Development of a catalytic mitigation system for VAM - Stage 3 - 20 litre per min VAM flow Technical Development Unit

This report describes work undertaken towards the development of a process for the catalytic conversion of Ventilation Air Methane (VAM).

1. The reactor operating at up to 20 l min-1 VAM flow rate. The performance of a combustion catalyst is examined, focussing the performance of the catalyst under conditions where the gas stream contains water vapour, carbon dioxide and other impurities. The second section of the project was to undertake a preliminary design of a full scale catalytic process which has the capability of converting a VAM flow of 300 m3s-1, assuming 7000 ppm of CH4, 30,000 ppm of water vapour, 10000 ppm of CO2 and mine dust and that the catalyst operating conditions determined in the experimental work translates to full scale operation.

2. Understand the heat input requirement for the large-scale reactor. Our analysis suggests that the use of an external heat source results in a significant cost increase to the process operation. The adiabatic temperature rise in this context gives an estimation of the potential energy input obtainable for a given methane concentration. While adding methane as a heat source is most attractive and the lowest cost heat source, its effect on the cost of the process is significant and adds significantly to the cost of operation. Thus high efficiency recovery requirements and associated with that, a lowering of the catalyst temperature are crucial factors in the overall process viability.

3. Assess and optimise operating conditions. The viability of the application of catalytic combustion is underpinned by two primary catalytic features; operation at as low a temperature, and with as little catalyst, as possible. Detailed testing of a range of catalysts suggest a hydrophobic supported catalyst may be less prone to poisoning by water vapour. In response, a novel Pd supported on TS-1 combustion catalyst was synthesized and tested in methane combustion under lean and under highly humid conditions.

4. Assess the hazards involved with catalytic oxidation on an underground mine site. A high-level hazard analysis performed on the proposed design was conducted in part to meet with ACARP project requirements but also to ensure that any possible development or upscaling is done so with necessary safety foresight. Importantly, this analysis was applied using a structured risk assessment methodology. A risk matrix was defined and it was concluded that the most significant risk exist to the mining operation was associated with thermal runaway, due to an elevated concentration of methane in the VAM mitigation system.

5. Examining the chemical stability and durability of commercially available VAM catalysts. The characteristics of a commercial Pd/Al2O3 catalyst after long-term stability tests were investigated, with the objective of understanding catalyst deactivation phenomena. It was found that the deactivation is primarily due to palladium migration and particle growth and is the most prominent in the presence of water vapour. The formation of α-Al2O3 during long-term stability tests explains the changes in pore structures which is responsible for re-dispersion of palladium particles.

THE FINAL REPORT IS AVAILABLE FROM THE ACARP WEB SITE.  THE PREVIOUS STAGE ONE AND TWO REPORTS ARE ATTACHED TO THIS FINAL REPORT.