Dynamic modelling of the absorber of a post-combustion CO2 capture plant: Modelling and simulations

Modelling work related to carbon dioxide (CO₂) capture technologies is of great importance with respect to the design, control, and optimization of the capture process. Development of dynamic models as such is important since there is much information embedded with the dynamics of a plant which cannot be studied with steady state models. A model for the absorption column of a post-combustion CO₂ capture plant is developed following the rate based approach to represent heat and mass transfer. The Kent–Eisenberg model is used to compute the transfer and generation rates of the species. Sensitivity of the model for different physiochemical property correlations is analyzed. The predictions of the dynamic model for the capture plant start-up scenario and operation of the absorption column under varying operating conditions in the up-stream power plant and the down-stream stripping column are presented. Predictions of the transient behaviour of the developed absorber model appear realistic and comply with standard steady state models.     

精馏过程的动态模拟

在各类典型精馏过程稳态模型的基础上,建立了6类典型非稳态精馏模型,并对动态精馏过程的开环响应进行了模拟计算.计算结果表明,实际精馏塔内存在的非平衡效应和惯性效应对非稳态精馏的动态响应过程有很大影响,其中惯性效应的影响更为突出.本文建立的三维非平衡混合池动态精馏模型充分地考虑了精馏过程中的非平衡效应和惯性效应,因此相信能够更适合于模拟实际的动态精馏过程.     

An aggregation model reduction method for one‐dimensional distributed systems

A method for deriving reduced dynamic models of one‐dimensional distributed systems is presented. It inherits the concepts of the aggregated modeling method of Lévine and Rouchon originally derived for simple staged distillation models and can be applied to both spatially discrete and continuous systems. The method is based on partitioning the system into intervals of steady‐state systems, which are connected by dynamic aggregation elements. By presolving and substituting the steady‐state systems, a discrete low‐order dynamic model is obtained. A characteristic property of the aggregation method is that the original and the reduced model assume identical steady states. For spatially continuous systems, the method is an alternative to discretization methods like finite‐difference and finite‐element methods. Implementation details of the method are discussed, and the principle is illustrated on three example systems, namely a distillation column, a heat exchanger, and a fixed‐bed reactor. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

动态实时优化策略下的分层式预测控制及其在化工过程中的应用

针对化工过程中那些因存在批处理、含有物料回流环节而很难达到稳态的过程以及一些因扰动的存在而很难精确地操作在一个设定点处的非线性过程,采用常规的稳态优化会产生低效或失效优化解的问题,提出一种动态实时优化策略。即在多层控制结构中的RTO层采用动态优化而非常规的稳态优化,依照过程的优化操作信息在满足过程动态规律和物料、产品市场价格变化的条件下实现生产的经济利润最优,事例仿真结果表明该方法的可行性和有效性。     

Dynamic modelling of an industrial R2R FCC unit

The aim of this study is to obtain a model that can simulate the performance of an industrial fluid catalytic cracking (FCC) unit in steady and dynamic state, and which will subsequently be used in studies of control and real time optimisation. In this paper, a dynamic model for a R2R type FCC unit is presented. The model includes the riser, the stripper/disengager, the regeneration system and the catalyst transport lines. Mass, energy and pressure balances are performed for each of these sections.Simulation results for steady state are presented and compared qualitatively to those obtained from previous FCC models. The dynamic behaviour of the system is explored through two perturbations in open loop, one on the fresh feed flow rate and one on the air flow rate to the first regenerator. The results illustrate the consistency of the model and are in agreement with what has been observed in studies available in the open literature.     

Dynamische Prozeßsimulation in der industriellen Praxis

Dynamic process simulation in industrial practice. Dynamic process simulation is gaining in importance in process development and plant design. In addition to simulation tools for steady state calculations and optimization, recent years have seen increased development of software tools suitable for dynamic simulation. In particular, dynamic process models have been developed for various unit operations at universities and in industry. Application of the models includes synthesis and analysis of the control structure, start-up and shut down, safety assessments, optimization, and training. In addition, dynamic flowsheet programs analogous to the steady state programs were developed. Wider use of these program systems requires increased flexibility, solving procedures, user interfaces, model library, interfaces to external programs, etc. The present article is intended not only to describe the state of the art and describe some typical applications, but in particular to examine the demands placed on dynamic process simulation and the simulators and to delineate the current limitations of dynamic process simulation from an industrial viewpoint.     

Steady state and dynamic modeling of spiral wound wastewater reverse osmosis process

Reverse osmosis (RO) is one of the most important technologies used in wastewater treatment plants due to high contaminant rejection and low utilization of energy in comparison to other treatment procedures. For single-component spiral-wound reverse osmosis membrane process, one dimensional steady state and dynamic mathematical models have been developed based on the solution-diffusion model coupled with the concentration polarization mechanism. The model has been validated against reported data for wastewater treatment from literature at steady state conditions. Detailed simulation using the dynamic model has been carried out in order to gain deeper insight of the process. The effect of feed flow rate, pressure, temperature and concentration of pollutants on the performance of the process measured in terms of salt rejection, recovery ratio and permeate flux has been investigated.     

