Control Of Distillation Column Research Articles

Adaptive robust control of oil and gas production objects

The article discusses a synthesis algorithm for objects with identification and parameter tuning. The algorithm is made on the basis of software and is tested for the formation of control effects in distillation column control circuit used in oil and gas processing production. It is shown that the control method suggested for a distillation column is not less effective in comparison with a control method that pre-tuned a preset proportional and integral differential controller. The suggested controller parameter tuning is not required and is made as the mentioned algorithm functions. Moreover, in the article it is possible to find the research results of testing in conditions of various level noise, control limitations, and controlled object parameter shift.

Ceramics coating materials for corrosion control of crude oil distillation column: Experimental and theoretical studies

Corrosion of stainless steels in atmospheric crude oil distillation column was studied in presence and absence of the ceramic coatings at different temperatures and exposure times using the weight loss technique. Thermal spray coating method was employed to deposit the coating. Weight loss of the stainless steel increased with temperature and time, and significantly decreased in the presence of a coating. Maximum coating efficiency of 93.3% was approached in the presence of Al2O3 coating. Surface morphology investigations using atomic force microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy showed a lower corrosion effect in the presence of a coating. Thickness and porosity of coating were determined to be the most significant factors. Mathematical and statistical analyses were performed as a powerful tool for data representation. Second-order polynomial and exponential models were suggested to represent weight loss data as a function of time and temperature with high correlation coefficients. Corrosion rate data varied with temperature according to the Arrhenius equation. Activation energy without coating is lower, than that with the coating, which indicates that the reaction needs a lower energy in the absence of coating. Petroleum chemistry data and local investigations showed that the main factor influencing the corrosion of crude oil distillation columns is the sulphur content, which had a significant effect more than other contaminates of crude oil.

Composition–Temperature Cascade Control of Dividing-Wall Distillation Columns by Combining Model Predictive and Proportional–Integral Controllers

Although dividing wall technology is very effective for process intensification of distillation, the resultant dividing-wall distillation columns (DWDCs) exhibit strongly interactive and highly nonlinear behaviors, which may pose great challenges to process operations. Proportional–integral (PI) controllers can stabilize the operation of the DWDC, but their performances are frequently far from satisfactory. Model predictive control (MPC) can potentially improve performance sharply, but the stringent requirements on the qualities of the embedded model considerably lower its robustness. To suppress these two deficiencies, in this work a cascaded control structure by combining the MPC and PI controllers is proposed for the DWDC. The PI controllers regulate the stage temperature in the inner layer, serving to quickly stabilize the DWDC, while the MPC directly controls the product compositions in the outer layer, addressing the strongly interactive and highly nonlinear behaviors of the DWDC. Two typical cases,...

Modified Backstepping Algorithm and its Application to Control of Distillation Column

A novel robust algorithm is proposed for control of plants under parametric and structural uncertainties, as well as, external bounded disturbances. The algorithm design is based on the modified backstepping approach that allows to compensate mismatched disturbances under presence of nonlinearities. The obtained results are extended to control of network systems with nonlinear agents and with nonlinear links in the presence of mismatched disturbances. Effectiveness of the proposed algorithm is demonstrated on control of a distillation column which is described by parametric and structurally uncertain differential equation in presence of external bounded disturbances. It is assumed that only scalar input and output of the distillation column are available for measurement, but not their derivatives. The developed algorithm provides output tracking of a smooth bounded reference signal with a required accuracy at a finite time. The synthesis of control algorithm is separated into ρ steps, where ρ is an upper bound of the relative degree of the distillation column model. Therefore, the dynamical order of the proposed algorithm is equal to ρ. The sufficient conditions of the closed-loop stability is formulated and proved by using methods of stability of singular perturbed differential equations and Lyapunov functions. The simulations illustrate effectiveness of the proposed algorithm and confirm analytical results.

