Nano-Structured Sorbent Injection Strategies for Heavy Metal Capture in Combustion Exhausts

Abstract

Nano-structured sorbent injection is a promising technique for heavy metal capture in combustion systems. The importance of sorbent injection strategies, including the form of the sorbent and its injection location for metal capture and removal is investigated in this study. A multi-component tri-modal aerosol dynamic model was employed to understand the evolution of heavy metals and sorbents, as well as their interactions in the incineration system. Experiments were conducted to assess the performance of in-situ generated SiO₂, compared with bulk Ti-PICL sorbent, in capturing lead and cadmium from a demilitarization incineration system. Nano-structured SiO₂ generated in-situ was found to be more efficient than the bulk Ti-PICL sorbent because it offers a higher external surface area for condensation. The sorbent injection location is important as it affects the physical properties of the sorbent and the pathway for heavy metal capture. Extensive sintering and reduction in the surface area were observed when sorbent was injected into high temperature flue gas, i.e., directly into the combustor. However, when injected into much lower temperature flue gas, the pathway for heavy metal capture was altered from condensation to inter-particle coagulation due to the nucleation of heavy metal species. This study further revealed that new emission standards can be readily met with an optimal sorbent injection strategy.

Acknowledgments

This work was supported in part by a SBIR Phase II contract (DACA42-03-C-0029) from the U. S. Army Construction Engineering Research Laboratory (CERL) through Triton Systems, Inc. Discussions with Drs. Apoorva Shah, Triton Systems, Inc., and V. Boddu, CERL, Urbana−Champaign, IL, are gratefully acknowledged.

Notes

*sorbent injection location

*estimated from pure cadmium value.

**Gmelin, H. (1969).