The invention comprises a coal-fired burner system for use in a drum mix asphalt plant or drum dryer used for producing asphalt paving composition.
Coal to fire the burner is ground to a -200 mesh size by an air-swept rotary impact mill, and a classifier at the exit from the mill controls the size of the particles leaving the mill.
The pulverized coal particles are recovered from the exhaust airflow exiting the mill by a fiber filter collector and temporarily stored in a small surge bin.
Coal is metered from the surge bin into a primary air conduit leading to the burner.
The availability of a small but ready supply of coal in the surge bin provides quick response to a need for increased coal while avoiding the dangerous storage of large quantities of pulverized coal dust. As the weight of coal dust in the surge bin decreases, control circuitry provides for the processing of additional coal to maintain a ready supply of processed coal in the surge bin.
Use of a burner having swirl vanes to create a short cyclonic flame pattern permits the burner to be mounted directly in the upper end of the drum without the need for a separate combustion chamber, but without sending a long flame into the mixing area of the drum where liquid asphalt is introduced, which would cause a fire hazard and pollution problem.
United States Patent 4638747