Control of pH neutralization process using simulation based dynamic programming

The pH neutralization process has long been taken as a representative benchmark problem of nonlinear chemical process control due to its nonlinearity and time-varying nature. For general nonlinear processes, it is difficult to control with a linear model-based control method so nonlinear controls must be considered. Among the numerous approaches suggested, the most rigorous approach is the dynamic optimization. However, as the size of the problem grows, the dynamic programming approach suffers from the curse of dimensionality. In order to avoid this problem, the Neuro-Dynamic Programming (NDP) approach was proposed by Bertsekas and Tsitsiklis [1996]. The NDP approach is to utilize all the data collected to generate an approximation of optimal cost-to-go function which was used to find the optimal input movement in real time control. The approximation could be any type of function such as polynomials, neural networks, etc. In this study, an algorithm using NDP approach was applied to a pH neutralization process to investigate the feasibility of the NDP algorithm and to deepen the understanding of the basic characteristics of this algorithm. As the approximator, the neural network which requires training and the k-nearest neighbor method which requires querying instead of training are investigated. The approximator has to use data from the optimal control strategy. If the optimal control strategy is not readily available, a suboptimal control strategy can be used instead. However, the laborious Bellman iterations are necessary in this case. For pH neutralization process it is rather easy to devise an optimal control strategy. Thus, we used an optimal control strategy and did not perform the Bellman iteration. Also, the effects of constraints on control moves are studied. From the simulations, the NDP method outperforms the conventional PID control.     

Simulation of Heat Transfer and Oxygen Transport in a Czochralski Silicon System with and Without a Cusp Magnetic Field

1 INTRODUCTION The development of IC-technology requires large size Si wafer and Czochralski (Cz) process has domi-nated the production of single crystals for most of the materials used in the microelectronic industry. It was reported that the melt flow is stable when the wafer diameter is small. Converged solutions were obtained by using a laminar model. For example, Xiao and Derby[1] simulated the flow of oxide melt at Grashof number Gr =2.54×105, Oshima et al.[2] simulated the flo…     

WBRPLSR方法及其在化工软测量中的应用

及时测定化工过程变量,对确保生产过程稳定、有效控制产品质量具有重要意义.基于实时样本数据,采用偏最小二乘方法,以分块递归的方式,为过程变量建立软测量模型.在分析时序数据特性的基础上,引入加权策略,并提出选定相关参数的方法步骤,推导构建了加权分块递归偏最小二乘回归方法（WBRPLSR）.将该法实际应用于某公司PTA装置溶剂脱水塔,为塔釡排出液H₂O含量建立软测量模型,效果良好.与已有方法相比,它提高了建模效率,改进了预测性能.     

Measurement and simulation of dendritic growth of ice in cement paste

We re-examine experiments by Helmuth (1962) from which he concluded that ice grows in the pores of cement paste under heat-flow control, and that the internal temperature rises to the melting point given by the Gibbs-Thomson equation. We find that his conclusions are correct, but the growth rates he reports are misleading. Using experimental and computational methods, we show that the ice grows in the form of dendrites, which allows a constant growth rate under heat-flow control. A modification of the experimental procedure permits accurate measurement of the growth rate of ice in the pores.     

Application of fuzzy partial least squares (FPLS) modeling nonlinear biological processes

We applied a nonlinear fuzzy partial least squares (FPLS) algorithm for modeling a biological wastewater treatment plant. FPLS embeds the Takagi-Sugeno-Kang (TSK) fuzzy model into the regression framework of the partial least squares (PLS) method, in which FPLS utilizes a TSK fuzzy model for nonlinear characteristics of the PLS inner regression. Using this approach, the interpretability of the TSK fuzzy model overcomes some of the handicaps of previous nonlinear PLS (NLPLS) algorithms. As a result, the FPLS model gives a more favorable modeling environment in which the knowledge of experts can be easily applied. Results from applications show that FPLS has the ability to model the nonlinear process and multiple operating conditions and is able to identify various operating regions in a simulation benchmark of biological process as well as in a full-scale wastewater treatment process. The result shows that it has the ability to model the nonlinear process and handle multiple operating conditions and is able to predict the key components of nonlinear biological processes.     

