Findings on the use of a Ca-based sorbent as an oxygen carrier precursor in a Chemical Looping Combustion unit

Limestone Chemical Looping Combustion (L-CLCTM) is a novel process to burn sulfurous fuels with intrinsic desulfurization and CO2 capture. L-CLCTM is based on using calcium-based sorbents as precursors for CaSO4 formation, which is used as an oxygen carrier. Its principle lies in the in-situ sulfur retention process performed in fluidized bed combustors burning solid fuels with high sulfur content. The target redox pair for the oxygen transference to the fuel is CaSO4/CaS. In this research work, experimental tests burning CH4, syngas and H2 with a moderate H2S concentration were conducted in a continuous CLC unit. This experimental campaign is first in a kind as there is hardly information about the CaSO4/CaS pair for the L-CLCTM process. High combustion effi-ciencies were achieved at moderate temperatures (800-850 degrees C) when burning H2 and syngas (-96-99 %). Likewise, low CH4 combustion efficiency (-59 %) was found even operating at a temperature as high as 945 degrees C. Additionally, experimental tests at different Ca/S molar ratios were performed. They revealed that it was possible to reach suitable sulfur retention values (-82 %) by using a Ca/S molar ratio of 2.25. This value resulted in a very feasible ratio since it is commonly used in fluidized bed combustors.

Automated summary

L-CLCTM is a novel process that combines combustion and desulfurization with CO2 capture. Experimental tests show that high combustion efficiencies can be achieved at moderate temperatures, and a Ca/S molar ratio of 2.25 can result in suitable sulfur retention values.