Greenhouse Gas Emissions from Internally Circulating Fluidized Bed Gasification and Secondary Chemical Production Systems for Chemical Recycling of Waste Plastics

This study applied life cycle assessment (LCA) methods to evaluate the greenhouse gas (GHG) emissions produced when treating 100 t/day of waste plastics (WP) in an internally circulating fluidized-bed gasifier (ICFG) for chemical recycling (oilification and gasification) versus thermal recycling in a waste incineration facility. The GHG emissions from secondary chemical production (i.e., NH3, CH3OH, and CH4), after introducing the product gas from the ICFG gasification into an adjacent chemical production plant, were also analyzed. The net GHG emissions from oilification, gasification (where produced heavy oil is used for fuel), gasification (where produced heavy oil is used for chemicals), and incineration and power generation are 1390.6, 2159.7, 1241.1, and 2258.25 kg-CO2eq/t-WP, respectively. These results suggest that waste utilization to produce chemicals will be more advantageous for recycling WP than waste utilization to produce energy. The net emissions of GHG from NH3 (1379.9 kg-CO2eq/t-WP), CH3OH (1381.8 kg-CO2eq/t-WP), and CH4 (1280.2 kg-CO2eq/t-WP) synthetic processes were calculated using EcoInvent under the present conditions. Notably, for CH3OH- and CH4-related processes, the CO and CO2 from the ICFG-produced gas mixture can be used as feedstock for chemical products, and the emitted CH4 can be used directly as a product. Net GHG emissions can be significantly reduced by supplying external H2 to convert the CO and CO2 in the ICFG product gas to corresponding products (i.e., 1084.9, 882.2, 678.6 kg-CO2eq/t-WP in the NH3, CH3OH, and CH4 processes, respectively, according to EcoInvent). Overall, the combustion of WP in the ICFG regeneration chamber produces GHG emissions, and subsequent processes produce additional gases, both of which have a significant effect on the GHG emissions of the entire system. Therefore, to enable carbon neutrality in plastic recycling processes, the combustion of char and other products in the ICFG must be minimized.