Process system engineering in wastewater treatment process

This paper reviews the research and development of process system engineering (PSE) in the wastewater treatment process (WWTP). A diverse range of PSE applications have evolved in the wastewater treatment process, such as modeling, control, estimation, expert system, fault detection and monitoring system. This article describes several types of PSE that have proven to be effective in WWTP. The merits and shortcoming of PSE and its detailed applications are presented. Since its development is the forefront in WWTP, a reasonable review of the research progress in this field is addressed.     

Modeling and simulation of a multistage absorption hydration hybrid process using equation oriented modeling environment

Separation of light hydrocarbon mixtures is one of the most important topics in chemical engineering research. With development of theories on hydrate equilibriums and kinetics, researchers are trying to apply hydration based separation technology to industrial applications. It is increasingly important to develop the corresponding simulation strategies for process design purposes. In this work we use an equation oriented modeling environment, named Aspen Custom Modeler^® (ACM^®), which enables rapid model development and provides powerful simulation solvers. With the help of ACM^®, a multistage absorption hydration hybrid process (AHHP) for refinery dry gas separation is modeled and simulated. Sensitivities of key parameters such as water content and absorbent flow rate, are analyzed. Features of the multistage AHHP are discussed. For comparison, based on an industrial data, a butane absorption process is established and simulated. Economic evaluation shows that the multistage AHHP is competitive compared to current absorption process.     

改进的信息流图及其在精馏塔建模与仿真中的应用

计算机动态建模与仿真中,人们最常用的用以辅助进行交流和讨论以及文档化相关成果与决策的分析、设计方法及表示法是信息流图（information flow diagram）。在前人研究的基础上,提出了一种改进的、更为完善的信息流图表示法。该表示法共包含三大类、九小类组成元素,基本能够完全覆盖计算机动态建模与仿真中所有种类的数学公式及其他模型表达方式。最后,以精馏塔的动态建模与仿真为例,详细说明了改进的信息流图的具体应用情况。事实证明,改进的信息流图不仅为相关工作人员提供了良好的沟通媒介,还使人们能够更加容易地从先前的仿真模型构建项目中复用需求和设计组件等,从而提高了仿真模型构建的效率和质量。     

Development of a batch manager for dynamic scheduling and process management in multiproduct batch processes

A batch manager is developed for the dynamic scheduling and on-line management of process operations. The developed system consists of a process monitoring module and a dynamic scheduling module. When a deviation from the initial schedule is detected in a process monitoring module, dynamic scheduling is performed in the dynamic scheduling module and the initial schedule is adjusted to the proper schedule by using rescheduling algorithms presented in this paper. The adjusted schedule is shown in the process monitoring module. The dynamic scheduler in the batch manager copes with several unexpected process events of batch process operations by adjusting the EST (Earliest Start Time) of equipment, redetermining the batch path and reassigning tasks to equipment. This study focuses on the implementation of a batch manager with on-line dynamic scheduling for batch process management. Examples of fodder production batch processes illustrate the efficiency of the algorithms. This paper was supported by nondirected research fund, Korea Research Foundation, 1997.     

Toward a better comprehension and modeling of hysteresis cycles in the water sorption–desorption process for cement based materials

The aim of this work is to describe a method based on a simple representation of the pore size distribution, which is able to predict hysteresis phenomena encountered in water sorption–desorption isotherms, particularly for cementitious materials. The hysteresis effect due to network constrictivity is taken into account in order to extend models of transfer in porous media to situations involving wetting–drying cycles. This is not achieved in earlier models and their performance in terms of prediction in such conditions is thus limited. The present modeling is based on an idealized pore size distribution. This has three modes, associated with C–S–H pores, medium capillary pores, and large capillary pores including consideration of cracks. The distribution is assessed from the chemical composition of the cement, the formulation of the material, the degree of hydration, the total water porosity and the intrinsic permeability.     

