CO₂ removal by Ca-based sorbents in a packed-bed reactor: Kinetic study and aspen plus simulation

ABSTRACT

In this work, carbonation reaction of CO₂ with lime was investigated at both pellet scale and pilot reactor scale. A modified grain model was developed in order to evaluate the kinetic parameters of the reaction. Pellet-scale experiments were carried out in a thermogravimetric analysis (TGA) system providing the data for the model parameters calculation and also confirming the model with experimental data. The activation energy was about 29 kJ/mol for calcined calcium carbonate. Aspen Plus software was used to simulate the packed-bed reactor behavior in order to investigate the accuracy of the kinetic data obtained by the mathematical model.

KEYWORDS:

• Aspen plus
• carbonation reaction
• modified grain model
• simulation
• TGA

Nomenclature

a CA/CAb, dimensionless gas concentration	=
CA Gas concentration in the pellet ($\mathrm{m}\mathrm{o}\mathrm{l}/\mathrm{c}{\mathrm{m}}^3$)	=
CAb Bulk gas concentration ($\mathrm{m}\mathrm{o}\mathrm{l}/\mathrm{c}{\mathrm{m}}^3$)	=
De Effective diffusivity of gas A in the pellet (m2/s)	=
De0 Initial effective diffusivity of gas A in the pellet (m2/s)	=
DP Effective diffusivity of gas A in the product layer ($\mathrm{c}{\mathrm{m}}^2/\mathrm{s}$)	=
DP0 Initial effective diffusivity of gas A in the product layer ($\mathrm{c}{\mathrm{m}}^2/\mathrm{s}$)	=
ks Surface rate constant ($\mathrm{c}{\mathrm{m}}^4/\mathrm{m}\mathrm{o}\mathrm{l}.\mathrm{s}$)	=
L0 Thickness of pellet (m)	=
r** Dimensionless unreacted radius of the grain	=
rgo Radius of the grain (m)	=
MB Solid reactant molecular weight (g/gmol)	=
S0 Reaction surface area per unit volume (m2/m3)	=
y Dimensionless position in the pellet	=
Z Ratio of molar volume of solid product to solid reactant	=
$\delta$ Variation ratio of the pore diffusion	=
$\epsilon$ Pellet porosity	=
${\epsilon }_0$ Initial pellet porosity	=
${\rho }_B$ True density of the solid reactant ($\mathrm{g}\mathrm{r}/\mathrm{c}{\mathrm{m}}^3$)	=
${\theta }_{MG}$ Dimensionless time $\frac{k_s{C}_{AG}{M}_B}{{\rho }_B{r}_{g0}}t$	=
$\sigma$ Thiele modulus for the pellet, $\frac{{\mathrm{R}}_0}{2}\sqrt{{\mathrm{k}}_{\mathrm{s}}\left(1-{\epsilon }_0\right)/{\mathrm{D}}_{\mathrm{e}}{\mathrm{r}}_{\mathrm{g}0}}$	=
${\sigma }_g$ Thiele modulus for the grain $\sqrt{k_s{r}_{g0}/2D_P}$	=
t time (s)	=