Characterization of fly ash carbons derived due to the implementation of NOx clean air act amendments

One of the more extensively used approaches for meeting the Title IV of the 1990 Clean Air Act Phase-I has been the installation of low-NOx burners. Although these technologies have been proven effective in reducing NOx emissions, they have also resulted in an increase in the concentration of unburned carbon in the fly ash. This has restricted the principal use of ash in the cement industry, since the unburned carbon tends to adsorb the air-entrainment admixtures (AEAs), that are added to the cement to prevent crack formation and propagation. However, very little is known about the properties of fly ash carbons and any information regarding their properties is watched closely by the utility industry. Accordingly, the work reported here represents the first characterization of the bulk properties of unburned carbon concentrates that have been isolated to purities up to 86% by using density gradient centrifugation. The density of like carbon forms isolated from two fly ashes appears to be quite similar, regardless of the source of the fly ash. The H/C atomic ratios are ∼ 0.028-0.016, indicating a high degree of condensation. The BET surface areas are relatively low, ranging from 10 to 60 m²/g, and most of the pores are in the mesopore range (2-50 nm in width). For both series of fly ash samples, the surface area was found to increase linearly with increasing particle density.