Sustainability enabled hot mix plants a must for today and a bright tomorrow
Much before “sustainability” became a buzzword in the industries world over, the asphalt industry especially in the west, had already initiated research and field trials that have constantly ensured the viability of asphalt as an environmentally sound construction material.
MAC, which specially features a dryer drum positioned alongside the bag filter and filler storage unit
The main reason for this runaway success is due to the asphalt mix’s inherent recycle-ability. Asphalt pavement is unique not only in its recycle friendly nature but also its renewability. It is comprised of approximately 95 % aggregates (crushed rocks and sand) and about 5 % of bitumen.
When asphalt pavement is reused in a new asphalt mix, just as the old aggregates become part of the aggregate content of the new mix, the old bitumen is also rejuvenated and becomes an active part of the bonding glue that holds the new pavement together, resulting in preserving another valuable natural resource. These features and others make asphalt pavements a very unique material for recycling. No doubt today in the west it is the most recycled material. America alone, recycles around a whooping 100 million tons plus of old reclaimed asphalt road pavement with over 60 million tons reused in new asphalt mixes.
The Road Ahead
Unlike the west which enjoyed some breather to bring up their asphalt plants to meet the rising environmental needs, India definitely will not be able to enjoy any such luxury of time.
The rising global concern and pressure, due to the serious effect of climate change being experienced globally and the necessity to be environmentally friendly will force asphalt producers in India to jump the learning curve and deliver asphalt mixes which are sustainable. The legislation would be easy to bring in, however most asphalt mix producers, will not find it easy to produce such mixes, if the investment in to the equipment they make in today, is not geared to face such challenges.
Ongoing concerns about the environment and sustainable development have led to significant changes in the design of hot-mix asphalt plants in Europe.
Some of the most significant developments of recent years include:
- Improved control of emissions, including dust, with ever-diminishing tolerance levels and the control of volatile compounds such as PAH and Nox.
- Recognition of the contribution of certain gases, such as CO₂ and COx, to the greenhouse effect.
- The desire to develop designs that lead to significantly reduced energy consumption, both for heating purposes and for the drying of aggregates.
- The recognition of depleting natural resources, increasing a need for recycling, low carbon mixes etc…
A very notable example of one of these technical solutions is the Marini Asphalt Compact Plant (MAC) concept, which specially features a dryer drum positioned alongside the bag filter and filler storage unit, as shown in the figure.
The latest MARINI concept resulted in a plant with absolutely no duct between the filter and dryer unit other than a smartly designed pre-separator and a filler recovery system that is gravity-fed.
These well thought designs coupled with a very efficient waste heat recovery system resulted in lower energy requirements for heating, such as a 4% saving for the burner due to a 10°C reduction in the heating temperature, which translates to around 88 000 ltrs of fuel & subsequent reduction in carbon emissions annually under Indian production conditions.
A strategically placed filler system which reduced the material transfer conveyors and moving components led to a 45% reduction in kW over this circuit.
Another significant saving stems from the recovery of heat by induction, which is transferred to the top of the drum towards the filler storage unit. Heat losses were further curtailed by energy conserving designs on various units of the asphalt plant.
Massive reduction in Fuel Consumption and Carbon Emissions
Marini MAC concept raised the industry’s bar higher by using a special Flame Carving system on the burner unit. A dual air burner with Blue air assist combustion technology is delivering Indian contractors a massive saving of up to 600 000 ltrs of fuel annually.
The intuitively designed dryer internals coupled with this latest burner technology, adaptable to numerous greener fuels guarantees conformance to very strict emission levels.
Recycling from 45 – 100 %
These massive savings in fuel and carbon emissions are further extended to the next level by the ability to process high content recycled asphalt. The standard Marini MAC concept can process up to 45 % Recycled Asphalt. With an easy to add-on module, the MAC, can enable contractors to use up to 100 % recycled asphalt pavements, as shown in the photo.