Hi,

This is my first post in forum (reading this forum for a long time

I am working in a steam power plant and have a few queries related to condensate pots and flow measurement.

Initially I thought pots are only used in steam side level measurements .. Like HP heaters, drum level etc., I saw a hookup in my plant where pots are used for flow measurement. So these are my doubts..

1. What is the purpose of using condensate pots in flow measurement? (flow nozzle) is it just to equalize the initial dp (no flow)?
(In my case pots are used in all dp flow measurement. Even in water service)

2. Should pots be at same level in vertical flow nozzle installation?

3. In steam services should the impulse pipe from primary root valve of flow nozzle to condensate pot be insulated?

 

1. The purpose of condensate pots in steam flow measurement is to isolate or seal the transmitter from excessive temperature exposure by isolating the steam pressure through a column of condensed water.

Why does your plant use seal pots on water?

I'm not sure. Theoretically, differences in the temperature of the condensate water in the impulse legs can induce an error when the difference exceeds about 20 deg C (due to the difference in water density) over a relatively significant height, but I doubt any place doing DP flow measurement for water service with DP's inherent 4:1 turndown cares about this particular error component. If one is selling steam, maybe this error is important, but not for water service.

Please, ask around for why it's done that way, come back and tell us.

2. Should pots be at same level in vertical flow nozzle installation?

The pots should be at an equal/same/identical elevation, but if they are not, then the difference in elevation must be 'calibrated out' or 'zeroed out'. Smart DP transmitters can be 'zero correct'ed for differences in seal pot elevation.

David Spitzer has an article explaining why ASME-MFC-8M has the piping configurations using seal pots for DP steam flow measurement:

http://www.flowcontrolnetwork.com/articles/print/understanding-your-standards
http://tinyurl.com/pzoc3aw
http://preview.tinyurl.com/pzoc3aw

Earlier instrumentation piping diagrams show the condensate seals installed at the same elevation:

11-64 Seal Chambers mounted in vertical line
http://i61.tinypic.com/1rpugy.jpg

11-65 Installation on vertical line - meter below line - vena contracta taps
http://i61.tinypic.com/f0stqu.jpg