Study On Adsorption Of Mercury By Biomass Char With Non-Isothermal Preparation Condition

The emission of mercury in flue gas from coal-fired power plants has attracted the attention of researchers all over the world.Adsorbent injection has become one of the promising control technologies for coal-fired flue gas pollution.Reducing costs and improving efficiency are the key issues affecting the application of technology.The flue gas of the power plant has the high temperature and low oxygen atmosphere conditions.After the biomass particles are fed in,the bio-char can pyrolysis under this atmosphere condition and the mercury in the flue gas can be adsorbed under suitable conditions subsequently,mercury can be removed from flue gas.Due to the non-isothermal process of bio-char preparation and adsorption,it is necessary to study the mercury adsorption characteristics of bio-char prepared in non-isothermal.Bio-char was prepared by pyrolysis of biomass with different particle size at different temperatures.In this dissertation it was found that bio-char with 58-75?m particle size had the best adsorption capacity,so this particle size was chosen as the research object.The pore structure and surface functional groups were characterized under the conditions of four temperature rising conditions of5?/min,10?/min,15?/min and isothermal,and the final pyrolysis temperatures of 400?,600?,800?and 1000?.At the same time,3%,5%,7%oxygen concentration,10%,15%,20%carbon dioxide concentration were selected to study the effect of preparation atmosphere on the microcosmic characteristics of bio-char.The results showed that with the increase of pyrolysis temperature,the content of functional groups on the surface of bio-char decreased gradually,and the pore structure parameters increased first and then decreased.The optimum temperature was 600°C,and the BET specific surface area was150.261 m~2/g prepared by isothermal at 600°C.Changes in the heating rate can lead to changes in the pore structure due to the thermal stress caused by the temperature change.As the concentration of oxygen increases,the number of functional groups on the surface of bio-char decreases,it is concluded that oxygen can promote pyrolysis of biomass.The pore structure parameters decreased first and then increased,and the prepared at 7%concentration was the best,the BET specific surface area is 195.897m~2/g.This indicates that during the pyrolysis of biomass,pore development experiences are generated,expanded,connected,and collapsed,and thus exhibit fluctuating changes.The effect of carbon dioxide is similar to that of oxygen,but with less impact.After analyzing the micro-characteristics of bio-char prepared under different pyrolysis conditions,mercury adsorption performance was studied.The final temperature of pyrolysis increased from 400°C to 600°C,and the mercury adsorption capacity of bio-char significantly increased.At 800°C,there is a certain degree of decline and there is a significant decrease at 1000°C.The adsorption efficiency of bio-char prepared at different heating rates has some differences,which is related to the different micro-characteristics.Generally,the heating rate is best at 10°C/min.The optimum variable temperature pyrolysis conditions were a pyrolysis temperature of 600°C and a heating rate of 10°C/min.The cumulative adsorption capacity of 10000 s reached 1500 ng/g.With the increase of oxygen concentration,the mercury adsorption capacity of bio-char first decreased and then increased;while under the carbon dioxide atmosphere,the mercury adsorption performance decreased first,then increased and then decreased.The mercury adsorption characteristics of bio-char under different adsorption conditions were studied.In the early stage of mercury concentration rising,the mercury adsorption capacity of bio-char increased.When the concentration continued to increase,and the adsorption capacity tended to be stable,which accorded with the adsorption isotherm equation.The increase of temperature could reduce the bio-char mercury adsorption performance significantly,the accumulative adsorption in 3000s at the adsorption temperature of 150°C is 76.34%lower than the adsorption temperature of 50°C,it is concluded that it was physical absorption.The presence of oxygen could partially promote the mercury adsorption performance of bio-char.When the oxygen concentration is 7%,the accumulated adsorption in 10000s is increased by 28.87%compared to0%oxygen concentration.The reason might be that oxygen could promote the oxidation of elemental mercury,thus improving the bio-char mercury adsorption capacity.Sulfur dioxide could compete with elemental mercury for adsorption,thus reducing bio-char mercury adsorption capacity.When the concentration of sulfur dioxide is 2000mg/m~3,the accumulated adsorption in 7000s is decreased by 66.27%compared to the concentration of 0%.Due to the interaction between the dispersive force of carbon dioxide non-polar molecules and the surface atoms of activated carbon into polar molecules,the conversion of elemental mercury could be promoted,and thus the ability of bio-char mercury adsorption could be remarkably promoted.The concentration of 20%compared to 0%,10000s accumulated adsorption increased by 90.67%.