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What is the difference between asphalt plant and batch plant?

Author: becky

Jul. 02, 2024

Drum vs. Batch Plant: Learn the Differences That Will Make ...

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Often, preparing an asphalt mixture is compared to baking a cake. A contractor needs to make sure he/she has an accurate recipe and proper ingredients and that he/she blends everything at the correct ratios and &#;bakes&#; the mixture to produce a beautiful, homogeneous final product that everyone will be happy with &#; a blend that will perform as anticipated when properly applied on a roadway.

There are two basic types of plants that are used in the process of making asphalt mixtures: batch plants and drum plants.

Batch vs. Drum

Batch plants make small accurate &#;batches&#; of asphalt mixture through a process that is repeated over and over until the total tonnage for a project has been manufactured.

The advantages

They offer the highest level of flexibility in production.
They manufacture a very high-quality finished product due to the accurate measurement of each batch produced.
Batch size and production capacity can vary based on the designs of the plants themselves.
Due to the intermittent production process, plant operators can easily switch back and forth between different mix recipes if necessary.

Drum plants, on the other hand, prepare the asphalt mix through a continuous process and require the use of silos for temporary storage prior to the mix being trucked to the paving location.

The advantages

There is no interruption in the production process as there is a continuous flow of aggregate and liquid asphalt into the drying/mixing chamber.
There are several different configurations of drum plants, all depending on how the aggregate flows in relation to the hot air, which is responsible for heating and drying the materials.
In parallel flow, the aggregate and air flow in the same direction through the chamber.
In counter-flow plants, the aggregate and air flow in opposite directions through the chamber.
In double drum or double barrel plants, there is an outer shell through which the aggregate flows before coming in contact with the hot air inside the chamber.
Regardless of the configuration, it is a continuous process that creates a homogeneous mixture that can be manufactured at a high rate (sometimes as high as 600-800 tons per hour).

Common components to both styles of plants:

Cold Feed Bins &#; used to meter the different aggregates into the drying chamber
Liquid Asphalt (Binder) Storage Tanks &#; storage of the liquid component of the final mixture
Drying Chamber &#; vital component responsible for heating and drying the aggregate through the use of hot air
Dust Collection System &#; often referred to as a baghouse, it captures fine sand and dust particles and returns them to the mix
Storage Silos &#; necessary for the continuous production of a drum plant, used in batch plants to increase production rates and throughput, and must be insulated and sometimes heated to prevent temperature loss

Main differences:

In drum plants, there is no interruption in the production process as there is a continuous flow of aggregate and liquid asphalt into the drying/mixing chamber. There are several different configurations of drum plants, all depending on how the aggregate flows in relation to the hot air, which is responsible for heating and drying the materials. In parallel flow, the aggregate and air flow in the same direction through the chamber. In counter-flow plants, the aggregate and air flow in opposite directions through the chamber. In double drum or Double Barrel plants, there is an outer shell through which the aggregate flows before coming in contact with the hot air inside the chamber. Regardless of the configuration, it is a continuous process which creates a homogeneous mixture that can be manufactured at a high rate (sometimes as high as 600-800 tons per hour).

The ways that aggregate and bitumen (liquid asphalt) are metered into the final mix are different in batch plants and drum plants. In batch plants, the aggregate and asphalt binder are weighted using load cells for accuracy. The aggregate is dried first and then weighted into the pugmill based on the agency-approved Job Mix Formulation (JMF). In drum plants, flow meters and calibrated feed belts are used to measure the liquid and aggregate components into the mixing chamber. Because the drying and mixing are done in conjunction in the drum plant, the need to regularly monitor the moisture content of the aggregate stockpiles is vital to producing a high-quality finished product.

Another difference between the two plant types is the actual mixing of the aggregate and asphalt inside the mixing chamber. In batch plants, the pugmill uses arms with paddles attached to them, thus creating a forced or physical mixing of the components. Also, the batch times can be adjusted to facilitate more mixing of the materials when necessary. In a drum plant, the mixing is a result of the rotation of the drum combined with the flight pattern inside, which creates a falling curtain of material. The only practical way to lengthen this process is to slow down the production rate of the plant.

In batch plants, Rosphalt® asphalt additives, supplied in meltable poly bags, are added directly into the pugmill. In drum plants, the injection point of the Rosphalt® asphalt additives can vary depending on configuration, but historically they have been added through the RAP (Recycled Asphalt Pavement) collar with the return dust from the baghouse or through a mineral filler silo and added with the aggregate into the mixing drum.

Typical Drum Plant Configurations

Illustrations Provided by Astec Inc

At the end of the day, an experienced plant operator can produce a high-quality asphalt mixture regardless of the type of plant being used. There are benefits to each type, and adhering to customer or agency specifications, both have been used with great success for many years. The Rosphalt® asphalt additives offered by Chase Construction Products have been used successfully in both styles of production plant to create highly rut/shove resistant, flexural fatigue resistant, waterproofing surfaces and interlayer courses for nearly 40 years and are continued to be used where agencies require the highest performance in some of the most difficult environmental conditions for asphalt mixtures.

