Rotary Dryer Aggregate
From the cold bin, the rl800 is brought through a cold elevator and into the dryer to be heated and dried at the required temperature. This dryer is a cylinder with a certain length and diameter based on the maximum planned production capacity per hour.
Dryers have the function of: (1) removing the water content on the aggregate; and (2) heat the aggregate to the required temperature. The components found in the dryer system are:
- The cylinder rotates (dryer) which is generally a diameter of 91 cm to 305 cm and a length of 610 cm to 1219 cm.
- Burner kettle (burner) which contains gas or fuel oil to turn on the heater.
- Fan (fan) as part of the dust collector system and has the main function to provide air or oxygen in the heating system.
The drying system is installed in a series of rows of blades made of concave metal plates which are welded in various shapes and attached to the surface inside the cylinder. These blades (flight cup) are used to lift and drop the aggregate so that the drying of the aggregate becomes evenly distributed. Typical blades (flight up) are shown in Figure 8. The shape of the dryer, rotation speed, diameter, length, number and design of the blades (flight cup) affect the length of time required for the drying process in the aggregate drying system. Therefore, the number, shape and arrangement of the blades must be considered for drying efficiency. Furthermore, the dried aggregate is flowed to the hot elevator (hotelevator) through the exhaust door located at the end of the dryer.
Figure 8. Typical spoons on the dryer
In the drying unit ( dryer ) to consider several factors in order to obtain asphalt mixture that qualify, among other things:
- Calibration of temperature gauges and check heating temperature. Changes in the quantity of aggregate entering the dryer unit as a result of setting the cold bin opening can cause overheating (the amount of aggregate entering is reduced while the burner heat remains).
- Combustion must be complete, this can be indicated from the color of the smoke coming out of the chimney is white and the burning flame is blue. The black smoke color indicates incomplete combustion. An example of the result of incomplete combustion is, when taking the aggregate from the hot bin, the aggregate looks black and covered with soot. As a result of this, the asphalt cannot enter the pores of the aggregate and also cannot adhere properly to the aggregate.
- The moisture content in the aggregate must be to a minimum, therefore do a quick check of the moisture content; Take an appropriate sample, then pass a dry mirror, or spatula over the aggregate. Observe the amount of moisture that condenses on the mirror or spatula surface. Aggregate that still contains moisture will prevent the asphalt from sticking to the aggregate, so the asphalt mixture behaves as if it was excess bitumen.