Saturated steam measurment

[DJCherre]

Trying to measure the discharge flow from a steam jet ejector. The motive steam is superheated, suction is off of a vessel of boiling water, and I'm told that many attempts to measure the discharge steam flow have failed due to it possibly having water droplets. A vendor of a V-Cone meter told me it would work, but I'm hesitant to cut into a 12" line if I'm not sure. Any suggestions? We're currently using several calculations based on jet pressures & energy balance and they never match up...
Thanks,
Dean

 

[hacksaw]

what is the discharge pressure, available straight run, and what are your accurracy requirements?

 

[CARF]

DJ,

If the steam is really superheated in can NOT have water droplets, agree?

You may try a Vortex measurement.

Vortex meters are used in numerous branches of industry to measure the volume flow of liquids, gases and steam.

Applications in the chemicals and petrochemicals industries, for example, in power generation and heat-supply systems involve widely differing fluids: saturated steam, superheated steam, compressed air, nitrogen, liquefied gases, flue gases, carbon dioxide, fully demineralized water, solvents, heattransfer oils, boiler feedwater, condensate, etc.

Vortex meters are particularly popular in all sectors of industry for metering steam.

Vortex meters measure volume flow, but steam systems are generally rated by mass or energy content, so these meters are frequently used in combination with a pressure and/or temperature sensor and a flow computer.

The Prowirl 73 vortex meter combines everything necessary for the direct mass metering of saturated steam:

flow computer, temperature and flow metering all in a single device.

http://www.endress.com

Hope this helps,
CARF

 

[DJCherre]

Thanks for the replies. First to hacksaw: discharge P is 5-7 psig. We just did a bunch of repiping to decrease DP in the discharge piping to help the jet's recovery, so any meter would have to be low DP. Straight run is lousy, about 6' of pipe available in an 18" line! For accuracy 1000 lb/hr out of 100,000 lb/hr span would be nice, 2000 would be acceptable.
CARF, i agree the superheated steam won't have droplets, just not sure what's coming out of the jet. In the past they've tried ultrasonic (poor signal), turbine (fouled), and venturi (unstable signal). Didn't try vortex. Would vortex be ok if there were droplets? i.e. the jet suction pot may not be designed with enough de-entrainment height? I believe vortex also requires some straightrun, so we may be doomed by the tight piping.
Thanks,
Dean

 

[hacksaw]

1-2% accurracy is asking a lot. You be hard pressed to get much better than 20% regardless of you mesurement given typical operating budgets. You can have a wet stream with droplets by entrainment and partial condensation etc.

Mat bal on the measureable streams seems about as good as you can get on this one, good luck

 

[DJCherre]

I guess that's about where I was, but thought I'd see if there was a miracle cure. To be honest I wasn't even aware when I wrote this post that we only had 4 total pipe diameters available due to the recent repiping... So I suppose we'll keep trying to improve the calcuation. This flow has a huge impact on optimization of a reactive-distillation column, so that's why we're looking for good accuracy.
Thanks again,
Dean