Chemical reactors

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INTRODUCTION
Chemical reactors are one of the most important plants in chemical industry. Their operation, however, is corrupted with various uncertainties. Some of them arise from varying or not exactly known parameters, as e.g. reaction rate constants, heat transfer coefficients. In other cases, operating points of reactors vary or reactor dynamics is affected by various changes of parameters or even instability of closed loop control systems. Application of robust control approach can be one of ways overcoming all these problems. In this project, a simple method for design of robust PID controllers and IMC is presented. The approach is used for design of a robust PID and IMC for the CSTR. The reactor has three uncertain parameters: the reaction enthalpy, the reaction rate constant and the overall heat transfer coefficient. The control input is volumetric flow rate of the coolant and the controlled output is the temperature of the reacting mixture.



GENERAL
It is a branch of control theory that explicitly deals with uncertainty in its approach to controller design. Robust control methods are designed to function properly so long as uncertain parameters or disturbances are within some set. Robust controller methods aim to achieve robust performance and stability in the presence of bounded modeling errors.


LINEAR AND NONLINEAR SYSTEM
A system is said to be linear if it obeys the principle of superposition and homogeneity. The principle of superposition states that the response of a system to a weighed sum of signals is equal to the corresponding weighed sum of the response of the system to each of the individual input signals.
Example of linear system,
y = ax + b dx/dt



TIME DOMAIN SPECIFICATIONS
DELAY TIME
It is the time taken for response to reach 50% of the final value, for the very first time.
RISE TIME
It is time taken for response to rise from 0 to 100% for the very first time. For under damped system, the rise time is calculated from 0 to 100%. But for over damped system it is the time taken by the response to rise from 10 to 90%. For critically damped system, it is the time taken for response to rise from 5 to 95%.
PEAK TIME
It is the time taken for the response to reach the peak value for the very first time or it is the time taken for the response to reach the peak overshoot.
PEAK OVERSHOOT
It is defined as the ratio of the maximum peak value measured from final value to the final value.
1.4.5 SETTLING TIME
It is defined as the time taken by the response and stay within a specified error. It is usually expressed as % of final value. The usual tolerable error is 2% or 5% of the final value.

MOTIVATION TO THIS WORK
In most of the literatures the CSTR is modeledas a linear one and the nonlinearities are not properly handled the system is modeled as single input-single output or multi input–multi output. But in practices the CSTR is a multi input-multi output process and the input output relationship of the various inputs of the process. So it is require to handle the nonlinearities by proper analysis and design a suitable controller for this nonlinear process. So this work deals with the nonlinear analysis of CSTR and design of a proper controller.