Carbon dioxide recovery by means of tsa in a sound assisted fluidized bed of fine activated carbon

A large decrease in CO2 emissions through capturing and separation will be required to keep greenhouse gases at tolerable levels (1). Though several CO2 capture technologies have been proposed, temperature swing adsorption (TSA), consisting in adsorbing the CO2 on a solid material and, then, inducing the sorbent regeneration and CO2 recovery by a temperature increase and gas purge, has the potential to become one of the leading techniques by complementing or replacing the current absorption technology due to its low energy requirement (2). With reference to the sorbent, great attention is focused on fine powders (3). Indeed, sorbent in the form of fine powders can be the substrate to realize new highly specific materials whose properties can be tuned at a molecular level and, besides that, most of the commercial adsorbent materials are generally available in the form of fine powders (3). In this respect, sound assisted fluidization is considered to be one of the best technological alternatives to handle and process large amounts of fine powders (4). Moreover, it has already been proved to promote and remarkably enhance the CO2 capture on fine sorbents, due to large gas-solid contact efficiency, high rate of mass/heat transfer and low pressure drops (5,6). This work is focused on the CO2 desorption process by TSA in a sound-assisted fluidized bed (40mm ID) of fine activated carbon (Sauter mean diameter = 0.39m). In particular, desorption tests have been performed under ordinary and sound assisted fluidization conditions (140dB - 80Hz) in order to assess the capability of the sound in promoting and enhancing the desorption process efficiency in terms of CO2 recovery and purity and desorption time (td). The results obtained show that the application of the sound results in higher desorption rates, CO2 recovery and purity. Very regular and stable desorption profiles can be obtained under sound assisted fluidization conditions (Fig. 1). This stability makes it possible to successfully realize a cyclic adsorption/desorption process. Then, the effect of desorption temperature (Tdes) (25 - 150°C) and N2 purge flowrate (45.2 – 90.4Nl h-1) on the regeneration efficiency has also been assessed (Fig. 2a and b). An increase of both of them positively affect the desorption process in terms of enhanced desorption kinetics. Increasing temperatures also yield higher CO2 purities, whereas, no remarkable dilution effect has been observed when increasing the N2 flow rate. Finally, the activated carbon keeps its performances over 16 adsorption/desorption cycles, in terms of amount of CO2 adsorbed (nads), breakthrough time (tb) and fraction of bed used at tb (W), due to the stability of the regeneration process under sound-assisted fluidization conditions (Fig. 3c). Please click Additional Files below to see the full abstract

