Investigating the catalyitc combustion of methane and BTEX in a counter-diffusive radiant heater

• Main Author: Jodeiri Naghashkar, Naeimeh
• Other Authors: Robert E. Hayes (Chemial and Materials Engineering)
• Format: Others
• Language: en
• Published: 2011
• Subjects: combustion; methane; catalytic
• Online Access: http://hdl.handle.net/10048/1777

This research was aimed at investigating a counter-diffusive catalytic reactor for mitigation of methane and BTEX emissions from the natural gas dehydration process. A commercial radiant heater unit was used in the experiments and the effect of methane flow rate on its conversion was studied. Methane conversion decreased with increasing methane feed rate. It was found that the external diffusion of oxygen through the boundary layer was the limiting factor in the system. Complete methane conversion was achieved when the oxygen diffusion limitation was overcome by inducing convective air flux in the boundary layer in front of the catalyst pad. To simulate natural gas dehydration emissions, which contain excess amount of water, the effect of addition of liquid water and water vapor on methane combustion was also studied. Small volumes of liquid water did not affect the methane combustion, however, at 2 g/min liquid water, which is comparable to the amount of water produced during the reaction, combustion was inhibited. Added water vapor did not show any influence on combustion efficiency. The presence of pentane and toluene, representing the non-aromatic hydrocarbons and BTEX substances in the emissions, inhibited methane conversion due to the competition for oxygen since pentane and toluene are easier to oxidize compared to methane. Two-dimensional modeling of the radiant heater system was conducted using the COMSOL Multiphysics software package. Comparing the model data for methane conversion with experimental results revealed similar decreasing trend in conversion with increasing the methane flow rate; however, the model under-predicted the conversion. Increasing the mass transfer coefficient, resulted in improved methane conversion, confirming the dominance of mass diffusion limitation in the system. In fact, the real mass transfer coefficient was 1.5-2 times higher than the values originally used in the model. Changing the kinetic parameters did not significantly improve the conversion leading to the conclusion that the catalytic radiant heater system is not kinetically controlled. Developing the three-dimensional model of the system in Fluent revealed that the fuel distribution in the system is not a significant factor, in agreement with experimental observation. === Chemical Engineering