高效再生催化裂化装置多稳态分析:反应温度开/闭环控制条件对热反馈机制的影响

针对催化裂化反应-再生系统在提升管反应温度开环和闭环控制条件下的输出与输入多稳态问题,分析了烧焦罐式高效再生催化裂化反应-再生系统在两种条件下随着CO助燃剂添加量变化时的多稳态分布。在反应温度开环条件下,因再生温度与反应温度的耦合程度较低,使系统移热曲线呈单调递增,导致了系统出现3个稳态操作点。在反应温度闭环控制条件下,提升管反应器和再生器间热反馈机制发生改变,由于再生剂循环量可以作为额外的自由度对再生温度和反应温度之差进行补偿,再生器和提升管反应器的耦合程度增强,使得系统只会在助燃剂添加量极低时才会出现多个稳态点,而在基准操作条件下只有一个稳态点,规避了系统在提升管反应温度开环时的多个稳态点的问题。     

CO燃烧状况可调的催化裂化装置多稳态分析

考虑到一氧化碳(CO)助燃剂作为调控系统CO燃烧状况的操作手段会影响催化裂化装置的多稳态,在已有的烧焦罐式高效再生催化裂化装置反应-再生系统动态机理模型的基础上,扩展了再生器内CO燃烧的机理模型,并将CO助燃剂的添加量与再生器内CO的燃烧状态进行定量的关联。在对再生器进行热量衡算的基础上,绘制出再生器的放出-移出热量曲线,确定了系统的3个稳态操作点,并根据放热反应器稳态热稳定性斜率条件分析了稳态点的热稳定性。针对炼厂CO助燃剂添加量设计较为保守的问题,分析了减少助燃剂添加量对系统操作的影响,指出CO助燃剂的添加量会影响到系统两个高温稳态点之间的操作空间从而影响到装置控制系统设计的苛刻度。     

气相法聚乙烯工艺冷凝态操作模式的稳定性和动态行为

气相法聚乙烯工艺冷凝态操作模式由于显著提高了循环气移热能力和反应器时空产率,已成为流化床乙烯聚合工艺的主流操作模式。建立了气相法聚乙烯工艺冷凝态操作模式的数学模型,包括流化床反应器模型,多级换热器模型和反应温度、压力以及循环气组成的控制模型。基于此,采用流程模拟方法,计算了系统在反应器温度采用闭环控制时的稳态解;根据系统对小扰动的动态响应特点,定性判断了反应器温度采用开环控制和闭环控制时聚合反应系统的稳定性;考察了系统对1-己烯分压和催化剂进料速率的阶跃响应特性。结果表明,反应器温度采用闭环控制时,聚合反应系统在所考察操作条件下均是稳定的,而采用开环控制时,解曲线被分叉点分割为稳定区域和不稳定区域。反应器温度对1-己烯分压阶跃变化的动态响应表明聚合反应系统存在长、短周期两类振荡,表明冷凝态操作模式下乙烯聚合反应过程是一个多控制回路耦合的复杂过程。     

气相法聚乙烯工艺冷凝态操作模式的稳定性和动态行为

气相法聚乙烯工艺冷凝态操作模式由于显著提高了循环气移热能力和反应器时空产率,已成为流化床乙烯聚合工艺的主流操作模式。建立了气相法聚乙烯工艺冷凝态操作模式的数学模型,包括流化床反应器模型,多级换热器模型和反应温度、压力以及循环气组成的控制模型。基于此,采用流程模拟方法,计算了系统在反应器温度采用闭环控制时的稳态解;根据系统对小扰动的动态响应特点,定性判断了反应器温度采用开环控制和闭环控制时聚合反应系统的稳定性;考察了系统对1-己烯分压和催化剂进料速率的阶跃响应特性。结果表明,反应器温度采用闭环控制时,聚合反应系统在所考察操作条件下均是稳定的,而采用开环控制时,解曲线被分叉点分割为稳定区域和不稳定区域。反应器温度对1-己烯分压阶跃变化的动态响应表明聚合反应系统存在长、短周期两类振荡,表明冷凝态操作模式下乙烯聚合反应过程是一个多控制回路耦合的复杂过程。     

