SiO_2/S涂层与硫磷抑制剂对轻石脑油裂解结焦的影响

Effects of SiO_2/S coating and sulfur phosphorous inhibitor on coking in light naphtha cracking

引言 乙烯裂解炉辐射段炉管结焦是制约乙烯装置长周期运行的主要因素。裂解炉管的结焦会引起[1]：①管壁热阻增加,传热效率降低,裂解炉能耗增加;②炉管内径变小,流体压降增加,装置处理量减少;③炉管内壁渗碳,材料性能弱化;④周期性的清焦引起炉管热疲劳现象,

Coking tests were carried out on the inner surface of after-service HP40 cracking tube at 850℃ with naphtha as feed,and the anti-coking properties of anti-coking SiO2/S coating and sulfur phosphorous coking inhibitor were investigated.The effect of SiO2/S coating and sulfur phosphorous coking inhibitor on coke formation was studied.Scanning electron microscopy（SEM）,X-ray energy dispersion spectrometry（EDS）and X-ray diffraction（XRD）were used to characterize the morphology and structure of the inner surface of after-service HP40 cracking tube and the morphology of coke on the surface.The structure of coke was analyzed by TGA,elemental analysis and Raman spectroscopy.The results showed that the changes of the inner surface conditions of after-service HP40 cracking tube led to accelerated catalytic coking.When the mass fraction of sulfur phosphorous inhibitor was 200 μg·g-1,coke deposition was reduced by 69%.SiO2/S coating could inhibit catalytic coking,and coke was mainly deposited in the spalled SiO2/S coating region.Coke formation was reduced by 65% for SiO2/S coating only.When the combination of sulfur phosphorous coking inhibitor and SiO2/S coating was applied,the interference of HS radicals,originating from sulfur phosphorous inhibitor decomposition,with the heterogeneous noncatalytic mechanism in the cracking via radical termination and hydrogen Abstraction reactions resulted in an optimum mass concentration of sulfur phosphorous coking inhibitor.The combination of sulfur phosphorous coking inhibitor at the mass concentration of 50 μg·g-1plus SiO2/S coating would result in a decrease in coke formation up to 97%.Coke deposited on the inner surface of after-service HP40 cracking tube had a highly condensed structure with a high boiling point and a low graphitization degree.The use of SiO2/S coating and sulfur phosphorous inhibitor led to a decrease in the graphitization degree of the coke to a certain extent.