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Pressure Reducing Valve - Flow Sizing

Pressure Reducing Valve - Flow Sizing

(OP)
Hello Experts,

In plant we have 1.5 inch liquid nitrogen line with pressure 9 barg. I want to reduce that pressure upto 6 barg using a pressure reducing valve. Vendor will require the minimum and maximum flow through PRV, how do I calculate it?

Any spreadsheets will be highly appreciated.

RE: Pressure Reducing Valve - Flow Sizing

How can we know the minimum and the maximum flow for your application?

Dejan IVANOVIC
Process Engineer, MSChE

RE: Pressure Reducing Valve - Flow Sizing

(OP)
@EmmanuelTop If the question is wrong or you require more inputs, do tell mate. I think I will have to finalize flow requirement and then size it accordingly

RE: Pressure Reducing Valve - Flow Sizing

Sanchem,
What my esteemed colleague is saying is that only you can know what flow your process needs/has/uses. Obviously you will need to know this flow so a suitable PRV can be sized. So assuming there is no flow meter on the liquid nitrogen line then you are going to have to work out or at least estimate what the nitrogen flow is. You are the only person that can do that because we know nothing about your process.

You may have to obtain a whole lot of data from your process so that you can get some implied flow value
For example, look at how much nitrogen your whole plant uses over what time frame. This may give you a ball park flow range.
What ever the process is that requires the nitrogen may have some pumps , pressure gauges, or even just design details that may give you some useful information. If you are using the nitrogen for cooling then maybe you can get some rough data from the change in temperature and the heat load on the system.

Then again it may be easier to put in a flow meter or a install valves on a trial and error basis. If you install a valve with known performance you may well be able to reverse engineer the system based on pressure reduction to get a flow value.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Pressure Reducing Valve - Flow Sizing

sanchem,

The question is wrong.

The flowrate is up to you to decide based on your process requirements. You might want 2m3/hr max or 20. We have no idea.

Ashtree has some good ideas for you to try or ask the process engineer or model the system in something like HYSYS. Look at the line list or the heat and mass balance.

Is this a new plant or existing?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Pressure Reducing Valve - Flow Sizing

(OP)
Thank you Ashtree and LiitleInch for your kind suggestions.

Here is what I did to estimate the flowrate. This is an existing line in an existing plant.

We were using Liquid nitrogen at 9 kg/cm2g to purge a reactor but as this vessel is not designed for more than 8 kg/cm2g we have decided to install a pressure reducing valve which will bring down the pressure to say 5-6 kg/cm2g. Currently the operators were manually controlling the pressure below 8 kg/cm2g.

So based on the trends pressure rise in the vessel in certain time, I calculated max Nitrogen flow coming from this line and I am sizing the PRV accordingly.

I hope this is somewhat correct method. Your comments?

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