Temperature inferential control of a reactive distillation column with double reactive sections

Abstract Temperature inferential control (TIC) is studied for a reactive distillation column with double reactive sections (RDC-DRSs) processing a hypothetical two-stage consecutive reversible reaction (A + B ↔ C + D, C + B ↔ E + D with αD > αB > αC > αA > αE). Because of the complicated dynamic behaviors, the controlled stages by sensitivity analysis lead to great steady-state deviations (SSDs) in top and bottom product purities. Since TIC involves considerably reduced settling times in comparison with direct composition control, small SSDs in product qualities correspond generally to small transient deviations (TDs) in product qualities. An objective function that measures SSDs in product qualities is formulated to represent the performance of a TIC system and an iterative procedure is devised to search for the best control configuration. The application of the procedure to the RDC-DRS gives considerably suppressed TDs and SSDs in top and bottom product qualities as compared with the one by sensitivity analysis. The method is simpler in principle and less computationally intensive than the current practice. These striking outcomes show the effectiveness of the proposed principle for the development of TIC systems for complicated reactive distillation columns.

Simultaneous Design and Control of a Ternary Reactive Distillation Column with Inert Material

AbstractProcess integration means significant challenges in operating a chemical process dynamically due to its complexity. One example is the ternary reactive distillation with inert material. Based on the heuristic approach, chemical process design and process control are performed independently one after another. This may lead to infeasible solutions either in process design and control or in both. The application of simultaneous design and control, formulated as mixed‐integer dynamic optimization (MIDO) problems, increased rapidly in the last decade. Simultaneous process design and control, including control structure selection and control parameters, is devised for the challenging benchmark problem of a ternary reactive distillation with inert material. The improved process design and control is obtained by solving the MIDO problem.

Distillation Column Hierarchical Control

This paper treats the problem of hierarchical control of a butylene-butane distillation column (BBDC). A hierarchical control system with three levels is proposed for BBDC. First hierarchical level, which is represented by the column with its conventional automation, is simulated and the results led to the idea of using a decoupler for the process crossed channels. Thus, it is proposed a nonlinear decoupler which determines automatically its parameters and type. At the second hierarchical level are implemented two internal model controllers for the top and bottom concentrations. Finally, the third hierarchical level consists of an optimal control system for the butylene-butane separation process.

Appropriate selections of distillation column control variable to improve integrating material recycle response

The distillation column control strategy in a standalone column ensures a safe and stable column operation by holding the purities/or impurities in distillate and bottoms product streams. In general, the sensitivity analysis method provides the column control variable which contributes in robust process operation, however, in this example the importance of control variables selection through different methods are compared for a specific case study wherethe distillation column is located/placed inside the recycle loops of two different recycle streams. The control variables for distillation column located within two different recycle loops is first selected using sensitivity analysis shows an integrating (ramp like) recycle flow rate for a nominal (±10%) throughput change. Later, a thorough dynamic analysis is implemented with control variables obtained from different methods to understand this peculiar recycle response. Further, these methods are discussed to improvise the dynamic response.

Simulation and Control of Bench-Scale Distillation Columns Using a Switched Reflux Strategy

The undeniable importance of industrial distillation has motivated hundreds, if not thousands of theoretical and applied research projects. A considerable amount of those projects has used a bench or pilot scale distillation columns to have experimental confirmation of the proposed innovations. Nevertheless, the automatic control of bench scale distillation columns is not as straightforward as it appears to be, due to the low magnitude of the involved material flows. To precisely manipulate low magnitude flows, special low flow control valves are necessary; this results in high instrumentation costs which are not desirable at bench nor pilot scale. This work treats the simulation and control of a low cost, bench scale column with an electrically heated reboiler and water-cooled condenser. It uses a version of an on-off valve as an actuator to control the distillate composition of the desired product. The use of a solenoid valve results in a discontinuous reflux flow, which changes the continuous dynamical model of the distillation column to a piecewise dynamical one. In other words, it can be assumed that the column switches between zero and infinite reflux ratio instantly. The resulting piecewise dynamic model is studied and analyzed, and because of this analysis, the dynamic implications of this strategy in the operation of the column are used to tune a PID-PWM controller and to formulate general recommendations to attain an efficient composition control in the distillate.

