【作者】 张莹莹；

【导师】 辛峰；

【作者基本信息】 天津大学 ， 化学工程， 2009， 博士

【摘要】 本文在分析乙烷裂解炉模拟研究的历史、现状和发展趋势的基础上,进行乙烷裂解炉炉膛与炉管之间热传递和管内反应过程的数值模拟以及操作条件优化的研究。研究内容包括以下几个方面:(1).以区域法为基础,建立炉膛与炉管之间传热的数学模型。编制直接交换面积的计算程序。通过对比文献数据,验证了计算程序的可靠性。(2).采用耦合法对KTI-SMK乙烷裂解炉进行数值模拟。此方法能够描述热炉膛与炉管之间热传递及管内反应过程相互间耦合关系:分别以活塞流、缩壳模型以及区域法描述管内流体流动、气固非均相反应以及炉膛传热。将工业生产中所得的现场数据与模拟计算结果进行比较,两者基本吻合,从而证明了所建立的乙烷裂解炉管烧焦过程数学模型以及计算程序的合理性。模拟计算获得了裂解炉管内详细的温度、焦炭厚度、热通量分布等参数,揭示了裂解炉管内传热、传质及反应过程的基本特征及其相互作用规律,为乙烷裂解炉烧焦程序的优化提供了依据。(3).流体在流经炉管弯头处的返混程度加强,因此采用CSTR模型描述此处流体的流动,即采用PFR与CSTR串连的反应器模型对烧焦过程进行模拟计算。(4).恒定炉膛操作条件,调整炉管入口气体流量和温度,对烧焦过程进行模拟计算,得到:①入口温度分别是580℃,670℃,管材耐受的极限温度1100℃条件下,安全烧焦允许的最大空气流量曲线。②在入口温度在620℃时,得到预测烧焦过程管壁最高温度的拟合方程,拟合方程的计算值与烧焦模拟的计算值的误差最大为15℃。对采用恒定炉管入口空气、水蒸汽流量方式烧焦的裂解炉,该拟合方程对优化其烧焦程序,保证安全烧焦,有一定的指导意义。(5).结合后续废热锅炉的操作特性,提出了设计烧焦程序的基本步骤,以及调优目前烧焦程序的新方法:根据炉管出口温度调节进口气体流量和入口温度,得到非恒定炉管入口气体流量、炉管入口温度方式下的新烧焦程序。模拟结果表明:新程序的烧焦时间与目前实际烧焦时间相仿,但管内残碳量、空气及水蒸汽的累计消耗量有所降低,炉管出口CO2体积分率和空气与水蒸汽的流量比都在允许的生产控制范围内,最高管壁温度低于管材的极限温度。(6).保持裂解炉炉膛的操作条件,利用复形调优的优化方法,针对恒定炉管入口气体流量和温度的烧焦方式,求出了以烧焦时间最短为目标的最优操作条件。该操作条件下,烧焦时间明显缩短,管壁最高温度小于管材的极限耐受温度,属安全烧焦操作范围。本文所得结果,对改进现有气体原料裂解炉烧焦程序及在新型和新建裂解炉设计与开发建设中提出科学、合理的烧焦程序具有指导意义。更多还原

【Abstract】 Based on a detailed review of literatures about simulation and analysis of status and development trends of ethylene pyrolysis furnace, a comprehensive numerical simulation and operating optimizations were done in this paper after combining heat transfer between furnace and coil with the details of decoking process. The main points of this thesis are as follows:(1). The mathematic model of heat transfer between furnace and coils was built on the basis of zone methods. The calculation program for direct heat transfer areas was edited and used to calculate and compare with the data from book, the results had a good agreement with the reference.(2). The industrial ethane pyrolysis furnace was simulated by coupling heat transfer between furnace and coils as well as reactions in coils The plug flow reactor model and the shrinking core model and zonal approach method were used to describe the fluid flow, gas–solid heterogeneous reactions of decoking in coils and heat transfer in furnace, respectively, a general model, can fully and almost accurately describe heat transfer between furnace and coils in decoking process, was obtained. Because of an agreement of the simulation results with the plant data, the correctness of the coupled model and calculation program can be certified. The profiles of temperature, coke thickness, heat flux and so on can be acquired from simulation, these results revealed the basic characters of heat and mass transfers as well as their inherent and interactional rules that provides basises for the optimization of decoking operation.(3). There are some enhanced back-mixing of fluid in bend sections of the coil, and therefore, in the tube elbow, a CSTR model was used to describe fluid mixing, that is, PFR and CSTR in series was used to describe the coil in decoking process with the coupling method.(4) Adjusting tube inlet gas flow and temperature with invariable furnace operating conditions, simulations were done and results were:①under the condition of inlet temperature 580℃, 670℃, external tube skin temperature limitation 1100℃, the biggest security decoking air flow rate curve was gained and under these curves are safe operating zones.②A fitting equations in order to forecast external tube skin maximum temperature when the inlet temperature at 620℃.the maximum calculated value error of fitting equation with the simulated value is 15℃. This fitting equation can help decoking procedure optimization and ensure safety to the pyrolysis furnace which adopt the inlet temperature 620℃and the unchanged gas flowrate.(5). Considering the operation demand of waste heat boiler that is just behind of colis, a basic steps for design of decoking procedure was proposed, a new optimization method was put forward by adjusting coil inlet process gas flowrate and/or CIT once COT was not satisfied.Using the new approach, decoking procedures as well as simulation results could be obtained simultaneously. At the same usage of fuel and air in furance, the new decoking procedure derived from the above method gave approximately the same decoking time with the plant present operation, but total consumptions of steam and air was less than the plant present, residue coke is less than that of the plant present procedure, CO2 volume fraction at coil outlet and the ratio of steam and air were in the control range, the temperatures on external tube skin were below the up limitation of coil material.(6). Keeping pyrolysis furnace operation as well as gas flow rate and the temperature at coil inlet no changes from the beginning to the end, a complex optimization was used to get the shortest decoking time, an optimum operation condition was obtained, in the meantime the maximum external tube skin temperature is less than the uplimit of tolerance of coil materialThis work provided valuable fundamentals for developing an advanced on-line coke-burning procedure for the ethylene production and directing the design of a novel pyrolysis process.更多还原