Oxygen Carrier Carbon Deposition Suppression Method For Chemical Looping Combustion Based On CO₂ Hypoxia Dilutio And Low-Temperature Combustion

Chemical looping combustion（CLC）can produce higher concentrations of CO₂and H₂O,CO₂ can be separated by condensation and other methods.It is possible to achieve low-cost capture of CO₂.The carbon deposits formed on the surface of the oxygen carrier in the process affect the sustainability of combustion and reduce the CO₂ capture efficiency.In this dissertation,the Fe₂O₃/Al₂O₃ oxygen carrier and different coals are subjected to direct chemical looping combustion simulation experiments at different temperatures and different CO₂ concentrations in a fixed bed.The carbon deposits（elemental phase carbon,char,soot）and PAHs produced by combustion are analyzed.Study the inhibition of oxygen carrier carbon deposition under CO₂ hypoxia dilutio and low-temperature combustion conditions.The specific results are as follows:Regarding the formation of carbon deposits,at the same CO₂ concentration and at different temperatures,the amount of elemental phase carbon produced decreases with the increase in temperature.The amount of elemental phase carbon produced by CLC at 850°C is already small enough;the amount of char produced is an upward trend from 550℃to 650℃.When the temperature is 650℃and above,it continues to decrease to 950℃and rises again;except for the working condition of 850℃,the amount of soot produced at different temperatures increases with the increase of temperature.At 850°C,the formation of carbon black can be more inhibited,and there is no large amount of elemental phase carbon.At the same temperature,with different CO₂ concentrations.As the proportion of CO₂ inflow increases,the overall change trend of the amount of elemental phase carbon produced fluctuates.When the proportion of CO₂ is 20%,60%,100%,the amount is less;the amount of char produced increases with the proportion of CO₂inflow.The overall formation of a fluctuating pattern contrary to the trend of elemental phase carbon,when the proportion of CO₂ is 0%,40%,80%,the generation amount is relatively small;the proportion of CO₂ that generates less soot is 0%,40%,80%,the overall fluctuating trend is similar to that of char,and the amount of soot generated is the least at 650°C and 80%CO₂.Regarding the generation of Polycyclic Aromatic Hydrocarbons（PAHs）,at different temperatures,the total amount of PAHs generated increases with the increase of temperature.At 950°C,both the single ring number and the total amount are the maximum value in all working conditions.The amount of six-ring PAHs generated,except for the lower temperature at 650°C,was lower than the previous one,and the rest all increased with the increase in temperature.The introduction of CO₂ has a significant inhibitory effect on the second and third rings of PAHs,and it also has a certain inhibitory effect on the production of high-ring PAHs.After the introduction of CO₂,when the proportion of CO₂ is 20%,the total amount of PAHs at 550°C,650°C,750°C,850°C and the amount of six rings are all smaller than those without CO₂.The low-ring（second and third-ring）generation of CO₂ operating conditions is generally lower than that of non-CO₂operating conditions.When different coal samples are at 650℃and the CO₂ intake ratio is 20%,the formation of bicyclic PAHs is very small,and their different carbon content,volatile content,n（H）/n（C）and other coal structures are not affect the inhibitory effect of CO2on bicyclic PAHs.In summary,when the CO₂ ratio is 20%,60%,and 100%at higher temperatures,elemental phase carbon will be effectively suppressed;when the CO₂ ratio is 0%,40%,and 80%,it is beneficial to the suppression of char;as much as possible at low temperatures,the CO₂ ratio of 0%,40%and 80%is the working condition to effectively inhibit soot.In this experiment,the soot production is the least when the CO₂ ratio is 80%at 650°C.