乙烷裂解制乙烯过程反应动力学模型的研究进展

随着乙烯工业的不断发展及能源结构的不断调整,裂解乙烯原料呈现多样性。近年来,乙烷裂解制乙烯技术逐渐成为工业生产的热点。乙烷作为乙烯生产的优选原料,不仅具有收率高、纯度高、质量高的产品优势,同时具有投资低、成本低、能耗低的生产优势。作为裂解炉模拟的核心,研究乙烷裂解过程中的反应动力学模型可为工业生产提供精准预判。随工业应用范围的逐步扩大,该领域的理论研究也将迎来新的高潮。本工作对乙烷裂解的工艺优势、乙烷裂解反应动力学模型及结焦反应动力学模型的研究现状进行了总结。裂解反应动力学模型被分为经验模型、机理模型、分子反应动力学模型,结焦反应动力学模型被分为催化结焦、自由基结焦。针对未来的研究方向提出了新的展望,认为经验模型在裂解炉自动控制中的应用、自由基反应动力学模型的深入研究、乙烷与其他原料的共裂过程、裂解反应动力学与CFD技术的融合及基于多种生成机理建立结焦反应动力学模型五个方面将是今后需要关注的领域。     

开口扭曲片圆管强化传热与流动阻力特性模拟

In the industrial application of ethylene pyrolysis tubular heating furnace, the fluid transferred from horizontal to rotary flow by adding twisted slices internals, which increased the tangential velocity and strengthened the flushing effect on the tube wall, so as to achieve the purpose of enhancing heat transfer. Based on the second generation of twisted slices, the structure was improved, and RNG k?ε turbulence model was used to simulate the flow details inside the furnace tube. The longitudinal vorticity structure, resistance coefficient, Nusselt number Nu, comprehensive heat transfer coefficient PEC and the coupling coordination between velocity vector field and temperature gradient field in different twisted slice structures were compared and analyzed. The results showed that the structure with "slit" openings along the wall can reduce the loss of flow resistance while increased the strength of fluid swirl. The resistance coefficient of twisted slices with opening structure of 7 mm length, 2 mm width and 2 mm interval was 93.75% of the first generation and 8.67% more than the second generation, but the comprehensive heat transfer coefficient was 1.56% higher than that of the second generation and 1.29 times of the smooth tube. It can be considered that the optimized structure improved the stability of longitudinal vortex structure as well as strengthened the coupling between flow and heat transfer. Besides, along the central opening of the slices, the resistance coefficient at the twisted slices increased, resulting in larger local losses.     

FCC沉降器结焦问题的研究进展

沉降器是催化裂化中油气与催化剂分离过程的重要设备。沉降器的结焦问题易导致非计划停工,严重影响催化裂化装置的长周期运行,因此抑制或减缓沉降器结焦成为该领域的研究热点之一。综述了国内外有关沉降器结焦问题的研究进展,以期为沉降器的优化操作提供参考。首先对沉降器结焦的部位及原因进行了分析,从化学反应角度分析了结焦的内因是反应油气中液相重组分的存在;从流场分布、压力分布、催化剂含量分布和温度分布解析结焦的外因。进而阐述了结焦物的基本特性,按照不同方法对结焦物进行了分类和特性的比较。其次,从化学反应过程和油剂流动、焦体沉积与增长过程两方面总结了结焦的机理,并总结了操作条件(原料性质、催化剂含量、反应温度、再生剂温度和油/剂比)和沉降器结构(粗旋与顶旋连接结构、快分系统)对结焦的影响规律。最后根据结焦机理和影响因素,从优选反应物和优化操作条件、优化沉降器结构2个方面提出了抑制或减缓结焦问题的具体措施。提高沉降器温度和降低油气分压可从操作条件方面降低结焦的可能性,优化粗旋与顶旋连接结构、优化快分系统、优化分离器入口结构和顶旋升气管结构等措施可以改善沉降器内流场分布,进而抑制结焦。