100万吨/年大型催化裂解装置反再系统工艺设计

工业催化裂化装置从技术发展的角度来说,最基本的是反应—再生形式和催化剂性能两个方面的发展。催化裂化装置一般由三个部分组成,即:反应—再生系统,分馏系统,吸收稳定系统。先后经历了固定床催化裂化、移动床催化裂化和流化床催化裂化。60年代出现了分子筛催化剂,由于它具有活性高、选择性和稳定好,占据主导地位的流化床反应器又发展为提升管反应器。同时还促进了再生技术的发展。陆续出现了两段再生、高效再生和完全再生等新技术。本设计结合当今世界的新工艺,新设备。在反应器、再生器、旋风分离器和提升管等设备方面都有很详细的大量计算。在工艺技术方面到达了装置技术先进,经济合理。     

前置烧焦式催化裂化装置稳态模拟:再生器取热器负荷对过程的影响

应用本文作者课题组开发的前置烧焦式催化裂化装置过程模拟平台,对某工业装置进行现场条件下的稳态模拟,并完成全装置模型的校正及验证。在此基础上,模拟分析了再生器取热器负荷对该装置操作产生的影响。模拟结果显示,改变再生器取热器的负荷,能够有效调节两器热量平衡,在确保工艺范围不超限的前提下提高装置剂油比,原料油转化率提高,装置产品分布得到有效调节,但是使得密相床再生器密相区床层温度降低,从而影响再生器的再生效果,不利于提升管进口再生催化剂初始活性的提高。     

催化裂化装置反再系统动态模拟精细化与控制系统“工艺优先”配对设计

催化裂化是目前炼油厂中的核心加工工艺,其反应-再生系统是一个多变量紧密耦合的复杂系统,动态模拟和控制系统设计难度较大。目前,催化裂化装置在进行动态建模时设置了大量假设条件,与实际状况存在诸多不符,另外当前的控制回路配对方法未考虑工艺要求,也不适用于催化裂化这样的开环不稳定系统。基于以上原因,以已建立的反应-再生系统数学模型为基础,建立精细化动态模型,对反应器和再生器模型进行真实逼近,不再忽略气相动态变化,将原模型中气相对时间的导数项恢复,通过离散化的分布参数系统模型,对离散化模型中每段提升管和烧焦罐的时变变量加入时滞。仿真结果表明,精细化动态模型更加接近实际化工生产过程。根据上述模型搭建仿真平台,通过对不稳定的反再系统进行工艺优先的控制系统设计,首先根据化工工艺设计控制回路保证系统的稳定性,然后基于相对增益阵方法设计剩余变量配对,在降低了高维系统设计复杂度的同时保证了生产过程安全。设计结果表明,对于催化裂化装置反再系统,基于工艺特性完成控制回路配对后,剩余变量无须再添加多余的控制回路就能保证控制系统的稳定性和适当的控制性能。     

催化裂化提升管反应器流动反应耦合模型研究进展

催化裂化(FCC)工艺在重质油轻质化过程中发挥着重要作用, 而FCC提升管反应器的模型化是催化裂化新工艺与新装备的开发、催化裂化装置稳定操作与生产调优等常需做的工作。本文首先根据流动模型与反应模型不同的集成方式对提升管反应器流动-反应耦合模型进行了归纳与分类, 并回顾了国内外流动-反应耦合模型的研究历程, 指出了耦合模型的发展趋势;随后对当前研究较多的计算流体力学(CFD)流动-反应耦合模型进行了较为全面的阐述, 包括对耦合模型的应用场合、模型求解解耦方法的研究情况等均作了介绍, 同时还分析了该类耦合模型所存在的不足之处, 并指出工业提升管反应器在线采样技术的开发在耦合模型的验证工作上的必要性;最后, 对FCC提升管反应器流动-反应耦合模型研究进行了总结与展望, 以期能够为FCC提升管反应器模型化新方法的提出以及耦合模型的验证工作等研究给予借鉴和指导。     

流化催化裂化反应器的技术进展

介绍并讨论了近期开发的流化催化裂化反应器,包括两段串联反应器、双提升管反应器、下行式反应器、多段进料反应器以及新型提升管反应器端口结构技术。以新型反应器为核心技术的各种催化裂化新工艺可以有效地提高催化裂化反应的转化率和选择性,减少非理想产品产率,也可以改善产品质量,生产环境友好的清洁燃料油品。此外新型提升管反应器端口结构还可以抑制设备结焦,延长流化催化裂化(FCC)装置的开工周期。     

