Recently i have been to site, where are came across below issue, please help anyone if they can

our customer has one 11KL capacity argon gas cylinder at one location, @11.6 bar pressure (Argon gas is in liquid form in tank, comes to gas form once out of tank)

at outlet (1 inch) of tank about 25 mtrs after one V Cone meter (1/2 Inch) is installed along with flow computer, after that this meter same line of 1 inch run for 250 to 300 Mtrs, in this runs it takes about 18 Elbow of inline and reach to end user place

on this place again there is V cone meter installed of same size as previous only K factor is bit different. also Flow computer settings are same too.

now we have checked flow of both meters we found there is difference of 10% in meter readings
first meter at client place reads 400 m3 (day total) and second meter reads 360 m3 (day total)

please help me to understand if its normal, also below are some points for more clarity


1. Temperature at both meter is locked at 30 Deg c (location is in INDIA), as RTD connected is not working, but if i feel if i fix temp at both flow computers at 30 deg c, there should not be an issue. when i was on site, atmospheric temp is 25 deg c

2. after End user meter, there is small accumulator (500 ltr) vessel connected to line which has a small solenoid connected to it, set at 4 Bar pressure, so when End user consumes gas and pressure goes below 4 bar, valve opens and suddenly gas penetrate into accumulator vessel.
so basically, when end user meter gives some flow (by creating SP and DP) at same time client meter do not give that high flow. Hence, we are not comparing with instantaneous flow, but client wants day volume should match near

please advice

 

1. We have to assume, because it is not stated, that there is no outlet between the two flow meters, no means of consuming the gas between the two meters. Is that true?

2. I would assume that if the design static pressure values were used for calculating the spec'd DP/flow rate for the V-cone, then you should get a lower flow rate at the downstream meter because the static pressure loss over 18 elbows and 25m of piping.

a. Do the static inlet pressure values on each of the sizing sheets for each of the flow meters reflect the pressure drop (upstream static pressure) between the two meter locations?
b. Have you measured the inlet static pressure at both of the meter locations to see how close the actual pressure is to the design pressure?

3. What kind of flow computer,volumetric or mass? Does the flow meter expect a temperature signal and a static pressure signal to calculate mass flow, or is it a totalizer that totals the output of a volumetric flow DP transmitter?

4. The gas temperature influences its flow measurement. The ambient temperature can affect the gas temperature which in turn affects the volumetric flow rate measurement. It all depends on flow rates and how long the gas resides in the piping. If the gas temperature changes from the design temperature and there is no gas temperature measurement to use for a mass flow rate compensation calculation then there is a flow rate measurement error.

a. When you say "temperature at both meter(s) is locked at 30 Deg C" what do you mean? Is the ambient temperature of the meter locations and the piping controlled to 30°C?

b. Is the design temperature used to calculate the flow meter's spec'd output 30°C? I would think that the design temperature would be a lower temperature because the gas has boiled off from a liquid state, absorbing heat in that process.

5. "accumulator (500 ltr) vessel connected to line which has a small solenoid connected to it, set at 4 Bar pressure, so when End user consumes gas and pressure goes below 4 bar, valve opens and suddenly gas penetrate into accumulator vessel".

If the downstream pressure drops below 4bar and the solenoid valve opens, then the gas in the accumulator at 4 bar must flow out of the accumulator into the process because the accumulator's pressure is higher than the process pressure. Flow is not into the accumulator, but out of the accumulator under those conditions.

 

Hi David,

1. Yes, there is no other supply point in between two meters, confirmed

2. As a visual observation we are getting static pressure drop between two meters is hardly 10 PSIG, during design these elbows and all not considered, but we tried to do some math's for this and its gives us max 1% error should come as pipe is 1 inch only.

a. Pressure drop at both meters is normal
b. pressure is matching, (meters are design for 0-500 PSIG)

3.Volumetric flow only (MODEL Scanner 2000, make sensia )

4. so you mean to say, temp will affect reading, here i would like to ask i freeze temp 30 Deg c for both meters
in this case, can we justify on paper that difference between two meters will be 10%

a. what i mean here is in flow computer, in input data i have override it with value 30, so irrespective of outside temp or gas temp, flow computer will use 30 deg c to calculate flow

b. noted, but i still don't understand, but when i fixed that temp for calculation, so will it affect the flow calculation

5. how it goes outside accumulator is not our concern, out gas sale happens on meter reading,


Vaibhav Date
[email protected]