Flow rate of nitrogen from bulk tank into assembly plant

[DuckCommander]

I am currently trying to measure the flow rate and/or volume of a low pressure nitrogen line. We use high pressure (3200 psi) and low pressure (150 psi) lines coming from a 3000 gallon liquid nitrogen tank. I am trying to measure the amount of low pressure nitrogen that we use on a monthly basis to determine the cost and possible cost savings. The low pressure comes from the bulk tank, through a vaporizer, into the assembly facility through 3/4" piping at 150 psi and enters the plant at ambient temperature. We use approximately 10,000 gallons of nitrogen per month, including high pressure and low pressure.

I have recently purchased a flow meter that 0-20 SLPM, with 1/8" fittings. I have spoken with representatives constantly to see if this would restrict the flow of the line. I do not see how going from 3/4" to 1/8" over any period of length will not have some effect on the pressure or flow. I have the fittings to put this flow meter in line with the low pressure system, I just do not want to hurt the overall system. Any help on this would also be very appreciated.


Thanks,
DuckCommander

 

[hacksaw]

just remember the vendors pressure drop statement is predicated on the N2 flow you have provided

how much pressure drop are experiencing in the 3/4" line

 

[Latexman]

There will be some effect, but will it be noticable? Unfortunately, to answer that question requires a lot of data, including peak flow rates, which you cannot measure. 3/4" to 1/8" is a huge change! Three pipe sizes difference. THATS HUGE!!! Can you estimate the usage at each destination in the system and add them up? If so, do a survey, figure it out, and do it right the first time. If not, I'd recommend you have 3/4" isolation valves upstream and downstream and put a 3/4" by-pass with valve around the new meter and isolation valves in case it restricts flow too much. That way you can restore flow capacity quickly, and you can switch to and test a bigger flow meter "on the fly".

Good luck,
Latexman

 

[PEDARRIN2]

1. You need to look at your flow meter. If you are using 10,000 gallons of LN2 per month, that is about 21 scfm on a continous basis. In S L/m that is about 600 so you should not be using that flow meter for the whole flow.

2. Make sure the flow meter is calibrated at the density,pressure, and temperature you are working with. I ran into this with a similar situation where the flow meter was calibrated with air at 14.7 psia and 59 F and the process fluid was nitrogen at 90 psig (104.7 psia) and variable temperatures (see #3). If not, you will have to include a factor to account for these differences.

3. The process temperature from a liquid nitrogen vaporizer is typically 30 F lower than ambient - so the temperature of the gas will vary widely from winter to summer. This must be taken into account with the flow meter calibration.

 

[MiketheEngineer]

Can you weigh the tank every week or month??

 

[hacksaw]

use of 3/4" pipe is not surprizing for practical reasons (installation related), the
worse case N2 usage appears to be 60 lbs/hr or so, a rather small flow if it is continuous (24/7) usage, if not then you need to quantify the peak usage.

you can accomplish this in part by performing pressure survey of the installation

regardless of the meter size or type, it is a good idea to provide a block and bypass piping.

you can guage the flow in part if you repeat the pressure survey by partially closing a block valve near the supply point

if the flow is not quantifiable ahead of time, then install a rotameter suited to the pressure for a quick and less expensive measurement.

 

[Compositepro]

" I am trying to measure the amount of low pressure nitrogen that we use on a monthly basis to determine the cost"
How is it possible to not already know this? You must get a bill from your N2 supplier.

 

[IRstuff]

1/8" does sound a bit small. We had nothing less than 1/4" lines in a small research semiconductor fab.

If you knew you had 3/4" lines, why would you have purchased a 1/8" flow meter?

TTFN
faq731-376