耦合法模拟乙烷裂解炉烧焦过程

以KTI-SMK型乙烷裂解炉为研究对象,采用同时计算炉膛和炉管传热的耦合法模拟了空气和水蒸气的混合烧焦过程,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,计算出烧焦过程中管内气体温度分布、管壁温度分布、焦炭厚度分布、炉管出口碳氧化合物含量和炉管出口气体温度.其中,烧焦时间、炉管出口碳氧化合物含量和炉管出口气体温度的计算结果与生产数据基本相符.按目前的烧焦程序进行模拟,结果表明,烧焦结束时,管内依然残留5%的焦炭,管壁最高温度低于管材极限,说明现采用的烧焦工艺还可以进一步优化.     

乙烯装置裂解炉的烧焦过程模拟

裂解炉炉管内壁的烧焦过程是个炉管温度、压力、浓度和焦炭厚度随时间,沿空间变化的动态过程。基于蒸汽-空气法烧焦机理分析,假定沿炉管烧焦反应动力学参数和反应热不变,建立了蒸汽-空气烧焦过程机理模型。针对中石化镇海炼化分公司乙烯装置裂解炉BA104的实际烧焦参数结合有限元求解进行了流程模拟。流程模拟结果与实际过程的对比证实了所建立的工业裂解炉蒸汽-空气烧焦过程模型的可行性和有效性,为实现烧焦过程的闭环优化控制奠定了基础。     

煤制气甲烷化反应过程析碳热力学研究

基于Aspen Plus模拟软件,对煤制气甲烷化反应过程中的析碳现象进行了热力学研究,作出了析碳判别图.结果表明,原料中氢氧物质的量比小于5时,温度越高,析碳可能性越大,大于5时则相反;对于具有不同氢氧碳比例的原料来说,压力对析碳的影响并不相同;对于企业托普索甲烷化工艺中的甲烷化反应器来说,起始反应器和末尾反应器(第一台反应器和第五台反应器)出口气体组成点落在相应温度下的析碳区,有析碳的可能性,但通过调节水蒸气比例可以减少或消除析碳.     

浆态床蒽醌加氢反应器模拟

基于浆态床二维轴对称流体力学模型,结合蒽醌加氢反应动力学、物质输送与扩散方程和热量传递模型,构建了浆态床蒽醌加氢反应器数学模型,获得了浆态床内气液固三相流场分布、组分浓度分布、温度分布及停留时间分布等关键信息。模拟结果表明：浆态床内物料呈现中心向上而壁面向下的循环流动特征,流体返混强烈,液体的返混状态接近于全混流,气体返混状态近似为两级等体积全混流;反应物浓度或催化剂含量表现为底部高而顶部低的分布规律,浆态床底部的反应更为强烈,气液传质特性对于蒽醌加氢反应有较大影响;受进料影响,温度分布为底部低而顶部略高,通过夹套换热,全塔温差控制在5 K以内。反应器模型的模拟结果与工业数据符合较好,可应用于工业装置的设计及优化。     

基于动力学模型的合成气完全甲烷化回路系统模拟分析

为了研究工艺条件对某甲烷化工业装置回路系统的影响,利用Aspen Plus软件建立了多级绝热甲烷化反应器回路系统动力学模型,动力学方程由Fortran编程嵌入模型中,模拟结果与实际运行值吻合较好。本文进而考察了不同工艺参数对甲烷化回路系统的影响,结果表明:循环比对各级反应器的出口温度、热点位置、出口气中CO_2及CH_4含量影响显著,但对产品气中CH_4含量影响较小;增大原料气流量,仅使各级反应器的热点位置后移,对各反应器出口温度、气体组成和产品气质量的影响可以忽略;提高进料温度,各级反应器的出口温度随之升高、出口气中CO_2含量增加、CH_4含量下降,产品气中CH_4含量略微降低;氢碳比的变化,对各级反应器出口气组成及产品气中CH_4含量影响显著,对第四反应器的出口温度影响也很大,但对第一至第三反应器的温度分布影响不大,氢碳比由2.8增至3.2,产品气CH_4含量呈先增大后减小的趋势,验证了氢碳比为3是甲烷化反应系统的最优值。     

焦炉煤气非催化部分氧化的数值模拟

用Fluent软件对焦炉煤气非催化部分氧化制取合成气的反应器内的温度场、浓度场和平衡气体组成进行了数值模拟.结果表明,氧气与焦炉煤气比是决定气化温度和出口合成气成分的关键.随着氧气与焦炉煤气比的增加,气化温度升高.在氧气与焦炉煤气质量比为0.14时,反应器出口的有效气体(H2+CO)含量达到最大值,焦炉煤气中的CH4几乎完全转化.在距反应器喷嘴0.05 m处反应器内达到了最高温度3 300 K,在0.1 m处H2和CO及CO2均达到平衡,CH4在该点降到最低点.     

