Acetylene pyrolysis in a jet-stirred-reactor for low pressure gas carburizing process – Experiments, kinetic modeling and mixing intensity investigations by CFD simulation

Abstract

Low-pressure gas carburizing is used to harden steel, it has been shown to be a source of considerable PAH (Polycyclic Aromatic Hydrocarbon) pollution. Some PAH, like benzo[a]pyrene, are carcinogenic, and activities such as furnace maintenance and cleaning operations may thus represent a risk to workers. Occupational exposure during these operations should therefore be reduced. Benzene is a specific chemical marker of PAH, and the aim of the study was to understand its formation. Acetylene pyrolysis was experimentally performed in a jet-stirred-reactor in the laboratory, in conditions close to those encountered in industrial processes (1173 K and 8 kPa). Products of pyrolysis were analyzed by gas chromatography (TCD, FID) at the outlet from the reaction zone. The influence of residence time in the reactor was studied. A detailed kinetic model assuming an ideal continuous stirred tank reactor was used to describe the formation of chemical compounds and validate experimental data. CFD simulations were performed to characterize the reactor’s hydrodynamics by applying the theory of the free jet. They allowed putting forward one explanation to understand the deviation between experiments and the kinetic model.