Fluidization of ash for CO2 capture in high temperature chemical looping process

Abstract

This study aims to develop fluidizable and cost-effective carbon capture sorbent from waste with the target to be utilized in a high-temperature chemical looping process. Fly and bottom ashes used in this study are generated from the municipal solid waste incineration and gasification plants in Singapore, which are from a commercial-scale incinerator and Waste-to-Energy Research Facility (WTERF), a research-based gasification facility. Ashes studied are incineration bottom ash (IBA), gasification fly ash (GFA), and air pollution control (APC) ash. Properties and related parameters of each ash type are explored, namely the minimum fluidizing velocity (Umf), particle density, Geldart group classification, particle size distribution (PSD) and elemental analysis. Special attention will be given to Umf, particularly the multiple factors affecting Umf values of the ashes. These parameters would determine the suitability of the ash to be used in a fluidized bed reactor (FBR) for carbon capture through high-temperature looping process. A cold model FBR at room temperature is used to measure these parameters. Different pre-treatment, ash type, and size range of particles used are considered. Flow velocity is increased and decreased (subsequently) to determine the forward and backward Umf of that sample. Triplicate tests are performed and the average Umf is then calculated. The heterogeneity and uncertain fluidization behaviours of the ashes are observed, and analysis methods are developed to derive proper results from the data collected. Measured Umf values are tabulated and analyzed for the relationships between parameters, with significant correlation between particle density and Umf for different pre-treatments, and weak correlation for mass loss because of the entrainment of ash and attrition as observed based on the change in PSD. Future study should target sequestering of carbon using chemical looping in FBR, especially relating to how pre-treatment results in different properties for each ash sample, affecting Umf, mass loss, and their other properties.