Double Barrel® Drum Dryer / Mixer

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Combination Aggregate Dryer/Drum Mixer

Astec brings you the Double Barrel dryer/drum mixer, the mixer of choice over any other. The Double Barrel dryer/ drum mixer combines the latest in hot mix technology with other great Astec features. Get guaranteed productivity and top quality mixes while keeping operating costs per ton of mix low and meeting the most stringent environmental codes. Stationary, relocatable and portable versions all perform to the same high standards.

Available In Three Styles

Need the quick setup and mobility of a portable plant, or the flexibility and operating capacity of a stationary? Maybe the best of both? Astec gives you the freedom to design a hot mix facility to your precise needs. The Double Barrel dryer/drum mixer can be configured for the three styles of Astec asphalt plants: stationary, relocatable and portable.

Features & Benefits

  • The Double Barrel's unique design uses the entire drum for production of RAP to 50%
  • Sequential mixing allows better temperature equalization throughout the mix
  • Astec patented V-flights for veiling of material over a wide range of tonnages
  • Virgin aggregate temperature is measured to automatically adjusting the burner
  • RAP, bitumen (AC), and fines enter without contact to the dryer flame
  • RAP enters the mixing sequence first where it contacts the super heated virgin materials Fines are introduced to the mixing process last for proper coating
  • Adjustable mixing paddles for flexibility
  • Self cleaning drum reduces buildup in the mixing chamber
  • Hydraulic door provides safe access to the outer mixing chamber from the ground
  • The outer chamber is lined with insulation to capture heat from the drying process
  • Chain or trunnion drive configurations are available
  • Compatible with the Astec Green Pac warm mix systems

Sequential Mixing

    Built For Efficiency

    No matter what style or facility configuration you have, you can take advantage of the most thermally efficient dryer/mixer available – the Astec Double Barrel®.
      • The stationary style is available in a range of capacities from 200 TPH to 600 TPH.

      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.

      • Setup is simpler and optional future plant movement is easier with a relocatable design.

      Efficiency Data

      Virgin Mixes

      • The Double Barrel dryer/drum mixer 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.
      • The portable Double Barrel dryer/drum mixer can be readied for travel in a few hours.

      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. Astec baghouse stack emissions meet federal standards even when high temperature (330°F) mixes are made.

      • Thick insulation installed underneath the stainless steel outer shell helps prevent heat loss.

      Minimize Oxidation

      Oxidation in the mixing chamber is minimized in the Double Barrel drum mixer. As recycle heats in the mixing chamber by contact with the hot aggregate, moisture in the recycle is driven off as steam. The steam atmosphere in the mixing chamber allows very little free oxygen and gas movement. Although steam may react with the liquid asphalt and vaporize some light oils, these vapors are drawn into the burner flame and incinerated. The same is true for emissions created by additives to Superpave or other modified mixes.

    The Drying Process

    The Astec Double Barrel® drum mixer and control system are designed to move aggregate effortlessly through the mix process with maximum efficiency.
      • Aggregate enters the drum through an inlet chute designed to keep material flowing.

      Free Flow Into The Drum

      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.

      • A look at Astec state-of-the-art flighting from the aggregate end.

      Flights Serve Three Functions

      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.
      • A view of combustion flights located near the burner end of the dryer.

      Measure Actual Temperature

      Once heated and dried, the aggregate leaves the drying chamber and enters the mixing chamber.

      At this point, an infrared sensor measures the temperature of the hot aggregate and automatically adjusts burner output to keep aggregate at the required temperature.

      This unique Astec feature makes it easier for you to control mix temperatures and to turn out mixes that conform to specifications.

      • The aggregate temperature is measured as it leaves the inner drum through the aggregate exit openings with reinforced wear plates.

      Control Systems

      TCII or PMII systems control and monitor proportional control of aggregate feeders and the blending of asphalt, recycle, shingles, and additives. Both systems work with WM2000 which controls silo load out, inventory, and sales transactions. Upgrade to TCII controls for more flexibility and expansion options.

    The Mixing Process

    The Double Barrel® dryer/drum mixer's long mixing chamber and stationary outer shell provide the ability for adding ingredients sequentially. This unique design produces a more consistent mix.
      • The sequential mixing process is especially well suited for making mixes with RAP.

      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.

      • Liquid AC enters the drum when aggregates and RAP have reached the proper temperature.
      • Mixing paddles ensure that liquid AC thoroughly coats all of the aggregate.
      • Baghouse fines enter the mix last so they don't soak up all of the liquid AC.

      Mix Long For A Better Product

      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 AC

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

      Embed Fines Into The AC 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 AC because the AC has been well distributed before fines are added.

    Run Clean even with 50% RAP

    The innovative Astec Double Barrel® dryer/drum mixer is designed to reduce emissions and minimize oxidation in the mixing chamber. The result is a better mix and easier permitting.
      • The RAP by-pass chute is incorporated to easily divert RAP to a waiting loader or truck during plant shut-down, or calibration.

      RAP Inlet

      RAP enters directly into the mixing chamber and does not contact the hot gas stream of the dryer. Because the RAP is heated by the hot aggregate, not the burner, the Double Barrel dryer/drum mixer runs clean, even at 50% RAP.

