control is a dynamic process explain
Answers
Process Control is the active changing of the process based on the results of process monitoring. Once the process monitoring tools have detected an out-of-control situation, the person responsible for the process makes a change to bring the process back into control.
Answer:
A Short Introduction to Process Dynamics and Control
Process Control
Process control is the study and application of automatic control in the field of chemical engineering.
The primary objective of process control is to maintain a process at the desired operating conditions,
safely and efficiently, while satisfying environmental and product quality requirements. Proper
application of process control can actually improve the safety and profitability of a process. Even
though rapidly decreasing costs of digital devices and increasing computer speed have enabled high‐
performance measurement and control systems, it is not an easy task to achieve this because modern
plants tend to be difficult to operate due to high complexity and highly integrated process units.
The possibility of improving the performance and the profitability is illustrated by the figures below. Impurity
In this example, acceptable product quality requires that the impurity of the product is below the limit
indicated in the figures. However, we do not want to make the product purer than necessary, because it
would increase the production costs. The figure to the left illustrates a situation where the impurity
fluctuates a lot, but the quality requirements are fulfilled. The figure in the center illustrates that the
fluctuations can be reduced by better control. Then it is possible to increase the average impurity in the
product, as illustrated by the figure to the right, without violation of the quality requirements.
Obviously, this also reduces the production costs.
As a consequence of global competition, rapidly changing economic conditions, and stringent environ‐
mental and safety regulations, process control has become increasingly important in the process
industries. It is also clear that the scope and importance of process control technology will continue to
expand. Consequently, chemical engineers need to master this subject in order to be able to design and
operate modern plants.
Process Dynamics
A process is a dynamical system, whose behavior changes over time. Control systems are needed to
handle such changes in the process. Thus, it is important to understand the process dynamics when a
control system is designed. Mathematically, the process dynamics can be described by differential
equations. Unsteady‐state (or transient) process behavior then corresponds to a situation, where (at
least some) time derivatives of the differential equations are nonzero.
Transient operation occurs during important situations such as start‐ups and shutdowns, unusual
process disturbances, and planned transitions from one product grade to another. Even at normal
operation, a process does not operate at a steady state (with all time derivatives of the differential
equations exactly zero) because there are always variations in external variables, such as feed
composition or cooling medium temperature. Thus, knowledge of steady‐state (or static) process
properties, taught in many engineering courses, is not sufficient for control design.