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This paper evaluates an elementary reaction mechanism for Hg0 oxidation in coal-derived exhausts consisting of a previously formulated homogeneous mechanism with 102 steps and a new three-step heterogeneous mechanism for unburned carbon (UBC) particles. Model predictions were evaluated with the extents of Hg oxidation monitored in the exhausts from a pilot-scale coal flame fired with five different coals. Exhaust conditions in the tests were very similar to those in full-scale systems. The predictions were quantitatively consistent with the reported coal-quality impacts over the full range of residence times. The role of Cl atoms in the homogeneous mechanism is hereby supplanted with carbon sites that have been chlorinated by HCl. The large storage capacity of carbon for Cl provided a source of Cl for Hg oxidation over a broad temperature range, so initiation was not problematic. Super-equilibrium levels of Cl atoms were not required, so Hg was predicted to oxidize in systems with realistic quench rates. Whereas many fundamental aspects of the heterogeneous chemistry remain uncertain, the information needed to characterize Hg oxidation in coal-derived exhausts is now evident: complete gas compositions (CO, hydrocarbons, H2O, O2 NOx, SOx), UBC properties (size, total surface area), and the ash partitioning throughout the exhaust system are required.

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“HyPr-RING” is a new H2 production process using carbonaceous fuels in which the fuel is reacted with subcritical steam and a calcium-based CO2 sorbent. We investigated the applicability of this process to organic matter by examining the performance of the process with fuels of differing volatility. The gasification rate and relative contributions of the volatile and “char” components to H2 production were investigated by using dried sewage sludge with a high volatile component concentration, coal with an intermediate volatile component concentration, and coal char with a low volatile component concentration. During the initial thermal decomposition, carbon in the fuels rapidly decreased with time and was converted to carbonaceous gas of CH4 and C2H6 in addition to H2. The amount of the decrease depended on the volatile content in the fuels. Following this initial rapid stage, the residual carbon appeared to become charlike, even for the high volatile content fuel. The gasification rate became slow, and the gasification shifted to favor H2 production in a molar ratio of H2 to CH4 that approximated the equilibrium composition for a char and steam reaction. NaOH catalytically promoted H2 production even for the sludge.