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Hydrothermal carbonization (HTC) allows the conversion of organic waste into a solid product called hydrochar with improved fuel properties. Olive tree pruning biomass (OTP), a very abundant residue in Mediterranean countries, was treated by HTC to obtain a solid fuel similar to coal that could be used in co-combustion processes. Three different reaction temperatures (220, 250, and 280 °C) and reaction times (3, 6, and 9 h) were selected. The hydrochars obtained were extensively analyzed to study their behavior as fuel (i.e., ultimate, proximate, fiber and thermogravimetric analysis, Fourier-transform infrared spectroscopy (FTIR), activation energy, and combustion performance). The concentrations of cellulose, hemicellulose, and lignin in the samples depict a clear and consistent trend with the chemical reactions carried out in this treatment. Regarding O/C and H/C ratios and HHV, the hydrochars generated at more severe conditions are similar to lignite coal, reaching values of HHV up to 29.6 MJ kg−1. The higher stability of the solid is reflected by the increase of the activation energy (≈60 kJ mol−1), and ignition temperatures close to 400 °C. With this, HTC is a proper thermal treatment for the management of raw OTP biomass and its further conversion into a solid biofuel.

The yield and composition of the biocrude obtained by hydrothermal liquefaction (HTL) of Nannocloropsis gaditana using heterogeneous catalysts were evaluated. The catalysts were based on metal oxides (CaO, CeO2, La2O3, MnO2, and Al2O3). The reactions were performed in a batch autoclave reactor at 320 °C for 10 min with a 1:10 (wt/wt) microalga:water ratio. These catalysts increased the yield of the liquefaction phase (from 94.14 ± 0.30 wt% for La2O3 to 99.49 ± 0.11 wt% for MnO2) as compared with the thermal reaction (92.60 ± 1.20 wt%). Consequently, the biocrude yields also raised in the metal oxides catalysed HTL, showing values remarkably higher for the CaO (49.73 ± 0.9 wt%) in comparison to the HTL without catalyst (42.60 ± 0.70 wt%). The N and O content of the biocrude obtained from non-catalytic HTL were 6.11 ± 0.02 wt% and 10.50 ± 0.50 wt%, respectively. In this sense, the use of the metal oxides decreased the N content of the biocrude (4.62 ± 0.15–5.45 ± 0.11 wt%), although, they kept constant or increased its O content (11.39 ± 2.06–21.68 ± 0.03 wt%). This study shows that CaO, CeO2 and Al2O3 can be promising catalysts based on the remarkable amount of biocrude, the highest values of C, H, heating value, energy recovery, and the lowest content of N, O and S.

Hops are critical to the brewing industry. In commercial hop drying, a large bulk of hops is dried in multistage kilns for several hours. This affects the drying behavior and alters the amount and chemical composition of the hop oils. To understand these changes, hops of the var. Hallertauer Tradition were dried in bulks of 15, 25 and 35 kg/m² at 60 °C and 0.35 m/s. Additionally, bulks of 25 kg/m² were also dried at 65 °C and 0.45 m/s to assess the effect of change in temperature and velocity, respectively. The results obtained show that bulk weights significantly influence the drying behavior. Classification based on the cone size reveals 45.4% medium cones, 41.2% small cones and 8.6% large cones. The highest ΔE value of 6.3 and specific energy consumption (113,476 kJ/kgH2O) were observed for the 15 kg/m² bulk. Increasing the temperature from 60 °C to 65 °C increased the oil yield losses by about 7% and myrcene losses by 22%. The results obtained show that it is important to define and consider optimum bulk and process parameters, to optimize the hop drying process to improve the process efficiency as well the product quality.

This manuscript investigates the supercritical carbon dioxide (sCO2) power cycle employed in the power block of concentrated solar power (CSP) plants—solar tower—as an alternative for solar desalination, developed with either distillation or reverse osmosis. This concept is investigated as a possible up-scaling of the SOLMIDEFF project, originally based on a hot-air micro gas turbine combined with a solar dish collector. For the upscaled concept, five different sCO2 cycles are considered, chosen amongst the best-performing configurations proposed in the literature for CSP applications, and modelled with Thermoflex software. The influence of ambient conditions is studied, considering two minimum cycle temperatures (35 °C and 50 °C), corresponding to Santa Cruz de Tenerife and Abu Dhabi, respectively. The results show that the low temperatures at the inlet of the heat rejection unit compromise the viability of distillation technologies. On the other hand, the high thermal efficiency achieved by these cycles, especially with the recompression and partial cooling layouts, reduces the specific energy consumption when combined with reverse osmosis (RO), below that of photovoltaic (PV)+RO. Feed-water preheating is explored as a solution to further reduce energy consumption, concluding that its actual interest is not clear and strongly depends on the location considered and the corresponding water quality standards.

