Oxygen Carrier Aided Combustion (OCAC) of Solid Recovered Fuel (SRF) and coal in a 1 MWth CFB pilot plant using Ilmenite
Alexander Kuhn, Christoph Graf, Dennis Hülsbruch, Jochen Ströhle, Bernd Epple
Abstract
Oxygen Carrier-Aided Combustion (OCAC) has been extensively studied for biomass and coal combustion, yet its application to Solid Recovered Fuel (SRF) remains underexplored. This study investigates the use of ilmenite as an oxygen carrier in a 1 MW th circulating fluidized bed (CFB) pilot plant, systematically analyzing SRF-Coal co-firing at 60 %, 70 %, and 100 % SRF (by heating value). The stepwise increase in SRF share is particularly relevant for retrofitting coal-fired CFB boilers. A direct comparison between ilmenite and quartz sand as bed materials evaluates ilmenite’s influence on exhaust gas composition. Additionally, four in-bed gas measurements (IBGMs) were conducted at a height of 4.2 m for 70 % SRF and 100 % SRF, providing unique insights into combustion characteristics within the reactor – critical for operational optimization but rarely reported in the literature. The study highlights key SRF-specific challenges – such as heterogeneity, high volatile content, and contaminant presence – contrasting them with biomass to emphasize the study’s importance. The results demonstrate that ilmenite enhances combustion efficiency by transporting oxygen to fuel-rich zones, particularly in areas near the fuel feed, mitigating oxygen deficiencies and improving the oxidation of volatile components. Compared to quartz sand, ilmenite led to significant reductions in CO (up to 69 %), CH 4 (up to 95 %), and NO (up to 7 %). Furthermore, findings suggest that OCAC with ilmenite enables more uniform combustion, offering promising pathways for retrofitting coal-fired plants with high SRF shares while maintaining low emissions and stable operation.