Mercury removal performance of brominated biomass activated carbon injection in simulated and coal-fired flue gas

Abstract

Brominated biomass activated carbon, with impactful gaseous mercury removal performance, has become a novel cost-effective and environment friendly alternative adsorbent for activated carbon. In this paper, the mercury removal behavior of brominated rice husk activated carbon (RHAC-Br) injecting was investigated in a simulated flue gas entrained-flow experimental system, a pilot-scale 0.3 MWth circulating fluidized bed combustion (CFBC) system, and an industrial-scale 75 t/h CFBC boiler system, respectively. For comparison, the mercury removal performance of brominated coconut husk activated carbon (CHAC-Br) and brominated coal-based activated carbon (CAC-Br) was also studied in simulated and coal-fired flue gas. Combined with the nitrogen adsorption-desorption and X-ray photoelectron spectroscopy analyses, the three sorbents were characterized and analyzed on their mercury removal features in different scale experiments. The results showed that in the entrained-flow experimental system, the increase of injection amount and initial mercury concentration promotes mercury removal of RHAC-Br, with the optimum removal temperature of 120 °C, and the following order for Hg0 removal efficiency for the three sorbents: η (CAC-Br) > η (CHAC-Br) > η (RHAC-Br). Further investigation carried out in the pilot-scale 0.3 MWth CFBC facility indicated that both injection temperature and mercury removal behavior of the three sorbents in coal-fired flue gas are quite different from those in the simulated flue gas, mainly as a result of large proportion of Hg2+ and Hgp. The mercury removal performance of RHAC-Br is comparable to that of a commercial activated carbon (CAC-Br). The outcome conducted in the industrial-scale 75 t/h CFBC boiler system demonstrated that the RHAC-Br injection is as efficient as CAC-Br injection, verifying that the brominated biomass activated carbon could be an effectively alternative adsorbent for the brominated activated carbon in the application for large-scale coal-fired boiler systems.