Steam Flow Switch


Thread Starter

Ben Janvier

I am presently starting up a new cogeneration plant and the customer has forgotten to install a flow transmitter on the extraction line or a indication switch on the extraction non-return valve. This makes it very difficult for us to release the desuperheater valve for control since we don't know if a steam flow is present or not (don't want to inject water in an empty pipe. The customer has purchased an anubar flowmeter but the delivery will be long. I would like to add some redundancy to the flow signal and was wondering if any of you would have experience in steam flow switch (would be the same concept as a minimum air flow switch for a BMS)

Thank you
flow switch in steam (given the velocity) is a bit iffy.

you do have pressure and temperatures that can be used to infer flow?

This is a superheated medium (dry steam) so I am not too sure why it would be iffy.... When we are starting to extract, the MP extraction valve is wide open - yes we could use the difference between two pressure transmitters located on either side of the control valve to infer flow but since the dP is almost zero this strategy is not really applicable here.

Unfortunately, a wide open valve and a very low dP makes it hard to catch the positive flow - this is what I am looking for a flow switch.

Since the reason for injecting water is to cool the steam down, temperature would seem to be an obvious interlock solution. I'm not quite sure how you would do this because I don't have your P&ID.
not always considered a practical option where the stream flow varies, and feed forward control based on the steam flow is required.

you are aware of difficulties in getting representative steam temperature due to the distance required for the injected water to evaporate and the steam temperature to equalize. that only makes the issue worse with changing flow conditions and the need for tight control of steam temperature.
- The MP Extraction port from the turbine is sending steam to the MP header.

- The MP header can also be fed from a separate PRV.

- When the steam temperature measurement downstream of the MP extraction port shows a high temperature, I don't know if I should inject water since I cannot be sure that steam is actually flowing from the turbine to the MP header. This is why I would need a flowmeter. In the meantime, I am looking for a flow switch that I have a non-zero flow coming from the turbine (so that I don't fill the steam line with sprawater)

We are talking about a 0-80,000 pph steam, 160 psig.