ASTEC HOLDS KEY TO HIGH-RAP MIX PRODUCTION

In today’s market, many asphalt producers are producing a wide range of mixes at a single plant.

Switching between virgin and high RAP mixes, hot mix (HMA) and warm mix (WMA), along with significantly varying tonnage rates, can cause large swings in stack temperatures.

In today’s market, many asphalt producers are producing a wide range of mixes at a single plant.  Switching between virgin and high RAP mixes, hot mix (HMA) and warm mix (WMA), along with significantly varying tonnage rates, can cause large swings in stack temperatures. 

If these temperature swings exceed the limits of the Baghouse, adjustments to the flighting arrangement must be made to prevent any damage to the Baghouse. These changes can be costly and time consuming, especially if they are needed when the mix type changes.

To solve this problem, Astec has created the V-Pack™ Stack Temperature Control System.  The V-Pack™ System can extend the range of mixes that can be produced without requiring the flights be adjusted. 

The system’s unique drum “V-flights” has a deep V-shape and its use of Variable Frequency Drives (VFDs) provides control of the drum rotational speed which is the key to the control system managing an asphalt plant’s exhaust gas temperature and increasing overall efficiency.

The V-Pack™ Stack Temperature Control System automatically controls exhaust gas temperature across a range of mix types and operating conditions by making drum speed changes. 

The system keeps Baghouse temperatures relatively stable as the mix temperature changes and even as mix types change from hot mix to warm mix; from virgin to high RAP and from dense-graded to open-graded mixes. These kinds of production changes would cause Baghouse temperature changes of over 100° F (38° C) without the V-Pack™ Stack Temperature Control System.

The system uses the V-flights to produce a uniform veil of virgin aggregate across the entire drum, regardless of how full the drum is, the plant’s production rate or the RAP percentage used.  This is what enables drum speed changes to be effective as a means of controlling stack temperature. Since the V-flights shower uniformly without regard to how much material is in them, they never leave a hole in the veil.

The Astec V-Pack™ Stack Temperature Control System monitors the exhaust gas temperatures at the Baghouse inlet as the primary reference for control.  As the exhaust gas temperature rises, the control system checks it against a set point. 

When the temperature exceeds the set point, the control system speeds-up the drum rotation, controlling temperature to the set point. The drum speed can be varied by the system from a minimum of about seven rpm to a maximum of about 12 rpm (eight rpm is the normal speed for Astec drums without this system).

Applications of the V-Pack™ Stack Temperature Control System enable Astec to provide asphalt plants that produce mix with RAP content from zero to 70% without any physical changes to flights or other plant equipment and without loss of production rate capacity or fuel efficiency. 

Astec-equipped plants are also able to produce dense-graded virgin mixes and open-graded friction course with the same ease and efficiency.