Modeling Study of High Temperature Pyrolysis of Natural Gas

High temperature
pyrolysis (HTP) is a commercial process to convert
methane to acetylene. The HTP process consists of two reaction zones,
followed by a quenching zone. In this work, a pilot scale HTP process
was modeled to assess the effect of the amount of fuel burned and
the cracking gas composition on acetylene and polycyclic aromatic
hydrocarbon (PAH) production. The HTP process is simulated using a
chemical reactor network, which consists of a series of ideal reactors.
The composition of cracking gas in the second reaction zone varied
from methane to hexane. The propensity of the feed to form acetylene
vs PAH at a given process condition was determined using a detailed
chemical kinetic mechanism. The chemical kinetic mechanism was developed
using an automated mechanism generation software package, the Reaction
Mechanism Generator (RMG). Compared to existing pyrolysis mechanisms
that can only be used to model the cracking of a finite number of
species, RMG can be used to model the cracking of any arbitrary species
consisting of carbon, hydrogen, and oxygen. The modeling results showed
that the C2 yield is largely independent of either overall
φ or cracking gas carbon number. In contrast, the lumped aromatic
yield appears to have a positive correlation with both overall φ
and cracking gas carbon number. Sensitivity and rate of production
analyses were performed to identify the important pathways that lead
to the formation of aromatics for various feed compositions.