Dynamic modeling of a solar receiver/thermal energy storage system based on a compartmented dense gas fluidized bed

Fluidized beds may be considered a promising option to collection and storage of thermal energy of solar radiation in Concentrated Solar Power (CSP) systems thanks to their excellent thermal properties in terms of bed-to-wall heat transfer coefficient and thermal diffusivity and to the possibility to operate at much higher temperature. A novel concept of solar receiver for combined heat and power (CHP) generation consisting of a compartmented dense gas fluidized bed has been proposed to effectively accomplish three complementary tasks: collection of incident solar radiation, heat transfer to the working fluid of the thermodynamic cycle and thermal energy storage. A dynamical model of the system laid the basis for optimizing collection of incident radiative power, heat transfer to the steam cycle, storage of energy as sensible heat of bed solids providing the ground for the basic design of a 700kW th demonstration CSP plant

AERATION AND MIXING BEHAVIOURS OF BINARY MIXTURES OF NANO-SIZED POWDERS UNDER SOUND VIBRATION

The aeration behaviour of three different nano-sized powders, Al2O3, Fe2O3 and CuO, fluidized under the application of acoustic fields of different intensities (125-150 dB) and frequencies (50-300 Hz) has been characterized. The characterization of the fluidization of binary mixtures of Al2O3 and Fe2O3 has been also investigated under the application of acoustic fields of 120 Hz and of two different intensities, 130 and 135 dB, and varying the relative amount of two powders from 17 to 50 %wt of Fe2O3. The addition of Fe2O3 has a beneficial effect on fluidization quality of Al2O3 even for the lowest amount of Fe2O3. Under the effect of sound, mixing between Al2O3 and CuO nanopowders has been also quantitatively characterized by the Scanning Electron Microscopy with X-ray microanalysis (SEM/EDS) analysis of captured samples. Mixing between aggregates of the two powders takes only few minutes. However, mixing also occurs inside aggregates but this process requires times of the order of 80-150 minutes, depending on the feeding order of two powders

Chemical engineering and industrial ecology: Remanufacturing and recycling as process systems

Climate change and resource scarcity are just two of the planetary crises that make radical socio-economic change essential if human society is to be sustainable. Chemical engineering is a skill-set that can make a unique contribution to the socio-economic transition, going beyond new technological processes to provide a system-level understanding of economic activities from the perspective of industrial ecology. This paper provides an example by applying process system analysis to the use, re-use, remanufacturing, and recycling of material products. Unlike the ‘circular economy’ approach, the analysis starts from the stock of goods and materials in use in the economy and models the flows required to build up, operate, and maintain the stock. Metrics are developed to account for the effect of stock growth on demand for materials. The significance of the analysis is illustrated for four metals whose industrial ecologies are at different levels of maturity: lead, copper, aluminium, and lithium. Extending product life through re-use and remanufacturing is crucial for resource efficiency, using labour to reduce demand for energy and non-renewable resources. If end-of-life products are processed to recover individual elements, the cost penalties increase rapidly with the decreasing concentration of valuable materials and increasing number of materials in the mixture. Thus, shifting from a linear economy (make−use−dispose) to closed-loop use of materials involves rethinking product design to reduce the number of materials used. Material substitution to reduce demand for scarce materials needs to look beyond equivalence of function to consider changing patterns of use in the regenerative economy

A brief overview on valorization of industrial tomato by-products using the biorefinery cascade approach

The industrial processing of tomato leads to substantial amounts of residues, typically known as tomato pomace or by-products, which can represent as much as 10% by weight of fresh tomatoes. At present, these residues are either used as feedstock for animals or, in the worst case, disposed of in landfills. This represents a significant waste because tomato pomace contains high-value compounds like lycopene, a powerful antioxidant, cutin, which can be used as a starting material for biopolymers, and pectin, a gelling agent. This article presents an overview of technologies that valorize tomato by-products by recovering added-value compounds as well as generating fuel for energy production. These technologies include operations for extraction, separation, and exploitation of lycopene, cutin and pectin, as well as the processes for conversion of the solid residues to fuels. Data collected from the review has been used to develop a biorefinery scheme with the related mass flow balance, for a scenario involving the tomato supply chain of Regione Campania in Italy, using tomato by-products as feedstock

The effect of temperature on the minimum fluidization conditions of industrial cohesive particles

