Senin, 07 Mei 2012

Batch standards find their way into nonbatch industries

Ask a control engineer from the petrochem industry if he/she has heard of the ISA-88 and 95 standards and he/she will likely say "yes," followed by a comment along the lines of "they are the batch standards and don't apply to us." It is true that both these standards came from the batch environment and were designed to address batch issues. More and more engineers from petrochem companies are showing up at common-interest groups for the standards. Even at this year's WBF (formerly World Batch Forum) North American conference, held in Baltimore, it became clear that these standards are opening eyes in industries and applications outside of batch. Not only are they able to provide structure and portability to many types of sequential operations in continuous processes, but they are also able to provide a design methodology for many other applications within the manufacturing environment. Control and application engineers in many companies not traditionally linked with batch per se have found that these batch control standards' models and structures have helped in developing detailed control functions' design for their nonbatch processes. Modularization of the control functions-based ISA-88 batch control standard can improve a control project whether it is a batch, continuous or discrete process.

ISA-88 in continuous control. The ISA-88 batch control standard is providing significant benefits to users and suppliers of batch control systems worldwide. Although the standard is primarily designed for batch processes, it is also being applied successfully in various manufacturing industries. This is because the structure required for flexible manufacturing mirrors the structure required for many batch processes, even though the underlying process is often continuous or discrete. The standard allows collapsing hierarchy levels, where one or more levels of functions may be eliminated, as needed, making it very adaptable for many different applications.

Batch control engineers have long joked that a continuous process is a huge batch process with very long cycle times. That may be a somewhat facetious statement, but continuous processes do use sequences in many of their operations and continuous manufacturers are turning to ISA-88 as a way to provide a standardized means of designing and implementing these operations across their sites.

Continuous processes use sequenced operations for startups, shutdowns and transitions from one product to another. The latter often means manipulating many setpoints, changing lineups and the possibility of introducing error. Some continuous manufacturers have found that using an ISA-88 approach to design and implement the recipes for each new transition state helps to reduce the time taken for a transition and for the process to come back to a steady state. It also reduces potential errors from shift to shift and operator to operator.

The same is also true of startups and shutdowns. Continuous processes run for so long between planned shutdowns that manufacturers have turned to ISA-88 to help with the design of sequences to ensure that startups and shutdowns are done safely, with minimum disruptions.
A different view of process analysis. ISA-88 is also starting to find application in another "bastion" of the petrochem world—process analysis. Analyzers in the process industries are small "batch" processes. A sample is taken from a line, transported to an analyzer, the analysis is performed and the data sent to the control strategy (after error checking). The "batch" standards may be able to improve cycle times and get better coordination between process and analysis. Paul McKenzie introduced the concept of a batch analytical recipe (BAR) in his keynote speech at the WBF forum and said that the whole process of setting up an analyzer should lend itself to an ISA-88 approach. The instrument setup, sample preparation and system suitability criteria all lend themselves to an ISA-88 approach and definition using the BAR concept.

ISA-95 as a design and integration methodology.

As the petrochem companies and other traditionally continuous companies wrestle with integrating their business and control systems, many of them are turning to ISA-95 as a methodology to help them in this process. In fact, many of the major ERP systems' suppliers are using the B2MML schemas developed by WBF's XML working group to help facilitate these integrations—be they from batch, continuous or discrete industries.

It is clear that batch control problems and their solutions are not unique to batch processes and the so-called batch industries. They can also be applied to continuous and discrete processes, packaging lines and material storage facilities. The batch control standards committees always believed that the batch standard models could also be applied to areas that are not strictly batch. In fact, recently the Make2Pack joint working group between the WBF and the Open Modular Architecture Controls User Group has developed standards for packaging machine control based on ISA-88 standards. It is also clear that the desire for refining and petrochem companies to integrate their business and control systems will inevitably pull them closer to the ISA-95 standards.

Maybe they should change the name of the standards to "manufacturing standards".

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