加工低硫原料对加氢裂化装置的影响及对策

长庆石化1.2Mt/a加氢裂化装置原料油是长庆减压柴油,硫含量为0.0950%(质量分数),经过水洗后循环氢中H2S浓度范围在100～200μg/g,不足以保持裂化催化剂的酸性中心,甚至可能会导致催化剂硫化度降低,活性降低,造成加氢效果不理想、反应器床层温度变化等不良反应。装置实际运行情况也验证了如上结论。长庆石化在装置运转初期采用加注二甲基二硫化物(DMDS)进行补充硫化,加注量基本维持在50t/月,全年增加成本800万元。经分析研究后,决定进行停硫试验,以进一步观察和分析停硫对反应的影响和可行性。停硫试验表明,停硫对反应状况产生了一定的影响,循环氢中H2S浓度迅速下降,催化剂活性随之下降,致使反应温度被迫提升了约2℃,但这主要发生在停硫初期一周内,试验后期的反应状况比较稳定,加氢催化活性趋于稳定,这也可能与原料中硫含量有所提高有关。之后恢复注硫措施,催化剂活性得到大幅恢复,转化率回升。开发新型廉价的硫化剂或探索成本较低的补硫方法是目前亟待解决的问题。经分析,可尝试利用单质硫磺作为硫化剂,但其工业化可行性有待进一步研究探索。

Effect of Low-sulfur Feedstock on Hydrocracking Unit and Countermeasures

PetroChina Changqing Petrochemical Company＇s 1.2Mt/a hydrocracking unit uses vacuum gas oil as feedstock with a sulfur content of 0.0950% （mass fraction）.After water wash,the concentration of H2S in the circulating hydrogen is 100-200μg/g,which is insufficient to maintain the acid sites of cracking catalyst and may even lead to a decline in the sulfidity of catalysts,thus reducing the activity of catalysts.This will cause poor hydrogenation effect,changes in the bed temperatures of reactors and some other bad results.The performance of the unit also validated the above estimations.In the initial stage after the unit went into operation,Changqing Petrochemical Company carried out post-curing by adding DMDS at a rate of 50t/month.The cost of adding DMDS reached eight million Yuan per year.After a study ,the company decided to stop feeding sulfur to see the effect,on reactions,and feasibility of stopping sulfur injection.The experiment showed a certain effect of stopping sulfur injection on reactions：the concentration of H2S in circulating hydrogen dropped rapidly and consequently the activity of catalysts declined,forcing researchers to raise reaction temperature by about 2℃.However,this only happened in the first week of the stoppage of the sulfur feed and reactions thereafter were relatively stable with the activity of hydrogenation catalysts tending to stabilize.This might be related to the fact that the content of sulfur in the feedstock had risen.After sulfur injection was restored,the activity of catalysts resumed rapidly and the conversion rate rose back.The immediate task is to develop new types of cheap curing agents or to find a low-cost post-curing method.Analysis suggests that sulfur can be used as curing agent.But its commercial viability is yet to be studied.