A Sustainable Power Production System Based on Integrated Supercritical Water Gasification of Brewer's Spent Grains and Carbon Dioxide Capture

Abstract

Globally, brewery operations generate over 37 million tonnes of by-products annually, with brewers' spent grains (BSG) representing the predominant fraction. Due to their high moisture content, BSG are costly and challenging to manage using conventional disposal methods. Supercritical water gasification (SCWG) offers a promising thermochemical conversion route for the efficient treatment and valorization of BSG, particularly given its ability to process wet biomass without the need for energy-intensive drying. Therefore, this article proposes a concept of an integrated SCWG combined cycle (IGCC) with a carbon dioxide capture unit toward the improvement of circularity of this industrial sector. A simplified Aspen Plus model was implemented to analyze the whole concept in terms of energy efficiency and sustainability. Results indicate that higher temperatures promote increased hydrogen molar fractions in syngas, whereas lower temperatures favor the formation of methane. The syngas lower heating value varies between 10.81 and 32.75 MJ/Nm(3). Syngas produced at 900 degrees C, 350 bar, and 5% biomass-to-water ratio achieves a maximum cold gas efficiency of 36.55%. The sensitivity analysis allowed us to define the SCWG operating conditions at a 5% biomass-to-water ratio, 600 degrees C, and 350 bar that maximize the performance of the combined cycle. The combined cycle achieved a performance efficiency of 49.32%, corresponding to a net biomass-to-electricity efficiency of 16.6% and a negative emission factor of 574.95 kg CO2/MWh for the IGCC plant. This study founds relevancy for the brewery industry when showing that their by-products can be used to produce cleaner energy, improving the circularity and sustainability of their economy while contributing to the reduction of the carbon footprint.