Simulation of Combustion and Thermal-Flow Inside a Pyroscrubber

Abstract

A pyroscrubber is the device used in 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, ashes, or emissions (e.g. CO, NOx and SOx) in the flue gas finally discharged. Motivated by the need to maximize the energy recovery and reduce pollutant emission from the pyroscrubber, a 3-D computational model is developed to simulate the combustion and thermal-flow phenomena inside the pyroscrubber to help seek means to reduce emissions and increase energy density for downstream power generation. CFD model validation is achieved by comparing baseline case results with the plant measurement data of temperature and NOx emission. 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 helps to efficiently utilize the main chamber space. A well balanced amount of excess air is favorable in generating more energy output and lowering NOx emission. Incomplete combustion with sub-stoichiometric air cuts NOx emission, but leads to less total energy output, lowers gas temperature and increased CO emission. A multistage burning strategy is introduced and studied and results show it successfully cuts emission without compromising energy (electricity power) output.