The Hydration Behavior of Partially Sulfated Fluidized Bed Combustor Sorbent

Abstract

The efficiency of limestone sorbent utilization in fluidized bed combustors (FBCs) is low, because of incomplete sulfation of CaO. Hydration of the FBC ash can reactivate the partially sulfated sorbent, and the hydrated ash can be reinjected into the combustors as the SO2 sorbent. In this work, the rate of hydration, which is of primary importance in the reactivation process, is studied for FBC ash. The effects of major rate factors, temperature and particle size, are analyzed. At ambient temperature, the degree of hydration is well below 100% after 4 h of testing, suggesting the existence of a barrier to the complete conversion of CaO. The particle size effect on hydration rate appears to be complex, but can be interpreted in terms of the effects of heat and mass transfer. A model is proposed that gives a consistent description of the hydration behavior, and methods for enhancing the hydration are discussed.

Calcium looping sorbents for CO2 capture

“…Used sorbent reactivated with water for 1 min can reach 70% of the initial conversion of natural sorbent. There are many factors that affect the hydration of synthetic sorbents, but ultrasonic hydration could be a solution for reactivating this type of material [151], which was first proposed by Wang, Wu and Anthony [156] to enhance hydration in sulphated sorbent. However, direct water hydration is far from ideal due to the energy penalty caused by drying humid hydrated lime.…”

Investigation on the hydration of CFBC fly ash

“…2 show that the diffraction peaks of lime cannot be found after hydration for 6 h, and most of the lime in F0 is slaked at 1 h. The reason is that lime formed at about 800-900°C is highly reactive and can hydrate to Ca(OH) 2 in several hours [2,[29][30][31][32].…”

Experimental Study of HCl Capture Using CaO Sorbents: Activation, Deactivation, Reactivation, and Ionic Transfer Mechanism

“…It is possible that the highly exothermic hydration reaction leads to inner-pore expansion and inter-particle attrition, which favorably change the sorbent morphology. Reactivation of the deactivated CaO sorbents using hydration was previously reported for the purpose of CO 2 /SO 2 capture, − and this is the first study showing that this reactivating method is also effective for this specific HCl capture scheme.…”

“…This drastic decrease in both surface area and pore volume can be used to explain the loss of chloridation reactivity after these two processes. When hydration is applied, an obvious increase in surface area and pore volume occurs to the deactivated CaO sorbent, which indicates that the closed pore structure is reopened by hydration. − Combined with the result from TGA test 3, it can be inferred that the reactivating effect of hydration is likely a result of a physical process such as inter-particle attrition and inner-pore expansion rather than a chemical/crystal change from CaCO 3 -CaO to Ca(OH) 2 -CaO . On the basis of the experimental results and morphological analysis, it can be concluded that specially tailored precipitation (activation) and hydration (reactivation) are two effective methods that can improve or restore CaO sorbents’ morphological structure, which can subsequently lead to the enhanced HCl capture performance.…”