流动模型方法及其在化工中的应用

(续上一讲)例2:在例1所示管式反应器中等温进行某一级反应,已知反应速率常数ｋ=021/Ｓ、反应空时τ=10Ｓ、实际反应出口转化率为0784。①若不考虑流体返混(即按平推流模型)计算,其反应出口转化率为多少?②若考虑流体返混,分别按多釜串联、轴向扩散、单平推流循环和等空时双平推循环模型计算,其反应出口转化率各为多少?③若按流体返混达到最大的全混流模型计算,其反应出口转化率又为多少?解:①不考虑流体返混(平推流模型)　Ｘ=1-ｅ-ｋτ=1-ｅ-02×10=0865②考虑流体返混(ａ)多釜串联模型先由流体返混无因次方差σ2求出多釜串联模型参数ＮＮ=1…     

乙烷裂解炉安全烧焦及条件优化

采用耦合炉膛和炉管传热的计算方法,模拟KTI—SMK型裂解炉的烧焦过程。首先对恒定炉管入口烧焦气流量和温度模式的烧焦程序进行安全烧焦条件的计算,并用复形调优法计算出优化的烧焦条件为水蒸气流量1861kg／h,空气流量597kg／h,炉管人口温度626℃,烧焦时间8．2h。随后验证了该操作条件,得到管壁最高温度为1047℃,管内残炭量和烧焦时间分别低于目前装置烧焦程序模拟结果。     

温度特性对理想反应器效率的影响

本文利用数值分析方法,研究了温度特性对理想全混流反应器(CSTR)和平推流反应器(PFR)效率的影响。研究结果表明:在等温条件下,对于在理想反应器中发生的单一一级不可逆反应,PFR的效率高于CSTR;在绝热条件下,对于在理想流动反应器中发生的单一一级不可逆反应,当反应为放热反应时,CSTR的效率高于PFR;当反应为吸热反应时,PFR的效率高于CSTR。基于上述比较结果可知,理想反应器的效率不仅与其类型相关,而且还与反应器的温度特性及反应的热效应有关。上述结果可对理想反应器的选型提供有效的指导。     

基于自适应谱方法的裂解炉烧焦模型化简策略

炉管烧焦是乙烯裂解炉的重要操作，准确的烧焦模型是优化控制烧焦过程、提高烧焦效率的重要前提。常见的烧焦过程机理模型为偏微分方程的形式，具有无穷维、时空耦合的特点，计算复杂度高，难以满足实时优化和控制对轻量级模型的需求。为此提出一种基于自适应谱方法的乙烯裂解炉烧焦过程轻量级模型化策略。首先，针对炉管生焦与烧焦过程焦层变化特点，将炉管自适应划分为有焦段和无焦段。其次，使用Legendre多项式作为空间基函数分别对有焦段和无焦段分布参数近似降维，建立烧焦过程控制输入与炉管内焦层厚度分布、温度分布的时间维系数的集中参数模型，避免因直接使用谱方法近似拟合带局部特征的分布参数系统而产生较大误差的问题。     

SIMULATION AND OPTIMIZATION OF COIL DECOKING IN ETHANE PYROLYSIS FURNACE

A detailed model of coupled heat transfer in the firebox and coke oxidation in the coils of a commercial ethane pyrolysis furnace was developed to simulate the decoking process. The model was created by combining a plug flow reactor model, the shrinking core model, and the zonal approach method to approximately describe the fluid flow in the coils, the gas-solid heterogeneous reactions of coke gasification, and the heat transfer in the furnace. The simulation accurately modeled the decoking time and CO₂ mole fraction at the coil outlets. The model may be used to evaluate existing decoking processes, and new decoking procedures can be investigated by iterative approximation. The model can be used to validate the following steady-state operating conditions: coil outlet temperature, coil inlet temperature, decoking time, coil outlet CO₂ mole fraction, and the maximum external tube wall temperature, resulting in lower consumption of steam and air and a reduction in residual coke. This work has provided essential information for the development of advanced on-line coke-burning procedures for ethylene production.     

Simulation of the decoking of an ethane cracker with a steam/air mixture

A combined furnace and reactor calculation is performed for the simulation of the decoking of an ethane cracker with a steam/air mixture. Different gas-solid reaction/diffusion models with a corresponding texture model describing the solid phase changes during the decoking operation are combined with kinetics for the decoking by combustion and gasification, determined based on experimental data [Heynderickx, G.J., Schools, E.M., Marin, G.B., 2005. Coke combustion and gasification kinetics in ethane steam crackers. A.I.Ch.E. Journal 51 (5), 1414-1428]. By comparing the calculated coil outlet temperatures and the calculated partial pressures of carbon dioxide at the coil outlet with the measured values in an industrial unit, the need for a general gas-solid reaction/diffusion model and the corresponding decoking kinetics is confirmed. The decoking time for an industrial unit is simulated adequately.     

