• Energy Research

The paper reports on experiments of glucose gasification with water in supercritical conditions (SCW). The adoption of these process conditions revealed advantages in terms of biomass conversion efficiency as the resulting liquid phase includes some important compounds (Acetic Acid, 5-HFM, furfurals). In addition the high operative pressures allow either to consider the possibility to use this technology inside the steam cycle in order to produce power and liquid/gaseous biofuels such as synthetic natural gas and/or methanol/DME(di methyl ether). In fact, from the experimental tests, it was possible to evaluate that using glucose, that is the main intermedia of SCW gasification from wet biomass, is possible to estimate a syngas production of about 100 lt e 200 lt for each kg of glucose fed, while the global gasification efficiency was of about 10e18%. Syngas product to SCWG has been analysed and the main results shows that, in the range investigated, CO content was 40e50%vol., H2 10e15%, CH4 10e20%, C2þ2 e8% and at the end CO2 with a volume content of about 20e30% and then with lower calorific value of about 20 MJ/Nm3. Analysis on the liquid phase was carried out and the main results has been an high production of both 5-hydromethil furfural and 2-Furaldehyde that have a great potential as “carbon- neutral” feedstock for fuels and green chemicals.

The production of biofuels from renewable sources is a major challenge in research. Methanol, ethanol, dimethyl ether (DME), synthetic natural gas (SNG), and hydrogen can be produced from syngas which is the result of the gasification of biomasses. Syngas composition varies according to the gasification technology used (such as fixed bed reactors, fluidized bed reactors, entrained flow reactors), the feedstock characteristics, and the operating parameters. This paper presents a review of the predominant biomass gasification technologies and biofuels obtained from syngas by biomass gasification.

Astaxanthin and lutein, antioxidants used in nutraceutics and cosmetics, can be extracted from several microalgal species. In this work, investigations on astaxanthin and lutein extraction from Haematococcus pluvialis (H. pluvialis) in the red phase were carried out by means of the supercritical fluid extraction (SFE) technique, in which CO2 supercritical fluid was used as the extracting solvent with ethanol as the co-solvent. The experimental activity was performed using a bench-scale reactor in semi-batch configuration with varying extraction times (20, 40, 60, and 80 min), temperatures (50, 65, and 80 °C) and pressures (100, 400, and 550 bar). Moreover, the performance of CO2 SFE with ethanol was compared to that without ethanol. The results show that the highest astaxanthin and lutein recoveries were found at 65 °C and 550 bar, with ~18.5 mg/g dry weight (~92%) astaxanthin and ~7.15 mg/g dry weight (~93%) lutein. The highest astaxanthin purity and the highest lutein purity were found at 80 °C and 400 bar, and at 65 °C and 550 bar, respectively.

Abstract The gasification of biomass in supercritical water is a promising technology for hydrogen production and the paper reports a thermodynamic analysis, based on minimization of Gibbs free energy, of the gasification with supercritical water of different biomass and agro-food residues: almond shells, digestate from wastewater treatment, algae and manure sludge. Numerical simulations were performed in order to assess the effect of temperature, pressure and biomass-to-water ratio on gas-phase yield and composition. A partial energy integration was also discussed, by considering the energy recovery from a turbine expansion of the gas-phase stream leaving the gasifier. The proposed thermodynamic approach allows predicting not only gasification efficiency of gasifier but also energy balance on the entire gasification process. Results showed that the dry substrates (almond shells and algae more than digestate and sludge) tend to form more carbon monoxide. Besides, data comparison revealed that the produced hydrogen comes from biomass and water for high process temperature, while when temperature decreases, the thermodynamic path tends to promote water formation from the hydrogen of the dry biomass.

Haematococcus pluvialis microalgae in the red phase can produce significant amounts of astaxanthin, lutein, and fatty acids (FAs), which are valuable antioxidants in nutraceutics and cosmetics. Extraction of astaxanthin, lutein, and FAs from disrupted biomass of the H. pluvialis red phase using carbon dioxide (CO2) in supercritical fluid extraction (SFE) conditions was investigated using a bench-scale reactor in a semi-batch configuration. In particular, the effect of extraction time (20, 40, 60, 80, and 120 min), CO2 flow rate (3.62 and 14.48 g/min) temperature (50, 65, and 80 °C), and pressure (100, 400, and 550 bar.) was explored. The results show the maximum recovery of astaxanthin and lutein achieved were 98.6% and 52.3%, respectively, at 50 °C and 550 bars, while the maximum recovery of FAs attained was 93.2% at 65 °C and 550 bars.

Abstract The most common system for flue gas desulfurization (FGD) is the wet scrubbing process in which, the contact between the flue gases to be treated and an alkaline sorbent such limestone is realized with the correspondent production of gypsum. The production of gypsum represent a perfect example of how is possible to obtain a new product for the market starting from the need of environmental protection (the sulphur dioxide (SO2) removal). Today, limestone is ground in long drum mill reaching a size in the range 5–10 mm. With the intent of increasing the specific surface area of limestone and consequently the gypsum production, the raw limestone was treated in a high-energy mill. The performance of such micronized limestone in terms of gypsum production and SO2 removal were then evaluated by means of a bench scale desulfurization test. Subsequently, a feasibility study with the goal to verify the possible advantages simulating the application of the micronized limestone on a full-scale Waste-to-Energy (WtE) plant was realized. Results showed how the micronization process occurred securely, with a greater production of gypsum and better performance in terms of SO2 removal. Additionally, the micronization solutions tested in the present study showed the suitability also from economic and environmental point of view. Since there are many power plants or WtE plants worldwide and, in many cases, they adopt a wet FGD, this study may be attractive for plant operators. The greater production of gypsum through the use of micronized limestone may help reduce the consumption of raw materials, which increased in recent years due to growing demand of the building industry.

Abstract Combining anaerobic digestion (AD) and thermochemical/hydrothermal processes is an interesting solution for the treatment and valorisation of agricultural waste. Most of the recent investigations focused on the solid digestate valorisation obtaining syngas and char, the latter for solutions different from land applications. However, there are few investigations based on hydrothermal processes aimed at enhancing the value of liquid digestate. In order to fill this gap, the study aims at verifying the technical feasibility of the combined treatment of AD and supercritical water gasification (SCWG). The experimentation was carried out at a full scale AD plant fed by 110 t/d of buffalo manure (81.8%) and maize silage (18.2%). Methodologically, the study first envisaged a bench-scale experimental phase concerning SCWG and then a theoretical phase aimed at quantifying the mass and energy balances with reference to the AD + SCWG and AD schemes. SCWG was examined using a plug flow reactor working at 550 °C and 250 bar for residence times of 20 min. For feed in the range of 4–14 mL/min, it was possible to produce a syngas with a higher heating value (22 MJ/kg organic content) and with a gas yield of about 13 mol/kg of dry-digestate. Carbon gasification and global gasification efficiency were of 35 and 45%, respectively. Results of the theoretical phase confirmed the energy sustainability of the AD + SCWG scheme although the added value was the production of green chemicals including syringaldehyde (7.6–11.6 kg/d), acetic acid (1.0–6.5 kg/d) and glucose (0.5–5.8 kg/d) with total estimated production in the range 10.2–33.5 kg/d.