In order to understand the factors responsible for changes in the fluidization behaviour of industrial particles at high temperatures, an experimental campaign was performed using a 140 × 1000 mm heated gas fluidized bed. Five powder cuts sieved out of the same mother powder covering Group B, A and C of Geldart's classification were investigated over a range of temperatures from ambient to 500 °C. The results show that the mean size distribution affects significantly the fluidization behaviour of the materials investigated. In particular, significant differences were observed in the fluidization behaviour of the coarsest samples (Group B-A) and finest samples (Group A-C). The minimum fluidization conditions were compared with the prediction of the Ergun equation. The comparison was satisfactory only when accounting for the experimental values of the bed voidage. In fact, the non-monotonic trend of the minim velocity for fluidization with increasing temperature cannot be explained only with the effects of temperature on the bed fluid dynamics. But several others are the observed effects on the fluidization behaviour due to the temperature rise that can be ascribed to the enhanced interparticle forces: 1) the increase of the peak of pressure drops, close to the minimum for fluidization, in the fluidization curve at increasing gas velocities; 2) the increase for the finest samples of the hysteresis in the fluidization curves, considering the fluidization and defluidization branches of the curve; 3) a greater tendency of the bed to expand homogeneously; 4) the increasing difference between the parameters of the Richardson-Zaki equation found with a fitting procedure on the experiments and those found using the Richardson-Zaki correlations and the theoretical terminal velocity. Furthermore, in the cases where larger interparticle forces were expected, the X-Ray facility allowed to identify different internal structures within the bed. Mostly vertical channels but also, in the case of the finest powder tested, horizontal channels

Hydrodynamic Characterization of GULF STREAM Circulation in a Pilot Scale Fluidized Bed Combustor

The present study addresses the hydrodynamics of a pilot-scale fluidized bed combustor with a focus on the establishment of "Gulf Stream" circulation patterns as a solids mixing promoter. Time-resolved pressure signals measured at different locations in the bed and in the plenum were analyzed in the time, frequency and phase-space domains. Results were matched against qualitative characterization of fluidization patterns by visual observation of the bed surface

Detection and estimation of capillary interparticle forces in the material of a fluidized bed reactor at high temperature by powder flow characterization

Two ceramic powder samples having different compositions of surface impurities and particle size distributions were considered. These two samples resulted from a high temperature fluidized bed reactor which in its operation showed changes of working condition that might be attributed to the onset of strong interparticle forces. The flow behaviour of these powders was characterized by the High Temperature Annular Shear Cell (HT-ASC), between ambient temperature and 500 °C. Furthermore, a model is developed to relate the change of the powder flowability to the formation of a liquid phase due to the melting of particle impurities present on the particle surface. In particular, the model is used to predict, on the base of the salt composition, the intensity of the interparticle forces at different temperatures. The interparticle forces predicted by the model can be compared with those that can be inferred from the powder flow properties measured with the HT-ASC. Therefore, it is demonstrated that it is possible to derive a theoretical model to predict interparticle forces in a particulate material relevant to fluidized bed reactor, on the basis of the impurities composition. Furthermore, it is demonstrated the possibility to correctly estimate the intensity of average interparticle forces in the same kind of material by the interpretations of bulk flow properties measured with a shear tester, even in the case in which capillary forces take the place of the much weaker van der Walls forces. More in general, the paper suggests a method by which powder rheology can be used to indirectly evaluate the effects of the interparticle forces on fluidization processes even in case in which strong capillary interaction occur

Selective laser sintering of ceramic powders with bimodal particle size distribution

This paper addresses the possibility of carrying out Selective laser sintering (SLS) using powders obtained as mixtures of particles of different size. The beam source used in the experiments was a CO2 laser tube with a nominal power of 40W. The materials used were model Glass beads and a real ceramic material characterized by irregular shape of the particles. Bimodal distributed powders were generated by mixing samples characterized by different narrow particle size distributions. Single layer sintered specimens were obtained with a laser scanning speed of 50 mm/s and 8W beam. The sintered specimens were studied by means of microphotography and were characterized in terms of bulk density and tensile strength.Results show that the strength of the sintered specimen is significantly dependent upon the amount of fines in the powder mixture, in spite of the limited effects on the specimen thickness and density. In particular, the highest strength of the sintered material are observed with the highest fraction of fines in the originating powder mixture. In order to estimate the value of the forces between particles of different size produced by the sintering action, the model developed by Liu et al. (2017), based on the Rumpf (1958) approach, was purposely adapted. The application of the model revealed that in our process conditions the connection between large and fines particles is significantly weaker than the force between particles of the same size. The model also indicates that the strength of the sintered materials from mixtures can potentially increase up to values significantly higher than those of the materials sintered starting from the unimodal powder components

ATTRITION OF BED MATERIALS AND FUEL PELLETS FOR FLUIDIZED BED GASIFICATION APPLICATION

This paper reports on a study of the attrition/fragmentation behavior of different bed materials and fuel pellets for application in fluidized bed gasification. Three different bed materials displaying catalytic activity, namely fresh and sintered dolomite and a Ni-alumina catalyst, were tested for their resistance to fragmentation and attrition in fluidized bed. The fresh dolomite displayed extensive particle breakage upon calcination and a large production of attrited fines during fluidized bed operation. The other two materials were much more resistant to attrition and appeared to be suitable for further long-term operation testing. The attrition/fragmentation resistance of three pelletized fuels, one based on wood and the other two on a mixture of wood and coal, was also characterized under both inert and gasification conditions. Pellet breakage by primary fragmentation upon devolatilization appeared to be rather limited for all fuels. On the contrary, attrition of carbon fines from the char particles during gasification was extensive, due to a gasification-assisted attrition mechanism