Get the users engaged in batch control

Design what you want up front and keep it consistent, then get production to own, build and validate the recipes

By Dave Perkon, technical editor

Siemens BannerWhen you hear “user,” you may think of the operators. Certainly, they are important users, but the focus of a recent implementation at Evonik is on the intermediate user—the people who actually own and build some of the recipes. The new Evonik batch processing plant in Pasadena, Texas, uses a Siemens SIMATIC PCS 7 to control production of approximately 30 unique amine-based materials manufactured in three reactor systems and a separation system for production of flexible and rigid polyurethane foams.

The project had several challenges due to the diversity of products with dissimilar chemistries. "The equipment needed to be flexible enough to safely handle the different operations," said Alan Abel, lead process controls engineer at Evonik in Wichita, Kansas, and supporting batch automation at other Simatic PCS 7 sites. "It required significant batch flexibility to produce all products. It also had a reactor/filter system that must ‘chase itself,’ requiring a robust system for batch allocation and tracking—finishing one batch while starting a second batch."

Evonik is one of the world’s leading specialty chemicals companies with over 34,000 employees and $14 billion in sales worldwide. Approximately 80% of Evonik’s sales come from market-leading positions, which it is systematically expanding.

Abel presented “Engaging the Users in Batch Process Control” at the Siemens 2017 Automation Summit in Boca Raton, Florida, where he explained some of the challenges imposed by the project's diverse operating requirements of multi-use equipment. He also discussed how batch structure development and recipe design can create a flexible, safe solution that the users can support with minimal control engineer interaction.

Batch structure development

"It's important to carefully create a batch structure or the recipes will be hard to use and may not have the flexibility needed," stated Abel. "Our guiding principles were provided by S88. An automation philosophy was also followed, and we created a work process for defining structures."

The S88 terminology creates a common vocabulary by defining things such as phase and module control. It also provides a model with which to build a modular format, creating logical groups such as units and defining the functions, phases and procedures.

"Some of the automation philosophy we thought was important related to complicated and sometimes parallel movement of multiple products through the process—it was managed as a group," said Abel. "This made the equipment modules useable by operators independent of recipe and variations in operation based on the source. We also wanted flexibility, so we made the phase boundaries and strategies sufficiently granular to provide flexible use of equipment at the recipe level."

From a work process standpoint, “We found that having the P&IDs available along with personnel with production knowledge was very helpful,” said Abel. "An experienced employee highlighted the P&ID with colors unique to equipment and instrument function, such as setting temperatures," he said. "Also, several reviews of the set operating procedures by the production, process and controls team allowed us to understand and segregate the equipment into units."

A spreadsheet was used to begin batch model definition, and final EM/phase definition was produced as a Word document to start coding. "Siemens PCS 7 Simatic Batch easily integrates the physical and procedural models using Sequential Function Charts (SFC-Types) and the phase instances automatically generated by the batch tools," said Abel. "These recipe phases, accessible from the recipe editor, enabled process and production engineers to transfer their technical knowledge directly to process and equipment operation through flexible recipe building."

Recipe design

"One hurdle we had to overcome was that our sister production site and operation teams were most familiar with flat recipe," said Simeon Vogiatzis, process controls engineer responsible for automation at Evonik’s Pasadena, Texas, facility. "Operators found flat recipes easier to follow and troubleshoot. A disadvantage is that a flat recipe is not truly S88-compliant, and you can put units where ever you want with little structure. It’s easier to follow unit use within a hierarchal recipe. With hierarchal, each flow link is its own unit and there is an operation in each unit."

As a compromise, they added additional organization in the recipe to be closer to S88 requirements, said Vogiatzis. "To do this, we created operations by using substructures that acted like multi-unit operations," he said. "This produced consistency between recipes across products as they all follow the same path, making the recipe easier to track with clear landmarks."

An initial build was done using mock recipes in Visio diagrams to check if any strategies were missing. "The control team then used these diagrams to create operations and programmed the first revision of recipes," said Vogiatzis. "After high-level issues were resolved and major systems created, production was able to manage and maintain recipes, and needed only limited intervention from controls team."

Specific tools allowed the production team to do more with the phases without much intervention by the controls team. “Command blocks were huge for us," said Vogiatzis. They allowed controlled stop, hold, abort, etc. of phases or transitions, and reduced modifications to logic. “Using math in transitions was also another big one for us,” he added. “It alleviated the need for additional tag collects."

While they relied on safety systems to put everything to safe positions, they wanted to continually monitor phases, “So they were set and forget,” noted Vogiatzis. "For example, if we needed to put a temperature, pressure or control to a hold state, we typically made a continuous phase. It simplified the hold logic by keeping it in a phase instead of handling it at the recipe level."

While controls engineers still own the engineering station, keeping the users engaged streamlined the change process with production owning recipes that they could quickly modify to meet new requirements. "Sharing functions and responsibilities of automation improved team collaboration," Vogiatzis said. "The use of substructures made recipes more consistent and easier to modify, and equipment module design made it simpler for operators to execute complex operations independent of recipes. The design made it easier for users to understand the operation, and Safety Matrix allowed visualization and troubleshooting."

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