We are always happy to educate our customers. Contact us if you have any questions.

Asphalt Batch Plant VS Drum Mix Plant - Atlas Industries

A hot mix plant is a combination of several components both electrical and mechanical working in sync to make a product which we call as HMA (Hot mix asphalt). The combination of these components allow cold aggregates to heat and then mix the same with liquid bitumen and minerals in varying proportions to produce asphalt mix as per requirements.

These plants can be categorized as stationary and portable. Usually the stationary plant components are fixed and portable plant components are on wheels facilitating movement from place to place.
Hot mix asphalt plants can also be categorized as continuous type and batch type. Continuous plants produce asphalt mixture in continuous operation and batch type plants produce HMA in batch.

In continuous mixing plants, the ingredients are added, dried and mixed continuously in a drum. In batching plant, the ingredients are pre-weighed as per the required amount and then added into a separate pug mill mixer to form a batch.

The two basic types of asphalt plants used in the process of making hot mix asphalt are asphalt drum mix plants and batch plants.

Batch plants vs Drum plants

Asphalt batch plants will make hot mix asphalt in fixed batches. One by one batches are continuously made to make hot mix asphalt.

Some of the advantages of asphalt batch plant are:

It offers best quality of hot mix asphalt.
The flexibility offered is best.
It is possible to edit batch sizes and mix material designs frequently.
The control systems are very advanced allowing user to have multiple options.
The level of pollution control is better than a drum mixer.

On the other hand, drum mixers are very much preferred in developing countries. They produce HMA in a continuous process. They are good for small to medium sized projects. The end product quality is not as accurate as a batch plant.

Some of the advantages of continuous drum mixers are:

The initial cost is low compared to batch plant.
The land required to set up is less compared to batch plant.
The process here is continuous. Meaning uninterrupted production is there.
It is easy to have a higher capacity machine without exponentially increase in its price.

The functioning of both the plants is different but the main purpose is to make hot mix asphalt as per the requirement.

Counter flow asphalt plant is also a continuous plant but featuring a different technology compared to the traditional drum plant. In counter flow plant, the flow of aggregate and flame direction is opposite. Dust suction is done at the point where the aggregates enter the drum. Counter-flow plants can feature a single drum for drying and mixing or two drums (separate for drying and mixing) or drum for heating and a mixer for mixing.

Usually drum plants are smaller than the asphalt batch plant and require less space, less energy and less efforts to run. The components are also less in the drum asphalt plants which make them easy to transport and ship.

Contact us to discuss your requirements of small batching plant for sale. Our experienced sales team can help you identify the options that best suit your needs.

Here is what we are going to mention in the article below:

Common operations and components to both the batch and drum type.
Operation of parallel flow asphalt mixing plant.
Process of counter flow asphalt mixer.
Working of asphalt batch mix plants.

There are certain common operations common to both the types and the components are also similar. They are as below:
1. Component: Aggregate feeder
Operation: Cold aggregate storage and feeding

2. Component: Drum and burner
Operation: Drying and mixing (parallel flow) | Drying of aggregates (Batch type)

3. Component: Fuel tank for dryer burner
Operation: Storage and supply of fuel to the burner.

4. Component: Primary scalping screen and charging conveyor
Operation: Removal of oversized material before the aggregates enter the drum.

5. Component: Primary and secondary pollution control units
Operation: Collection of heavy and fine particles.

6. Component: Asphalt tanks
Operation: Storage and heating of bitumen.

7. Component: Filler bins
Operation: Storage and transfer to filler material.

8. Component: RAP feeder
Operation: Feeding of recycled material.

9. Component: Control panel
Operation: Controlling of the entire plant.

10. Component: Storage silo
Operation: Storage of hot mix asphalt before dispatch.

Operation of parallel flow asphalt mixing plant:

The operation of parallelflow type of asphalt mixing plant is a continuous process where the ingredients are added by proportions to the cold feed bins. The feeder bins store the cold aggregates in separate bins and transfer the same to the drying drum. The main difference between this process and the batch plants starts here. Here there is a single drum which heats and mixes in a single chamber (drum). Aggregates are introduced to the burner end of the drum and the flow of aggregates and the burner flame is parallel to each other and hence the name parallel flow asphalt mixing plant. Before introduction into the drum, the aggregates have to pass through a primary scalping screen. This will help to remove the oversized aggregates and prevent them from entering the drum. Once the cold aggregates enter the drum, they are treated by the flame which makes them hot and ready for mixing with the hot bitumen and other additive. As the drum rotates, the aggregates move towards the other end of the drum. Liquid bitumen is added to the aggregates on the other half of the drum. This liquid bitumen flows by a pump which is controlled by a variable speed drive. So the flow of aggregates determine the addition of bitumen and minerals into the drum. If the aggregate flow is more, the control panel sends message to the bitumen drive which sends the bitumen in set proportion to the aggregates. If the aggregate flow drops, the control panel will send signal to the bitumen drive thereby decreasing the inflow of the bitumen into the drum. Minerals and RAP are also added into the second half of the drum where the temperature is much lower. The introduction of minerals and recycled asphalt is also controlled by a variable speed drive just like the bitumen.

