Better Dust Control

Baghouse dust control

When used to smooth out baghouse dust sags and surges — the slide gate under the incline auger is opened to feed the dust into the boot of the 30-tph bucket elevator, the dust fills the silo while the discharge mechanism speed is constantly adjusted by the automatic dust flow controller, the dust flow control is set near the anticipated dust percentage expected, and when the dust silo high or low level indicators report a level extreme, the operator changes the dust flow set point accordingly.

Mineral filler control

Mineral filler is normally added as a percentage of total mix or total aggregate. Therefore, it is important to measure just mineral filler. The same equipment can be used as above by moving the flow scale auger from the discharge of the baghouse incline auger to the silo discharge. The down side to this is the mix is not being protected from dust sags and surges.

Fiber

Fiber is now being added in asphalt primarily to reduce asphalt oil drain down in an open graded friction course. Cellulose fiber (typically 0.3 percent of total aggregate) is more oil absorbent than mineral fiber (typically 0.4 percent of total aggregate). The fiber introduction methods are often dictated by DOT specs.

Batch plant

Fiber is introduced into a batch plant by several methods:

1) Some manufacturers provide pre-weighed bags and the operator introduces a bag into the pugmill directly for each batch.

2) The fiber can be delivered as it is continuously being weighed by a fiber feeding machine into the pugmill. Fiber is normally blown into asphalt spray. Wet mix time will have to be extended if the fiber-feeding machine cannot deliver all the fiber during the asphalt oil discharge time.

3) The fiber can be delivered as aggregate is being charged into the aggregate weigh hopper. Fibers may get damaged and find its way into the scavenge air stream.

Continuous mix plant

When fiber is introduced into a continuous mix plant, it is important to blow the fiber directly into the asphalt spray before it has a chance to become airborne.

Fibers are packaged in smaller 40 to 50 pound bags or in larger bales weighing 600 to 1,600 pounds. A plant running at 200 tph will consume 20 pounds of cellulose fiber a minute making it very easy for a fiber machine loading person to keep up with production. Counting bags every few minutes allows the operator to know his fiber machine is keeping up.

Larger jobs may require bales to be used. A fiber feeding machine holding 2000 pounds would need charging every 100 minutes.

Information provided by Clarence Richard Co., www.clarencerichard.com