二氯乙烷裂解炉的数值模拟与分析
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摘要
二氯乙烷裂解炉是热裂解法制备氯乙烯单体工艺中关键的工艺设备之一,对其操作过程进行数学模拟和开展深入的研究工作,在维持裂解炉的正常生产、节约燃料、提高产量和经济效益等方面具有重要的理论和现实意义。裂解炉中存在着燃烧、传热、传质等复杂流体的流动,建立由偏微分方程组成的管式裂解炉数学模型求解困难。计算流体力学(Computational Fluid Dynamics,CFD)可以对这些复杂流体的流动进行详细的数值计算。它综合了计算数学、计算机科学、流体力学、科学可视化等多种学科,为现代科学中许多复杂流动与传热问题提供了有效的解决方法。本文主要利用CFD技术对裂解炉辐射室进行数值模拟与分析。
管式加热炉内部炉管的裂解反应与管外的辐射传热是相互影响而又分别独立的两部分。本文分别以二氯乙烷裂解炉中反应管内的反应过程和辐射室内的热传递过程为对象,通过计算机进行了数学模拟与分析。本文主要进行了以下的研究工作:
1.结合别洛康法计算裂解炉辐射室的传热模型,建立了整个管式裂解炉的数学模型并确定了模型中的参数。利用所建立的数学模型,分别研究了进料温度、氧含量、燃料量等操作变量对裂解炉的转化率和热效率的影响,得出了所研究的管式加热炉较优的操作条件。结合某石化厂二氯乙烷裂解单元装置的DCS数据进行了模拟计算。实例结果表明,本文建立的数学模型基本符合实际生产状况,可用于管式加热炉的模拟计算。这些对于指导实际生产操作以及进一步对工业裂解炉的优化设计提供了参考依据。
2.研究了数值计算中的网格划分技术以及控制方程的离散化格式,针对裂解炉的物理结构特点,选用Gambit对裂解炉辐射段进行几何建模,采取分块结构、非结构化自适应网格,对火嘴周围进行网格加密处理,建立整个裂解炉辐射室的网格模型,同时确定裂解炉数值模拟的边界条件类型。
3.研究了流体动力学的基本原理,建立了二氯乙烷裂解炉辐射段的流体控制方程、传热方程、燃烧方程以及辐射方程。根据裂解炉的结构确定边界条件,采用FLUENT软件对上述方程进行数值求解。计算得到裂解炉内部流场、温度场以及浓度场分布的相关信息,这些数据可为裂解炉的优化操作、设计和工程改造提供很多有价值的信息。
The dichloroethane cracking furnace is an important device in the manufacture of vinyl chloride monomer (VCM) by heat cracking method. A detailed study on the furnace is both theoretically and practically valuable for its daily maintenance, energy saving, productivity improvement and economic performance. Inside the furnace, there is a complicated flow process, which involves combustion, heat transfer and mass transfer phenomenon. Therefore building an accurate and reliable mathematical model is the necessary precondition for further research of furnace. Computational Fluid Dynamics (CFD), as a new subject embracing calculation mathematics, computer science, fluid dynamics and visible technology etc, provides effective solutions to the complicated flow and heat transfer problems in modern science. CFD can perform numerical calculation to analyze the complicated flowing characteristics inside the dichloroethane cracking furnace.
In this paper, both the reaction process in reaction tube and heat transfer in radiation chamber are numerically simulated on computer . The simulation results are then analyzed in detail. The contributions of the research are as follows.
Firstly, a mathematical model of tube cracking furnace is set up, whose parameters are determined by the method ofъелоконь. The effect of multi-operation variables, such as feeding temperature, oxygen content and fuel content, on the conversion and heat efficiency of cracking furnace is studied to obtain the optimum operation conditions within the specific tube heating furnace by the mathematic model. A simulation is performed based on the data of DCS from the equipment of dichloroethane cracker in a petrifaction company. The result shows that the mathematic model in this paper is reliable; the result is accorded with the data of actual production well and can be used to perform simulation for tube heating furnace.
Secondly, based on the principal theorem of adaptive grid creating method, the use of self-adaptive mesh refinement method for unstructured mesh provides a good mesh-creating solution for the complicated configuration of cracking furnace by Gambit. Meanwhile, boundary condition of cracking furnace is determined for numerical simulation.
