Computational Fluid Dynamics Modeling of Acetylene Pyrolysis for Vacuum Carburizing of Steel

Abstract

The operation of vacuum carburizing plants suffers from the production of unwanted byproducts like tarry hydrocarbons and soot. In order to identify mechanisms which influence the amount and the composition of these byproducts, the pyrolysis of commonly used gaseous hydrocarbons has been investigated under the conditions of vacuum carburizing of steel. Purposely, this investigation included a close look at the interaction of the pyrolysis reactions in the gas phase with the surface reactions leading to the carburization of the steel. Simulation results for the homogeneous pyrolysis of acetylene under vacuum carburizing conditions obtained with our own model are compared with measurements and with results received with commercially available modeling tools. Furthermore, experimental results of the vacuum carburizing of steel are presented and compared with simulation results. The paper focuses on the applicability of the own model and of commercial software tools for process simulation required for optimizing the vacuum and low pressure carburizing of steel.

Influence of Flow and Pressure of Carburising Mixture on Low-Pressure Carburising Process Efficiency

“…Acetylene and Aceylene mixtures 100% Acetylene (C 2 H 2 ) [16] Acetylene + Nitrogen a Acetylene + Hydrogen b [17] Acetylene + Etylene (C 2 H 4 ) + Hydrogen c [5] Acetylene The decomposition process of carboniferous gases (light hydrocarbons) at high temperature(s) is well-studied [11][12][13][18][19][20][21][22][23][24]. The dosage of gas quantity is optimised based on empirical formulas such as the Harris equation (1944) [9,25] or numerical formulas [26].…”

Detailed kinetic modeling of the formation of toxic polycyclic aromatic hydrocarbons (PAHs) coming from pyrolysis in low-pressure gas carburizing conditions

“…The model was used to compare PAH formation during the pyrolysis of three different hydrocarbons: acetylene, ethylene and propane. These reactants were chosen because they are the compounds most used in low-pressure gas carburizing [37] and because they represent an alkyne, an alkene and an alkane, respectively.…”

“…This study aims to develop a model of hydrocarbon pyrolysis in gas carburizing conditions, i.e. at low pressure and at temperature ranging from 1173 to 1323 K [1,37], but without taking into account the presence of steel pieces. It focuses on the formation of the sixteen EPA-PAHs, which are not all modeled up to now in available mechanisms.…”

Modeling of vacuum pulse carburizing of steel

“…The steel surface becomes nearly immediately saturated with when high acetylene flow is used. Due to strong catalytic properties of iron for acetylene, about 70-80% of all acetylene molecules reach the steel surface and decompose on it [33][34][35]. In this case we propose to calculate the mass transfer coefficient as [36]:…”