I've encountered Ejector Freezing several times and it usually occurs when an ejector pulls a HIGH VACUUM and there is a relatively LOW GAS FLOW and the process water is VERY COLD. This may occur at lower altitudes, but I've only seen it above 5000 feet, where I'm located.
These conditions are more prevalent in the winter months, with lower water demand using less chlorine and the incoming water reaching near freezing temperatures. With the lower gas flows, there is less "heat" energy to warm up the ejector AND we can have very high vacuum, which can raise the freezing temperature of the water spray in the check valve assembly of the ejector.
As the boiling point of water, which is lower (200 Deg.) at this higher altitude, the temperature that water apparently turns to ice at this altitude is higher. This seems strange, but I've seen this with pop bottles coming out of a Coke machine. It was in the summer and the machine was putting out bottles that were so cold, that when the top was removed, the soda inside started freezing immediately! Was a scary thing to watch. The only thing that had happened was that the internal pressure of the bottle was released.
A mist can develop in the venturi section of the ejector and starts to freeze. It can then build up in the check valve section of the ejector and can STOP gas flow altogether.
This heater assembly was designed to alleviate this problem. It adds heat to the gas, which can be enough to keep the ejector from freezing.
It would be constructed of CPVC plastic pipe, which has a higher temperature rating than the PVC normally used for the gas supply. It is sized one size larger than the supply line and has the heat tape, shown as small circles along the pipe, and there is a plug in the center with fins to force flow against the inside of the heated pipe and because of the fins, flow around it, for heat transfer.
The darker colored pieces near the middle are temperature sensors set to 110 Degrees Fahrenheit. There are two for safety. They actually make Digital Controls w/ Displays that are relatively cheap, if this is desired.
There is insulation around the heat tape, to keep the heat in, and all of this is enclosed in a larger pipe for an enclosure. The are union fittings on each end for service.