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

Role of Sound Vibration during Aeration of Nano-Sized Powders

The behaviour of two different nano-sized powders, Al2O3 (40 nm) and SiO2 (15 nm), during aeration has been investigated in a laboratory scale fluidized bed. The fluidization quality of both powders is very poor without application of acoustic fields even if some bed expansion has been found. The application of acoustic fields of intensities larger than 135 dB and frequencies close to 120 Hz is able to increase the fluidization quality of both powders. Sound is also able to promote an apparent self-fluidization of a relatively thin portion of the upper part of the bed. The possibility that there is an efficient mixing between aggregates during aeration has been highlighted by experiments using a tracer powder

Binary mixtures of biomass and inert components in fluidized beds: experimental and neural network exploration

Considering the little understanding of the hydrodynamics of multicomponent particle beds involving biomass, a detailed investigation has been performed, which combines well-known experimental and theoretical approaches, relying, respectively, on conventional pressure drop methods and artificial neural network (ANN) techniques. Specific research tasks related to this research work include: i. to experimentally investigate by means of visual observation the mixing and segregation behavior of selected binary mixtures when varying the biomass size and shape as well as the properties (size and density) of the granular solids in cold flow experiments; ii. to carry out a systematic experimental investigation on the effect of the biomass weight and volume fractions on the characteristic velocities (e.g., complete fluidization velocity and minimum slugging velocity) of the investigated binary mixtures in order to select the critical weight fraction of biomass in the mixtures beyond which the fluidization properties deteriorate (e.g., channeling, segregation, slugging); iii. to analyze the results obtained in about 80 cold flow experiments by means of ANN techniques to scrutinize the key factors that influence the behavior and the characteristic properties of binary mixtures. Experimental results suggest that the bed components’ density difference prevails over the size difference in determining the mixing/segregation behavior of binary fluidized bed, whereas the velocities of minimum and complete fluidization increase with a growing biomass weight fraction in the bed. The training of ANNs demonstrated good performances for both outputs (Umf and Ucf); in particular, the best predictions have been obtained for Umf with a MAPE1 <4% (R2=0.98), while for Ucf the best ANN returned a MAPE of about 7% (R2=0.93). The analysis on the importance of each individual input on ANN predictions confirmed the importance of particle density of the bed components. Unexpectedly, results showed that morphological features of biomass have a limited importance on Ucf

Dynamics of Stocks and Flows in a Regenerative Economy

This seminar will present a “trailer” for material in a book – “Living well on a Finite Planet: a systems approach to sustainability, society and economy” - by Roland Clift, George Martin and Simon Mair, to be published by Springer in 2023. The book will develop an approach to socio-economic restructuring that looks beyond the Circular Economy to envisage a repurposed economy addressing the three components of sustainability: economy, environment, and society. Rather than the usual economic concern with flows, the analysis takes an industrial ecology approach: it starts from demand for the services provided by the stock of products and materials in use and works out from there, through analysis of remanufacturing and recycling, to the associated material flows which are treated as responses rather than drivers. An earlier analysis, developed by Stahel and Clift, has been extended to stocks that change over time, to generate simple metrics accounting for the effect of stock growth on material demand allowing for product life. Applying the analysis to selected scarce metals shows how it can help to understand the development of “closed loop” systems. It also reveals why setting targets in terms of “circularity” can have perverse consequences

Modeling Mercury Capture by Powdered Activated Carbon in a Fluidized Bed Reactor

A steady state model of mercury capture on activated carbon in a bubbling fluidized bed of inert material is presented. The model takes into account the fluidized bed fluid-dynamics, the presence of both free and adhered carbon in the reactor as well as mass transfer limitations and mercury adsorption equilibrium. The activated carbon adsorption parameters and the relative amount of free versus adhered carbon in the reactor have been estimated with purposely designed experiments. Model results are compared with results from mercury capture experiments conducted with commercial powdered activated carbon at 100°C in a lab-scale pyrex fluidized bed of inert particles. The role of free versus adhered carbon in determining the overall mercury capture efficiency is discussed

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

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

Thermal behaviour of fluidized beds directly irradiated by a concentrated solar radiation

Directly-irradiated fluidized bed reactors are very promising in the context of concentrated solar power applications as they can be operated at process temperatures high enough to perform thermochemical storage with high energy density. The present study aims at experimentally investigating the direct interaction between a concentrated simulated solar radiation and a fluidized bed by measuring the time-resolved bed surface temperature with an infrared camera under different fluidization gas velocities. The effect of a localized generation of bubbles was investigated too, by injecting a chain of bubbles through a nozzle located just at the centre of the concentrated solar beam. The obtained results encourage the localized generation of bubbles, just at the larger value of the impinging radiative heat flux, as a strategy to reduce the overheating of the bed surface and, as a consequence, the energy losses related to fluidizing gas and radiative re-emission