      • As recycle heats in the mixing chamber by contact with the hot aggregate, moisture in the recycle is driven off as steam. Steam displaces oxygen in the mixing chamber reducing the potential for mix oxidation.

      Hydrocarbons and Steam

      There is a continuous release of steam as the RAP is introduced and heated. This is one of the keys to the success of the Double Barrel as a processor of RAP – steam blankets the superheated virgin aggregate and RAP displacing the oxygen. As a result there is less oxidation of the mix. As the RAP dries, blue smoke emissions can also be produced along with steam. Steam and blue smoke are pulled into the burner flame by the baghouse fan. The hydrocarbons in the blue smoke are incinerated while the steam simply passes to the baghouse and out of the exhaust stack.

    Four Burner Options

    Astec burners offer the latest in reliable burner technology combined with complete one-source responsibility.
      • The Whisper Jet® burner uses high quality, field-proven components.
      • The Phoenix Talon burner delivers low emissions combined with energy efficiency.
      • Choose the Phoenix Phantom burner if achieving the lowest possible emissions is important.
      • Take advantage of one of the lowest cost fuels available with the Phoenix Coal burner.

      The Astec burner group engineers the burners to customer specifications and manufactures each in a state-of-the-art facility. Prior to shipment, each burner is tested on one of Astec’s tri-fuel (oil, gas & coal) test stands to ensure fast and easy start-up at installation.

    Built to Last

    After millions of tons of mix production, the Astec Double Barrel® dryer/drum mixer proves itself to be the most reliable and lowest maintenance dryer/drum mixer available to producers.
      • The chain drive motor features fluid couplings for reduced motor loads at start-up.

      You Won't Find A Better Drive System

      Saddle chain drives have proven to be the most reliable method of driving a drum. The saddle chain drive is outfitted with heavy-duty roller chain, including offset sidebars and case-hardened bushings. Astec heavy-duty drive components are made to last.

      • Thrust rollers restrain the drum before and after.

      Trunnions And Thrust Rollers

      Four trunnions and two thrust rollers keep the drum aligned and in position. Astec trunnions are made of solid-steel hardened to 421-512 Brinell. They feature extra-large, double-spherical roller bearings of the same type used for railcars. The trunnion bearings are guaranteed unconditionally for a life of one million tons of mix. Thrust rollers are scrub-resistant for reduced roller wear.

      • Trunnions are super heavy and easy to adjust.

      Take Trouble Out Of Trunnion Alignment

      Each trunnion base is angled to the frame so that a dowel pin in the base is in line with the exact center of the drum. The trunnion base pivots around the pin, making it easy to keep the trunnion aligned with the drum while making thrust adjustments. Good trunnion alignment means better performance and longer equipment service life.

      • Tires are attached by butterfly spokes which isolate them from drum expansion.

      Drum Tires Last Long And Run Smoothly

      Two extra-large, solid-steel tires encompass the inner drum and support the Double Barrel dryer/drum mixer. They attach to the drum by means of butterfly spokes that isolate them from drum expansion. This attachment method has proved reliable in millions of tons of operation. The drum can expand without distorting and without stressing the tire and its attachments. Hot-forged from solid billets of 1030 carbon steel, the tires provide a yield strength of 90,000 psi with a Brinell hardness of 220-260. Precision-machining to a tolerance of 30 thousandths of an inch and with a 250 root mean square (RMS) finish gives you ultra-smooth operation.

    Superior Design

    The Astec Double Barrel drum/dryer mixer is constructed to the highest quality standard with proven wear materials and easy access for maintenance.
      • A centrally located powerhouse shortens cable runs for easier handling.

      Crews Appreciate Pre-Wiring

      Relocatable and portable facilities are pre-wired and pre-piped for a quick and easy setup. The main power panel is centrally located in the facility, and components and wiring are designed for short cable runs, making it easier to handle cables in the field.

      • The interior of the dryer drum can be reached by a convenient access door on the inlet breeching.
      • Conveniently located access doors provide for easy maintenance for Astec burners.

      Access Is Safe And Easy

      No other drum mixer gives you complete access to the mixing chamber from ground level like the Double Barrel dryer/drum mixer. A large door rises hydraulically for full access to the entire length of the mixing chamber allowing you to be able to service mixing shanks and tips from the outside of the drying drum shell. A separate, smaller access door allows quick inspection of the mixing chamber. The interior of the dryer drum is reached through an access door at the inlet breeching. Key maintenance items on the burner, unlike those on a conventional counter-flow mixer, are located outside. They stay cool and are easily reached for service or inspection.

      • All components, like these mixing paddles, are constructed to the highest quality standards.

      Lower Your Maintenance Cost

      The cost of maintaining the Double Barrel dryer/drum mixer is comparatively low because Astec uses proven wear materials. Ni-hard mixer paddle tips and wear plates in the mixing zone stand up to ton after ton of abrasive material. The burner end of the drum is fabricated from Cor-Ten®, a high-strength, low-alloy steel for superior heat resistance. The mixing chamber is made from structural-quality carbon steel and lined with 3/4-inch Ni-Hard wear plates.

    Anatomy of the Double Barrel

    The Astec Double Barrel dryer/drum mixer offers low cost performance in stationary, relocatable and portable versions.
    Illustration showing the inner drum drying zone of the Astec Double Barrel

    Illustration showing the outer shell mixing zone of the Astec Double Barrel