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• Astec Double Barrel

ASTEC DOUBLE BARREL

The Double Barrel dryer/drum mixer combines the latest in hot mix technology with other great Astec features. You'll get guaranteed productivity and top quality mixes while keeping operating costs per ton of mix low and meeting the most stringent environmental codes.
Efficient drying followed by thorough mixing is made simpler with the right system. 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.

LOWER YOUR COST PER TON

What allows the Double Barrel dryer/drum mixer to make mix at lower cost compared to other drum mixers?

There are two things:

First, a unique design uses the entire drum length for drying. Other systems have to utilize one end of the drum as the mixing chamber, making the drying portion shorter. They then have to use higher temperatures to compensate for the shortened drying chamber. Astec's longer drying times let you dry more efficiently.

Second, the material in the mixing chamber captures heat radiated from the drying process. A thick layer of insulation surrounded by the stainless steel shell holds heat in as well. No energy is wasted.

EFFICIENCY DATA

Virgin mixes:

• The Double Barrel makes 9% more tons per hour (tph) than a conventional counter-flow drum mixer and burns 3% less fuel.
• The Double Barrel dryer/drum mixer produces 15% more tph than a parallel-flow drum mixer and burns 5% less fuel.

Mixes with 50% reclaimed asphalt product (RAP):

• The Double Barrel dryer/drum mixer produces 14% more tph than a counter-flow mixer and burns 12% less fuel.
• The Double Barrel dryer/drum mixer makes 24% more tph than a parallel-flow mixer and burns 19% less fuel.

DRYING

The drying process begins when the virgin aggregate enters the inner drum through a rubber seal and gravity chute. The seal restricts air entry into the drum while allowing the aggregate to pass through. The angle of the clad lined inlet chute keeps material flowing freely into the drum.

Three different types of flights move the material through the drying chamber. They are especially designed for three separate functions.

• Conditioning flights break up any clumps or sticky material as the aggregate enters.
• Showering flights make sure that the material is veiled evenly through the hot gas stream.
• Combustion zone flights prevent aggregate from impinging on the flame while spreading the material to maximize radiant heat transfer.

SEQUENTIAL MIXING

To make good mix on a consistent basis, you have to add materials in the right order and at the right time. That's where you can rely on Astec's exclusive sequential mixing process. Ingredients are added to the hot dry aggregate in an order that allows better temperature equalization and even distribution of all particles throughout the mix.

Astec's extraordinarily long mixing chamber allows long mixing times. Long mixing times, together with Astec's sequential mixing, ensure uniform and consistent incorporation of all mix materials. So even if you're dealing with high raw material variance or heavily modified or sticky mixes, the Double Barrel dryer/drum mixer helps you produce homogenous, strong mixes.

Add Recycle First

First in the mixing sequence, recycle material is added to the aggregate in the mixing chamber. Recycle enters into the mixing chamber through a rubber seal. Recycle, which may be RAP, roofing shingles, crumb rubber, or a mixture thereof, is heated by contact with the hot virgin aggregate. When running recycle, the virgin aggregate is heated to higher temperatures than usual.

Coat All Aggregate With Bitumen

At the point where virgin and recycled materials are at the proper temperature and thoroughly mixed, bitumen is injected into the mixing chamber. The 4-foot long bitumen manifold thoroughly douses the mix. As the mix moves through the mixing chamber, it is continually stirred by mixing paddles.

Embed Fines Into The Bitumen Layer

Baghouse fines and other additives enter the mixing chamber and become embedded in the thick layer of asphalt coating the rock. Astec's sequential mixing keeps fines from soaking up more than their share of bitumen because the bitumen has been well distributed before fines are added.

RUN CLEAN, EVEN WITH 50% RAP

RAP enters directly into the mixing chamber and does not contact the hot gas stream of the dryer. This is an important advantage because the atmosphere in the mixing chamber minimizes emissions. The Double Barrel dryer/drum mixer runs clean, even at 50% RAP. Using recycle materials can produce significant savings without any loss of mix quality and without causing any visible emissions from the baghouse.

OPTION TO GO "GREEN"

The latest innovation from Astec saves energy and eliminates smoke and emissions without compromising mix quality. The optional Double Barrel Green System uses water to produce a foamed warm mix asphalt that is odourless, smokeless and longer lasting. Unlike other warm mix methods, the Double Barrel Green System does not require the addition of expensive commercial additives. Instead, the injection of water along with the liquid asphalt cement causes the liquid asphalt to foam and expand in volume. The foaming action helps the liquid asphalt coat the aggregate at a temperature that normally is in the range of 110 - 130˚C versus traditional temperatures of 150 - 170˚C.