MagMill Concept
The MagMill is a selective dry screening and magnetic separation process that is integrated into the existing coal pulverizers to remove unwanted coal constituents prior to combustion. The MagMill can reduce emissions of mercury and/or sulfur, improve boiler performance by reducing ash components that contribute to slagging and/or erosion, and reduce coal costs by upgrading poor quality coals.
Within a pulverizer, coal falls down a central feed pipe onto a rotating table in the bottom portion of the pulverizer. As the table rotates, the coal is slung radially outward and crushed as it passes underneath gigantic steel tires which roll in grooves on the table. Hot air blown from underneath the rotating table enters the grinding chamber through a gap at the outer circumference of the rotating table. This hot air both dries the coal and sweeps the fine particles released in the crushing upward to the classifier at the top of the mill. Oversize particles are returned for additional grinding and the fine particles are blown directly to the burners.
Because of their weight and hardness, the minerals in the feed coal require more passes underneath the rollers than does the relatively soft hydrocarbon component of the coal. The minerals, therefore, become concentrated on the grinding table.
In the MagMill configuration a stream rich in these hard-to-grind minerals such as iron pyrite is withdrawn through the wall of the pulverizer to the magnetic separator. Outside the pulverizer the material is processed through mechanical and magnetic separators to reject the minerals and to recover the carbon which is returned to the mill for grinding to specification.
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