The topic of this paper is minimum cost operative planning of pressurized water supply networks over a finite horizon and under reliable demand forecast. Since this is a very hard problem, it is desirable to employ sophisticated mathematical algorithms, which in turn calls for carefully designed models with suitable properties. The paper develops a nonlinear mixed integer model and a nonlinear programming model with favorable properties for gradient-based optimization methods, based on smooth component models for the network elements. In combination with further nonlinear programming techniques (Burgschweiger et al. in ZIB Report ZR-05-31, Zuse Institute Berlin, 2005), practically satisfactory near-optimum solutions even for large networks can be generated in acceptable time using standard optimization software on a PC workstation. Such an optimization system is in operation at Berliner Wasserbetriebe.
Mathematical decision support for operative planning in water supply systems is highly desirable; it leads, however, to very difficult optimization problems. We propose a nonlinear programming approach that yields practically satisfactory operating schedules in acceptable computing time even for large networks. Based on a carefully designed model supporting gradient-based optimization algorithms, this approach employs a special initialization strategy for convergence acceleration, special minimum up and down time constraints together with pump aggregation to handle switching decisions, and several network reduction techniques for further speed-up. Results for selected application scenarios at Berliner Wasserbetriebe demonstrate the success of the approach.
A new normalization concept for convective drying of hygroscopic particulates is introduced. Both, intraparticle drying kinetics and sorption equilibrium are considered separately, and integrated into a new heterogeneous fluid bed model for coupled heat and mass transfer. Experiments were carried out using spherical y-Al,O, particles. Sorption isotherms, as well as drying curves, for single particles and fluidized beds have been measured. Batch fluid bed drying curves appear to be predictable on the basis of single particle and material equilibrium data and with the help of the model. All model parameters are directly taken, or estimated from fluidization literature, without any fitting.On presente un nouveau concept de normalisation pour le sechage convectif de particules hygroscopiques. La cinetique de stchage intraparticulaire et I'bquilibre de sorption sont consideres separement et integres dans un nouveau modele a lit fluide heterogene pour modeliser le transfert de chaleur et de matiere couple. Des experiences ont ete menees a I'aide de particules spheriques de y-Al,O,. On a mesure des isothermes de sorption, ainsi que des courbes de sechage, pour des particules simples et des lits fluidises. Les courbes de sechage en lit fluide discontinu semblent pouvoir &re predites sur la base des donnees d'equilibre des particules seules et des materiaux et avec I'aide du modele. Tous les parametres du modele sont pris directement, ou estimes a partir de donnees de fluidisation de la litterature scientifique, sans aucun calage.Keywords: drying, fluidized bed, hygroscopic particles, modelling.on-hygroscopic and hygroscopic materials differ in N their drying behavior like pure water and a salt solution.The latter shows a reduced vapor pressure at its surface, resulting in a lower drying rate. The influence of sorption on the mass transfer can be described by modifying the equation for the mass flux in a way, that the driving force is not built with the vapor-liquid but the sorptive equilibrium, subsequently expressed in terms of an air moisture content Ye . The quantity Yeq depends on the solids moisture content X ?the analogon of salt concentration) and temperature, and replaces the vapor-liquid-equilibrium moisture content Y, (the gas moisture content at adiabatic saturation) for convective drying. This modified kinetic approach has been introduced both, in a single particle (Equation 3 1) and a fluid bed model (Equation 16). The novelties following from this basic modification are explained in this contribution.Tsotsas (1994) presented a method for the determination of fluid bed drying curves from single particle drying kinetics using a fluid bed model. The fluid bed model has been refined and validated by Tsotsas (1997, 1998) so that all fluid bed parameters are known or predictable. Single particle drying kinetics enter this fluid bed model in normalized form as proposed by van Meel (1958).The respective normalized drying rate v is defined as the quotient of the actual drying rate tipg, and the drying rate of th...
Due to their lower energy consumption, permanent magnet synchronous motor (PMSM) submersible pumps have been introduced in ground water well field operation. Besides direct savings of energy, the introduction of PMSM pumps together with the required variable frequency converters offers new operational scenarios to meet the seasonally varying water demand. In this work, potential energy savings of variable speed submersible pumps were investigated. A ground water well field consisting of 13 wells and their transport pipes was modeled in the hydraulic modeling software EPANET 2.0. Using MS visual basic for applications, EPANET was coupled with MS Excel and a genetic algorithm to identify the most energy efficient combination of pump speeds. For the simulated well field, the total specific energy demand required for pumping was significantly lower in partial load operation as compared to nominal pump speed operation. For low and moderate flow scenarios, energy savings in the range of 20% compared to nominal speed operation can be achieved. These findings were confirmed by a monitoring campaign in the well field. Combining hydraulic simulation and optimization using genetic algorithms, the best efficiency scenario for operation of ground water well fields can be found.
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