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The Tesla turbine is an original expander working on the principle of torque transmission by wall shear stress. The principle – demonstrated for air expanders at lab scale has some attractive features when applied to two-phase expanders: it is suitable for handling limited flow rates (as is the case for machines in the range from 500W to 5 kW), it can be developed to a reasonable size (rotor of 0.1 to 0.25 m diameters), with acceptable rotational speeds (which range from 500 to 10000 rpm). The original concept was revisited, designing it for two-phase operation and considering not only the rotor configuration but the whole machine. The flow model was developed using complete real fluid assumptions including several new concepts such as bladed channels for the stator, labyrinth seals, and a rotating diffuser. Preliminary design sketches are presented, and results discussed and evaluated.

Supercritical CO2 cycles are a promising technology, but their performance drops for hot cold source, in hot and arid environments, typical of a CSP field. The adoption of CO2-based mixtures as working fluid can turn supercritical CO2 cycles into transcritical cycles even at high temperatures, with performance improvement and significant power block cost reduction. The concept is addressed within the SCARABEUS project, an EU funded Horizon 2020 project dedicated to the use of CO2-based mixtures for CSP plants. In this work, the use of the CO2+C6F6 mixture as working fluid for a power cycle coupled with a solar tower is analysed. The potentiality of the mixture is presented, given its very low toxicity and its good thermal stability limits. Comparisons with the sCO2 cycle is performed for some typical configurations, in order to underline the advantages of the mixture, and a preliminary design of the turbine is presented, developed in a 1D tool.

In the pathway towards decarbonization, hydrogen can provide valid support in different sectors, such as transportation, iron and steel industries, and domestic heating, concurrently reducing air pollution. Thanks to its versatility, hydrogen can be produced in different ways, among which steam reforming of natural gas is still the most commonly used method. Today, less than 0.7% of global hydrogen production can be considered low-carbon-emission. Among the various solutions under investigation for low-carbon hydrogen production, membrane reactor technology has the potential, especially at a small scale, to efficiently convert biogas into green hydrogen, leading to a substantial process intensification. Fluidized bed membrane reactors for autothermal reforming of biogas have reached industrial maturity. Reliable modelling support is thus necessary to develop their full potential. In this work, a mathematical model of the reactor is used to provide guidelines for their design and operations in off-design conditions. The analysis shows the influence of temperature, pressures, catalyst and steam amounts, and inlet temperature. Moreover, the influence of different membrane lengths, numbers, and pitches is investigated. From the results, guidelines are provided to properly design the geometry to obtain a set recovery factor value and hydrogen production. For a given reactor geometry and fluidization velocity, operating the reactor at 12 bar and the permeate-side pressure of 0.1 bar while increasing reactor temperature from 450 to 500 °C leads to an increase of 33% in hydrogen production and about 40% in HRF. At a reactor temperature of 500 °C, going from 8 to 20 bar inside the reactor doubled hydrogen production with a loss in recovery factor of about 16%. With the reactor at 12 bar, a vacuum pressure of 0.5 bar reduces hydrogen production by 43% and HRF by 45%. With the given catalyst, it is sufficient to have only 20% of solids filled into the reactor being catalytic particles. With the fixed operating conditions, it is worth mentioning that by adding membranes and maintaining the same spacing, it is possible to increase hydrogen production proportionally to the membrane area, maintaining the same HRF.

The carbonation of alkaline wastes is an interesting research field that may offer opportunities for CO 2 reduction. However, the literature is mainly devoted to studying different waste sequestration capabilities, with lame attention to the reliability of the data about CO 2 reduction, or to the possibilities to increase the amount of absorbed CO 2 . In this work, for the first time, the limitation of some methods used in literature to quantify the amount of sequestered CO 2 is presented, and the advantages of using suitable XRD strategies to evaluate the crystalline calcium carbonate phases are demonstrated. In addition, a zero-waste approach, aiming to stabilize the waste by coupling the use of by-products and the possibility to obtain CO 2 sequestration, was considered. In particular, for the first time, the paper investigates the differences in natural and accelerated carbonation (NC and AC) mechanisms, occurring when municipal solid waste incineration (MSWI) fly ash is stabilized by using the bottom ash with the same origin, and other by-products. The stabilization mechanism was attributed to pozzolanic reactions with the formation of calcium silicate hydrates or calcium aluminate hydrate phases that can react with CO 2 to produce calcium carbonate phases. The work shows that during the AC, crystalline calcium carbonate was quickly formed by the reaction of Ca(OH) 2 and CaClOH with CO 2 . On the contrary, in NC, carbonation occurred due to reactions also with the amorphous Ca. The sequestration capability of this technology, involving the mixing of waste and by-products, is up to 165 gCO 2 /Kg MSWI FA, which is higher than the literature data., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

This paper investigates the influence of the support material and its thickness on the hydrogen flux in Palladium membranes in the presence of sweep gas in fluidized bed membrane reactors. The analysis is performed considering both ceramic and metallic supports with different properties. In general, ceramic supports are cheaper but suffer sealing problems, while metallic ones are more expensive but with much less sealing problems. Firstly, a preliminary analysis is performed to assess the impact of the support in the permeation flux, which shows that the membrane permeance can be halved when the H 2 diffusion through the support is considered. The most relevant parameter which affects the permeation is the porosity over tortuosity ratio of the porous support. Afterward, the different supports are compared from an economic point of view when applied to a membrane reactor designed for 100 kg/day of hydrogen, using biogas as feedstock. The stainless steel supports have lower impact on the hydrogen permeation so the required membrane surface area is 2.6 m 2 compared to 3.6 m 2 of the best ceramic support. This ends up as 5.6 €/kg H 2@20bar and 6.6 €/kg H 2@700bar for the best stainless steel support, which is 3% lower than the price calculated for the best ceramic support., Competing Interests: The authors declare no conflicts of interest.