Carbon Dioxide Capture from Flue Gas Using Regenerable Sodium-Based Sorbents

• Main Author: Liang, Ya
• Other Authors: Elizabeth J. Podlaha
• Format: Others
• Language: en
• Published: LSU 2003
• Subjects: Chemical Engineering
• Online Access: http://etd.lsu.edu/docs/available/etd-0702103-151700/

The overall objective of this project is to develop a simple and inexpensive process to separate carbon dioxide (CO2) as an essentially pure stream from a fossil fuel combustion gases using a regenerable sodium-based sorbent. This objective of this phase of the project is to evaluate CO2 capture using sodium-based sorbents in single-cycle and multicycle tests as a function of calcination and carbonation conditions. The sorbent precursors investigated were sodium bicarbonates supplied by Church and Dwight, Inc., and natural trona supplied by Solvay. All precursors were first calcined to sodium carbonate and then converted to sodium bicarbonate (NaHCO3) or Wegscheiders salt (Na2CO3?NaHCO3) through reaction with carbon dioxide and water vapor. Both sodium bicarbonate and Wegscheiders salt are regenerated to sodium carbonate when heated, producing a nearly pure CO2 stream after condensation of water vapor. An electrobalance reactor (thermogravimetric analyzer) and a fixed-bed reactor system were used to study the reaction rate and achievable sorbent capacity as a function of carbonation temperature, carbonation gas composition, and calcination temperature and atmosphere. Sorbent reproducibility and durability were studied in multi-cycle tests. Electrobalance tests show that sodium bicarbonate (SBC) samples had better performance than Trona samples. Lower carbonation temperature (60oC) and higher CO2/H2O concentrations resulted in faster reaction rate and larger sorbent capacity. More severe calcination conditions had a more significant negative effect on Trona than SBC sorbents. In addition, a small amount SO2 (<0.1%) resulted in a cumulative decrease in CO2 removal capacity with increasing carbonation cycle number. Results from 1.5-cycle fixed-bed reactor tests indicate that better CO2 removal efficiency for SBC-3 was achieved at a lower carbonation temperature of 60oC, where average prebreakthrough concentrations corresponded to approximately 75% CO2 removal. There was no obvious deterioration with cycle number. Instead, improved performance between cycle 1 and the remaining cycles was clear for SBC Grades 1 and 3 under the reaction conditions investigated. Prebreakthrough CO2 removal (at the third carbonation sample) increased from 63% in cycle 1 to about 90% for the remaining cycles at 60oC carbonation.