Tailoring solar-assisted calcium looping for polyethylene terephthalate (PET) steam gasification: Combined effect of carbonation and calcination temperatures on process performance

The solar-assisted calcium looping process has gained more and more interest in recent years. It allows both the capture of CO2 and the storage of solar energy during sorbent regeneration, removing the request of auxiliary fuels for heat supply. The effect of carbonation or calcination temperatures on calcium looping performance has been widely studied but mainly based on individual factors. This study investigated the combined effect of carbonation and calcination temperatures on sorbent deactivation and solar energy carrying capacity of a solar-assisted calcium looping process (10 calcination‑carbonation cycles) in a directly irradiated fluidized bed, to obtain the optimized operating temperatures with conceptual reference to the integration with polyethylene terephthalate (PET) steam gasification. The investigated carbonation and calcination temperatures were 600–700 °C and 800–900 °C, respectively, while the inlet CO2 concentration during carbonation was set at 10%v following previous results on PET steam gasification. The experimental results showed that increasing the calcination temperatures promoted the deactivation, while the carbonation temperature had a negligible effect. Fitting parameters of deactivation models were obtained by varying carbonation and calcination temperatures and performed well in process prediction, which broadens the application of these models at different operating temperatures. The best optimized condition of the solar-assisted calcium looping process for maximal averaged carbonation degree and energy carrying capacity was at carbonation temperature of 600 °C and calcination temperature of 800 °C. However, considering hydrogen yield and heat transfer to gasification, the second-best set (carbonation temperature of 650 °C and calcination temperature of 850 °C) would be preferable for the PET steam gasification process. The results of process optimization for all temperature combinations were provided, so that the required condition can be accordingly chosen also for the integration of other processes with solar-assisted calcium looping.