Plantwide Control Research Articles

Optimization of Control System of Petroleum Refinery Isomerization Unit by Plant-Wide Control Principles

Industrial process control system due to integration of equipment, existing material and energy recycle streams and their effects are extraordinary importance. The process in terms of safety, product quality and control stability have a challenge when there was defects in a process control system. The isomerization process is gaining importance in the presence of refining context due to upgrading the octane number of light naphtha fractions and also simultaneously reduces aromatic compounds especially benzene content. In this study, the isomerization unit control system of Imam Khomeini Oil Refinery Company (IKORC, shazand, Iran), by defined four controllers include: the temperature controller on pre-heater exchanger, the concentration controller on depentanizer, deisopentanizer and deisohexanizer towers. This work is based on the nine principles of the plant-wide process control, was investigated. It should be noted that currently lack these four controllers in isomerization unit, confront this unit to challenge in dealing with sudden disturbances. The results show that obtained data from dynamic simulation by Aspen Hysys v7.3 had an acceptable compliance with the principles of plant-wide process control theory.

Control of cryogenic extractive distillation process for separating CO2–C2H6 azeotrope

The existence of heterogeneous azeotrope of CO2–C2H6 makes it difficult to separate CO2 from the hydrocarbons in the associated gas by cryogenic extractive distillation process. A four-column extractive distillation system using natural gas liquid as heavy solvent is used to separate CO2–C2H6 azeotrope. Carbon dioxide, ethane, propane and butane are recovered from the top of the extractive distillation column, deethanizer, depropanizer and debutanizer respectively. The C3+ hydrocarbon mixture called natural gas liquid is recovered at the bottom of the debutanizer, one part of which is transported as NGL product and the other part is pumped back near the top of the extractive distillation column as solvent.The purpose of this paper is to develop an effective plant wide control structure for this four-column extractive distillation system. Fixed reflux ratio and reflux/feed ratio control structure are used to investigate the controllability of four-column extractive distillation. Results show that both control structures have successfully realize the dynamic simulation of the extractive distillation process. However, under the disturbance of feed flow rate and composition, the controllability of reflux/feed ratio control structure on purity of top distillation products is better than that of fixed reflux ratio control structure. The reflux/feed ratio controller of four columns can adjust the reflux ratio in real time according to the disturbance of feed flow and composition, which greatly improves the stability of the top distillation products purity.

Plantwide control systems design and evaluation applied to biodiesel production

Chemical processes have complex dynamic behaviors due to the presence of recycle streams, heat integration and several unit operations being interconnected, leading to interaction problems among variables and difficulties in completing an effective process control. Plantwide control methodologies aim to establish control systems for entire chemical plants; however, it is possible to obtain different control solutions. This work proposes that the evaluation of different plantwide control structures for a specific process could be carried out using key performance indicators (KPIs) to determine which control method best meets the industry strategic goals. In order to evaluate the proposed approach a typical biodiesel process model was implemented in Aspen Plus Dynamics; the selected KPIs were the dynamic disturbance sensitivity and an economic indicator that represents the variation of the ratio between the product’s selling price and the raw material cost over time. It was observed that both KPIs allowed a view of the plantwide control system performance and aided in choosing a set of designed controllers. However, the economic indicator enables one to choose a set of designed controllers that reduce the variability of the economic indicator by around 74% while providing a slight increase in the indicator mean value.

Simplified plantwide control structure for the diethyl oxalate process

The diethyl oxalate process features two reaction sections with two of the fresh feeds (oxygen and ethanol) and a recycle stream containing nitric oxide fed into the first reactor, which produces ethyl nitrite and water. Water is removed in a distillation column and the ethyl nitrite is fed to the second reactor along with the third fresh feed (carbon monoxide). Diethyl oxalate and nitric oxide are produced in this reactor. The product diethyl oxalate is recovered in a distillation column, and the nitric oxide is recycled back to the first reactor. The intermediate components (nitric oxide and ethyl nitrite) and inert nitrogen circulate between the two reaction sections.A recent paper proposed a plantwide control structure for this complex process that requires four on-line composition controllers to handle disturbances in throughput and the compositions of the three fresh feed streams. The purpose of this paper is to demonstrate that a less complex control structure with only one composition measurement can achieve stable regulatory control.

