| Fluidized catalytic cracking(FCC)is an important secondary processing process of crude oil and a critical means of lightening heavy oil.FCC unit is the main emission source of refinery exhaust gas,and has always been the focus of refinery environmental protection supervision.At the present stage,the type and amount of pollutants in the exhaust gas discharged by FCC units are still unclear,which is not conducive to the control and supervision of FCC pollutants by the refinery enterprises.In this paper,we take three sets of typical FCC units with different processes as the research object,including a partial regeneration unit(U1)without a CO boiler,a partial regeneration unit with a CO boiler(U2),and a full regeneration unit(U3).Based on the FTIR field monitoring data,the emission factors of the flue gas pollutants of three FCC units were developed,and the uncertainty of the emission factors caused by the difference of the FCC process was analyzed.Finally,the FCC flue gas pollution caused by the wet flue gas desulfurization process was discussed.Finally,the impact of the wet flue gas desulfurization process on the emission and monitoring of FCC flue gas pollutants is discussed separately,aiming to improve the resolution of the refinery's atmospheric emission source inventory,and provide a scientific reference for the emission reduction and supervision of pollutants.The main research contents are as follows:(1)Optimizing the FTIR method suitable for monitoring complex FCC pollutants by using different detection methods.The gasmet DX4000 portable monitoring instrument based on the FTIR principle was used to conduct on-site monitoring of the pollutant components of three typical FCC units,and it was found that many unknown pollutants were monitored,such as methane,ethylene,benzene,styrene,hydrogen cyanide et.al;through the correlation analysis of the changes in the concentration of CO and HCN in FCC flue gas,to assess whether the emission of CO in the FCC flue gas can be controlled to limit the emission of HCN;at the same time,the SO2 and NOx emission concentrations monitored by FTIR and CEMS were compared,and it was found that the SO2 and NOx results monitored by FTIR were 9-10 times and 4-5 times that of CEMS,respectively.(2)Based on the monitoring data of FTIR,the emission factors of flue gas pollutants of three FCC units based on the coke burn-off rate and the processing rate were developed respectively,and the influence of different factors in the FCC process on the pollutant emission factors was analyzed.The results show that the emission factors of three FCC units are significantly different.Among them,coke properties,regeneration type and CO boiler have the most obvious impact on pollutant emissions.The effects of the three on the emission of different types of pollutants(sulfur compounds,nitrogen compounds and carbon compounds)in the flue gas are discussed separately.(3)Analyzed the concentration changes of SO2,NH3 and H2O in the FTIR monitoring results,and found that the three trends are quite consistent.Further factor analysis shows that the emission of SO2,NH3 and H2O is controlled by a common factor.The condensate of FCC flue gas in U1 was analyzed by ion chromatography.The analysis results showed that the FCC flue gas after wet desulfurization would carry many water vapor,excess ammonia and soluble salts.The results of TG-MS analysis showed that ammonium sulfite was the main components of these soluble salts are also responsible for the strong correlation between SO2,NH3 and H2O,which also indicates that the hot-wet sampling process will overestimate the emissions of NH3 and SO2.Finally,the influence of the wet flue gas desulfurization process on the emission and monitoring of pollutants in flue gas under different FCC processes is summarized,which provides guidance for selecting appropriate pollutants control equipment and monitoring methods. |
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