Everyday 60 million gallons of drinking water are sanitized by a regional water plant, which adds accurate doses of ammonia gas into its water system. The entry of liquid ammonia resulted in the previous controllers breaking, this was caused by the thermal differential sensors present inside the meters.
Ordinary thermal MFCs have sensors, which are programmed to increase the temperature of gas to a particular range. Heat is conducted in a much better manner by liquids than by gases, and even a very small amount of liquid leads to rapid cooling of the elements present inside. As the drop is detected, the temperature regulator consumes an increasing amount of power for heating purposes.
Liquid can accidentally flow in to a gas flow controller. Environmental monitoring stations carry out measurements in all weather conditions, the potential sources include melting snow, condensation, and rain. Fuel cell systems form moisture by mixing hydrogen with oxygen, and this situation could become risky as a result of accidental exposure. At times a backflow event may occur when a fluid tank is gas sparging.
There is a Cure
Getting liquids into an Alicat system has its own benefits. Unlike thermally based instruments, Alicat flow controllers and flow meters work on the principle of differential pressure. Gas flow turbulence present inside the instrument is eradicated by a structure that develops a laminar flow. Measurement is carried out for the variations in pressure between the two ends of the laminar stack.
The water treatment plant didn't want to keep repurchasing meters every time fluid entered the device. The plant employed Alicat meters as a replacement for its usual thermal instruments. The plant can now just purge the system with a high-pressure flush of ammonia gas every time the liquid ammonia enters the meters, and then resume its sanitizing process (Figure 1).
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Figure 1. One of the Alicat Mass Flow Controllers at a water treatment plant, which solved a big failure problem.
Dry it Out
Liquids that enter the Alicat meter/controller and remain there a long time cause the interaction of dissimilar metals. To prevent this situation, the assembly must be placed under vacuum conditions. Gentle heat ranging between 50 to 60°C and hard vacuum of 0.25 psi or less are recommended, as they will help the liquid to evaporate through the small channels in the instrument.
In situations where suspended solids are present in the liquid, drying the liquid may form grit and a residue could be left behind by the solution. There can also be very rare instances where the contamination is heavy enough to hamper with the laminar flow conditions required for precise measurements. In such cases, isopropyl alcohol can be used to flush the instrument. Alicat’s service department can provide the service of disassembling, cleaning, and recalibrating.
Conclusion
It is recommended to always have Alicat’s controllers with 316L stainless steel components. These controllers are known for their resistance to corrosion, they the highest tolerance degree for liquids and are virtually identical.
Customers, such as air quality monitoring companies and the water treatment plant, are now using Alicat’s differential pressure controllers instead of the ordinary thermal controllers, because of issues faced while using the ordinary controllers.
Alicat mass flow controllers and meters are considered to be a perfect choice for customers at risk.
Download the brochure for more information about Alicat's Mass Flow Controllers
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This information has been sourced, reviewed and adapted from materials provided by Alicat Scientific.
For more information on this source, please visit Alicat Scientific.