The world is a batch

ISA 88 gives process automation a native language for batch processes, and much more. Editor in Chief Walt Boyes reports on the state of the batch in the September cover story for CONTROL magazine.

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“It is a very large task,” Henne continues, “to transfer a paper system to an automated software system, but it’s easy to do using S88’s unit cell concept. We’re using eProcedure manual phase control for batch. eProcedure hooked into a batch engine would be a real boon to batch processing. eProcedure is like Lego blocks…everybody here is excited about it!”

EaglePicher is still in the beginning implementation stage of its project. “We’re still in the early stages, but the ‘aha!’ for engineers and operators is that the framework stays the same with S88 instead of an ISO procedure and a traveler,” adds Henne. “Doing things consistently will reduce variability, and the numbers will go up on throughput, and go down on waste. We expect it to be a principal tool in the future.”

Henne says that the structure of S88 is going to continue to drive process improvement at EaglePicher. “One of my operators wanted to just go all the way to the SPC control charts,” he says. “The batch system has added feedback at a higher trust level, and the operators want to start using eProcedure as ‘instructions,’ so we can capture data and put it right into the database, replacing paper logs.”

Henne says that acceptance of batch processing theory by his operators has been excellent. “When they see it, they want it. We haven’t yet extrapolated design into our fully automated PLC-based stuff, because we’re focusing on the discrete manual procedures. The operators want to go all out.”

Some Batch Mythology
Control columnist Greg McMillan says (with his tongue firmly in his cheek), “Process control doesn’t apply to batch processes. Use that time-tested fixed sequence. After all, that batch cycle time is a tradition, and the golden batch sure looks shiny.” He goes on to point out that simply following the process flow diagram (See Figure 3 below) will not guarantee the optimal outcome. “Process engineers don’t think in terms of changing state,” he says. “They are used to seeing a ‘snapshot’ of the process, and trying to control a continually changing process to a snapshot. This doesn’t work well.”

FIGURE 3: WHAT YOU SEE IS WHAT YOU GET
Batch Process
Controlling feeds may not control concentrations in a batch process. (Click image to view an enlarged PDF).

McMillan points out that most process descriptions don’t take into account the variability of time in the process. “The process industry,” he says, “has large and variable time delays and time lags from batch-cycle times, vessel-mixing times, volume-residence times, transportation delays, resolution limits, dead band, and measurements.” Each of these must be accounted for in the batch control system.

Batching the Enterprise
The ISA S95 standard, Enterprise/Control System Integration, was developed in parallel with ISA’s S88 batch standard, and was developed by some of the same people from some of the same antecedents, like Process Automation Hall of Famer Ted Williams’ Purdue manufacturing model. In the past two years, S95 has been granted wide acceptance and adoption, with both enterprise automation giants SAP and Microsoft having decided that optimizing manufacturing operations requires more than counting “goesintas” and “goesoutas,” and knowing the cost of raw materials and labor. In the meantime, it has become clear that much of the discussion of S88’s upper levels describe the same territory as S95, but with somewhat different terminology. Consequently, a working group has been formed by the two standards committees to regularize the terminology of the two standards, so they can be used simultaneously and interchangeably to describe manufacturing from the control loop to the annual report.

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Many companies support the batch standard. Most suppliers have batch standard-compatible systems and software.

To Learn More…
The new, second edition of Batch Control Systems (ISA Press, 2006) by William M. Hawkins and Thomas G. Fisher, is one of the best places to start.

Another good book to add to your batch library is Applying S88: Batch Control from a User’s Perspective (ISA Press, 2000) by Jim Parshall and L.B. Lamb.

One of the best reference libraries on batch processing and the batch standard is the “WBF Body of Knowledge.” This reference library will eventually house all of the papers given at every annual WBF Conference. WBF produces two conferences per year, one in the U.S. and one in Europe. The 2006 WBF Europe Conference will be in Mechelen, Belgium, Nov. 13-15, and the 2007 WBF North American Conference, “Meeting of the Minds,” will be in Baltimore, Md., on April 30-May 4. More information on both conferences can be found at www.wbf.org.

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