(480i) Chemical Looping Process for Post-Combustion Carbon Capture Using Calcium Hydroxide: Process Integration and Performance Results

Calcium-based solid sorbents such as calcium oxide and calcium hydroxide can be used in a chemical looping scheme for the capture of carbon dioxide from flue gas streams, and both CaO and Ca(OH)₂ have been successfully demonstrated at the pilot-scale for CO₂ removal. Calcium-based sorbents have several process advantages when compared to other carbon capture processes such as amine scrubbing and oxy-combustion. They include being derived from a cheap and abundant mineral, limestone, possessing a high CO₂ carrying capacity (786 g CO₂/kg), potentially removing all acid gases produced, and having the ability to increase the net electricity generation of a power plant. If calcium oxide is the sorbent, then CO₂ is removed in a CaO-CaCO₃ cyclic loop in a two reactor system-Carbonator and Calciner. The Ohio State University has developed a process wherein calcium hydroxide is used as the solid sorbent for CO₂ removal in a Ca(OH)₂-CaCO₃-CaO cyclic loop using three reactors-Carbonator, Calciner, and Hydrator. Ohio State has demonstrated the simultaneous removal of CO₂ and SO₂ using calcium hydroxide at the 120 kW_th-scale and established its superior reactivity compared to CaO. In addition, a high-temperature steam hydrator using a bubbling fluidized bed has been constructed and tested. The Ca(OH)₂-CaCO₃-CaO process was simulated in Aspen Plus using the results obtained from experiments. The power plant type and level of CO₂ capture constrain the process integration options while also controlling the solids flow requirements and parasitic energy consumption. They are also the primary factors that affect the process performance. Ultimately, the performance results of the process is reflected in the cost of electricity, which is the single, most critical factor in assessing a post-combustion carbon capture process. The requirements and constraints placed on both a CaO-CaCO₃ and a Ca(OH)₂-CaCO₃-CaO cyclic loop and their effect on process performance at different levels of carbon capture for post-combustion carbon capture have been investigated.