【作者】 崔秋凯；

【导师】 山红红；

【作者基本信息】 中国石油大学 ， 化学工程与技术， 2010， 博士

【摘要】 根据国家节能减排的要求,各企业已将如何降低硫氧化物(SOx)排放问题提到了重要日程。降低催化裂化烟气中SOx排放的研究工作早在20世纪70年代就已经开始,到目前为止,主要的方法有洗涤法、加氢处理法和添加硫转移剂法。在催化裂化反再系统中添加硫转移剂是最方便、快速、有效和廉价的烟气脱硫方法。关于镁铝尖晶石(Mg-Al-spinel)型硫转移剂的研究已经相对比较成熟;但是,大多数此类硫转移剂都含有钒氧化物,致使硫转移剂的制造和使用都会造成环境污染。为此,研究具有高脱硫活性但不含钒氧化物的硫转移剂具有重要的意义。本文首先详细研究了硫转移剂中各种活性组分以及它们之间复配对其脱硫效果和再生能力的影响;考察了制备方法和原料性质对硫转移剂的结构性质和脱硫效果的影响。实验结果表明:稀土的主要作用是提高SO2转化成SO3的速度;铁的主要作用体现在还原阶段;而在含有铁的硫转移剂体系中钒的作用并不明显,证明钒不是一种必不可少的金属。对比酸法、碱法和浸渍法三种制备方法,发现酸法溶胶凝胶法制备的硫转移剂的脱硫效果较好,且制备方法简单,比较适合放大生产。生产过程中原料的加入顺序会对硫转移剂的脱硫效果产生影响,应根据工艺选择合适的加料顺序。硫转移剂的生产中可以选择适量的金属氧化物替代硝酸盐,这既能保持硫转移剂的脱硫效果,又能降低生产过程中氮氧化物(NOx)排放量。高脱硫活性的硫转移剂应该同时具有较多的活性中心和丰富发达的孔道。因此,本文提出并采用扩孔剂来提高硫转移剂的比表面积和孔容,该方法能明显提高硫转移剂的氧化吸硫能力和还原再生性能。在硫转移剂组成确定的前提下,利用本实验室的提升管循环流化床装置研究了SO2形成规律以及硫转移剂的还原再生性能。烟气中SO2的浓度与原料中的硫含量和硫的类型紧密相关。原料中的硫含量越高,烟气中SO2浓度越高,但其浓度并不与原料硫含量成线性关系。此外,延长催化剂在反应器中的停留时间,烟气中SO2的浓度降低;而提高反应温度,剂油比,汽提蒸汽量,烟气中的硫含量都先略有增加后降低。但汽提蒸汽和反应温度的影响幅度较小。这些操作条件同样对硫转移剂的脱硫性能存在不同程度的影响,适当降低反应温度,延长催化剂在提升管中的停留时间都有利于提高硫转移剂的再生能力;提高再生器的温度和主风流量,延长在再生器中的停留时间都有利于提高硫转移剂的脱硫率。在实验室的提升管循环流化床催化裂化装置上的评价结果表明,制备的不含钒硫转移剂具有较高的脱硫能力和较强的还原再生性能,经过长时间的运转后仍能达到80%以上的脱硫率。在中国石油大港石化公司160万t/a催化裂化装置上进行工业试验,进一步证实使用该硫转移剂可以较大幅度地降低催化裂化再生烟气中SO2的排放。加入量占催化剂藏量的2%以后,烟气中SO2脱除率能达到90%以上。硫转移剂的加入没有对产品分布和产品质量带来不利的影响,没有影响催化裂化装置的正常操作以及后续装置的运转。大多数炼厂都使用CO助燃剂,如能将硫转移剂赋予一定的助燃功能,可降低助剂的使用成本。本文在前期研制的硫转移剂中,引入铜,并适当调整铈的用量,制备出了硫转移和CO助燃双功能助剂。增加助剂中铜的含量或铈的含量都有利于提高硫转移剂的助燃活性,但是铜含量过高,硫转移剂的脱硫活性降低较为明显,在硫转移剂中引入2%的铜,其助燃剂活性就高于目前常用的铜铝-铈铝复合氧化物,且具有较高的脱硫稳定性和助燃稳定性。更多还原

