Modelling and Simulation of pH Neutralization Plant Including the Process Instrumentation

In this chapter, we aim to show the facilities available in Matlab/Simulink to model control loops. For this, it is implemented a simulator in Matlab/Simulink, which shows details about the modelling of each component in a pH neutralization plant, where pH and tank level are simulated and controlled in a CSTR (Continuous Stirred Tank Reactor). Both loops are modelled considering the plant itself, the measuring and actuating instruments and the control algorithms. The pH neutralization is normally a difficult process to control, due to the non-linearity caused by the titration curve (Asuero & Michalowski, 2011), mainly when strong acids and bases are involved. It is presented the equations (linear or non-linear) corresponding to the loop elements and how they are translated into a Simulink model and how blocks are created in Simulink to ensemble the components of the loop. Another objective is to show a case in which a P&ID diagram of the control system is presented and how it is used to reach an equivalent Simulink model. All the model parameters, initial conditions and data related to the simulations are inserted in a Matlab file and it is stressed how it can generate a well-documented project. It is also addressed the option to create a batch in Matlab, which enables to automatically simulate the plant in different conditions and to plot graphs of different responses, in order to compare the behaviour of distinct situations. To exemplify that and validate the model, tests were performed considering set point variations (servo mode) and disturbances (regulatory mode).