The drive to increase the use of recyclable materials into hot mix asphalt is well known to the industry and aligns with carbon reduction goals. But in many respects Australia lags behind the world in both allowing the use of high recycled content asphalt through modern specifications, and also the plant technology that can make it a reality.
Initially driven by an inherent quest to innovate, and subsequently emphasised by strict new regulatory emissions requirements in its home country, German company Benninghoven has developed and implemented a solution to optimise recycled content in asphalt whilst also maximising the use of recycled materials. That solution is the hot gas generator concept employed on its Recycling Priority Plant – or RPP model asphalt plants.
Benninghoven’s hot-gas generator technology, as employed on their RPP plants, allows fresh asphalt mixes to contain over 90 per cent reclaimed asphalt – more than with any other recycling system on the market.
Australian producers using modern style asphalt plants can typically introduce anywhere from 15 to 50 per cent reclaimed asphalt pavement (RAP) in their mixes. This is achieved by a combination of dryer injected recycled material and some more sophisticated plants adopting direct steam-controlled entry into the pugmill.
Achieving RAP percentages higher than 50 per cent creates a challenge – to exceed 50 per cent RAP typically forces producers to use a direct RAP heating process, whereby a burner is installed to a parallel drum using a direct flame method. This process cannot heat the RAP to the desired temperature. It also degrades the bitumen and comes with high maintenance loads as the build up inside the drum produces high emissions. In Germany, this parallel flow drum technology has been outdated for many years.
Benninghoven has overcome these issues through the introduction of a high-tech hot gas generator (HGG). The hot gas generator heats RAP using super-heated air that is recycled over and over. This technology has been with Benninghoven for more than five years and undergone rigorous testing and refinement.
The HGG uses counterflow drum technology that allows the RAP to be gently heated to bring it up to a usable temperature without direct flame heating. The HGG also utilises the very latest in lifter design that eliminates the vast majority of the cleaning requirement. The process avoids the material being exposed to burner flame, which greatly reduces emissions. As a result, the virgin material does not have to be added to the mixing process and overheated in order to reach the required final mix temperature level (around 140°C to 180°C for hot asphalt). This saves a significant amount of energy in addition to greatly reducing emissions.
Rob Messner, Sales Lead for Benninghoven in Australia and New Zealand, explains this further.
“In a traditional plant, the RAP with adhering bitumen would be ‘burned’ by direct firing. But with the hot gas generator, the RAP is heated indirectly to gently bring it to the optimum processing temperature,” he explains.
“This technology therefore enables much higher percentages of RAP to be incorporated than is currently possible with most of the asphalt plants operating in Australia.”
Secondary benefits: emissions reduction
As a further benefit of the hot gas generator technology, the process of recycling the heating air over and over further lowers the emissions by burning most of the hydrocarbons contained in the exhaust gas flow. In Germany, this means that the plant emissions are kept well within the requirements imposed by the TA Luft regulation – the regulation covering air quality requirements from stationary sources.
Real world experience shows thats plants equipped with the hot gas generator have reduced emissions well below the TA Luft requirements for many years to come. With the current trend toward achieving a ‘net zero carbon future,’ this technology can enable current asphalt producers to take a material step toward achieving that goal.
Under the new Luft regulations in Germany, asphalt plants are required to have real time monitoring of emissions. Any operation of the plant outside the regulation limits are immediately transmitted to the authorities.
Whilst this type of compliance monitoring is not yet required in Australia, it is easy to envisage a time in the years ahead as the drive to reduce emissions gets into full swing where this could become a reality. The mere thought of that happening may create some concern to asphalt producers today, according to Messner.
“The good news is that Benninghoven has a solution available that will not only comply with a similar regulatory mandate, but also enable a potential doubling of RAP content from what is commonly achieved in Australia now,” Messner says.
Planning for the future: new plant or staged upgrade
Recognising the current local environment and also what may lay ahead as far as regulatory and specification requirements go, Messner says Benninghoven has designed a staged approach to adopting the RPP technology.
“Someone looking to get a new Benninghoven RPP asphalt plant can procure a city class RPP 3000 Plus or 4000 today that will enable up to 40 per cent RAP production using the established process. However, due to the design of the RPP plant, the hot gas generator and the related elements can be retrofitted at a later date to turn that facility into an advanced high tech RPP/HGG facility capable of 90 per cent plus recycled content, reduced emissions, and greater production flexibility,” he explains.
“This is a great option for future proofing a near term asphalt plant investment, while offering potential owners a level of flexibility going forward that is debatably unmatched by other offerings available today.”
Messner says the latest RPP asphalt mixing plant is a direct result of Benninghoven’s focus on innovation.
“These advancements are the direct result of the innovation focus of industry leader Benninghoven, a Wirtgen Group company. Benninghoven is known for taking the lead, producing cutting edge technology through research, development and testing, then making it available on a global level, demonstrating excellence in engineering that we expect to see from a German company,” he says.
“Benninghoven also understands that the high RAP capability is not for all producers. So, we continue to update and advance our plant portfolio, keeping quality, technology and efficiency at the fore front.”
Further information is available from: www.wirtgen-group.com
This article was originally published in the November edition of our magazine. To read the magazine, click here.