ISEP – DEQ – Comunicações em eventos científicos
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- The importance of drop coalescence in a stirred liquid-liquid extraction (Kühni) columnPublication . Gomes, M. L. A. C. N.; Guimarães, M. M. L.; Zamponi, G.; Stichlmair, J.; Regueiras, P. F. R.; Cruz-Pinto, J. J. C.; Cox, Michael; Hidalgo, Manuela; Valiente, ManuelExperiments performed at low agitation speeds, using the high interfacial tension toluene (dispersed)-water (continuous) system, in a pilot plant Kühni column, show that coalescence events are generally present and cannot be neglected in column-type liquid-liquid contactors, especially when the goal is the accurate modelling of the transient processes for control purposes. In this work, the features of this behaviour and the applicability to this situation of a new, fast and precise, recently developed algorithm, 1 that describes the dynamic behaviour of an agitated column, is illustrated. Experiments were performed at low agitation speeds, using the above high interfacial tension system. The simulations show reasonably good agreement with the experimental results and provide insight on the underlying behaviour mechanisms and important guidelines for the accurate modelling of the dynamics of the column.
- Incidence of nitrate, nitrite, chloride and phosphate in groundwater in Modivas, PortugalPublication . Silva, Susana; Sousa, José; Ramalhosa, M. J.; Antão, M. Cristina; de Sá Barroso, Maria de Fátima; Pina, Maria de Fátima; Pina, Maria de Fátima; Delerue-Matos, Cristina; Delerue-Matos, Cristina; Beleza, VitorinoThe aim of this project consisted in the evaluation of chemical quality of groundwater in domestic wells situated in the village of Modivas, which belongs to the district of Porto, in north of Portugal. The population doesn’t have a public water supply system and the groundwater is a significant source for domestic, livestock breeding and agricultural use. The quality of water samples were collected from domestic wells with an approximate deph of 15m and the quality has been investigated with respect to pH, conductivity, temperature, nitrate, nitrite, phosphate and chloride. Geographical coordinates were also measured at each location, using a GPS device. The obtained results show that a strong nitrate contamination exists in the studied area. A very small percentage of wells (2%) were above the guideline for nitrite. As for the other parameters (chloride and phosphate) the results never exceeded the legal limit.
- Re-utilization of sewage sludges as a precursor for activated carbon productionPublication . Gutiérrez, Maria S. C.; Rocha, Maria J.; Mendes, Sandra S.; Freitas, Maria Madalena; Silva, Paula; Beleza, VitorinoThe possibility of re-utilization of sewage sludges from wastewater treatment plants as raw-material for activated carbon production was investigated. Activated carbons were prepared from secondary sludges by physical activation with carbon dioxide. Pyrolysis was carried out in nitrogen atmosphere at 873 K during 3 h. Physical activation was performed in pure CO2 flow, for 1h, at temperatures between 1123 and 1223 K. Global yields of the process range from 30 to 4o wt %. Activated carbons have surface areas from 60 to 100 m?/g and micropore volumes up to 0,020 cm3/g. Porous structure presents about 50% microporosity. A chemically activated sample (H.SO,, 973 K, 15 min, N, flow) was also prepared for comparative purposes. Results show that activated carbons produced have potential to be used as pollutant adsorbent, but further optimization studies will be needed in order to improve its porous structure.
- Studies of particulate fouling for a water-kaolin suspension flowing in a horizontal square section channelPublication . Ribeiro, A. M.; Ferreira, V.; Campos, J. B. L. M.; Beleza, VitorinoExperimental particulate fouling studies were carried out for an aqueous suspension of kaolin at a concentration of6 kg/m, flowing at 2.99 x 103 m3/s in a square section horizontal channel and using stainless steel deposition plates. Fouling resistance curves obtained for three positions on the bottom deposition plates showed an initial enhancement of heat transfer, but as the deposition process continued, the fouling resistance increased until it reached a constant value. Measurements of the mass and the thickness of the dry kaolin deposits on the plates at the end of the experiment (144 days) showed that deposition was higher for the bottom plates than for the top ones.
- Precise and Fast Computer Simulations of the Dynamic Mass Transfer Behaviour of Liquid-Liquid Agitated ContactorsPublication . Guimarães, M. M. L.; Regueiras, P. F. R.; Ribeiro, L. M.; Madureira, C. M. N.; Cruz-Pinto, J. J. C.Algorithms for solving the population balance equations for the transient drop volume (v) and solute concentration (c) distributions and the dispersed phase hold-up of a continuous flow liquid-liquid system, with simultaneous drop coalescence and breakage, are very complex and make heavy demands on computing time, of the order of m4 (m being the number of discrete classes used). This paper simplifies and accelerates our already fast, recently developed algorithm, for the most common situation where a full description of the above bivariate (v and c) behaviour is not required. The mathematical foundations of the algorithm are developed and it is shown that meaningful, precise and very fast (oc m2) dynamic simulations of the full drop size distribution and of the width of the solute concentration distribution within each drop size fraction may be achieved in less than 8% of the real process time for a continuous flow stirred vessel, using an ordinary 486DX2/66MHz microcomputer. Besides the excellent time performance of the algorithm, the other important feature is that, as the full size-concentration distribution does not need to invoked or computed, a substantial economy in working memory is also achieved. Actual dynamic simulations of mass transfer and reacting systems have been performed. Limitations of space only compel us to restrict the discussion to mass transfer systems. The applicability of these techniques to real control situations is also highlighted.
