• Energy Research

Concentrating solar power (CSP) technologies with energy storage can greatly enhance the dispatchability and the exploitation of solar energy in different applications. In this context, the present study addresses coupling CSP with calcium looping (CaL) along the 2-fold perspective of accomplishing: (a) carbon capture and sequestration or utilization (CCSU); (b) thermochemical energy storage (TCES). The experimental campaign, aimed at assessing limestone performances over extended cycling under realistic operating conditions, was performed in a fluidized bed reactor directly irradiated by a simulator of concentrated solar radiation. Infrared thermography was used to map the fluidized bed surface during "solar-driven" calcination. Experimental results indicated that TCES operating conditions yield a more reactive material due to the development of better microstructural properties, as inferred from N- and Hg-intrusion porosimetry, which reflect the different thermal history experienced by sorbent material. Working out of process variables in terms of density of energy storage revealed that the CSP-CaL integrated process can represent an attractive alternative option to commercial technologies based on molten salts.

Coupling of traditional combustion technologies with solar thermal energy is fundamental to enlarge the field of applicability and to lower the costs of renewable energy sources. A possible solution is represented by direct irradiation of a flame with concentrated solar energy, so as to increase its temperature thanks to the high absorption coefficient of combustion by-products such as soot particles. In this study, we use a detailed model of soot formation and oxidation to simulate the behaviour of a coflowing diffusion ethylene flame with and without the exposure to a concentrated solar radiation. Modelling data are compared with experimental data reported in the literature. Results confirm that our model is able to reproduce the effect of radiation both matching the temperature and soot volume fraction increase. Successively, a modified version of the solar-combustion hybrid system has been setup to test the effect of solar light orientation on the combustion process. A simulator of concentrated solar energy has been used to directly irradiate the flame from the top. Thermocouple-based temperature measurements highlighted that the flame effectively absorbed solar radiation.

An innovative process layout for sludge waste management based on chemical looping combustion and flue gas methanation is analyzed in this work. The technical performance of the system was assessed by considering that the flue gas is first purified and then mixed with a pure hydrogen stream sourced from an array of electrolysis cells to produce methane. The life cycle assessment (LCA) and life cycle cost (LCC) methodologies were applied to quantify the environmental and economic performances of the proposed process, and a hotspot analysis was carried out to recognize its most critical steps. The proposed system was then compared with a reference system that includes both the conventional waste management pathways for the Italian context and methane production. Finally, to account for the variability in the future economic climate, the effects of changes in landfill storage costs on sewage end-of-life costs for both the proposed and reference systems were evaluated. With respect to 1 kg/h of sewage sludge with 10%wt of humidity, the analysis shows that the proposed system (i) reduces landfill wastes by about 68%, (ii) has an end-of-life cost of 1.75 EUR × kg−1, and (iii) is environmentally preferable to conventional sewage sludge treatment technologies with respect to several impact categories.

The performance of a perovskite-based oxygen carrier for the partial oxidation of methane in thermochemical energy storage applications has been investigated. A synthetic perovskite with formula La0.6Sr0.4FeO3 has been scrutinized for Chemical Looping Reforming (CLR) of CH4 under fixed-bed and fluidized-bed conditions. Temperature-programmed reduction and oxidation steps were carried out under fixed-bed conditions, together with isothermal reduction/oxidation cycles, to evaluate long-term perovskite performance. Under fluidized-bed conditions, isothermal reduction/oxidation cycles were carried out as well. Results obtained under fixed-bed and fluidized-bed conditions were compared in terms of oxygen carrier reactivity and stability. The oxygen carrier showed good reactivity and stability in the range 800–1000 °C. An overall yield of 0.6 Nm3 of syngas per kg of perovskite can be reached per cycle. The decomposition of CH4 catalyzed by the reduced oxide can also occur during the reduction step. However, deposited carbon is easily re-gasified through the Boudouard reaction, without affecting the reactivity of the material. Fluidized-bed tests showed higher conversion rates compared to fixed-bed conditions and allowed better control of CH4 decomposition, with a H2:CO ratio of around 2 and CO selectivity of around 0.8. However, particle attrition was observed and might be responsible for a loss of the inventory of up to 9%w.

