How do you design a process control system for a chemical plant?

Analyze the process dynamics, which are the relationships between the inputs and outputs of the process. You can use mathematical models, simulation tools, or experimental data to study how the process responds to changes in the manipulated variables (such as flow rates, pressures, or temperatures) and the disturbance variables (such as raw material properties, ambient conditions, or equipment failures). This analysis will help you understand the process behavior, characteristics, and limitations.

Design of control for an automated industrial system can be represented by the following major steps formulated in "An Industry Guide to Control System Engineering. A Condensed Guide to Automation Control System Specification, Design and Installation".

1. Design requirements and specifics must be formulated in a paper document (computer file) so that it can be easily understood and interpreted by anyone in the future. The document will contain data and ideas developed during the Identification phase. At this step the process or actions to take place is defined by means of a “sequence of operations” description. The sequence should show or list each operational step of the automated process.
2. The next step in the design is to develop a schematic in the form of a drawing that shows the logical wiring of an automated control system. It is normal practice to show input type devices on the left-hand side of drawings and output devices on the right-hand side.
3. The next step after finalizing schematic is creating a panel layout drawing. Here, all the components are mounted to a structure (the subpanel) and wired, and then the subpanel are mounted in the control system enclosure.
4. In the following step, the Bill of Materials (BOM) is built showing all components in the automated control system, their quantities, designations that allow to identify the components on the schematic, descriptions of the components, and part numbers.
5. Finally, a wiring diagram (interconnecting diagram) is developed that is used for installation by the electrician for routing the wiring between various components and enclosures of the control system (enclosures, cabinets, external devices, junction boxes, conduits, wireways, etc.) The wiring diagram includes conduit sizes, distances, number of conductors between devices, wire sizes, colors, wire numbers, terminal blocks, etc.