CO2 capture with calcined dolomite: the effect of sorbent particle size

Abstract

This investigation is set in the more comprehensive study of an innovative fluidized bed reformer configuration for producing hydrogen from either biomass/

Determination of Kinetic and Diffusion Parameters Needed to Predict the Behavior of CaO-Based CO2 Sorbent and Sorbent-Catalyst Materials

“…The calculated intraparticle profiles of CO 2 concentration highlighted that pore diffusional resistances are negligible for the investigated case of study (Figure S3), as expected for particles smaller than about 500 μm …”

“…The calculated intraparticle profiles of CO 2 concentration highlighted that pore diffusional resistances are negligible for the investigated case of study (Figure S3), as expected for particles smaller than about 500 μm. 60 It should be stressed here that the TGA experimental data shown in Figure 1 and Figure 3 were preliminarily utilized to determine the characteristic time in the chemically-and diffusion-controlled regimes. However, each characteristic time was obtained considering a subset of the experimental CaO conversion and a purposely drawn equation: the subset concerning the very beginning of CaO conversion and eq 7, on one hand, and that characterized by X(t) ≥ 0.4 and eq 10, on the other hand.…”

“…The application of the Weisz-Prater criterion allowed predicting a Ni catalyst effectiveness factor close to 1, for SMR at the experimental conditions. On the other hand, as far as CO 2 sorption is concerned, fluidized bed adsorption tests with calcined dolomite showed that CaO dynamic conversion is affected very slightly by particle size up to 780 μm.…”

“… At the beginning of the CO 2 capture process by means of such a sorbent, CO 2 concentration at the active CaO grain surface coincides with that inside pores ( C CO2,c  C CO2,s ), since no CaCO 3 product layer has formed yet on the whole active sorption surface. By implementing this assumption directly in eq , one obtains the kinetic law characterizing the fast initial chemically controlled regime of CBN (eq ) and the related CaO molar balance (eq ): Equation can be further manipulated when applied to fine CSCM particles studied in this work ( d p < 500 μm), for which CO 2 diffusion offers negligible pore mass transfer resistances; ,, then, it is assumed that CO 2 concentration inside the particle pores is practically uniform and so approaches external bulk values ( C CO2,s ≈ C CO2,bulk ). This implies that eq can be treated as an ordinary differential equation and solved by separation of variables, obtaining the linearized eq : Equation was used in each TGA test, in order to determine values of the group , that is, of τ CBN , as the slope of the regression line of points obtained from TGA experimental data, for X < 0.4: this boundary value was fixed according to experimental X ( t ) trends (Figure ) obtained for CaO15Ni10 and CaO54Ni10; anyway, it may be different for other materials, without affecting the methodology proposed here.…”

“…Equation 8 can be further manipulated when applied to fine CSCM particles studied in this work (d p < 500 μm), 60 for which CO 2 diffusion offers negligible pore mass transfer resistances; 30,44,62 then, it is assumed that CO 2 concentration inside the particle pores is practically uniform and so approaches external bulk values (C CO2,s ≈ C CO2,bulk ). This implies that eq 8 can be treated as an ordinary differential equation and solved by separation of variables, obtaining the linearized eq 9: , that is, of τ CBN , as the slope of the regression line of points i k j j j j j j y…”