Double Barrel® X™ Dryer/Drum Mixer

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Aggregate Dryer With External Asphalt Pavement Mixer

The Double Barrel X system runs mix with up to 50% RAP*.

The Double Barrel® X™ system separates the drying process from the mixing process, thereby providing a very reliable tool to be used for the purpose of recycling reclaimed asphalt pavement (RAP). With a Double Barrel X system, a plant can process both warm and hot asphalt mixes with up to 50% RAP content while maintaining zero opacity at the stack.

*50% RAP based on 5% RAP moisture

Features & Benefits

  • The liquid AC only enters at the mixing chamber, so virtually no build-up is produced in the dryer.
  • The outer mixing chamber on the dryer gently mixes recycle with dry hot aggregate maximizing heat and binder transfer between RAP, aggregate, and selected admixtures in a rarefied oxygen atmosphere.
  • The external mixer vigorously mixes virgin liquid asphalt cement, as well as other admixtures.
  • Counter-rotating mix paddles in the external pugmill increase mix agitation.
  • The plant can process asphalt mixes with up to 50% RAP* content while maintaining zero opacity at the stack. * at 5% moisture content

Double Barrel® X Relocatable (Up to 50% RAP)

Drum Size Mixing Chamber TPH (MTPH)
6’ x 33’ (1.8m x 10m) 19’ (5.8m) 200 TPH (181 MTPH)
7’ x 38’ (2.1m x 11.6m) 22’ (6.7m) 300 TPH (272 MTPH)
8’ x 41’ (2.4m x 12.2) 22.5’ (6.9m) 400 TPH (363 MTPH)
9’ x 47’ (2.7m x 14.3m) 22.5’ (6.9m) 500 TPH (454 MTPH)
10’ x 50’ (3m x 15.2m) 22.5’ (6.9m) 600 TPH (544 MTPH)

Double Barrel® X Portable (Up to 50% RAP)

Drum Size Mixing Chamber TPH (MTPH)
6’ x 33’ (1.8m x10m) 19’ (5.8m) 200 TPH (181 MTPH)
7’ x 37’ (2.1m x 11m) 19’ (5.8m) 300 TPH (272 MTPH)
8’ x 38’ (2.4m x 11.6m) 21’ (6.4m) 400 TPH (363 MTPH)

Double Barrel X

As aggregate enters the drum from the conveyor, it passes through the flop gate, which minimizes air leakage into the drum. From there, it passes through a series of veiling flights that transfer the heat from the burner to the aggregate. The aggregate then exits the inner drum, dropping down into the outer drum shell, where paddles sequentially mix in RAP in a flame free environment. In this zone, the constituents are mixed for the remainder of the drum length and dust/filler are added before mix exits to the external mixer. As the mix exits, liquid AC is added. All constituents are thoroughly mixed in an external mixer.

Inlet Feed Chute

  • The 66° gravity inlet chute is lined with ceramic tiles to minimize wear to the chute.
  • A sealed flop gate minimizes air leaking into the baghouse. Minimizing air leakage is important, because excessive air leakage will result in decreased production.
  • Slinger feeder also available.
  • 1.) Virgin Material Enters
  • 2.) Dry Mix Exits Inner Drum
  • 3.) Mix Moves To External Pugmill
  • 4.) Final Mix Exits
Aggregate Entry
Recycle Entry
Baghouse Dust Entry
Optional Rotary Mixer

Double Barrel X
DRYING (Inner Drum)

The Astec Double Barrel X dryer with external mixer is designed to move aggregate through the mix process with maximum efficiency. Drying of the virgin aggregate is the first step in the process and takes place in the inner portion of the Double Barrel drum. The drying process begins when the virgin aggregate enters the inner drum through a sealed gravity chute. The flop gate restricts air entry into the drum while allowing the aggregate to pass through. The angle of the ceramic-lined inlet chute keeps material flowing freely into the drum. State-of-the-art flights move the material through the drying zones. Once dried and heated, the aggregate leaves the drum through exit openings and enters the outer chamber where RAP and dust/filler are added before mix exits to the external mixer.

