• Energy Research

Abstract The aim of this work was to provide a complete exergy and energy analysis of three biogas upgrading technologies: amine scrubbing, water scrubbing and membrane separation processes. Biogas production and treatment represents a key-process for the application of Circular Economy principles, since allows to reuse/reconvert industrial by-products or agro-industrial waste in a product that can be used in different energy demanding sectors, after proper cleaning and upgrading processes. The three technologies here reported have been implemented in Aspen Plus flowsheets, and were used to upgrade a biogas to biomethane, meeting the UNIT/TS 11537:2019 standards for Biogas to be injected in the gas grid. Each units of all the simulated processes have been analysed calculating total exergy feed, total exergy produced and exergy loss, distinguishing that lost for irreversibility and as waste. Water scrubbing was characterized by the highest values of exergy efficiency (94.5%) and methane recovery (99%), whereas the lowest exergy efficiency belonged to membrane separation (90.8%) that returned also the largest specific energy consumption (0.94 kWh/m3 STP). Conversely, amine scrubbing was characterized by the lowest specific energy consumption value (0.204 kWh/m3 STP) but by an exergy efficiency of 91.1%.

Abstract The aim of this work was to provide a complete exergy and energy analysis of a biogas upgrading technology: pressure swing adsorption. This technology has going to be widely used in Europe, because allowed to reach very high methane recovery (93.4%) and Wobbe Index (50.81 MJ/m3 STP) values. In this study, the upgrading process has been implemented in Aspen Plus and Aspen Adsorption dynamics simulation environment and the biogas was upgraded to biomethane, meeting the UNIT/TS 11537:2019 standards for Biogas to be injected in the gas grid. The upgrading technology has been analysed in terms of process efficiency, also considering CH4 total loss, energy and utilities requirements in dynamic conditions. Each units of the simulated process have been analysed calculating total exergy feed, total exergy produced and exergy loss, distinguishing that lost for irreversibility and as waste. The obtained CH4 recovery at steady cycle state was 93.4%, the CH4 purity in the obtained biomethane was 97.13% whereas the productivity reached a value of 0.143 kg/h·kgads reaching an overall exergy efficiency of 88%.

In recent years, an alarming increase in CO2 emissions has been noticed [...]

The increasing attention towards climate change and greenhouse gas emissions makes the exploitation of renewable energy sources one of the key pathways for sustainable power generation or chemical production [...]

Abstract Water-splitting thermochemical cycles have emerged as a possible solution for the decentralized production of hydrogen using solar energy. A useful tool to select the most promising thermochemical cycles among those proposed in the literature is represented by the exergy analysis. In this context, the exergy and energy analyses of the zinc/zinc oxide thermochemical water-splitting cycle, coupled with the production of electrical energy in a fuel cell, are here carried out and discussed. The aim has been to identify the steps in the process characterized by the highest inefficiencies and to propose possible solutions to increase the overall thermodynamic efficiency. Calculations were carried out using the commercial process simulator PRO/II. The cycle consists of two steps: (i) the endothermic thermal reduction of solid zinc oxide to liquid zinc and oxygen, carried out in a solar thermo-reactor at 2025 °C, and (ii) the non-solar, exothermic hydrolysis of zinc to form hydrogen and solid zinc oxide. This work reports three possible process schemes based on the zinc/zinc oxide redox reactions, each differing from the others in terms of envisaged modes of heat recovery. In addition, the effect of carrying out the hydrolysis step under adiabatic, rather than isothermal conditions, has been analysed. Four values of conversion were considered (1, 0.9. 0.8, and 0.7) and the effect on fuel cell power generation, utility consumption, and energy and exergy efficiency was evaluated. It was found that the exergy efficiency increased from about 14% for the classical zinc/zinc oxide cycle to almost 40% in the most efficient scenario considered here. The variation of hydrogen conversion in the fuel cell led to a decrease in generated power, from 16.41 MW at hydrogen conversion of 1 down to 11.48 MW at hydrogen conversion of 0.7.

To ensure a sustainable future for the steel industry, it is crucial to develop decarbonization solutions that enable steel production from low-grade iron ores. This article presents a techno-economic assessment of an innovative industrial-scale process for producing green steel from low-grade ores with net-negative carbon dioxide (CO2) emissions. The process includes a hydrometallurgical stage, where iron oxides are selectively dissolved by oxalic acid into ferric salts (Fe3+). These salts are then reduced to ferrous iron (Fe2+) through a photoreduction process using only light energy. In the subsequent pyro-reduction stage, the iron salts are converted into metallic iron with carbon monoxide and hydrogen as reducing agents. The oxalic acid used in the process is regenerated through the electrolytic reduction of CO2, requiring an external CO2 supply, while hydrogen is produced via alkaline water electrolysis. Results indicate that green steel can be produced with a levelized cost of production of 1093.32 $/tSTEEL, assuming renewable energy costs of 30 $/MWh. The main limitation of the process is its high energy demand, primarily due to the endothermic nature of metal oxide dissolution and the energy consumption of the electrolyzers. However, with expected improvements in electrolyzer efficiency, energy consumption is anticipated to decrease, further lowering production costs.

Abstract This work provides a complete exergy analysis of municipal solid waste incineration process. The work was based on a previous study, and was enriched considering the possibility to increase the O2 %mol in the combustion air, up to oxy-combustion conditions. Two configurations have been considered, with and without flue gas recirculation, and the environmental aspects of oxy-combustion were taken into account, as well as its exergetic cost. The flue gas was used in a boiler for high pressure steam production, expanded in three turbines for power generation. The exergy analysis allowed to identify the process units characterized by major irreversibility and exergy loss as waste. The results showed that the flue gas recirculation led to an exergy efficiency increase of the whole process of about 3% (from 31.1% up to 34% at adiabatic flame temperature equal to 1200 °C). The O2 %mol increase in the combustion air allowed to reduce the flue gas flowrate, leading to environmental benefits. Oxygen-enriched air adoption led to limited exergetic improvements, due to the exergy cost of the air separation unit. The specific energy generation of the plant increased at fixed combustion chamber temperature adopting flue gas recirculation.

The paper represents the “state of the art” on sustainability in construction materials. In Part 1 of the paper, issues related to production, microstructures, chemical nature, engineering properties, and durability of mixtures based on binders alternative to Portland cement were presented. This second part of the paper concerns the use of traditional and innovative Portland-free lime-based mortars in the conservation of cultural heritage, and the recycling and management of wastes to reduce consumption of natural resources in the production of construction materials. The latter is one of the main concerns in terms of sustainability since nowadays more than 75% of wastes are disposed of in landfills.