EXPERIMENTAL ANALYSIS OF THE DRYING KINETICS OF A FOOD PRODUCT

ABSTRACT

A laboratory system allowing for the characterization of the thin-layer drying kinetics of olive bagasse at relatively high temperatures was designed and constructed. The system, which permits a wide range of operating velocities and temperatures, up to 700°C, allowed the weight loss of the sample to be monitored continuously. Constant drying conditions were maintained using an on-line computer. The drying conditions investigated in this study included combustion products of atmospheric air and propane with dry-bulb temperatures ranging from 125°C to 250°C, relative humidity lower than 1% and gas velocities ranging from 0.5 to 2.0 m/s.     

Agglomeration in fluidised bed gasification of biomass

Three promising biomass fuels for southern Mediterranean regions were tested for their agglomeration tendency in an atmospheric lab-scale fluidised bed (FB) gasifier using quartz and olivine as bed materials. The defluidisation temperatures of the energy crops Giant Reed (Arundo donax L.) and Sweet Sorghum bagasse were respectively approx. 790 °C and 810 °C, in both bed materials, while the agro industrial residue olive bagasse caused defluidisation of the quartz bed at 830 °C and olivine bed at > 850 °C. Agglomerates from these tests were analysed with SEM/EDS. Coatings and necks between bed particles were formed due to ash derived potassium silicate melt. For the first two fuels cluster-type agglomerates around remains of char particles were observed. Thermodynamic equilibrium simulations of each chemical system were performed to cross examine the predicted ash melting temperatures and chemistry with experimental findings. Predictions of potassium liquid compounds, like K₂O·SiO_2(l) were verified by EDS analyses on the particle coatings. FB gasification of olive bagasse resisted defluidisation up to higher temperatures because of its lower potassium and higher calcium content, especially in the case of olivine bed. The latter experimental finding coincided with thermodynamic predictions.     

Stress and Failure Prediction for the Drying,Tempering, and Cooling of Extruded Durum Semolina

ABSTRACT

This work presents a method to predict the stress and breakage that is caused by the drying of hygros-copic materials. Stresses were predicted for a viscoclasic cylinder with the properties of extruded durum semolina, or pasta noodles. The stresses were calculated as functions of the transient moisture and tem-perature gradients in the material which were predicted for the combined processes of drying, tempering,and cooling. The time and radial position of failure were predicted based on failure data for extruded semolina.

Isotherm data for extruded durum semolina were obtained for temperatures from 40 to 60°C and for relative humidities from 75 to 95%. The results were fit with a modified form of Henderson's equation.Thermal conductivities were measured for temperatures from 30 to 50°C and a moisture range of 12 to 27% (dry basis).

A drying model based on the principles of irreversible thermodynamics; (Fortes, 1978; Fortes and Okos, 1981a, 1981b) was used to successfully predict drying curves for a range of experimental conditions. Transient moisture and temperature profiles were calculated numerically, and a receding evapora-tion front was predicted to exist. Drying was predicted to be a coupled liquid, vapor, and heat transport phenomena.

The drying data were used in a stress analysis of a Maxwell viscoelastic cylinder to predict trends in stress development under various contiitions of combined drying, tempering, and cooling. High temperature-high humidity drying, HTHH, (lOO°C, 65% RH) was compared with low temperature-low humidity drying, LTLH, (53°C, 13% RH). The HTHH drying offered definite advantages in terms of reduced product breakage susceptibility. The reasons for those advantages were increased failure strength and a decreased moisture gradient at the end of drying. In a five-stage drying process, the cooling stage was shown to have a significant impact on the predicted levels of stress and on the strength of the extruded material. Analysis of the model suggested that gradual temperature and humidity transitions from stage to stage in multistage processes were important to product quality.     