Distributed Control System Application for Distillation Column

The entangled nature of various continuous production processes, such as chemical processing, oil and gas, and water treatment, continue to require the advanced process control capabilities of the Distributed control system (DCS) in order to aggregate and analyse a large amount of data at the same instant of time. This paper aims to enhance the flexibility in controlling and monitoring of distillation column by configuring and developing a HMI using DCS with SCADA. DCS provides high scalability, solutions to complexity, redundancy, high adaptability to frequent process changes, hybridized to incorporate PLCs and PCs to control complex functions and to provide reporting services. Hence the optimized control of distillation column has been achieved via DCS.

Firefly algorithm based multivariable PID controller design for MIMO process

Distillation is the process of separating the components or substances from a liquid mixture by selective boiling and condensation. It is one of the most underestimated fields of chemical engineering and has been around for well over hundred years. This paper deals with the tuning of centralized and decentralized Multivariable PID controller for Wood and Berry distillation column using Firefly algorithm (FA). FA uses controller parameters as decision variables and minimization of IAE as objective function. At the end of the search, optimum solutions for controller parameters are obtained which upon implementation provides challenging results for both top and bottom products. Simulation has been carried out using Matlab/Simulink platform.

Cascade Active Disturbance Rejection Control of a High-Purity Distillation Column with Measurement Noise

Control of high-purity distillation columns is a challenging problem due to their unique characteristics, such as complex dynamics, high nonlinearity, and interaction between the control loops. In this paper, a cascade control strategy, based on active disturbance rejection control, is proposed for a high-purity distillation column. With the proposed strategy, it is shown that the distillation column is almost decoupled by using the extended state observer to estimate and reject the effects of both the internal plant dynamics and the external disturbances. Considering measurement noise, an extended state observer that switches between two gain values is proposed. On the basis of this scheme, the extended state observer can quickly estimate the system state and also reduce the effect of measurement noise. Finally, the simulation results evidence the efficacy of the proposed method.

Simultaneous Design and Control of Catalytic Distillation Columns Using Comprehensive Rigorous Dynamic Models

This work addressed the rigorous modeling of catalytic distillation columns by simultaneously considering relevant phenomena such as pressure drop across the column, tray capacity constraints, non-ideal behavior of both liquid and vapor, and the column’s hydrodynamics, yet to be considered in earlier modeling studies for catalytic distillation. The developed model is applied for the simultaneous optimal design and control of catalytic distillation units, taking into account economic and set-point tracking objective functions balanced though a proposed weighting parameter estimation methodology. Results for a column for the production of ethyl tert-butyl ether show the advantages of a more comprehensive model regarding design and control decisions in comparison with previous studies: design specifications were met during the entire time horizon without sacrificing economic profitability.

Neuro estimator-based inferential extended generic model control of a reactive distillation column

This work aims at proposing a neuro estimator (NE)-based inferential extended generic model controller (IEGMC) for an ethylene glycol reactive distillation (RD) column. This nonlinear control system comprises of a model-based controller (i.e., EGMC), an artificial neural network (ANN)-based estimator (i.e., NE) and an ANN-based soft sensor for composition inferencing. At first, the NE is designed for the RD column to compute the state variables exclusively required for simulating the control action of the EGMC. We subsequently formulate the NE-based EGMC controller. As a further development, a soft sensor has been proposed to infer the bottom composition of the RD column and the resulting controller in conjunction with this soft sensor is called NE-based inferential EGMC controller. For the representative ethylene glycol system, the bottommost tray has been identified as the most sensitive stage and thus, used to infer the composition. Performing simulation tests, it is investigated that the proposed NE-based IEGMC is superior to the inferential proportional integral (IPI) controller.

