G. Massarani

DRYING OF PASTES IN SPOUTED BEDS OF INERT PARTICLES : DESIGN CRITERIA AND MODELING

ABSTRACT The drying of pastelike materials can be performed well in spouted beds (SB) of inert particles. In this work the drying performance of pastes in conical pastes in conical spouted beds is analyzed as a function of column dimensions, fluid flow characteristics and paste properties. imulated data on fluid flow together with the experimental results on drying of different pastelike materials are presented and discussed to provide criteria for the design of a conical spouted bed dryer for suspensions.

BIXIN POWDER PRODUCTION IN CONICAL SPOUTED BED UNITS

ABSTRACT Recent work has demonstrated that the red carotenoid bixin is easily extracted from Bixa orellana seeds by particle attrition and impact rather than by solvent extraction. This technique may require a previous step for drying seeds at a safe temperature to preserve pigment quality. A spouted bed (SB) with a draft tube is the most appropriate equipment to process both seed drying and bixin extraction at low operational costs. Operational parameters of the SB unit are optimized as a function of the powder production rate. The maximum air inlet temperature for drying the seeds is also specified. A high performance liquid chromatography method has been developed for the semi-quantitative determination of bixin content in the powder produced. Results show that this SB unit can be more competitive than ball mill equipment.

Treatment of milk industry effluent by dissolved air flotation

In this work, the application of the flotation technique by dissolved air (FAD) to the treatment of milk industry effluent (milky effluent) is analyzed. Initially, batch studies were carried out in a column built of acrylic with an external diameter of 2.5 cm and 50 cm in height. Afterwards, the performance of a flotation tank with a 5.5 L capacity in the treatment of the milky effluent was addressed. In continuous mode of operation, separation efficiencies up to 90% were obtained for the experiments carried out at a saturation pressure of 4 atm and having a ratio of feed flow rate (Qa) to saturated liquid flow rate equal to 1. The separation efficiency for flocculated milk was estimated from the overall mass balance for the flotation tank. Separation efficiencies obtained agreed very well with the experimental results collected for Qa/QLs ratios lower than 1.

Homogeneous hydraulic and pneumatic conveying of solid particles

A discussion is provided of the difficulties and limitations involved in the application of the one-dimensional two-phase flow model to estimate pressure gradients associated with the transport of particles. Two particular cases are investigated, namely, hydraulic conveying and pneumatic transport. The validity of the model is checked by comparing experimental data with predicted values of pressure gradients and void fractions. New approaches for estimating the interaction forces in hydraulic and pneumatic transport are proposed. It is demonstrated that, despite its limitations, the two-phase flow model may provide good predictions for the pressure gradients.

Comparative study of flotation techniques for the treatment of liquid effluents.

Abstract This work aimed to study the performance of three different induced air flotation units (flotation column, flotation tank and centrifugal flotation in hydrocyclone) for the treatment of a synthetic dairy effluent. Under continuous operation, it was possible to achieve removal efficiencies of milky material in suspension up to 90%, both for the flotation column and the flotation tank units. Using the centrifugal flotation unit in hydrocyclone, it was possible to decrease up to 45% of all suspended material in the effluent, with a clarified flow rate approximately three times greater than those found for the previous flotation units. In the centrifugal flotation unit, better results were obtained for air flow rate ‐ feed flow rate ratios (Qair/QL) greater than 0.15, and for underflow ‐ overflow ratios (Qu/QO) lower than 1.0.

Grain drying in countercurrent and concurrent gas flow - modelling, simulation and experimental tests.

ABSTRACT Mathematical models and numerical techniques for simulation of parallel flow grain drying has been proposed and tested. Concurrent flow drying has been simulated using a steady state model. In order to overcome numerical difficulties that appears in simulation of countercurrent flow drying under operational conditions that leads to thermodynamics equilibrium in any section of the dryer stage, a robust approach has been developed based on simulation of the operation starting from initial transient conditions. A lab unit for grain drying has been developed, composed of a countercurrent flow stage coupled on a concurrent flow stage. The mathematical models and numerical techniques has been tested through the comparison between calculated results and experimental data measured for com drying.

Study on batch sedimentation simulation: establishment of constitutive equations

Abstract The constitutive equations which characterize a porous medium are in general established from a study of the filter cakes, but the inherent differences in the processes for forming the cakes by means of filtration or sedimentation, make it difficult to properly characterize these sediments. Dynamic data of a batch sedimentation process as a function of variation in the height of the interfaces and the solid concentration profile, have been used to evaluate the parameters of constitutive equations for sediments. Starting from experimental data and from a model of the batch sedimentation process, and considering the coexistence of two distinct zones during the test—that of free settling and that of compression, coupled with balanced equations of global mass and height restriction-simulations were made and the parameters of the equations were evaluated by adjusting the results of the model to the experimental data.

Wastewater treatment by flotation

This work deals with the performance analysis of a separation set-up characterized by the ejector-hydrocyclone association, applied in the treatment of a synthetic dairy wastewater effluent. The results obtained were compared with the results from a flotation column (cylindrical body of a hydrocyclone) operated both batch and continuously. As far as the experimental set-up studied in this work and the operating conditions imposed to the process, it is possible to reach a 25% decrease in the total effluent chemical oxygen demand (COD). This corresponds approximately to 60% of the COD of the material in suspension. The best results are obtained for ratios air flow rate-feed flow rate (Qair/QL) greater then 0.15 and for ratios underflow rate-overflow rate (Qu/Qo) lower than 1.0.

Influence of the flocculating agent in sedimentation and performance of a non flocculent strain of Zymomonas mobilis in the ethanol production process

The influence of the flocculating agent was studied in the performance (measured by microbial growth and ethanol production) of a non flocculent strain of Zymomonas mobilis, as well as the potentiality of the sedimentation process in the separation of the biomass from the fermentation broth. Among the flocculating agents studied, it was verified that both tannin and the polyelectrolyte yielded good results with regard to cellular performance. However, with regard to sedimentation tannin is more adequate to be used in processes involving Zymomonas mobilis.

Modelling of the dispersed air flotation process applied to dairy wastewater treatment

The aim of this work was to develop a mathematical model for a continuously operating flotation tank to provide the scale-up and optimization of the separation system. The fluid dynamic of the tank was assumed to be a perfect mixture and the flotation kinetics to be a first-order reaction, as suggested by the batch operation. The experiments were carried out in a continuously operating 60 L tank, used in the treatment of a synthetic dairy waste at its isoelectric point. A mathematical model that describes the behavior of a continuously operating flotation tank used in the treatment of a synthetic dairy waste at its isoelectric point is not only proposed, but also validated with experimental data.