Virgin aggregate passes through the inner chamber of the Double Barrel X dryer drum. The virgin material then passes out of the inner dryer chamber to the outer chamber of the drum. RAP and baghouse fines are introduced in the outer chamber of the drum where they mix with the already-heated virgin aggregate. As the AC on the RAP softens, the baghouse fines evenly coat the RAP.

Preconditioning the RAP through the outer chamber of the Double Barrel X dryer drum flashes off moisture in the drum, thus eliminating the problems associated with scavenger systems.

Longer Drying Chamber

The Double Barrel X dryer with external mixer features the industry's longest drying chamber. The entire length of the drum is used for drying virgin aggregate. The long drying chamber assures that the virgin aggregate has adequate time for thorough drying.

1.) Virgin Material Enters

2.) Conditioning Flights

Break up any clumps or sticky material when the aggregate first enters drum.

Fine material has a tendency to clump together in clusters when wet, particularly in the presence of clays. The conditioning flights break up these clumps to ensure all particles will shower evenly.

3.) V-Flights

Provide greater uniformity of the aggregate veil through the gas stream during the drying process, across a wide variety of mix designs and tonnage rates.

The v-shaped notch in the flights allows material to start pouring out of the flight at the beginning of revolution. The material in the bucket continues to pour out until the rotation is complete. This is what provides the even veil of material. The v-flight is also larger than the standard flight, allowing it to carry the same amount of aggregate even with the notch.

U.S. Patent No. 9,835,374

4.) Combustion Flights

Prevent aggregate from impinging on the flame while spreading the material to maximize radiant heat transfer.

The combustion flights are made of stainless steel, which lasts much longer than traditional carbon steel. The flights overlap one another, creating a shield that minimizes the radiant heat that hits the drum shell to keep it from overheating.

Double Barrel X

The Double Barrel X dryer with external mixer employs two mixing technologies proven for over a quarter century in the HMA industry:

  • The outer mixing chamber on the dryer gently mixes recycle with dry hot aggregate maximizing heat and binder transfer between RAP, aggregate, and selected admixtures in a rarefied oxygen atmosphere.
  • The external mixer vigorously mixes virgin liquid asphalt cement, as well as other admixtures.

Separating the drying process from the mixing process provides a very reliable plant to be used for the purpose of recycling reclaimed asphalt pavement (RAP). The concept allows for RAP to be pre-conditioned through the external part of the Double Barrel® dryer before being discharged to the external mixer.

Sequential mixing ensures ingredients are added to the hot mixture in an order that allows better temperature equalization and even distribution of all particles throughout the mix.

  • 1.) Recycle Entry
  • 2.) Baghouse Dust Entry
  • 3.) Liquid Asphalt Entry
Sequential Mixing (Step 1)

1.) Recycle Entry

RAP (Recycled Asphalt Pavement) material is added to the aggregate in the mixing chamber.

First in the mixing sequence, recycle enters into the mixing chamber through the recycle inlet. Recycle, which may be RAP, roofing shingles, crumb rubber, or a mixture thereof, is heated by contact with the hot virgin aggregate.

Sequential Mixing (Step 2)

2.) Baghouse Dust Entry

Baghouse fines are added after the RAP, where they are thoroughly mixed before addition of liquid AC.

Next, baghouse fines and other additives enter the mixing chamber. In this chamber they are able to be thoroughly incorporated with the aggregates before liquid asphalt cement is added to the mix.

Sequential Mixing (Step 3)

3.) Liquid Asphalt Entry
(Optional warm mix system shown)

Liquid asphalt is injected through the AC inlet or optional Warm Mix System as mix enters the external mixer.

At the point where virgin and recycled materials and baghouse fines are thoroughly blended and at the proper temperature they move from the Double Barrel dryer and mixer into an external mixer. As the materials enter the external mixer, liquid asphalt cement (AC) is injected. The external mixer combines all materials, producing a high quality high RAP mix.

Gas Flow
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 dryer/drum mixer as a processor of RAP – steam blankets the superheated virgin aggregate and RAP, displacing 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.

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.

Steam from the Double Barrel dryer/drum mixer is passed to the baghouse and out the exhaust stack.

