A pyroscrubber is a device used in the petroleum coke calcining industry to oxidize the carbonaceous contents, including hydrocarbon volatiles of the exhaust gas from the calcination kiln, so as to recover energy to produce electricity and leave no more than small traces of unburned volatiles, solid carbon, ash, or emission (e.g., CO, NOx , and SOx ) in the flue gas discharged. Motivated by the need to maximize the energy recovery and reduce the pollutant emission from the pyroscrubber, a 3D computational model is developed to simulate the combustion and thermal-flow phenomena inside a pyroscrubber to guide an investigation of the means to reduce emissions and increase exergy output for downstream power generation. Computational fluid dynamics model validation is achieved by comparing the baseline case results with the plant measurement data of the temperature at three different locations, high bay, middle of the chamber, and exit, as well as NOx emissions at the exit. The simulation results show that the specially designed high-bay wall structure generates a strong mixing zone, forcing combustion to happen at an earlier stage and helping to efficiently utilize the main chamber space. A well-balanced amount of excess air is favorable in generating more energy output and lowering NOx emissions. Incomplete combustion with substoichiometric air cuts NOx emissions, but leads to less total energy output, lowers gas temperature, and increases CO emissions. A multistage burning strategy is introduced and studied and results show that it successfully cuts emission without compromising energy (electricity power) output.