Behavior of Cr during coal combustion: An overview

Abstract

The paper overviews all essential aspects related to Cr behavior during coal combustion and was written with the aim of mitigating its negative impact on human health and surrounding environment. Attention is paid to its concentrations and modes of occurrence in coal, to its volatility and partitioning among coal combustion streams as well as to promising strategies enhancing Cr retention and mitigating its emissions. As Cr behavior is a complex phenomenon, the paper discusses also the most significant affecting factors, such as combustion temperature, flue gas composition and the presence of interacting species (Cl, S, P, major elements, H2O, O-2, CO2 or N-2 atmosphere), using various adsorbents/additives etc. In relation to mitigating its negative environmental impact, special attention is drawn to evaluation of its two dominant valence states - trivalent and hexavalent Cr - regarding their toxicity, modes of occurrence in coal and ashes, their behavior during combustion and namely their mobility from coal combustion ashes. Due to a world-wide trend to co-combust coal with wastes in power stations, important characteristics related to waste materials are also included in evaluation.