Experimental Results and Computer Simulations for Post-Combustion Carbon Dioxide Removal Using Limestone

Amid growing concerns of global climate change, governmental entities and industry throughout the world are performing research on the capture and sequestration of carbon dioxide (CO₂). Coal accounts for nearly half of the United States electricity generation and 40% of the world’s electricity generation. This directly translates into 33% of the United States CO₂ emissions and 40% of the world’s CO₂ emissions produced from coal-combustion power plants for electricity generation. Not surprisingly, a significant emphasis has been placed on capturing CO₂ produced from coal-combustion power plants. To date, though, no large-scale power plant employs the use of carbon capture technologies.

Under the leadership of Professor Liang-Shih Fan and his research group at The Ohio State University, a process that employs a solid sorbent to reactively remove CO₂ from coal combustion flue gas has been developed. The Carbonation-Calcination Reaction (CCR) Process relies on a carbonation reaction with a metal oxide to remove the CO₂ and a subsequent calcination reaction to produce a pure stream of CO₂ while regenerating the metal oxide. An additional benefit to the CCR process is the ability of the sorbent to simultaneously remove sulfur dioxide (SO2) present in the flue gas stream.

Upon successful bench-scale experiments, a 20 pound per hour coal combustion facility was erected to demonstrate the CCR Process. With the ability to capture greater than 90% CO₂ and greater than 99% SO2 on a once-through basis with a commercially available calcium-based sorbent, the facility was re-renovated for multicylic investigations.

Consistent CO₂ removals over multiple cycles were obtained using an intermediate hydration reaction for reactivation of the calcium oxide sorbent. The hydration reaction reverses and eliminates any effect of sintering that occurs during the calcination reaction. Due to its inherently small particle size, along with an increase in surface area and pore volume upon spontaneous dehydration, calcium hydroxide is able to maintain constant CO₂ removals.

Computer simulations integrating the CCR Process into a power plant shows a high level of compatibility due to its high-temperature operation. Energy penalties between 15% and 20% were obtained, with compression of CO₂ while producing a pure, dry stream of CO₂ ready for sequestration.