DEVELOPMENT OF THE CHARACTERISTIC DRYING CURVE FOR CASSAVA CHIPS IN MONOLAYER

ABSTRACT

Drying kinetic curves and modelling for cassava chips were determined using a pilot-size air dryer. Operating conditions involved temperatures ranging from 35 to 90 ° C, air flow velocities from 0.5 to 2.0 m/ s, and air moisture content from 0.005 to 0.060 kg water/ kg dry air. Sorption isotherms at temperatures of 23, 45 and 60 ° C were obtained. Results for the drying experiments can be used to calculate the optimal drying conditions for dehydration of cassava roots in multilayers     

DRYING OF SUGAR BEET PULP USING A LABORATORY AIR DRIER

ABSTRACT

Drying curves for sugar beet pulp were obtained in a laboratory-scale air drier. Dehydration conditions were: temperatures in the range of 35 to 90 ^°C, air flow velocities of 0.5 to 2.0 m/s, and air moisture content of 0.005 to 0.06 kg water/kg air. Using data from thin layer experiments, a mathematical model was derived to describe the dehydration behaviour under the described conditions. The model was able to predict data obtained from deep bed experiments. Results from this work could be used to develop a design methodology for dryers that operate at relatively low temperatures (<90^°C).     

BATCH DRYING OF SHELLED CORN IN TWO-DIMENSIONAL SPOUTED BEDS WITH DRAFT PLATES

ABSTRACT

Geometrically similar spouted beds with draft plates were used to obtain the drying characteristics of freshly harvested shelled corn with 0.28 to 0.31 kg/kg initial moisture content at different air inlet temperatures and bed heights. Thermal equilibrium between air and grains was achieved at minimum spouting conditions. The drying kinetics of shelled corn in a drafted two-dimensional spouted bed was found to be of the "thin layer" type. Expressions for the model parameters in Page's equation accounting for the bed geometry, grain moisture content, and drying conditions were developed.     

A SIMPLIFIED MODEL FOR DETERMINATION OF MOISTURE DIFFUSIVITY OF DATE FROM EXPERIMENTAL DRYING CURVES

ABSTRACT

Experimental drying curves for Tunisia Deglet Nour dates were obtained in a laboratory dryer under different drying conditions The air temperature was varied from 30 to 69^°C, relative humidity from 11.6 to 47.1 % and air velocity from 0.9 to 2.7 m/s. A numerical method to obtain a solution of a diffusion equation in which the diffusivity depends upon temperature and moisture content has been proposed to investigate the moisture movement in a date by assuming the sample to be a homogenous infinite cylinder. To rind the fitting moisture and temperature dependent diffusivity, the calculated drying curves are compared with the observed drying curves and an empirical equation for the moisture diffusivity of the date has presented as a function of temperature and moisture. It has been shown that the moisture distribution in the date during drying can be obtained by using the empirical equation presented.     

THIN-LAYER DRYING CHARACTERISTICS OF ROUGH RICE AT LOW AND HIGH TEMPERATURES

Abstract

Thin-layer drying characteristics of rough rice were determined at temperature ranging from 11.8 to 51 °C and for relative humidities ranging from 37.1% to 91.3%, with initial moisture contents in the range of 24.7 to 41.6% dry basis. An oven, a self contain air conditioning unit, recently developed in Japan, was used for this experiments. With this apparatus, very smooth drying curves were obtained. The data of sample weight, and dry and wet bulb temperatures of the drying air were recorded continuously throughout the drying period for each test. The drying process was terminated when the moisture content change in 24 h was less than 0.2 % d.b. (weight change was less than 0.05 g). The final points were recorded as the dynamic equilibrium moisture contents.

The drying data were than fitted to the Page model. The model gave a very good fit for the moisture content with an average standard error of 0.294 % d.b? Both the drying parameters, K and N, are function of drying air temperature and relative humidity. The effect of variable initial moisture content was also described effectively by the empirical Page model. The drying time employed had a large effect on the K and N values. The results presented here, over typically 5 day drying, will be useful in the long term moisture transfer process occurring during ventilated storage.     

Electrical Properties of Precipitated Lignins from Different Black Liquors

Abstract

Some corelations over the structure and dielectric properties of precipitated lignins from different waste black liquors of various modified soda and kraft pulping of bagasse have been discussed. The dielectric and the electrical properties at the same temperatures and frequencies ranges for the tested samples showed some differences which seems to be attributed to the difference in the structure and intermolecular interaction between lignin molecules. These differences are discussed on the basis of the molecular structure obtained from the infrared spectra. The conduction mechanism in the case of kraft and kraft sulfite lignins is due to electron transfer from the valence band to the conduction band by thermal activation.     

