In Antwerp, Evonik recently successfully tested the ring topology for Profibus and Profibus PA, which is available with the new Version 7 of Simatic PCS 7.

Evonik Industries is a modern industrial group based in Germany, with business activities all over the world. In its three business areas of chemicals, energy, and real estate, Evonik occupies leading market positions. Evonik concentrates on steadily improving its market and customer focus as well as on operational excellence, establishing an even stronger presence in attractive growth regions, and focusing on the impetus generated by innovations.

At its production site in Antwerp, Evonik runs two facilities for the synthesis of hydrogen peroxide. Hydrogen peroxide is an environmentally friendly chemical that is used for various oxidation reactions, wastewater treatment, waste gas scrubbing, and disinfecting applications. Both synthesis facilities are supplied with hydrogen by pipelines; the hydrogen is then turned into hydrogen peroxide in a multistage process. The plant facility also includes two tank farms for intermediate storage of the hydrogen peroxide in different concentrations, as well as a dispatch department.

(Photo: Evonik Industries)

Targeted change to fieldbus architecture

At the Antwerp site, Evonik is in the process of gradually changing over the communication at the process level to fieldbus technology. Fieldbuses are becoming increasingly established in the chemical industry because of the time and cost savings due to lower installation expenses, lower hardware costs, and extended diagnostic possibilities. Fieldbus systems such as Profibus also enable generally higher performance than classic alternatives such as Hart communication.The unrestricted availability of the process control system and the related communication infrastructure is top priority in the hydrogen peroxide production plant. That is why Evonik modernized the process control technology with Simatic PCS 7 in the course of changing over to the fieldbus system and implemented the new version of PCS 7, which supports a ring topology for both Profibus and Profibus PA. This produces consistently redundant wiring at the fieldbus level, contributing significantly to plant availability. A line break in the fiber-optic cables laid in the area of the production plant no longer leads automatically to a partial or total breakdown in fieldbus communication.

This redundancy concept is relatively new and plugs a previous gap in fieldbus communication for process automation. The fieldbus is set up with coupler and media redundancy, whereby the connection between the PA network to which the individual field devices are connected and the master Profibus infrastructure is made via DP/PA couplers. These couplers have an integrated diagnostic-slave function and therefore support standardized fieldbus diagnosis from the control center.

Evonik also tried out a new connection technique at the process level. Evonik previously used PA field distributors with M12 connectors and had the problem of short circuits and electrolysis effects caused by penetration of the connectors by water, which kept causing equipment failures. The cable screw connections of the Simatic AFD active field distributors for connecting the main cable and the stub cables, in contrast, have proven to be ideal for use in harsh environments. There has not been a single fault caused by water penetration since their commissioning nine months ago.

Pilot project completed successfully

For Evonik, this first use of a Profibus PA ring was more or less a field trial under production conditions, and the experience to date is all positive. The entire system operates robustly and without any significant problems. The complete project execution, up to commissioning, was a time- and cost-saving enterprise.

(Photo: Siemens AG)

Redundancy in Profibus PA

With the new Version 7 of Simatic PCS 7, a redundant Profibus PA network can be set up, thanks to a newly developed concept that consists of couplers and intelligent field distributors as hardware. Active field distributors (AFDs) integrate Profibus PA field devices via four short-circuit-proof spur line connections in a Profibus PA ring with automatic bus termination. Hot swapping of an AFD is possible, and correct functioning of the Profibus PA devices on the AFDs is not influenced by this. The Profibus PA ring is connected to two FDC 157-0 DP/PA couplers of a DP/PA router, which can be operated on a single or redundant Profibus network.

Advantages of ring architecture:

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