Abstract:

The efficient conversion and optimal utilization of heavy oil has great practical significance to the national economic development. Fluid catalytic cracking (FCC) is an effective vehicle for heavy oil upgrading. However, the riser, as a key component of the FCC unit, is characterized by the non-uniform “core-annuals” flow structure with relatively significant gas and solids backmixing which may result in low reactant conversion and product selectivity. The downer reactor, where gas and solids move downward co-currently has unique features such as the plug-like flow structure and much more uniform gas-solid distribution compared to the riser reactor. The downer is therefore acknowledged as a novel multiphase flow reactor with great potential in upgrading heavy oil. However, low solids holdup and poor initial gas-solid contacting hinder the promotion of the downer reactors. In this paper, previous studies on increasing solids concentration and initial gas-solid mixing in the downer reactors are summarized. Studies on the mechanism of increasing solids concentration and promoting initial mixing will not only enrich the fundamental research but also benefit the promotion of the downer reactor in its applications.

Key words: fluidized-bed, hydrodynamics, reactors, downer, high density, solids distribution, inlet structure

摘要：

重质油高效转化和优化利用是国民经济发展的重大需求,具有十分重要的现实意义和战略意义。提升管催化裂化一直是重油轻质化的重要手段,但提升管的不均匀环核结构及气固返混特性降低了重油转化率和产品选择性。相对于提升管,下行床具有近平推流流型及气固短停留时间的优点,处理重油具有潜在优势。但下行床内颗粒浓度过低且气固初始接触较差限制其推广及应用。本文综述了提高下行床颗粒浓度及改善颗粒初始分布的相关文章,指出了深入研究下行床的颗粒增浓机制及气固初始混合可以丰富下行床的基础研究并推动其工业应用。

关键词: 流化床, 流体动力学, 反应器, 下行床, 高密度, 颗粒浓度, 入口结构