Sorbents for the oxidation and removal of mercury

What is this patent about?

’430 is related to the field of emission control for fossil fuel combustion and gasification systems. Specifically, it addresses the technical challenge of removing elemental and oxidized mercury from flue gas streams, where low concentrations and short contact times often render conventional activated carbon treatments inefficient or cost-prohibitive.

The underlying idea behind ’430 is that the mercury-capture performance of activated carbon is significantly enhanced by the presence of reactive bromine species, which facilitate the oxidation of elemental mercury into a more easily captured form. Rather than relying on the slow, natural seasoning of carbon in a flue gas stream, the invention utilizes halogen promotion to create active cationic sites on the carbon surface that stabilize the transition state of mercury oxidation, allowing for near-instantaneous capture.

The claims of ’430 focus on a method of separating mercury by introducing a bromine-based additive—such as Br2, HBr, or a bromide compound—directly into the coal or the combustion chamber. This is followed by injecting an activated carbon sorbent into the resulting mercury-containing gas downstream, where the sorbent interacts with the halogen-enriched environment to effectively bind the mercury before being separated from the gas stream.

In practice, the invention allows for the in-flight promotion of the sorbent, where the activated carbon reacts with the halogen promoter already present in the gas stream to form a highly reactive promoted sorbent. This mechanism eliminates the need for complex off-site pre-treatment of the carbon. The system can be further optimized using a feedback loop where mercury levels are monitored downstream to dynamically adjust the sorbent injection rate or the amount of bromine additive introduced at the front end.

This approach differs from prior solutions by moving away from expensive, pre-impregnated reagents like gold or triiodide, which are difficult to regenerate. By utilizing bromine species to create a chemically modified carbon structure, the invention achieves high removal efficiencies even in low-chlorine environments. Furthermore, the method supports the use of larger sorbent particles that can be physically separated from fly ash, enabling the sorbent to be regenerated and reused while preserving the quality of the ash for industrial applications.