Domino Theory

Can ISA88 and ISA95 Knock Down the Barriers Between Batch and Continuous Processing?

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By Rich Merritt

For several years now, ISA88 has been accepted worldwide as a way to define recipes and control batch processes, and ISA95 is gaining more acceptance as a way to connect batch control systems to higher- level software, such as data historians and ERP. But users and vendors are beginning to discover that both ISA88 and ISA95 can be used for more than just batch.

Take Steve Rubin, president of Longwatch in Norwood, Mass., for example. Longwatch makes video surveillance equipment that connects to HMI/SCADA systems via plant industrial networks, such as Modbus or Ethernet. Longwatch lets operators actually see the process equipment they are monitoring on HMI workstations (Figure 1).

Video snapshots
Figure 1: Longwatch allows operators to monitor a process and see it at the same time. Video snapshots  can be scheduled in ISA88 and stored away in batch records for visual confirmation that process steps were carried out properly.

Rubin has been demonstrating Longwatch systems to pharmaceutical companies as a way to verify that operators actually add the ingredients or perform other scheduled operations when they’re supposed to. He suddenly realized that commands to take video snapshots could be integrated into ISA88 recipes, and the video images, time stamps and event logs could be sent to historians and FDA documents via ISA88 and ISA95.

“This opens up a whole new venue for us,” says Rubin. “Thanks to ISA88 and ISA95, we can provide any company that’s controlling a regulated process with video proof that operations, steps and procedures are actually being carried out when required, and embed the information into an historical record that can be called up when needed.”

He’s not the only one who was surprised by the capabilities of ISA88 and ISA95. These two standards are being used for everything from continuous process control to packaging equipment and robots. The toughest sell is to continuous control, whose advocates remain unconvinced. But the times they are a’changin’, and a marriage of batch and continuous looms—especially since many ISA88 and ISA95 applications are already living in sin, some without the knowledge of their continuous control parents.

Continuous Control Isn’t Continuous

Most people identify ISA88 with pure batch control and recipe formulations. But ISA88 allows procedures, steps, logic and other functions to be defined, which means it can be used to define continuous processes too. That’s because continuous processes aren’t really continuous.

As my old boss, Dr. Ray Copeland at CRISP Systems in Columbus, Ohio, used to say, “Most continuous processes are actually piece-wise continuous.” That means even continuous processes have non-continuous elements, such as start-up, ramp-up, shutdown, emergency shutdown, clean-in-place, and so on. Tanks have to be filled and emptied, requiring on/off control of valves and pumps. One way to look at a continuous process is that it is really a batch process with a very long steady state in the middle.

Steam generation might be considered a continuous process, but Jean Vielle, president of Control Chain Group, a consulting engineering company in Paris, France, says it can be defined in ISA88 as a procedure with operations, phases and control modules (Figure 2). “Setting up the ISA88 definition for Boiler 1 can easily be replicated for Boilers 2 and 3,” says Vielle. “This simplifies configuring a steam generation process.”

steam generation
Figure 2: Some people may think steam generation is a continuous process, but it can be defined in ISA88 for steam generation.

Steve Zarichniak, of Honeywell Process Solutions, says Honeywell used ISA88 in a customer’s continuous process. “At a specialty polymers plant, the customer was faced with the problem of making a grade change every three days,” says Zarichniak. Each grade change took up to half a day with the old system, and at least one complete shutdown happened every year because of “poor operator transition technique.”
By using ISA88, the plant was able to define transitions and grade changes for many different products and dozens of possible transitions from one product to another. “After converting to ISA88 and automating ‘best practice’ transitions, the company cut off-prime product by 20% and saved over $2 million per year,” says Zarichniak.

Companies all over the world are using ISA88 in similar non-batch applications. But the toughest sell appears to be to the continuous control people.

Selling ISA88 to Continuous Control Advocates

Lynn Craig, past chairman of the SP88 committee that wrote the ISA88 standard, says that ISA88 is a good way to handle all the non-continuous aspects of a process. “The biggest sources of potential problems in a continuous process are start-up and shutdown procedures, plus any other procedures that operators don’t do often,” says Craig. “This is because these are mostly manual processes and depend on operator skill and training. Continuous processes sometimes run for weeks and months between start-up and shutdown, so the operators don’t do a procedure often enough to stay sharp on the details. Computers don’t forget anything, so if the procedures are defined in ISA88, then they’ll be done exactly the same way every time and are no longer dependent upon the skill of the operator.”

Doing manual processes incorrectly can shut a unit down. Honeywell’s Dr. Wayne Gaafar says, “In petrochemical and refining processes, start-up and shutdown often are the most dangerous times because if things get in the wrong state at the wrong time, then it creates a dangerous abnormal state that could result in an incident.” If start-up or shutdown go awry during a simple grade change, the process unit may have to go into an emergency shutdown, which might take it off line for days, instead of for a few hours. This can cost millions of dollars, just because of “poor operator transition technique.”

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