甲醇制烯烃装置催化剂细粉跑损问题剖析

某1.8 Mt/a甲醇制烯烃(MTO)工业化装置长期存在严重的催化剂细粉跑损问题。对比典型流化催化裂化(FCC)催化剂和工艺设计，对MTO装置催化剂进行物性分析和反应-再生系统工艺核算。结果发现：相比于FCC催化剂，MTO催化剂平均粒度更大、密度相当、抗磨损性能更好、更容易被旋风分离(旋分)器分离，因此颗粒物性不是其平衡催化剂中细粉跑损问题的根本原因。MTO装置再生器中稀相沉降空间高度偏低且操作气速更高，导致再生器旋分系统颗粒浓度过高；再生器两级旋分实际入口线速均高于传统设计值范围，导致其压降远超设计值；再者，料腿埋入再生器密相床层的长度高，易造成旋分器(尤其是二级旋分器)料腿内形成很高的堆积料柱，料柱易架桥或失流化，进而造成料腿“固泛”和分离效率严重下降。总之，再生器结构及其旋分系统设计的不合理是导致该MTO装置平衡催化剂中难以保留细粉的关键原因。

Root Cause of Fine Catalyst Particle Loss in Methanol to Olefin Unit

 A methanol to olefin (MTO) unit (1.8 Mt/a) in a coal-to-chemical plant has a serious problem of catalyst fine particle loss since the unit was put into operation. This causes that equilibrium catalysts with particle size less than 40 μm is far less than the designed data. To find the root cause of fine catalyst particle loss, through comparing with typical FCC catalyst and process design, catalyst physical properties (including particle size distribution, particle density and attrition index) and operation parameters of the reaction regeneration system (including particle entrainment in the freeboard, cyclone inlet velocity, pressure drop and dust outlet structure which could impact performance of cyclone system) were investigated. It was found that, in comparison with FCC catalyst, MTO catalyst has larger particle size, similar particle density, and better anti-attrition performance. Therefore, their physical properties are not the root cause of fine catalyst loss in equilibrium catalysts. However, several factors in the regenerator could have negative impacts on cyclone separator efficiency and stable operation, i.e. high superficial gas velocity in the freeboard, low disgangement height, high pressure drops of cyclones and high immersed length of dipleg in the dense bed. All of them can increase the difficulty of dust discharging from the dipleg outlets (especially in the second stage cyclones) due to formation of high dust packing column in the diplegs, where bridging and flooding are easier to occur. They also can lead to abnormal operation of cyclones and aggregation of the lost particle fines. In summary, improper design of regenerator and cyclone separators are the root cause of serious fine catalyst particle loss in the MTO unit.