The solar gasification of biomass represents a promising avenue in which both renewable solar and biomass energy can be utilized in a single process to produce synthesis gas. The type of oxidant plays a key role in solar-driven biomass gasification performance. In this study, solar gasification of beech wood biomass with different oxidants was thermodynamically and experimentally investigated in a 1.5 kWth continuously-fed consuming bed solar reactor at 1200 °C under atmospheric pressure. Gaseous (H2O and CO2) as well as solid (ZnO) oxidants in pellet and particle shapes were utilized for gasifying beech wood, and the results were compared with pyrolysis (no oxidant). As a result, thermodynamic predictions provided insights into chemical gasification reactions against oxidants, which can support experimental results. Compared to pyrolysis, using oxidants significantly promoted syngas yield and energy upgrade factor. The highest total syngas yield (63.8 mmol/gbiomass) was obtained from biomass gasification with H2O, followed by CO2, ZnO/biomass mixture (pellets and particles), and pyrolysis. An energy upgrade factor (U) exceeding one was achieved whatever the oxidants, with the maximum U value of 1.09 from biomass gasification with ZnO, thus highlighting successful solar energy storage into chemical products. ZnO/biomass pellets exhibited greater gas yield, particularly CO, thanks to enhanced solid–solid reaction. Solid product characterization revealed that ZnO can be reduced to high-purity Zn through solar gasification, indicating that solar-driven biomass gasification with ZnO is a promising innovative process for CO2-free sustainable co-production of metallic Zn and high-quality syngas.

This research aims at evaluating the performance of a combined system of biochar gasification and a sorption-enhanced water–gas shift reaction (SEWGS) for synthesis gas production. The effects of mangrove-derived biochar gasification temperature, pattern of combined gasification and SEWGS, amount of steam and CO2 added as gasifying agent, and SEWGS temperature were studied in this work. The performances of the combined process were examined in terms of biochar conversion, gaseous product composition, and CO2 emission. The results revealed that the hybrid SEWGS using one-body multi-functional material offered a greater amount of H2 with a similar amount of CO2 emissions when compared with separated sorbent/catalyst material. The gasification temperature of 900 °C provided the highest biochar conversion of ca. 98.7%. Synthesis gas production was found to depend upon the amount of water and CO2 added and SEWGS temperature. Higher amounts of H2 were observed when increasing the amount of water and the temperature of the SEWGS system.

Livestock manure has a high ammonium content that can limit its direct application on soil as a fertiliser in nitrate-vulnerable zones. Treatment technologies that are able to extract ammonium from livestock manure allow it to be concentrated in small volumes, making it cheaper and easier to transport and use as fertiliser in crop areas where there is a deficit of nitrogen. This study proposed using low-temperature vacuum evaporation to treat pig slurry in order to obtain marketable products that can be used as fertilisers and help close the nitrogen cycle. Two different configurations and scales were used. The first was a seven-litre laboratory-scale evaporator complemented with a condenser, a condensate trapper, an acid trap and a vacuum pump operated at −90 kPa vacuum pressure and at three different temperatures: 50.1 ± 0.2 °C, 46.0 ± 0.1 °C and 45.3 ± 1.3 °C. The second, Ammoneva, is an on-farm pilot-scale evaporator (6.4 m3), capable of working in four-hour batches of 1 t of liquid fraction of pig slurry with an operating temperature of 40–45 °C and −80 kPa vacuum pressure. The laboratory-scale evaporator, which features several novel improvements focused on increasing ammonia recovery, showed a higher nitrogen removal efficiency from the liquid fraction of pig slurry than the on-farm pilot plant, achieving 84% at 50.1 °C operation, and recovering most of it in ammonia solution (up to 77% of the initial nitrogen), with 7% of the ammonia not recovered. The Ammoneva pilot plant achieved a treated liquid fraction with 41% of initial nitrogen on average, recovering 15% in the ammonia solution in the acid trap; so, the NH3 gas absorption step needs to be further optimised. However, due to the simplicity of the Ammoneva pilot plant, which is easily placed inside a 20-foot container, and the complete automation of the process, it is suitable as an on-farm treatment for decentralised pig slurry management. The implementation of the novel design developed at laboratory-scale could help further increase recovery efficiencies at the pilot-plant scale.