The exhaust gases are sucked towards the discharge end of the drum and are treated first by primary and then by secondary dust collector. Primary dust collector is a cyclone device which traps most of the heavy dust and settles them not allowing them to enter the secondary dust collector. Secondary dust collector is usually venture scrubber type wet dust collector or a bag house filter which settles the lighter particles and prevent them from escaping. Wet dust collectors use water jets to trap and treat them to cyclonic effect to settle the dust. Bag filters do not require water to clean and it cleans the dust by trapping them to bags made of special material designed for this purpose.

The mixed material is dispatched from the other end of the drum and is transferred to a storage silo or to a truck. If it is transferred to a hot mix silo, it can be loaded into the truck.

Process of counter flow asphalt mixer:

The process of counter flow plant is similar to the parallel flow plant and is a continuous process. Here also the entry and quantity of bitumen and minerals is controlled by the flow of aggregates just like the parallel flow plant.

The main differentiating factor lies in the flow of aggregates compared to the burner flame position which is opposite and hence the name counter flow. Even the flow of exhaust gases is from the point where aggregates enter the drum. The addition of bitumen, RAP and minerals is behind the burner flame. This addition of bitumen, RAP and minerals can be in the same drum or in a separate drum or in a separate mixer. This prevents bitumen, RAP and minerals from getting in direct contact with the flame. The main advantage of a counter-flow plant is that it will allow addition of RAP into the mix.

The addition of liquid bitumen, RAP and minerals is controlled by a variable speed drive and is synchronized with the flow of aggregates just like in the parallel-flow asphalt mixers.

Here we can see that there is only a single drum. The flow of aggregate and burner flame is opposite and the addition of RAP and liquid bitumen is just behind the burner flame.

There are two separate chambers: first is counter flow drum only for drying of virgin aggregates, second is the pug mill type mixing unit for mixing of hot aggregates with RAP and liquid bitumen.

Here there are two drums one above the other. The drum which received the virgin aggregates is fitted with the burner on the other side and only drying of aggregates takes place in this drum. Covering this drum is a drum which allows entry of liquid bitumen and RAP. Aggregates after heating are transferred to the outer drum through openings in the inner drum.

Working of asphalt batch mix plants:

This asphalt batch mix plants features the most advance technology. It is best for getting quality HMA. The process-working starts when cold aggregates are fed to the appropriate aggregate feeder bins. They then are metered from the hoppers individually and move towards the drying drum. In between they have to pass though a primary scalping screen for removal of oversized materials. A conveyor takes the cold aggregates collectively into the drying drum. The drum featured here is counterflow type and the dry aggregates move from one end to the burner end by the help of the drum rotation. During this process they get fully dried. The aggregates get transferred from one end to the other and leave the burner end of the drum to fall on a elevator. This elevator is fully covered and it takes the aggregates to the top end of the tower unit where vibrating screens is placed.

Dust collection is done at the entry point of the aggregates and treated by a primary and secondary dust collector. Here the primary dust collector is cyclone type and the secondary dust collector can be wet scrubber or a bag house.

The screens are inclined horizontally and are of different sieve sizes depending on the mix material requirement. Once the aggregates pass thought the vibrating screen, they are separated and placed in different bins just below the vibrating screen. This separation is according to the size of the aggregates. This screen has provision for removal of oversize and overflow material. In certain asphalt batch plants, there is a separate bin which stores RAP material. The aggregates are stored in the bins separately and the bins open as per the batch which is set. Here the quantity of each size of aggregates can be controlled as per requirement. At the same time, the bitumen which is stored in the bitumen tanks is flowed from the tanks below by an asphalt pump into a bucket near the mixer. This bucket weighs the bitumen and then pumps the same into the mixer. Before the entry of the bitumen into the mixer, hot aggregates (and RAP) have already entered the mixing unit. The material already in the mixing unit is as per the desired ratio. The mixing time of the twin shaft mixer can be set as per requirement.

After mixing, the HMA is discharged into a storage silo or into waiting trucks below which takes them to the job sites.

View simple video explaining the difference below:

CONCLUSION:
You are going to make a long term investment. It is important that you understand your primary requirement and then select a product accordingly. There are many companies offering drum and asphalt batching plant for sale. Before buying an equipment it is important to check all asphalt plant parts and ensure that it meets or exceeds your requirement. It is equally important that the equipment that you are buying is easy to use, maintain, transport and is easy on the pocket. This is one investment which can yield a lot of money, if taken care.

Want more information on stationary asphalt mixing plant wholesalers? Feel free to contact us.

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