TECHNOLOGY
Traditional burners applied to asphalt plants use the air from the environment ( sucked in by an exhaust fan with constant turning speed ) and a mechanical fan ( called a blower ) to provide the amount of air needed for combustion inside the dryer drum .
turning speed ) and a mechanical fan ( called a blower ) to provide the amount of air needed for combustion inside the dryer drum . The control over the airflow for combustion is carried out by a component that is called a damper , placed in the gases ’ outlet to the environment , which controls the pressure of the plant by manipulating the flow of the gases . There is an optimum combustion ratio of 13:1 ( thirteen volumes of air for one volume of fuel ) and the airflow variation is dependent on the position of the damper , since the exhaust flow is constant .
The latest combustion technology in plants accurately and automatically control the optimum air-to-fuel ratio . In this technology , all the combustion air is mechanically supplied by the plant ( without air suction from the
environment ) through two fans ( a blower and an axial fan ). Called ‘ total air ’, it works in a closed loop from an internal pressure input of the dryer and automatic variation of the airflow by the variation of the rotational speed of the exhauster , which transports the gases from the dryer to the filter and later to the atmosphere . This way , only the air used for combustion is heated , resulting in fuel economy . Electric power is also saved , as the largest plant engine , the exhauster , turns according to the demand .
Control over mixing time
During the design of an asphalt concrete project in the laboratory , the mixing time between aggregates and binder depends on the characteristics of the materials . If the plant is a large-scale laboratory , the mixing time should also vary according to the properties of the materials . Therefore , an external pug mill mixer has been developed , which automatically controls the mixing time according to the requirements of the materials and as determined by the operator before or during production .
The technology is based on the control over the material outlet area between the mixer and the drag elevator . When this outlet area is reduced , the blend is trapped within the mixer , increasing the material volume and the mixing time , keeping the production of the plant constant . If the outlet area is open , the asphalt mix leaves the mixer more freely , decreasing the volume of material in the mixer and the mixing time , while still maintaining constant production .
In the past , asphalt plants had to adapt to materials and project characteristics , with variable productivity . With these new technologies , productivity is constant , regardless of inputs and projects , and the quality is reached according to the parameters established in the project . n
About the author
Aggregates and binder mixing inside the asphalt plant . During the design of an asphalt concrete project in the laboratory , the mixing time between aggregates and binder depends on the characteristics of the materials .
Marcelo Zubaran is a product and application engineer at Ciber Equipamentos Rodoviários , a Brazilbased member of the Wirtgen Group that specialises in developing and manufacturing equipment for building , maintaining , and repairing roads .
26 _ QUARRY SA | NOVEMBER 2017