Thermal plasma assisted pyrolysis and gasification of RDF by utilizing sequestered CO2 as gasifying agent

Abstract

A growing global population coupled with rising industrialization has led to an ever increasing energy demand, which in turn forced us to turn to fossils without sufficient consideration of the consequences. The most serious consequence, as is evident today, is the increase in CO2 levels responsible for adverse climate change, which compelled the United Nations to develop the Sustainable Energy Goal 13 (SDG-13), calling for immediate action to combat climate change and its effects. On the other hand, the increase in population has also resulted in a tremendous increase in waste generation, necessitating the need for safe and sustainable waste treatment. Over recent years, research has been concentrating on advanced thermal plasma technology to valorize diverse wastes into useful energy. The generated syngas can be utilized for energetic (such as heat and electricity) and chemical (such as methanol and dimethyl ether) end applications. The current investigation analyzes the viability of the thermal plasma system (a water-stabilized DC plasma torch) for the pyrolysis, partial pyrolysis, and gasification of refuse-derived fuel (RDF) coupled with the implementation of the CCUS concept using waste CO2 as a gasifying agent (which is planned to be separated from flue gas coming from waste combustion) and converting it into CO in the syngas through plasma valorization of RDF. A comparative evaluation of the attributes, impurities, and yield of syngas and the generation of solids (ash and char) is carried out along with the analysis of performance parameters for four different cases (with variable inputs of CO2, namely 173, 62, 26 and 0 L/m with gasification ratio ranging from 1.04 to 0.4). The syngas constituents are compared to the equilibrium compositions deduced by developing an equilibrium model in Aspen Plus (V 11.0) thermodynamic environment and are found to be close to the theoretical compositions. The highest gas yield is found for Case-I with 3.44 m3/kg due to the maximum carbon conversion, while the minimum gas yield is assessed as 1.60 m3/kg for Case-IV with high char production. Furthermore, H2 production was found to be almost the same for all cases (1.06–1.12 m3/kg of fuel). Furthermore, energetic efficiencies for all the four cases (63 %, 60 %, 62 % and 58 %) clearly reveal an encouraging energy balance. The theoretical maximum values of contaminants such as NH3, H2S, HCl, HF and HBr are calculated and a design of a syngas cleaning system is proposed. The promising results of the study can be considered a small but significant step towards SDG-13.