蜡沉积厚度随时间变化规律的模型研究

在分析蜡沉积过程的基础上, 基于一定的假设条件, 建立了蜡沉积厚度随时间变化的模型。通过提取蜡沉积厚度随时间变化曲线的数据, 拟合了模型中的待求常数, 并对模型计算值和实验值的吻合程度进行了分析。结果表明:对数模型、指数模型及动平衡模型均能反映蜡沉积厚度随时间的变化趋势, 对数模型与实验值的吻合程度最好;指数模型和动平衡模型所得的结果与实验结果的吻合程度相当, 在沉积初期, 指数模型的吻合程度高于动平衡模型, 但当沉积时间接近实验规定时间时, 动平衡模型的吻合程度高于指数模型;所建立的模型简单实用, 能够反映沉积厚度随时间变化的增长快慢趋势, 不同实验数据应用时仍需对各模型的计算精度进一步验证, 从而使得选用模型能更好地符合实际。     

SIMULATION AND OPTIMIZATION OF THE ELECTRO-REDUCTION PULSED COLUMN FOR THE SEPARATION OF URANIUM AND PLUTONIUM

ABSTRACT

A computational model for separation of uranium and plutonium in an electro-reduction pulsed column was developed based on the diffusion model. The model contained steady state simulation, dynamic simulation, and optimum calculation. A numerical calculation method for this model has been proposed. With this model, a calculation for an electro-reduction experiment of uranyl nitrate in a pulsed column was carried out. The calculated results were consistent with the experimental results in the literature. A comparison of the dynamic and the steady state simulations at equilibrium and an optimum calculation were also conducted. This model provides a guide for further experimental study of this process.     

水泥浆体屈服应力和黏度与其测试分析影响因素研究

采用RHEOLAB QC型旋转黏度计,分别以转速与剪切速率为控制变量测定了水泥浆体稳态流变曲线,分别用Couette转换与流变模型研究了水泥浆体屈服应力和黏度与测试及分析影响因素之间的关系.结果表明:Couette转换能反映测试条件变化对屈服应力和黏度的影响;增大试样筒与转子的间距,由转速转化的剪切速率增大,颗粒迁移作用增强,动态屈服应力递减,塑性黏度递增;增大试样筒外壁的摩擦系数,浆体与外筒壁间相对运动情况不发生变化,对动态屈服应力与塑性黏度基本无影响;依据拟合相关系数,流变模型中Herschel-Bulkley模型的吻合程度最好;依据结果标准差,Herschel-Bulkley模型的动态屈服应力结果稳定性最好,Bingham与改进Bingham模型的塑性黏度结果的稳定性相差不大.     

聚丙烯环形反应器模拟与分析：（Ⅱ）动态特性和操作稳定性

建立了聚丙烯环形反应器动态数学模型,通过模拟计算,研究了工艺参数扰动时聚丙烯环形反应器的动态响应规律、反应器结构参数对动态特性的影响,并对冷却水流量和冷却水入口温度进行了动态操作稳定性分析。     

COMPARTMENTAL MODELS FOR SEPARATION COLUMNS

1 INTRODUCTIONRigorous dynamic models for multicomponent staged separation columns,based on thematerial and energy balance relationships for each of the stages,are usually of highdimensionality and high stiffness.Its solution needs very efficient integration algorithm.Although in the last decade a number of fast and efficient integration algorithms havebeen developed ,it is still extremely time-consuming to solve dynamic models for     

基于漂移流理论的蒸汽发生器动态特性

以大亚湾核电站U型管自然循环蒸汽发生器为研究对象,根据蒸汽发生器上升通道沸腾段特点,建立了适合工程应用的漂移流模型动态方程。在验证稳态工作特性及与漂移流理论所涉及的关键参数准确性的基础上,进行了蒸汽发生器动态特性仿真与分析。结果表明,所建立的漂移流模型能够较准确地反映蒸汽发生器两相流的流动与换热特性。随着扰动的添加蒸汽发生器各参数都表现出合理的变化趋势,并准确地模拟出“虚假水位”现象,且负荷越高水位对扰动的响应速度与程度越大。     

Lag phase model for transient growth of pseudomonas putida on phenol

The successful design of large‐scale bioreactors requires the ability to predict both steady‐state and dynamic operating conditions. At the same time, mathematical models should not be too complex in order to reduce experimental work required to determine kinetic parameters. A simple model which predicts the behaviour of batch and transient continuous culture operations is presented and experimentally verified. The model is based on two regions of metabolic activity: the lag phase and the active phase. Pseudomonas putida growing on phenol as a substrate in a well‐mixed bioreactor was tested in three modes of operation: batch, continuous start‐up and continuous step‐change. The model is demonstrated to predict all the qualitative aspects of the dynamic phases of growth and is quantitatively accurate.     

