Orifice Plate Measuring Flow Away From Calculated Value!

[CrushedBidder]

Hi,



I need ur support to point out our current issue with one of orifice plates at Refinery site. It is measuring LPG produced from Overhead of Platformer Stabilizer Column. The issue is unclear for us until this moment;

The orifice was calculated and its transmitter was calibrated for a full range of 222 TPD of LPG for delta pressure of 0.5 barg. The calculation was checked through software and confirmed that the data is suitable for orifice plate with bore size 27 mm. The current issue is; the transmitter of this orifice plate is reading over range "IOP" lively and DP was checked at site to be found 0.7 bar which makes sense for having "IOP" reading at DCS. However, the actual flow based on other downstream transmitters are showing around 70 TPD coming from this line ! and it goes to the sphere as a final destination. So we are sure this flow should be lesser than what the transmitter is showing (>222 TPD) ! The high DP 0.7 bar around this orifice at site is making us without a clue!

We took plenty of actions trying to understand why we have a high DP where; the impulse lines were changed, the transmitter was changed with a new one, a live pressure gauge was installed at site to measure DP around impulse line. With all of these actions, yet the DP is high "~0.7" bar.

What is missed here? Please advise,

I attached the calc sheet for this orifice.

 

[btrueblood]

Temperature and pressure at the orifice are reading what? Temp and pressure at the downstream transmitters are what? What is the chemical composition of the gas, any water in the mix?

 

[CrushedBidder]

I attached required data;

https://files.engineering.com/getfi...5e-8705-429f2ee8065d&file=Flow_Calc_Sheet.pdf

https://files.engineering.com/getfi...90e-9113ae818e8d&file=Compositions_of_LPG.png

https://files.engineering.com/getfi...-4c1c-8e69-92e3f5089322&file=LPG_LAB_Data.png

https://files.engineering.com/getfi...d3e-a492b674bb80&file=LPG_Flow_Controller.JPG

 

[hacksaw]

The vapor pressure of your propane component is 13 BarA, chances are, the vapor pressure of the actual fluid is even greater.

You may be dealing with two phase flow though your meter.

 

[hacksaw]

Reviewing your documents, the meter calc specifies "liquid" service with a density of 508 kg/m3

when I run my calc's, I get density of 38.5 kg/m3 with SG relative to air of 1.584
Haven't used those calcs in ages and may have some units a bit off, but food for thought

Good luck

 

[btrueblood]

What hacksaw says...you've got significant amounts of ethane and methane as well, so you are likely having 2-phase (gas bubbles in liquid) flow.

 

[hacksaw]

and possible liquid buildup unless mounted vertically,

but fundamental questions regarding his "fluid" claimed as overhead gas, with liquid properties

 

[hacksaw]

The pid sketch suggest the flow meter is in a pump discharge
The overhead gas is passed through a water cooled HEX

 

[hacksaw]

What the process owner didn't tell you was that a you were asked to install a failed design!
Good luck.

 

[georgeverghese]

Without knowing more, would suggest that, in volatile LPG service, the impulse lines should be remote sealed.
Looking at your PFD, presume water is decanted at the ovhd reflux drum ?? Is there LPG dehydration further down the line before the other FT near the sphere which is reading 70TPD?
Assuming this is in Oman, the impulse line temp could be as high as 65degC, so is your max normal LPG bubble point temp > 65degC at the min operating pumping pressure from P8212/13/27 ? If LPG bubble point temp is less than 65degC, the impulse lines must be remote sealed.