Mercury Adsorption and Oxidation Performance of an Iron-Based Oxygen Carrier during Coal Chemical Looping Process

TL;DR

This study explores how an iron-based oxygen carrier affects mercury during coal combustion and gasification processes.

Contribution

The study identifies three mechanisms—enhanced mercury release, adsorption, and oxidation—by an iron-based oxygen carrier.

Findings

The iron-based oxygen carrier enhances mercury release from coal and oxidizes Hg0 to Hg2+.

Mercury adsorption decreases with increasing temperature, but oxidation increases.

The oxygen carrier physically absorbs Hg0 and Hg2+ and forms complexes with mercury.

Abstract

During chemical looping combustion (CLC) and chemical looping gasification (CLG) of coal, the release, migration, and speciation of mercury in coal are significantly influenced by oxygen-carrier materials; however, the underlying mechanism remains inadequately addressed. In this work, the effect of a typical iron-based oxygen carrier on the release behavior of mercury from a bituminous coal and a lignite was investigated based on the Ontario-Hydro method. It is found that the effect of the iron-based oxygen carrier is attributed to three aspects: the enhanced release rate of mercury from coal, the adsorption of the released mercury, and the oxidization of gaseous Hg0 into Hg2+. With the increasing temperature, the adsorbance of mercury by the iron-based oxygen carrier decreases, while the oxidation of mercury enhances. Even at 900 °C, the adsorbance of mercury by the oxygen carrier remained at 0.1687 g/g, with a relative content of Hg2+ at 22.55%. Additionally, it was observed that iron-based oxygen carriers can physically absorb both Hg0 and Hg2+, while chemisorption refers to complex-compound formation between the iron-based oxygen carrier and mercury.

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