Dynamic Simulation and Plant-Wide Control for Flexible Operation of Subcritical Coal-Fired Power Plant Integrated with Solvent-Based Post-Combustion Co2 Capture

Dynamic Simulation and Plant-Wide Control for Flexible Operation of Subcritical Coal-Fired Power Plant Integrated with Solvent-Based Post-Combustion Co2 Capture

Data-Driven Plant-Wide Control Performance Monitoring

In this work a new data-driven plant-wide control performance monitoring methodology is proposed. The main constitutive parts of the suggested method are based on three well-known research areas fr...

Neurofuzzy-Based Plant-Wide Hierarchical Coordinating Optimization and Control: An Application to Zinc Hydrometallurgy Plant

In this paper, a novel three-layer coordinating optimization and control strategy involving fuzzy neural networks (FNNs) is proposed for industrial plant-wide control. This strategy includes a coordinator (top layer), local optimizers (middle layer), and local controllers (bottom layer). The coordinator determines and coordinates set-points of production indices for each process in the plant, aiming to achieve plant-wide optimal control. The local optimizers optimize individual unit and deliver the information to the coordinator. The controllers calculate optimal control inputs for the processes according to the set-points. Model predictive control (MPC) is used in this layer. Also used are FNNs with a gradient-based learning algorithm, which are trained to represent the models of the processes that are controlled by MPC. By constructing a Lyapunov function, convergence of the FNNs is established. Experiments are carried out in the largest zinc hydrometallurgy plant in China. The results demonstrate performance of our strategy in tracking the set-points and saving processing costs. Moreover, the strategy achieves a more optimal overall plant operation when compared to the same FNN-based MPC scheme that does not use the coordinator.

Energy Efficient Styrene Process: Design and Plantwide Control

The paper deals with conceptual design and simulation of an energy efficient process for manufacturing styrene by ethylbenzene dehydrogenation in adiabatic reactors using superheated steam as inert...

Design and control of an energy-efficient alternative process for separation of Dichloromethane-Methanol binary azeotropic mixture

Design and control of an energy and cost efficient separation process is deduced amongst several evaluated separation alternatives for Dichloromethane-Methanol binary mixture. Separation process evaluation for this specific binary mixture has not received much attention in the open literature so far. In the present study, several other significant alternatives (Pressure swing distillation, Extractive distillation and Azeotropic distillation) for the separation of the mixture have been explored and compared with the single reported work published earlier wherein separation using pressure swing batch distillation method has been discussed. Steady state analysis reveals that out of these evaluated alternatives; Extractive distillation is the best method in terms of economics and energy efficiency. The TAC of the extractive distillation method (best amongst four alternatives studied including the published work of PSBD method) was found to be 27.62% less than that of the second best from the list, which is Pressure Swing Batch Distillation method (Heat integration variant). The saving by extractive distillation method will result in significant benefits based on the futuristic surge in compound annual growth rate in the production of Dichloromethane-Methanol. Further, a plantwide control structure is designed for the recommended extractive distillation flow sheet which is further evaluated for throughput and composition disturbances. The present study will be helpful in designing the real process plants for the separation of Dichloromethane-Methanol binary mixture.

Plant-Wide Control Framework for a Grinding Mill Circuit

This article proposes a generic plant-wide control framework that can be used to develop a hierarchical control structure (regulatory control, supervisory control, and optimization) to operate a single-stage closed grinding mill circuit in an economically optimal manner. An economic objective function is defined for the grinding mill circuit with reference to the economic objective of the larger mineral processing plant. A mineral processing plant in this study consists of a comminution and a separation circuit and excludes the extractive metallurgy at a metal refinery. The operational performance of a comminution circuit as represented by a single-stage grinding mill circuit, primarily depends on the performance of the grinding mill. Since grind curves define the operational performance range of a mill, grind curves are used to define the set points for the economic controlled variables for optimal steady-state operation. For a given metal price, processing cost, and transportation cost, the proposed str...

Parallel Switching Regulatory Control of Iron Ore Flowrate from Multiple Feeders with Time Delay

The suitable performance of an industrial process needs regulatory control loops to adjust the main process variables to their especified reference values (set-points), and to compensate eventual load disturbances on the process. Regulatory control is fundamentally used in the industry for stabilizing process variables, and it’s generally implemented through the SCADA architeture of the plantwide control system. The absence or inefficiency of control in an industrial process generally implies in losses of productivity so that regulatory control is a key issue for improving process performance. In this context, this article presents the development and implementation of a control strategy for regulating the output mass flow (in t/h) of a crushing plant in the Carajás Iron Ore Processing Factory. The plant has eight feeders in parallel, and the goal was to control such feeders so that the resulting output flow matches a specified production set-point (in t/h). The article first explains the process, the control problem, and the transfer function model of the process. Subsequently, one’s presented the control strategy, which was based on a switching between a constant and a PI control action. The suitability of the strategy was investigated through computational simulations. Finally, the results and conclusions are discussed

