Batch mix asphalt plant is the most widespread type of asphalt plant in the world and their popularity lies in the fact that they guarantee top quality and maximum flexibility.
What is a Batch Mix Asphalt Plant?
The name comes from the fact that the asphalt is produced in batches every 40-50 seconds, depending on the capacity of the plant and the mixing specifications.
How does an Asphalt Batching Plant work?
Aggregates are collected from the stock piles on site and loaded into the cold feeders with a mechanical shovel. Each cold feeder contains a specific aggregate size and is fitted with its own extractor belt. Nowadays, plants have a minimum of four cold feeders but can be fitted with many more, depending on the flexibility of work and the requirements of the grading curve.
Via a transporter belt, the aggregates are fed into the dryer drum for moisture extraction and heating to the correct temperature, ready for mixing and coating with bitumen.
The role of the dryer-drum in a batch asphalt plant
The dryer drum is nothing other than a rotating cylinder, with a series of flights on the inside which have the function of lifting the virgin material and heating it through contact with the hot air produced by a burner.
The heat of the flame inside the dryer is conveyed to the aggregates via thermal radiation. It is natural that a considerable amount of gas, dust and elements of combustion are produced inside the dryer, and these are then passed through a bag filter before being released into the atmosphere.
The bag filter
Due to increasingly restrictive limits for atmospheric emissions together with new technologies for greater filter efficiency, problems related to environmental impact have now been greatly simplified.
Materials collected in the filter, commonly known as filler (even though this is an improper use of the term, since the material isn’t always screened through the 0.063 mm screen), is collected at the bottom by an auger, then conveyed into a surge hopper, ready to be weighed and re-fed into the mixer in the correct quantity.
The filler plays a fundamental role in regulating the asphalt adhesion and improving the bitumen binding to the aggregates.
The Mixing Tower: the the main characteristic of the Batch Mix Asphalt Plant
Once they are dried, the aggregates reach a temperature of 150-160°C in the dryer and are then transported to the reselecting screen by means of a bucket elevator.
In the vibrating screen, the materials are newly separated by the meshes on the basis of the size required. Once separated, the hot aggregates are fed into the appropriate compartment (4 to 6) and are kept as hot as possible until they are ready to be weighed.
The mixer consists of an armoured hopper, on the inside of which there are two rotating arms with paddles. The counter-rotation of these two arms mixes the aggregates, bitumen and filler until a homogeneous mix is produced.
The advantages of the Batch Asphalt Mixing Plant
Consequently, in batch plants (as opposed to continuous plants) the hot aggregates, filler and bitumen are first weighed and then fed into the mixer. After mixing, the asphalt is discharged from the mixer in the storage bin or directly onto the trucks.
Batch plants are therefore a guarantee of maximum flexibility, great versatility and are ideal for urban situations where it is necessary to satisfy a range of different production specifications and to promptly respond to the various needs of the clients.