空间太阳能热动力系统回路的动态模拟

空间太阳能热动力发电系统的工作过程是一动态过程,系统的运行规律受太阳光照期和阴影期交替变化的影响.为了掌握空间太阳能热动力发电系统各参数的动态变化规律,采用集总参数法,从部件的数学模型出发,根据各参数间的相互耦合关系,建立了空间太阳能热动力系统的动态数学模型,对10 kW空间太阳能热动力发电系统的运行过程进行了动态数值模拟.结果表明：如果相变蓄热材料处于两相状态,相变蓄热物质的温度和系统发电功率就比较稳定;一旦相变蓄热材料进入单相状态,相变蓄热材料的温度和系统发电功率就会发生波动;要使系统的发电功率比较稳定,必须合理选择聚能器的面积,保证相变蓄热材料一直处于两相状态.     

Empirical strategies for open-loop on-line optimization

Two empirical strategies for open-loop on-line optimization are developed as alternatives to the use of mechanistic process models. These strategies are based on on-line identification of dynamic multi-input single-output (MISO) and multi-input multi-output (MIMO) models. The steady state gain of these models provides information for steady state optimization. Desirability functions, originally developed for multi-objective optimization, are utilized as objective function modifiers for constrained on-line optimization. The integration of dynamic model identification and desirability functions results in an on-line optimizer which combines fast optimizing speed with the ability to predict future encroachments on constraint boundaries. Corrections to the search direction are based on these predictions, reducing the probability of actual constraint violation. The optimization strategies are tested by simulation on nonlinear multivariable interacting systems at two levels of complexity: a CSTR supporting a multiple reaction and a fluid catalytic cracker. Both methods were effective in avoiding violation of constraints but the MIMO strategy required fewer steps to reach an optimum and was less prone to generate a nonfeasible optimization step.     

液速陡变时液固流化床中颗粒浓度的变化模型

在液速陡变时,分别考察了铅直管液固流化床内粒径为225 μm和511 μm的玻璃微珠的体积分数分布随时间变化的规律,发现大小颗粒在不同的液速变化幅度下都呈现出同样的体积分数变化趋势.联立颗粒速度和颗粒的连续方程式模拟颗粒的体积分数变化过程,建立了一个相对简单的颗粒体积分数变化的数学模型.在模型中,用定常状态的空隙率方程...     

Closed-loop dynamic real-time optimization with stabilizing model predictive control

Dynamic real-time optimization (DRTO) is a supervisory strategy at the upper level of the industrial process automation architecture that computes economically optimal set-point trajectories that are in turn passed on to the lower-level model predictive control (MPC) for tracking. The economically optimal solution, in several process industries, could lead to operating the plant at or around an unstable steady state. The present article accounts for this by developing a closed-loop DRTO (CL-DRTO) formulation that enables handling unstable operating points via an underlying MPC with stability constraints. To this end, a stabilizing MPC that handles trajectory tracking for unstable systems is embedded within the upper-level DRTO. The resulting CL-DRTO problem is reformulated by applying a simultaneous solution approach. The economic benefits realized by the proposed strategy are illustrated through applications to both linearized and nonlinear dynamic models for single-input single-output and multi-input multi-output continuous stirred tank reactor case studies.     

Modeling, simulation and control of dimethyl ether synthesis in an industrial fixed-bed reactor

Dimethyl ether (DME) as a clean fuel has attracted the interest of many researchers from both industrial communities and academia. The commercially proven process for large scale production of dimethyl ether consists of catalytic dehydration of methanol in an adiabatic fixed-bed reactor. In this study, the industrial reactor of DME synthesis with the accompanying feed preheater has been simulated and controlled in dynamic conditions. The proposed model, consisting of a set of algebraic and partial differential equations, is based on a heterogeneous one-dimensional unsteady state formulation. To verify the proposed model, the simulation results have been compared to available data from an industrial reactor at steady state conditions. A good agreement has been found between the simulation and plant data. A sensitivity analysis has been carried out to evaluate the influence of different possible disturbances on the process. Also, the controllability of the process has been investigated through dynamic simulation of the process under a conventional feedback PID controller. The responses of the system to disturbance and setpoint changes have shown that the control structure can maintain the process at the desired conditions with an appropriate dynamic behavior.     

Improved frequency response model identification method for processes with initial cyclic‐steady‐state

A new nonparametric process identification method is proposed to obtain the frequency response model from given process input and output data. The proposed algorithm can estimate exact models for all desired frequencies. It is applicable to various process conditions (initial/final steady‐state, initial steady‐state/final cyclic‐steady‐state, and initial/final cyclic‐steady‐state) and requires a smaller amount of memory than previous methods. Also, it provides the exact models even in the presence of a static disturbance and shows an acceptable robustness to measurement noises. © 2011 American Institute of Chemical Engineers AIChE J, 2011