二甲醚精馏塔实验研究与模拟计算

建立了用于二甲醚精制的精馏塔实验流程,实验测定了在操作工艺条件下的精馏结果。以平衡级理论为依据建立二甲醚精馏过程的数学模型,根据研究体系在通常情况下沸点相差较大、液相非理想性的特点,建立序贯收敛的循环嵌套迭代计算方法对模型进行求解,模拟计算结果与实验数据结果吻合较好。对二甲醚精馏塔的模拟分析结果表明：塔顶要得到含量不小于99 %(mol)二甲醚产品,维持操作压力1 MPa、在精馏塔中部进料的情况下,进料量不超过22 mol·h^-1为宜;回流比要根据进料液中二甲醚组分含量控制在一定范围内;进料液中二氧化碳含量高低对产品二甲醚纯度和收率影响显著,在进入精馏塔之前尽可能地将二氧化碳除去是必要的。     

Nonlinear model-based dissolved oxygen control in a biological wastewater treatment process

The dissolved oxygen (DO) concentration has been an important process parameter in the biological wastewater treatment process (WWTP). In this paper, we propose a nonlinear control scheme to maintain the dissolved oxygen level of an activated sludge system. Without any linearization or model reduction, it can directly incorporate the nonlinear DO process model with on-line estimation of the respiration rate (R) and the oxygen transfer rate (K_La). Simulation results show that it outperforms a control performance of the PID controller. Since it incorporates the process disturbance and nonlinearity in the controller design, the suggested method can efficiently deal with the operating condition changes that occur frequently in the wastewater treatment process.     

Steady-state and dynamic modeling of indirect partial oxidation of methane in a wall-coated microchannel

Steady and dynamic characteristics of catalytic indirect partial oxidation (combined total oxidation and steam reforming) of methane to hydrogen in a wall-coated microchannel are investigated using computational techniques. Steady-state behavior is initially modeled using a two-dimensional axisymmetrical wall-coated reactor model. Considering the small channel diameter, adiabatic operation and negligible transport resistances, response of the microchannel is also investigated using a one-dimensional pseudohomogeneous tubular reactor model. Simulations of the microchannel are carried out using both models for different feed conditions ranging between 1.89 and 2.24 for CH₄/O₂ and 1.17–2.34 for H₂O/CH₄. Outcomes from both models are found to be close, allowing the use of the low-cost one-dimensional model in dynamic simulations. Analysis of transients during the system start-up indicate that steady state is reached between 100 and 120 s depending on the feed composition. Product temperature and flow rates obtained from steady-state and dynamic simulations are found to be close with some differences arising from the finite difference-based numerical method used to solve partial differential equations of the dynamic model. Dynamic responses of the microchannel to several disturbances in the feed are analyzed. The response to a step increase in the inlet oxygen flow rate (decrease of CH₄/O₂ from 2.24 to 1.89) is the elevation of temperature by ca. 100 K, which in turn leads to ca. 33% in hydrogen yield, and the time to reach the new steady state is around 90 s. If the disturbance involves an increase in inlet steam flow, temperature and hydrogen yield decrease in time to a local minimum within 10 s and then gradually increase to the subsequent steady state within 50 s ending up with net reductions of ca. 1.6% and 9%, respectively.     

Numerical modeling,simulation, and experimental validation of predicting fiber diameter in wide‐slot positive‐pressure spunbonding process

An air‐drawing model of polypropylene (PP) polymer and an air jet flow field model in wide‐slot positive‐pressure spunbonding process are established. The influences of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on the fiber diameter have been studied. The predicted fiber diameter agrees with the experimental data as well. The effects of the processing parameters on the fiber diameter have been investigated. The air jet flow field model is solved by means of the finite difference method. The numerical simulation computation results of distribution of the fiber diameter match quite well with the experimental data. The air‐drawing model of polymers is solved with the help of the distributions of the air velocity. It can be concluded that the higher air velocity and air temperature can yield the finer fibers diameter. The higher inlet pressure, longer drawing segment length, smaller air knife edge, longer exit length, smaller slot width, and smaller jet angle can all cause higher air velocity and air pressure along z‐axis position, which are beneficial to the air drawing of the polymer melt and thus to reduce the fiber diameter. The experimental results show that the agreement between the predicted results and the experimental measured data is very better, which verifies the reliability of these models. Also, they reveal great prospects for this work in the field of computer‐assisted design (CAD) of spunbonding process. POLYM. ENG. SCI., 58:1371–1380, 2018. © 2017 Society of Plastics Engineers     