Model-based Control of Vapor-recompressed Batch Distillation Column

This article provides a comparison of control strategies for an economically attractive vapor-recompressed batch distillation (VRBD) column. A VRBD column exhibits nonlinear dynamics with strong inter-stream interactions due to energy-integration, which can give rise to difficulties in controlling the operation using traditional linear controllers. In this paper, we propose and compare model-based control strategies such as linear quadratic regulator (LQR), linear model predictive control (LMPC) and Globally linearizing controller (GLC) for a VRBD column to achieve desired distillate purity with minimum energy consumption. The effectiveness of these control strategies is illustrated using a simulation case study of benzene/toluene separation in a VRBD column.

Integrated Process Design and Control of Cyclic Distillation Columns

Integrated process and control design approach for cyclic distillation columns is proposed. The design methodology is based on application of simple graphical design approaches, known from simpler conventional distillation columns. Here, a driving force approach and McCabe-Thiele type analysis is combined. It is demonstrated, through closed-loop and open-loop analysis, that operating the column at the largest available driving force results in an optimal design in terms of controllability and operability. The performance of a cyclic distillation column designed to operate at the maximum driving force is compared to alternative sub-optimal designs. The results suggest that operation at the largest driving force is less sensitive to disturbances in the feed and inherently has the ability to efficiently reject disturbances.

Control properties of driving force based distillation columns design

So far, not much is known about the controllability of distillation columns derived from algorithms as there are many types of algorithms exist and many forms of mixtures to be separated. It is therefore aimed in this study to analyse the controllability of a distillation columns design method, known as the driving force approach. This study makes use of a four stage methodology and those stages are; sequence design, energy comparison, sensitivity comparison, and controllability comparison. In the first stage, a distillation columns sequence is designed based on the driving force algorithm. In the second stage, the energy consumption of the different designs is compared. In the third stage, the sensitivity of the different designs is compared and in the final stage the relative gain array method is used to determine the interaction between the designs’ control loops. The methodology is applied to a five component hydrocarbon mixture. Results showed that while the driving force design is the most energy efficient and robust, it does not have the best controllability.

Controlling the Oil Rectification Process in a Primary Oil Refining Unit Using a Dynamic Model

The composition of Devonian oil has been simulated using an experimental true-boiling-point (TBP) curve, and the physicochemical properties (density, molecular weight, enthalpy, etc.) of the feedstock arriving at the plant have been calculated. The optimization criterion proposed is the calculation of the yield of light fractions. The optimization problem with constraints on variables (initial and final boiling points of light fractions) and constraints in the form of inequalities (overlapping neighboring fractions) using the function fmincon has been solved and implemented in the programming environment Matlab. A nonlinear dynamic model of the oil rectification process has been developed and implemented. The Matlab ode 15s solver and the explicit second-order Euler method have been used to develop the model. The model in the form of a system of algebraic–differential equations has been applied to the distillation column control system of an atmospheric pipe still at a small oil refinery. In the case of controlling according to the model, the column profile temperatures are maintained at optimal (preset) values and the quality of the petroleum products is also maintained. A comparison has been made between two operating modes of the distillation column in the processing unit. The results of the study suggest the following. The method of controlling in accordance with the model provides an increase in the recovery of light products through the use of optimization and the dynamic model, shortening of the overlap intervals of the temperatures of the gasoline and diesel fractions, and a decrease in deviations of the boiling points of petroleum products.

Closed-loop simulation of decentralized control using RGA for uncertain binary distillation column

This paper presents the results of closed-loop simulation for the decentralized control of uncertain distillation column. The RGA (Relative Gain Array) RGA analysis was used as the basis for selecting the configuration of the decentralized control system. PI controller obtained was then tuned with optimization methods. The simulation results show that the RGA analysis requires accurate range for uncertain systems. In addition, closed-loop simulation results confirm the RGA analysis.

Closed-loop simulation of decentralized control using RGA for uncertain binary distillation column

This paper presents the results of closed-loop simulation for the decentralized control of uncertain distillation column. The RGA (Relative Gain Array) RGA analysis was used as the basis for selecting the configuration of the decentralized control system. PI controller obtained was then tuned with optimization methods. The simulation results show that the RGA analysis requires accurate range for uncertain systems. In addition, closed-loop simulation results confirm the RGA analysis.