(536d) A Comparative Evaluation of Ca-Based Wastes for a Oxy-Fuel Circulating Fluidized Bed Combustor

Limestone (CaCO₃) particles are used for SO₂ absorbants or CO₂ carriers for various circulating fluidized bed (CFB) processes, such as oxy-fuel combustion, CO₂ capture process, and chemical looping hydrogen reactors. In oxy-fuel combustions, limestone directly injected into CFB risers combines with SO₂ to produce calcium sulfate (CaSO₄) via direct desulfurization reaction or indirect desulfurization reaction. In this study, Ca-based wastes such as eggshells or seashells was investigated as the alternatives of limestone particles. Since the loop-seal in oxy-fuel CFB processes is generally operated under CO₂ rich conditions, calcined Ca-based wastes are exposed to high CO₂ partial pressure conditions through the recirculation section for an extended period and re-injected into the riser as recarbonated wastes. To evaluate the usage of Ca-based wastes for oxy-fuel CFB combustions, their reactivities of calcination, recarbonization, and direct desulfurization were studied in a thermogravity analyzer (TGA) under oxy-fuel combustion conditions. Also, the morphological changes of Ca-based wastes were evaluated using XRD, FE-SEM, and other analysis methods. The TGA experiments show that recarbonation contributes to CaSO₄ conversion. Increasing the desulfurization efficiency using recarbonation can reduce the fixed investment and operating costs of oxy-fuel CFB plants because only desulfurization in the furnace is able to meet SO₂ emission regulations or lower the flue gas desulfurization (FGD) dependence.