Air Drying Kinetics of Potato Cylinders

ABSTRACT

An experimental air tunnel dryer was used to investigate the kinetics of moisture transport in potato cylinders (Solanum tuberasum). Acoordingly, the experimental results, represnting only falling-rate drying behaviour and hence. dehydration completely controlled by internal mass transfer, were interpreted on the basis of Fick's diffusional model for non-stedy state radial diffusion. The effects of air velocity and temperature on the drying rate were studied. with he temperature being the principal controlling factor. Analysis of the drying curves by the method of slopes resulted in a variable effective moisture diffusivity. Shrinkage as a function of moisture content under various drying conditions was investigated. The volumetric shrinkage of the samples was affected mainly by air velocity. whilst air temperature had a negligible effect. Good agreement was obtained between the experimental apparent density data and the predicted correlation.     

EXPERIMENTAL RESEARCH ON DRYING CHARACTERISTICS OF LITCHI

Abstract

The changes of inner temperature and drying characteristics of rind, membrane, flesh and stone of Litchi were investigated under constant relative humidity of drying medium at different temperatures at atmospheric and decompression conditions. Results show that the membrane resists moisture from moving the flesh or stone to rind. Decompression drying is helpful to the moisture evaporation of the fruit; when the moisture content lowers to a certain critical point, the drying rate is higher than that of atmospheric drying. Drying curves are very different from those of seeds drying or particle drying. In the drying process, temperature of Litchi whole fruit rises quickly at the beginning to a maximum region, then falls to a minimum before rising again slowly. All the phenomena are due to the composite structure of Litchi.     

Principal Component Analysis of the Hydroxymethylation of Sugarcane Lignin: A Time-Depending Study by FTIR

Abstract

The hydroxymethylation of Acetosolv lignin from sugarcane bagasse was studied at 40°C between 0.25 and 8 h by Fourier-transformed infrared spectroscopy (FTIR). Principal Component Analysis (PCA) of the spectra has determined that addition of formaldehyde to the lignin fragments was completed within 4 h. After that time, only condensation of the fragments occurs, leading to a resol-type crosslinked resin. PCA performed in selected regions of the FTIR spectra showed that the same results are also obtained for the stretching region of O-H and C-H within the range from 2800 to 3800 cm^?1, which is not usually considered in the spectroscopic evaluations of modified lignins.     

The Effect of Path Diffusion on The Effective Moisture Diffuslvlty in Carrot Slabs

ABSTRACT

In order to evaluate the effect of path diffusion on the average moisture diffusivity in carrot. drying curves for different shaves (slices and cylinders) and temperatures of 50, 60 and 70°C were ohtained takine into consideration the use of an average leneth of carrot sample (slice thickness or the cylinder radio). The. results showed significant differences betuecn radial and axial average diffusivities. Significant differences were also observed between core and annular diffusivity. The experimenta1 drying curves did not show enough evidence on the effect of drying temperature on the average moisture diffusivity.     

WOOD DRYING MODELLING BASED ON THE WATER POTENTIAL CONCEPT: HYSTERESIS EFFECTS

ABSTRACT

The boundary absorption curve of the moisture content - water potential relationship of aspen sapwood was determined at 20°C. In order to quantify the impact of the hysteresis of the relationship on the results obtained with a wood drying model based on water potential, the results obtained were merged to the boundary desorption curve and hypothetical scanning curves were used to model the forced convection drying of aspen sapwood.

A strong hysteresis was found between the boundary desorption and absorption curves, the moisture content being higher in desorption than in absorption at a given water potential. The effect of the hysteresis on the simulation results was found to be significant. The results show that differences in the predicted drying time as high as 25% can occur depending on the moisture content - water potential curve used. This demonstrates that the sorption history of wood should be considered in the development of wood drying models.     

Drying and Heat Transfer Characteristics for a Novel Fluidized Bed Dryer

Abstract

The use of a fluidized bed dryer with a lateral air flow and mechanical agitation to the drying of sludge from a wastewater treatment plant was investigated. Experimental curves of moisture content vs. drying time, as well as heat transfer coefficients and the size characteristics of the products, were determined at temperatures between 80°C and 110°C, a stirring rate of 55 rpm and air velocity of 0.9 m/s for 3 kg sludge batches with initial moisture contents of 0.55 and 0.65 (d.b.). Experimental drying kinetics were compared with values derived from three models based on Fick's second law, namely: the constant diffusivity model, the simplified variable diffusivity model, and the modified quasi-stationary model.     

