Abstract
The energy sustainability of producing biofuel from wet bioresidues needs proper energy integration to ensure sustainable exploitation. This study analyses the potentials of combined hydrogen, heat, power, and LOHC (Liquid Organic Hydrogen Carrier) production from the residues of citrus juice production, at a factory scale. In this work, the main constituents of LOHC are DME (Dimethyl ether) and methanol. The proposed system is based on air-steam gasification and direct CO2-to-DME process, integrated with hydrogen purification and a CHP unit. The DME reactor is operated at 30 bar in the temperature range 493-533 K. A thermodynamic model, which is validated experimentally, simulates the proposed polygeneration system. In addition to the potential amount of biofuel, hydrogen production, and net power production, the energy and exergy efficiencies are analyzed. Despite the variation of LOHC yield with the temperature, the results show that the whole system’s energy efficiency is not affected, while the small difference among the exergy efficiencies is negligible.
Highlights
Global warming and depletion of fossil fuel energy resources are two of the most significant challenges of these years
Is possible to observe that the CO2 conversion progressively increases with temperature, achieving a maximum value of 21.2 % at 533 K, while, a decreasing of dimethyl ether (DME) selectivity (SDME) from 51.9 % to 36.5 % between 493 K and 533 K. These results shows that the system works under a prevailing kinetic regime with CO2 conversion values always lower than that expected from thermodynamic equilibrium data (> 26% at 533 K), at all reaction temperature considered, which is in accordance with other authors [10][14][12][13][21][22][23][24][15]
A slight but regular decrease of SMeOH is recorded throughout the temperature range investigated, attaining a threshold value at 533 K, as a result of the increased competition between the methanol synthesis rate and its dehydration to DME
Summary
Global warming and depletion of fossil fuel energy resources are two of the most significant challenges of these years. A rapid transition towards renewables energy systems is crucial to avoid climate change and its dangerous consequences for humanity. Among the primary renewable energy sources, biomass covers a crucial role, with a share of 60% of the total global renewable energy use [3,4]. Different materials, such as waste, agriculture residue [5,6], and forest residues have been studied and applied as feedstock for gasification and syngas production in a temperature range 973–1773 K [7,8,9]. As biomass gasification technologies were improved [3], biomass-derived syngas has been often combined in biorefinery platforms to produce liquid bio-fuels and/or chemicals via Fischer–Tropsch (FT) technology [10,11]
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