Steam Flow Measurement in Vertical Downflow #400

A hot condensate pot is indication of a leak somewhere. If the impulse line is deadheaded at the instrument, and there are no leaks back to the condensate pot, and no leak at the condensate pot, it will do its job and collect condensate that will equalize to ambient temperature. With no leaks, the surface area of condensate to HP steam is the only source of heat transfer. That should be very small.

During an outage, block in the system at the header and pressure check your pots and lines to find the source. Or, alternatively, you can block in the impulse lines below the pots and wait to see if the pot cools. If it does, then replace the impulse line.

Thanks for the reply. I have run my hand over the entire impulse line to check for leaks, and found none. These impulse lines were just replaced as well.
Another odd aspect is BOTH boilers have the same flow station before they come together in a Y, and both exhibit the same exact symptoms: Hi side impulse line (w/ condensate pot) is hot about a foot past the condensate pot, low side is cool. I have pictures of the setup I can send to anyone if they like, to get a better idea of the installation. Very odd.

Suggest that you repipe the impul;se lines so that both condensate pots are below the DeltaP meter, then up to the meter. The small amount of heat transfer at condensate-to-steam interface will still create more cndensate, that will "spill" down the HP line to the meter, warming the pipe and causing some static head on the meter. With the loops below the meter, this phenomenon will be the same on both sides of the meter.

That sounds as though there is an equalizer valve leakage. Are the impulse lines connected through a manifold block or through a piping valve arrangement?

The impulse lines are connected to a block manifold which is attached to the Rosemount 3095MV transmitter. The issue with false signal is sometimes the transmitter will read zero as it should, but other times it read a steady value above zero; often it is 100 kpph out of 700 kpph full scale. I believe this is due to a difference in condensate levels in the impulse legs, and this scenario is inconsistent, it will not always read the same error. if we open the equalizing valve, it will read zero and stay there for some time, not sure how long. However the error will always return for both boilers when no flow is passing though the measuring station, so the condensate levels will not remain consistent I think. Thanks!

When you can, try closing the high side block valve on the equalizer manifold for a couple of hours to see if that has an effect on the temperature of the condensate pot.

If that doesn't provide a clue, partially close the block valve at the steam header to provide a dampening effect on exchange between the seal-pot and the header. You may be dealing with a venturi effect drawing your condensate back into the header.

When you open the equalizer valve and it reads zero, do you have one of the impulse lines blocked in? If you are getting zero with either side blocked in and the equalizer open, that is correct. If it reads zero with both sides open and the equalizer open, that's a calibration issue.

Check the Rosemount 3095MV book for set up details, if you are uncertain. Also, the Rosemount customer service rep will be happy to help you troubleshoot the problem.

Good luck!

Thanks for The help. I am a little confused though. If there is no real DP in the process line, then if I have both impulse legs open to the process and I open the equalizing valve, I should see a zero, correct? If I keep one of the impulse lines sealed, and I open the equalizing valve, the condensate level might not equalize in both legs. If one leg is sealed, the condensate might be kept higher than the open leg due to no air available to displace the condensate. (Like holding soda in a straw by keeping one end in your mouth, as you remove the straw from the glass of soda). I would think I want all block valves open… Thanks-

You are correct, insofar as equalizing the condensate line levels. However, if you have all valves open, you create an open path from the high side to the low side of the orifice. Any DP across the orifice will push your condendate back into the steam header. The proper way to equalize the condensate levels in both lines is to let physics take its course. In other words, the condensate is self equalizing over delta Temp of the condensate pot.