Julio L. Bueno

Characterization of Spanish biomass wastes for energy use.

Energy plays an important role in the worlds present and future. The best way to absorb the huge increase in energy demands is through diversification. In this context biomass appears as an attractive source for a number of environmental, economical, political and social reasons. There are several techniques used to obtain energy from biomass. Among these techniques, the most commonly used throughout the world is a thermo-chemical process to obtain heat. To optimize the combustion process in adequate reactors, a comprehensive study of the characterization of biomass fuel properties is needed, which includes proximate analysis (determination of moisture, ash, volatile and fixed carbon content), ultimate analysis (C, H, N, S and O composition) and calorimetry, focusing on biomass fuels obtained in Spain.

Biomass proximate analysis using thermogravimetry.

This work proposes a 25 min-last thermogravimetric method as a tool to determine biomass samples proximate analysis data (moisture, ash, volatile matter and fixed carbon contents) just by direct measure of weight changes on each samples TG chart. Compared with international standards commonly used to that aim, TG is a faster and easier to develop technique. Obtained results were satisfactory, with AEE under 6% for moisture and volatile matter, close to 10% for fixed carbon determination and AAD of 1.6 points for ash content.

Diffusion coefficients in supercritical fluids: available data and graphical correlations

The methods for obtaining reliable data on diffusion coefficients at high pressure have received great attention over the last 15 years. This interest has been due to the importance that supercritical fluids have assumed in some industrial areas, mainly in emerging separative operations based on mass transfer mechanisms. This review includes all the available data of diffusion coefficients in supercritical fluids at infinite dilution. Revised literature includes references until 1998. Frequent types of graphical correlation were analyzed.

Determination of binary diffusion coefficients of benzene and derivatives in supercritical carbon dioxide

Abstract The Taylor—Aris method is applied to calculate binary diffusion coefficients in supercritical carbon dioxide under quasi-infinite dilution conditions by means of the Giddings and Seager chromatographic technique. Benzene, toluene, ethylbenzene, n -propylbenzene and cumene have been tested at 40, 50 and 60°C in the pressure range 150–350 bar. The data have been correlated with temperature, pressure, density and viscosity, obtaining significant dependences and useful equations for obtaining new data by interpolation.

Measurement of diffusion coefficients for 2-nitroanisole, 1,2-dichlorobenzene and tert-butylbenzene in carbon dioxide containing modifiers

The molecular diffusion coefficients of 2-nitroanisole, 1,2-dichlorobenzene and tert-butylbenzene in supercritical carbon dioxide and carbon dioxide containing modifiers were determined by using the Taylor–Aris dispersion technique. Experimental values are reported for temperatures ranging from 313 to 333 K and pressures between 15.0 and 35.0 MPa. The influence of pressure, temperature, density and viscosity on the binary diffusion coefficients was examined. The addition of low proportions of methanol and n-hexane as modifiers had an important effect on the diffusion coefficient of the three solutes.

Determination of kinetic parameters for biomass combustion.

The aim of this work is to provide a wide database of kinetic data for the most common biomass by thermogravimetric analysis (TGA) and differential thermogravimetry (DTG). Due to the characteristic parameters of DTG curves, a two-stage reaction model is proposed and the kinetic parameters obtained from model-based methods with energy activation values for first and second stages in the range 1.75·10(4)-1.55·10(5)J/mol and 1.62·10(4)-2.37·10(5)J/mol, respectively. However, it has been found that Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose model-free methods are not suitable to determine the kinetic parameters of biomass combustion since the assumptions of these two methods were not accomplished in the full range of the combustion process.

The regrowth of phytoplankton cultures after UV disinfection.

This study addresses how cultures of three phytoplankton species -Chaetoceros calcitrans, Chlorella autotrophica and Phaeocystis globosa - can recover from the effects of UV-C exposure if the cells are placed in a rich medium. Flow cytometry and pulse amplitude modulation (PAM) were used to determine cell recovery after UV treatment. The recovery of C. calcitrans was complete 9 days after treatment. For C. autotrophica, the recovery was noticeable 5 days after treatment. P. globosa only recovered if the UV dose did not exceed 7.3×10(5) μWs/cm(2). The recovery of the UV-treated cultures introduced to a regrowth medium, compared with the recovery of the irradiated cultures kept in their original environment, had two main characteristics: cell recovery was slower but was more efficient. This pattern of recovery has very important implications for real ballast water management systems because such systems discharge treated water into the environment.

Evolution of phytoplankton cultures after ultraviolet light treatment.

Introducing invasive species in new environments through ballast water is a specific problem of contamination and has recently become one of the main concerns of Maritime Organizations. Ultraviolet-C radiation (UV-C) is a technological alternative to prevent this maritime pollution. This study addresses the effect of UV-C on different phytoplankton cultures and also the ability to recover following exposure to damage. A UV-C low-pressure lamp irradiates the cultures. The distance from the source and the thickness of the layer prevent part of the energy from reaching the culture and the disinfective process is diminished. Some cultures such as Chlorella autotrophica and Chaetoceros calcitrans can easily recover from UV-C damage. However, Phaeocystis globosa does not have this ability. C. calcitrans forms cysts and exhibits two different behaviours depending on the dose applied.

Sedimentation of coal slurries: A procedure for the determination of the flocculated-solid flux curve useful for the design of continuous settling tanks

Abstract Batch sedimentation tests with coal mining wastes have been carried out in a wide range of concentrations and flocculant dosages in an original prototype of photosensible sedimentograph. In spite of the peculiarities of the slurries studied, the experimental procedure and the way the data have been fitted to an empirical equation can be extended to any suspension as a useful tool in the preliminary design of settlers, whatever the nature and the complexity of a slurry may be.

Experimental binary diffusion coefficients of benzene and derivatives in supercritical carbon dioxide and their comparison with the values from the classic correlations

Abstract Experimental data for diffusion coefficients obtained by supercritical fluid chromatography (SFC) according to the Taylor–Aris dispersion method are compared with results from predictive equations for dense fluids. The goodness of fit and the bias of the correlation only suggest a slight empirical correction in these equations not specifically formulated for supercritical fluids (SCFs) and justify a persevering effort in experimentation oriented to the development of generalized models.