- Introduction of the parameter 'Total Organic Carbon' (TOC) as a standard for the quality control of swimming pool waterPublication . Beleza, Vitorino de Matos; Costa, Rosária Santos; Baptista, Marta Pinto; Beleza, Vitorino; Pereira, IsabelSwimmers introduce organic compounds into swimming pools due to the transferring of sweat, saliva, skin, hair, urine, feces, among other materials, to the water. Water quality control in the tank must include some chemical parameters that will quantitatively reflect the presence of these contaminants in the water. Oxidability to permanganate is included in the regulations and norms of public swimming pools in most developed countries. According to the Portuguese norm NP-731, permanganate oxidability is determined by the oxidation of organic compounds in the water by potassium permanganate in acidic conditions when boiling for 10 minutes. |n fact, this procedure detects all reductants oxidized by the essay conditions, whether organic or inorganic. To overcome these limitations, several entities suggested the determination of Total Organic Carbon (TOC). lsocyanuric acid, H30;C;N;, is used as a stabilising agent for free chlorine. In its combustion, cyanuric acid is totally oxidised, and the products of this reaction are carbon dioxide, which contributes to the TOC value, water and nitrogen. Analytical confirmation of the carbon:isocyanuric acid relationship was performed in the Centro de Estudos de Aguas laboratory, achieving ‘the value of 0.27 quite close to the theoretical relation carbon:isocyanuric acid (0.28). This relationship will help to definition of a maximum value for TOC in swimming pool water, in function of its depth.
- Sustainability issues in swimming pools and spasPublication . Martins, Florinda; Beleza, Vitorino; Pereira, IsabelThis paper discusses sustainability applied to swimming pools and spas. Sustainability is nowadays a subject that crosses every human activity and health, sport and recreational activities are no exception. Well being is a target of modern society and can not be dissociated from social, environmental and economic aspects.
- Efficient computer simulation of the dynamics of na agitated liquid-liquid extraction columnPublication . Guimarães, M. M. L.; Gomes, M. L.; Regueiras, P. F. R.; Ribeiro, M. L.; Cruz-Pinto, J. J. C.Given the difficulties associated with experimentation upon liquid-liquid extraction processes, computer simulation of these processes has recently acquired great relevance and usefulness as complement, if not an alternative, to direct experimentation. This is becoming increasingly attractive, as both the power and the availability of personal computing increase. Recently, Ribeiro (1995), Ribeiro ef al. (1997)) developed a fast and precise algorithm, adapting population balance models as Coulaloglou and Tavlarides' (1977) for the dispersed phase breakage and coalescence, and both the rigid and the oscillating drop models as proposed by Cruz-Pinto ef al. (1983), for mass transfer. The algorithm enabled the simulation’ of the evolution in time of the trivariate joint distribution of drop properties in two-phase continuous mixers, in steady and transient states. A simplified version of this algorithm, that calculates the drop size distribution and the mean and standard deviation of solute concentration within each volume class, was further developed by Regueiras ef al (1996). In this work, the applicability of this simplified algorithm to the dynamic simulation of a Kithni liquid-liquid extraction column is illustrated. A transport model was developed from previous models of Cruz-Pinto (1979). Coulaloglou and Tavlarides’ (1977) drop interaction model was again adopted. It is shown that the algorithm is able to describe both the transient and the steady-state behaviour of a Kihni pilot column (Technical University of Munich), and the simulation runs that were made show good agreement with the experimental results. The present version of the algorithm predicts local hold-ups and drop size distributions at different column stages. So far, the results do not include mass transfer, but future work will contemplate this feature.
- THE SIMULATION OF INTERACTING LIQUID-LIQUID DISPERSIONS - A NEW ALGORITHM AND ITS POTENTIALITYPublication . Guimarães, M. M. L.; Cruz-Pinto, J. J. C.; Regueiras, P. F. R.; Madureira, C. N. M.[Abstract] The simulation of interacting liquid-liquid dispersions undergoing mass transfer and/or chemical reactions is a major chemical engineering problem, that has not yet been satisfactorily solved. The difficulties do not exclusively lie on the experimental validation of the models and their predictions, but are still rooted on the inability of current algorithms to describe the real nature of the dispersion, namely its full trivariate structure - distribution of drop volumes (v), ages (tT) and _= solute concentrations (c) - where v, t and ce are not satistically independent. A survey is given of the authors' latest, recently published (1,2), work and a detailed discussion is then presented of the fine structure and behaviour of the dispersion; the major requirement of an adequate statistical analysis of the simulation results is also dealt with. The paper ends with the authors views on possible trends of future research on this topic.
- Insights on the use of wind speed vertical extrapolation methodsPublication . Pintor, A.; Pinto, C.; Mendonça, J.; Pilão, Rosa Maria; Pinto, P.The present work aims to study the influence of using different methods for wind speed extrapolation in energy production calculations. A dataset of 21 meteorological masts from several landscape characteristics and locations, with at least one year of 10-minute wind speed/direction data, was used as the basis for calculations. Both the power law through estimation of wind shear coefficients, and the logarithmic-based profile using WAsP, were used as mathematical models for predicting wind shear. Wind speed extrapolation was performed either from the top-most height, using a distance method that incorporated all measurement heights, or using the function for wind shear coefficient prediction. It was found that using the logarithmicbased profile was the less reliable of all studied methods. The study showed that the most accurate method was the power law with wind shear coefficients estimated from the two upper heights closest to the extrapolation height, by wind direction sector of 30º, and the wind speeds extrapolation from the topmost height of the two. It is suggested that the use of this method reduces uncertainty in AEP estimates.
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