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Improving the Performance of Asphalt Plant Components
Posted Thu March 25, 2004 @12:00PM
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Application by Ricardo Barbosa Damian,
CIBER Equipamentos Rodoviários Ltda. (member of the Wirtgen Group)
and Marcus Reis,
ESSS

Modern, efficient and innovative, CIBER is located in Porto Alegre, Brazil and has as its core business the manufacture and sale of machinery and equipment for road construction and maintenance.

Experimental development of portable asphalt plant components requires time and is an expensive process. In order to offer products with lower energy consumption and more compact dimensions, and that meet environmental regulations, CIBER chose CFX-5 computational fluid dynamics software to assist in analyzing many of the complex processes involved in asphalt production. These processes include combustion, solids drying, liquid and solid mixture, solid-air separation and filtration and pneumatic transport of particles.


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Large quantities of dust are carried by the exhaustion of combustion gases during the drying of aggregate matter inside the rotary dryer. This dust should be recovered for the bitumen production process and environmental regulations do not allow it to be delivered to the atmosphere. A large part of an asphalt plant is taken up by air filtering equipment.

Using CFD allowed us to simulate how changes in the design of various dust collection components would affect component performance and longevity. We were able to vary the design of the bag house and pre-separator to maintain and even improve performance while decreasing size. In all we analyzed pre-separators such as cyclones and our own static separator (SE), the bag house, the dust impact mass flow meter and the rotary dryer.

The computer simulation predictions of the flow inside these components are improving their performance, reducing the energy losses, reducing their dimensions and providing better understanding of some critical erosion points. Even for complex flow fields, the numerical results are in accordance with field measurements highlighting the enormous potential of the CFX on asphalt plant design. It has reduced the design cycle and the costs involved.

asphalt plant
After using CFX to design more compact equipment it was possible to decrease the size of an asphalt plant from three platforms to a single platform.

 

Two-phase flow inside the SE
Two-phase flow inside the SE was modeled to predict dust collecting efficiency and abrasion intensity. The simulations showed better dust collecting efficiency than the cyclone model.

 

Dust pathlines
The maximum dust speed within the SE was not greater than 30 m/s, the value required for erosion. Experimental studies validated these results.

 

Flow in the bag house
By using pleated bags and improving the airflow distribution, CIBER was able to develop a new bag house that is the smallest one currently used for an up to 120 ton/hour asphalt plant.

 

Flow in the bag house inlet
The bag house model manufactured by CIBER had internal air distribution problems that caused some of the filtering bags to have a very short life. Using CFX-5 it was determined that the non-uniform distribution was caused by the shape of the air inlet. Bags with high wear were located in regions of high velocity.

 

Flow in the bag house inlet
A new inlet for the bag house was designed and iterated using CFX analysis, until an improved design was found and implemented. Because of more uniform air distribution, the efficiency was increased and it was possible to decrease the size of the bag house and increase the longevity of the filtering elements.

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