A mathematical model has been developed for the i-CFB deNO(x) reactor, which is designed for the hydrocarbon-based selective catalytic reduction (HC-SCR) process. The i-CFB model consists of three submodels: hydrodynamics, NOx adsorption, and reaction kinetics. The modeling results show good agreement with the experimental data. It is observed from the simulation that the performance of the i-CFB reactor is very sensitive to gas bypass from the draft tube to the annulus (R-d.a) but is less sensitive to the converse (R-a.d). The solids circulation rate (G(s)) has little effect on the overall deNO(x) efficiency. The analysis of NOx adsorption and reduction at both the annulus and the draft tube zones revealed that solids residence time in the reduction zone is too short for the NOx reduction reaction for the current i-CFB reactor design. A large reduction zone could significantly enhance the overall deNO(x) efficiency. The optimum reduction zone area ratio (A(R)/A(total)) should be similar to 0.65-0.7. Further increases in the A(R)/A(total) ratio will decrease NOx conversion. It is also observed that the performance of the i-CFB at higher A(R)/A(total) ratios is less sensitive to gas bypass from the reduction zone to the adsorption zone. The deNO(x) efficiency of i-CFB reactor becomes more sensitive to NOx adsorption capacity at higher A(R)/A(total) ratios.