A new mathematical model Was proposed to predict in-duct mercury capture efficiency and determine the effect of sorbent properties on mercury capture by sorbent injection. The model was based on external film mass transfer assumption and included mass balance and adsorption isotherm. Adsorption parameters of the sorbent were determined by the fixed-bed mercury adsorption experiments and other modeling parameters were estimated from literatures. The model verification was conducted by comparing with the experimental results of mercury capture by raw and bromine modified activated carbon (R-AC and AC-Br) injection in an entrained flow reactor. The results show that there is a reasonable agreement between the modeling prediction and the experimental results, which demonstrates that this model can provide a rational prediction results and be used to estimate sorbent consumption cost. In both the experimental and modeling cases, mercury capture efficiencies are improved with smaller sorbent particle size, longer sorbent residence time and larger sorbent concentration. The in-duct mercury capture rate of AC-Br was improved significantly compared to that of R-AC. The simulation of in-duct mercury capture by sorbent injection demands taking into account the additional mercury capture by deposited activated carbon on the duct wall. The model parameters, including sorbent concentration, particle size, equilibrium constant K, external film mass transfer coefficient and residence time have important effects on the in-duct mercury capture rate by sorbent injection. (C) 2015 Elsevier B.V. All rights reserved.