during the coating, and also the inter-particle friction and the particle circulation velocity in the bed.

Energy Efficiency and Drying Kinetics of Recycled Paper Pulp

In this work, the influences of the air temperature and velocity on the drying kinetics of recycled paper pulp were analyzed. The increase of both variables positively influences the process, concerning the final moisture content and the drying time. However, optical microscopy and visual observation showed worse quality of the paper for drying conditions of high air temperature and velocity, presenting less uniformity and overdried surfaces. The dryer energy efficiency was evaluated by performance parameters and the results were compared with the ones obtained for other types of industrial paper dryers, presenting good agreement.

Slot-Rectangular Spouted Bed: Hydrodynamic Stability and Effects of Operating Conditions on Drying Performance

A new spouted-bed configuration (rectangular cross-section with air entry through two bottom slots) was investigated as a dryer of milk and a paste mixture of milk and blackberry pulp. The aim was to analyze hydrodynamic stability and the effects of operating conditions on powder production efficiency. For the best conditions of paste-feeding flow rate, air temperature and inert type, hydrodynamic was stable and powder production efficiency was greater than 75%. The slot-rectangular spouted bed allowed for tripling of the paste-feeding flow rate at a lower air velocity compared to the conventional geometry, showing its potential for process scale-up.

Coating and Drying in Spouted Bed: Influence of the Liquid-Particle Work of Adhesion

The aim of this work is to analyze the resulting process: coating or drying, and the respective fluid dynamic behavior, by bottom-spraying polymeric suspensions on a spouted bed of inert particles. Glass beads, ABS®, polypropylene (PP), and polystyrene (PS) were chosen as inert particles and were analyzed and characterized by their physicochemical properties. The polymeric suspensions were characterized by density, surface tension, rheology, and wettability. The fluid dynamic behavior of the bed was correlated with the particles and suspensions characteristics for each process: coating and drying. Each process performance was correlated with the polymeric suspension-particle work of adhesion.

Intermittent drying of beans in a spouted bed

Carioca beans are a highly nutritious grain, in terms of the amount of protein, iron and potassium as well as carbohydrates and fiber and as a source of vitamins. The moisture content of recently picked beans is too high for good preservation and storage, resulting in the need for drying before packaging. In this work, the drying of Carioca beans in a laboratory scale spouted bed under intermittent conditions of the drying air was experimentally analyzed. Experiments carried out consisted of two types of intermittent regime: intermittence in the spout regime, referred to as spouted/fixed bed and intermittence of the air supply to the bed, called spouted bed/rest. The results were compared to those for bean drying in a spouted bed dryer without intermittence.

CONVECTIVE HEAT TRANSFER DURING COATING OF PARTICLES IN TWO-DIMENSIONAL SPOUTED BEDS

ABSTRACT This work deals with the evaluation of gas-to-particle convective heat transfer in a process of coating of particles in two-dimensional spouted beds. A detailed calculus routine is presented and two correlations of heat transfer coefficient, for the spout and annular regions are derived. The study is performed with two, two-dimensional spouted beds with different sizes and with two different particles, placebo and soybean.