Development And Study Of Cu-containing Rice Husk Char For Mercury Removal In Oxyfuel Combustion Atmosphere

The emission of carbon dioxide will cause greenhouse effect,which will endanger the natural environment and affect the survival of organisms.Oxyfuel combustion technology can capture carbon dioxide and effectively reduce carbon emissions,which has good application prospects.However,there are many unresolved problems in oxyfuel combustion technology,which hinder its practical application.One of these problems is the removal of mercury from oxyfuel combustion atmosphere,therefore it is necessary to develop and study efficient mercury adsorbents adapted to oxyfuel combustion atmosphere.In this paper,rice husk char was prepared by pyrolysis of agricultural waste rice husk at high temperature,and Cu Cl₂ solution was used to wash and modify the char sample to obtain Cu-containing rice husk char,the characteristics and mechanism of mercury removal under simulated oxyfuel combustion atmosphere were investigated combined with experiments and simulations.Firstly,the physicochemical properties of the rice husk char before and after the impregnation modification were analyzed.The results showed that after the solution impregnation modification,the surface pore structure of rice husk char was greatly improved,the number of micropores was greatly increased,and the specific surface area was also increased,which enhanced the adsorption area of rice husk char and facilitated the physical adsorption of mercury.And the modification also produces phenolic hydroxyl groups,C-Cl groups and carboxyl groups,which are functional groups that enhance the chemisorption of mercury.In addition,the experimental results showed that the rice husk char modified by impregnation with 0.15 mol/L Cu Cl₂ solution had the best performance for mercury removal,and therefore this char sample was also investigated as the adsorbent for mercury removal in the subsequent experiments.Next,the effects of inlet mercury concentration,reaction temperature and different flue gas components on the performance of Cu-containing rice husk char were investigated.The results showed that the increase of inlet mercury concentration enhanced the performance of Cu-containing rice husk char,while the high temperature decreased the physical adsorption of mercury.O₂ will replenish the oxygen on the surface of rice husk char and promote the production of Hg²⁺that can be easily removed.Both HCl and NO are capable of reacting with Hg⁰,with the reaction products Hg Cl₂ and Hg（NO₃）₂,respectively.SO₂ will compete with Hg for the active adsorption sites to inhibit the removal of mercury,and on the other hand,it will react with mercury to form Hg SO₄ to promote the removal of mercury.Finally,the mercury adsorption properties of rice husk char and Cu-containing rice husk char were analyzed from a microscopic perspective using density flooding theory.The results show that the adsorption of mercury by rice husk char is physical adsorption,and the van der Waals forces between them originate from the electron transfer that occurs during the adsorption process.Cu-containing rice husk char mainly achieved the purpose of mercury removal through chemisorption.During the adsorption process,one of the Cu-Cl bonds of Cu Cl₂ molecule will break,and the resulting Cu and Cl atoms will bind to Hg,thus immobilizing Hg inside the Cu Cl₂ molecule,which is also consistent with the results of XPS analysis.The Cu-containing rice husk char developed and studied in this paper still maintains good performance of mercury removal under oxyfuel combustion atmosphere,it can be utilized in oxyfuel combustion coal-fired power plants.The experimental results and analysis also provide theoretical guidance for the future development of more efficient adsorbents for mercury removal.