The main function of a pyroscrubber in petroleum coke calcining process is to oxidize the carbonaceous contents, including hydrocarbon volatiles, of the exhaust gas from the calcination kiln, so as to leave no more than small traces of unburned volatiles, solid carbon, ashes, or emissions (e.g. CO, NOx and SOx) in the flue gas finally discharged. To maximize the energy recovery and reduce pollutant emission from the pyroscrubber, 3-D computational models are developed using FLUENT to simulate the combustion and thermal-flow phenomena inside the pyroscrubber. The results show the 3-D behavior of the flow, the reaction inside the pyroscrubber, effect of different amounts of air injection with respect to combustion efficiency, energy output and NOx emission. A multistage burning strategy is introduced and studied and results show it successfully cuts emission without compromising energy output. A particle combustion model with the homogeneous gas combustion model is also developed and incorporated to investigate CO emission.