Supercritical water gasification of grape marc: process scheme and energy analysis

Purpose The wine-making and distillatory sectors produce huge amount of grape marc residual from the industrial processes. Considering the high moisture content (~70%) of grape marc, it seemed interesting to analyze its exploitation as a source of hydrogen and power through supercritical water gasification (SCWG). Methods SCWG of grape marc was studied from a process point of view. A conceptual design for SCWG was developed capable to separate hydrogen from the syngas produced and to convert the mechanical energy of the compressed syngas into power by means of turbines. The process was simulated by the means of the commercial software Aspen PlusTM at different operating conditions: grape marc in the feed in the range: 5-25%; SCWG temperature and pressure in the range 500-900°C and 250-350 bar, respectively. Results The hydrogen production greatly increases by increasing the SCWG temperature, while the effect of pressure and feed biomass concentration is less significant. The feed grape marc concentration allowing for an auto-thermal regime (i.e. the reactive step is sustained by burning the syngas produced) was calculated. Notably, at the temperature of 900°C, which assures the best performances in terms of H2 production, the process is not thermally self-sufficient in the whole range of biomass concentration analyzed. Main conclusions At the best auto-thermal operating conditions (700°C, 250 bar, grape marc in the feed: 20.55 %wt) the designed SCWG process coupled with PEMFC allows for a net power production of more than 170 kW for a plant throughput of 1000 kg/h.