重催反再与分馏先进控制系统的开发和应用

介绍了大庆石化总厂与美国ＨｏｎｅｙｗｅｌｌＨｉ－ＳｐｅｃＳｏｌｕｔｉｏｎｓ公司合作开发的以鲁棒多变量预估控制技术为核心的重油催化裂化装置反应再生与分馏先进控制系统的功能目标、方案设计和技术关键，并以半年的实际考核数据说明了该系统的良好应用效果，从而为石化企业指出了一条提高经济效益的有效途径。     

Moisture transport in heated concrete, as studied by NMR, and its consequences for fire spalling

During the past 30 years concrete has developed enormously in both strength and durability. A drawback of these improvements is the increased risk of explosive spalling in case of fire. The moisture inside the concrete plays an important role in the spalling mechanism. In order to study the moisture migration inside concrete during intense heating, a dedicated nuclear magnetic resonance (NMR) setup was built. This setup can be placed inside a 1.5-T MRI scanner.With this setup one-dimensional moisture profiles can be measured while the concrete sample is heated up to 250 °C. Besides concrete, measurements were performed on fired-clay brick and calcium-silicate brick.The results show that water inside the concrete sample is superheated to a temperature of 170 °C, which results in an increased pressure inside the concrete. A model was developed to predict the movement of the observed drying front.     

Tray efficiency in the air-water-solid system without reaction and its application

This work deals with the investigation of tray efficiency with the gas-liquid-solid three phases and its application in the suspension catalytic distillation (SCD) process. The experimental data of tray efficiency under different conditions were measured by utilizing the desorption of oxygen dissolved in water by air. A method of estimation of tray efficiency for the gas-liquid-solid three phases was put forward and its suitability was also verified. This method was developed on the basis of the AIChE method for gas-liquid two phases. As an application example of this modified AIChE method, the SCD process for synthesizing cumene, based on equilibrium stage (EQ) model incorporating tray efficiency, was simulated.     

Optimization and simulation of the Sabatier reaction process in a packed bed

The Sabatier reaction in a testing packed bed was investigated experimentally and theoretically, and was used to convert waste carbon dioxide and hydrogen to provide needed water for closing the life‐support loop on orbit in space. A three‐dimensional model including fluid flow, gas dispersion, heat and mass transfer, and chemical reaction was developed by coupling some semi‐empirical correlated equations in chemical engineering science into computational fluid dynamics theory. Good agreements between the simulating results and experimental data for the effect of some parameters on reaction verified this model, for example, heat exchange between reactor and atmosphere, the material property of reactor, the catalyst deactivated and gas mass flux and so on. By using this model as the designing tools, an optimized packed bed is proposed. Compared with the testing packed bed, the relevant reactor length can be reduced from 220 to 150 mm with the same hydrogen conversion and lower pressure drop. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2879–2892, 2016     

19通道多孔陶瓷膜渗透过程的CFD模拟

根据Darcy定律,建立了多孔陶瓷膜中渗透流动的CFD计算模型,定量描述了纯水在多孔陶瓷膜中的渗流情况。根据CFD模型,采用有限体积法,模拟计算出四种平均孔径陶瓷膜的纯水通量,并与实验值进行了对比,结果吻合较好。采用该模型,定量计算出19通道陶瓷膜中每个通道对整体陶瓷膜渗透通量的贡献,并分析了其中的变化规律,为多孔陶瓷膜的构型优化奠定了基础。