工业渣油催化裂化过程六集总组合反应器模型

工业渣油催化裂化反应主要发生在提升管段和出口的沉降器段的复杂流体动力学区域。通过对工业现场装置流程和过程数据的分析,将发生裂化反应的整个反应器中提升管部分作为活塞流反应器(PFR)和沉降器部分作为全混流反应器(CSTR)的串联组合反应器,并按照渣油催化裂化反应特点建立了简化的6集总组分的串行和并行动力学反应网络模型。所建立的稳态催化裂化反应产率预测模型在数学上表现为提升管部分的微分方程组和沉降器部分的代数方程组。模型设置7个装置因数来校正模型的计算产率与实测产率之间的偏差,并采用工业现场数据回归装置因数。通过对工业装置数据的计算比较,得到的模型产率预测精度很好地满足在线软测量计算要求。     

Steady state multiplicity in an UOP FCC unit with high-efficiency regenerator

The possibility of existence of multiple steady states in fluid catalytic cracking (FCC) units has a major impact in the supervision of these systems. The origins of these behaviours are usually due to the exothermicity of the catalyst regeneration reactions and to the strong interactions between the reactor and the regenerator system.Prior work has focused on modelling and control problems of different operating FCC units. However, none of these studies have considered a high-efficiency regenerator. This paper presents an analysis of the existence of output and input multiple steady states in an UOP FCC unit with a high-efficiency regenerator.The influence of unit disturbances and model uncertainties, such as coke composition and cracking enthalpy, in the output multiplicity, was studied and the results show that the high-efficiency regenerator exhibits at least three multiple output steady states and a maximum of five output steady states, in the operating range considered. Moreover, the state multiplicity analysis revealed that input multiplicity can be present in this FCC unit, depending on the choice of the control structure, and that operating the unit in full combustion mode can prevent instabilities due to input and output multiplicities. Therefore, these results can be used to guide the design of the most appropriate control structures in industrial applications. For the FCC unit with high-efficiency regenerator the most appropriate control structure corresponds to the control of the riser reactor temperature and the oxygen level in the flue gas, with the catalyst circulation rate and the combustion air flow rate, respectively.     

Experimental study of the ignition behaviour of an adiabatic SRC-II coal liquefaction reactor

Experimental data are presented which describe the thermal behaviour of a bench-scale adiabatic coal liquefaction reactor operating in an open loop. The reactor employed external feedback control for maintaining adiabaticity. Conditions for both ignition and quench have been found for coal liquefaction at SRC-II operating conditions where repeated ignition/quench behaviour was demonstrated. No stable steady states were found between 450 °C and 475 °C for SRC-II operation. Ignition occurred at a feed temperature of ≈415 °C. The low steady states occurred at conditions of essentially no heat generation; at a very low extent of reaction. Some unexpected evidence of a preheater effect on reactor ignition was observed; however, the effect of preheater temperature profiles on reactor performance was not systematically studied.     

Identification and control of a riser‐type FCC unit

This paper addresses the use of feedforward neural networks for the steady‐state and dynamic identification and control of a riser type fluid catalytic cracking unit (FCCU). The results are compared with a conventional PI controller and a model predictive control (MPC) using a state space subspace identification algorithm. A back propagation algorithm with momentum term and adaptive learning rate is used for training the identification networks. The back propagation algorithm is also used for the neuro‐control of the process. It is shown that for a noise‐free system the adaptive neuro‐controller and the MPC are capable of maintaining the riser temperature, the pressure difference between the reactor vessel and the regenerator, and the catalyst bed level in the reactor vessel, in the presence of set‐point and disturbance changes. The MPC performs better than the neuro controller that in turn is superior to the conventional multi‐loop diagonal PI controller.     

Modelling FCC units under steady and unsteady state conditions

A FCC phenomenological‐based model is presented in this study. This model accounts for the behaviour of the riser, the stripper and the regenerator. Both the reactor and the regenerator are incorporated in the model using detailed reaction kinetics. Catalyst regeneration allows for both catalytic and non‐catalyzed combustion of CO to CO₂. Overall, the model is constituted by a set of ordinary differential equations, relatively easy to solve and suitable for steady and unsteady state simulation of FCC units. The proposed model avoids, as much as possible, empirical expressions being suitable for simulation of industrial FCC units and process control studies.     