To promote the integration between solar-driven torrefaction, Power-to-Gas, and Chemical Looping Combustion (CLC) systems, this work numerically analyzes the performances of a novel process layout. Several agro-industrial residues were considered as fuels. CuO supported on zirconia and Ni supported on alumina were considered as oxygen carrier and methanation catalyst, respectively. Torrefied samples were purposely obtained by means of experimental runs carried out for 30 min at 300 °C in a lab-scale fixed bed reactor under a nitrogen atmosphere. Under the adopted conditions it was attained an increase in the lower heating values (LHV) of the selected feedstocks by about 14-49 %, depending on the different composition and reactivity of the parent biomass. Based on these data, it was estimated that, with respect to 10 kg h-1 torrefied biomass fed to the CLC system, a total thermal power production in the range of 28-58 kW can be achieved. CO2 conversion degrees of above 98 % were evaluated for the methanation unit in all considered scenarios. Considering different locations in Italy, PV field sizes ranging from 45 m2 up to 1392 m2 were evaluated for the solar-driven torrefaction unit. Wider sizes were calculated for the hydrogen production one, ranging from 3366 m2 up to 5598 m2. Eventually, an electric energy storage efficiency of around 16 % was assessed for the proposed layout. Finally, it was found that moving from the adopted torrefied feedstocks to the produced gaseous fuel, an increase in the LHV by about 44-55 % can be attained, while concurrently, CO2 emissions are favorably decreased by 98 %.

Calcium Looping (CaL) is a promising post-combustion CO2 capture and storage technique. Thermal input to the calciner, which is needed to sustain the endothermicity of sorbent regeneration, is usually accomplished via oxy-combustion of an auxiliary fuel. The idea behind the present study is to couple CaL with a Concentrated Solar Power (CSP) system, so that all the thermal energy required in the calciner is supplied by a renewable source. The integration of a CaL cycle with a CSP system offers several potential technical, economical and environmental advantages, but must cope with the inherently unsteady nature of incident solar power. The cyclic character of incident solar power as compared with steady CaL operation could be managed in different ways. In the present study a simple scheme of integrated CaL-CSP process is suggested, based on storage of the excess incident power during the daytime as calcined sorbent, which is eventually utilized in the CaL loop during the nighttime. A preliminary assessment of the performance of this integrated scheme is accomplished by means of model computations. The model is based on a population balance model on sorbent particles, which takes into account the cyclic operation of the system. The parameters of the solar field and the influence of the main operating parameters (sorbent residence time, sorbent/CO2 inlet molar ratio, fluidization velocity) on carbonation degree and efficiency, on sorbent loss by elutriation, on thermal power demand at the calciner and on thermal power produced in the carbonator have been assessed.

Chemical looping combustion (CLC) is a promising carbon capture technology allowing integration with high‐efficiency Brayton cycles for energy production and yielding a concentrated CO2 stream without requiring air separation units. Recently, dynamically operated fixed bed reactors have been proposed and investigated for CLC. This study deals with the technoeconomic assessment of a CLC process performed in packed beds. Following a previously published work on the topic, two different configurations are considered: one relying on a single oxygen carrier (Cu/CuO based) and the other on two in–series oxygen carriers (Cu/CuO based first, Ni/NiO based later). For both configurations, relevant process schemes are devised to obtain continuous power generation. Despite slightly larger capital costs, two‐stage CLC performs better in terms of efficiency, levelized cost of electricity, and avoided CO2 costs. Fuel price and high–temperature valves costs are identified as the main variables influencing the economic performance. The use of two in–parallel packed bed reactors (2.0 m length, 0.7 m internal diameter) enables a power output of 386 kWe, a net electric efficiency of 37.2%, a levelized cost of electricity of 91 € MWhe −1, and avoided CO2 costs of 55 € tonCO2 −1 with respect to a reference pulverized coal power plant.