【作者】 郑志伟；

【导师】 杨朝合； 赵辉；

【作者基本信息】 中国石油大学 ， 化学工程与技术， 2010， 硕士

【摘要】 加热炉是石油化工行业的主要加热设备,同时也是高能耗设备,加热炉的节能降耗是节能工作的重点环节。通过研究炉内传热过程来提高能源利用率,已成为技术创新的工作重点。本课题以某石化公司500万吨/年的常压加热炉为模拟对象,根据计算流体力学的基本原理,建立了管式加热炉炉管内外耦合传热的数学模型。根据所建立的耦合传热模型,对常压加热炉内的稳态传热过程进行模拟。通过与现场标定数据进行对比分析,验证了加热炉模型的准确性。同时,针对炉管周向热强度分布不均匀的问题,提出了强化传热的优化方案,通过优化前后的模拟结果分析,验证了优化方案的可行性。采用分区耦合的方法研究了常压加热炉辐射段内的流动、燃烧和管内外传热的工艺过程。计算中,实现了燃烧器、炉膛、炉管整体几何结构的建模和网格划分,选用标准k-湍流模型、非预混燃烧模型和离散坐标辐射传热模型,将炉管黑度定为0.8,模拟得到了炉内的流场、温度场及炉管表面温度和热强度分布的详细信息。炉膛温度及炉管表面热强度模拟结果与常压炉测定数据和设计数据非常吻合。结果表明,底部燃烧器的高速射流在炉膛下部产生较大回流区,对炉膛内烟气温度分布的均匀性至关重要;另外,炉管管壁温度和热强度分布存在明显的非均匀性,影响炉管使用寿命。以炉管表面热强度分布为边界条件,采用MATLAB编程,进行了管内一维流动计算,得到炉管出口的温度、压力和气化率数值,通过与常压炉测定数据比较,证明了所建加热炉耦合传热模型的可行性和准确性。通过单根炉管的模拟结果可知,在单面辐射炉中,炉管周向和轴向的温度和热强度分布存在明显的不均匀性,向火侧的热强度明显高于背火侧。在炉管背火侧的一定范围内增加适量的钉头或翅片,可以提高背火侧的受辐射面积。改造后,翅片管背火侧的辐射热强度比光管提高了14%左右,平均辐射热强度比光管提高了7%左右,同时,翅片管向火侧的辐射热强度仅为背火侧的1.18倍,周向热强度分布趋向均匀。该方案有效提高了炉管背火侧的热强度和炉管平均热强度,改善了炉管周向热强度分布,提高了炉膛热强度和加热炉热效率,延长了加热炉安全运行周期,对实现节能减排具有重要意义。更多还原

【Abstract】 As a main heating equipment in petrochemical industry, furnace consumes a lot of energy. The energy-saving of furnace is the focus of energy conservation links. The study of heat transfer process in the furnace to improve energy efficiency has become the focus of technological innovation. With the basic principles of computational fluid dynamics, the structural parameters and operating conditions of the atmospheric heater, this subject established the mathematical model of tube furnace by the whole-coupling method. According to the established whole-coupling heat transfer model, the steady-state heat transfer process in the furnace was simulated. Compared with the field calibration data, this paper got the optimal simulation model and parameters. At the same time, a plan of enhancing heat transfer was proposed. By analyzing the simulation result before and after optimization, the feasibility of the plan was validated.The processes of fluid flow, combustion and heat transfer between the flue gas and tube without any simplification in the firebox of atmospheric heater were studied with the whole coupling method. The geometrical model and the dividing of grid of the combustor, combustion chamber and furnace tube were generated. The standard k- turbulent model, the non-premixed combustion model and the discrete ordinate transfer radiation model were used to simulate the furnace. The internal emissivity of the furnace tube was defined as 0.8 in the model. Detailed information about the flow field, temperature field, the temperature and heat flux distribution in tube skin was obtained. Results showed that the high velocity of bottom combustors’jet flow resulted in large recirculation zone of flue gas, which played an important role in the uniformity of flue gas temperature in the bottom of the furnace. In addition, non-uniform distribution of temperature and heat flux existed in the furnace tube skin, which affected the service life of furnace tube. Defining the tube skin’s heat intensity distribution as the boundary condition, this paper carried out a one-dimensional flow calculation in the pipe using MATLAB programming. The temperature, pressure and gasification rate values in the outlet were calculated by the program, and were consistent with the field calibration result.Based on the results of single tube’s simulation, it was concluded that the furnace tube’s circumferential and axial distribution of the temperature and heat intensity were not uniformly distributed in the single-sided radiation heating furnace. Front side’s heat intensity was significantly higher than the back side’s. A certain amount of nail head or fin within an acceptable range of tube’s back side can improve the area of access to radiation. After transformation, the finned tube’s average radiant intensity increased 7%, and the back side’s radiant intensity improved 14%. Meanwhile, the radiant heat intensity of the front side was only 1.18 times of back side’s, the distribution of circumferential heat intensity tended to uniform. As a result, the back side’s heat intensity, the average heat intensity and the heat intensity distribution in tube circumference were improved by this innovation, also it can improve the thermal efficiency of furnace, extend the safe operation period and achieve energy-saving.更多还原