Ca-based sorbents as precursors of oxygen carriers in chemical looping combustion of sulfurous fuels

Limestone Chemical Looping Combustion process (LCL-C T) patented by Alstom Power Inc. proposes the formation of a CaSO4 oxygen carrier via sulfur retention process when supplying a Ca-based sorbent together with sulfurous fuels in the fuel reactor. In the present research work, four Ca-based sorbents, three limestones and one dolomite with different physico-chemical characteristics, have been evaluated as oxygen carrier precursors during consecutive redox cycles by thermogravimetric analysis. 5% H-2 and 3000 vppm H2S (N-2 to balance) and 10% O-2 (N-2 to balance) were selected as reducing and oxidizing gases, respectively. Additionally, an anhydrite ore has also been studied for comparison purpose. Results from SEM-EDX characterization of the sorbent particles revealed the existence of three different sulfation patterns: (1) uniform distribution, (2) core-shell structure and (3) high sulfur content with high limitation to be converted into CaSO4. All sorbents exhibited high oxygen transport capacity (R-oc = 13.3-20.8%), except for the material showing pattern (3) (R-oc = 2.6%). Likewise, the materials presented high reactivity with rate index values ranged between 11.0 and 18.8%/min. Therefore, the Ca-based sorbents herein assessed can be considered suitable precursors for the formation of CaSO4 based oxygen carriers to be used in CLC systems burning sulfurous fuels.

Automated summary

Four different physico-chemical characteristics of Ca-based sorbents were evaluated as suitable precursors for CaSO4-based oxygen carriers in CLC systems.