Study On Clogging Mechanism Of FCC Slurry Filter Element

As a commonly used FCC slurry purification process,the filtration method has the problems of short filtration period,frequent switching,and easy destruction of the filter element.The clogging of the filter element is the key to these problems,making the slurry filter unable to meet the normal industrial operation requirements.In this paper,based on four kinds of typical FCC slurrys from Zhanjiang,Dongying,Jingbo and Changling,and the plugging mechanism of catalytic cracking slurry filter was studied.The main research contents include the causes,processes and influencing factors of blockage formation.The cause of the blockage was studied.The properties of the blockage were analyzed by SEM,elemental analyzer,Fourier transform infrared spectroscopy and nuclear magnetic resonance spectrometer.The results were compared with the original slurry and show that: The gap between the particles of the blockage is large,the aggregation is loose;the irregular particle shape is present;the structure is compact,and the surface has obvious sedimentary ripples.The blockage is more highly entangled or condensed than the original slurry.Blockage is a kind of polar macromolecular substance with high aromaticity,low content of alkane structure and strong unsaturation.It is mainly derived from resin and asphaltene in the original slurry,and further condensed with a fused aromatic hydrocarbon in the original slurry.Based on the analysis of blockage causes,a pretreatment scheme was proposed to remove the asphaltene components in the four FCC slurries.The study found that for different properties of the slurry,the pretreatment conditions are different.After pretreatment,the asphaltene of the slurry is basically removed,the solid content is reduced by about 90%,the catalyst particles in the catalytic slurry are mostly contained in the asphaltenes.By analyzing the thermogravimetric-difference heat curve of the catalytic slurry before and after pretreatment,the change of chemical composition and structure with temperature of the catalytic slurry in the filter working zone are studied,to describe the formation process of the blockage.The formation process of a FCC slurry filter blockage should include the following three steps:(1)In the initial filtration stage,the catalytic slurry is dominated by the condensation exothermic reaction;(2)During the backwashing stage,the internal temperature of the filter drops,and the weak bond breakage in the catalytic slurry dominates.Before the next filtration,the filter will undergo a warming phase.As the temperature rises,the breaking of the strong bond begins to dominate;(3)When re-filtering,the temperature is further increased,and the unwashed material in the backwashing stage and the catalyst particles in the slurry are enriched on the outside of the filter element,and are associated with the condensed aromatic hydrocarbon to form a blockage micelle.The entry of the micelle into the microporous structure of the filter element eventually leads to clogging of the filter element.The experimental study on the factors affecting the blockage shows that increased asphaltene and resins content promotes the formation of blockage,but the effect of asphaltenes is more pronounced;the higher the reaction temperature,the more likely the clogging occurs,and as the content of asphaltenes increases,the effect of temperature increases;and the longer the stay time,the more likely it is to block.