二氯乙烷裂解管式反应器二维模拟

建立了二氯乙烷在管式反应器中进行气相热裂解的二维模型 ,模型考虑了二氯乙烷热解生成氯乙烯的主反应和生成焦前体的副反应以及气体密度变化对裂解反应的影响 .模拟计算表明 ,二氯乙烷和氯乙烯的浓度沿径向分布平坦 ;但是管内近壁面处由于存在边界层 ,始终存在着明显的径向温差 ;近管壁处始终是裂解的高速率区 ,副反应也主要发生在管壁区 .表明确定最优的炉管管径时必须考虑提高裂解速率与降低结焦速率之间的平衡 .在距进口量纲 1管程 0 .3左右的管壁处裂解速率达到最高 ;副反应速率的最大点位于出口管壁处 .与工业数据比较后发现 ,炉管出口的转化率、选择性、出口压力和温度等数据与模型预测值一致 ,表明模型具有较高的可信度     

下行床反应器热试装置设计与开发

气固并行向下流动的下行床反应器比提升管具有气固接触时间短、气固速度及浓度径向分布更为均匀、气固轴向返混大大减少、易实现高固气比操作等特点。在下行床反应器小型热试装置开发过程中,为发挥下行床的技术优势,重点研究和解决了反应器出入口结构、原料雾化、高温高流通量下固体循环量测量与控制等几个关键性的工程问题,为下行床反应器的热试研究和应用开发提供了基础。     

丙烷脱氢Cr_2O_3/Al_2O_3催化剂烧焦再生过程的模型化与模拟(英文)

A heterogeneous model is developed for the regeneration of the Cr2O3/Al2O3 catalyst for the propane dehydrogenation process by considering the internal mass transfer and external mass/heat transfer during the coke combustion. Simulation shows that under practical operating conditions, multi-steady states exist for the catalyst pellets and the catalyst temperature is sensitive to gas temperature. However, at increased mass flow rate or lowered oxygen concentration, multi-steady states will not appear. Under the strong influences of film diffusion, the coke in the packed bed reactor will first be exhausted at the inlet, while if the film diffusion resistance is decreased, the position of first coke exhaustion moves toward the outlet of the reactor.     

基于Aspen Plus的焦炉煤气甲烷化工艺模拟及分析

焦炉煤气作为优质的二次能源,利用焦炉煤气甲烷化合成天然气(SNG)是焦炉煤气资源化利用的最佳方式。借助Aspen Plus软件,采用BWRS状态方程,设定主要工艺参数,对绝热式三段固定床焦炉煤气甲烷化工艺进行模拟计算分析,通过调节循环率和水蒸汽添加量控制反应器出口温度,模拟结果与实际试验数据较吻合,证明模拟可靠。考察了循环率、分流率、原料气组成、进口气压力和空速对反应器出口温度和组成的影响,结果表明循环率和分流率对反应器出口温度和转化率影响明显。     

丙烷脱氢制丙烯催化剂烧焦过程的模型化

在丙烷脱氢制丙烯反应过程中,由于焦的沉积使催化剂活性不断降低,而且失活速度很快,催化剂需频繁烧焦再生。在研究了丙烷脱氢催化剂烧焦过程内外扩散影响的基础上,采用内扩散效率因子修正的均匀烧焦物理模型,建立了综合考虑内外扩散影响的绝热固定床非均相动态烧焦数学模型,用于指导反应器的设计和操作优化。通过对Cr₂O₃/Al₂O₃脱氢催化剂烧焦过程模拟,可更深入地认识烧焦过程的变化规律。     

合成气制二甲醚三相淤浆床反应器的数学模型研究

A mathematical model for a bubble column slurry reactor is presented for dimethyl ether synthesis from syngas. Methanol synthesis from carbon monoxide and carbon dioxide by hydrogenation and the methanol dehydration are considered as independent reactions, in which methanol, dimethyl ether and carbon dioxide are the key components. In this model, the gas phase is considered to be in plug flow and the liquid phase to be in partly back mixing with axial distribution of solid catalyst. The simulation results show that the axial dispersion of solid catalysts, the operational height of the slurry phase in the bubble column slurry reactor, and the reaction results are influenced by the reaction temperature and pressure, which are the basic data for the scale-up of reactor.     

CFD study on partial oxidation of methane in fixed-bed reactor

Partial oxidation of methane (POM) is a preferred method for synthesis gas, which usually occurs in fixed bed reactors. In this paper, the discrete element method (DEM) is used to reconstruct the structure of a reactor bed via simulating the process of filling the reactor with catalyst. The particle resolved CFD physical model with the detailed micro-kinetcis of the POM reaction was established to study the interaction among reactant flow, heat and mass transfer, and reaction in the fixed bed. The gas composition and temperature distribution in the reactor were obtained based on the simulation results. The effects of the space velocity and the reaction temperature on the CH₄ conversion, catalyst selectivity, and catalyst surface coke formation were analyzed. The simulation results show that the temperature hot spots of the catalyst in the bed occur at the inlet and the temperature increases further near the wall. With the increase in space velocity, the conversion rate of CH₄ decreases gradually, and the selectivity does not change significantly. As the temperature increases, the conversion rate of CH₄ gradually increases and the selectivity decreases. The risk of coke formation on the catalyst surface rises axially and the C species concentration is relatively higher near the outlet. Appropriately increasing the gas velocity and increasing the temperature helps to reduce the surface coke accumulation of the catalyst.