【Abstract】 According to the national requirements of saving energy and reducing emissions, many companys committed to reduce SOx emission. The study on reducing SOx emission for FCC flue gas has already begun in the early 1970s. So far, general methods include washing, hydrotreating and adding sulfur transfer additive. Adding sulfur transfer additive to the reactor and regenerator system of FCCU is the fastest, cheapest, most convenient and effective method for flue gas desulphurization. Comparatively, the study on magnesium aluminum spinel-based sulfur transfer additive is more mature. However, most of these additives contain vanadium oxide, which causes new pollution in the process of production and utilization. Therefore, developing the sulfur transfer additive without vanadium is very important.The role of different active components in the sulfur transfer additive on SO2 removal and regeneration performances were discussed in this paper. Moreover, the effect of preparation methods and raw material properties were investigated. The results showed that rare earth may increase the rate of SO2 converting to SO3, and iron may accelerate the reducing rate of sulfur transfer additive. The fact that the vanadium oxide in sulfur transfer additive system with iron does not play important role was verified by experiments. Comparing alkali method, acid method with impregnation method, it was found that the sulfur transfer additive prepared by gel with acid exhibited better desulfurization performance, and possessed the characterization of simple preparation and suitability to produce in large scale. The sequence of adding raw materials during the production of sulfur transfer additives affected SO2 removal performance, so proper sequence should be chosen. Using metal oxide instead of nitrate may reduce NOx emissions and keep high SO2 removal. Sulfur transfer additives need both abundant active sites and pores. The method, which increasing the BET specific surface area and pore volume by using pore-expanding agents, was devised and adopted in this paper. This method could obviously increase oxidizability and reducibility of the sulfur transfer additives. The affecting factors of SO2 formation in FCC reaction-regeneration systems and the reducibility of sulfur transfer additives were investigated in the riser circulating fluidized bed units. The SO2 concentration in flue gas related to sulfur content and raw materials closely. It increases with sulfur content of raw materials non-linearly. In addition, the concentration of SO2 decreases with the prolonging of residence time; and it increases first and then decreases with the increasing reaction temperature, catalyst/oil ratio and stripping steam content. But reaction temperature and stripping steam do not affect it much. These operating conditions also affect the performance of sulfur transfer additives in various extents. The regeneration performance of sulfur transfer additives increased with increasing reaction temperature and prolonging residence time in the riser. The SO2 removal performance rises with the increase in regeneration temperature, quantity of regeneration air and the extention of residence time in the regenerator.The sulfer transfer additive was evaluated in the riser circulating fluidized bed unit. The results confirmed that the additives without vanadium oxide show excellent SO2 removal and regeneration performances. The rate of SO2 removal is more than 80% during the long running process. The commercial test of the sulfur transfer additive was carried out in a 1.6 million t/a FCCU in Dagang Petrochemical Company, PetroChina Corporation. The results also confirmed that the additive may remove most of SO2 in the FCCU flue gas. Adding 2% additive, more than 90% SO2 was removed. Moreover, adding the additive did not affect the distribution and quality of the products, and the operation of the unit.If sulfur transfer additives can promote the combustion of CO, the cost of using additives may be reduced because it is unnecessary to use CO combustion-promoting additives alone. Through introducing Cu and adjusting the amount of Ce in the sulfur transfer additives, a bifunctional additive combining SO2 removal and CO combustion was prepared. The combustion-promoting performance of the bifunctional additives improves with the content of Cu or Ce. However, the SO2 removal performance drops obviously when excessive Cu was loaded. The additive with 2% CuO has ideal SO2 removal performance and the similar combustion-promoting performance as that of copper-cerium aluminium composite oxides.更多还原