Takuya Hirata

Carbon dioxide capture technology for coal fired boiler

Publisher Summary This chapter discusses the consequences of the flue gas impurity removal test obtained by the capture test for CO2 from the flue gas of coal fired boilers. This process is performed using the pilot plant constructed in the Mitsubishi Heavy Industries (MHI) Hiroshima R&D center. This plant has boilers, dust separator, flue gas processing apparatuses, and the desulfurizing system of the wet limestone gypsum method (FGD). The CO2 recovery system is includes a rinse tower to remove sulfur oxides present in the flue gas, a cooling tower to cool the flue gas, an absorbing tower to capture CO2 by “KS-1 solvent,” a water washing tower to recover solvent components accompanying the flue gas from the CO2 absorbing tower, and a regenerating tower to strip CO2 by heating the solvent absorbing CO2 with steam. The purity of the CO2 captured from the flue gas of the coal fired boilers is approx. 99.8 %-dry, which meets the requirement of 95% or higher in purity generally required for CO2EOR. When the concentration of sulfur oxides flowing into the CO2 recovery system is high, the accumulation of heat stable salt, particularly sulfate, increases to cause the deterioration of the solvent. To solve this problem, sulfur oxides must be pre-processed and removed on the downstream side of the CO2 recovery system beforehand.

Hydration structure of CO2-absorbed 2-aminoethanol studied by neutron diffraction with the 14N/15N isotopic substitution method.

Neutron diffraction measurements were carried out for CO2-absorbed aqueous 11 mol % 2-aminoethanol (MEA) D2O solutions (corresponding to 30 wt % MEA solution) in order to obtain information on both the intramolecular structure and intermolecular hydration structure of the MEA carbamate molecule in the aqueous solution. Neutron scattering cross sections observed for (MEA)0.11(D2O)0.89, (MEA)0.11(D2O)0.89(CO2)0.06, and (MEA)0.11(D2O)0.89(DCl)0.11 solutions with different (14)N/(15)N ratios were used to derive the first-order difference function, ΔN(Q), which involves environmental structural information around the nitrogen atom of the MEA molecule. Intramolecular geometry and intermolecular hydration structure of MEA, protonated MEA (MEAD(+)), and MEA carbamate (MEA-CO2) molecules were obtained through the least-squares fitting of the observed Δ(N)(Q) in the high-Q region and the intermolecular difference function, Δ(N)(inter)(Q), respectively. In the aqueous solution, the MEA molecule takes the gauche conformation (dihedral angle, ∠NCCO = 45 ± 3°), suggesting that an intramolecular hydrogen bond is formed. On the other hand, values of the dihedral angle ∠NCCO determined for MEAD(+) and MEA-CO2 molecules were 193 ± 4° and 214 ± 8°, respectively. These results imply that the intermolecular hydrogen bonds are dominated for MEAD(+) and MEA-CO2 molecules. The intermolecular nearest neighbor N···O(D2O) distance for the MEA molecule was determined to be 3.13 ± 0.01 Å, which suggests weak intermolecular interaction between the amino-nitrogen atom of MEA and water molecules in the first hydration shell. The nearest-neighbor N···O(D2O) distances for MEAD(+) and MEA-CO2 molecules, 2.79 ± 0.03 and 2.87 ± 0.04 Å, clearly indicate strong hydrogen bonds are formed among the amino group of these molecules and neighboring water molecules.