Optimal operation of parallel dead-end filters in a continuous bio-based process

Dead-end cake filtration as one of the first unit operations deployed in biochemical production plants has been subject of academic investigation for many decades. The recurrent discrete reinitialisation events are challenging from a process control point of view, especially in a continuous downstream line. The complexity that arises when multiple units are operated in parallel seems to have received little attention. This work aims at illustrating this complexity and delineates the arising plantwide control problem. Guidelines for optimised operation are derived from general process understanding and at hand of an industrial case study. The need for a predictive model to solve multiple scheduling problems is identified, and a mathematical model based on conventional filtration theory is derived. Due to raw material variability and operational uncertainties, the predictions are found to be too imprecise for deployment. This is expected to be representative of many bio-based processes, where manual scheduling needs to be integrated effectively into plantwide control structures.

Plantwide control structure design of a complex hydrogenation process with four recycle streams

Abstract Design for plantwide control (PWC) is significantly important for stable, safe, and efficient operation of complicated processes. In this work, dynamic simulation and effective PWC structures were investigated for a novel dimethyl oxalate (DMO) hydrogenation process for ethylene glycol (EG) production. This process is a typical reaction-separation process with four recycle streams that poses challenges due to integrated effects and interactions among different sections. Single-end temperature control was applied in the initial control structure CS1, while it failed to handle disturbances due to the interactions and integrated effects. Then, the initial CS1 was modified with a cascade control to address this problem. The control structure CS2 also achieved stable control through using different criteria for selecting temperature control variables in distillation columns. And the robust control structure CS3 characterized with a feedforward ratio control significantly shortened the response time and reduced transient deviation. The control performances of these control structures were assessed by criteria in terms of DPT and IAE. The results show that CS3 provides the most effective control. This work will be valuable for the design of PWC structures for complex reaction-separation processes.

Assessment of the Plantwide Control Structure in a Pectin Production Plant

Abstract Real application studies constitute a relevant part of academic plantwide control research, as they promote industrial awareness and ideally acceptance. Especially in the area of bio-based processes, few works have been documented. These processes are characterised by large uncertainties, batch-operated units, and time-delayed measurements, which ultimately results in comparably low levels of automation. This work features the application of a stepwise plantwide control structure synthesis framework to an industrial bio-based production plant. Firstly, this is to give an indication of whether plantwide control is apt for this type of process. Secondly, it highlights specifically where substantial challenges arise during the application.

Gold Recovery Modeling Based on Interval Prediction for a Gold Cyanidation Leaching Plant

The production index of gold cyanidation leaching process has an important influence on the economic benefits of the plant-wide hydrometallurgical process. In the actual leaching production process, due to the fluctuations of the previous procedure, the leaching process is often affected by the uncertainty and process disturbance. And hence, the prediction accuracy of the traditional point prediction models (such as ANN: Artificial Neural Network) decreases seriously and cannot provide any quantified information about the uncertainty or process disturbance. To solve the above problem, the interval prediction technique based on Radial Basis Function (RBF) ANN is proposed and used to model a gold cyanidation leaching plant encountering uncertainty and process disturbances in this paper. The objective function trained in the interval prediction model is not based on the prediction error, but the comprehensive measure index, namely, the coverage width criteria, which consists of the prediction interval coverage probability and the prediction interval normalized averaged width. Compared to the traditional point prediction, when the process uncertainty and disturbances are present, the interval prediction model will provide more helpful process information to the operators or process designers for determining further optimization and control strategies. The simulation and practical application results show that most of the real values of gold recovery can be covered between the upper and lower bounds with a predefined probability, which indicates the effectiveness and reliability of the interval prediction model, thus laying an important foundation for plant-wide optimization and control.

