Understanding oxygen generators day-to-day
February 11, 2022 By Ron Hill
Aside from providing water to the fish, there is nothing so vital as the supply of oxygen. Oxygen loss or failure can devastate a farm, which is why modern farmers have very tight and well-maintained oxygen systems with redundancy built in for protection against failure. Onsite oxygen generation systems have become a popular choice for many operations, especially remote sites. Maintaining the generating units is one of the most important tasks onsite, given their vital nature. Being proactive by having a good monitoring program and having vital spare parts on hand is the best way to minimize both downtime and maintenance costs.
PSA-style gas generators
Pressure swing adsorption (PSA) -style oxygen generators are the industry standard for self oxygen supply. These units operate on the knowledge that air is composed of 78 per cent nitrogen, 21 per cent oxygen, and one per cent other gases. PSA is a process whereby compressed air is passed through a molecular sieve which adsorbs the nitrogen from the air, pulling it out of the air mixture.
The air mixture that passes through the sieve is almost pure oxygen. The sieve can only adsorb so much nitrogen, thus, when the sieve is ‘full’ of nitrogen, the valves close to shut off the flow of air, and the chamber de-pressurized, allowing the nitrogen to escape the sieve and be released by the unit. PSA generators are built with two separate PSA systems in each, so a constant flow of oxygen can be maintained: one side is providing oxygen while the other is emptying its sieve.
Oxygen, oil and spontaneous combustion
One would be remiss not to mention the potential danger of exposing hydrocarbons like grease and oil, to pressurized oxygen. Pressurized oxygen will ignite grease and oil spontaneously, without an ignition source. There must never be any oil or grease found around or on an oxygen generator. The room where the unit is stored can have no oil or grease on the floor or walls. A loose fitting or a pin hole leak becomes an extreme human safety risk if exposed to oil. Any fittings and tools used on the oxygen system should always be wiped clean before starting. Aquaculture novices rarely have much experience with compressed gases or oxygen generators, and should be made very aware of this safety concern immediately upon hiring.
Monitoring an oxygen generator
There are many brands, styles, and sizes of PSA-style gas generators, as there are many applications in and out of aquaculture. Each day at the same time, purity, pressure, and flow should all be checked and recorded. Any deviation of these values requires follow up. Purity issues or deviations should be looked at very carefully and should suggest to staff that a problem is developing.
Sophisticated units may have their own touch screen and onboard monitoring systems. While these conveniences can be very helpful for daily monitoring, they must be double checked from time to time. Every unit needs to have a port installed for monitoring purity, even if there is a purity reading on the touchscreen.
A handheld oxygen monitor, such as the Maxtec analyzer, is an essential tool for any facility generating their own oxygen. It is a very quick operation to use a handheld oxygen analyzer to check purity at the port and is a necessary redundancy to in-situ purity monitoring. Further than just checking the gauges and values, it is important to listen to the sounds the unit is making and observe the two systems cycle back and forth. Changes in sound can indicate bad valves, loss of seal, or issues with the filter.
Troubleshooting an oxygen generator can be a frustrating task at times because it is part of a system and is affected by the other parts. Upon initial frustration trying to identify the source of an oxygen issue after inspecting the gas generator, take a step back and look at the system as a whole. Start from heart of the system, the compressor, and start following the flow of air/oxygen, inspecting as you go. Compressor issues will directly affect the performance of the oxygen generator, thus, keeping the compressor in top condition is as essential as maintaining the oxygen generator itself. Look at the air filters and dryer and look at the electronic drains for the compressed air tank – issues with any of these can affect oxygen generation.
A logbook should be kept for each unit, recording all relevant information on the machine including changes to the system, start-up and shutdown of units, maintenance and repairs performed, as well as any other relevant information pertaining to the operation of the unit. Two to three staff members should be involved in monitoring and recording information in the logbook to provide redundancy. A logbook gives staff reference to what was done and when, information invaluable for troubleshooting.
Following the manufacturers’ maintenance schedule is extremely important for the efficiency and longevity of a PSA generator; maintenance is directly tied to the life of the unit. The sieve in the oxygen generator must be protected, moisture is the enemy. If the filtration or drying is inadequate, the sieve will start to fail.
Lise Marsh, independent representative at AirSep Corporation and long-time PSA provider, forwards that for Airsep PSAs “with proper preventative maintenance your sieve can last a lifetime, it all depends on maintaining a proper schedule for service.”
The solution for proper maintenance will depend on the farm. Some farms have maintenance staff inhouse, others will use local contractors to make service calls, and others will buy the service plan directly from the manufacturer/distributor. Regardless, a maintenance plan needs to exist and be followed, someone has to be watching. There are significant cost differences between these options, which may constrain some operations.
Manufacturer or dealer service plans can be expensive but are a great option for proper maintenance. However, a farm chooses to provide service, it is better to pay for the maintenance and commit the time necessary to be ahead of issues, rather than wait until the unit stops working, be down, and have to pay for the unit to be fixed. The cost of proper maintenance is always less than repair/replacement, plus down time costs, for a sophisticated piece of equipment.
With so vital a system, staff need to be well prepared for inevitable failure. “You must be ready for the winter blackout at midnight,” Lise Marsh warns, “farms must be prepared for every failure you can think of.” The system must be setup for, and preparedness must exist, for ugly circumstances. A plan must be in place for unit failure and for quick repair. When a unit fails and the farm is using their backup supply, the farm now has no backup – restoring the down system is of the utmost importance because if the backup fails, has maintenance issues of its own, or there is issues getting supplies of liquid replenished, there is a huge problem.
Whether there is a maintenance staff onsite or contracted out, an adequate supply of spare parts needs to be on hand. Always keep parts in stock at the facility in case of supply chain issues; COVID-19 has proven this to be good practice. If service is contracted out, encourage the service provider to keep parts on hand for emergencies or have the provider maintain the stock at the facility. Filters, mufflers, and solenoid valves are the most essential parts to keep on hand, circuits and certain circuit boards can also be a good idea depending on the model. The best way to determine what to keep on hand is to consult the owner’s manual and reach out to the manufacturer/distributor to see what pieces they suggest keeping on hand and what parts are needed for routine maintenance. Manufacturer parts are usually the best, there is no reason to cut corners on something so important.
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