CO2 CAPTURE BY TEMPERATURE SWING ADSORPTION IN A SOUND ASSISTED FLUIDIZED BED OF FINE POWDERS

Adsorption using solid sorbents is recognized to be attractive to complement or replace the current absorption technology for CO2 capture due to its low energy requirement. However, the development of new highly specific CO2 adsorbent is necessary: a solution is represented by fine materials, whose properties can be tuned at a molecular level by means of functionalization processes to tailor their CO2 capture performance. Another point to be addressed is the adoption of an adequate reactor configuration, which can, on one hand, fully exploit the potential and properties of these new-concept adsorbent materials by maximizing the contact between the CO2 molecules and the adsorbent particles, and, on the other hand, improve the heat transfer. In this respect, a fluidized bed could be a good solution, due to larger gas-solid contact efficiency, higher rate of mass and heat transfer and lower pressure drops. In particular, a more suitable reactor configuration is a sound assisted fluidized bed, namely provided with a system for the generation of acoustic vibrations to overcome the high interparticles forces characterizing fine powders. On these bases, the present PhD thesis focuses on the CO2 capture process by temperature swing adsorption on fine porous materials in a sound assisted fluidized bed. In order to perform adsorption/desorption tests, a laboratory scale sound assisted fluidized bed experimental rig has been set up. It is equipped with a system for the sound generation and with a continuous analyzer for the CO2 concentration measurement in the effluent gas stream. For the regeneration tests the reactor is externally heated by an ad-hoc designed heating jacket, provided with a window to allow the fluidization quality to be visually assessed. Both common adsorbent materials, two activated carbons, zeolite HZSM-5 and zeolite 13X, and a highly specific adsorbent material, a metal organic framework HKUST-1, were used. The experimental results show that the application of the sound can improve the fluidization quality as well as the adsorption efficiency (by maximizing the gas-solid contact) of all the selected adsorbent materials in terms of remarkably higher breakthrough time, adsorption capacity, fraction of bed utilized until breakthrough and adsorption rate. The experimental campaign has been also carried out, at ambient temperature and atmospheric pressure, in order to highlight the effect of some operating variables on the adsorption performances, i.e. sound intensity (120-140dB) and frequency (20-300Hz), CO2 partial pressure (0.05-0.15atm) and fluidization velocity (0.1-4.5cm/s). In particular, increasing sound intensities yield better adsorption performances, whereas, sound frequency has a not monotone effect on the fluidization quality and adsorption efficiency. The CO2 capture capacity increases with CO2 partial pressure, coherently with the partial pressure being the thermodynamic driving force of the adsorption process. Finally, the dependence of the breakthrough time on the contact time is linear for the tests performed in ordinary conditions, whereas, it is not monotone for the sound assisted tests. At the end of the experimental campaign, all the investigated adsorbent materials have been compared and their different adsorption behaviours explained on the basis of their textural properties. In particular, it has been found that there is a specific pore size range, 8-12 Å, which is the key factor affecting the adsorption capacity of the studied materials under the investigated operating conditions. Desorption tests have been performed on the materials characterized by the best adsorption performances, the HKUST-1 and one activated carbon at atmospheric pressure. In particular, an extra-situ regeneration strategy (150°C under a vacuum of 50mbar) has been developed to study the stability of HKUST-1 to cyclic adsorption/desorption operations, since HKUST-1 presents problems of thermal stability, limiting the desorption temperature to be used in a temperature swing adsorption process. The results show that HKUST-1 is very stable, keeping its adsorption performances over 10 adsorption/desorption cycles. As regards the activated carbon, two strategy of temperature swing adsorption have been tested in the sound assisted fluidized bed. The first regeneration strategy is an isothermal purge consisting in combining the effect of increasing temperature and decreasing CO2 partial pressure. The second regeneration strategy, heating and purge, consists in separating the thermal effect from the purging one. The application of the sound makes it possible, from one hand, to remarkably increase the desorption rate and, on the other, to significantly enrich the recovered CO2 stream. CO2 recovery and purity have opposing trends: higher desorption times yield a higher CO2 recovery, but lead to a lower CO2 purity of the desorbing stream. The desorption rate is positively affected by both desorption temperature (25-150°C) and N2 purge flow rate (45.2-90.4Nl h-1). The purity of the recovered CO2 stream is increased by increasing desorption temperatures, whereas, it is not affected by change of the N2 purge flow rate since dilution does not depend on the purge flow rate but only on the purge volume. The results obtained show that heating is very effective since 80% of the captured CO2 can be can be recovered with a 100% purity at a bland desorption temperature of 130°C. It is worth noting that for each desorption temperature the heating and purge strategy always makes it possible to enrich the stream of CO2 recovered with respect to the standard purge strategy, the CO2 recovery level being the same. The possibility to use the activated carbon in a cyclic operation has been also assessed: it is very stable, keeping its adsorption performances over 16 adsorption/desorption cycle. Finally, considerations about the energy cost and scale-up of the proposed technology for CO2 capture by temperature swing adsorption have also been reported

Sound-Assisted Fluidization for Temperature Swing Adsorption and Calcium Looping: A Review

Fine/ultra-fine cohesive powders find application in different industrial and chemical sectors. For example, they are considered in the framework of the Carbon Capture and Storage (CCS), for the reduction of the carbon dioxide emissions to the atmosphere, and in the framework of the thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. Therefore, developing of technologies able to handle/process big amounts of these materials is of great importance. In this context, the sound-assisted fluidized bed reactor (SAFB) designed and set-up in Naples represents a useful device to study the behavior of cohesive powders also in the framework of low and high temperature chemical processes, such as CO2 adsorption and Ca-looping. The present manuscript reviews the main results obtained so far using the SAFB. More specifically, the role played by the acoustic perturbation and its effect on the fluid dynamics of the system and on the performances/outcomes of the specific chemical processes are pointed out

Fluidized Bed Combustion and Gasification of Fossil and Renewable Slurry Fuels

This article provides a comprehensive review of the state of the art and more recent developments of the thermochemical treatments of slurry fuels in fluidized beds (FB). The review focuses on FB combustion and gasification of slurry fuels based on coal, biomass, sludge, and wastes from industry, agriculture, and the civil sector. The investigations at research and industrial levels over the last decades are presented and discussed, highlighting the adopted technological solutions, the results in terms of feasibility and efficiency, and the perspectives of future development. The different behavior between bubbling and circulating beds was addressed, in particular the optimal choice depending on the process (combustion/gasification/pyrolysis) and fuel properties (e.g., water content). Fundamental studies on interactions between the slurry fuels and the hot bed materials are also reviewed. The cumulative trend of reviewed investigations over the last decades depicts the abandonment of coal‐based mixtures used in large plants, and the growing interest in the use of biomass‐based slurries for small size application. In this respect, the shift from coal to biomass opens new challenges because of the different properties of biomass (density, fibrous structure, spontaneous degradation, hydrophilic behavior, etc.). Biomass‐based slurries circumvent problems posed by using solid dry biomass, particularly in handling, storing, and feeding. Although slurry fuels represent a narrow sector, the results of the research investigations and the experience gained with coal can be exploited to contribute to the achievement of a circular approach based on renewable resources in the near future

