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Published14 Dec Abstract This paper introduces a calculation procedure for modeling and control simulation of a condensate distillation column based on the energy balance structure.

In this control, the reflux rate and the boilup rate are used as the inputs to control the outputs of the purity of the distillate overhead and the impurity of the bottom products. The modeling simulation is important for process dynamic analysis and the plant initial design. In this paper, the modeling and simulation are accomplished over three phases: the basic nonlinear model of the plant, the full-order linearised model, and the reduced-order linear model.

The reduced-order linear model is then used as the reference model for a model-reference adaptive control MRAC system to verify the applicable ability of a conventional adaptive controller for a distillation column dealing with the disturbance and the model-plant mismatch as the influence of the plant feed disturbances.

Introduction Distillation is the most popular and important separation method in the petroleum industries for purification of final products. Distillation columns are made up of several components, each of which is used either to transfer heat energy or to enhance mass transfer.

A typical distillation column contains a vertical column where trays or plates are used to enhance the component separations, a reboiler to provide heat for the necessary vaporization from the bottom of the column, a condenser to cool and condense the vapor from the top of the column, and a reflux drum to hold the condensed vapor so that liquid reflux can be recycled back from the top of the column.

Calculation of the distillation column in this paper is based on a real petroleum project to build a gas processing plant to raise the utility value of condensate. The nominal capacity of the plant is tons of raw condensate per year based on 24 operating hours per day and working days per year. The basic feed stock data and its actual compositions are based on [ 1 ].

Most of distillation control systems, either conventional or advanced, assume that the column operates at a constant pressure. Pressure fluctuations make the control more difficult and reduce the performance. The L-V structure, which is called energy balance structure, can be considered as the standard control structure for a dual composition control distillation.

In this control structure the liquid flow rate and the vapor flow rate are the control inputs. The objective of the controller is to maintain the product outputs concentrations and despite the disturbance in the feed flow and the feed concentration Figure 1 Distillation flowsheet.

The goals of this paper are twofold: first, to present a theoretical calculation procedure of a condensate column for simulation and analysis as an initial step of a project feasibility study, and second, for the controller design: a reduced-order linear model is derived such that it best reflects the dynamics of the distillation process and used as the reference model for a model-reference adaptive control MRAC system to verify the ability of a conventional adaptive controller for a distillation process dealing with the disturbance and the plant-model mismatch as the influence of the feed disturbances.

In this study, the system identification is not employed since experiments requiring a real distillation column are still not implemented yet. So that a process model based on experimentation on a real process cannot be done. A mathematical modeling based on physical laws is performed instead. Further, the MRAC controller model is not suitable for handling the process constraints on inputs and outputs as shown in [ 2 ] for a coordinator model predictive control MPC.

Process Model and Simulation The feed can be considered as a pseudobinary mixture of Ligas iso-butane, -butane and propane and Naphthas iso-pentane, -pentane, and higher components.

The column is designed with trays. The model is simplified by lumping some components together pseudocomponents and modeling of the column dynamics is based on these pseudocomponents only [ 3 ]. For the feed section, the operating pressure at the feed section is given at 4. The feed temperature for the preheater is the temperature at which the required phase equilibrium is established.

Consulting the equilibrium flash vaporization EFV curve at 4. For the rectifying section, the typical pressure drop per tray is 6.

Thus, the pressure at the top section is 4 atm. Also consulting the Cox chart, the top section temperature is determined at. Then, we can calculate the reflux flow rate via the energy balance equation. For the stripping section, the column base pressure is approximately the pressure of the feed section 4. Consulting the EFV curve and the Cox chart, the equilibrium temperature at this section 4.

Then, we can calculate the reboiler duty or the heat input to increase the temperature of stripping section from to. Table 1 summarizes the initial calculated data for the main streams of input feed flow rate Condensate , output distillate overhead product: LPG and output bottom product Raw gasoline.


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