Poor maintenance of PSA plants can lead to low output, as well increase employees’ exposure to safety risks.
By installing inexpensive and suitably designed Pressure Swing Adsorption (PSA) equipment, a gold mine should be able to meet all of its tonnage oxygen requirements. In contrast with Vacuum Pressure Swing Adsorption (VPSA) plants, which require a costly and somewhat hazardous booster compressor, PSA plant, (although less efficient), generally is able to produce oxygen at pressures suitable for most mine applications. Nonetheless, the effectiveness and efficacy of PSA equipment, even from reputable OEMs, depends heavily on the level of planned maintenance by suitably-trained personnel.
Foxolution, which specialises in on-site PSA oxygen generation (Foxolution is a company that is extensively involved in on-site PSA oxygen generation plant projects), concedes that there is a general lack of the planned maintenance of these plants, which impacts negatively on their output and which gives rise to pressing safety concerns.
Specifically, Kerry Motherwell, Foxolution’s Principal Engineer, singles out poor sparger nozzles maintenance as one of the areas that affects oxygen utility. “Sparger nozzles have a finite lifespan and can fail prematurely if the manufacturer’s maximum throughput is exceeded”. Defective sparger nozzles generally create large bubbles that result in inefficient mass transfer between the oxygen and the slurry. Furthermore, the defective nozzles often allow slurry back into the oxygen pipework, as they oftentimes cannot seal when compromised.
Addressing the problem of nozzle failure, Motherwell observes that the entire sparger assembly has to be removed, cleaned out, a replacement nozzle fitted and then placed back in service. He cautions that this is a messy job in a toxic environment as the slurry contains cyanide.
While efficient oxygen generation in a PSA plant is important, safety should be the first priority. Motherwell points out that a general lack of awareness of the many oxygen hazards from senior management right down to the individuals responsible for the oxygen plant, exposes the operators to serious risk. Motherwell says: “Many employees responsible for oxygen plant maintenance are clueless regarding oxygen hazards. Oftentimes their clothes become saturated with oxygen during undocumented maintenance procedures – one spark and they are gone.”
Besides, installation and maintenance teams have been seen to pay little attention to oxygen cleanliness / materials compatibility. On numerous occasions Motherwell has found that a hydrocarbon-based pipe sealant or a non-oxygen compliant PTFE thread tape has been used to seal screwed connections. Flanged connections have been found to have been sealed with non-compliant gasket material and it has been observed that the the pipeline / sparger internals on occasions have been cross-contaminated with a hydrocarbon-based grease / release agent used to lubricate the bolts that secure the said flanges. Ideally, an oxygen-compatible grease or an oxygen-compatible dry-lube should be used for the application.
Concernedly, Motherwell observes, while mine management is aware that oxygen hazards exist, they generally leave PSA operating and maintenance safety matters in the hands of safety officers, whom he has often found, are generally not trained regarding oxygen hazards. He reveals that most of the oxygen plants that he has visited at mine sites, have never trained their operators on the hazards associated with the on-site manufacture, storage, distribution and usage of oxygen gas.
Furthermore, oxygen equipment vendors do not appear to belabor the importance of oxygen safety – even though they are obliged to do so. Ideally, oxygen safety should form part of the induction training along with the other hazards – cyanide for instance.
Indeed all told, sound maintenance practices coupled with structured training can ensure that PSA plants produce high quality oxygen in the required quantities, both safely and cost effectively. In the long run, adopting this synergistic strategy this will reduce oxygen-related incidents, plant downtime, improve gold recoveries and reduce cyanide usage.