Jean-Rodolphe Puiggali

ANALYSIS OF THE DRYING OF RESIDUAL SLUDGE: FROM THE EXPERIMENT TO THE SIMULATION OF A BELT DRYER

ABSTRACT The drying of residual sludge is a current environmental problem not sufficiently described in the literature, hence research investigations on this dewatering process are required. This paper proposes a modelling of a conveyor dryer belt. However the study of residual sludges dewatering in order to design or simulate drying equipment requires some experimental investigations. An analysis in terms of drying kinetics is proposed in this paper. Specific experiments were also needed in order to better describe some particular aspects such as crusting, shrinkage, and particle size impact. According to these data some analytical expressions have been derived and integrated in a belt dryer model. The set of air operating conditions (T, RH, v) was reduced to a single parameter, the drying potential. The results of the simulations show that a conveyor belt dryer is not well adapted to activated sludge. This is essentially due to a crust phenomenon. For a PVC industrial sludge this kind of dryer is more efficient and allows drying with reasonable residence times. Several simulations were run in order to point out the relevant parameters of the process.

DRYING OF SHRINKING MATERIALS : MODELLINGS WITH SHRINKAGE VELOCITY

ABSTRACT An attempt is proposed to modelize the coupling effects between heat transport, mass transport and solid shrinkage during the drying of like gels products. A special attention is laid upon the different ways to determine the solid displacement. Some experimental results are presented to validate the modelling approach.

Experimental Determination and Modeling of Sorption Isotherms of Tropical Fruits: Banana, Mango, and Pineapple

Abstract Sorption isotherms of banana, mango, and pineapple have been experimentally found at 40, 50, and 60°C by use of the salt method for a range of water activities from 0.056 to 0.85. The sorption capacity of these fruits increases with the temperature for a given water activity. The experimental curves have been simulated by the GAB and BET models. The BET model ensures a better representation of the experimental results for water activity lower than 0.35 with maximum deviation of 1.0, 1.5, and 2.0 kgw · kgdm−1 for respectively banana, mango and pineapple. On the contrary, the GAB model enables the representation of the whole desorption isotherms and the estimation of the water content corresponding to monolayer saturation and of the isosteric heat of sorption. It also takes into account the temperature effect. The isosteric sorption heat of the three studied products are deduced from experimental results and empirical correlations are proposed leading to a satisfactorily representation.

Modeling of Banana Convective Drying by the Drying Characteristic Curve (DCC) Method

Abstract Experimental convective drying tests of banana have been carried out for different air conditions to show the influence of air temperature, absolute humidity and speed on the drying rate. The analysis of the drying rate evolution as a function of product water content enables the identification of fourth drying phases: temperature rising (phase 1), exponentially decreasing drying rate (phase 2), linearly decreasing drying rate (phase 3) and very low drying rate (phase 4). The temperature rising phase 1 being very short and the last phase 4 being not reached during typical drying, the drying characteristic curve (DCC) has been represented by two different mathematical functions fitting phases 2 and 3. Their parameters have been determined by minimization of the quadratic errors between experimental and theoretical curves. It leads to a unique curve (the DCC) representing all air drying conditions the integration of which enables the calculation of the product water content with a maximum error of 0.09 between experimental and simulated values.

DESCRIPTION AND ANALYSIS OF TIMBER DRYING KINETICS

ABSTRACT In this paper an experimental and semi-analytical technique is described that provides a method of estimating a macroscopic drying kinetics curve and internal moisture content profiles is described. Moisture gradients and the time evolution of these gradients are analysed as a function of the air drying parameters (dry-bulb, wet-bulb temperature and the velocity) and the product parameters (thickness and density). The material used as an illustration is a maritime-pine-wood.

Influence of heartwood-sapwood proportions on the drying kinetics of a board

SummarySeveral properties have been measured for pinewood samples, corresponding to the region within the heartwood or the sapwood, with the aim of treating wood as a heterogeneous medium when modelling the drying process. A two driving-force model is used to compare a homogeneous and a heterogeneous approach to the drying of a pinewood board. The main difference between the two theoretical descriptions is a specific boundary condition for the inter-region, which may generate jumps of the moisture content fields. Experimental and numerical results are presented and some comments are made concerning the use of the heterogeneous model.

Crack Appearance during Drying of an Alumina Gel: Thermo-Hydro-Mechanical Properties

Most heterogeneous catalyst supports used in refineries are composed of porous alumina ceramics. Drying has been identified as a critical process for final product mechanical strength. In the literature, numerous papers deal with drying-induced stresses, which can lead to crack initiation. However, there are few papers devoted to experimental study of drying conditions that promote cracking. The objective of this work is to enhance knowledge of cracking behavior, specifically by studying alumina gel drying. First, the relation between drying conditions and first crack initiation is studied experimentally. Then a complete thermo-hydro-mechanical characterization of the alumina gel is made, including moisture content as a parameter.

Effects of Freeboard Volatile Release During Fluidized Bed Incineration of a Model Waste

This paper describes a model for the fluidized bed combustion of volatile matter from waste. This waste is assumed to be composed of wood, cardboard and PVC. The model assumes that a fraction of the volatile content is released within the freeboard, as a result of both pyrolysis and transport of the devolatilizing particles. The model describes precisely the diffusion-controlled combustion of the volatile matter within the bed, on the basis of a hydrodynamic model of the bed, combined with energy and mass balance equations. The results of the model show that the release of volatiles in the freeboard may increase the freeboard temperature by 200 K and may multiply the emissions of NO 25 times.

Liquid Pressure Measurement in Filtration–Compression Cell

Filtration-compression cells are usually used during laboratory tests to describe the behavior of materials submitted to mechanical dewatering processes. Among the parameters measured, the liquid pressure at the surface of the filtration cake is a good indicator of the dewatering evolution. However, in the classically designed cells, the information given by pressure transducer during the expression phase does not confirm the theory. A new design of the piston is proposed and studied in this paper. A pseudo piston is added ahead of the pressure transducer in order to avoid the contact with the solid forming the cake during the expression stage. Experiments were carried out on different compressible materials: talc, kaolin, and activated sludge. Every experiment showed that the liquid pressure at the surface of the cake reached zero at the end of the dewatering test, even for extremely compressible cakes.

Quality of CFD models for jet flow analysis for the design of burners and boilers

CFD models are increasingly used for the design and optimisation of boiler combustion chambers. Numerous commercial codes are available, and the user is confronted with making a proper choice for a particular application. In this paper, the accuracy and effectiveness of the popular code FLUENT™ is investigated in terms of the different turbulence models and numerical schemes that are bundled in the software. The tests are performed for different simple experiments, involving classical hydrodynamic conditions with no combustion. The conclusion of these tests involves also the additional criterion of the computational time required for achieving a reasonable accuracy.