The Double Barrel dryer/drum mixer combines the functions of a dryer and a continuous-process mixer in one compact, efficient system. Drying of the virgin aggregate is the first step in the process and takes place in the inner drum. Mixing of aggregate and other ingredients follows, in the outer, stationary shell.
Astec has just launched the new Double Barrel® HR which facilitates the mixing of higher levels of RAP and Virgin Aggregate in a specially designed Double Barrel®, which also encompasses the mixing of the RAP/Virgin mixture with bitumen and additives in an external twin-shaft synchronous mixer.
The benefits of the Double Barrel® HR
- 60%+ RAP at 5% RAP moisture
- 70% RAP at 3% RAP moisture
The Double Barrel® features state of the art drying technology (V-PAC™) which includes variable frequency drive, V-flights, exhaust temperature control and optional WMA system.
Virgin material enters the dryer and is dried in the inner drum over 160-200 seconds.
Just beneath the burner cone, the virgin material drops out of the dryer into the mixing chamber where RAP is added. The virgin aggregate and RAP are gently and thoroughly mixed over 60-87 seconds. As the RAP is introduced, there is a continuous release of steam as the RAP is heated. This is one of the keys to the success of the Double Barrel as a processor of RAP; the steam which is produced blankets the superheated virgin aggregate and RAP displacing the oxygen and resulting in less oxidation.
Fines are introduced further along the mixing chamber where they incorporated into the mix over 45-60 seconds.
The premixed virgin aggregate/RAP/fines blend then enters the external twin-shaft synchronous mixer where it is vigorously mixed with bitumen.
The external mixer provides many benefits, allowing the addition and mixing of additives. It provides product flexibility – production of emulsion mixes, coloured mixes, and ‘cold mix’ with optional components. It also provides process flexibility – allows for additional mix time and anticipation/control of process temperature excursions.
Emissions are dealt with effectively as steam and any blue smoke passing to the bag house are consumed by the burner flame. Providing high RAP addition with clear exhaust.
Due to the virgin material temperatures required for high % RAP addition, as an additional process safety measure, a temperature suppression system which blankets both mixing chambers with inert gas (steam) can be fitted.
DBHR Drum features
V-PAC™ Stack Temperature Control (Patent Pending)
- Provides positive control of bag house temperature
- Enables running mixes ranging from virgin WMA to high RAP and open grades mixes without flight changes
External Synchronous Twin-shaft Mixer
- Allows for greater separation of bitumen from hot virgin aggregate
- Allows for even longer mixing of hot virgin aggregate/RAP in mixing chamber
Combustion Zone Drum Enhancements
- Shell material change allows for higher temperatures at high %RAP
- Flight material change allows for higher temperatures at high %RAP
- Flight design change eliminates shell wear and protects shell from radiation
The stainless steel drum shell allows higher temperatures when running high % RAP. The stainless steel combustion flight incorporates a special flight design which eliminates drum shell wear, protects the drum shell from radiation and maximizes radiation input to the virgin aggregate.
Patented Astec WMA System (part of V-PAC™
- Enhanced mix compaction and temperature reduction with no additives
What is the V-PAC™ Stack Temperature Control?
Incorporating the unique Astec V-flight, a variable frequency drive (VFD) drum drive is utilised to balance the drum exhaust temperature. VFD allows the operator to control veil density by changing drum rotational speed. Stack and mix temperatures can be controlled by increasing or decreasing the drum speed
- Increase in speed will decrease stack temperature
- Decrease in speed will increase stack temperature
A feedback drum speed control is also specified to hold stack temperature steady.
The Astec V-flight has a v-shaped notch that allows the flight to more evenly veil at both high and low tonnage rates. The flight is taller than ordinary flights so that the entire flight carries a similar amount of material when completely full.
- Higher RAP % results in lower tonnages through drying zone, causing flights to only partially fill
- V-flights allow veiling over a wider range of tonnages
Available in the UK
In the UK, BG Europa (UK) Ltd has retained strong links with Astec Inc., co-ordinating with them to promote their range of equipment in the UK and as stockists of genuine Astec parts.
BG Europa (UK) Ltd was established in 1988 from the Barber Greene England company following Barber Greene’s acquisition by Astec. Technology and expertise existing within Barber Greene at that time was incorporated within BG Europa (UK) Ltd. This expertise has been utilised to develop equipment integrating new technologies whilst retaining the traditional quality and dependability of Barber Greene.
BG Europa (UK) Ltd
Suffolk CB8 8PQ
+ 44 (0) 1440 821155
+ 44 (0) 1440 821156