Mine Site Greenhouse Gas Mitigation » Mine Site Greenhouse Gas Mitigation
Catalytic oxidation offers a potential technology for the mitigation of ventilation air methane (VAM) emissions. A VAM catalytic system has been developed over several projects, with this project exploring how the system reacts to potential changes in feed conditions and how it will be implemented in a pilot-scale reactor. The requirements were determined to achieve the desired VAM conversion with a structured catalyst support and assess the inherent safety under such conditions.
Catalytic oxidation of methane to carbon dioxide via supported Pd/TS-1 catalyst was conducted on a 1.5 - 2 L/min basis, scaled from packed-bed micro scale (300 mL/min). To maintain safe and stable long term testing modifications to a Technical Development Unit (TDU) were made. To stabilise humidity automatically levelled bubbler and chiller were added, which resulted in a reduced variation of the data due to external sources. This increased the stability of the analytical equipment, resulting in more data to be accurately collected. Telemetry such as thermocouple and capacitance manometers were used at important locations to monitor the systems state.
Catalytic coating of structured supports was tested, with an optimum ratio of catalyst to binder in the solids fraction determined, producing good adhesion of catalyst to the surface, while having no noticeable detriment on conversion. Tests were completed on deposition rate on plates to standardise surface area, and to allow modification of the surface to determine the effect on deposition. From this it was found that catalyst deposition was increased on rough surfaces. Mechanical adhesion tests were conducted via a well-used ultrasonic method, where mass losses of 1 - 2 % were observed.
Pd/TS-1 catalysts were tested long-term over 500 hours to determine if a 90%+ conversion could be maintained. Two Pd/TS-1 catalysts were tested, Pd/TS-1 and Pd/TS-1*. Pd/TS-1 was tested under 1.5 L/min VAM flow and was shown to deactivate over time. By 500 hours the reactor temperature was increased from 490oC, to 540oC to maintain >90% conversion. The modified Pd/TS-1* however, was tested at 2.0 L/min and did not require an increased temperature to achieve >90% conversion, maintaining a reactor temperature of 480oC for 500 hours.
Understanding how the conversion and conditions of the reaction change with varying methane concentrations is a crucial step to determine the minimum operating conditions required to maintain a certain conversion and it is anticipated that these operational changes will affect the heat exchanger operation.