前置烧焦罐式高效再生器催化裂化装置稳定性分析

对前置烧焦罐式高效再生器催化裂化装置反应-再生系统动态机理模型进行空间离散化,然后做线性化处理,得到了线性化状态空间模型．采用控制理论中的线性系统稳定性判据──特征值分析法分析反应-再生系统的稳定性．在控制二密相床和汽提段藏量的条件下,线性状态空间模型的全部特征值的实部在很宽的操作范围内都为负值,证明所研究的反应再生系统（线性化系统）是稳定的．     

Multiplicity of steady states in fluidized bed reactors—V: The effect of catalyst decay

A simplified two-phase model is used to investigate the behaviour of non-isothermal fluidized bed reactors experiencing catalyst decay. The investigation shows that for highly exothermic reaction it is almost always desirable to operate the reactor at the middle unstable steady state, since it gives higher accumulative yield than both the high and the low temperature steady states. A simple feedback control scheme with time varying set point is suggested to stabilize the middle steady state. The dynamic behaviour and stability of the system is investigated for the open-loop reactor (uncontrolled) and the closed loop reactor (controlled).     

Absorption with exothermic reaction in a falling film column

A gaseous reactant is absorbed in a liquid with a positive heat of absorption. It reacts with the liquid by an exothermic, irreversible first order reaction. Analysis of a CSTR for this process has shown that up to 5 steady state solutions may exist even though the system appears to be quite simple with only one reaction. The existence of an extraordinary large number of steady state solutions is explained by the coupling between absorption and reaction: A low temperature gives no reaction, a high temperature prevents absorption of the gas and hence leads to mass transfer control of the reaction, while an intermediate temperature may permit operation at a third (stable) steady state. In between the stable steady states one finds (as us two unstable steady states.We extend the analysis of the CSTR to the distributed system of a falling film reactor, and we treat both the transient situation in the entrance partAn eigenanalysis of the steady states shows that temperature rise across the gas film may lead to 3 stable steady states even if an isothermal model is     

Steady-state modeling and bifurcation behavior of circulating fluidized bed membrane reformer-regenerator for the production of hydrogen for fuel cells from heptane

The production of hydrogen for fuel cells by steam reforming of heptane is investigated in a Circulating Fluidized Bed Membrane Reformer-Regenerator (CFBMRR) system (A.I.Ch.E. Journal 49(5) (2003) 1250). Palladium based hydrogen permselective membranes are used for hydrogen removal and dense perovskite oxygen permselective membranes are used for oxygen introduction. A series of pseudo-steady-state simulations show that when the catalyst is not regenerated, the circulating nickel reforming catalyst deactivates quickly and the “half catalyst activity life” for efficient production of hydrogen is quite short, especially at high temperatures. Efficient continuous catalyst regeneration can keep the catalyst activity high (∼1.0). With continuous catalyst regeneration, autothermal operation for the entire adiabatic reformer-regenerator system is achievable when the exothermic heat generated from the catalyst regenerator is sufficient to compensate for the endothermic heat consumed in the riser reformer. This type of autothermal operation becomes less likely at high steam to carbon feed ratios. This is due to the fact that carbon deposition rate decreases leading to the decrease of autothermal circulating feed temperature and energy-based hydrogen yield (adiabatic hydrogen yield in autothermal reformer-regenerator system). Multiplicity of the steady states for the reformer is possible for this configuration. With the steam to carbon feed ratio as the bifurcation parameter, multiplicity occurs between the two bifurcation points 1.444 and 2.251 mol/mol. In this multiplicity region, the energy-based hydrogen yield at the upper steady state with high regenerator output temperature is surprisingly the lowest one. While it is the highest one at the lower steady state with low regenerator output temperature. The maximum energy-based hydrogen yield is about 15.58 moles of hydrogen per mole of heptane fed at the lower steady-state when steam to carbon feed ratio is very close to the bifurcation value of 1.444 mol/mol. After removing the sweep gas steam by downstream cooling and de-humidification, the product hydrogen from steam reforming of hydrocarbons can be used for fuel cells with high purity (∼100%).     

Multiplicity of the steady state in fluidized bed reactors—IV. Fluid catalytic cracking (FCC)

A mathematical model for fluid catalytic cracking units is developed. The model takes into account the kinetics of the cracking reactions, as well as the kinetics of coke combustion in the regenerator. A numerical scheme is developed for the solution of the model equations. It is found that multiplicity of the steady states extends over a wide scope of operating variables and parameters. The model investigates the effects of catalyst circulation rate and gas oil flow rate, which have a strong effect on the reactor temperature and hence yield and selectivity. The phenomenon of hysteresis has been investigated. The model can be used for yield optimization and steady state control.