Triboelectrostatic removal of unburned carbonaceous matter from coal combustion ash

摘要

The ASTM C618 standard for the use of fly ash as an admixture in Portland cement quantifies a maximum LOI (loss-on-ignition) of 6% for the ash. This LOI is predominantly caused by unburned carbon. Because most of this carbon is physically, rather than chemically, mixed with the ash, physical separation techniques can be applied to decrease the LOI to acceptable and industrially relavent levels.One such separation technique employs the principals of triboelectrostatics. It can be used to establish a positive charge on carbon particles and a negative charge on ash particles. When such differentially charged particles are passed through an electric field, they can be separated into two products having low (～2%) and high (～40%) LOI values. Such dry processing is influenced by physical and chemical properties of the ash, including particle size and size distribution, particle morphology, forms of carbon and ash, and surface constituents. These properties and important processing parameters will be discussed relative to the purification of combustion fly ash.