乙烯裂解炉燃烧传热的CFD模拟

为了掌握乙烯炉炉膛内的热场分布规律,本文采用CFD方法对SL-Ⅱ型工业乙烯裂解炉辐射段内所发生的燃烧、辐射传热、烟气流动等过程进行了耦合模拟,并且详细地分析了炉膛内流场及温度场的分布情况。其中,裂解炉的几何模型按照工程图纸1:1的比例建立;网格划分在专业网格生成软件ICEM11.0中完成;计算采用标准k-ε双方程模型模拟湍流,漩涡耗散/有限速率燃烧反应模型(EDM/FRC)模拟侧壁烧嘴的预混燃烧和底部烧嘴的非预混燃烧,离散传递模型(DTM)模拟炉膛辐射传热,计算过程在CFX5.0中完成。计算得到了裂解炉炉膛内流场、温度场分布的详细信息,模拟结果与工业实测数据吻合较好。模拟结果表明,在底部烧嘴的射流核心区周围形成了大范围的回流,过渡段拐角处有小范围的回流现象;炉膛长度、宽度、高度方向都存在明显的温度梯度,说明传统的炉膛传热计算方法假定温度分布均匀是不准确的;炉膛的高温区主要集中在炉高4.5 m处;炉膛上部的热量,由于侧壁烧嘴的加入而得到了很好地补充,说明侧壁烧嘴的安装位置合理。研究结果表明CFD模拟是目前为止研究裂解炉内热场分布规律最为有效的手段之一,对于未来乙烯裂解炉的设计与优化作用很大。

CFD simulation of combustion and heat transfer in ethylene cracking furnace

Three dimensional coupled simulation of flow,combustion and radiation heat transfer in the firebox of SL-II industrial ethylene cracking furnace was carried out in CFD software CFX5.According to actual sizes of furnace,three dimensional geometric model was established with ration of 1:1,and the mesh was generated by software ICEM11.0.Standard κ-ε turbulence model,discrete transfer radiation model and eddy-dissipation/finite-rate model were employed to describe turbulent flow,radiation heat transfer and combustion separately in the calculation.The detailed distributions of temperature,velocity field were obtained.Simulation result shows that circumfluence appeared around fuel jet center above the bottom burners with small circumfluence in the crossover section as well.The flow and temperature field were asymmetric and uneven in the furnace,which means that it is incorrect to simulate heat transfer by assuming even temperature distribution in the conventional calculation method.Meanwhile,a high temperature zone was found at the height of 4.5 m in the furnace.With the addition of side burners,the heat was supplemented properly in the upper section of the firebox.From the simulation results,which has a good agreement with the industrial data and reality,it is deduced that CFD simulation is one of the most effective tool to study the thermal field in the ethylene cracking furnace,furthermore instructing the design and optimization of ethylene cracking furnace.