There's no research on how many process control engineers were Boy Scouts, but it must be a high ratio because being prepared is so essential to both groups. For example, readying complex unit operations for start-up requires awareness of numerous details and completing many tasks, but upgrading process controls at the same time is even more intensive, and demands even more careful planning—hopefully to simplify and resolve some of these complications.
Case in point: Evonik Corp.'s plant in Mobile, Ala., has been preparing to upgrade the automation on several units within the plant. This application for producing animal nutrition products includes sequential column start-up, crystallization, filtering, and regular daily flush out procedures. In parallel, the firm is also upgrading the column from its phased-out APACS+ control system to newer PCS 7 controls from Siemens.
"This migration is happening in two phases dictated by our shutdown schedule," says Patrick Spomer, senior project engineer for process control at Evonik Corp. "The first is converting the HMI for the APACS+ operating system, implementing new Siemens Industrial PCs, migrating to the PCS 7 architecture, and adding the AS410-5H controller and network infrastructure. The second phase is converting the APACS+ I/O to PCS 7 I/O, and taking into account safety instrumented system (SIS) considerations."
Spomer presented, "A sequence saved is a penny earned: implementing SFC types on dual-leg PCS 7 systems" on the second day of Siemens Automation Summit 2017 on June 28 in Boca Raton, Fla. He reported that this section of the Mobile site has about 5,000 I/O overall, while the immediately affected process has 300-400 I/O. So far, the sequencing basic engineering is done, and detailed engineering will begin in several weeks. The PCS 7 hardware and sequencing will be implemented this fall, and the start-up is scheduled for next April.
Managing the 'gray' phase
Despite organizing the upgrade into two phases, Spomer adds there can be a three- to five-year "gray phase" between when the APACS+ OS HMI conversion is complete and when the I/O conversion phase is implemented. "Plants and personnel can get into a lull between phases where they may forget that a migration is happening, and they may rip and replace some components when needed without notifying anyone," explained Spomer. "This is why the design and plan for our PCS 7 project includes a specific philosophy that requires all new sequential and I/O programming to go in the PCS_7 system. Our system audit, what we have and whether it can meet project requirements, shows we have all the pieces necessary to add value during the gray phase."
The audit of the operation unit’s Siemens system showed it’s legacy architecture included APACS+ Advanced Control Modules (ACM) and IO, QUADLOG SIS control modules and IO. Adding a new PCS 7 AS410-5H controller will now communicate to the existing APACS+ system via Industrial Ethernet Modules (IEM’s) while maintaining communication to new ET200M standard and HART I/O, SIMOCODE Pro low voltage motor-management, and control devices via PROFINET and PROFIBUS. This is known as a dual-leg system. The upgrade at Evonik's site will also upgrade its network architecture from 5-Mbps Modulbus and 1 Mbps for I/O with one scan rate to 1-Gbps industrial Ethernet, 100-Mbps PROFINET, 12-Mbps PROFIBUS DP and 9 selectable scan rates as fast as 10 milliseconds.
New sequencing philosophy
"We were facing hours and hours of sequencing on major equipment, programmed as ladder logic diagrams (LLD) and per our modernization plan we would redo them in three to five years," says Spomer. "However, we believe that 'successful migrations tackle future requirements, while satisfying today's needs,' so we adopted Evonik's process control sequential function chart (SFC) philosophy. This really allows us to achieve our goal which is to migrate from APACS+ while phasing out our LLD’s and APACS+ sequencing.”
Spomer adds the advantages of Evonik's plan include:
- The infrastructure is in place with IEMs to facilitate communication between the legacy APACS+ and PCS 7 AS410H controllers, utilizing a common PCS 7 OS HMI
- Migration path forward is promoted during the gray phase
- HMI functions implemented via SFC visualization faceplates are now auto-generated from the PCS 7 configuration
- Removes up to two times the implementation cost of LLD via detailed engineering labor reduction
- SFC type can be applied to multiple unit operations requiring same sequence
The disadvantage of Evonik's philosophy is that the overall implementation is initially more complex than before. Plus, to insure communications and cycle time synchronization around our process, we decided to hardwire the QUADLOG I/O into the PCS 7 system where critical communications were required.
Steps to implementation
Spomer reported the vital pieces in Evonik's column start-up and sequential controls upgrade are:
- I/O communication from APACS+ are setup properly
- I/O communication to the PCS 7 controller are ready to receive the data
- Performance requirements are met including scan rates and cycle times for the passing of the data and new configuration execution
Benefits and savings
Spomer added that implementing SFC functions on Evonik's HMI will save an estimated 500 man-hours due to:
- Savings on a per sequence basis because multiple sequences will now be identical
- No sequence recreation from APACS+ to PCS 7 once ACM controllers are removed
- LLD being phased out by SFC/CFC to allow for programming and HMI advantages
"The value gained during gray phase of migration includes linking phases together with configuration, and promoting our new philosophyin the plant, putting new I/O as PCS 7 I/O," added Spomer. "During phase 2's piecewise I/O hardware conversion, we'll easily stage-swap I/O, and there will be minimal programming necessary outside of channel driver software."
In addition, Spomer added that SFC HMI's advanced process library (APL) faceplates provide a significant new advantage for operators to run successful sequences, while SFC code enables APACS+ I/O to PCS 7 I/O transitions without major, future reconfiguration. "We're also saving on engineering configuration costs by using SFC Type bulk engineering capability," he added. “The SFC HMI faceplates today provide operators with graphical and numerical information of where they are in the process without a need to view the engineering logic – which can help reduce cycle times and improve safety. SFC Types, once implemented, will now be used for HMI graphic process visualization in a future training system with Siemens SIMIT simulation software that we'll put in next year to train future operations exercises.”