Short-Term Wastewater Influent Prediction Based on Random Forests and Multi-Layer Perceptron

Influent flow rate is a crucial parameter closely related to the plant-wide control of wastewater treatment plants (WWTPs). In this study, a random forest (RF) model and a multi-layer perceptron (MLP) model are developed for hourly influent flow rate prediction at a confidential WWTP in Canada. Both models perform well on predicting influent flow rate one-step ahead. The coefficient of determination (R2) values of MLP and RF for the testing data set are 0.927 and 0.925, respectively. Furthermore, the multi-step ahead prediction accuracy of the proposed models is discussed. To improve the multi-step ahead prediction accuracy of the RF model, time-tag information is transformed to numerical values and then fed into the RF model as input. The R2 values of the RF model for the testing data set with and without time-tag information are 0.334 and 0.811, respectively. The results show that the RF model’s performance for multi- step ahead prediction is heavily affected by the time-tag information. Including time-tag information as input could dramatically improve the multi-step ahead prediction accuracy. In this study, the RF model shows more robust performance than the MLP model on solving short-term wastewater influent prediction problems. Influent flow rate is a crucial parameter closely related to the plant-wide control of wastewater treatment plants (WWTPs). In this study, a random forest (RF) model and a multi-layer perceptron (MLP) model are developed for hourly influent flow rate prediction at a confidential WWTP in Canada. Both models perform well on predicting influent flow rate one-step ahead. The coefficient of determination (R2) values of MLP and RF for the testing data set are 0.927 and 0.925, respectively. Furthermore, the multi-step ahead prediction accuracy of the proposed models is discussed. To improve the multi-step ahead prediction accuracy of the RF model, time-tag information is transformed to numerical values and then fed into the RF model as input. The R2 values of the RF model for the testing data set with and without time-tag information are 0.334 and 0.811, respectively. The results show that the RF model’s performance for multi-step ahead prediction is heavily affected by the time-tag information. Including time-tag information as input could dramatically improve the multi-step ahead prediction accuracy. In this study, the RF model shows more robust performance than the MLP model on solving short-term wastewater influent prediction problems.

Dynamic simulation and control of feed conditioning system for CO2 capture

There are several CO2 removal technologies currently applied in the commercial and production scale. One of the potential technologies currently being evaluated for offshore CO2 separation is Centrifugal Fluid Separation technology, specifically Supersonic Gas Separation (SGS). It is potentially better than the conventional solutions such as membrane in terms of CAPEX, hydrocarbon losses, footprint, tonnage and power requirement. However, the stringent requirement of cryogenic temperature and high pressure of its feed requires a robust feed conditioning process plant. There are limited studies on the simulation and control design which are crucial to test the stability and dynamic responses of the feed conditioning plant. This paper investigates the optimal regulatory plant-wide control strategy for the feed conditioning plant subjected by various disturbances in temperature, pressure and feed CO2 composition.

Design of plantwide control and safety analysis for diethyl oxalate production via regeneration-coupling circulation by dynamic simulation

In this article, the plantwide control of a novel process for diethyl oxalate production via two steps is investigated. The unique feature of this process is that there is a closed regeneration-coupling circulation. It results in that two steps should be matched properly and mass balance for overall reaction should be satisfied precisely. An effective control structure using a feedforward ratio with composition controller is determined.Later, safety analysis for this process is investigated by the integration of dynamic simulation and HAZOP (hazard and operability analysis). In comparison with heuristic HAZOP, quantitative deviations can be introduced. Quantitative variation trends and change rates of important variables can be determined. Determining increase rate in temperature and pressure is significantly important, since response time as indirect indictor can be used to assess the possibility of risk. Finally, a general procedure based on simulation for design and safety analysis of chemical process is proposed.

Plantwide Control of the Formic Acid Production Process Using an Integrated Framework of Simulation and Heuristics

Formic acid (FA) is an essential chemical, but its process design and control have not received much attention in the literature. This contribution describes the design of a plantwide control (PWC) structure for the intricate FA process having reactive distillation (RD), multiple liquid and gas recycles, as well as a snowballing effect. In this process, methyl formate (MF) is produced from methanol (MA) and carbon monoxide (CO), and then it undergoes a hydrolysis reaction in RD to produce FA and also MA for the first reaction. The presence of an RD in addition to a continuous stirred tank reactor (CSTR) coupled with three recycles makes control of the FA process interesting and challenging. This work employs a systematic method for PWC design, namely, an integrated framework of simulation and heuristics (IFSH), which is easy to implement and uses process simulators as well as heuristics in PWC design. The performance of the developed PWC structure was evaluated for various disturbances, using several crit...

Distributed Model Predictive Control of an Amine Gas Sweetening Plant

This paper addresses the plant-wide control of the amine gas sweetening plant using distributed model predictive control. The plant is fed natural gas containing sour gases (hydrogen sulfide and carbon dioxide), which are removed by absorption in monoethanolamine solution. A plant decomposition algorithm based on modularity maximization for distributed parameter systems is used to obtain the optimal decomposition for distributed model predictive control. Comparisons are drawn among the performance and computational requirements of distributed, decentralized, and centralized model predictive controls.