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Asphalt mixing plants

Benninghoven_Asphalt mixing plant #1

The trick's in the mix

Asphalt pavement is the go-to material in the road construction industry. To get a final product with just the right properties, you need flexible recipe processing and high-precision dosing. Benninghoven mixing plants get the right mix every time thanks to their sophisticated BLS3000 control systems, based on B&R's APROL process control technology.

Of the approximately six million miles of paved roads and highways across North America and Europe, between 90 and 95 percent are surfaced with asphalt. On top of that, you have all the asphalt used for parking lots and airport runways, or as sealant for fodder silos and insulation for residential buildings. This versatile material has a multitude of applications that impact virtually every area of our lives. In road construction alone, the many uses of asphalt call for a wide range of different mixtures. These include mixtures aimed at reducing noise pollution, porous mixtures for improved handling of storm water as well as more energy-efficient warm-mix materials that allow paving at lower temperatures. According to the German Asphalt Pavement Association, Germany alone lays around 50 million metric tons of asphalt per year, mixed in more than 700 plants across the country.

Asphalt mixing plants from Germany's Mosel region

In the town of Mülheim an der Mosel, Benninghoven builds the mixing plants needed to meet this tremendous demand. Now in its fourth generation of Benninghoven leadership, the company's 880 employees specialize in the manufacture of asphalt mixing plants, with more than 80 percent vertical integration. These plants are put to use all over the world. The largest of which, a two-tower plant in Finland, has been operating since 2009 with a total output of 720 metric tons per hour.

Benninghoven_Asphalt mixing plant #2
Mobility is a key requirement in hot recycling of damaged pavement. The mobile drum operates with a heated tilting hinge. Hydraulic legs provide precise vertical positioning. (Source: Benninghoven)

New challenges demand new ways of thinking

Benninghoven's success is based on constant observation of market trends and the continuous pursuit of technological improvement. Fifty years ago, there were no more than a handful of recipes to chose from – today the variations are countless. The aspects of environmental protection and conservation of resources are driving research into materials that can be processed at ever lower temperatures. The share of recycled material included in the mix has grown to over 90 percent. Special mixing techniques and additives allow for lower mixing and laying temperatures, which in turn improves working conditions, allows for cold-weather paving and makes the finished surface available for use sooner. In addition to being more environmentally sound, advanced production methods also improve the durability of roadway surfaces. New processes such as emulsifying the bitumen in water help improve both the energy efficiency of production as well as the quality of the mixture.

Modular process control system

The challenges of state-of-the-art asphalt mixing have led to a steadily rising degree of automation. Benninghoven recognized that its previous controller was no longer able to handle the increasingly complex requirements. "Even before we began our evaluation, it was clear that we would no longer be able to do without the functionality of a full-fledged process control system," recalls Hans Adam, head of Benninghoven's electrical engineering department. A primary focus during development was integrating the real-time system – i.e. direct control of the process – in order to handle the complex new recipes and ensure high-precision dosing and quality control. Another key requirement arose from the large numbers of individual software modules that would need to be mixed and matched to provide the required functions for any given project.

B&R's APROL process control tees it up

"We saw quickly that even a conventional process control system couldn't meet these requirements," explains Adam. "Then we came across B&R's APROL process control system and X20/X67 controllers at the 2008 SPS IPC Drives in Nuremberg. Even before B&R had finished their presentation, we knew APROL came very close to exactly what we were looking for."

The controller that Benninghoven developed around APROL, the BLS3000, is now a standard feature of every plant the company builds. The distributed architecture of the automation level and the excellent support for migration make it particularly well-suited for modernizing plants with outdated technology.

Modular structure eases development

Each of the plant's subsystems is defined as a technology module. The hardware designers are able to select freely from B&R's entire range of X20 and X27 components. The rugged X67 modules are particularly helpful since they eliminate the inconvenient control cabinet installation otherwise required in harsh environments. Thanks to jitter-free communication over the fast real-time POWERLINK fieldbus, dosing data can be transferred with more than enough precision and synchronization. The absolute freedom in the selection of a network topology further facilitates this approach. "What also spoke in favor of B&R was the fact that the system design wouldn't have to be reworked in the future to accommodate the safety technology we plan to add," adds Adam.

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The mobile mixing plant with a silo that holds up to 30 tons of material and can be loaded directly from a truck. (Source: Benninghoven)

"With our APROL-based BLS3000, we're able to meet the high demands on investment planning and provide the necessary transparency for documentation of internal processes." Hans Adam, Head of Electrical Engineering, Benninghoven GmbH & Co. KG

Complete in-house engineering safeguards know-how

On the software end, the individual technology functions are implemented in object-oriented form as hyper macros, all developed fully in-house. For the basic system functions, Benninghoven's developers drew from the extensive APROL function libraries, which allows them to profit from their continuous development and testing. "It was important that we keep our know-how in our own hands," says Adam, "because that's our key to differentiating ourselves on the market."

When a new plant is developed, engineers at various locations draw from the central database of software modules to assemble the functions they need. By providing this capability, APROL has the additional benefit of making teams more productive.

In the fast lane to success

Many of the functions introduced by Benninghoven are now being requested explicitly in the design specifications presented by construction firms – a fact that gives Adam and his colleagues confidence that they are on the right track. "When our plant control system is winning us large international contracts, that tells us we made the right decision."

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