Title : Gasification of solid wastes for high-purity hydrogen and syngas production with CO2 capture
Abstract:
To mitigate the escalating challenges posed by global warming, it is imperative to transition from the predominant use of fossil fuels to sustainable alternatives. Gasification of carbonaceous wastes presents a promising solution by converting waste into gas products, hydrogen (H2) and syngas. H2 serves as a clean energy carrier, while syngas acts as a key feedstock for synthesizing valuable chemicals. However, conventional steam gasification requires significant water and energy inputs to enhance H2 production, thus increasing costs and CO2 emissions. In this research, we propose an in-situ steam gasification of biosolids, utilizing its self-contained moisture and earth-abundant calcium-oxide (CaO) as efficient CO2 adsorbent and catalyst. This approach demonstrates comparable performance to conventional steam gasification process by consuming a large amount of fresh water and energy for generating steam. It yields high-purity H2 (70.2 vol%) in Stage 1 and syngas (93.3 vol%) in Stage 2. The molar ratio of H2 to CO in Stage 2 was 2.0, an optimal composition of syngas to be directly used as feedstocks for downstream processing. Additionally, the low-energy content of biosolids was compensated by introducing waste plastics as a co-gasification feedstock. When the plastic/biosolid blend ratio is 1:6, a highest syngas yield of 500 NmL/gdry waste and a highest energy recovery efficiency of 43.5% is achieved. Furthermore, by introducing CO2 into a Stage 3, an additional CO production up to 147 NmL/gdry waste was obtained when the CO2 concentration was 25 vol%, confirming that captured CO2 can be utilized as an efficient gasification agent for maximizing carbon conversion. This novel process not only enhances the energy recovery efficiency from solid wastes but also contributes to negative net CO2 emissions in waste gasification.
