Study on the effects of carrier and modifier on mercury adsorption behavior over halides modified sorbents using temperature programmed desorption method

Abstract

Halides modified sorbents injection equipped with dust removal units is considered as the most promising technology for elemental mercury (Hg0) removal from coal-fired flue gas. However, Hg0 adsorption behavior over different halides modified sorbents remains controversial. In this study, the effects of carriers (activated carbon and neutral Al2O3) and modifiers (NaCl, NaBr, CuCl2, and CuBr2) on the behavior of Hg0 adsorption over modified sorbents were investigated using temperature programmed desorption (TPD) method. Both mercury adsorption experiments and TPD experiments were conducted in the bench-scale fixed bed. The results indicated that CuBr2-modified activated carbon (AC) showed the best mercury removal performance due to the lower bond energy of CuBr2. The decomposition temperature of mercury compounds generated on AC was different from that on neutral Al2O3. Further analysis indicated that the modifiers with lower bond energy could release halogens during modification. The released halogens could react with AC to form active CCl or CBr group. Moreover, the lower bond energy of modifiers made it easier for halogens to release. But Al2O3 carrier could not react with modifiers to form active group during modification. The Hg0 adsorption process over modified Al2O3 could be explained by Langmuir-Hinshelwood mechanism.