Studies on Several Fly Ashes and Their Modified Materials for CO2 Capture

Abstract

In recent years, global warming and climate change caused by the greenhouse gas emissions has given rise to widespread concerns. CO2 has been considered as the principal greenhouse gas of interest, and fossil-fuel-fired power plants have been deemed as the largest stationary sources of CO2 emission. It is imperative to capture CO2 from these sources to reduce the global CO2 emissions. Lately, capturing CO2 from flue gas using solid absorbents shows promising for CO2 abatement. For the cost-effective CO2 capture process and the recycling of environmental pollutants, deprecated resources have been utilized for CO2 capture from flue gas. In this work, fly ashes derived from different raw materials were tried as solid CO2 sorbents for flue gas treatment. To improve their CO2 capture capacities, the ashes were modified by different polyamines. An experimental demonstration on CO2 capture behaviors of fresh ashes and modified sorbents in simulated flue gas atmosphere of 40°C, 15% CO2 + 15% H2O and balanced N2 was presented in detail with a fixed-bed reactor system. CO2 capture capacities of fresh ashes were calculated as 0.56 mmolCO2/g, 0.32 mmolCO2/g, 0.44 mmolCO2/g and 0.83 mmolCO2/g, respectively. By contrast, CO2 capture capacities of amine-modified samples had been enhanced as 0.38 mmolCO2/g, 0.65 mmolCO2/g, 1.07 mmolCO2/g, 0.85 mmolCO2/g and 1.17 mmolCO2/g. The optimal sample of TEPA-modified biomass ash (TEPA-BA) with CO2 capture capacity of 1.17mmolCO2/g was screened. The optimal candidate was then selected for further investigation of the effects of temperature, CO2 concentration and H2O concentration on its CO2 capture behaviors. The results indicated that CO2 capture capacity would increase with the increase of temperature in the range of 30 to 40 °C and decrease with the increase of temperature in the range of 40 to 60°C, increase with the increase of CO2 concentration in the range of 5% to 20%, increase with the increase of H2O concentration in the range of 0% to 15% and decrease with the increase of H2O concentration in the range of 15% to 20%. The results in this work could provide basic data as a guidance for further applying the sorbents in practical operations.