1.) RAP enters drum

2.) Heated virgin aggregate and RAP generate steam and blue smoke

3.) Steam and hydrocarbons are pulled into the flame

4.) Burner flame incinerates the hydrocarbon smoke

5.) Steam, dust and fines exit drum through exhaust stack to the baghouse

Pulse Jet Baghouse

Pulse jet baghouses remove particulates from the exhaust stream to efficiencies greater than 99.95%, and typically lower emissions to less than one quarter of EPA standards. During the cleaning mode, blowpipes direct bursts of compressed air into two rows of bags at a time. The shock and momentary back-flow produced by the compressed air pulse causes the bags in the section to expand and expel the collected dust cake from the surface, allowing it to drop into the hopper.

†Emission performance is typical, but not guaranteed.

Reverse Pulse Baghouse

Reverse pulse baghouses utilize a damper and a rotating turret to force air directly into the bag filters opposite the normal flow direction. Cleaning is accomplished by isolating a single section of filter bags then reversing the flow of air through them causing gentle expansion. Accumulated dust dislodges from the bag filters and drops into the hopper beneath. Cleaning sequence and timing is adjustable from the control house.

Double Barrel X
Features (Inner Drum)

After hundreds of millions of tons of mix production, the Astec Double Barrel dryer/drum mixer proves itself to be the most reliable and cost effective dryer/drum mixer available to producers.

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 maintain face contact between the tire and trunnion while making adjustments. Good trunnion alignment means better performance and longer equipment service life.

Two solid-steel tires encompass the drum and support the Double Barrel dryer/drum mixer.

A saddle chain drive is outfitted with a heavy-duty roller chain, including offset sidebars and case-hardened bushings. These heavy-duty drive components are made to last.

1.) Silencer
2.) Burner
3.) Trunnion

4.) Drop Out Holes to Outer Mixing Drum
5.) High-chrome Mixing Paddles with Ductile Iron Shanks

6.) Sprocket and Saddle Chain
7.) Drive Motor (trunnion drive available)
8.) Butterfly Spokes

  9.) Drum Tire
10.) Trunnion
11.) Access Door to Inner Drum

Adjustable steel trunnions with railroad duty bearings
Drum Tires
Hot-forged from solid billets of alloy steel and precision machining, provides ultra-smooth operation
Thrust Rollers
Thrust rollers on either side of the tire restrain the drum
Dryer Access
The interior of the dryer drum is accessed through a door on the inlet breeching

Double Barrel X
Features (Outer Drum)

The cost of maintaining the Double Barrel dryer/drum mixer is comparatively low, because Astec uses proven wear materials. High-chrome, heat-treated, 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, as well as the mixing chamber outershell, are fabricated from a high-strength, low-alloy steel for superior heat-resistance and lined with wear plates at critical wear areas.

Mixing Paddles

High-chrome, bolt-on tips with ductile iron shanks for longevity in the field.

  • 1.) RAP Entry
  • 2.) Stainless Steel Skin With Insulation
  • 3.) Infrared Aggregate Temperature Sensor
  • 4.) Hydraulic Access Door
  • 5.) Mix Discharge Chute
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. A RAP by-pass chute is incorporated to easily divert RAP to a waiting loader or truck during clean out of bins or calibration.
Thick Insulation
4" thick insulation under the outer skin of the mixing chamber minimizes heat loss and increases efficiency. In addition, temperature resistant ceramic fiber insulation is used in critcal high-heat areas.
Temperature Sensor
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 to control mix temperatures and to turn out mixes that conform to specifications.
Hydraulic Access Door
A large hydraulically operated access door allows easy service of mixing shanks and tips from the outside of the drying drum.

Stack Temperature Control System

Astec’s V-Pac Stack Temperature Control System uses v-flights and a variable frequency drive (VFD) drum to help facilitate producing many different types of mixes, while controlling stack temperature, without the added cost and time of flight changes. Astec’s v-flights shower along the edge of its notch, as well as its tips, creating a wider veil that increases the effectiveness of the veil by exposing more material to hot gases.

U.S. Patent No. 8,863,404