Environmental sustainability of closed-loop regeneration of NaHCO3 in CO2 utilization-driven desulfurization ash: From the perspective of integrated hybrid life cycle assessment

The closed-loop regeneration of NaHCO3 by treating sodium-based desulfurization ash (SDA) using CO2 in flue gas and ammonia by-products demonstrates an attractive perspective of low-cost sodium-based dry desulfurization (SDD) application. To push generation reuse of desulfurization ash into more practices, taking the application in coking plants as a case, this study first compares the environmental and economic performance of four scenarios of flue gas desulfurization (FGD) and desulfurization ash disposal by integrated hybrid life cycle assessment (IHLCA) with life cycle costing. Compared with process-based LCA, IHLCA captures more environmental impacts through the economic input-output (EIO) system, especially 36.40-67.89% of terrestrial ecotoxicity comes from the EIO system. Based on evaluation results of four scenarios, among the ten environmental impact categories (excluding photochemical oxidation), the SDD scenario with NaHCO3 regeneration by CO2 and ammonia (S2) is not only the most environmentally friendly route, but also has the lowest total hourly operating cost. These are mainly due to the offsetting effect of by-products replacing traditional chemicals on the total impact and avoiding landfill and raw material transportation. Furthermore, sensitivity analysis also shows that when technical parameters change, the environmental and economic performance of S2 still remains the best, except for the case when the NaHCO3 regeneration rate is 60%. The findings will be valuable for the selection and optimization of FGD in coking plants, incineration plants, and others.