Steam DP Flow Measurement - Long Impulse Lines
Steam DP Flow Measurement - Long Impulse Lines
(OP)
Looking for anyone with experience in DP steam flow measurement with impulse lines (wet legs) 30-40 ft. in length. Having issues with the steam flow tracking the condensate flow. We're looking at a possible imbalance in the liquid legs that isolate the DP transmitter from live steam. When the legs are filled and the transmitter is zeroed at start-up, the steam measurement is reliable. After a certain period of time, the steam measurement tails off (appears to read low) and doesn't track the condensate output in a closed loop system. The DP transmitter is mounted below the primary DP flow sensor and the tubing (1/2" SS) slopes continously downward. I believe that the vent valves of the DP transmitter are oriented correctly to avoid trapped air in the diaphragm. In addition, we have found no evidence of a leak path across the equalizer valve in the manifold.
Additional Notes: Pipe Size: 30". Pipe run: Horizontal. Steam Pressure: 100 PSI. Steam Temp: Slightly above Saturation. Reading low DP's during turbine test phase(understanding that there will be an error induced at the liquid/vapor interface in wet legs due to a dynamic equalibrium). Condensate (reference) Meter: Mag
We have three other sensors in service with no problems, the only difference being that the liquid legs are only 4-5 feet in length. For what it's worth, we're measuring geothermal steam (probably not related). Has anyone experienced issues with running liquid legs 30-40 feet or more using a DP flow meter on steam? We are not concerned with absolute accuracy at start up. The problem is that the steam meter tracks the condensate meter, then falls off dramatically. Any help or advice would be greatly appreciated.
Additional Notes: Pipe Size: 30". Pipe run: Horizontal. Steam Pressure: 100 PSI. Steam Temp: Slightly above Saturation. Reading low DP's during turbine test phase(understanding that there will be an error induced at the liquid/vapor interface in wet legs due to a dynamic equalibrium). Condensate (reference) Meter: Mag
We have three other sensors in service with no problems, the only difference being that the liquid legs are only 4-5 feet in length. For what it's worth, we're measuring geothermal steam (probably not related). Has anyone experienced issues with running liquid legs 30-40 feet or more using a DP flow meter on steam? We are not concerned with absolute accuracy at start up. The problem is that the steam meter tracks the condensate meter, then falls off dramatically. Any help or advice would be greatly appreciated.





RE: Steam DP Flow Measurement - Long Impulse Lines
how much condensate are you losing done stream of the meter & how much superheat are you using
RE: Steam DP Flow Measurement - Long Impulse Lines
A note in "Best Practice Guide: Impulse Lines for Differential-Pressure Flowmeters" by UK's NEL group, Page 13, section 2.9:
Steam recommendations:
Spirax Sarco do not recommend the use of condensate pots except for superheated steam applications . . .
http://w
Do you have condensate pots installed?
RE: Steam DP Flow Measurement - Long Impulse Lines
Dan, thank you for the valuable link. We do not recommend condensate pots either. Visiting the jobsite in a couple of weeks to see if they were installed any way.
What you're saying about the high side flashing and driving down the DP makes sense.
I have some charts showing steam vs condensate measurements. I'll try to post tose as well.
Thanks guys.
RE: Steam DP Flow Measurement - Long Impulse Lines
you may also need to consider pre-filling filling the impulse lines from grade, you'll need block and bleeds at the meter connection and at the transmitter for that and a hand pump for the fill fluid
with saturated steam cannot imaging that flashing a a problem unless you are experiencing large swings in pressure
by the way, are you using drain holes on your plate...if not the condensate build up up stream alters the meter coefficient, resulting in less d/p for a given flow...
RE: Steam DP Flow Measurement - Long Impulse Lines
If u sketch up your installation with writing of elevations
we can help you.
Thankyou
RE: Steam DP Flow Measurement - Long Impulse Lines
RE: Steam DP Flow Measurement - Long Impulse Lines
Thanks.
RE: Steam DP Flow Measurement - Long Impulse Lines
in steam we always put them in the lower quadrant of the pipe i.e. +/- 40Deg from bottom, you are close enough, the big issue with these meters is low d/p and increased sensitivity to level off-sets
check you vendor drawing of the device if it is available to see the installation guide lines.
good luck with your project
RE: Steam DP Flow Measurement - Long Impulse Lines
The solution was relocating the transmitter to just below the DP element
Geothermal steam - perhaps something like sulphur settles out in one line more than the other.
You don't mention condensate pots, these are very important for a flow application, just using a tee wont gaurantee the level in both lines is the same
RE: Steam DP Flow Measurement - Long Impulse Lines
RE: Steam DP Flow Measurement - Long Impulse Lines
I've run long impulse lines in steam with no issues.
Pamela K. Quillin, P.E.
Quillin Engineering, LLC
RE: Steam DP Flow Measurement - Long Impulse Lines
Thanks for your responses. I've returned from the sight with some photos. Although NEL recommends the shortest impulse lines possible for gas and steam flow, I am in concurrence with Pamela and we have had success with with long impulse lines (where it can't be avoided). Under the new Eng-tips format, I'm trying to figure out how to post photos. When I figure it out, I'll post some.
I can tell you that the major problem we found was that the impulse lines ran horizontal from the DP instrument head with no slope for roughly 30 feet (with 3 horizontal bends) BEFORE sloping downward roughly 45 feet to the DP transmitter. For liquids and steam flows with liquid legs, the impulse lines should slope continuously downward (at least 4 in. per foot) free from peaks, dips or sharp bends where entrained air can collect).
RE: Steam DP Flow Measurement - Long Impulse Lines
I ran my impulse lines straight down to 4' above grade from the orifice plate way up in the pipe rack. I'd have to think about the horizontal run's impact on the measurement because head is head and horizontal doesn't contribute to head, which you know better than me.
Pamela K. Quillin, P.E.
Quillin Engineering, LLC
RE: Steam DP Flow Measurement - Long Impulse Lines
Remember that the signal is square root, it only takes a fraction of an inch to throw the zero out the window.
Transmitters are for transmitting signals so use it.
I also feel condensate pots are essential for a steam flow although "Experts" seem to feel to the contrary.
Roy
RE: Steam DP Flow Measurement - Long Impulse Lines
RE: Steam DP Flow Measurement - Long Impulse Lines
Pamela K. Quillin, P.E.
Quillin Engineering, LLC