THE MOISTURE SORPTION ISOTHERMS OF CEFOTAXIME SODIUM SALT

ABSTRACT

The water sorption isotherms of the cefotaxime sodium salt were determined at 30 and 40° C. Cefotaxime sodium salt was maintained at equilibrium relative humidities ranging from 40 to 80 %. Equilibrium moisture content was determined by the Karl Fischer method. The moisture sorption isotherms showed that the equilibrium moisture decrease while the temperature increase. The experimental curves of equilibrium humidity were fitted by different models (Bradley, Halsey, Henderson, Kuhn, Smith and Iglesias and Chirife and GAB). Parameters of each equations were determined by non-linear regression analysis. The best fit was obtained by Iglesias and Chirife model. The isosteric heat of moisture sorption calculated by Claussius Clapeyron equation varied from 64·45 to 48·03 kJ/mol when moisture content changed from 7 to 9·5 %.     

Comparison of Drying Rate Curves of Porous Solids in Superheated Steam to Those in Air

ABSTRACT

Drying of porous solids was experimentally investigated in superheated steam as well as in air. Drying rate curves, including critical moisture contents, in steam at subatmospheric pressure, were compared to those for air at atmospheric pressure; moreover, they were compared to those for steam at atmospheric pressure as well. The former comparison was carried out under conditions of sample temperatures of 41.8–42.5°C (which were nearly equal to saturation temperatures of 42.1–42.2°C at pressures of 8.23–8.30 kPa) for the constant rate period in steam and the corresponding sample temperatures of 42.0–45.0°C (which were close to the wet-bulb temperatures) for the constant rate period in air. There were distinct differences between normalized drying rate curves, including critical moisture contents in steam and in air at the above similar sample temperatures for materials of baked clay, firebrick, and cemented glass balloons over the minimum value of 8.3 × 10^?3 µm and up to the maximum value of 1.2 × 10² µm in cumulative pore-size distributions: longer constant rate periods and lower critical moisture contents in steam than in air, and higher drying rates in steam than in air for the falling rate period. Moreover, the latter comparison of the drying rates in steam at subatmospheric pressure to those in steam at atmospheric pressure revealed that the differences in normalized drying rates between subatmospheric pressure and atmospheric pressure were small for both materials under mild external conditions. These findings were common to the baked clay, firebrick, and cemented glass balloons over a wide range of pore-size distributions studied in the present work, as well as sintered coarse glass beads as previously reported.     

Production of activated carbon from olive bagasse by physical activation

Activated carbons were produced from olive bagasse and their characteristics were investigated. Olive bagasse was first carbonized at 500 °C in N₂ atmosphere. Then, the obtained chars were activated with steam. The effects of activation temperature and duration were examined. The resultant activated carbons were characterized by measuring their porosities and pore size distributions. The activated carbons produced had the BET surface areas ranging from 523 to 1106 m²/g. The total pore volume was increased from 0.2981 to 0.6067 cm³/g. Adsorption capacity was demonstrated by the iodine numbers. The surface chemical characteristics of activated carbons were determined by FTIR spectroscopic method and Boehm's titration method. The microstructure of the activated carbons prepared was examined by scanning electron microscopy (SEM). The experimental data was proved that the properties of activated carbons depend on the final temperature of the process and duration of treatment at the final temperature.     

HYDROGEN TRAIPB-NUUEAR MAGNETIC RESONANCE FOR INDUSTRIAL MOISTURE 8EN8MG

ABSTRACT

A procedure was developed based on a three-component physical model to simulate the drying characteristics of Laird lentils. In this model, the cotyledons were simplified as a homogeneous slab where moisture transfer was governed by a one-dimensional diffusion equation, and the hilum and seedcoat were considered as two parallel routes for moisture to escape from a seed. The simulation procedure was verified with the experimental data from thin-layer drying testing on samples of 19.0 to 24.5% initial moisture content at temperatures from 23 to 80°C and relative humidities from 5 to 70%. Using previously obtained information on the transport properties of the cotyledons, the seedcoat, and the hilum, the simulation followed the drying data closely over temperatures between 23 and 60°C.