It is interesting to note that control projects generally fall into two categories: 1. A new control process or 2. Enhance or copy an existing control process. Tackling either of these options need to follow a similar approach. Sometimes the individuals tasked with these projects feel that they can worry about the details later. “I’ll just slap together some control blocks that makes me feel good and we will fix it later”. This potentially will cause problems or provide a less than desirable result when the task is done.

The first thing that must be done is to collect all of the details of the process. This would begin with the Piping and Instrument Diagrams (P&ID), Duct and Instrument Diagrams (D&ID) and all related Process Descriptions. This information will provide a starting point for understanding what the electrical, mechanical and process engineers have developed for that batch or continuous process. These diagrams will identify the locations of the existing or proposed instruments and how they report information of the overall process. By reviewing the Process Descriptions, the control engineer or technician can recommend additional instruments or request additional information from the process engineers.

Once the process has been clarified and understood, the control specialist can identify all of the control and process components and obtain the specifications for each of these components. The component specifications can be compared with the results desired from the overall process. Considerations for particular component selection or accuracy could be driven due to extreme sensitivity regarding pressure, temperature, level or flow. Additional considerations may be driven by Transfer of Custody (TOC) applications, Environmental/Emissions Regulatory Agencies or simple economics of the process.

Protection of the equipment and process components must also be considered. Details of pumps, reactors, heaters, condensers, towers, valves and process flow must be understood. Component suppliers or the process system engineers will have the details and limitations associated with each of these components. If these documents have not been delivered to the engineers, then it is up to the control professional to obtain this information. (Documentation – Documentation – Documentation). The high and low limitations must be respected. The resulting control schemes and process piping must be able to protect these components.

Once the control professionals have become “one with the documentation” they can begin their tasks to configure an overall control scheme. Control schemes should be generated from the top – down. You need to begin at the 50,000 foot level with an overall view and drive down to the details at ground level. The Control Professionals’ 50,000 foot view must be beat against the view that the Process Engineers have envisioned. Any deviations between views must be conformed so the process and associated control scheme are consistent. At this point the Control Professional can begin narrowing down the vision and working toward the intimate details.

This is where we begin to find problems.

The next blog will be covering some of the problems areas:

Next time – Pumps and flow problems

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