Comparison of Experimental Results with Thermodynamic Equilibrium Simulations of Supercritical Water Gasification of Concentrated Ethanol Solutions with Focus on Water Splitting

Abstract

Supercritical water gasification (SCWG) is a process in which biomass reacts with supercritical water to produce H2 and CH4-rich gas. The water-to-biomass ratio is a crucial variable in SCWG that affects the energy efficiency of the process. Despite the clear concept, systematic studies on water consumption during the formation of gaseous products are lacking. This study aims to determine the water consumption in SCWG of organic feedstock. Ethanol was used as an organic model compound since mass balances of complex biomasses like lignocelluloses are often incomplete due to the formation of solid deposits. The ethanol concentration ranged from 1.2 to 72 wt %, and complete gasification was achieved in all cases. Water consumption decreased with an increase in ethanol concentration due to enhanced methanation reactions with increasing organics. Stoichiometric calculations and ASPEN HYSYS simulations confirmed the experimental results, showing equilibrium gas compositions in the reaction system.

Energetic Assessment of SCWG Experiments with Reed Canary Grass and Ethanol Solution on Laboratory and Pilot Scale

“…Thus, the carbon is completely transferred to the gas phase and the carbon distribution in the products is always the same under similar conditions. For ethanol, this is the case under the chosen conditions, as can be seen in previous work [31]. The gas composition is influenced by catalysts added to the system and can vary.…”

“…In the present experiment, no catalyst was added to the system, and thus thermodynamic equilibrium was not reached. Once potassium is added to the reaction the gas composition is changed, as shown in [31], and with that also the heating value of the product gas. As shown in this study, the calculations can easily be adjusted to new feed materials and product gas compositions.…”

“…In the case of ethanol gasification, 99.8 w of the carbon is contained in the product gas and only 0.2 wt.% is contained in the efflu The gasification of ethanol is generally more effective and easier than the gasificatio biomass due to the less complex structure. The ethanol molecule is easily decompo with few intermediates [31,42,43]. During the decomposition of biomass, many inter diates are formed, some of which form solid deposits [3,10,44].…”

Investigating Salt Precipitation in Continuous Supercritical Water Gasification of Biomass

“…In the current lab plant with the chosen throughput, the residence time is very low (D'Jesus found that residence times well above 2 min are necessary to gasify 5 wt.% corn silage at T = 650 • C completely [8]), but still sufficient for some organics. This becomes clear when gasifying ethanol solutions (up to 72 wt.% ethanol), with no salts in it [59]. Long-time operation with CE = 100% was achieved by Dutzi et al [59].…”

“…This becomes clear when gasifying ethanol solutions (up to 72 wt.% ethanol), with no salts in it [59]. Long-time operation with CE = 100% was achieved by Dutzi et al [59]. RCG obviously requires a higher residence time, as seen in the currently achieved CE.…”