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Two phase flow measurement for gas application

Hi Everyone ,

I have a client who have recently switched to coriolis meters from Daniel for measuring the gas flow rate from a 2 phase vertical separator. They have mentioned the majority of the gas produced will be methane along with other impurities. However the separation efficiency of the separator can vary between 75 to 90%. Therefore , I was wondering the effect this can have  on the over all performance of the flow measurement and what to expect, how will the volumeteric flow rate and density react to changes in  wetness of the gas (liquid in gases). 

we have currently supplied a CMF400H sensor coupled with a 2700 transmitter with 2 intrinsically safe outputs. I came across the option of two phase flow options (2 phase flow timeout , 2 phase low limit , 2 phase high limit) for density measurement  in Pro Link III . It will be great if someone could explain,  how to implement these parameters to tackle two phase scenario as best as possible. 

Many thanks 

Alan 

alan thomas

• 21 Aug 2016 5:54 AM
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5 Replies

• Cara Wilmer

  

  • 22 Aug 2016 3:39 PM

  Alan,
  
  The performance of a Coriolis meter in 2-phase flow will depend on a number of things:
  
  • amount of 2nd phase in process
  • installation orientation
  • velocity though the meter
  • flow regime (constant liquid, or periodic)
  • desired measurement (total mass, gas only mass, volume @ standard conditions)
  
  The first thing to do is to make sure that installation and sizing best practices are followed. For gas with liquid applications, the sensor should be mounted with flow downward in flag position (U-shaped part sticking out like a flag in the wind). Sizing should be such that flow rate is as close to the nominal flow rate as possible, given pressure drop constraints.
  
  The options for how to best deal with the errors associated with 2-phase flow depends on what the desired measurement is (measure both phases, or ignore the liquid), and whether the liquid is constant or intermittent.
  
  The density will typically increase with an increase in liquid, but a more sensitive detector of mist/liquid may be drive gain. We have 3rd party testing that shows the sensitivity of drive gain to 2-phase conditions and have written some algorithms around using drive gain to detect 2-phase conditions, that can help for intermittent 2-phase conditions.
  
  The 2-phase slug limits you mentioned are intended for liquid processes where entrained gas can cause over-read of liquid-only process variables. They way that they work is that when the density is outside of the limits set, the meter will output 0 flow rate.
  
  I hope this answers your questions. Please let me know if you would like more information.

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• Tom O'Banion

  

  • 22 Aug 2016 4:07 PM

  In reply to Cara Wilmer:

  Hi Alan- to add to what Cara has shared, we have a fairly new software program that might be ideal here- it's called Advanced Phase Measurement, and can "learn" your process and greatly improve accuracy under challenging 2-phase flow conditions. See www2.emersonprocess.com/.../Advanced-Phase-Measurement-Manual-20030076.pdf for more information. Let us know where you and/or the client is and one of our Technical Sales folks would be eager to discuss and review. As Cara points out, sizing and installation are very important to get decent measurement. Density measurement is quite sensititive to two-phase flow, so that will be even more challenging than measuring (mass) flow.

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• alan thomas

  

  • 26 Aug 2016 9:29 AM

  In reply to Tom O'Banion:

  Thanks a lot to both Cara and Tom for your valuable insight into 2 phase measurement .
  
  Just to describe further on the separator setup. It is a vertical separator with a 6"inch gasline using 4" CMF400H and the maximum flow rate expected between the range of 0- 90 MMSCF/D . It is used for under balanced drilling campaign . As you have advised the Coriolis is installed in the stand up position with the flow direction from top to bottom . For our knowledge and anticipating these questions from our client, can you please elaborate the options or configurations available within the 2700 transmitter model to best tackle the below scenario and measure :
  
  1) Both phases if required
  2) Ignore the liquid part while measuring , when there is a constant liquid part
  3) Ignore the liquid part while measuring, when there is a intermittent liquid part
  
  Moreover, we highly doubt they will be willing to upgrade the current transmitters to the more advanced 5700 transmitters considering the current market. However , we can propose these transmitters in the future .
  
  Awaiting your feedback .
  
  Thanks and Beast regards
  
  Alan T

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• Jared Drennen

  

  • 1 Sep 2016 5:19 PM

  In reply to alan thomas:

  Hi Alan. There are very few settings in an "out-of-the-box" 2700 transmitter that can appropriately manage measurement performance under regularly occurring two-phase conditions. Setting appropriate slug-flow limits, density cutoffs, and/or creative use of damping can smooth out the erratic flow signals during such liquid slugging, but you are still left with either measuring the combined fluid mixture, or nothing at all. The appropriate solution for this application is our newest licensed software option for the 5700 Series Transmitter platform called Advanced Phase Measurement (or APM). APM has the ability to ignore the large density and flow swings caused by liquid loading and apply appropriate compensation values in their place during such slugging events. A more limited version of APM is available for 800 series core processors and/or 2700 transmitters called Transient Bubble Remediation (or TBR). I will caution you that APM is much more functional "out-of-the-box", while TBR will require a qualified technician to set it up onsite in the field. Manuals for both of these options are available on our website: www.MicroMotion.com. Please work with your local sales channel to learn more about these options, or to receive a more qualified recommendation for your specific process conditions.

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• alan thomas

  

  • 5 Sep 2016 4:53 AM

  In reply to Jared Drennen:

  thanks a lot for your feedback.

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