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16 June 2009

Batch process and ISA88 diverge on flexibility

“The title of this presentation could have been ‘What do you do when your process doesn’t fit S88?’ or it could have been ‘What happens when you run out of tools on your Honeywell tool belt?’ ” kidded Genentech’s Thomas Crowl.

There is a gap in S88 (ISA88) that does not show what to do when the equipment in the process changes, according to Crowl. He probably knows.

Crowl spoke to a session at the Honeywell Users Group in Phoenix on Tuesday about ISA88 implementation. He is a long time member of the ISA88 standards committee and a leader of batch processes at Genentech.

ISA88, Batch Control, is a series of standards on batch control in industrial automation systems. Its scope is to provide guidelines for the design and specifications of batch control systems. It draws from and supplements existing standards and recommended practices of ISA and other organizations. Its purpose is to provide standards and recommend practices as appropriate for the design and specification of batch control systems as used in the process control industries.

“We’re rewriting ISA88 now, without destroying what’s there, to make some changes to cover this sort of dilemma, and to make it more international in language and practice. Meanings of English words are different in different countries, and we want to address that,” said Crowl.

For instance, ISA88 assumes the equipment does not change in a process. It assumes the equipment has a limited number of things that it can do and that the variations from product to product are in the recipe.

So, what do you do when the equipment changes from product to product? That is the sort of situation Crowl faces in his plant. When they change product they run equipment in and out.

Crowl ran some quotes from ISA88:

• “The recipe contains neither scheduling nor equipment control.”
• “… permits batch processing equipment to make many different products without having to redefine equipment control for each product.”
• “Equipment control is not considered to be part of the recipe.”

Crowl gave several options to try when product and equipment change. He has tried all of them, and they all have their pros and cons.

• Add recipe parameter(s) for each phase with equipment differences
• Run a campaign changeover recipe that changes the equipment configuration
• Change the controller configuration when you change the equipment configuration
• Build some logic to change the equipment configuration

“ISA88 doesn’t cover everything,” Crowl said. “There are lots of ways to skin a cat.”

—Nicholas Sheble