Intelligent wiring

Dr. Christine Eckert

Back in 1912, Rudolf Diesel anticipated that the future of fuel would belong to vegetable oils. Now, almost 100 years later, biodiesel is the ultimate trend. There is a good reason for this: its production generates no waste and all by-products are re-used. It is biodegradable and does not harbour any risks for soil or ground water. As an additive, biodiesel improves the lubricating properties of conventional diesel fuels even in small quantities. Nordbrandenburger Umesterungswerke (NUW) in Schwedt/Oder is committed to processing raw vegetable oil, mainly from rape seed, into fatty acid methyl ester, otherwise known as biodiesel. 220,000 tons of vegetable oil and fatty acids a year will in future be transformed into 210,000 tons of this renewable energy source. Its by-products are approximately 15,000 tons of high quality glycerine, which is predominantly used by the pharmaceutical industry.

After a twelve-month construction period, the first stage of the production plant was commissioned in November 2005 with the ester transformation process. From January 2006 the glycerine distillation line was also up and running. Integration with the media of the neighbouring PCK refinery ensures high supply security. This makes it possible to use the existing infrastructure to transport raw materials and products, which are delivered and dispatched cost-effectively and in an environmentally friendly way by rail. The proximity to the refinery has another site advantage: the biodiesel produced can be used there directly as an additive. The modern production plant is designed to emit a minimum amount of contaminants into the air and water. The company has invested a total of approximately 42 million euros in the new biodiesel facility. The technical service provider Elcon automation & engineering supplied the plant’s entire automation technology from the initial planning through engineering to commissioning. The Schwedt plant has some 1300 I/Os, of which 530 are Profibus PA measuring points.

The decision in favour of Profibus PA was not a difficult one for the operator. The Managing Director of NUW, Theodor Niesmann, was already familiar and experienced with Profibus technology from his former position as operating manager of a sister company. It was the task of the engineering service provider to select the supplier of the fieldbus installation system. He was particularly convinced by the thoroughness of the products and services from Pepperl+Fuchs. “The decisive factor was that we could build a uniform and homogeneous system architecture with FieldConnex for bus integration in hazardous areas and the high-power trunk concept using field barriers“, stresses Thorsten Bille, Managing Director of Elcon automation & engineering. “At the time there was no other manufacturer capable of offering all the necessary Profibus PA interface components from a single source.“ Another important aspect was the high standard and commitment of P+F’s after sales support. The manufacturer’s competent hotline permits rapid troubleshooting whatever the problem. The installation technology is also scaleable and thus especially variable. This will benefit the client, for example, if the solution needs to be expanded at any time in the future. Thanks to FieldConnex and the SegmentChecker planning software, the company was able to carry out sizing flexibly on site. The software assists with capturing and evaluating the electrical and physical conditions. It can check quickly and easily whether the energy balance is correct and sufficient for the intended cable length and determine the magnitude of the actual voltage drop at the field barriers.

All components required for communication between the Profibus master and the connected slaves are matched in the FieldConnex system in such a way that the desired topology can be built in a very short time in a modular fashion. Limitations often arise if the supply system power is too low, but because FieldConnex combines intrinsic safety with increased safety, sufficient power can be supplied via intelligent modules like the segment transceiver. The segment transceiver is also responsible for establishing the connection between the Profibus DP of the control system and the Profibus PA in the hazardous area. Due to its modular design, several PA segments can be connected to the Profibus DP extremely efficiently via a single gateway. The supply system power is then directed via the high-power trunk (type of protection Ex e) to the field barriers and converted to up to four intrinsically safe outputs for field devices in explosion zones 1 and 0. Additional components like valve control modules, isolation amplifiers and various gateways enable individual fine tuning of each system.

One important advantage of Profibus PA technology is its ability to transfer additional measurements besides the primary ones. The mass meter, for example, does not only provide the mass but also the density or temperature. The digital communication protocol transfers the data from freely configurable counters, which can be used directly for dosing tasks. If conventional technology is installed, extra hardware such as HART-capable I/O cards is needed to transfer these variables. As a welcome side-effect, the standardised transfer of these supplementary values also cuts the costs for engineering in the control system. The fieldbus can do much more than this, however: thanks to the diagnostic options provided by the Profibus protocol, many problems can be detected at an early stage. This reduces outages and increases plant availability.

All field signals in the hazardous area for which there is no Profibus PA interface are bundled by the remote process interfaces (RPIs). Conventional field devices can thus be used in a fieldbus environment. Besides the classic commercial arguments of price and delivery times, the RPIs also make technical sense. RPIs are very straightforward to install. They are mounted on a special rail referred to as a power rail. All supply and data lines are automatically connected. The components and design of the RPIs (power supply module, power rail, etc.) are either identical or very similar to the main PA components. The switch cabinet engineering is simplified and its design standardised. The same applies to the RPI signal modules, which are identical to the manufacturer’s conventional switching and isolation amplifiers. The uniform supply, connections and size also speed up familiarisation, engineering and cabinet fitting. However, the RPIs are equally convincing during operation: the components can be hot-swapped without any adverse effects. In addition, they offer a variety of diagnostic options by leveraging the functionality of the HART field devices connected to the remote I/Os. The power supply and the external and internal buses can be designed redundantly for maximum availability.

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FieldConnex

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Biodiesel