Improvement of the Manufacturing Process of Tungsten Carbide-Cobalt Hard Metals by the Application of Sound Assisted Fluidization for the Mixing of the Powders

In this work, the technology of sound assisted fluidization has been used as an alternative mixing method to obtain homogeneous powder mixtures (WC, Co, and polyethylene glycol (PEG)) to be used in the standard steps of hard metal production. A preliminary experimental campaign was carried out to optimize the process parameters (sound intensity/frequency and fluidization velocity) to perform the mixing process. After that, the obtained powder mixture was pressed and subjected to the sintering process. The quality of the final sintered products was assessed by using different techniques (SEM analysis, magnetic properties analysis, relative density, and Vickers hardness). The effects of two operating variables, mixing temperature and shaping pressure, were also studied aiming at improving the quality of the final products in terms of reduced porosity and enhanced density and hardness. Finally, also the effect of the addition of an inhibitor (Cr3C2) to the mixture was assessed. © 2017 American Chemical Society

A comparison between interparticle forces estimated with direct powder shear testing and with sound assisted fluidization

Understanding the role of the interparticle forces in fluidization of cohesive powders is crucial for a proper application of fluidization to these type of powders. However, a direct measure of the interparticle interactions (IPFs) is challenging, mainly because cohesive particles cannot be fluidized under ordinary conditions. That is the reason why IPFs are typically measured using a rheological approach. The aim of this study is, therefore, to evaluate the IPFs of cohesive powders under actual fluidization conditions, by using an experimental and theoretical approach. In particular, a sound assisted fluidized bed apparatus was used to achieve a fluidization regime of the particles. Then, the cluster/subcluster model was applied to calculate IPFs, starting from the experimental data. The obtained IPFs were then compared to those evaluated by using a shear testing approach

A comparison between interparticle forces estimated with direct powder shear testing and with sound assisted fluidisation

In recent years an increasing numbers of industries (e.g. interested in the manufacture of cosmetics, foods, plastics, catalysts, energetic materials, biomaterials, micro-electromechanicalsystems have been attracted to fine and ultrafine particles fluidization, particularly thanks to their special chemical and physical properties. It has become gradually more and more important to understand how to control and to process these particles. Although several studies have been carried out on the effect of IPFs on the fluidization, satisfactory understanding of the phenomena that governed the dynamics of the bed has not yet been achieved. Moreover, a direct measure of the particle-particle interactions and their dependency on the particle properties and on the process conditions in a fluid bed reactor is challenging. In the last years many researches started to look at the rheological measurements as a possible way to understand the fluidization behaviour. The aim of the work is to connect flow properties of the bulk solid evaluated with shear testingwith interparticle interactions in fluidization. In particular, IPFs of fine/ultrafine powders under actual fluidization conditions are obtained by using sound assisted fluidization. With this technique proper fluidization of these cohesive particles is achieved and the results obtained from the experimental tests are analysed in the view of the cluster/subcluster model to calculate IPFs. The obtained values of the IPF intensities were then compared to those evaluated by using direct powder shear testing characterization, analysed with the help of the Rumpf-Molerus approach. An excellent quantitative agreement between the forces found with these two completely independent techniques was found

Aluminum foam made via a new method based on cold gas dynamic sprayed powders mixed through sound assisted fluidization technique

Metal foams are an interesting class of materials with very low specific weight and unusual physical, mechanical and acoustic properties due to the porous structure. In recent years several manufacturing techniques were developed. The limit of these techniques is that it is difficult, even if impossible, to manufacture precursors and then foams able to reinforce complex shaped components; this drawback, to date, limits the application of metal foams. This proof of concept paper is focused on the study of an innovative manufacturing technique able to produce complex shaped precursors. The key idea is to spray a powder mixture (made of both aluminum alloy powders as metal matrix and titanium hydride particles as foaming agent) through the cold gas dynamic spray on a free shape metallic substrate and then carry out the foaming process. A preliminary granulometric analysis was carried out to estimate the particles mean size and then sound assisted (140dB–80 Hz) fluidization process was used to achieve a homogenous and deep mixing between the fine metal powders and the blowing agent ones. In particular, two different types of mixtures with 1 wt% and 2.5 wt% of TiH2 were investigated; moreover, air compressed as well as helium were used as CGDS carrier gas in order to ensure a higher impact velocity and a better compacting of the powders. Finally, the cross sections of manufactured solid foams were observed by means of a SEM microscope for having information about internal metallurgical phenomena as well as the distribution and morphology of foam cells. Macrographs of created porous structures showed the effectiveness of the developed innovative manufacturing process