ISA has released a new technical report on automating continuous process operations. We examine the framework and nomenclature it provides for developing automated procedures.
ISA recently released Technical Report ISA-TR106.00.01-2013, Procedure Automation for Continuous Process Operations — Models and Terminology. This Technical Report is the continuous-process cousin to the well-known ISA Standard ANSI/ISA-88.00.01-2010 – Batch Control Part 1: Models and Terminology. It provides nomenclature and a framework for developing automated procedures for continuous process plants.
Why was this document issued as a Technical Report (non-normative) instead of a Standard (normative)?
First, the committee undertook the effort as a survey of the current practices in the industry rather than as a dictate of “what to do.”
Second, the committee found wide variations in the names used at different layers of the plant equipment hierarchy from industry to industry. Rather than pick a particular name set, as ISA-88 did, the committee presents in the Technical Report a table showing the variability in naming, giving various process sectors leeway to automate along their preferred structure and using their naming conventions.
One common terminology didn’t exist on which to standardize. The models presented use a particular naming, but there’s lots of room left to users to interpret and modify the models to suit their purposes.
Finally, the committee didn’t want to have the effect of non-normative examples, such as the phase state model in ISA-88, becoming de facto industry standards against which vendor offerings are judged. This leaves vendors the freedom to provide a range of tools of varying complexity (or better, simplicity) to automate processes.
A fundamental difference between automation of batch processes and automation of continuous processes is how the automated procedures start and end. For a typical ISA-88 batch procedure, the equipment starts idle, receives batch ingredients or a batch from a prior unit, does some processing, then transfers the batch to the next unit and ends up ready for the next batch. By the nature of producing finite batches, the procedure is necessarily “closed-ended.”
Procedures for continuous processes are different. They’re intended to simply move the process from one state (commonly called a “mode of operation”) to another.
For example, an automated start-up of a distillation unit might need to take the column from a cold idle state to a heated state. A second procedure might take the column from the heated state, begin product feed, and take the column to an operating state.
Yet another procedure might be activated when a surge or flood is detected in the column to alleviate the condition and bring it back to an optimal steady state. And, of course, there might be multiple procedures to take the column back to a heated-ready state, then to a cool shutdown state.
Procedures might cascade down through the physical hierarchy, from the enterprise to the site and on down through the plant and plant area to the units and equipment, and even to devices such as transmitters, pumps and actuators.
For example, the site might have a procedure to follow for shutdown and evacuation in the event of a natural disaster such as a hurricane or tsunami. Parts of the procedure might be executed by people from written checklists, while other parts of the procedure may be automated to a lesser or greater degree.
The shutdown of the distillation column above might be fully automated, but other procedures for taking the plant to a safe state ready for evacuation might be fully automated or have parts automated, might be done with online checklists or other electronic guidance, or might be performed manually from paper. ISA-TR106.00-01-2013 provides the framework for understanding how to make automated and non-automated procedures play nicely together.
The Work Continues
Future work for the ISA 106 committee includes Technical Reports on work practices for choosing, designing, developing, testing and commissioning automated procedures, development of example procedures and more.
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