【作者】 高光英；

【导师】 李鑫钢；

【作者基本信息】 天津大学 ， 化学工程， 2009， 博士

【摘要】 乙烯是石油化工中最重要的基础原料之一。烃类热裂解是乙烯工业生产乙烯和丙烯的主要方法,而裂解炉是整个乙烯工业的核心装置。建立裂解炉数学模型,对裂解炉内流动、传热、传质和反应等过程进行详细、定量的研究与分析,成为裂解炉设计和优化裂解炉操作的有效手段。在综合考虑裂解炉裂解过程发生的化学反应、传热和裂解气流动压力降等过程基础上,建立了乙烯裂解炉稳态操作数学模型。该模型包括管内化学反应动力学模型、炉膛辐射室传热模型、管内外传热模型、裂解气流动压力降模型等。对Kumar石脑油裂解过程分子动力学模型进行了系统研究,并根据文献数据推导了二次反应动力学参数。分别采用实验数据和工业数据对裂解炉稳态操作数学模型进行了验证,裂解产物收率与实测数据吻合良好,表明建立的裂解炉稳态操作数学模型是可靠的。建立了能够描述裂解炉动态过程的数学模型。采用本文完善了Kumar结焦动力学模型,模拟反应管内的结焦过程。利用模型对国内某一台裂解炉进行了动态仿真,预测了生产周期及产品收率、压力降、停留时间、能耗和结焦速率等生产参数随生产时间的变化规律,与工业运行规律吻合良好。采用以上裂解炉动态数学模型,研究了影响乙烯裂解炉操作的温度、稀释蒸汽比、压力和扩径比等参数,定量考虑以上操作参数对产品收率、停留时间、耗能、结焦过程和生产周期等生产参数的影响。结果表明:(1)在相同进料情况和一定温度操作范围内,沿管长不断升高裂解气温度可以提高石脑油裂解深度和乙烯收率,同时裂解炉能耗增大、裂解气停留时间缩短、结焦速度增大、操作周期缩短。(2)固定石脑油流量,随着蒸汽稀释比的增大,石脑油裂解深度减轻、乙烯收率下降、丙烯的收率稍微上升,同时裂解炉能耗增加、裂解气停留时间缩短、结焦速度下降、操作周期延长。(3)固定总摩尔流量,随着蒸汽稀释比的增大,石脑油裂解深度稍有加深,乙烯收率稍有增大,丙烯的收率稍微下降;裂解炉能耗下降、裂解气停留时间增长、结焦速度下降、操作周期延长。(4)固定进料流量与组成不变,保持裂解气沿管长的温度分布与原操作一致,随着出口压力的增大,石脑油裂解深度减轻、乙烯收率上升、丙烯的收率稍微下降;裂解炉能耗增加、裂解气停留时间增长、结焦速度上升、操作周期缩短。(5)固定进料流量与组成不变,保持裂解气沿管长的温度分布与原操作一致,固定炉管出口压力与原操作一致,随着扩径比的增大,石脑油裂解深度加深、乙烯收率上升、丙烯的收率下降;炉管压力降下降、裂解气停留时间增长、结焦速度上升、操作周期大致缩短。建立了包含原料、燃料、水蒸汽和清焦等操作成本的、符合实际生产过程条件约束的乙烯裂解炉过程操作优化数学模型,对实际的工业裂解炉进行操作参数优化,可使经济效益提高20%以上。建立了裂解炉管自由基反应理论和计算流体力学耦合数学模型,同时建立了针对石脑油裂解自由基反应机理的FLUENT物性数据库,对裂解炉管内所发生的流体流动、热量传递、质量传递和自由基链反应理论的裂解反应等复杂过程进行系统的综合数值模拟研究。本文建立的模型可以对乙烯裂解过程进行可靠的模拟与预测,对工业装置的设计和运行具有指导意义。更多还原

【Abstract】 Ethylene is the one of the most important building blocks used in the petrochemical industry. Thermal cracking of hydrocarbons (e.g. naphtha) is the main route for the manufacturing of ethylene and propylene. Thermal cracking furnace is the‘heart’of the whole ethylene manufacturing process. Building of cracking furnace mathematical model to investigate the flow, heat transfer, mass transfer and cracking reactions is becoming an effective way to decide furnace design and optimal production operation.The first part is the development of cracking furnace steady-state mathematical model considering cracking reactions, heat transfer and pressure drop when process gas flow through tube reactor. The mathematical model consists of a continuity equation for each component, an energy equation and a pressure drop equation. Kinetics data for reverse reactions were not given in Kumar paper. Reverse reaction kinetic parameters were calculated. The reaction equilibrium constants for these reverse reactions were extracted from original reference. Experiment data and industrial production data were used to verify steady-state mathematical model. Simulation results were consistent with experiment data and industrial production data very well.The second part is the development of cracking furnace dynamic-state mathematical model on the base of strict chemical process conservation mechanism. Coke buildup on the internal tube wall was also included using Kumar coke deposit model. Dynamic production process of an industrial furnace was simulated. Run length (i.e. the time between two consecutive decoking operations) and other production parameters changing with manufacture time were predicted, including product yields, pressure drop, process gas residence time, energy consumption and coke rate. The simulation results matched the industrial production data very well.Based on the cracking furnace dynamic-state mathematical model, various case studies were then carried out to investigate the impact of the process gas temperature profile, inlet steam to naphtha ratio, pressure and diameter ratio of second pass to the first pass so that the ethylene/propylene product yields, run length, residence time, energy consumption and other operation parameters can be evaluated. The results show that(1) With the same operation parameters, increasing process gas temperature along tube can raise ethylene yield and energy consumption, shorten process gas residence time and manufacture time.(2) Fixing naphtha feed and with the same operation parameters, increasing inlet steam to naphtha ratio can decrease ethylene yield and process gas residence time, raise energy consumption, prolong manufacture time.(3) Fixing total feed and with the same operation parameters, increasing inlet steam to naphtha ratio can raise ethylene yield and process gas residence time, decrease energy consumption, prolong manufacture time.(4) With the same operation parameters, increasing outlet pressure can raise ethylene yield and energy consumption, prolong process gas residence time, shorten manufacture time.(5) With the same operation parameters, increasing diameter ratio of second pass to the first pass can raise ethylene yield, decrease pressure drop of the whole tube, prolong process gas residence time, shorten manufacture time.Process optimization was applied to the operation of this industrial tubular reactor. Operation profit was used as objective function. The process gas temperature profile and steam to naphtha ratio in the feed were used as optimisation variables. The effects of coking on reduction of manufacturing time and the decoking cost have been considered. After optimization, the furnace profit can be improved obviously.Numerical simulation model for cracking tube reactor was developed. Naphtha free radical reaction model and computation fluid mechanics model were considered at the same time in the cracking tube reactor simulation model. FLUENT physical property data library was set up for naphtha free radical reaction model. Cracking tube reactor can be simulated considering fluid flow, heat transfer, mass transfer, and free radical reactions contemporaneously.更多还原