STUDIES ON SEVERAL FLY ASHES AND THEIR MODIFIED MATERIALS FOR CO_2 CAPTURE

摘要

In recent years, global warming and climate change caused by the greenhouse gas emissions has given rise to widespread concerns. CO_2 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 CO_2 emission. It is imperative to capture CO_2 from these sources to reduce the global CO_2 emissions. Lately, capturing CO_2 from flue gas using solid absorbents shows promising for CO_2 abatement. For the cost-effective CO_2 capture process and the recycling of environmental pollutants, deprecated resources have been utilized for CO_2 capture from flue gas. In this work, fly ashes derived from different raw materials were tried as solid CO_2 sorbents for flue gas treatment. To improve their CO_2 capture capacities, the ashes were modified by different polyamines. An experimental demonstration on CO_2 capture behaviors of fresh ashes and modified sorbents in simulated flue gas atmosphere of 40°C, 15% CO_2+ 15% H_2O and balanced N_2 was presented in detail with a fixed-bed reactor system. CO_2 capture capacities of fresh ashes were calculated as 0.56 mmolCO_2/g, 0.32 mmolCO_2/g, 0.44 mmolCO_2/g and 0.83 mmolCO_2/g, respectively. By contrast, CO_2 capture capacities of amine-modified samples had been enhanced as 0.38 mmolCO_2/g, 0.65 mmolCO_2/g, 1.07 mmolCO_2/g, 0.85 mmolCO_2/g and 1.17 mmolCO_2/g. The optimal sample of TEPA-modified biomass ash (TEPA-BA) with CO_2 capture capacity of 1.17mmolCO_2/g was screened. The optimal candidate was then selected for further investigation of the effects of temperature, CO_2 concentration and H_2O concentration on its CO_2 capture behaviors. The results indicated that CO_2 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 CO_2 concentration in the range of 5% to 20%, increase with the increase of H_2O concentration in the range of 0% to 15% and decrease with the increase of H_2O 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.