Steam gasification of Greek lignite and its chars by co-feeding CO2 toward syngas production with an adjustable H2/CO ratio

Low-rank lignite is among the most abundant and cheap fossil fuels, linked, however, to serious environmental implications when employed as feedstock in conventional thermoelectric power plants. Hence, toward a low-carbon energy transition, the role of coal in world's energy mix should be reconsidered. In this regard, coal gasification for synthesis gas generation and consequently through its upgrade to a variety of value-added chemicals and fuels constitutes a promising alternative. Herein, we thoroughly explored for a first time the steam gasification reactivity of Greek Lignite (LG) and its derived chars obtained by raw LG thermal treatment at 300, 500 and 800 degrees C. Moreover, the impact of CO2 addition on H2O gasifying agent mixtures was also investigated. Both the pristine and char samples were fully characterized by various physicochemical techniques to gain insight into possible structure-gasification relationships. The highest syngas yield was obtained for chars derived after LG thermal treatment at 800 degrees C, due mainly to their high content in fixed carbon, improved textural properties and high alkali index. Steam gasification of lignite and char samples led to H-2-rich syngas mixtures with a H-2/CO ratio of approximately 3.8. However, upon co-feeding CO2 and H2O, the H-2/CO ratio can be suitably adjusted for several potential downstream processes. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.