Thirdly, based on the fundamental principle of CFD, the corresponding fluid control equation, heat-transfer equation, combustion equation and radiation equation are set up respectively. The principal boundary condition is determined according to configuration of cracking furnace and DCS data of some chemical factory. The couple algorithm for pressure-velocity coupling scheme are employed in cracking furnace modeling. These equations are solved and useful information is achieved about the flow field, temperature field and density field about the inner combustion of cracking furnace.
管式加热炉内部炉管的裂解反应与管外的辐射传热是相互影响而又分别独立的两部分。本文分别以二氯乙烷裂解炉中反应管内的反应过程和辐射室内的热传递过程为对象,通过计算机进行了数学模拟与分析。本文主要进行了以下的研究工作:
1.结合别洛康法计算裂解炉辐射室的传热模型,建立了整个管式裂解炉的数学模型并确定了模型中的参数。利用所建立的数学模型,分别研究了进料温度、氧含量、燃料量等操作变量对裂解炉的转化率和热效率的影响,得出了所研究的管式加热炉较优的操作条件。结合某石化厂二氯乙烷裂解单元装置的DCS数据进行了模拟计算。实例结果表明,本文建立的数学模型基本符合实际生产状况,可用于管式加热炉的模拟计算。这些对于指导实际生产操作以及进一步对工业裂解炉的优化设计提供了参考依据。
2.研究了数值计算中的网格划分技术以及控制方程的离散化格式,针对裂解炉的物理结构特点,选用Gambit对裂解炉辐射段进行几何建模,采取分块结构、非结构化自适应网格,对火嘴周围进行网格加密处理,建立整个裂解炉辐射室的网格模型,同时确定裂解炉数值模拟的边界条件类型。
3.研究了流体动力学的基本原理,建立了二氯乙烷裂解炉辐射段的流体控制方程、传热方程、燃烧方程以及辐射方程。根据裂解炉的结构确定边界条件,采用FLUENT软件对上述方程进行数值求解。计算得到裂解炉内部流场、温度场以及浓度场分布的相关信息,这些数据可为裂解炉的优化操作、设计和工程改造提供很多有价值的信息。
The dichloroethane cracking furnace is an important device in the manufacture of vinyl chloride monomer (VCM) by heat cracking method. A detailed study on the furnace is both theoretically and practically valuable for its daily maintenance, energy saving, productivity improvement and economic performance. Inside the furnace, there is a complicated flow process, which involves combustion, heat transfer and mass transfer phenomenon. Therefore building an accurate and reliable mathematical model is the necessary precondition for further research of furnace. Computational Fluid Dynamics (CFD), as a new subject embracing calculation mathematics, computer science, fluid dynamics and visible technology etc, provides effective solutions to the complicated flow and heat transfer problems in modern science. CFD can perform numerical calculation to analyze the complicated flowing characteristics inside the dichloroethane cracking furnace.
In this paper, both the reaction process in reaction tube and heat transfer in radiation chamber are numerically simulated on computer . The simulation results are then analyzed in detail. The contributions of the research are as follows.
Firstly, a mathematical model of tube cracking furnace is set up, whose parameters are determined by the method ofъелоконь. The effect of multi-operation variables, such as feeding temperature, oxygen content and fuel content, on the conversion and heat efficiency of cracking furnace is studied to obtain the optimum operation conditions within the specific tube heating furnace by the mathematic model. A simulation is performed based on the data of DCS from the equipment of dichloroethane cracker in a petrifaction company. The result shows that the mathematic model in this paper is reliable; the result is accorded with the data of actual production well and can be used to perform simulation for tube heating furnace.
Secondly, based on the principal theorem of adaptive grid creating method, the use of self-adaptive mesh refinement method for unstructured mesh provides a good mesh-creating solution for the complicated configuration of cracking furnace by Gambit. Meanwhile, boundary condition of cracking furnace is determined for numerical simulation.
Thirdly, based on the fundamental principle of CFD, the corresponding fluid control equation, heat-transfer equation, combustion equation and radiation equation are set up respectively. The principal boundary condition is determined according to configuration of cracking furnace and DCS data of some chemical factory. The couple algorithm for pressure-velocity coupling scheme are employed in cracking furnace modeling. These equations are solved and useful information is achieved about the flow field, temperature field and density field about the inner combustion of cracking furnace.
引文
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