Transforming carbon-intensive coal-fired power plants into negative emission technologies via biomass-fired calcium looping retrofit

Calcium looping is a promising CO2 capture technology due to reduced energy and economic penalties compared to mature solvent scrubbing technologies and the potential for achieving negative emissions. This study examined the potential for transforming coal-fired power plants into negative CO2 emission technologies via retrofit of calcium looping with biomass co-firing in the calciner. The results confirmed that co-firing 30% biomass with coal in the calciner was sufficient for the retrofitted process to achieve negative CO2 emissions (-3.9 gCO2/kWh). Such a retrofit scenario had a net efficiency of 29.9% and a levelised cost of electricity of 81.1–81.4 €/MWh. Alternative approaches to calcium looping design were also explored to maximise the techno-economic viability of the retrofitted process. It was shown that by reducing the CO2 capture rate in the carbonator to 70%, the retrofitted process maintained the same net efficiency as the reference retrofit scenario. This modification resulted in a 1.8–5.0% reduction in the levelized cost of electricity. Moreover, reducing the fraction of flue gas fed to the carbonator to 80% resulted in a 0.6%-point reduction in efficiency penalty compared to the reference retrofit scenario. Although this adjustment led to specific CO2 emissions of 109.0 gCO2/kWh (4.0% higher than the reference retrofit), the emissions remained 86.2% lower than those of the unabated host plant. Notably, the levelized cost of electricity in this scenario was 6.2–7.5% lower than that for the reference retrofit scenario. Overall, this study demonstrated that by incorporating biomass co-firing, the calcium looping retrofits can transform the existing coal-fired power plants into negative CO2 emission technologies or, at the very least, improve the techno-economic viability of CO2 capture. Future research should address the broader environmental impact and potential challenges associated with biomass co-firing in coal-fired power plants retrofitted with calcium looping.