Development of Value-Added Products from Fly Ash Carbons

Abstract

The implementation of increasingly stringent Clean Air Act Regulations by the coal utility industry has resulted in an increase in the concentration of unburned carbon in coal combustion fly ash. Unburned carbon, also referred to as fly ash carbon, is nowadays regarded as a waste product and its fate is mainly disposal, due to the present lack of efficient routes for its utilization. However, the increasingly severe regulations on disposal may demand the utility industry to begin offsetting coal combustion with natural gas, or require additional coal cleaning to remove the ash prior to combustion, or simply start utilizing the unburned carbon. Accordingly, this work focuses on the development of two routes for the generation of premium carbon products from the unburned carbon present in fly ash: (1) feedstock for the production of activated carbons and (2) replacement for calcined petroleum coke in the production of carbon artefacts. Steam activation of the unburned carbon generated activated carbons with surface areas up to 688m2/g, and increasing the activation time from 60 to 120 minutes resulted in higher surface areas at the expense of some solid yield. However, increasing the steam activation time resulted in widening of both micro- and mesopores due to pore enlargement and removal of some pore walls. For the carbon artefacts, the baking yields are very similar for all the carbon bodies investigated, around 90%, as expected from the similar thermal history of petroleum coke and fly ash carbons. The densities of the green and baked carbon bodies produced with only petroleum coke are slightly higher than those of the carbon bodies prepared using fly ash carbon, probably due to the small particle size distribution of the formulations when using fly ash carbons.