The Ca-Cu Looping Process Using Natural Cao-Based Materials as Co2 Sorbent in a Packed Bed : Operation Strategies to Accommodate Activity Decay

The Ca-Cu looping process is a promising CO2 capture technology designed to produce H2 and power from a fuel gas, while obtaining a separated CO2-rich gas suitable for subsequent reuse or permanent storage. This process has been mainly proposed to be carried in multiple packed-bed reactors arranged in parallel, as this configuration allows the operation at high pressure, which minimizes the CO2 leakage and leads to more compact systems. The use of inexpensive and widely available calcium-based sorbents (i.e. limestone) would facilitate the scale up of this technology. Cu-based materials are stable in the long term, but natural calcium-based sorbents lose its activity rapidly after a short number of calcination/carbonation cycles until they achieve a residual CO2 sorption capacity. A balanced CuO/CaCO3 ratio in bed composition is crucial for a suitable performance of the Ca-Cu looping process, as an excess of CuO in the bed will generate more heat than required for the calcination, and consequently the formation of excessive temperature profiles that can damage the materials and potentially jeopardize the operation of the reactor. This work proposes a novel operation strategy valid for all packed-bed Ca-Cu looping processes consisting on loading the sufficient amount of CuO in the reactors to calcine only a small and well-defined fraction of CaCO3 in every cycle during the transient period in which the calcium-based sorbent is losing activity. In this way, there will be an excess of CaCO3 in the bed that ensures temperatures below 900 ºC during operation. The feasibility of this operation strategy is demonstrated for the decarbonisation of blast furnace gas (BFG) via Calcium Assisted Steel-mill Off-gas Hydrogen production process (CASOH), in which BFG is converted into a H2/N2 product gas, while a concentrated CO2 gas stream is obtained separately. A dynamic reactor model that incorporates realistic characteristics for commercial Cu- and Ca-based materials has been used to simulate the CASOH process during successive cycles. The results show that the BFG can be converted into a H2-rich gas (35 vol.%) diluted in N2, whereas a CO2-rich product gas is obtained during the sorbent regeneration stage maintaining the solids bed at moderate temperatures below 900 ºC