Calcination of calcium-based sorbents at pressure in a broad range of CO2 concentrations

Abstract

The calcination reaction of two limestones and a dolomite with different porous structures was studied by thermogravimetric analysis. The effects of calcination temperature (1048-1173 K), particle size (0.4-2.0 mm), CO 2 concentration (0-80 %) and total pressure (0.1-1.5 MPa) were investigated. SEM analysis indicated the existence of two different particle calcination models depending on the sorbent type: a shrinking core model with a sharp limit between the uncalcined and calcined parts of the particle and a grain model with changing calcination conversion at the particle radial position. The appropriate reaction model was used to determine the calcination kinetic parameters of each sorbent. Chemical reaction and mass transport in the particle porous system were the main limiting factors of the calcination reaction at the experimental conditions. A Langmuir-Hinshelwood type kinetic model using the Freundlich isotherm was proposed to account the effect of the CO 2 during sorbent calcination. This allowed us to predict the calcination conversion of very different sorbents in a broad range of CO 2 partial pressures. Total pressure also inhibited the sorbent calcination. This fact was accounted by an additional decrease in the molecular diffusion coefficient with increasing total pressure with respect to the indicated by the Fuller's equation.

Kinetic analysis of a Cu-based oxygen carrier: Relevance of temperature and oxygen partial pressure on reduction and oxidation reactions rates in Chemical Looping with Oxygen Uncoupling (CLOU)

“…At these conditions, it is possible to use different adsorption isotherms to obtain the value of . García-Labiano et al [29] selected the Freundlich isotherm to properly describe the CaCO 3 calcination [29]. In this case, the use of the Freundlich isotherm successfully described the effect of CO 2 concentration on the CaCO 3 calcination rate, which showed an effect of the CO 2 concentration on the reaction rate similar to the O 2 effect observed for the reduction reaction in this work.…”

Degradation study of a novel polymorphic sorbent under realistic post-combustion conditions

“…This equilibrium line was calculated using equation 5 [37] and was supported with thermodynamic modelling using the ThermoVader excel add-in [38]. From application of equation 5 and the thermodynamic data, it was calculated that the temperature required for calcination under 100% CO2 at atmospheric pressure is at least 898 ± 4 °C.…”

Reactivity of Oxygen Carriers for Chemical-Looping Combustion in Packed Bed Reactors under Pressurized Conditions

“…If the solid structure contains more metal than oxygen according to the stoichiometry (a so-called oxygen deficient situation), the formation of oxygen vacancies is possibly the rate limiting step. These vacancies are formed according to equation (3). In this equation, V 0 is an oxygen vacancy, O(s) is an oxygen atom in the solid matrix and O 2 (g) is gaseous oxygen molecule.…”