Distillation Column Analysis

Abstract–Distillation column has always been and will continue to be one of the most important thermal separation equipment used in various types of industries for various applications, i.e. in oil refineries, in water purification/ desalinisation plants, in pharmaceutical industriesetc. Modelling and simulation of distillation column are not new to the process and control engineer. The model used for distillation column varies from the simple to quite complex, depending on the assumption made in the material balance and energy balance equations to describe the distillation column behaviour. This paper discuss about the dynamic modelling of continuous binary distillation column in Matlab tool and the response analysis while varying the assumptions

In the stripping section, the less volatile component is enriched while in the rectifying section the more volatile component is enriched. The top product is condensed by the condenser from which there is a reflux flow back to the top of the column to enhance the purity of the product. Figure 2.Binary distillation column operation

In order to achieve the purest form of a component or to achieve the desired composition of a product depending according to the requirement, we need to manipulate &control various variables of the distillation column such as temperature of trays, reflux flow rate, distillate flow rate, vapor boil up rate and the pressure in the column. These variables may vary in practice due to different reasons. This paper is organized as follows. Section-II gives some basic details about the modelling of binary distillation column by using fundamental modelling approach. Section-III gives the details about how we can simulate dynamic model of distillation column in Matlab tool. Section-IV will shows the steps to be followed to derive FOPDT model. Section-V will discuss about Ziegler-Nicholas PID tuning method. Finally in Section-VI and Section-VII,conclusion is made and the work that can be extended in future is mentioned

However, this modelingmethod is quite complex for the controller design, because it requires a huge amount of computation and simplifications.

Empirical modeling method

The empirical modeling utilizes the input and output data from the operation of the column to build the relationship between the input and the output. This method is also known as “Black box modeling” because inner dynamics are not considered. With this type ofmodelling, the understanding of the inner dynamics of the column does not required. So, the computation can be reduced.

But by using this technique, we must to carry out experiments on the real distillation column, and the results may not be applied for another distillation column, even the results from one distillation column can be different if the distillation column’s conditions are different between the experiment and the real operation of the distillation column.

Hybrid modeling